Author name code: asplund
ADS astronomy entries on 2022-09-14
author:"Asplund, Martin"
------------------------------------------------------------------------
Title: The Gaia-ESO Public Spectroscopic Survey: Motivation,
implementation, GIRAFFE data processing, analysis, and final data
products
Authors: Gilmore, G.; Randich, S.; Worley, C. C.; Hourihane, A.;
Gonneau, A.; Sacco, G. G.; Lewis, J. R.; Magrini, L.; Francois, P.;
Jeffries, R. D.; Koposov, S. E.; Bragaglia, A.; Alfaro, E. J.; Allende
Prieto, C.; Blomme, R.; Korn, A. J.; Lanzafame, A. C.; Pancino, E.;
Recio-Blanco, A.; Smiljanic, R.; Van Eck, S.; Zwitter, T.; Bensby, T.;
Flaccomio, E.; Irwin, M. J.; Franciosini, E.; Morbidelli, L.; Damiani,
F.; Bonito, R.; Friel, E. D.; Vink, J. S.; Prisinzano, L.; Abbas,
U.; Hatzidimitriou, D.; Held, E. V.; Jordi, C.; Paunzen, E.; Spagna,
A.; Jackson, R. J.; Maiz Apellaniz, J.; Asplund, M.; Bonifacio, P.;
Feltzing, S.; Binney, J.; Drew, J.; Ferguson, A. M. N.; Micela, G.;
Negueruela, I.; Prusti, T.; Rix, H. -W.; Vallenari, A.; Bergemann,
M.; Casey, A. R.; de Laverny, P.; Frasca, A.; Hill, V.; Lind, K.;
Sbordone, L.; Sousa, S. G.; Adibekyan, V.; Caffau, E.; Daflon, S.;
Feuillet, D. K.; Gebran, M.; Gonzalez Hernandez, J. I.; Guiglion,
G.; Herrero, A.; Lobel, A.; Merle, T.; Mikolaitis, S.; Montes, D.;
Morel, T.; Ruchti, G.; Soubiran, C.; Tabernero, H. M.; Tautvaisiene,
G.; Traven, G.; Valentini, M.; Van der Swaelmen, M.; Villanova, S.;
Viscasillas Vazquez, C.; Bayo, A.; Biazzo, K.; Carraro, G.; Edvardsson,
B.; Heiter, U.; Jofre, P.; Marconi, G.; Martayan, C.; Masseron, T.;
Monaco, L.; Walton, N. A.; Zaggia, S.; Aguirre Borsen-Koch, V.; Alves,
J.; Balaguer-Nunez, L.; Barklem, P. S.; Barrado, D.; Bellazzini, M.;
Berlanas, S. R.; Binks, A. S.; Bressan, A.; Capuzzo-Dolcetta, R.;
Casagrande, L.; Casamiquela, L.; Collins, R. S.; D'Orazi, V.; Dantas,
M. L. L.; Debattista, V. P.; Delgado-Mena, E.; Di Marcantonio, P.;
Drazdauskas, A.; Evans, N. W.; Famaey, B.; Franchini, M.; Fremat, Y.;
Fu, X.; Geisler, D.; Gerhard, O.; Gonzalez Solares, E. A.; Grebel,
E. K.; Gutierrez Albarran, M. L.; Jimenez-Esteban, F.; Jonsson, H.;
Khachaturyants, T.; Kordopatis, G.; Kos, J.; Lagarde, N.; Ludwig,
H. -G.; Mahy, L.; Mapelli, M.; Marfil, E.; Martell, S. L.; Messina,
S.; Miglio, A.; Minchev, I.; Moitinho, A.; Montalban, J.; Monteiro,
M. J. P. F. G.; Morossi, C.; Mowlavi, N.; Mucciarelli, A.; Murphy,
D. N. A.; Nardetto, N.; Ortolani, S.; Paletou, F.; Palous, J.;
Pickering, J. C.; Quirrenbach, A.; Re Fiorentin, P.; Read, J. I.;
Romano, D.; Ryde, N.; Sanna, N.; Santos, W.; Seabroke, G. M.; Spina,
L.; Steinmetz, M.; Stonkute, E.; Sutorius, E.; Thevenin, F.; Tosi,
M.; Tsantaki, M.; Wright, N.; Wyse, R. F. G.; Zoccali, M.; Zorec,
J.; Zucker, D. B.
Bibcode: 2022arXiv220805432G
Altcode:
The Gaia-ESO Public Spectroscopic Survey is an ambitious project
designed to obtain astrophysical parameters and elemental abundances
for 100,000 stars, including large representative samples of the
stellar populations in the Galaxy, and a well-defined sample of 60
(plus 20 archive) open clusters. We provide internally consistent
results calibrated on benchmark stars and star clusters, extending
across a very wide range of abundances and ages. This provides a
legacy data set of intrinsic value, and equally a large wide-ranging
dataset that is of value for homogenisation of other and future
stellar surveys and Gaia's astrophysical parameters. This article
provides an overview of the survey methodology, the scientific aims,
and the implementation, including a description of the data processing
for the GIRAFFE spectra. A companion paper (arXiv:2206.02901)
introduces the survey results. Gaia-ESO aspires to quantify both
random and systematic contributions to measurement uncertainties. Thus
all available spectroscopic analysis techniques are utilised, each
spectrum being analysed by up to several different analysis pipelines,
with considerable effort being made to homogenise and calibrate the
resulting parameters. We describe here the sequence of activities up to
delivery of processed data products to the ESO Science Archive Facility
for open use. The Gaia-ESO Survey obtained 202,000 spectra of 115,000
stars using 340 allocated VLT nights between December 2011 and January
2018 from GIRAFFE and UVES. The full consistently reduced final data set
of spectra was released through the ESO Science Archive Facility in late
2020, with the full astrophysical parameters sets following in 2022.
Title: The Gaia-ESO Public Spectroscopic Survey: Implementation,
data products, open cluster survey, science, and legacy
Authors: Randich, S.; Gilmore, G.; Magrini, L.; Sacco, G. G.; Jackson,
R. J.; Jeffries, R. D.; Worley, C. C.; Hourihane, A.; Gonneau, A.;
Viscasillas Vàzquez, C.; Franciosini, E.; Lewis, J. R.; Alfaro, E. J.;
Allende Prieto, C.; Blomme, T. Bensby R.; Bragaglia, A.; Flaccomio, E.;
François, P.; Irwin, M. J.; Koposov, S. E.; Korn, A. J.; Lanzafame,
A. C.; Pancino, E.; Recio-Blanco, A.; Smiljanic, R.; Van Eck, S.;
Zwitter, T.; Asplund, M.; Bonifacio, P.; Feltzing, S.; Binney, J.;
Drew, J.; Ferguson, A. M. N.; Micela, G.; Negueruela, I.; Prusti,
T.; Rix, H. -W.; Vallenari, A.; Bayo, A.; Bergemann, M.; Biazzo, K.;
Carraro, G.; Casey, A. R.; Damiani, F.; Frasca, A.; Heiter, U.; Hill,
V.; Jofré, P.; de Laverny, P.; Lind, K.; Marconi, G.; Martayan, C.;
Masseron, T.; Monaco, L.; Morbidelli, L.; Prisinzano, L.; Sbordone,
L.; Sousa, S. G.; Zaggia, S.; Adibekyan, V.; Bonito, R.; Caffau,
E.; Daflon, S.; Feuillet, D. K.; Gebran, M.; González Hernández,
J. I.; Guiglion, G.; Herrero, A.; Lobel, A.; Maíz Apellániz,
J.; Merle, T.; Mikolaitis, S.; Montes, D.; Morel, T.; Soubiran,
C.; Spina, L.; Tabernero, H. M.; Tautvaišienė, G.; Traven, G.;
Valentini, M.; Van der Swaelmen, M.; Villanova, S.; Wright, N. J.;
Abbas, U.; Aguirre Børsen-Koch, V.; Alves, J.; Balaguer-Núnez,
L.; Barklem, P. S.; Barrado, D.; Berlanas, S. R.; Binks, A. S.;
Bressan, A.; Capuzzo--Dolcetta, R.; Casagrande, L.; Casamiquela, L.;
Collins, R. S.; D'Orazi, V.; Dantas, M. L. L.; Debattista, V. P.;
Delgado-Mena, E.; Di Marcantonio, P.; Drazdauskas, A.; Evans, N. W.;
Famaey, B.; Franchini, M.; Frémat, Y.; Friel, E. D.; Fu, X.; Geisler,
D.; Gerhard, O.; González Solares, E. A.; Grebel, E. K.; Gutiérrez
Albarrán, M. L.; Hatzidimitriou, D.; Held, E. V.; Jiménez-Esteban,
F.; Jönsson, H.; Jordi, C.; Khachaturyants, T.; Kordopatis, G.; Kos,
J.; Lagarde, N.; Mahy, L.; Mapelli, M.; Marfil, E.; Martell, S. L.;
Messina, S.; Miglio, A.; Minchev, I.; Moitinho, A.; Montalban, J.;
Monteiro, M. J. P. F. G.; Morossi, C.; Mowlavi, N.; Mucciarelli, A.;
Murphy, D. N. A.; Nardetto, N.; Ortolani, S.; Paletou, F.; Palouus, J.;
Paunzen, E.; Pickering, J. C.; Quirrenbach, A.; Re Fiorentin, P.; Read,
J. I.; Romano, D.; Ryde, N.; Sanna, N.; Santos, W.; Seabroke, G. M.;
Spagna, A.; Steinmetz, M.; Stonkuté, E.; Sutorius, E.; Thévenin,
F.; Tosi, M.; Tsantaki, M.; Vink, J. S.; Wright, N.; Wyse, R. F. G.;
Zoccali, M.; Zorec, J.; Zucker, D. B.; Walton, N. A.
Bibcode: 2022arXiv220602901R
Altcode:
In the last 15 years different ground-based spectroscopic surveys
have been started (and completed) with the general aim of delivering
stellar parameters and elemental abundances for large samples of
Galactic stars, complementing Gaia astrometry. Among those surveys,
the Gaia-ESO Public Spectroscopic Survey (GES), the only one performed
on a 8m class telescope, was designed to target 100,000 stars using
FLAMES on the ESO VLT (both Giraffe and UVES spectrographs), covering
all the Milky Way populations, with a special focus on open star
clusters. This article provides an overview of the survey implementation
(observations, data quality, analysis and its success, data products,
and releases), of the open cluster survey, of the science results and
potential, and of the survey legacy. A companion article (Gilmore et
al.) reviews the overall survey motivation, strategy, Giraffe pipeline
data reduction, organisation, and workflow. The GES has determined
homogeneous good-quality radial velocities and stellar parameters for a
large fraction of its more than 110,000 unique target stars. Elemental
abundances were derived for up to 31 elements for targets observed with
UVES. Lithium abundances are delivered for about 1/3 of the sample. The
analysis and homogenisation strategies have proven to be successful;
several science topics have been addressed by the Gaia-ESO consortium
and the community, with many highlight results achieved. The final
catalogue has been released through the ESO archive at the end of
May 2022, including the complete set of advanced data products. In
addition to these results, the Gaia-ESO Survey will leave a very
important legacy, for several aspects and for many years to come.
Title: VizieR Online Data Catalog: (non-)existence of five sparse
open clusters (Kos+, 2018)
Authors: Kos, J.; de Silva, G.; Buder, S.; Bland-Hawthorn, J.; Sharma,
S.; Asplund, M.; D'Orazi, V.; Duong, L.; Freeman, K.; Lewis, G. F.;
Lin, J.; Lind, K.; Martell, S. L.; Schlesinger, K. J.; Simpson, J. D.;
Zucker, D. B.; Zwitter, T.; Bedding, T. R.; Cotar, K.; Horner, J.;
Nordlander, T.; Stello, D.; Ting, Y. -S.; Traven, G.
Bibcode: 2022yCat..74805242K
Altcode:
Stars observed as a part of the GALAH survey are selected
from the 2MASS catalogue (Skrutskie et al. 2006AJ....131.1163S,
Cat. VII/233). Depending on the observing mode, all the stars in a
1°radius field are in a magnitude range 12<V<14
for regular fields and 9<V<12 for bright fields. Most of the
data used in this work comes from the Gaia DR2 (Gaia Collaboration
2018A&A...616A...1G, Cat. I/345), which includes positions,
G magnitudes, proper motions and parallaxes for more than 1.3
billion stars. This part of the catalogue is essentially complete for
12<G<17, which is the range where we expect to find most of the
cluster stars discussed in this paper. There are, however, a few members
of the four alleged clusters that are brighter than G=12 and are not
included in Gaia DR2, but do not impact the results of this paper. We
also disregarded all stars with the proper motion error>0.5mas/yr
or parallax error>10 per cent. Radial velocities in Gaia DR2 are
only given for 7.2 million stars down to G=13. Because the precision
of radial velocities is significantly higher in the GALAH survey
(Zwitter et al. 2018MNRAS.481..645Z) than the Gaia data release, we
use GALAH values wherever available. Because GALAH has a more limited
magnitude range than Gaia, there are many stars for which Gaia DR2
radial velocities must be used. From the cluster stars used in this work
that have radial velocity measured in both Gaia DR2 and GALAH we find
no systematic differences larger than 0.2km/s between the two surveys,
so we can use whichever velocity is available. (7 data files).
Title: VizieR Online Data Catalog: Thorium in solar twins (Botelho+,
2019)
Authors: Botelho, R. B.; Milone, A. De C.; Melendez, J.; Bedell, M.;
Spina, L.; Asplund, M.; Dos Santos, L.; Bean, J. L.; Ramirez, I.;
Yong, D.; Dreizler, S.; Alves-Brito, A.; Yana Galarza, J.
Bibcode: 2022yCat..74821690B
Altcode:
The sample is composed of 67 solar twins (stars with effective
temperature, surface gravity, and metallicity around the solar values
within {+/-}100K in Teff and within {+/-}0.1dex in logg and [Fe/H]),
which were recently analysed by Spina et al. (2018MNRAS.474.2580S) and
Bedell et al. (2018ApJ...865...68B). Spina et al. (2018MNRAS.474.2580S)
derived their photospheric parameters by applying a line-by-line
differential spectroscopic analysis relative to the Sun through
equivalent width (EW) measurements of FeI and FeII lines. The estimated
typical errors in Teff, logg, [Fe/H], and {xi} (micro-turbulence
velocity) are, respectively, 4K, 0.012, 0.004dex and 0.011km/s. High
Accuracy Radial velocity Planet Searcher (HARPS) spectra are used
in this work to extract Th abundances. HARPS is an ultra-stable
echelle spectrograph installed on the 3.6m telescope of the European
Southern Observatory (ESO) at La Silla Observatory in Chile (Mayor
et al. 2003Msngr.114...20M). The HARPS spectra covers λ=3780-6910Å
under a resolving power R=115000. Each one-dimensional spectrum comes
from more than 50 stacked spectra that are previously Doppler-corrected
and carefully continuum normalized. (3 data files).
Title: Combined APOGEE-GALAH stellar catalogues using the Cannon
Authors: Nandakumar, Govind; Hayden, Michael R.; Sharma, Sanjib; Buder,
Sven; Asplund, Martin; Bland-Hawthorn, Joss; De Silva, Gayandhi M.;
D'Orazi, Valentina; Freeman, Ken C.; Kos, Janez; Lewis, Geraint F.;
Martell, Sarah L.; Schlesinger, Katharine J.; Lin, Jane; Simpson,
Jeffrey D.; Zucker, Daniel B.; Zwitter, Tomaž; Nordlander, Thomas;
Casagrande, Luca; Lind, Karin; Côtar, Klemen; Stello, Dennis;
Wittenmyer, Robert A.; Tepper-Garcia, Thor
Bibcode: 2022MNRAS.513..232N
Altcode: 2022MNRAS.tmp..866N
APOGEE and GALAH are two high resolution multi-object spectroscopic
surveys that provide fundamental stellar parameters and multiple
elemental abundance estimates for about half a million stars in the
Milky Way. Both surveys observe in different wavelength regimes and
use different data reduction pipelines leading to significant offsets
and trends in stellar parameters and abundances for the common stars
observed in both surveys. Such systematic differences/offsets in stellar
parameters and abundances make it difficult to effectively utilize
them to investigate Galactic abundance trends in spite of the unique
advantage provided by their complementary sky coverage and different
Milky Way components they observe. Hence, we use the Cannon data-driven
method selecting a training set of 4418 common stars observed by
both surveys. This enables the construction of two catalogues, one
with the APOGEE-scaled and the other with the GALAH-scaled stellar
parameters. Using repeat observations in APOGEE and GALAH, we find
high precision in metallicity (~0.02-0.4 dex) and alpha abundances
(~0.02-0.03 dex) for spectra with good signal-to-noise ratio (SNR >
80 for APOGEE and SNR > 40 for GALAH). We use open and globular
clusters to validate our parameter estimates and find small scatter in
metallicity (0.06 dex) and alpha abundances (0.03 dex) in APOGEE-scaled
case. The final catalogues have been cross-matched with the Gaia EDR3
catalogue to enable their use to carry out detailed chemo-dynamic
studies of the Milky Way from perspectives of APOGEE and GALAH.
Title: The internal rotation of the Sun and its link to the solar
Li and He surface abundances
Authors: Eggenberger, P.; Buldgen, G.; Salmon, S. J. A. J.; Noels,
A.; Grevesse, N.; Asplund, M.
Bibcode: 2022NatAs...6..788E
Altcode: 2022NatAs.tmp..119E
The Sun serves as a natural reference for the modelling of the various
physical processes at work in stellar interiors. Helioseismology
results, which inform us on the characterization of the interior of
the Sun (such as, for example, the helium abundance in its envelope),
are, however, at odds with heavy element abundances. Moreover,
the solar internal rotation and surface abundance of lithium have
always been challenging to explain. We present results of solar models
that account for transport of angular momentum and chemicals by both
hydrodynamic and magnetic instabilities. We show that these transport
processes reconcile the internal rotation of the Sun, its surface
lithium abundance, and the helioseismic determination of the envelope
helium abundance. We also show that the efficiency of the transport of
chemicals required to account for the solar surface lithium abundance
also predicts the correct value of helium, independently from a specific
transport process.
Title: The GALAH Survey: dependence of elemental abundances on age
and metallicity for stars in the Galactic disc
Authors: Sharma, Sanjib; Hayden, Michael R.; Bland-Hawthorn,
Joss; Stello, Dennis; Buder, Sven; Zinn, Joel C.; Spina, Lorenzo;
Kallinger, Thomas; Asplund, Martin; De Silva, Gayandhi M.; D'Orazi,
Valentina; Freeman, Ken C.; Kos, Janez; Lewis, Geraint F.; Lin, Jane;
Lind, Karin; Martell, Sarah L.; Schlesinger, Katharine J.; Simpson,
Jeffrey D.; Zucker, Daniel B.; Zwitter, Tomaž; Chen, Boquan; Cotar,
Klemen; Kafle, Prajwal R.; Khanna, Shourya; Tepper-Garcia, Thor;
Wang, Purmortal; Wittenmyer, Rob A.
Bibcode: 2022MNRAS.510..734S
Altcode: 2021MNRAS.tmp.3061S; 2020arXiv201113818S
Using data from the GALAH survey, we explore the dependence of elemental
abundances on stellar age and metallicity among Galactic disc stars. We
find that the abundance of most elements can be predicted from age and
[Fe/H] with an intrinsic scatter of about 0.03 dex. We discuss the
possible causes for the existence of the abundance-age-metallicity
relations. Using a stochastic chemical enrichment scheme that takes
the volume of supernovae remnants into account, we show the intrinsic
scatter is expected to be small, about 0.05 dex or even smaller if
there is additional mixing in the ISM. Elemental abundances show
trends with both age and metallicity and the relationship is well
described by a simple model in which the dependence of abundance
([X/Fe]) on age and [Fe/H] are additively separable. Elements can be
grouped based on the direction of their abundance gradient in the
(age,[Fe/H]) plane and different groups can be roughly associated
with three distinct nucleosynthetic production sites, the exploding
massive stars, the exploding white dwarfs, and the AGB stars. However,
the abundances of some elements, like Co, La, and Li, show large scatter
for a given age and metallicity, suggesting processes other than simple
Galactic chemical evolution are at play. We also compare the abundance
trends of main-sequence turn-off (MSTO) stars against that of giants,
whose ages were estimated using asteroseismic information from the K2
mission. For most elements, the trends of MSTO stars are similar to
that of giants. The existence of abundance relations implies that we
can estimate the age and birth radius of disc stars, which is important
for studying the dynamic and chemical evolution of the Galaxy.
Title: Distances, extinctions, and stellar parameters for stars in
SkyMapper DR3
Authors: Lin, Jane; Casagrande, Luca; Asplund, Martin
Bibcode: 2022MNRAS.510..433L
Altcode: 2021MNRAS.tmp.3066L
We present a Bayesian isochrone fitting machinery to derive distances,
extinctions, and stellar parameters (Teff, log g, and $\rm
[Fe/H]$) for stars in the SkyMapper data release 3 (DR3) survey. We
complement the latter with photometry from Gaia, 2MASS, and AllWISE,
in addition to priors on parallaxes and interstellar extinction. We
find our results to be in agreement with smaller samples of literature
values derived using spectroscopic/photometric method, with typical
uncertainties of order 130 K in effective temperature and 0.2 dex
in surface gravity and metallicity. We demonstrate the quality of
our stellar parameters by benchmarking our results against various
spectroscopic surveys. We highlight the potential that SkyMapper bears
for stellar population studies showing how we are able to clearly
differentiate metallicities along the Gaia red (~-0.4 dex) and blue
(~-1.1 dex) sequences using both dwarf and giant stars.
Title: The SAPP pipeline for the determination of stellar abundances
and atmospheric parameters of stars in the core program of the
PLATO mission
Authors: Gent, Matthew Raymond; Bergemann, Maria; Serenelli, Aldo;
Casagrande, Luca; Gerber, Jeffrey M.; Heiter, Ulrike; Kovalev, Mikhail;
Morel, Thierry; Nardetto, Nicolas; Adibekyan, Vardan; Silva Aguirre,
Víctor; Asplund, Martin; Belkacem, Kevin; del Burgo, Carlos; Bigot,
Lionel; Chiavassa, Andrea; Rodríguez Díaz, Luisa Fernanda; Goupil,
Marie-Jo; González Hernández, Jonay I.; Mourard, Denis; Merle,
Thibault; Mészáros, Szabolcs; Marshall, Douglas J.; Ouazzani,
Rhita-Maria; Plez, Bertrand; Reese, Daniel; Trampedach, Regner;
Tsantaki, Maria
Bibcode: 2022A&A...658A.147G
Altcode: 2021arXiv211106666G
We introduce the SAPP (Stellar Abundances and atmospheric Parameters
Pipeline), the prototype of the code that will be used to determine
parameters of stars observed within the core program of the PLATO
space mission. The pipeline is based on the Bayesian inference and
provides effective temperature, surface gravity, metallicity, chemical
abundances, and luminosity. The code in its more general version has a
much wider range of potential applications. It can also provide masses,
ages, and radii of stars and can be used with stellar types not targeted
by the PLATO core program, such as red giants. We validate the code on
a set of 27 benchmark stars that includes 19 FGK-type dwarfs, 6 GK-type
subgiants, and 2 red giants. Our results suggest that combining various
observables is the optimal approach, as this allows the degeneracies
between different parameters to be broken and yields more accurate
values of stellar parameters and more realistic uncertainties. For the
PLATO core sample, we obtain a typical uncertainty of 27 (syst.) ±
37 (stat.) K for Teff, 0.00 ± 0.01 dex for log g, 0.02
± 0.02 dex for metallicity [Fe/H], −0.01 ± 0.03 R⊙
for radii, −0.01 ± 0.05 M⊙ for stellar masses, and
−0.14 ± 0.63 Gyr for ages. We also show that the best results
are obtained by combining the νmax scaling relation with
stellar spectra. This resolves the notorious problem of degeneracies,
which is particularly important for F-type stars.
Title: Non-detection of 6Li in Spite plateau stars with
ESPRESSO
Authors: Wang, Ella Xi; Nordlander, Thomas; Asplund, Martin; Lind,
Karin; Zhou, Yixiao; Reggiani, Henrique
Bibcode: 2022MNRAS.509.1521W
Altcode: 2021MNRAS.tmp.2661W; 2021arXiv211003822E; 2021arXiv211003822W
The detection of 6Li in Spite plateau stars contradicts
the standard big bang nucleosynthesis prediction, known as the
second cosmological lithium problem. We measure the isotopic ratio
6Li/7Li in three Spite plateau stars: HD
84937, HD 140283, and LP 815-43. We use 3D non-local thermodynamic
equilibrium radiative transfer and for the first time apply this to
high-resolution, high signal-to-noise ratio data from the ultra-stable
ESPRESSO/Very Large Telescope spectrograph. These are among the
best spectra ever taken of any metal-poor stars. As the measurement
of 6Li/7Li is degenerate with other physical
stellar parameters, we employ Markov chain Monte Carlo methods to find
the probability distributions of measured parameters. As a test of
systematics, we also use three different fitting methods. We do not
detect 6Li in any of the three stars, and find consistent
results between our different methods. We estimate 2σ upper limits
to 6Li/7Li of 0.7, 0.6, and 1.7 per cent,
respectively, for HD 84937, HD 140283, and LP 815-43. Our results
indicate that there is no second cosmological lithium problem, as
there is no evidence of 6Li in Spite plateau stars.
Title: The GALAH+ survey: a new library of observed stellar spectra
improves radial velocities and hints at motions within M67
Authors: Zwitter, Tomaž; Kos, Janez; Buder, Sven; Čotar, Klemen;
Asplund, Martin; Bland-Hawthorn, Joss; Casey, Andrew R.; De Silva,
Gayandhi M.; D'Orazi, Valentina; Freeman, Ken C.; Hayden, Michael
R.; Lewis, Geraint F.; Lin, Jane; Lind, Karin; Martell, Sarah L.;
Schlesinger, Katharine J.; Sharma, Sanjib; Simpson, Jeffrey D.;
Stello, Dennis; Zucker, Daniel B.; Beeson, Kevin L.; de Grijs, Richard;
Nordlander, Thomas; Ting, Yuan-Sen; Traven, Gregor; Vogrinčič, Rok;
Watson, Fred; Wittenmyer, Rob
Bibcode: 2021MNRAS.508.4202Z
Altcode: 2020arXiv201212201Z; 2021MNRAS.tmp.2413Z
GALAH+ is a magnitude-limited survey of high-resolution stellar spectra
obtained by the HERMES spectrograph at the Australian Astronomical
Observatory. Its third data release provides reduced spectra with
new derivations of stellar parameters and abundances of 30 chemical
elements for 584 015 dwarfs and giants, 88 per cent of them in the
Gaia magnitude range 11 < G < 14. Here, we use these improved
values of stellar parameters to build a library of observed spectra
which is useful to study variations of individual spectral lines
with stellar parameters. This and other improvements are used to
derive radial velocities with uncertainties which are generally
within 0.1 km s-1 or ~25 per cent smaller than in the
previous release. Median differences in radial velocities measured
here and by the Gaia DR2 or APOGEE DR16 surveys are smaller than 30 m
s-1, a larger offset is present only for Gaia measurements
of giant stars. We identify 4483 stars with intrinsically variable
velocities and 225 stars for which the velocity stays constant over
≥3 visits spanning more than a year. The combination of radial
velocities from GALAH+ with distances and sky plane motions from
Gaia enables studies of dynamics within streams and clusters. For
example, we estimate that the open cluster M67 has a total mass of
~3300 M⊙ and its outer parts seem to be expanding, though
astrometry with a larger time-span than currently available from Gaia
eDR3 is needed to judge if the latter result is real.
Title: The solar carbon, nitrogen, and oxygen abundances from a 3D
LTE analysis of molecular lines
Authors: Amarsi, A. M.; Grevesse, N.; Asplund, M.; Collet, R.
Bibcode: 2021A&A...656A.113A
Altcode: 2021arXiv210904752A
Carbon, nitrogen, and oxygen are the fourth, sixth, and third most
abundant elements in the Sun. Their abundances remain hotly debated due
to the so-called solar modelling problem that has persisted for almost
20 years. We revisit this issue by presenting a homogeneous analysis
of 408 molecular lines across 12 diagnostic groups, observed in the
solar intensity spectrum. Using a realistic 3D radiative-hydrodynamic
model solar photosphere and local thermodynamic equilibrium (LTE)
line formation, we find log ϵC = 8.47 ± 0.02, log
ϵN = 7.89 ± 0.04, and log ϵO = 8.70 ±
0.04. The stipulated uncertainties mainly reflect the sensitivity of
the results to the model atmosphere; this sensitivity is correlated
between the different diagnostic groups, which all agree with the
mean result to within 0.03 dex. For carbon and oxygen, the molecular
results are in excellent agreement with our 3D non-LTE analyses of
atomic lines. For nitrogen, however, the molecular indicators give
a 0.12 dex larger abundance than the atomic indicators, and our
best estimate of the solar nitrogen abundance is given by the mean:
7.83 dex. The solar oxygen abundance advocated here is close to our
earlier determination of 8.69 dex, and so the present results do
not significantly alleviate the solar modelling problem. Full
Table 2 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/656/A113
Title: Erratum: The GALAH survey: Chemical homogeneity of the
Orion complex
Authors: Kos, Janez; Bland-Hawthorn, Joss; Buder, Sven; Nordlander,
Thomas; Spina, Lorenzo; Beeson, Kevin L.; Lind, Karin; Asplund,
Martin; Freeman, Ken; Hayden, Michael R.; Lewis, Geraint F.; Martell,
Sarah L.; Sharma, Sanjib; De Silva, Gayandhi; Simpson, Jeffrey D.;
Zucker, Daniel B.; Zwitter, Tomaž; Čotar, Klemen; Horner, Jonti;
Ting (丁源森), Yuan-Sen; Traven, Gregor
Bibcode: 2021MNRAS.508.4969K
Altcode:
No abstract at ADS
Title: Spectroscopy and Photometry of the Least Massive Type II
Globular Clusters: NGC 1261 and NGC 6934
Authors: Marino, A. F.; Milone, A. P.; Renzini, A.; Yong, D.; Asplund,
M.; Da Costa, G. S.; Jerjen, H.; Cordoni, G.; Carlos, M.; Dondoglio,
E.; Lagioia, E. P.; Jang, S.; Tailo, M.
Bibcode: 2021ApJ...923...22M
Altcode: 2021arXiv210615978M
Recent work has revealed two classes of globular clusters (GCs), dubbed
Type I and Type II. Type II GCs are characterized by both a blue and a
red red giant branch composed of stars with different metallicities,
often coupled with distinct abundances in the slow neutron-capture
elements (s-elements). Here we continue the chemical tagging of Type II
GCs by adding the two least massive clusters of this class, NGC 1261 and
NGC 6934. Based on both spectroscopy and photometry, we find red stars
in NGC 1261 to be slightly enhanced in [Fe/H] by ~0.1 dex and confirm
that red stars of NGC 6934 are enhanced in iron by ~0.2 dex. Neither
NGC 1261 nor NGC 6934 show internal variations in the s-elements,
which suggests a GC mass threshold for the occurrence of s-process
enrichment. We found a significant correlation between the additional Fe
locked in the red stars of Type II GCs and the present-day mass of the
cluster. Nevertheless, most Type II GCs retained a small fraction of Fe
produced by SNe II, lower than the 2%; NGC 6273, M54, and ω Centauri
are remarkable exceptions. In the Appendix, we infer for the first time
chemical abundances of lanthanum, assumed as representative of the
s-elements, in M54, the GC located in the nucleus of the Sagittarius
dwarf galaxy. Red-sequence stars are marginally enhanced in [La/Fe]
by 0.10 ± 0.06 dex, in contrast with the large [La/Fe] spread of most
Type II GCs. We suggest that different processes are responsible for the
enrichment in iron and s-elements in Type II GCs. * Based
on observations collected at the European Southern Observatory under
ESO program 0101.D-0109(A), and the NASA/ESA Hubble Space Telescope,
obtained at the Space Telescope Science Institute, which is operated
by AURA, Inc., under NASA contract NAS 5-26555.
Title: Chemical evolution of the Galactic bulge as traced by
microlensed dwarf and subgiant stars. VIII. Carbon and oxygen
Authors: Bensby, T.; Gould, A.; Asplund, M.; Feltzing, S.; Meléndez,
J.; Johnson, J. A.; Lucatello, S.; Udalski, A.; Yee, J. C.
Bibcode: 2021A&A...655A.117B
Altcode: 2021arXiv210611314B
Context. Next to H and He, carbon is, together with oxygen, the most
abundant element in the Universe and widely used when modelling the
formation and evolution of galaxies and their stellar populations. For
the Milky Way bulge, there are currently essentially no measurements of
carbon in un-evolved stars, hampering our abilities to properly compare
Galactic chemical evolution models to observational data for this still
enigmatic stellar population.
Aims: We aim to determine carbon
abundances for our sample of 91 microlensed dwarf and subgiant stars
in the Galactic bulge. Together with new determinations for oxygen
this forms the first statistically significant sample of bulge stars
that have C and O abundances measured, and for which the C abundances
have not been altered by the nuclear burning processes internal to
the stars.
Methods: Our analysis is based on high-resolution
spectra for a sample of 91 dwarf and subgiant stars that were obtained
during microlensing events when the brightnesses of the stars were
highly magnified. Carbon abundances were determined through spectral
line synthesis of six C I lines around 9100 Å, and oxygen abundances
using the three O I lines at about 7770 Å. One-dimensional (1D) MARCS
model stellar atmospheres calculated under the assumption of local
thermodynamic equilibrium (LTE) were used, and non-LTE corrections were
applied when calculating the synthetic spectra for both C and O.
Results: Carbon abundances was possible to determine for 70 of the 91
stars in the sample and oxygen abundances for 88 of the 91 stars in the
sample. The [C/Fe] ratio evolves essentially in lockstep with [Fe/H],
centred around solar values at all [Fe/H]. The [O/Fe]-[Fe/H] trend
has an appearance very similar to that observed for other α-elements
in the bulge, with the exception of a continued decrease in [O/Fe]
at super-solar [Fe/H], where other α-elements tend to level out. When
dividing the bulge sample into two sub-groups, one younger than 8 Gyr
and one older than 8 Gyr, the stars in the two groups follow exactly
the elemental abundance trends defined by the solar neighbourhood
thin and thick disks, respectively. Comparisons with recent models
of Galactic chemical evolution in the [C/O]-[O/H] plane show that the
models that best match the data are the ones that have been calculated
with the Galactic thin and thick disks in mind.
Conclusions: We
conclude that carbon, oxygen, and the combination of the two support
the idea that the majority of the stars in the Galactic bulge have a
secular origin; that is, they are formed from disk material. We cannot
exclude that a fraction of stars in the bulge could be classified as
a classical bulge population, but it would have to be small. More
dedicated and advanced models of the inner region of the Milky Way
are needed to make more detailed comparisons to the observations. Full Table 2 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or viahttp://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/655/A117
Based on data obtained with the European Southern Observatory
telescopes (Proposal ID:s 87.B-0600, 88.B-0349, 89.B-0047, 90.B-0204,
91.B-0289, 92.B-0626, 93.B-0700), the Magellan Clay telescope at the
Las Campanas observatory, and the Keck I telescope at the W.M. Keck
Observatory, which is operated as a scientific partnership among the
California Institute of Technology, the University of California,
and the National Aeronautics and Space Administration.
Title: High-resolution spectroscopic follow-up of the most metal-poor
candidates from SkyMapper DR1.1
Authors: Yong, D.; Da Costa, G. S.; Bessell, M. S.; Chiti, A.; Frebel,
A.; Gao, X.; Lind, K.; Mackey, A. D.; Marino, A. F.; Murphy, S. J.;
Nordlander, T.; Asplund, M.; Casey, A. R.; Kobayashi, C.; Norris,
J. E.; Schmidt, B. P.
Bibcode: 2021MNRAS.507.4102Y
Altcode: 2021MNRAS.tmp.1796Y; 2021arXiv210706430Y
We present chemical abundances for 21 elements (from Li to Eu)
in 150 metal-poor Galactic stars spanning -4.1 < [Fe/H] <
-2.1. The targets were selected from the SkyMapper survey and
include 90 objects with [Fe/H] ≤ -3 of which some 15 have [Fe/H]
≤ -3.5. When combining the sample with our previous studies, we find
that the metallicity distribution function has a power-law slope of
Δ(log N)/Δ[Fe/H] = 1.51 ± 0.01 dex per dex over the range -4 ≤
[Fe/H] ≤ -3. With only seven carbon-enhanced metal-poor stars in the
sample, we again find that the selection of metal-poor stars based
on SkyMapper filters is biased against highly carbon-rich stars for
[Fe/H] > -3.5. Of the 20 objects for which we could measure nitrogen,
11 are nitrogen-enhanced metal-poor (NEMP) stars. Within our sample,
the high NEMP fraction (55 per cent ± 21 per cent) is compatible
with the upper range of predicted values (between 12 per cent and 35
per cent). The chemical abundance ratios [X/Fe] versus [Fe/H] exhibit
similar trends to previous studies of metal-poor stars and Galactic
chemical evolution models. We report the discovery of nine new r-I
stars, four new r-II stars, one of which is the most metal-poor known,
nine low-α stars with [α/Fe] ≤ 0.15 as well as one unusual star with
[Zn/Fe] = +1.4 and [Sr/Fe] = +1.2 but with normal [Ba/Fe]. Finally, we
combine our sample with literature data to provide the most extensive
view of the early chemical enrichment of the Milky Way Galaxy.
Title: Detailed elemental abundances of binary stars: searching for
signatures of planet formation and atomic diffusion
Authors: Liu, Fan; Bitsch, Bertram; Asplund, Martin; Liu, Bei-Bei;
Murphy, Michael T.; Yong, David; Ting, Yuan-Sen; Feltzing, Sofia
Bibcode: 2021MNRAS.508.1227L
Altcode: 2021MNRAS.tmp.2246L; 2021arXiv210811001L
Binary star systems are assumed to be co-natal and coeval, and thus to
have identical chemical composition. In this work, we aim to test the
hypothesis that there is a connection between observed element abundance
patterns and the formation of planets using binary stars. Moreover,
we also want to test how atomic diffusion might influence the observed
abundance patterns. We conduct a strictly line-by-line differential
chemical abundance analysis of seven binary systems. Stellar atmospheric
parameters and elemental abundances are obtained with extremely
high precision (<3.5 per cent) using the high-quality spectra
from Very Large Telescope/ultraviolet-visual Echelle spectrograph
and Keck/high-resolution Echelle spectrometer. We find that four of
seven binary systems show subtle abundance differences (0.01-0.03
dex) without clear correlations with the condensation temperature,
including two planet-hosting pairs. The other three binary systems
exhibit similar degree of abundance differences correlating with the
condensation temperature. We do not find any clear relation between
the abundance differences and the occurrence of known planets in
our systems. Instead, the overall abundance offsets observed in the
binary systems (four of seven) could be due to the effects of atomic
diffusion. Although giant planet formation does not necessarily imprint
chemical signatures on to the host star, the differences in the observed
abundance trends with condensation temperature, on the other hand,
are likely associated with diverse histories of planet formation
(e.g. formation location). Furthermore, we find a weak correlation
between abundance differences and binary separation, which may provide
a new constraint on the formation of binary systems.
Title: The GALAH survey: effective temperature calibration from the
InfraRed Flux Method in the Gaia system
Authors: Casagrande, Luca; Lin, Jane; Rains, Adam D.; Liu, Fan;
Buder, Sven; Horner, Jonathan; Asplund, Martin; Lewis, Geraint F.;
Martell, Sarah L.; Nordlander, Thomas; Stello, Dennis; Ting, Yuan-Sen;
Wittenmyer, Robert A.; Bland-Hawthorn, Joss; Casey, Andrew R.; De
Silva, Gayandhi M.; D'Orazi, Valentina; Freeman, Ken C.; Hayden,
Michael R.; Kos, Janez; Lind, Karin; Schlesinger, Katharine J.;
Sharma, Sanjib; Simpson, Jeffrey D.; Zucker, Daniel B.; Zwitter, Tomaž
Bibcode: 2021MNRAS.507.2684C
Altcode: 2020arXiv201102517C; 2021MNRAS.tmp.2075C
In order to accurately determine stellar properties, knowledge of
the effective temperature of stars is vital. We implement Gaia and
2MASS photometry in the InfraRed Flux Method and apply it to over
360 000 stars across different evolutionary stages in the GALAH DR3
survey. We derive colour-effective temperature relations that take
into account the effect of metallicity and surface gravity over the
range $4000\, \rm {K}\lesssim T_{\rm {eff}}\lesssim 8000\, \rm {K}$,
from very metal-poor stars to supersolar metallicities. The internal
uncertainty of these calibrations is of order 40-80 K depending
on the colour combination used. Comparison against solar-twins,
Gaia benchmark stars, and the latest interferometric measurements
validates the precision and accuracy of these calibrations from F
to early M spectral types. We assess the impact of various sources
of uncertainties, including the assumed extinction law, and provide
guidelines to use our relations. Robust solar colours are also derived.
Title: VizieR Online Data Catalog: COMBS Survey. Metal-poor bulge
stars (Lucey+, 2021)
Authors: Lucey, M.; Hawkins, K.; Ness, M.; Debattista, V. P.; Luna,
A.; Asplund, M.; Bensby, T.; Casagrande, L.; Feltzing, S.; Freeman,
K. C.; Kobayashi, C.; Marino, A. F.
Bibcode: 2021yCat..75015981L
Altcode:
Based on observations collected at the European Southern Observatory
under ESO programme: 089.B-069 (1 data file).
Title: The GALAH survey: accreted stars also inhabit the Spite plateau
Authors: Simpson, Jeffrey D.; Martell, Sarah L.; Buder, Sven;
Bland-Hawthorn, Joss; Casey, Andrew R.; de Silva, Gayandhi M.;
D'Orazi, Valentina; Freeman, Ken C.; Hayden, Michael; Kos, Janez;
Lewis, Geraint F.; Lind, Karin; Schlesinger, Katharine J.; Sharma,
Sanjib; Stello, Dennis; Zucker, Daniel B.; Zwitter, Tomaž; Asplund,
Martin; da Costa, Gary; Čotar, Klemen; Tepper-García, Thor; Horner,
Jonathan; Nordlander, Thomas; Ting, Yuan-Sen; Wyse, Rosemary F. G.;
Galah Collaboration
Bibcode: 2021MNRAS.507...43S
Altcode: 2021MNRAS.tmp.1793S; 2020arXiv201102659S
The European Space Agency (ESA) Gaia mission has enabled the
remarkable discovery that a large fraction of the stars near the solar
neighbourhood are debris from a single in-falling system, the so-called
Gaia-Sausage-Enceladus (GSE). This discovery provides astronomers for
the first time with a large cohort of easily observable, unevolved stars
that formed in a single extragalactic environment. Here we use these
stars to investigate the 'Spite plateau' - the near-constant lithium
abundance observed in unevolved metal-poor stars across a wide range
of metallicities (-3 < [Fe/H] < -1). Our aim is to test whether
individual galaxies could have different Spite plateaus - e.g. the
interstellar medium could be more depleted in lithium in a lower
galactic mass system due to it having a smaller reservoir of gas. We
identified 93 GSE dwarf stars observed and analysed by the GALactic
Archaeology with HERMES (GALAH) survey as part of its Data Release
3 (DR3). Orbital actions were used to select samples of GSE stars,
and comparison samples of halo and disc stars. We find that the GSE
stars show the same lithium abundance as other likely accreted stars
and in situ Milky Way stars. Formation environment leaves no imprint
on lithium abundances. This result fits within the growing consensus
that the Spite plateau, and more generally the 'cosmological lithium
problem' - the observed discrepancy between the amount of lithium in
warm, metal-poor dwarf stars in our Galaxy, and the amount of lithium
predicted to have been produced by big bang nucleosynthesis - is the
result of lithium depletion processes within stars.
Title: VizieR Online Data Catalog: Carbon and oxygen in microlensed
bulge dwarfs (Bensby+, 2021)
Authors: Bensby, T.; Gould, A.; Asplund, M.; Feltzing, S.; Melendez,
J.; Johnson, J. A.; Lucatello, S.; Udalski, A.; Yee, J. C.
Bibcode: 2021yCat..36550117B
Altcode:
We perform a detailed analysis of C and O in 91 microlensed dwarf stars
in the Galactic bulge. Abundances were determined through spectral
line synthesis of three oxygen lines at 777nm and six carbon lines
at 910nm. The stellar sample traces the evolution of the Galactic
bulge, and is the same as previously analysed by Bensby et al. (2017,
Cat. J/A+A/605/A89) where stellar parameters and ages were taken
from. For each star we give the NLTE corrected C and O abundances,
and their uncertainties based on the same analysis but increasing
and decreasing the stellar parameters (effective temperature, surface
gravity, metallicity, microturbulence) with their uncertainties. The
abundances have been normalised to the Sun, based on our analysis of
the Sun, on a line-by-line basis. We also give the absolute abundances
for individual lines. For each carbon line we give a flag (0, 1, or 2)
depending on whether the spectral line is close to a telluric absorption
line or not: 0 = not affected; 1 = closer than 0.03nm to a weak telluric
line (depth smaller than 15% of the continuum level); 2 = closer than
0.03 nm to a strong telluric line (depth greater than 15 % of the
continuum level). 70 stars have the carbon abundance measured
and 89 stars have the oxygen abundance measured. (1 data file).
Title: Fundamental relations for the velocity dispersion of stars
in the Milky Way
Authors: Sharma, Sanjib; Hayden, Michael R.; Bland-Hawthorn, Joss;
Stello, Dennis; Buder, Sven; Zinn, Joel C.; Kallinger, Thomas;
Asplund, Martin; De Silva, Gayandhi M.; D'Orazi, Valentina; Freeman,
Ken; Kos, Janez; Lewis, Geraint F.; Lin, Jane; Lind, Karin; Martell,
Sarah; Simpson, Jeffrey D.; Wittenmyer, Rob A.; Zucker, Daniel B.;
Zwitter, Tomaz; Chen, Boquan; Cotar, Klemen; Esdaile, James; Hon,
Marc; Horner, Jonathan; Huber, Daniel; Kafle, Prajwal R.; Khanna,
Shourya; Ting, Yuan-Sen; Nataf, David M.; Nordlander, Thomas; Saadon,
Mohd Hafiz Mohd; Tepper-Garcia, Thor; Tinney, C. G.; Traven, Gregor;
Watson, Fred; Wright, Duncan; Wyse, Rosemary F. G.
Bibcode: 2021MNRAS.506.1761S
Altcode: 2020arXiv200406556S; 2021MNRAS.tmp.1513S
We explore the fundamental relations governing the radial and vertical
velocity dispersions of stars in the Milky Way, from combined studies
of complementary surveys including GALAH, LAMOST, APOGEE, the NASA
Kepler and K2 missions, and Gaia DR2. We find that different stellar
samples, even though they target different tracer populations and
employ a variety of age estimation techniques, follow the same set of
fundamental relations. We provide the clearest evidence to date that,
in addition to the well-known dependence on stellar age, the velocity
dispersions of stars depend on orbital angular momentum Lz,
metallicity, and height above the plane |z|, and are well described
by a multiplicatively separable functional form. The dispersions have
a power-law dependence on age with exponents of 0.441 ± 0.007 and
0.251 ± 0.006 for σz and σR, respectively,
and the power law is valid even for the oldest stars. For the solar
neighbourhood stars, the apparent break in the power law for older
stars, as seen in previous studies, is due to the anticorrelation
of Lz with age. The dispersions decrease with increasing
Lz until we reach the Sun's orbital angular momentum,
after which σz increases (implying flaring in the outer
disc) while σR flattens. For a given age, the dispersions
increase with decreasing metallicity, suggesting that the dispersions
increase with birth radius. The dispersions also increase linearly with
|z|. The same set of relations that work in the solar neighbourhood also
work for stars between 3 < R/kpc < 20. Finally, the high-[α/Fe]
stars follow the same relations as the low-[α/Fe] stars.
Title: VizieR Online Data Catalog: The solar CNO abundances (Amarsi+,
2021)
Authors: Amarsi, A. M.; Grevesse, N.; Asplund, M.; Collet, R.
Bibcode: 2021yCat..36560113A
Altcode:
Table 2 contains the parameters, measured equivalent widths, and
abundances inferred from the different models, for the 408 lines used
in the present analysis. (1 data file).
Title: The GALAH survey: Chemical homogeneity of the Orion complex
Authors: Kos, Janez; Bland-Hawthorn, Joss; Buder, Sven; Nordlander,
Thomas; Spina, Lorenzo; Beeson, Kevin L.; Lind, Karin; Asplund,
Martin; Freeman, Ken; Hayden, Michael R.; Lewis, Geraint F.; Martell,
Sarah L.; Sharma, Sanjib; De Silva, Gayandhi; Simpson, Jeffrey D.;
Zucker, Daniel B.; Zwitter, Tomaž; Čotar, Klemen; Horner, Jonti;
Ting, Yuan-Sen; Traven, Gregor
Bibcode: 2021MNRAS.506.4232K
Altcode: 2020arXiv201102485K; 2021MNRAS.tmp.1571K
Due to its proximity, the Orion star forming region is often used as
a proxy to study processes related to star formation and to observe
young stars in the environment they were born in. With the release of
Gaia DR2, the distance measurements to the Orion complex are now good
enough that the 3D structure of the complex can be explored. Here we
test the hypothesis that, due to non-trivial structure and dynamics,
and age spread in the Orion complex, the chemical enrichment of
youngest stars by early core-collapse supernovae can be observed. We
obtained spectra of 794 stars of the Orion complex with the HERMES
spectrograph at the Anglo Australian telescope as a part of the
GALAH and GALAH-related surveys. We use the spectra of ~300 stars to
derive precise atmospheric parameters and chemical abundances of 25
elements for 15 stellar clusters in the Orion complex. We demonstrate
that the Orion complex is chemically homogeneous and that there was
no self-pollution of young clusters by core-collapse supernovae from
older clusters; with a precision of 0.02 dex in relative alpha-elements
abundance and 0.06 dex in oxygen abundance we would have been able to
detect pollution from a single supernova, given a fortunate location of
the SN and favourable conditions for ISM mixing. We estimate that the
supernova rate in the Orion complex was very low, possibly producing
no supernova by the time the youngest stars of the observed population
formed (from around 21 to 8 Myr ago).
Title: VizieR Online Data Catalog: The GALAH+ Survey DR3 (Buder+,
2021)
Authors: Buder, S.; Sharma, S.; Kos, J.; Amarsi, A. M.; Nordlander,
T.; Lind, K.; Martell, S. L.; Asplund, M.; Bland-Hawthorn, J.; Casey,
A. R.; de Silva, G. M.; D'Orazi, V.; Freeman, K. C.; Hayden, M. R.;
Lewis, G. F.; Lin, J.; Schlesinger, K. J.; Simpson, J. D.; Stello,
D.; Zucker, D. B.; Zwitter, T.; Beeson, K. L.; Buck, T.; Casagrande,
L.; Clark, J. T.; Cotar, K.; da Costa, G. S.; de Grijs, R.; Feuillet,
D.; Horner, J.; Kafle, P. R.; Khanna, S.; Kobayashi, C.; Liu, F.;
Montet, B. T.; Nandakumar, G.; Nataf, D. M.; Ness, M. K.; Spina, L.;
Tepper-Garcia, T.; Ting, Y. -S.; Traven, G.; Vogrincic, R.; Wittenmyer,
R. A.; Wyse, R. F. G.; Zerjal M. GALAH Collaboration
Bibcode: 2021yCat..75060150B
Altcode:
This is the third data release of the GALAH survey. Data for the
GALAH survey are taken with the HERMES spectrograph on the 3.9-metre
Anglo-Australian Telescope (AAT) at Siding Spring Observatory. HERMES
is a fibre-fed high-resolution (R=28000) spectrograph optimized to do
Galactic archaeology from a 4m class telescope, with four discrete
optical wavelength channels covering 4713-4903Å, 5648-5873Å,
6478-6737Å, 7585-7887Å. (5 data files).
Title: The GALAH+ survey: Third data release
Authors: Buder, Sven; Sharma, Sanjib; Kos, Janez; Amarsi, Anish M.;
Nordlander, Thomas; Lind, Karin; Martell, Sarah L.; Asplund, Martin;
Bland-Hawthorn, Joss; Casey, Andrew R.; de Silva, Gayandhi M.; D'Orazi,
Valentina; Freeman, Ken C.; Hayden, Michael R.; Lewis, Geraint F.;
Lin, Jane; Schlesinger, Katharine J.; Simpson, Jeffrey D.; Stello,
Dennis; Zucker, Daniel B.; Zwitter, Tomaž; Beeson, Kevin L.; Buck,
Tobias; Casagrande, Luca; Clark, Jake T.; Čotar, Klemen; da Costa,
Gary S.; de Grijs, Richard; Feuillet, Diane; Horner, Jonathan; Kafle,
Prajwal R.; Khanna, Shourya; Kobayashi, Chiaki; Liu, Fan; Montet,
Benjamin T.; Nandakumar, Govind; Nataf, David M.; Ness, Melissa K.;
Spina, Lorenzo; Tepper-García, Thor; Ting, Yuan-Sen; Traven, Gregor;
Vogrinčič, Rok; Wittenmyer, Robert A.; Wyse, Rosemary F. G.; Žerjal,
Maruša; Galah Collaboration
Bibcode: 2021MNRAS.506..150B
Altcode: 2020arXiv201102505B; 2021MNRAS.tmp.1259B
The ensemble of chemical element abundance measurements for stars,
along with precision distances and orbit properties, provides
high-dimensional data to study the evolution of the Milky Way. With
this third data release of the Galactic Archaeology with HERMES (GALAH)
survey, we publish 678 423 spectra for 588 571 mostly nearby stars
(81.2 per cent of stars are within <2 kpc), observed with the
HERMES spectrograph at the Anglo-Australian Telescope. This release
(hereafter GALAH+ DR3) includes all observations from GALAH Phase 1
(bright, main, and faint survey, 70 per cent), K2-HERMES (17 per cent),
TESS-HERMES (5 per cent), and a subset of ancillary observations (8
per cent) including the bulge and >75 stellar clusters. We derive
stellar parameters Teff, log g, [Fe/H], vmic,
vbroad, and vrad using our modified version of
the spectrum synthesis code Spectroscopy Made Easy (SME) and 1D MARCS
model atmospheres. We break spectroscopic degeneracies in our spectrum
analysis with astrometry from Gaia DR2 and photometry from 2MASS. We
report abundance ratios [X/Fe] for 30 different elements (11 of which
are based on non-LTE computations) covering five nucleosynthetic
pathways. We describe validations for accuracy and precision, flagging
of peculiar stars/measurements and recommendations for using our
results. Our catalogue comprises 65 per cent dwarfs, 34 per cent
giants, and 1 per cent other/unclassified stars. Based on unflagged
chemical composition and age, we find 62 per cent young low-$\alpha$,
9 per cent young high-$\alpha$, 27 per cent old high-$\alpha$, and 2
per cent stars with [Fe/H] ≤ -1. Based on kinematics, 4 per cent are
halo stars. Several Value-Added-Catalogues, including stellar ages and
dynamics, updated after Gaia eDR3, accompany this release and allow
chrono-chemodynamic analyses, as we showcase.
Title: The chemical make-up of the Sun: A 2020 vision
Authors: Asplund, M.; Amarsi, A. M.; Grevesse, N.
Bibcode: 2021A&A...653A.141A
Altcode: 2021arXiv210501661A
Context. The chemical composition of the Sun is a fundamental
yardstick in astronomy, relative to which essentially all cosmic
objects are referenced. As such, having accurate knowledge of the
solar elemental abundances is crucial for an extremely broad range
of topics.
Aims: We reassess the solar abundances of all
83 long-lived elements, using highly realistic solar modelling and
state-of-the-art spectroscopic analysis techniques coupled with the
best available atomic data and observations.
Methods: The
basis for our solar spectroscopic analysis is a three-dimensional
(3D) radiative-hydrodynamical model of the solar surface convection
and atmosphere, which reproduces the full arsenal of key observational
diagnostics. New complete and comprehensive 3D spectral line formation
calculations taking into account of departures from local thermodynamic
equilibrium (non-LTE) are presented for Na, Mg, K, Ca, and Fe using
comprehensive model atoms with reliable radiative and collisional
data. Our newly derived abundances for C, N, and O are based on a 3D
non-LTE analysis of permitted and forbidden atomic lines as well as
3D LTE calculations for a total of 879 molecular transitions of CH,
C2, CO, NH, CN, and OH. Previous 3D-based calculations for
another 50 elements are re-evaluated based on updated atomic data,
a stringent selection of lines, improved consideration of blends,
and new non-LTE calculations available in the literature. For elements
where spectroscopic determinations of the quiet Sun are not possible,
the recommended solar abundances are revisited based on complementary
methods, including helioseismology (He), solar wind data from the
Genesis sample return mission (noble gases), sunspot observations
(four elements), and measurements of the most primitive meteorites
(15 elements).
Results: Our new improved analysis confirms
the relatively low solar abundances of C, N, and O obtained in
our previous 3D-based studies: log ϵC = 8.46 ± 0.04,
log ϵN = 7.83 ± 0.07, and log ϵO = 8.69 ±
0.04. Excellent agreement between all available atomic and molecular
indicators is achieved for C and O, but for N the atomic lines imply
a lower abundance than for the molecular transitions for unknown
reasons. The revised solar abundances for the other elements also
typically agree well with our previously recommended values, with only
Li, F, Ne, Mg, Cl, Kr, Rb, Rh, Ba, W, Ir, and Pb differing by more
than 0.05 dex. The here-advocated present-day photospheric metal mass
fraction is only slightly higher than our previous value, mainly due
to the revised Ne abundance from Genesis solar wind measurements:
Xsurface = 0.7438 ± 0.0054, Ysurface =
0.2423 ± 0.0054, Zsurface = 0.0139 ± 0.0006, and
Zsurface/Xsurface = 0.0187 ± 0.0009. Overall,
the solar abundances agree well with those of CI chondritic meteorites,
but we identify a correlation with condensation temperature such that
moderately volatile elements are enhanced by ≈0.04 dex in the CI
chondrites and refractory elements possibly depleted by ≈0.02 dex,
conflicting with conventional wisdom of the past half-century. Instead,
the solar chemical composition more closely resembles that of the
fine-grained matrix of CM chondrites with the expected exception of the
highly volatile elements.
Conclusions: Updated present-day solar
photospheric and proto-solar abundances are presented for 83 elements,
including for all long-lived isotopes. The so-called solar modelling
problem - a persistent discrepancy between helioseismology and solar
interior models constructed with a low solar metallicity similar to
that advocated here - remains intact with our revised solar abundances,
suggesting shortcomings with the computed opacities and/or treatment of
mixing below the convection zone in existing standard solar models. The
uncovered trend between the solar and CI chondritic abundances with
condensation temperature is not yet understood but is likely imprinted
by planet formation, especially since a similar trend of opposite sign
is observed between the Sun and solar twins.
Title: The GALAH survey: a census of lithium-rich giant stars
Authors: Martell, Sarah L.; Simpson, Jeffrey D.; Balasubramaniam,
Adithya G.; Buder, Sven; Sharma, Sanjib; Hon, Marc; Stello, Dennis;
Ting, Yuan-Sen; Asplund, Martin; Bland-Hawthorn, Joss; De Silva,
Gayandhi M.; Freeman, Ken C.; Hayden, Michael; Kos, Janez; Lewis,
Geraint F.; Lind, Karin; Zucker, Daniel B.; Zwitter, Tomaž; Campbell,
Simon W.; Čotar, Klemen; Horner, Jonathan; Montet, Benjamin;
Wittenmyer, Rob
Bibcode: 2021MNRAS.505.5340M
Altcode: 2021MNRAS.tmp.1346M; 2020arXiv200602106M
We investigate the properties of 1262 red giant stars with high
photospheric abundances of lithium observed by the GALAH and K2-HERMES
surveys, and discuss them in the context of proposed mechanisms for
lithium enrichment and redepletion in giant stars. We confirm that
Li-rich giants are rare, making up only 1.2 per cent of our giant star
sample. We use stellar parameters from the third public data release
from the GALAH survey and a Bayesian isochrone analysis to divide
the sample into first-ascent red giant branch (RGB) and red clump
(RC) stars, and confirm these classifications using asteroseismic
data from K2. We find that RC stars are 2.5 times as likely to be
lithium-rich as RGB stars, in agreement with other recent work. The
probability for a star to be lithium-rich is affected by a number of
factors, though the causality in those correlations is not entirely
clear. We show for the first time that primary and secondary RC stars
have distinctly different lithium enrichment patterns. The data set
discussed here is large and heterogeneous in terms of evolutionary
phase, metallicity, rotation rate, and mass. We expect that if the
various mechanisms that have been proposed for lithium enrichment in
evolved stars are in fact active, they should all contribute to this
sample of lithium-rich giants at some level.
Title: The GALAH Survey: using galactic archaeology to refine our
knowledge of TESS target stars
Authors: Clark, Jake T.; Clerté, Mathieu; Hinkel, Natalie R.;
Unterborn, Cayman T.; Wittenmyer, Robert A.; Horner, Jonathan; Wright,
Duncan J.; Carter, Brad; Morton, Timothy D.; Spina, Lorenzo; Asplund,
Martin; Buder, Sven; Bland-Hawthorn, Joss; Casey, Andy; De Silva,
Gayandhi; D'Orazi, Valentina; Duong, Ly; Hayden, Michael; Freeman, Ken;
Kos, Janez; Lewis, Geraint; Lin, Jane; Lind, Karin; Martell, Sarah;
Sharma, Sanjib; Simpson, Jeffrey; Zucker, Dan; Zwitter, Tomaz; Tinney,
Christopher G.; Ting, Yuan-Sen; Nordlander, Thomas; Amarsi, Anish M.
Bibcode: 2021MNRAS.504.4968C
Altcode: 2020arXiv200805372C; 2021MNRAS.tmp.1044C
An unprecedented number of exoplanets are being discovered by the
Transiting Exoplanet Survey Satellite (TESS). Determining the orbital
parameters of these exoplanets, and especially their mass and radius,
will depend heavily upon the measured physical characteristics of
their host stars. We have cross-matched spectroscopic, photometric, and
astrometric data from GALAH Data Release 2, the TESS Input Catalog and
Gaia Data Release 2, to create a curated, self-consistent catalogue of
physical and chemical properties for 47 285 stars. Using these data,
we have derived isochrone masses and radii that are precise to within
5 per cent. We have revised the parameters of three confirmed, and
twelve candidate, TESS planetary systems. These results cast doubt
on whether CTOI-20125677 is indeed a planetary system, since the
revised planetary radii are now comparable to stellar sizes. Our
GALAH-TESS catalogue contains abundances for up to 23 elements. We
have specifically analysed the molar ratios for C/O, Mg/Si, Fe/Si,
and Fe/Mg, to assist in determining the composition and structure of
planets with Rp < 4R⊕. From these ratios,
36 per cent fall within 2$\sigma$ sigma of the Sun/Earth values,
suggesting that these stars may host rocky exoplanets with geological
compositions similar to planets found within our own Solar system.
Title: r-Process elements from magnetorotational hypernovae
Authors: Yong, D.; Kobayashi, C.; Da Costa, G. S.; Bessell, M. S.;
Chiti, A.; Frebel, A.; Lind, K.; Mackey, A. D.; Nordlander, T.;
Asplund, M.; Casey, A. R.; Marino, A. F.; Murphy, S. J.; Schmidt, B. P.
Bibcode: 2021Natur.595..223Y
Altcode: 2021arXiv210703010Y
Neutron-star mergers were recently confirmed
as sites of rapid-neutron-capture (r-process)
nucleosynthesis1-3. However, in Galactic chemical
evolution models, neutron-star mergers alone cannot reproduce
the observed element abundance patterns of extremely metal-poor
stars, which indicates the existence of other sites of r-process
nucleosynthesis4-6. These sites may be investigated by
studying the element abundance patterns of chemically primitive
stars in the halo of the Milky Way, because these objects retain
the nucleosynthetic signatures of the earliest generation of
stars7-13. Here we report the element abundance pattern of
the extremely metal-poor star SMSS J200322.54−114203.3. We observe
a large enhancement in r-process elements, with very low overall
metallicity. The element abundance pattern is well matched by the
yields of a single 25-solar-mass magnetorotational hypernova. Such a
hypernova could produce not only the r-process elements, but also
light elements during stellar evolution, and iron-peak elements
during explosive nuclear burning. Hypernovae are often associated with
long-duration γ-ray bursts in the nearby Universe8. This
connection indicates that similar explosions of fast-spinning strongly
magnetized stars occurred during the earliest epochs of star formation
in our Galaxy.
Title: VizieR Online Data Catalog: GALAH survey. Galactic disc with
open clusters (Spina+, 2021)
Authors: Spina, L.; Ting, Y. -S.; de Silva, G. M.; Frankel, N.; Sharma,
S.; Cantat-Gaudin, T.; Joyce, M.; Stello, D.; Karakas, A. I.; Asplund,
M. B.; Nordlander, T.; Casagrande, L.; D'Orazi, V.; Casey, A. R.;
Cottrell, P.; Tepper-Garcia, T.; Baratella, M.; Kos, J.; Cotar, K.;
Bland-Hawthorn, J.; Buder, S.; Freeman, K. C.; Hayden, M. R.; Lewis,
G. F.; Lin, J.; Lind, K.; Martell, S. L.; Schlesinger, K. J.; Simpson,
J. D.; Zucker, D. B.; Zwitter, T.
Bibcode: 2021yCat..75033279S
Altcode:
In this study, we make use of three data sets: Gaia DR2 (Gaia
Collaboration, 2018A&A...616A...1G, Cat. I/345), APOGEE DR16
(Ahumada et al., 2020ApJS..249....3A) and GALAH+ (Wittenmyer et al.,
2018AJ....155...84W; Sharma et al., 2018, Cat. J/MNRAS/473/2004,
2019MNRAS.490.5335S; Buder et al., 2020, arXiv:2011.02505). In
this work, we used astrometric information from Gaia to identify the
stellar members of the 226 open clusters that potentially fall in the
footprints of the APOGEE or GALAH survey. Stellar coordinates
and astrometric solutions from Gaia are used for cluster membership
analysis. Radial velocities (RVs) provided by either Gaia, APOGEE,
or GALAH. (3 data files).
Title: The relationship between photometric and spectroscopic
oscillation amplitudes from 3D stellar atmosphere simulations
Authors: Zhou, Yixiao; Nordlander, Thomas; Casagrande, Luca; Joyce,
Meridith; Li, Yaguang; Amarsi, Anish M.; Reggiani, Henrique; Asplund,
Martin
Bibcode: 2021MNRAS.503...13Z
Altcode: 2021MNRAS.tmp..360Z; 2021arXiv210202135Z
We establish a quantitative relationship between photometric and
spectroscopic detections of solar-like oscillations using ab initio,
3D, hydrodynamical numerical simulations of stellar atmospheres. We
present a theoretical derivation as a proof of concept for our
method. We perform realistic spectral line formation calculations to
quantify the ratio between luminosity and radial velocity amplitude
for two case studies: the Sun and the red giant ϵ Tau. Luminosity
amplitudes are computed based on the bolometric flux predicted by
3D simulations with granulation background modelled the same way as
asteroseismic observations. Radial velocity amplitudes are determined
from the wavelength shift of synthesized spectral lines with methods
closely resembling those used in Birmingham Solar Oscillations
Network (BiSON) and Stellar Oscillations Network Group (SONG)
observations. Consequently, the theoretical luminosity to radial
velocity amplitude ratios are directly comparable with corresponding
observations. For the Sun, we predict theoretical ratios of 21.0
and 23.7 ppm [m s-1]-1 from BiSON and SONG,
respectively, in good agreement with observations 19.1 and 21.6 ppm
[m s-1]-1. For ϵ Tau, we predict K2 and SONG
ratios of 48.4 ppm [m s-1]-1, again in good
agreement with observations 42.2 ppm [m s-1]-1,
and much improved over the result from conventional empirical scaling
relations that give 23.2 ppm [m s-1]-1. This study
thus opens the path towards a quantitative understanding of solar-like
oscillations, via detailed modelling of 3D stellar atmospheres.
Title: The GALAH Survey: No Chemical Evidence of an Extragalactic
Origin for the Nyx Stream
Authors: Zucker, Daniel B.; Simpson, Jeffrey D.; Martell, Sarah
L.; Lewis, Geraint F.; Casey, Andrew R.; Ting, Yuan-Sen; Horner,
Jonathan; Nordlander, Thomas; Wyse, Rosemary F. G.; Zwitter, Tomaž;
Bland-Hawthorn, Joss; Buder, Sven; Asplund, Martin; De Silva, Gayandhi
M.; D'Orazi, Valentina; Freeman, Ken C.; Hayden, Michael R.; Kos,
Janez; Lin, Jane; Lind, Karin; Schlesinger, Katharine J.; Sharma,
Sanjib; Stello, Dennis
Bibcode: 2021ApJ...912L..30Z
Altcode: 2021arXiv210408684Z
The results from the ESA Gaia astrometric mission and deep photometric
surveys have revolutionized our knowledge of the Milky Way. There are
many ongoing efforts to search these data for stellar substructure to
find evidence of individual accretion events that built up the Milky
Way and its halo. One of these newly identified features, called Nyx,
was announced as an accreted stellar stream traveling in the plane
of the disk. Using a combination of elemental abundances and stellar
parameters from the GALAH and Apache Point Observatory Galactic
Evolution Experiment (APOGEE) surveys, we find that the abundances
of the highest likelihood Nyx members are entirely consistent with
membership of the thick disk, and inconsistent with a dwarf galaxy
origin. We conclude that the postulated Nyx stream is most probably
a high-velocity component of the Milky Way's thick disk. With the
growing availability of large data sets including kinematics, stellar
parameters, and detailed abundances, the probability of detecting
chance associations increases, and hence new searches for substructure
require confirmation across as many data dimensions as possible.
Title: The GALAH survey: tracing the Galactic disc with open clusters
Authors: Spina, L.; Ting, Y. -S.; De Silva, G. M.; Frankel, N.; Sharma,
S.; Cantat-Gaudin, T.; Joyce, M.; Stello, D.; Karakas, A. I.; Asplund,
M. B.; Nordlander, T.; Casagrande, L.; D'Orazi, V.; Casey, A. R.;
Cottrell, P.; Tepper-García, T.; Baratella, M.; Kos, J.; Čotar,
K.; Bland-Hawthorn, J.; Buder, S.; Freeman, K. C.; Hayden, M. R.;
Lewis, G. F.; Lin, J.; Lind, K.; Martell, S. L.; Schlesinger, K. J.;
Simpson, J. D.; Zucker, D. B.; Zwitter, T.
Bibcode: 2021MNRAS.503.3279S
Altcode: 2021MNRAS.tmp..491S; 2020arXiv201102533S
Open clusters are unique tracers of the history of our own Galaxy's
disc. According to our membership analysis based on Gaia astrometry,
out of the 226 potential clusters falling in the footprint of
the GALactic Archaeology with HERMES (GALAH) survey or the Apache
Point Observatory Galactic Evolution Experiment (APOGEE) survey,
we find that 205 have secure members that were observed by at least
one of the surveys. Furthermore, members of 134 clusters have
high-quality spectroscopic data that we use to determine their
chemical composition. We leverage this information to study the
chemical distribution throughout the Galactic disc of 21 elements,
from C to Eu. The radial metallicity gradient obtained from our
analysis is -0.076 ± 0.009 dex kpc-1, which is in
agreement with previous works based on smaller samples. Furthermore,
the gradient in the [Fe/H]-guiding radius (rguid) plane
is -0.073 ± 0.008 dex kpc-1. We show consistently that
open clusters trace the distribution of chemical elements throughout
the Galactic disc differently than field stars. In particular, at the
given radius, open clusters show an age-metallicity relation that has
less scatter than field stars. As such scatter is often interpreted
as an effect of radial migration, we suggest that these differences
are due to the physical selection effect imposed by our Galaxy:
clusters that would have migrated significantly also had higher
chances to get destroyed. Finally, our results reveal trends in the
[X/Fe]-rguid-age space, which are important to understand
production rates of different elements as a function of space and time.
Title: Exploring the Galaxy's halo and very metal-weak thick disc
with SkyMapper and Gaia DR2
Authors: Cordoni, G.; Da Costa, G. S.; Yong, D.; Mackey, A. D.; Marino,
A. F.; Monty, S.; Nordlander, T.; Norris, J. E.; Asplund, M.; Bessell,
M. S.; Casey, A. R.; Frebel, A.; Lind, K.; Murphy, S. J.; Schmidt,
B. P.; Gao, X. D.; Xylakis-Dornbusch, T.; Amarsi, A. M.; Milone, A. P.
Bibcode: 2021MNRAS.503.2539C
Altcode: 2020arXiv201101189C; 2020MNRAS.tmp.3219C
In this work, we combine spectroscopic information from the SkyMapper
survey for Extremely Metal-Poor stars and astrometry from Gaia DR2 to
investigate the kinematics of a sample of 475 stars with a metallicity
range of $-6.5 \le \rm [Fe/H] \le -2.05$ dex. Exploiting the action map,
we identify 16 and 40 stars dynamically consistent with the Gaia Sausage
and Gaia Sequoia accretion events, respectively. The most metal poor
of these candidates have metallicities of $\rm [Fe/H]=-3.31\, \mathrm{
and }\, -3.74$ , respectively, helping to define the low-metallicity
tail of the progenitors involved in the accretion events. We also find,
consistent with other studies, that ∼21 per cent of the sample have
orbits that remain confined to within 3 kpc of the Galactic plane, that
is, |Zmax| ≤ 3 kpc. Of particular interest is a subsample
(∼11 per cent of the total) of low |Zmax| stars with low
eccentricities and prograde motions. The lowest metallicity of these
stars has [Fe/H] = -4.30 and the subsample is best interpreted as the
very low-metallicity tail of the metal-weak thick disc population. The
low |Zmax|, low eccentricity stars with retrograde orbits are
likely accreted, while the low |Zmax|, high eccentricity pro-
and retrograde stars are plausibly associated with the Gaia Sausage
system. We find that a small fraction of our sample (∼4 per cent
of the total) is likely escaping from the Galaxy, and postulate that
these stars have gained energy from gravitational interactions that
occur when infalling dwarf galaxies are tidally disrupted.
Title: VizieR Online Data Catalog: Thick disc probability of GALAH
stars (Duong+, 2018)
Authors: Duong, L.; Freeman, K. C.; Asplund, M.; Casagrande, L.; Buder,
S.; Lind, K.; Ness, M.; Bland-Hawthorn, J.; de Silva, G. M.; D'Orazi,
V.; Kos, J.; Lewis, G. F.; Lin, J.; Martell, S. L.; Schlesinger, K.;
Sharma, S.; Simpson, J. D.; Zucker, D. B.; Zwitter, T.; Anguiano, B.;
da Costa, G. S.; Hyde, E.; Horner, J.; Kafle, P. R.; Nataf, D. M.;
Reid, W.; Stello, D.; Ting, Y. -S.; Wyse, R. F. G.
Bibcode: 2021yCat..74765216D
Altcode:
We present a data table listing the stars analysed in this work,
their GALAH object ID, UCAC4 catalogue ID, coordinates, thick disc
membership probability and distances. (1 data file).
Title: The COMBS Survey - II. Distinguishing the metal-poor bulge
from the halo interlopers
Authors: Lucey, Madeline; Hawkins, Keith; Ness, Melissa; Debattista,
Victor P.; Luna, Alice; Asplund, Martin; Bensby, Thomas; Casagrande,
Luca; Feltzing, Sofia; Freeman, Kenneth C.; Kobayashi, Chiaki; Marino,
Anna F.
Bibcode: 2021MNRAS.501.5981L
Altcode: 2021MNRAS.tmp...42L; 2020arXiv200903886L
The metal-poor stars in the bulge are important relics of the Milky
Way's formation history, as simulations predict that they are some
of the oldest stars in the Galaxy. In order to determine if they are
truly ancient stars, we must understand their origins. Currently, it
is unclear if the metal-poor stars in the bulge ([Fe/H] < -1 dex)
are merely halo interlopers, a unique accreted population, part of the
boxy/peanut-shaped bulge, or a classical bulge population. In this work,
we use spectra from the VLT/FLAMES spectrograph to obtain metallicity
estimates using the Ca-II triplet of 473 bulge stars (187 of which have
[Fe/H] < -1 dex), targeted using SkyMapper photometry. We also use
Gaia DR2 data to infer the Galactic positions and velocities along
with orbital properties for 523 stars. We employ a probabilistic
orbit analysis and find that about half of our sample has a >50
per cent probability of being bound to the bulge, and half are halo
interlopers. We also see that the occurrence rate of halo interlopers
increases steadily with decreasing metallicity across the full range of
our sample (-3 < [Fe/H] < 0.5). Our examination of the kinematics
of the confined compared to the unbound stars indicates the metal-poor
bulge comprises at least two populations; those confined to the
boxy/peanut bulge and halo stars passing through the inner galaxy. We
conclude that an orbital analysis approach, as we have employed, is
important to understand the composite nature of the metal-poor stars
in the inner region.
Title: Explosive nucleosynthesis of a metal-deficient star as the
source of a distinct odd-even effect in the solar twin HIP 11915
Authors: Yana Galarza, Jhon; Meléndez, Jorge; Karakas, Amanda I.;
Asplund, Martin; Lorenzo-Oliveira, Diego
Bibcode: 2021MNRAS.502L.104Y
Altcode: 2021MNRAS.tmpL..11G; 2021arXiv210110182G
The abundance patterns observed in the Sun and in metal-poor stars
show a clear odd-even effect. An important question is whether the
odd-even effect in solar-metallicity stars is similar to the Sun,
or if there are variations that can tell us about different chemical
enrichment histories. In this work, we report for the first time
observational evidence of a differential odd-even effect in the solar
twin HIP 11915, relative to the solar odd-even abundance pattern. The
spectra of this star were obtained with high-resolving power (140 000)
and signal-to-noise ratio (∼420) using the ESPRESSO spectrograph and
the VLT telescope. Thanks to the high spectral quality, we obtained
extremely precise stellar parameters (σ(Teff) = 2 K, $\sigma
(\rm {[Fe/H]})$ = 0.003 dex, and σ(log g) = 0.008 dex). We determine
the chemical abundance of 20 elements (Z ≤ 39) with high precision
(∼0.01 dex), which shows a strong pattern of the odd-even effect
even after performing galactic chemical evolution corrections. The
odd-even effect is reasonably well-reproduced by a core-collapse
supernova of 13 $\rm {M_{\odot }}$ and metallicity Z = 0.001 diluted
into a metal-poor gas of 1 $\rm {M_{\odot }}$ . Our results indicate
that HIP 11915 has an odd-even effect slightly different than the Sun,
thus confirming a different supernova enrichment history.
Title: From accurate stellar abundances to exoplanet structures
and compositions
Authors: Wang, Haiyang; Quanz, Sascha; Yong, David; Asplund, Martin;
Liu, Fan; Acuña, Lorena
Bibcode: 2021cosp...43E.518W
Altcode:
A major goal of exoplanet studies is to identify terrestrial
exoplanets with similar (or otherwise distinct) bulk and interior
properties to our Earth. Recent results have highlighted the urgent
need to include devolatilization to reduce exoplanetary interior
modelling degeneracies and to thereby achieve more accurate and
reliable results. Devolatilization - i.e. depletion of volatiles from
protoplanetary disks to planets - is crucial for obtaining accurate bulk
compositions for terrestrial planets from their host stellar abundances,
particularly for non-refractory elements (e.g. hydrogen, carbon, and
oxygen). Our pioneering devolatilization approach was benchmarked with
the proto-Sun and bulk Earth and other solar system rocky bodies. In
this work, we studied a sample of 15 small-planet-hosting stars and
obtained high-precision stellar parameters and chemical abundances for
up to 18 elements using observations from the 10m Keck Telescope. For
each planet host, we applied our devolatilization approach to obtain
the bulk elemental composition of the hypothetical, habitable-zone
terrestrial planets ("exo-Earths"). Our modelling shows that most
of these exo-Earths would have an Earth-like structure while their
mantle compositions would be rather diverse in terms of MgO:SiO$
_{2}$:FeO ratios. We then applied the same approach to the Galactic
Chemical Evolution (GCE)-corrected host stellar abundances and find
that the exo-Earth mantles are more oxidized, resulting in relatively
smaller core sizes compared to the previous modelling. We attribute this
modelling discrepancy mainly to the lower C/O ratios in these stars when
they (and the systems) were born. This work represents essential steps -
high-precision and homogenous analysis of stellar chemical abundances,
the application of GCE corrections, as well as the devolatilization
process - towards studying the properties of terrestrial exoplanets.
Title: Atomic data for the Gaia-ESO Survey
Authors: Heiter, U.; Lind, K.; Bergemann, M.; Asplund, M.; Mikolaitis,
Š.; Barklem, P. S.; Masseron, T.; de Laverny, P.; Magrini, L.;
Edvardsson, B.; Jönsson, H.; Pickering, J. C.; Ryde, N.; Bayo Arán,
A.; Bensby, T.; Casey, A. R.; Feltzing, S.; Jofré, P.; Korn, A. J.;
Pancino, E.; Damiani, F.; Lanzafame, A.; Lardo, C.; Monaco, L.;
Morbidelli, L.; Smiljanic, R.; Worley, C.; Zaggia, S.; Randich, S.;
Gilmore, G. F.
Bibcode: 2021A&A...645A.106H
Altcode: 2020arXiv201102049H
Context. We describe the atomic and molecular data that were used for
the abundance analyses of FGK-type stars carried out within the Gaia-ESO
Public Spectroscopic Survey in the years 2012 to 2019. The Gaia-ESO
Survey is one among several current and future stellar spectroscopic
surveys producing abundances for Milky-Way stars on an industrial
scale.
Aims: We present an unprecedented effort to create a
homogeneous common line list, which was used by several abundance
analysis groups using different radiative transfer codes to calculate
synthetic spectra and equivalent widths. The atomic data are accompanied
by quality indicators and detailed references to the sources. The
atomic and molecular data are made publicly available at the CDS.
Methods: In general, experimental transition probabilities were
preferred but theoretical values were also used. Astrophysical gf-values
were avoided due to the model-dependence of such a procedure. For
elements whose lines are significantly affected by a hyperfine structure
or isotopic splitting, a concerted effort has been made to collate the
necessary data for the individual line components. Synthetic stellar
spectra calculated for the Sun and Arcturus were used to assess
the blending properties of the lines. We also performed adetailed
investigation of available data for line broadening due to collisions
with neutral hydrogen atoms.
Results: Among a subset of over
1300 lines of 35 elements in the wavelength ranges from 475 to 685 nm
and from 850 to 895 nm, we identified about 200 lines of 24 species
which have accurate gf-values and are free of blends in the spectra of
the Sun and Arcturus. For the broadening due to collisions with neutral
hydrogen, we recommend data based on Anstee-Barklem-O'Mara theory, where
possible. We recommend avoiding lines of neutral species for which these
are not available. Theoretical broadening data by R.L. Kurucz should
be used for Sc II, Ti II, and Y II lines; additionally, for ionised
rare-earth species, the Unsöld approximation with an enhancement
factor of 1.5 for the line width can be used.
Conclusions: The
line list has proven to be a useful tool for abundance determinations
based on the spectra obtained within the Gaia-ESO Survey, as well as
other spectroscopic projects. Accuracies below 0.2 dex are regularly
achieved, where part of the uncertainties are due to differences in
the employed analysis methods. Desirable improvements in atomic data
were identified for a number of species, most importantly Al I, S I,
and Cr II, but also Na I, Si I, Ca II, and Ni I. The atomic and
molecular data are only available at the CDS via an anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/645/A106
Title: 3D NLTE spectral line formation of lithium in late-type stars
Authors: Wang, Ella Xi; Nordlander, Thomas; Asplund, Martin; Amarsi,
Anish M.; Lind, Karin; Zhou, Yixiao
Bibcode: 2021MNRAS.500.2159W
Altcode: 2020MNRAS.tmp.3205W; 2020MNRAS.500.2159W; 2020arXiv201015248W
Accurately known stellar lithium abundances may be used to shed
light on a variety of astrophysical phenomena such as big bang
nucleosynthesis, radial migration, ages of stars and stellar clusters,
and planet engulfment events. We present a grid of synthetic lithium
spectra that are computed in non-local thermodynamic equilibrium (NLTE)
across the STAGGER grid of three-dimensional (3D) hydrodynamic stellar
atmosphere models. This grid covers three Li lines at 610.4, 670.8,
and 812.6 nm for stellar parameters representative of FGK-type dwarfs
and giants, spanning Teff = 4000-7000 K, log g = 1.5-5.0,
$[\rm {Fe}/\rm {H}]= -4.0$ -0.5, and A(Li) = -0.5-4.0. We find that
our abundance corrections are up to 0.15 dex more negative than in
previous work, due to a previously overlooked NLTE effect of blocking
of UV lithium lines by background opacities, which has important
implications for a wide range of science cases. We derive a new 3D
NLTE solar abundance of A(Li) = 0.96 ± 0.05, which is 0.09 dex lower
than the commonly used value. We make our grids of synthetic spectra
and abundance corrections publicly available through the BREIDABLIK
package. This package includes methods for accurately interpolating
our grid to arbitrary stellar parameters through methods based on
Kriging (Gaussian process regression) for line profiles, and multilayer
perceptrons (a class of fully connected feedforward neural networks)
for NLTE corrections and 3D NLTE abundances from equivalent widths,
achieving interpolation errors of the order of 0.01 dex.
Title: Combined APOGEE-GALAH stellar catalogues using the Cannon
Authors: Nandakumar, Govind; Hayden, Michael R.; Sharma, Sanjib; Buder,
Sven; Asplund, Martin; Bland-Hawthorn, Joss; De Silva, Gayandhi M.;
D'Orazi, Valentina; Freeman, Ken C.; Kos, Janez; Lewis, Geraint F.;
Martell, Sarah L.; Schlesinger, Katharine J.; Lin, Jane; Simpson,
Jeffrey D.; Zucker, Daniel B.; Zwitter, Tomaz; Nordlander, Thomas;
Casagrande, Luca; Lind, Karin; Cotar, Klemen; Stello, Dennis;
Wittenmyer, Robert A.; Tepper-Garcia, Thor
Bibcode: 2020arXiv201102783N
Altcode:
APOGEE and GALAH are two high resolution multi-object spectroscopic
surveys that provide fundamental stellar parameters and multiple
elemental abundance estimates for about half a million stars in the
Milky Way. Both surveys observe in different wavelength regimes and
use different data reduction pipelines leading to significant offsets
and trends in stellar parameters and abundances for the common stars
observed in both surveys. Such systematic differences/offsets in
stellar parameters and abundances make it difficult to effectively
utilise them to investigate Galactic abundance trends in spite of
the unique advantage provided by their complementary sky coverage
and different Milky Way components they observe. Hence, we use the
\textit{Cannon} data-driven method selecting a training set of 4418
common stars observed by both surveys. This enables the construction
of two catalogues, one with the APOGEE scaled and the other with the
GALAH scaled stellar parameters. Using repeat observations in APOGEE
and GALAH, we find high precision in metallicity (~ 0.02-0.4 dex) and
alpha abundances (~ 0.02-0.03 dex) for spectra with good signal-to-noise
ratio (SNR > 80 for APOGEE, SNR > 40 for GALAH). We use open and
globular clusters to validate our parameter estimates and find small
scatter in metallicity (0.06 dex) and alpha abundances (0.03 dex)
in APOGEE scaled case. The final catalogues have been cross matched
with the Gaia EDR3 catalogue to enable their use to carry out detailed
chemo-dynamic studies of the Milky Way from perspectives of APOGEE
and GALAH.
Title: VizieR Online Data Catalog: TESS-HERMES Survey Data Release
1 catalog (Sharma+, 2018)
Authors: Sharma, S.; Stello, D.; Buder, S.; Kos, J.; Bland-Hawthorn,
J.; Asplund, M.; Duong, L.; Lin, J.; Lind, K.; Ness, M.; Huber, D.;
Zwitter, T.; Traven, G.; Hon, M.; Kafle, P. R.; Khanna, S.; Saddon,
H.; Anguiano, B.; Casey, A. R.; Freeman, K.; Martell, S.; de Silva,
G. M.; Simpson, J. D.; Wittenmyer, R. A.; Zucker, D. B.
Bibcode: 2020yCat..74732004S
Altcode:
The observations were obtained with the 4-m AAT located at Siding Spring
Observatory in Australia. We use the High Efficiency and Resolution
Multi-Element Spectrograph (HERMES), which can obtain spectra of up
to 360 science targets simultaneously. We find that our catalogue
of spectroscopic results is magnitude complete down to 12.1mag in the
TESS band for stars hotter than 4800K. In addition to spectroscopic
values, we also provide fundamental stellar properties inferred from
the Bayesian isochrone-based scheme, BSTEP. (1 data file).
Title: VizieR Online Data Catalog: Planet-hosting stars chemical
compositions (Liu+, 2020)
Authors: Liu, F.; Yong, D.; Asplund, M.; Wang, H. S.; Spina, L.;
Acuna, L.; Melendez, J.; Ramirez, I.
Bibcode: 2020yCat..74953961L
Altcode:
We present a differential analysis of 16 planet-hosting stars and 68
comparison objects using high-resolution, high S/N spectra. We obtained
high-precision stellar parameters and relative chemical abundance
ratios. Average uncertainties for Teff, logg, and [Fe/H] are 15K,
0.034cm/s2, and 0.012dex, respectively. (4 data files).
Title: The GALAH Survey: Chemical Clocks
Authors: Hayden, Michael R.; Sharma, Sanjib; Bland-Hawthorn,
Joss; Spina, Lorenzo; Buder, Sven; Asplund, Martin; Casey, Andrew
R.; De Silva, Gayandhi M.; D'Orazi, Valentina; Freeman, Ken C.;
Kos, Janez; Lewis, Geraint F.; Lin, Jane; Lind, Karin; Martell,
Sarah L.; Schlesinger, Katharine J.; Simpson, Jeffrey D.; Zucker,
Daniel B.; Zwitter, Tomaz; Chen, Boquan; Cotar, Klemen; Feuillet,
Diane; Horner, Jonti; Joyce, Meridith; Nordlander, Thomas; Stello,
Dennis; Tepper-Garcia, Thorsten; Ting, Yuan-sen; Wang, Purmortal;
Wittenmyer, Rob
Bibcode: 2020arXiv201113745H
Altcode:
Previous studies have found that the elemental abundances of a star
correlate directly with its age and metallicity. Using this knowledge,
we derive ages for a sample of 250,000 stars taken from GALAH DR3
using only their overall metallicity and chemical abundances. Stellar
ages are estimated via the machine learning algorithm $XGBoost$, using
main sequence turnoff stars with precise ages as our input training
set. We find that the stellar ages for the bulk of the GALAH DR3
sample are accurate to 1-2 Gyr using this method. With these ages,
we replicate many recent results on the age-kinematic trends of the
nearby disk, including the age-velocity dispersion relationship of
the solar neighborhood and the larger global velocity dispersion
relations of the disk found using $Gaia$ and GALAH. The fact that
chemical abundances alone can be used to determine a reliable age for
a star have profound implications for the future study of the Galaxy
as well as upcoming spectroscopic surveys. These results show that the
chemical abundance variation at a given birth radius is quite small,
and imply that strong chemical tagging of stars directly to birth
clusters may prove difficult with our current elemental abundance
precision. Our results highlight the need of spectroscopic surveys to
deliver precision abundances for as many nucleosynthetic production
sites as possible in order to estimate reliable ages for stars directly
from their chemical abundances. Applying the methods outlined in
this paper opens a new door into studies of the kinematic structure
and evolution of the disk, as ages may potentially be estimated for a
large fraction of stars in existing spectroscopic surveys. This would
yield a sample of millions of stars with reliable age determinations,
and allow precise constraints to be put on various kinematic processes
in the disk, such as the efficiency and timescales of radial migration.
Title: The GALAH Survey: non-LTE departure coefficients for large
spectroscopic surveys
Authors: Amarsi, A. M.; Lind, K.; Osorio, Y.; Nordlander, T.;
Bergemann, M.; Reggiani, H.; Wang, E. X.; Buder, S.; Asplund, M.;
Barklem, P. S.; Wehrhahn, A.; Skúladóttir, Á.; Kobayashi, C.;
Karakas, A. I.; Gao, X. D.; Bland-Hawthorn, J.; de Silva, G. M.; Kos,
J.; Lewis, G. F.; Martell, S. L.; Sharma, S.; Simpson, J. D.; Zucker,
D. B.; Čotar, K.; Horner, J.; GALAH Collaboration
Bibcode: 2020A&A...642A..62A
Altcode: 2020arXiv200809582A
Massive sets of stellar spectroscopic observations are rapidly becoming
available and these can be used to determine the chemical composition
and evolution of the Galaxy with unprecedented precision. One of the
major challenges in this endeavour involves constructing realistic
models of stellar spectra with which to reliably determine stellar
abundances. At present, large stellar surveys commonly use simplified
models that assume that the stellar atmospheres are approximately
in local thermodynamic equilibrium (LTE). To test and ultimately
relax this assumption, we have performed non-LTE calculations for
13 different elements (H, Li, C, N, O, Na, Mg, Al, Si, K, Ca, Mn,
and Ba), using recent model atoms that have physically-motivated
descriptions for the inelastic collisions with neutral hydrogen,
across a grid of 3756 1D MARCS model atmospheres that spans 3000 ≤
Teff/K ≤ 8000, - 0.5 ≤log g/cm s-2 ≤ 5.5,
and - 5 ≤ [Fe/H] ≤ 1. We present the grids of departure coefficients
that have been implemented into the GALAH DR3 analysis pipeline in
order to complement the extant non-LTE grid for iron. We also present
a detailed line-by-line re-analysis of 50 126 stars from GALAH DR3. We
found that relaxing LTE can change the abundances by between - 0.7 dex
and + 0.2 dex for different lines and stars. Taking departures from
LTE into account can reduce the dispersion in the [A/Fe] versus [Fe/H]
plane by up to 0.1 dex, and it can remove spurious differences between
the dwarfs and giants by up to 0.2 dex. The resulting abundance slopes
can thus be qualitatively different in non-LTE, possibly with important
implications for the chemical evolution of our Galaxy. The grids of
departure coefficients are publicly available and can be implemented
into LTE pipelines to make the most of observational data sets from
large spectroscopic surveys. Grids of departure coefficients can
be found online (<xref ref-type="bibr" rid="R3">http://Amarsi
2020</xref>http://) or by contacting the lead author directly.
Title: VizieR Online Data Catalog: Atomic data for the Gaia-ESO Survey
(Heiter+, 2021)
Authors: Heiter, U.; Lind, K.; Bergemann, M.; Asplund, M.; Mikolaitis,
S.; Barklem, P. S.; Masseron, T.; de Laverny, P.; Magrini, L.;
Edvardsson, B.; Joensson, H.; Pickering, J. C.; Ryde, N.; Bayo Aran,
A.; Bensby, T.; Casey, A. R.; Feltzing, S.; Jofre, P.; Korn, A. J.;
Pancino, E.; Damiani, F.; Lanzafame, A.; Lardo, C.; Monaco, L.;
Morbidelli, L.; Smiljanic, R.; Worley, C.; Zaggia, S.; Randich, S.;
Gilmore, G. F.
Bibcode: 2020yCat..36450106H
Altcode:
In general experimental transition probabilities were preferred but
theoretical values were also used. Astrophysical gf-values were avoided
due to the model-dependence of such a procedure. Synthetic stellar
spectra calculated for the Sun and Arcturus were used to assess
the blending properties of the lines. We also performed a detailed
investigation of available data for line broadening due to collisions
with neutral hydrogen atoms, which are included in the data table as
"Van der Waals broadening". The atomic data are stored in a single
table with one record for each transition. Hyperfine structure (HFS)
components and different isotopes are included as separate transitions,
where applicable. HFS components belonging to the same fine structure
transition can be identified by having the exact same label and J
value for both the lower and the upper levels. Both the preselected
lines and the background line list are included. Preselected lines can
be identified by having both non-empty (not '-') gf_flag and synflag
entries. The set of molecular data is stored in a separate table. We strongly encourage users of the Gaia-ESO line list to cite,
in addition to the overview article, the individual sources for the
atomic and molecular data used in a particular work. It is important
that providers of atomic data receive credit for their work by citing
the original publications. This is also a prerequisite for the continued
funding of this type of research. To facilitate citations of original
sources we provide, together with the data table, a BibTeX file with
the relevant entries. (4 data files).
Title: The GALAH survey: a new constraint on cosmological lithium
and Galactic lithium evolution from warm dwarf stars
Authors: Gao, Xudong; Lind, Karin; Amarsi, Anish M.; Buder, Sven;
Bland-Hawthorn, Joss; Campbell, Simon W.; Asplund, Martin; Casey,
Andrew R.; de Silva, Gayandhi M.; Freeman, Ken C.; Hayden, Michael R.;
Lewis, Geraint F.; Martell, Sarah L.; Simpson, Jeffrey D.; Sharma,
Sanjib; Zucker, Daniel B.; Zwitter, Tomaž; Horner, Jonathan; Munari,
Ulisse; Nordlander, Thomas; Stello, Dennis; Ting, Yuan-Sen; Traven,
Gregor; Wittenmyer, Robert A.; GALAH Collaboration
Bibcode: 2020MNRAS.497L..30G
Altcode: 2020MNRAS.tmpL.103G; 2020arXiv200605173G
Lithium depletion and enrichment in the cosmos is not yet well
understood. To help tighten constraints on stellar and Galactic
evolution models, we present the largest high-resolution analysis of
Li abundances A(Li) to date, with results for over $100\, 000$ GALAH
(Galactic Archeology with HERMES) field stars spanning effective
temperatures $5900\, \mathrm{K} \lesssim T_{\mathrm{eff}}\lesssim
7000\, \mathrm{K}$ and metallicities -3 ≲ [Fe/H] ≲ +0.5. We
separated these stars into two groups, on the warm and cool sides of
the so-called Li dip, a localized region of the Kiel diagram wherein
lithium is severely depleted. We discovered that stars in these two
groups show similar trends in the A(Li)-[Fe/H] plane, but with a
roughly constant offset in A(Li) of $0.4\, \mathrm{dex}$ , the warm
group having higher Li abundances. At $\rm [Fe/H]\gtrsim -0.5$ , a
significant increase in Li abundance with increasing metallicity is
evident in both groups, signalling the onset of significant Galactic
production. At lower metallicity, stars in the cool group sit on the
Spite plateau, showing a reduced lithium of around $0.4\, \mathrm{dex}$
relative to the primordial value predicted from big bang nucleosynthesis
(BBN). However, stars in the warm group between [Fe/H] = -1.0 and
-0.5 form an elevated plateau that is largely consistent with the BBN
prediction. This may indicate that these stars in fact preserve the
primordial Li produced in the early Universe.
Title: K2-HERMES II. Planet-candidate properties from K2 Campaigns
1-13
Authors: Wittenmyer, Robert A.; Clark, Jake T.; Sharma, Sanjib; Stello,
Dennis; Horner, Jonathan; Kane, Stephen R.; Stevens, Catherine P.;
Wright, Duncan J.; Spina, Lorenzo; Čotar, Klemen; Asplund, Martin;
Bland-Hawthorn, Joss; Buder, Sven; Casey, Andrew R.; De Silva, Gayandhi
M.; D'Orazi, Valentina; Freeman, Ken; Kos, Janez; Lewis, Geraint; Lin,
Jane; Lind, Karin; Martell, Sarah L.; Simpson, Jeffrey D.; Zucker,
Daniel B.; Zwitter, Tomaz
Bibcode: 2020MNRAS.496..851W
Altcode: 2020MNRAS.tmp.1681W; 2020arXiv200510959W
Accurate and precise radius estimates of transiting exoplanets
are critical for understanding their compositions and formation
mechanisms. To know the planet, we must know the host star in
as much detail as possible. We present complete results for
planet-candidate hosts from the K2-HERMES survey, which uses the
HERMES multi-object spectrograph on the Anglo-Australian Telescope
to obtain $R\sim 28\, 000$ spectra for more than 30 000 K2 stars. We
present complete host-star parameters and planet-candidate radii
for 224 K2 candidate planets from C1-C13. Our results cast severe
doubt on 30 K2 candidates, as we derive unphysically large radii,
larger than 2RJup. This work highlights the importance of
obtaining accurate, precise, and self-consistent stellar parameters
for ongoing large planet search programs - something that will only
become more important in the coming years, as TESS begins to deliver
its own harvest of exoplanets.
Title: Convective excitation and damping of solar-like oscillations
Authors: Zhou, Yixiao; Asplund, Martin; Collet, Remo; Joyce, Meridith
Bibcode: 2020MNRAS.495.4904Z
Altcode: 2020arXiv200510519Z; 2020MNRAS.tmp.1563Z
The last decade has seen a rapid development in asteroseismology thanks
to the CoRoT and Kepler missions. With more detailed asteroseismic
observations available, it is becoming possible to infer exactly how
oscillations are driven and dissipated in solar-type stars. We have
carried out three-dimensional (3D) stellar atmosphere simulations
together with one-dimensional (1D) stellar structural models of key
benchmark turn-off and subgiant stars to study this problem from a
theoretical perspective. Mode excitation and damping rates are extracted
from 3D and 1D stellar models based on analytical expressions. Mode
velocity amplitudes are determined by the balance between stochastic
excitation and linear damping, which then allows the estimation of the
frequency of maximum oscillation power, νmax, for the first
time based on ab initio and parameter-free modelling. We have made
detailed comparisons between our numerical results and observational
data and achieved very encouraging agreement for all of our target
stars. This opens the exciting prospect of using such realistic 3D
hydrodynamical stellar models to predict solar-like oscillations across
the Hertzsprung-Russell diagram, thereby enabling accurate estimates
of stellar properties such as mass, radius, and age.
Title: Detailed chemical compositions of planet-hosting stars -
I. Exploration of possible planet signatures
Authors: Liu, F.; Yong, D.; Asplund, M.; Wang, H. S.; Spina, L.;
Acuña, L.; Meléndez, J.; Ramírez, I.
Bibcode: 2020MNRAS.495.3961L
Altcode: 2020arXiv200509846L; 2020MNRAS.tmp.1553L
We present a line-by-line differential analysis of a sample of 16
planet-hosting stars and 68 comparison stars using high-resolution, high
signal-to-noise ratio spectra gathered using Keck. We obtained accurate
stellar parameters and high-precision relative chemical abundances
with average uncertainties in Teff, log g, [Fe/H], and
[X/H] of 15 K, 0.034 cm s-2 , 0.012 dex, and 0.025 dex,
respectively. For each planet host, we identify a set of comparison
stars and examine the abundance differences (corrected for Galactic
chemical evolution effect) as a function of the dust condensation
temperature, Tcond, of the individual elements. While we
confirm that the Sun exhibits a negative trend between abundance and
Tcond, we also confirm that the remaining planet hosts
exhibit a variety of abundance-Tcond trends with no clear
dependence upon age, metallicity, or Teff. The diversity in
the chemical compositions of planet-hosting stars relative to their
comparison stars could reflect the range of possible planet-induced
effects present in these planet hosts, from the sequestration of
rocky material (refractory poor) to the possible ingestion of planets
(refractory rich). Other possible explanations include differences
in the time-scale, efficiency and degree of planet formation,
or inhomogeneous chemical evolution. Although we do not find an
unambiguous chemical signature of planet formation among our sample,
the high-precision chemical abundances of the host stars are essential
for constraining the composition and structure of their exoplanets.
Title: The GALAH survey: multiple stars and our Galaxy. I. A
comprehensive method for deriving properties of FGK binary stars
Authors: Traven, G.; Feltzing, S.; Merle, T.; Van der Swaelmen, M.;
Čotar, K.; Church, R.; Zwitter, T.; Ting, Y. -S.; Sahlholdt, C.;
Asplund, M.; Bland-Hawthorn, J.; De Silva, G.; Freeman, K.; Martell,
S.; Sharma, S.; Zucker, D.; Buder, S.; Casey, A.; D'Orazi, V.; Kos,
J.; Lewis, G.; Lin, J.; Lind, K.; Simpson, J.; Stello, D.; Munari,
U.; Wittenmyer, R. A.
Bibcode: 2020A&A...638A.145T
Altcode: 2020arXiv200500014T
Context. Binary stellar systems form a large fraction of the Galaxy's
stars. They are useful as laboratories for studying the physical
processes taking place within stars, and must be correctly taken into
account when observations of stars are used to study the structure
and evolution of the Galaxy. The advent of large-scale spectroscopic
and photometric surveys allows us to obtain large samples of binaries
that permit characterising their populations.
Aims: We aim to
obtain a large sample of double-lined spectroscopic binaries (SB2s)
by analysis of spectra from the GALAH survey in combination with
photometric and astrometric data. A combined analysis will provide
stellar parameters of thousands of binary stars that can be combined
to form statistical observables of a given population. We aim to
produce a catalogue of well-characterised systems, which can in turn
be compared to models of populations of binary stars, or to follow-up
individual systems of interest.
Methods: We obtained a list
of candidate SB2 systems from a t-distributed stochastic neighbour
embedding (t-SNE) classification and a cross-correlation analysis of
GALAH spectra. To compute parameters of the primary and secondary star,
we used a Bayesian approach that includes a parallax prior from Gaia
DR2, spectra from GALAH, and apparent magnitudes from APASS, Gaia DR2,
2MASS, and WISE. We used a Markov chain Monte Carlo approach to sample
the posterior distributions of the following model parameters for
the two stars: Teff[1,2], logg[1,2], [Fe/H],
Vr[1,2], vmic[1,2], vbroad[1,2],
R[1,2], and E(B-V).
Results: We present results for
12 760 binary stars detected as SB2s. We construct the statistical
observables T1/T2, ΔVr, and
R1/R2, which demonstrate that our sample mostly
consists of dwarfs, with a significant fraction of evolved stars and
several dozen members of the giant branch. The majority of these binary
stars is concentrated at the lower boundary of the ΔVr
distribution, and the R1/R2 ratio is mostly close
to unity. The derived metallicity of our binary stars is statistically
lower than that of single dwarf stars from the same magnitude-limited
sample.
Conclusions: Our sample of binary stars represents
a large population of well-characterised double-lined spectroscopic
binaries that are appropriate for statistical studies of the binary
populations. The derived stellar properties and their distributions show
trends that are expected for a population of close binary stars (a <
10 AU) detected through double lines in their spectra. Our detection
technique allows us to probe binary systems with mass ratios 0.5 ≤q
≤ 1. Catalogue is only available at the CDS via anonymous ftp to
http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/638/A145
Title: VizieR Online Data Catalog: GALAH survey. FGK binary stars
(Traven+, 2020)
Authors: Traven, G.; Feltzing, S.; Merle, T.; van der Swaelmen, M.;
Cotar, K.; Church, R.; Zwitter, T.; Ting, Y. -S.; Sahlholdt, C.;
Asplund, M.; Bland-Hawthorn, J.; de Silva, G.; Freeman, K.; Martell,
S.; Sharma, S.; Zucker, D.; Buder, S.; Casey, A.; D'Orazi, V.; Kos,
J.; Lewis, G.; Lin, J.; Lind, K.; Simpson, J.; Stello, D.; Munari,
U.; Wittenmyer, R. A.
Bibcode: 2020yCat..36380145T
Altcode:
We here analyse a specific data-set: the extended GALAH dataset. This
consists of stellar spectra from the GALAH survey (reduced as explained
in Kos et al., 2017MNRAS.464.1259K), apparent magnitudes from a
variety of photometric catalogues (AAVSO Photometric All Sky Survey -
APASS; Henden et al. 2016, Cat. II/336, Gaia DR2; Gaia Collaboration
et al. 2018, Cat. I/345. Two Micron All Sky Survey - 2MASS; Skrutskie
et al. 2006, Cat. VII/233, Wide-field Infrared Survey Explorer - WISE;
Wright et al. 2010, Cat. II/311), and the parallax measurements from
Gaia DR2. The data provided in this catalogue are described in
Table A.1 of the paper. (1 data file).
Title: VizieR Online Data Catalog: COMBS survey. Galactic Bulge
metal-poor stars (Lucey+, 2019)
Authors: Lucey, M.; Hawkins, K.; Ness, M.; Asplund, M.; Bensby, T.;
Casagrande, L.; Feltzing, S.; Freeman, K. C.; Kobayashi, C.; Marino,
A. F.
Bibcode: 2020yCat..74882283L
Altcode:
Based on observations collected at the European Southern Observatory
under ESO programme: 089.B-069 (3 data files).
Title: The 3D non-LTE solar nitrogen abundance from atomic lines
Authors: Amarsi, A. M.; Grevesse, N.; Grumer, J.; Asplund, M.; Barklem,
P. S.; Collet, R.
Bibcode: 2020A&A...636A.120A
Altcode: 2020arXiv200312561A
Nitrogen is an important element in various fields of stellar and
Galactic astronomy, and the solar nitrogen abundance is crucial as a
yardstick for comparing different objects in the cosmos. In order to
obtain a precise and accurate value for this abundance, we carried out
N I line formation calculations in a 3D radiative-hydrodynamic STAGGER
model solar atmosphere in full 3D non-local thermodynamic equilibrium
(non-LTE). We used a model atom that includes physically motivated
descriptions for the inelastic collisions of N I with free electrons and
with neutral hydrogen. We selected five N I lines of high excitation
energy to study in detail, based on their strengths and on their
being relatively free of blends. We found that these lines are slightly
strengthened from non-LTE photon losses and from 3D granulation effects,
resulting in negative abundance corrections of around - 0.01 dex and -
0.04 dex, respectively. Our advocated solar nitrogen abundance is log
ɛN = 7.77, with the systematic 1σ uncertainty estimated
to be 0.05 dex. This result is consistent with earlier studies after
correcting for differences in line selections and equivalent widths.
Title: The GALAH survey: chemodynamics of the solar neighbourhood
Authors: Hayden, Michael R.; Bland-Hawthorn, Joss; Sharma, Sanjib;
Freeman, Ken; Kos, Janez; Buder, Sven; Anguiano, Borja; Asplund,
Martin; Chen, Boquan; De Silva, Gayandhi M.; Khanna, Shourya; Lin,
Jane; Horner, Jonathan; Martell, Sarah; Ting, Yuan-Sen; Wyse, Rosemary;
Zucker, Daniel; Zwitter, Tomaz
Bibcode: 2020MNRAS.493.2952H
Altcode: 2020MNRAS.tmp..333H; 2019arXiv190107565H
We present the chemodynamic structure of the solar neighbourhood
using 55 652 stars within a 500 pc volume around the Sun observed by
GALAH and with astrometric parameters from Gaia DR2. We measure the
velocity dispersion for all three components (vertical, radial, and
tangential) and find that it varies smoothly with [Fe/H] and [α/Fe]
for each component. The vertical component is especially clean, with
σ _{v_z} increasing from a low of 10 km s-1 at solar
[α/Fe] and [Fe/H] to a high of more than 50 km s-1 for
more metal-poor and [α/Fe] enhanced populations. We find no evidence
of a large decrease in the velocity dispersion of the highest [α/Fe]
populations as claimed in surveys prior to Gaia DR2. The eccentricity
distribution for local stars varies most strongly as a function of
[α/Fe], where stars with [α/Fe] < 0.1 dex having generally circular
orbits (e < 0.15), while the median eccentricity increases rapidly
for more [α/Fe] enhanced stellar populations up to e ∼ 0.35. These
[α/Fe] enhanced populations have guiding radii consistent with origins
in the inner Galaxy. Of the stars with metallicities much higher than
the local interstellar medium ([Fe/H] > 0.1 dex), we find that
the majority have e < 0.2 and are likely observed in the solar
neighbourhood through churning/migration rather than blurring effects,
as the epicyclic motion for these stars is not large enough to reach
the radii at which they were likely born based on their metallicity.
Title: The Stagger-grid: Synthetic stellar spectra and broad-band
photometry
Authors: Chiavassa, Andrea; Casagrande, L.; Collet, R.; Magic, Z.;
Bigot, L.; Thévenin, F.; Asplund, M.
Bibcode: 2020IAUGA..30..463C
Altcode:
No abstract at ADS
Title: Chemical evolution of the Galactic bulge as traced by
microlensed dwarf and subgiant stars. VII. Lithium
Authors: Bensby, T.; Feltzing, S.; Yee, J. C.; Johnson, J. A.; Gould,
A.; Asplund, M.; Meléndez, J.; Lucatello, S.
Bibcode: 2020A&A...634A.130B
Altcode: 2020arXiv200106222B
Lithium abundances are presented for 91 dwarf and subgiant stars in
the Galactic bulge. The analysis is based on line synthesis of the
7Li line at 6707 Å in high-resolution spectra obtained
during gravitational microlensing events, when the brightnesses of the
targets were highly magnified. Our main finding is that bulge stars
at sub-solar metallicities that are older than about eight billion
years do not show any sign of Li production; that is, the Li trend with
metallicity is flat or even slightly declining. This indicates that no
lithium was produced during the first few billion years in the history
of the bulge. This finding is essentially identical to what is seen for
the (old) thick disk stars in the solar neighbourhood, and adds another
piece of evidence for a tight connection between the metal-poor bulge
and the Galactic thick disk. For the bulge stars younger than about
eight billion years, the sample contains a group of stars at very
high metallicities at [Fe/H] ≈ +0.4 that have lithium abundances in
the range A(Li) = 2.6 - 2.8. In the solar neighbourhood the lithium
abundances have been found to peak at A(Li) ≈ 3.3 at [Fe/H] ≈ +0.1
and then decrease by 0.4-0.5 dex when reaching [Fe/H] ≈ +0.4. The
few bulge stars that we have at these metallicities seem to support
this declining A(Li) trend. This could indeed support the recent claim
that the low A(Li) abundances at the highest metallicities seen in
the solar neighbourhood could be due to stars from the inner disk, or
the bulge region, that have migrated to the solar neighbourhood. Table 1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/634/A130
Based on data obtained with the European Southern Observatory
telescopes (Proposal ID:s 87.B-0600, 88.B-0349, 89.B-0047, 90.B-0204,
91.B-0289, 92.B-0626, 93.B-0700), and the Magellan Clay telescope at
the Las Campanas observatory.
Title: The GALAH survey: temporal chemical enrichment of the
galactic disc
Authors: Lin, Jane; Asplund, Martin; Ting, Yuan-Sen; Casagrande,
Luca; Buder, Sven; Bland-Hawthorn, Joss; Casey, Andrew R.; De Silva,
Gayandhi M.; D'Orazi, Valentina; Freeman, Ken C.; Kos, Janez; Lind,
K.; Martell, Sarah L.; Sharma, Sanjib; Simpson, Jeffrey D.; Zwitter,
Tomaž; Zucker, Daniel B.; Minchev, Ivan; Čotar, Klemen; Hayden,
Michael; Horner, Jonti; Lewis, Geraint F.; Nordlander, Thomas; Wyse,
Rosemary F. G.; Žerjal, Maruša
Bibcode: 2020MNRAS.491.2043L
Altcode: 2019arXiv191105221L; 2019MNRAS.tmp.2724L
We present isochrone ages and initial bulk metallicities ([Fe/H]_{bulk},
by accounting for diffusion) of 163 722 stars from the GALAH Data
Release 2, mainly composed of main-sequence turn-off stars and
subgiants (7000 K> T_{ eff}> 4000 K and log g>3 dex). The local
age-metallicity relationship (AMR) is nearly flat but with significant
scatter at all ages; the scatter is even higher when considering the
observed surface abundances. After correcting for selection effects,
the AMR appears to have intrinsic structures indicative of two star
formation events, which we speculate are connected to the thin and
thick discs in the solar neighbourhood. We also present abundance
ratio trends for 16 elements as a function of age, across different
[Fe/H]_{bulk} bins. In general, we find the trends in terms of [X/Fe]
versus age from our far larger sample to be compatible with studies
based on small (∼100 stars) samples of solar twins, but we now extend
them to both sub- and supersolar metallicities. The α-elements show
differing behaviour: the hydrostatic α-elements O and Mg show a steady
decline with time for all metallicities, while the explosive α-elements
Si, Ca, and Ti are nearly constant during the thin-disc epoch (ages
≲ 12 Gyr). The s-process elements Y and Ba show increasing [X/Fe]
with time while the r-process element Eu has the opposite trend,
thus favouring a primary production from sources with a short time
delay such as core-collapse supernovae over long-delay events such as
neutron star mergers.
Title: VizieR Online Data Catalog: Lithium abundances in microlensed
bulge dwarfs (Bensby+, 2020)
Authors: Bensby, T.; Feltzing, S.; Yee, J.; Johnson, J. A.; Gould,
A.; Asplund, M.; Melendez, J.; Lucatello, S.
Bibcode: 2020yCat..36340130B
Altcode:
We perform a detailed analysis of Li in 91 microlensed dwarf stars in
the Galactic bulge. Li abundances were determined through spectral line
synthesis of the Li feature at 670.8 nm. The stellar sample traces
the evolution of the Galactic bulge, and is the same as previously
analysed by Bensby et al. (2017A&A...605A..89B, Cat. J/A+A/605/A89)
where stellar parameters and ages were taken from. For each star we
give the NLTE corrected Li abundance, the applied NLTE correction, and
uncertainties in the form of NLTE corrected Li abundances based on the
same analysis but increasing and decreasing the effective temperatures
with their uncertainties. 22 stars have "good" Li abundances (flag=0
in Flag column), and 69 stars have upper Li upper limits (flag=1 in
Flag column). The uncertainties are not given for the stars with Li
upper limit abundances (1 data file).
Title: The GALAH Survey: Chemically tagging the Fimbulthul stream
to the globular cluster ω Centauri
Authors: Simpson, Jeffrey D.; Martell, Sarah L.; Da Costa, Gary;
Horner, Jonathan; Wyse, Rosemary F. G.; Ting, Yuan-Sen; Asplund,
Martin; Bland-Hawthorn, Joss; Buder, Sven; De Silva, Gayandhi M.;
Freeman, Ken C.; Kos, Janez; Lewis, Geraint F.; Lind, Karin; Sharma,
Sanjib; Zucker, Daniel B.; Zwitter, Tomaž; Čotar, Klemen; Cottrell,
Peter L.; Nordlander, Thomas
Bibcode: 2020MNRAS.491.3374S
Altcode: 2019arXiv191101548S; 2019MNRAS.tmp.2703S
Using kinematics from Gaia and the large elemental abundance space
of the second data release of the GALAH survey, we identify two new
members of the Fimbulthul stellar stream, and chemically tag them to
massive, multimetallic globular cluster ω Centauri. Recent analysis
of the second data release of Gaia had revealed the Fimbulthul stellar
stream in the halo of the Milky Way. It had been proposed that the
stream is associated with the ω Cen, but this proposition relied
exclusively upon the kinematics and metallicities of the stars to
make the association. In this work, we find our two new members of the
stream to be metal-poor stars that are enhanced in sodium and aluminium,
typical of second population globular cluster stars, but not otherwise
seen in field stars. Furthermore, the stars share the s-process
abundance pattern seen in ω Cen, which is rare in field stars. Apart
from one star within 1.5 deg of ω Cen, we find no other stars observed
by GALAH spatially near ω Cen or the Fimbulthul stream that could be
kinematically and chemically linked to the cluster. Chemically tagging
stars in the Fimbulthul stream to ω Cen confirms the earlier work,
and further links this tidal feature in the Milky Way halo to ω Cen.
Title: The K2-HERMES Survey: age and metallicity of the thick disc
Authors: Sharma, Sanjib; Stello, Dennis; Bland-Hawthorn, Joss;
Hayden, Michael R.; Zinn, Joel C.; Kallinger, Thomas; Hon, Marc;
Asplund, Martin; Buder, Sven; De Silva, Gayandhi M.; D'Orazi,
Valentina; Freeman, Ken; Kos, Janez; Lewis, Geraint F.; Lin, Jane;
Lind, Karin; Martell, Sarah; Simpson, Jeffrey D.; Wittenmyer, Rob A.;
Zucker, Daniel B.; Zwitter, Tomaz; Bedding, Timothy R.; Chen, Boquan;
Cotar, Klemen; Esdaile, James; Horner, Jonathan; Huber, Daniel; Kafle,
Prajwal R.; Khanna, Shourya; Li, Tanda; Ting, Yuan-Sen; Nataf, David
M.; Nordlander, Thomas; Saadon, Mohd Hafiz Mohd; Traven, Gregor;
Wright, Duncan; Wyse, Rosemary F. G.
Bibcode: 2019MNRAS.490.5335S
Altcode: 2019MNRAS.tmp.2471S; 2019arXiv190412444S
Asteroseismology is a promising tool to study Galactic structure and
evolution because it can probe the ages of stars. Earlier attempts
comparing seismic data from the Kepler satellite with predictions from
Galaxy models found that the models predicted more low-mass stars
compared to the observed distribution of masses. It was unclear if
the mismatch was due to inaccuracies in the Galactic models, or the
unknown aspects of the selection function of the stars. Using new data
from the K2 mission, which has a well-defined selection function, we
find that an old metal-poor thick disc, as used in previous Galactic
models, is incompatible with the asteroseismic information. We use an
importance-sampling framework, which takes the selection function into
account, to fit for the metallicities of a population synthesis model
using spectroscopic data. We show that spectroscopic measurements of
[Fe/H] and [α/Fe] elemental abundances from the GALAH survey indicate
a mean metallicity of log (Z/Z⊙) = -0.16 for the thick
disc. Here Z is the effective solar-scaled metallicity, which is a
function of [Fe/H] and [α/Fe]. With the revised disc metallicities,
for the first time, the theoretically predicted distribution of seismic
masses show excellent agreement with the observed distribution of
masses. This indirectly verifies that the asteroseismic mass scaling
relation is good to within five per cent. Assuming the asteroseismic
scaling relations are correct, we estimate the mean age of the thick
disc to be about 10 Gyr, in agreement with the traditional idea of an
old α-enhanced thick disc.
Title: The GALAH survey and Gaia DR2: Linking ridges, arches, and
vertical waves in the kinematics of the Milky Way
Authors: Khanna, Shourya; Sharma, Sanjib; Tepper-Garcia, Thor;
Bland-Hawthorn, Joss; Hayden, Michael; Asplund, Martin; Buder, Sven;
Chen, Boquan; De Silva, Gayandhi M.; Freeman, Ken C.; Kos, Janez;
Lewis, Geraint F.; Lin, Jane; Martell, Sarah L.; Simpson, Jeffrey D.;
Nordlander, Thomas; Stello, Dennis; Ting, Yuan-Sen; Zucker, Daniel B.;
Zwitter, Tomaž
Bibcode: 2019MNRAS.489.4962K
Altcode: 2019MNRAS.tmp.2122K; 2019arXiv190210113K
Gaia DR2 has revealed new small-scale and large-scale patterns in
the phase-space distribution of stars in the Milky Way. In cylindrical
Galactic coordinates (R,φ ,z), ridge-like structures can be seen in the
(R,V_φ) plane and asymmetric arch-like structures in the (V_R,V_φ)
plane. We show that the ridges are also clearly present when the third
dimension of the (R,V_φ) plane is represented by < z >, <
V_z >, < V_R >, <[Fe/H]>, and < [α /Fe]>. The
maps suggest that stars along the ridges lie preferentially close to
the Galactic mid-plane (|z|< 0.2 kpc), and have metallicity and α
elemental abundance similar to that of the Sun. We show that phase
mixing of disrupting spiral arms can generate both the ridges and
the arches. It also generates discrete groupings in orbital energy
- the ridges and arches are simply surfaces of constant energy. We
identify eight distinct ridges in the Gaia DR2 data: six of them have
constant energy while two have constant angular momentum. Given that
the signature is strongest for stars close to the plane, the presence
of ridges in < z > and < V_z > suggests a coupling between
planar and vertical directions. We demonstrate, using N-body simulations
that such coupling can be generated both in isolated discs and in discs
perturbed by an orbiting satellite like the Sagittarius dwarf galaxy.
Title: Discovery of a 21 Myr old stellar population in the Orion
complex⋆
Authors: Kos, Janez; Bland-Hawthorn, Joss; Asplund, Martin; Buder,
Sven; Lewis, Geraint F.; Lin, Jane; Martell, Sarah L.; Ness, Melissa
K.; Sharma, Sanjib; De Silva, Gayandhi M.; Simpson, Jeffrey D.;
Zucker, Daniel B.; Zwitter, Tomaž; Čotar, Klemen; Spina, Lorenzo
Bibcode: 2019A&A...631A.166K
Altcode: 2018arXiv181111762K
Context. The Orion complex is arguably the most studied star-forming
region in the Galaxy. While stars are still being born in the
Orion nebula, the oldest part was believed to be no more than
13 Myr old.
Aims: In order to study the full hierarchy of
star formation across the Orion complex, we perform a clustering
analysis of the Ori OB1a region using new stellar surveys and derive
robust ages for each identified stellar aggregate.
Methods:
We use Gaia DR2 parameters supplemented with radial velocities from
the GALAH and APOGEE surveys to perform clustering of the Ori OB1a
association. Five overdensities are resolved in a six-dimensional
parameter space (positions, distance, proper motions, and radial
velocity). Most correspond to previously known structures (ASCC 16,
25 Orionis, ASCC 20, ASCC 21). We use Gaia DR2, Pan-STARRS1 and 2MASS
photometry to fit isochrones to the colour-magnitude diagrams of the
identified clusters. The ages of the clusters can thus be measured
with ∼10% precision.
Results: While four of the clusters
have ages between 11 and 13 Myr, the ASCC 20 cluster stands out at an
age of 21 ± 3 Myr. This is significantly greater than the age of any
previously known component of the Orion complex. To some degree, all
clusters overlap in at least one of the six phase-space dimensions.
Conclusions: We argue that the formation history of the Orion
complex, and its relation to the Gould belt, must be reconsidered. A
significant challenge in reconstructing the history of the Ori OB1a
association is to understand the impact of the newly discovered 21
Myr old population on the younger parts of the complex, including
their formation. Movie associated to Fig. 3 is available at https://www.aanda.org
Tables B.1-B.5 are only available at the CDS via anonymous ftp to
http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/631/A166
Title: The SkyMapper DR1.1 search for extremely metal-poor stars
Authors: Da Costa, G. S.; Bessell, M. S.; Mackey, A. D.; Nordlander,
T.; Asplund, M.; Casey, A. R.; Frebel, A.; Lind, K.; Marino, A. F.;
Murphy, S. J.; Norris, J. E.; Schmidt, B. P.; Yong, D.
Bibcode: 2019MNRAS.489.5900D
Altcode: 2019arXiv190906227D; 2019MNRAS.tmp.2195D
We present and discuss the results of a search for extremely metal-poor
stars based on photometry from data release DR1.1 of the SkyMapper
imaging survey of the southern sky. In particular, we outline our
photometric selection procedures and describe the low-resolution (R ≈
3000) spectroscopic follow-up observations that are used to provide
estimates of effective temperature, surface gravity, and metallicity
([Fe/H]) for the candidates. The selection process is very efficient:
of the 2618 candidates with low-resolution spectra that have photometric
metallicity estimates less than or equal to -2.0, 41 per cent have
[Fe/H] ≤ -2.75 and only approximately seven per cent have [Fe/H] >
-2.0 dex. The most metal-poor candidate in the sample has [Fe/H] <
-4.75 and is notably carbon rich. Except at the lowest metallicities
([Fe/H] < -4), the stars observed spectroscopically are dominated
by a `carbon-normal' population with [C/Fe]1D, LTE ≤ +1
dex. Consideration of the A(C)1D, LTE versus [Fe/H]1D,
LTE diagram suggests that the current selection process is
strongly biased against stars with A(C)1D, LTE > 7.3
(predominantly CEMP-s) while any bias against stars with A(C)1D,
LTE < 7.3 and [C/Fe]1D,LTE >
+1 (predominantly CEMP-no) is not readily quantifiable given the
uncertainty in the SkyMapper v-band DR1.1 photometry. We find that
the metallicity distribution function of the observed sample has a
power-law slope of Δ(Log N)/Δ[Fe/H] = 1.5 ± 0.1 dex per dex for
-4.0 ≤ [Fe/H] ≤ -2.75, but appears to drop abruptly at [Fe/H]
≈ -4.2, in line with previous studies.
Title: VizieR Online Data Catalog: Members of 5 cluster in Ori OB1a
association (Kos+, 2019)
Authors: Kos, J.; Bland-Hawthorn, J.; Asplund, M.; Buder, S.; Lewis,
G. F.; Lin, J.; Martell, S. L.; Ness, M. K.; Sharma, S.; de Silva,
G. M.; Simpson, J. D.; Zucker, D. B.; Zwitter, T.; Cotar, K.; Spina, L.
Bibcode: 2019yCat..36310166K
Altcode:
The Gaia DR2 parameters supplemented with radial velocities from the
GALAH and APOGEE surveys are used to perform clustering of the Ori
OB1a association. Table 1 contains the properties of 5 identified
clusters clusters, including ages (derived using Gaia DR2, Pan-STARRS1
and 2MASS photometry to fit isochrones to their colour-magnitude
diagrams). Tableb 1 - tableb 5 contain the identified members of the
different clusters. (6 data files).
Title: The lowest detected stellar Fe abundance: the halo star SMSS
J160540.18-144323.1
Authors: Nordlander, T.; Bessell, M. S.; Da Costa, G. S.; Mackey,
A. D.; Asplund, M.; Casey, A. R.; Chiti, A.; Ezzeddine, R.; Frebel,
A.; Lind, K.; Marino, A. F.; Murphy, S. J.; Norris, J. E.; Schmidt,
B. P.; Yong, D.
Bibcode: 2019MNRAS.488L.109N
Altcode: 2019arXiv190407471N; 2019MNRAS.tmpL.112N
We report the discovery of SMSS J160540.18-144323.1, a new ultra
metal-poor halo star discovered with the SkyMapper telescope. We
measure [{Fe}/{H}]= -6.2 ± 0.2 (1D LTE), the lowest ever detected
abundance of iron in a star. The star is strongly carbon-enhanced,
[{C}/{Fe}] = 3.9 ± 0.2, while other abundances are compatible with
an α-enhanced solar-like pattern with [{Ca}/{Fe}] = 0.4 ± 0.2,
[{Mg}/{Fe}] = 0.6 ± 0.2, [{Ti}/{Fe}] = 0.8 ± 0.2, and no significant
s- or r-process enrichment, [{Sr}/{Fe}] < 0.2 and [{Ba}/{Fe}] <
1.0 (3σ limits). Population III stars exploding as fallback supernovae
may explain both the strong carbon enhancement and the apparent lack of
enhancement of odd-Z and neutron-capture element abundances. Grids of
supernova models computed for metal-free progenitor stars yield good
matches for stars of about 10 M_⊙ imparting a low kinetic energy on
the supernova ejecta, while models for stars more massive than roughly
20 M_⊙ are incompatible with the observed abundance pattern.
Title: The COMBS survey - I. Chemical origins of metal-poor stars
in the Galactic bulge
Authors: Lucey, Madeline; Hawkins, Keith; Ness, Melissa; Asplund,
Martin; Bensby, Thomas; Casagrande, Luca; Feltzing, Sofia; Freeman,
Kenneth C.; Kobayashi, Chiaki; Marino, Anna F.
Bibcode: 2019MNRAS.488.2283L
Altcode: 2019arXiv190311615L; 2019MNRAS.tmp.1795L
Chemistry and kinematic studies can determine the origins of stellar
population across the Milky Way. The metallicity distribution function
of the bulge indicates that it comprises multiple populations, the
more metal-poor end of which is particularly poorly understood. It
is currently unknown if metal-poor bulge stars ([Fe/H] <-1 dex)
are part of the stellar halo in the inner most region, or a distinct
bulge population or a combination of these. Cosmological simulations
also indicate that the metal-poor bulge stars may be the oldest stars in
the Galaxy. In this study, we successfully target metal-poor bulge stars
selected using SkyMapper photometry. We determine the stellar parameters
of 26 stars and their elemental abundances for 22 elements using R∼
47 000 VLT/UVES spectra and contrast their elemental properties with
that of other Galactic stellar populations. We find that the elemental
abundances we derive for our metal-poor bulge stars have lower overall
scatter than typically found in the halo. This indicates that these
stars may be a distinct population confined to the bulge. If these stars
are, alternatively, part of the innermost distribution of the halo, this
indicates that the halo is more chemically homogeneous at small Galactic
radii than at large radii. We also find two stars whose chemistry is
consistent with second-generation globular cluster stars. This paper
is the first part of the Chemical Origins of Metal-poor Bulge Stars
(COMBS) survey that will chemodynamically characterize the metal-poor
bulge population.
Title: The GALAH survey: unresolved triple Sun-like stars discovered
by the Gaia mission
Authors: Čotar, Klemen; Zwitter, Tomaž; Traven, Gregor; Kos, Janez;
Asplund, Martin; Bland-Hawthorn, Joss; Buder, Sven; D'Orazi, Valentina;
de Silva, Gayandhi M.; Lin, Jane; Martell, Sarah L.; Sharma, Sanjib;
Simpson, Jeffrey D.; Zucker, Daniel B.; Horner, Jonathan; Lewis,
Geraint F.; Nordlander, Thomas; Ting, Yuan-Sen; Wittenmyer, Rob A.;
Galah Collaboration
Bibcode: 2019MNRAS.487.2474C
Altcode: 2019MNRAS.tmp.1341C; 2019arXiv190404841C
The latest Gaia data release enables us to accurately identify stars
that are more luminous than would be expected on the basis of their
spectral type and distance. During an investigation of the 329 best
solar twin candidates uncovered among the spectra acquired by the
GALAH survey, we identified 64 such overluminous stars. In order
to investigate their exact composition, we developed a data-driven
methodology that can generate a synthetic photometric signature
and spectrum of a single star. By combining multiple such synthetic
stars into an unresolved binary or triple system and comparing the
results to the actual photometric and spectroscopic observations,
we uncovered 6 definitive triple stellar system candidates and an
additional 14 potential candidates whose combined spectrum mimics
the solar spectrum. Considering the volume correction factor for a
magnitude-limited survey, the fraction of probable unresolved triple
stars with long orbital periods is ∼2 per cent. Possible orbital
configurations of the candidates were investigated using the selection
and observational limits. To validate the discovered multiplicity
fraction, the same procedure was used to evaluate the multiplicity
fraction of other stellar types.
Title: VizieR Online Data Catalog: Abundances for 79 Sun-like stars
within 100pc (Bedell+, 2018)
Authors: Bedell, M.; Bean, J. L.; Melendez, J.; Spina, L.; Ramirez,
I.; Asplund, M.; Alves-Brito, A.; Dos Santos, L.; Dreizler, S.; Yong,
D.; Monroe, T.; Casagrande, L.
Bibcode: 2019yCat..18650068B
Altcode:
To achieve sufficient signal-to-noise for high-precision abundance
work, we stacked >=50 observations for each star. All spectra were
taken with the High Accuracy Radial velocity Planet Searcher (HARPS)
spectrograph on the 3.6m telescope of the European Southern Observatory
(ESO), located at La Silla Observatory in Chile; with resolving power
R=115000 and wavelength coverage between 378-691nm. A majority of
the selected sample were observed by us in the course of a large ESO
observing program on HARPS (Melendez+ 2015Msngr.161...28M). Other stars
had a sufficient number of publicly available spectra in the online
ESO Science Archive Facility. The solar reference spectrum used
in this work was created by combining multiple exposures of sunlight
reflected from the asteroid Vesta. It was continuum-normalized in the
same manner as the target spectra and has S/N~1300/pix at 600nm. Spectra previously obtained with the MIKE spectrograph and analyzed
in Ramirez+ (2014A&A...572A..48R) were also used in some parts
of this analysis. These spectra have S/N~400/pix at 600nm, resolution
R=83000-65000 (on blue/red CCDs), and wavelength coverage between 320
and 1000nm. (2 data files).
Title: HERBS II: Detailed chemical compositions of Galactic bulge
stars
Authors: Duong, L.; Asplund, M.; Nataf, D. M.; Freeman, K. C.; Ness, M.
Bibcode: 2019MNRAS.486.5349D
Altcode: 2019MNRAS.tmp.1135D; 2019arXiv190402261D
This work explores the detailed chemistry of the Milky Way bulge using
the HERMES spectrograph on the Anglo-Australian Telescope. Here,
we present the abundance ratios of 13 elements for 832 red giant
branch and clump stars along the minor bulge axis at latitudes b =
-10○, - 7.5○, and -5○. Our
results show that none of the abundance ratios vary significantly with
latitude. We also observe disc-like [Na/Fe] abundance ratios, which
indicate that the bulge does not contain helium-enhanced populations
as observed in some globular clusters. Helium enhancement is therefore
not the likely explanation for the double red-clump observed in the
bulge. We confirm that bulge stars mostly follow abundance trends
observed in the disc. However, this similarity is not confirmed
across all elements and metallicity regimes. The more metal-poor
bulge population at [Fe/H] ≲ - 0.8 is enhanced in the elements
associated with core collapse supernovae (SNeII). In addition, the
[La/Eu] abundance ratio suggests higher r-process contribution, and
likely higher star formation in the bulge compared to the disc. This
highlights the complex evolution in the bulge, which should be
investigated further, both in terms of modelling; and with additional
observations of the inner Galaxy.
Title: Chemical (in)homogeneity and atomic diffusion in the open
cluster M 67
Authors: Liu, F.; Asplund, M.; Yong, D.; Feltzing, S.; Dotter, A.;
Meléndez, J.; Ramírez, I.
Bibcode: 2019A&A...627A.117L
Altcode: 2019arXiv190211008L
Context. The benchmark open cluster M 67 is known to have solar
metallicity and an age similar to that of the Sun. It thus provides
us with a great opportunity to study the properties of solar twins,
as well as the evolution of Sun-like stars.
Aims: Previous
spectroscopic studies of M 67 reported possible subtle changes in
stellar surface abundances throughout the stellar evolutionary phase,
namely the effect of atomic diffusion. In this study we attempt to
confirm and quantify more precisely the effect of atomic diffusion,
and to explore the level of chemical (in)homogeneity in M 67.
Methods: We presented a strictly line-by-line differential chemical
abundance analysis of two groups of stars in M 67: three turn-off
stars and three subgiants. Stellar atmospheric parameters and elemental
abundances were obtained with very high precision using the Keck/HIRES
spectra.
Results: The subgiants in our sample show negligible
abundance variations (≤0.02 dex), which implies that M 67 was born
chemically homogeneous. We note that there is a significant abundance
difference ( 0.1-0.2 dex) between subgiants and turn-off stars, which
can be interpreted as the signature of atomic diffusion. Qualitatively
stellar models with diffusion agree with the observed abundance
results. Some turn-off stars do not follow the general pattern, which
suggests that in some cases diffusion can be inhibited, or they might
have undergone some sort of mixing event related to planets.
Conclusions: Our results pose additional challenges for chemical
tagging when using turn-off stars. In particular, the effects of atomic
diffusion, which could be as large as 0.1-0.2 dex, must be taken into
account in order for chemical tagging to be successfully applied. Table A.1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/627/A117The
data presented here were obtained at the W.M. Keck Observatory, which is
operated as a scientific partnership among the California Institute of
Technology, the University of California, and the National Aeronautics
and Space Administration. The Observatory was made possible by the
generous financial support of the W.M. Keck Foundation.
Title: The Amplitude of Solar p-mode Oscillations from
Three-dimensional Convection Simulations
Authors: Zhou, Yixiao; Asplund, Martin; Collet, Remo
Bibcode: 2019ApJ...880...13Z
Altcode: 2019arXiv190513397Z
The amplitude of solar p-mode oscillations is governed by stochastic
excitation and mode damping, both of which take place in the surface
convection zone. However, the time-dependent, turbulent nature of
convection makes it difficult to self-consistently study excitation
and damping processes through the use of traditional one-dimensional
(1D) hydrostatic models. To this end, we carried out ab initio
three-dimensional (3D), hydrodynamical numerical simulations of the
solar atmosphere to investigate how p-modes are driven and dissipated
in the Sun. The description of surface convection in the simulations
is free from the tunable parameters typically adopted in traditional
1D models. Mode excitation and damping rates are computed based on
analytical expressions whose ingredients are evaluated directly from the
3D model. With excitation and damping rates both available, we estimate
the theoretical oscillation amplitude and frequency of maximum power,
{ν }\max , for the Sun. We compare our numerical results
with helioseismic observations, finding encouraging agreement between
the two. The numerical method presented here provides a novel way to
investigate the physical processes responsible for mode driving and
damping, and should be valid for all solar-type oscillating stars.
Title: HERBS I: Metallicity and alpha enhancement along the Galactic
bulge minor axis
Authors: Duong, L.; Asplund, M.; Nataf, D. M.; Freeman, K. C.; Ness,
M.; Howes, L. M.
Bibcode: 2019MNRAS.486.3586D
Altcode: 2019arXiv190309706D; 2019MNRAS.tmp.1069D
To better understand the origin and evolution of the Milky Way bulge,
we have conducted a survey of bulge red giant branch and clump stars
using the High Efficiency and Resolution Multi-Element Spectrograph
on the Anglo-Australian Telescope. We targeted ARGOS survey stars
with predetermined bulge memberships, covering the full metallicity
distribution function. The spectra have signal-to-noise ratios
comparable to, and were analysed using the same methods as the GALAH
survey. In this work, we present the survey design, stellar parameters,
distribution of metallicity, and alpha-element abundances along the
minor bulge axis at latitudes b = -10°, - 7.5°, and -5°. Our analysis
of ARGOS stars indicates that the centroids of ARGOS metallicity
components should be located ≈0.09 dex closer together. The vertical
distribution of α-element abundances is consistent with the varying
contributions of the different metallicity components. Closer to the
plane, alpha abundance ratios are lower as the metal-rich population
dominates. At higher latitudes, the alpha abundance ratios increase as
the number of metal-poor stars increases. However, we find that the
trend of alpha-enrichment with respect to metallicity is independent
of latitude. Comparison of our results with those of GALAH DR2 revealed
that for [Fe/H] ≈ -0.8, the bulge shares the same abundance trend as
the high-α disc population. However, the metal-poor bulge population
([Fe/H] ≲ -0.8) show enhanced alpha abundance ratios compared to the
disc/halo. These observations point to fairly rapid chemical evolution
in the bulge, and that the metal-poor bulge population does not share
the same similarity with the disc as the more metal-rich populations.
Title: VizieR Online Data Catalog: GALAH unresolved triple Sun-like
star (Cotar+, 2019)
Authors: Cotar, K.; Zwitter, T.; Traven, G.; Kos, J.; Asplund, M.;
Bland-Hawthorn, J.; Buder, S.; Dorazi, V.; de Silva, G. M.; Lin, J.;
Martell, S. L.; Sharma, S.; Simpson, J. D.; Zucker, D. B.; Horner,
J.; Lewis, G. F.; Nordlander, T.; Ting, Y. -S.; Wittenmyer, R. A.;
GALAH Collaboration
Bibcode: 2019yCat..74872474C
Altcode:
We provide a list of 329 Sun-like stars that were analysed for their
possible multiplicity based on their absolute magnitude and distance
derived from Gaia DR2 data. The GALAH proprietary spectra are used to
confirm their similarity with solar spectrum and to determine [Fe/H]
of the determined systems. We uncovered 20 candidates for unresolved
triple stellar systems that have to analysed with other approaches to
confirm their multiple nature. (1 data file).
Title: VizieR Online Data Catalog: Equivalent widths for six M67 stars
(Liu+, 2019)
Authors: Liu, F.; Asplund, M.; Yong, D.; Feltzing, S.; Dotter, A.;
Melendez, J.; Ramirez, I.
Bibcode: 2019yCat..36270117L
Altcode:
Atomic line data, as well as the measured equivalent widths, adopted
for our analysis. (2 data files).
Title: Keck HIRES spectroscopy of SkyMapper commissioning survey
candidate extremely metal-poor stars
Authors: Marino, A. F.; Da Costa, G. S.; Casey, A. R.; Asplund, M.;
Bessell, M. S.; Frebel, A.; Keller, S. C.; Lind, K.; Mackey, A. D.;
Murphy, S. J.; Nordlander, T.; Norris, J. E.; Schmidt, B. P.; Yong, D.
Bibcode: 2019MNRAS.485.5153M
Altcode: 2019arXiv190210611M; 2019MNRAS.tmp..627M
We present results from the analysis of high-resolution spectra obtained
with the Keck HIRES spectrograph for a sample of 17 candidate extremely
metal-poor (EMP) stars originally selected from commissioning data
obtained with the SkyMapper telescope. Fourteen of the stars have
not been observed previously at high dispersion. Three have [Fe/H]
≤ -3.0, while the remainder, with two more metal-rich exceptions,
have -3.0 ≤ [Fe/H] ≤ -2.0 dex. Apart from Fe, we also derive
abundances for the elements C, N, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn,
Co, Ni, and Zn, and for n-capture elements Sr, Ba, and Eu. None of
the current sample of stars is found to be carbon-rich. In general,
our chemical abundances follow previous trends found in the literature,
although we note that two of the most metal-poor stars show very low
[Ba/Fe] (∼-1.7) coupled with low [Sr/Ba] (∼-0.3). Such stars are
relatively rare in the Galactic halo. One further star, and possibly
two others, meet the criteria for classification as a r-I star. This
study, together with that of Jacobson et al. (2015), completes the
outcomes of the SkyMapper commissioning data survey for EMP stars.
Title: The GALAH survey and Gaia DR2: dissecting the stellar disc's
phase space by age, action, chemistry, and location
Authors: Bland-Hawthorn, Joss; Sharma, Sanjib; Tepper-Garcia, Thor;
Binney, James; Freeman, Ken C.; Hayden, Michael R.; Kos, Janez; De
Silva, Gayandhi M.; Ellis, Simon; Lewis, Geraint F.; Asplund, Martin;
Buder, Sven; Casey, Andrew R.; D'Orazi, Valentina; Duong, Ly; Khanna,
Shourya; Lin, Jane; Lind, Karin; Martell, Sarah L.; Ness, Melissa
K.; Simpson, Jeffrey D.; Zucker, Daniel B.; Zwitter, Tomaž; Kafle,
Prajwal R.; Quillen, Alice C.; Ting, Yuan-Sen; Wyse, Rosemary F. G.
Bibcode: 2019MNRAS.486.1167B
Altcode: 2018arXiv180902658B; 2019MNRAS.tmp..222B
We use the second data releases of the European Space AgencyGaia
astrometric survey and the high-resolution Galactic Archaeology with
HERMES (GALAH) spectroscopic survey to analyse the structure of
our Galaxy's disc components. With GALAH, we separate the α-rich
and α-poor discs (with respect to Fe), which are superposed in
both position and velocity space, and examine their distributions
in action space. We study the distribution of stars in the zV
z phase plane, for both Vϕ and VR, and
recover the remarkable `phase spiral' discovered by Gaia. We identify
the anticipated quadrupole signature in zV z of a tilted
velocity ellipsoid for stars above and below the Galactic plane. By
connecting our work with earlier studies, we show that the phase
spiral is likely to extend well beyond the narrow solar neighbourhood
cylinder in which it was found. The phase spiral is a signature of
corrugated waves that propagate through the disc, and the associated
non-equilibrium phase mixing. The radially asymmetric distribution
of stars involved in the phase spiral reveals that the corrugation,
which is mostly confined to the α-poor disc, grows in z-amplitude with
increasing radius. We present new simulations of tidal disturbance
of the Galactic disc by the Sagittarius (Sgr) dwarf. The effect on
the zV z phase plane lasts {≳ } 2 Gyr, but a subsequent
disc crossing wipes out the coherent structure. We find that the phase
spiral was excited {≲ } 0.5 Gyr ago by an object like Sgr with total
mass ∼3 × 1010 M⊙ (stripped down from ∼5
× 1010 M⊙ when it first entered the halo)
passing through the plane.
Title: Constraining the evolution of stellar rotation using solar
twins
Authors: Lorenzo-Oliveira, Diego; Meléndez, Jorge; Yana Galarza,
Jhon; Ponte, Geisa; dos Santos, Leonardo A.; Spina, Lorenzo; Bedell,
Megan; Ramírez, Iván; Bean, Jacob L.; Asplund, Martin
Bibcode: 2019MNRAS.485L..68L
Altcode: 2019arXiv190302630L; 2019MNRAS.tmpL..40L
The stellar rotation versus age relation is commonly considered a
useful tool to derive reliable ages for Sun-like stars. However,
in the light of Kepler data, the presence of apparently old and fast
rotators that do not obey the usual gyrochronology relations led to
the hypothesis of weakened magnetic breaking in some stars. In this
letter, we constrain the solar rotation evolutionary track using solar
twins. Predicted rotational periods as a function of mass, age, [Fe/H],
and given critical Rossby number (Rocrit) were estimated for
the entire rotational sample. Our analysis favours the smooth rotational
evolution scenario and suggests that if the magnetic weakened breaking
scenario takes place at all, it should arise after Rocrit
≳ 2.29 or ages ≳5.3 Gyr (at 95 per cent confidence level).
Title: The Li-age correlation: the Sun is unusually Li deficient
for its age
Authors: Carlos, M.; Meléndez, J.; Spina, L.; dos Santos, L. A.;
Bedell, M.; Ramirez, I.; Asplund, M.; Bean, J. L.; Yong, D.; Yana
Galarza, J.; Alves-Brito, A.
Bibcode: 2019MNRAS.485.4052C
Altcode: 2019arXiv190302735C; 2019MNRAS.tmp..667C
This work aims to examine in detail the depletion of lithium in solar
twins to better constrain stellar evolution models and investigate its
possible connection with exoplanets. We employ spectral synthesis in the
region of the asymmetric 6707.75 Å Li I line for a sample of 77 stars
plus the Sun. As in previous works based on a smaller sample of solar
twins, we find a strong correlation between Li depletion and stellar
age. In addition, for the first time we show that the Sun has the lowest
Li abundance in comparison with solar twins at similar age (4.6 ± 0.5
Gyr). We compare the lithium content with the condensation temperature
slope for a subsample of the best solar twins and determine that the
most lithium-depleted stars also have fewer refractory elements. We
speculate whether the low lithium content in the Sun might be related
to the particular configuration of our Solar system.
Title: The Detailed Science Case for the Maunakea Spectroscopic
Explorer, 2019 edition
Authors: The MSE Science Team; Babusiaux, Carine; Bergemann, Maria;
Burgasser, Adam; Ellison, Sara; Haggard, Daryl; Huber, Daniel;
Kaplinghat, Manoj; Li, Ting; Marshall, Jennifer; Martell, Sarah;
McConnachie, Alan; Percival, Will; Robotham, Aaron; Shen, Yue;
Thirupathi, Sivarani; Tran, Kim-Vy; Yeche, Christophe; Yong, David;
Adibekyan, Vardan; Silva Aguirre, Victor; Angelou, George; Asplund,
Martin; Balogh, Michael; Banerjee, Projjwal; Bannister, Michele;
Barría, Daniela; Battaglia, Giuseppina; Bayo, Amelia; Bechtol,
Keith; Beck, Paul G.; Beers, Timothy C.; Bellinger, Earl P.; Berg,
Trystyn; Bestenlehner, Joachim M.; Bilicki, Maciej; Bitsch, Bertram;
Bland-Hawthorn, Joss; Bolton, Adam S.; Boselli, Alessandro; Bovy,
Jo; Bragaglia, Angela; Buzasi, Derek; Caffau, Elisabetta; Cami, Jan;
Carleton, Timothy; Casagrande, Luca; Cassisi, Santi; Catelan, Márcio;
Chang, Chihway; Cortese, Luca; Damjanov, Ivana; Davies, Luke J. M.;
de Grijs, Richard; de Rosa, Gisella; Deason, Alis; di Matteo, Paola;
Drlica-Wagner, Alex; Erkal, Denis; Escorza, Ana; Ferrarese, Laura;
Fleming, Scott W.; Font-Ribera, Andreu; Freeman, Ken; Gänsicke,
Boris T.; Gabdeev, Maksim; Gallagher, Sarah; Gandolfi, Davide; García,
Rafael A.; Gaulme, Patrick; Geha, Marla; Gennaro, Mario; Gieles, Mark;
Gilbert, Karoline; Gordon, Yjan; Goswami, Aruna; Greco, Johnny P.;
Grillmair, Carl; Guiglion, Guillaume; Hénault-Brunet, Vincent;
Hall, Patrick; Handler, Gerald; Hansen, Terese; Hathi, Nimish;
Hatzidimitriou, Despina; Haywood, Misha; Hernández Santisteban,
Juan V.; Hillenbrand, Lynne; Hopkins, Andrew M.; Howlett, Cullan;
Hudson, Michael J.; Ibata, Rodrigo; Ilić, Dragana; Jablonka,
Pascale; Ji, Alexander; Jiang, Linhua; Juneau, Stephanie; Karakas,
Amanda; Karinkuzhi, Drisya; Kim, Stacy Y.; Kong, Xu; Konstantopoulos,
Iraklis; Krogager, Jens-Kristian; Lagos, Claudia; Lallement, Rosine;
Laporte, Chervin; Lebreton, Yveline; Lee, Khee-Gan; Lewis, Geraint F.;
Lianou, Sophia; Liu, Xin; Lodieu, Nicolas; Loveday, Jon; Mészáros,
Szabolcs; Makler, Martin; Mao, Yao-Yuan; Marchesini, Danilo; Martin,
Nicolas; Mateo, Mario; Melis, Carl; Merle, Thibault; Miglio, Andrea;
Gohar Mohammad, Faizan; Molaverdikhani, Karan; Monier, Richard;
Morel, Thierry; Mosser, Benoit; Nataf, David; Necib, Lina; Neilson,
Hilding R.; Newman, Jeffrey A.; Nierenberg, A. M.; Nord, Brian;
Noterdaeme, Pasquier; O'Dea, Chris; Oshagh, Mahmoudreza; Pace, Andrew
B.; Palanque-Delabrouille, Nathalie; Pandey, Gajendra; Parker, Laura
C.; Pawlowski, Marcel S.; Peter, Annika H. G.; Petitjean, Patrick;
Petric, Andreea; Placco, Vinicius; Popović, Luka Č.; Price-Whelan,
Adrian M.; Prsa, Andrej; Ravindranath, Swara; Rich, R. Michael; Ruan,
John; Rybizki, Jan; Sakari, Charli; Sanderson, Robyn E.; Schiavon,
Ricardo; Schimd, Carlo; Serenelli, Aldo; Siebert, Arnaud; Siudek,
Malgorzata; Smiljanic, Rodolfo; Smith, Daniel; Sobeck, Jennifer;
Starkenburg, Else; Stello, Dennis; Szabó, Gyula M.; Szabo, Robert;
Taylor, Matthew A.; Thanjavur, Karun; Thomas, Guillaume; Tollerud,
Erik; Toonen, Silvia; Tremblay, Pier-Emmanuel; Tresse, Laurence;
Tsantaki, Maria; Valentini, Marica; Van Eck, Sophie; Variu, Andrei;
Venn, Kim; Villaver, Eva; Walker, Matthew G.; Wang, Yiping; Wang,
Yuting; Wilson, Michael J.; Wright, Nicolas; Xu, Siyi; Yildiz,
Mutlu; Zhang, Huawei; Zwintz, Konstanze; Anguiano, Borja; Bedell,
Megan; Chaplin, William; Collet, Remo; Cuillandre, Jean-Charles;
Duc, Pierre-Alain; Flagey, Nicolas; Hermes, JJ; Hill, Alexis;
Kamath, Devika; Laychak, Mary Beth; Małek, Katarzyna; Marley, Mark;
Sheinis, Andy; Simons, Doug; Sousa, Sérgio G.; Szeto, Kei; Ting,
Yuan-Sen; Vegetti, Simona; Wells, Lisa; Babas, Ferdinand; Bauman,
Steve; Bosselli, Alessandro; Côté, Pat; Colless, Matthew; Comparat,
Johan; Courtois, Helene; Crampton, David; Croom, Scott; Davies, Luke;
de Grijs, Richard; Denny, Kelly; Devost, Daniel; di Matteo, Paola;
Driver, Simon; Fernandez-Lorenzo, Mirian; Guhathakurta, Raja; Han,
Zhanwen; Higgs, Clare; Hill, Vanessa; Ho, Kevin; Hopkins, Andrew;
Hudson, Mike; Ibata, Rodrigo; Isani, Sidik; Jarvis, Matt; Johnson,
Andrew; Jullo, Eric; Kaiser, Nick; Kneib, Jean-Paul; Koda, Jun;
Koshy, George; Mignot, Shan; Murowinski, Rick; Newman, Jeff; Nusser,
Adi; Pancoast, Anna; Peng, Eric; Peroux, Celine; Pichon, Christophe;
Poggianti, Bianca; Richard, Johan; Salmon, Derrick; Seibert, Arnaud;
Shastri, Prajval; Smith, Dan; Sutaria, Firoza; Tao, Charling; Taylor,
Edwar; Tully, Brent; van Waerbeke, Ludovic; Vermeulen, Tom; Walker,
Matthew; Willis, Jon; Willot, Chris; Withington, Kanoa
Bibcode: 2019arXiv190404907T
Altcode:
(Abridged) The Maunakea Spectroscopic Explorer (MSE) is an end-to-end
science platform for the design, execution and scientific exploitation
of spectroscopic surveys. It will unveil the composition and dynamics
of the faint Universe and impact nearly every field of astrophysics
across all spatial scales, from individual stars to the largest scale
structures in the Universe. Major pillars in the science program for MSE
include (i) the ultimate Gaia follow-up facility for understanding the
chemistry and dynamics of the distant Milky Way, including the outer
disk and faint stellar halo at high spectral resolution (ii) galaxy
formation and evolution at cosmic noon, via the type of revolutionary
surveys that have occurred in the nearby Universe, but now conducted at
the peak of the star formation history of the Universe (iii) derivation
of the mass of the neutrino and insights into inflationary physics
through a cosmological redshift survey that probes a large volume of
the Universe with a high galaxy density. MSE is positioned to become
a critical hub in the emerging international network of front-line
astronomical facilities, with scientific capabilities that naturally
complement and extend the scientific power of Gaia, the Large Synoptic
Survey Telescope, the Square Kilometer Array, Euclid, WFIRST, the 30m
telescopes and many more.
Title: 3D non-LTE line formation of neutral carbon in the Sun
Authors: Amarsi, A. M.; Barklem, P. S.; Collet, R.; Grevesse, N.;
Asplund, M.
Bibcode: 2019A&A...624A.111A
Altcode: 2019arXiv190308838A
Carbon abundances in late-type stars are important in a variety of
astrophysical contexts. However C I lines, one of the main abundance
diagnostics, are sensitive to departures from local thermodynamic
equilibrium (LTE). We present a model atom for non-LTE analyses of C
I lines, that uses a new, physically-motivated recipe for the rates
of neutral hydrogen impact excitation. We analyse C I lines in the
solar spectrum, employing a three-dimensional (3D) hydrodynamic
model solar atmosphere and 3D non-LTE radiative transfer. We find
negative non-LTE abundance corrections for C I lines in the solar
photosphere, in accordance with previous studies, reaching up to
around 0.1 dex in the disk-integrated flux. We also present the first
fully consistent 3D non-LTE solar carbon abundance determination:
we infer log ɛC = 8.44 ± 0.02, in good agreement with
the current standard value. Our models reproduce the observed solar
centre-to-limb variations of various C I lines, without any adjustments
to the rates of neutral hydrogen impact excitation, suggesting that
the proposed recipe may be a solution to the long-standing problem of
how to reliably model inelastic collisions with neutral hydrogen in
late-type stellar atmospheres.
Title: The GALAH survey: An abundance, age, and kinematic inventory
of the solar neighbourhood made with TGAS
Authors: Buder, S.; Lind, K.; Ness, M. K.; Asplund, M.; Duong, L.;
Lin, J.; Kos, J.; Casagrande, L.; Casey, A. R.; Bland-Hawthorn,
J.; de Silva, G. M.; D'Orazi, V.; Freeman, K. C.; Martell, S. L.;
Schlesinger, K. J.; Sharma, S.; Simpson, J. D.; Zucker, D. B.;
Zwitter, T.; Čotar, K.; Dotter, A.; Hayden, M. R.; Hyde, E. A.;
Kafle, P. R.; Lewis, G. F.; Nataf, D. M.; Nordlander, T.; Reid, W.;
Rix, H. -W.; Skúladóttir, Á.; Stello, D.; Ting, Y. -S.; Traven,
G.; Wyse, R. F. G.; GALAH Collaboration
Bibcode: 2019A&A...624A..19B
Altcode: 2018arXiv180405869B
The overlap between the spectroscopic Galactic Archaeology with HERMES
(GALAH) survey and Gaia provides a high-dimensional chemodynamical space
of unprecedented size. We present a first analysis of a subset of this
overlap, of 7066 dwarf, turn-off, and sub-giant stars. These stars have
spectra from the GALAH survey and high parallax precision from the Gaia
DR1 Tycho-Gaia Astrometric Solution. We investigate correlations between
chemical compositions, ages, and kinematics for this sample. Stellar
parameters and elemental abundances are derived from the GALAH spectra
with the spectral synthesis code SPECTROSCOPY MADE EASY. We determine
kinematics and dynamics, including action angles, from the Gaia
astrometry and GALAH radial velocities. Stellar masses and ages are
determined with Bayesian isochrone matching, using our derived stellar
parameters and absolute magnitudes. We report measurements of Li, C, O,
Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, as well
as Ba and we note that we have employed non-LTE calculations for Li,
O, Al, and Fe. We show that the use of astrometric and photometric
data improves the accuracy of the derived spectroscopic parameters,
especially log g. Focusing our investigation on the correlations between
stellar age, iron abundance [Fe/H], and mean alpha-enhancement [α/Fe]
of the magnitude-selected sample, we recover the result that stars
of the high-α sequence are typically older than stars in the low-α
sequence, the latter spanning iron abundances of -0.7 < [Fe/H] <
+0.5. While these two sequences become indistinguishable in [α/Fe]
vs. [Fe/H] at the metal-rich regime, we find that age can be used to
separate stars from the extended high-α and the low-α sequence even
in this regime. When dissecting the sample by stellar age, we find that
the old stars (>8 Gyr) have lower angular momenta Lz
than the Sun, which implies that they are on eccentric orbits and
originate from the inner disc. Contrary to some previous smaller scale
studies we find a continuous evolution in the high-α-sequence up
to super-solar [Fe/H] rather than a gap, which has been interpreted
as a separate "high-α metal-rich" population. Stars in our sample
that are younger than 10 Gyr, are mainly found on the low α-sequence
and show a gradient in Lz from low [Fe/H] (Lz
> Lz, ⊙) towards higher [Fe/H] (Lz <
Lz, ⊙), which implies that the stars at the ends of this
sequence are likely not originating from the close solar vicinity. The catalogue is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/624/A19
Title: 4MOST: Project overview and information for the First Call
for Proposals
Authors: de Jong, R. S.; Agertz, O.; Berbel, A. A.; Aird, J.;
Alexander, D. A.; Amarsi, A.; Anders, F.; Andrae, R.; Ansarinejad,
B.; Ansorge, W.; Antilogus, P.; Anwand-Heerwart, H.; Arentsen, A.;
Arnadottir, A.; Asplund, M.; Auger, M.; Azais, N.; Baade, D.; Baker,
G.; Baker, S.; Balbinot, E.; Baldry, I. K.; Banerji, M.; Barden,
S.; Barklem, P.; Barthélémy-Mazot, E.; Battistini, C.; Bauer, S.;
Bell, C. P. M.; Bellido-Tirado, O.; Bellstedt, S.; Belokurov, V.;
Bensby, T.; Bergemann, M.; Bestenlehner, J. M.; Bielby, R.; Bilicki,
M.; Blake, C.; Bland-Hawthorn, J.; Boeche, C.; Boland, W.; Boller,
T.; Bongard, S.; Bongiorno, A.; Bonifacio, P.; Boudon, D.; Brooks,
D.; Brown, M. J. I.; Brown, R.; Brüggen, M.; Brynnel, J.; Brzeski,
J.; Buchert, T.; Buschkamp, P.; Caffau, E.; Caillier, P.; Carrick,
J.; Casagrande, L.; Case, S.; Casey, A.; Cesarini, I.; Cescutti, G.;
Chapuis, D.; Chiappini, C.; Childress, M.; Christlieb, N.; Church, R.;
Cioni, M. -R. L.; Cluver, M.; Colless, M.; Collett, T.; Comparat, J.;
Cooper, A.; Couch, W.; Courbin, F.; Croom, S.; Croton, D.; Daguisé,
E.; Dalton, G.; Davies, L. J. M.; Davis, T.; de Laverny, P.; Deason,
A.; Dionies, F.; Disseau, K.; Doel, P.; Döscher, D.; Driver, S. P.;
Dwelly, T.; Eckert, D.; Edge, A.; Edvardsson, B.; Youssoufi, D. E.;
Elhaddad, A.; Enke, H.; Erfanianfar, G.; Farrell, T.; Fechner, T.;
Feiz, C.; Feltzing, S.; Ferreras, I.; Feuerstein, D.; Feuillet, D.;
Finoguenov, A.; Ford, D.; Fotopoulou, S.; Fouesneau, M.; Frenk, C.;
Frey, S.; Gaessler, W.; Geier, S.; Gentile Fusillo, N.; Gerhard,
O.; Giannantonio, T.; Giannone, D.; Gibson, B.; Gillingham, P.;
González-Fernández, C.; Gonzalez-Solares, E.; Gottloeber, S.; Gould,
A.; Grebel, E. K.; Gueguen, A.; Guiglion, G.; Haehnelt, M.; Hahn, T.;
Hansen, C. J.; Hartman, H.; Hauptner, K.; Hawkins, K.; Haynes, D.;
Haynes, R.; Heiter, U.; Helmi, A.; Aguayo, C. H.; Hewett, P.; Hinton,
S.; Hobbs, D.; Hoenig, S.; Hofman, D.; Hook, I.; Hopgood, J.; Hopkins,
A.; Hourihane, A.; Howes, L.; Howlett, C.; Huet, T.; Irwin, M.; Iwert,
O.; Jablonka, P.; Jahn, T.; Jahnke, K.; Jarno, A.; Jin, S.; Jofre,
P.; Johl, D.; Jones, D.; Jönsson, H.; Jordan, C.; Karovicova, I.;
Khalatyan, A.; Kelz, A.; Kennicutt, R.; King, D.; Kitaura, F.; Klar,
J.; Klauser, U.; Kneib, J. -P.; Koch, A.; Koposov, S.; Kordopatis, G.;
Korn, A.; Kosmalski, J.; Kotak, R.; Kovalev, M.; Kreckel, K.; Kripak,
Y.; Krumpe, M.; Kuijken, K.; Kunder, A.; Kushniruk, I.; Lam, M. I.;
Lamer, G.; Laurent, F.; Lawrence, J.; Lehmitz, M.; Lemasle, B.; Lewis,
J.; Li, B.; Lidman, C.; Lind, K.; Liske, J.; Lizon, J. -L.; Loveday,
J.; Ludwig, H. -G.; McDermid, R. M.; Maguire, K.; Mainieri, V.; Mali,
S.; Mandel, H.; Mandel, K.; Mannering, L.; Martell, S.; Martinez
Delgado, D.; Matijevic, G.; McGregor, H.; McMahon, R.; McMillan,
P.; Mena, O.; Merloni, A.; Meyer, M. J.; Michel, C.; Micheva, G.;
Migniau, J. -E.; Minchev, I.; Monari, G.; Muller, R.; Murphy, D.;
Muthukrishna, D.; Nandra, K.; Navarro, R.; Ness, M.; Nichani, V.;
Nichol, R.; Nicklas, H.; Niederhofer, F.; Norberg, P.; Obreschkow, D.;
Oliver, S.; Owers, M.; Pai, N.; Pankratow, S.; Parkinson, D.; Paschke,
J.; Paterson, R.; Pecontal, A.; Parry, I.; Phillips, D.; Pillepich,
A.; Pinard, L.; Pirard, J.; Piskunov, N.; Plank, V.; Plüschke, D.;
Pons, E.; Popesso, P.; Power, C.; Pragt, J.; Pramskiy, A.; Pryer,
D.; Quattri, M.; Queiroz, A. B. d. A.; Quirrenbach, A.; Rahurkar,
S.; Raichoor, A.; Ramstedt, S.; Rau, A.; Recio-Blanco, A.; Reiss, R.;
Renaud, F.; Revaz, Y.; Rhode, P.; Richard, J.; Richter, A. D.; Rix,
H. -W.; Robotham, A. S. G.; Roelfsema, R.; Romaniello, M.; Rosario, D.;
Rothmaier, F.; Roukema, B.; Ruchti, G.; Rupprecht, G.; Rybizki, J.;
Ryde, N.; Saar, A.; Sadler, E.; Sahlén, M.; Salvato, M.; Sassolas,
B.; Saunders, W.; Saviauk, A.; Sbordone, L.; Schmidt, T.; Schnurr,
O.; Scholz, R. -D.; Schwope, A.; Seifert, W.; Shanks, T.; Sheinis,
A.; Sivov, T.; Skúladóttir, Á.; Smartt, S.; Smedley, S.; Smith,
G.; Smith, R.; Sorce, J.; Spitler, L.; Starkenburg, E.; Steinmetz,
M.; Stilz, I.; Storm, J.; Sullivan, M.; Sutherland, W.; Swann, E.;
Tamone, A.; Taylor, E. N.; Teillon, J.; Tempel, E.; ter Horst, R.;
Thi, W. -F.; Tolstoy, E.; Trager, S.; Traven, G.; Tremblay, P. -E.;
Tresse, L.; Valentini, M.; van de Weygaert, R.; van den Ancker, M.;
Veljanoski, J.; Venkatesan, S.; Wagner, L.; Wagner, K.; Walcher,
C. J.; Waller, L.; Walton, N.; Wang, L.; Winkler, R.; Wisotzki, L.;
Worley, C. C.; Worseck, G.; Xiang, M.; Xu, W.; Yong, D.; Zhao, C.;
Zheng, J.; Zscheyge, F.; Zucker, D.
Bibcode: 2019Msngr.175....3D
Altcode: 2019arXiv190302464D
We introduce the 4-metre Multi-Object Spectroscopic Telescope (4MOST),
a new high-multiplex, wide-field spectroscopic survey facility under
development for the four-metre-class Visible and Infrared Survey
Telescope for Astronomy (VISTA) at Paranal. Its key specifications
are: a large field of view (FoV) of 4.2 square degrees and a high
multiplex capability, with 1624 fibres feeding two low-resolution
spectrographs (R = λ/Δλ 6500), and 812 fibres transferring light
to the high-resolution spectrograph (R 20 000). After a description of
the instrument and its expected performance, a short overview is given
of its operational scheme and planned 4MOST Consortium science; these
aspects are covered in more detail in other articles in this edition
of The Messenger. Finally, the processes, schedules, and policies
concerning the selection of ESO Community Surveys are presented,
commencing with a singular opportunity to submit Letters of Intent
for Public Surveys during the first five years of 4MOST operations.
Title: The GALAH survey: a catalogue of carbon-enhanced stars and
CEMP candidates
Authors: Čotar, Klemen; Zwitter, Tomaž; Kos, Janez; Munari, Ulisse;
Martell, Sarah L.; Asplund, Martin; Bland-Hawthorn, Joss; Buder, Sven;
de Silva, Gayandhi M.; Freeman, Kenneth C.; Sharma, Sanjib; Anguiano,
Borja; Carollo, Daniela; Horner, Jonathan; Lewis, Geraint F.; Nataf,
David M.; Nordlander, Thomas; Stello, Denis; Ting, Yuan-Sen; Tinney,
Chris; Traven, Gregor; Wittenmyer, Rob A.; Galah Collaboration
Bibcode: 2019MNRAS.483.3196C
Altcode: 2018MNRAS.tmp.2999C; 2018arXiv180707977C; 2019MNRAS.483.3196A
Swan bands - characteristic molecular absorption features of
the C2 molecule - are a spectroscopic signature of
carbon-enhanced stars. They can also be used to identify carbon-enhanced
metal-poor (CEMP) stars. The GALAH (GALactic Archaeology with Hermes)
is a magnitude-limited survey of stars producing high-resolution,
high-signal-to-noise spectra. We used 627 708 GALAH spectra to
search for carbon-enhanced stars with a supervised and unsupervised
classification algorithm, relying on the imprint of the Swan bands. We
identified 918 carbon-enhanced stars, including 12 already described
in the literature. An unbiased selection function of the GALAH survey
allows us to perform a population study of carbon-enhanced stars. Most
of them are giants, out of which we find 28 CEMP candidates. A large
fraction of our carbon-enhanced stars with repeated observations show
variation in radial velocity, hinting that there is a large fraction
of variables among them. 32 of the detected stars also show strong
Lithium enhancement in their spectra.
Title: 4MOST Consortium Survey 3: Milky Way Disc and Bulge
Low-Resolution Survey (4MIDABLE-LR)
Authors: Chiappini, C.; Minchev, I.; Starkenburg, E.; Anders, F.;
Gentile Fusillo, N.; Gerhard, O.; Guiglion, G.; Khalatyan, A.;
Kordopatis, G.; Lemasle, B.; Matijevic, G.; Queiroz, A. B. D. A.;
Schwope, A.; Steinmetz, M.; Storm, J.; Traven, G.; Tremblay, P. -E.;
Valentini, M.; Andrae, R.; Arentsen, A.; Asplund, M.; Bensby, T.;
Bergemann, M.; Casagrande, L.; Church, R.; Cescutti, G.; Feltzing,
S.; Fouesneau, M.; Grebel, E. K.; Kovalev, M.; McMillan, P.; Monari,
G.; Rybizki, J.; Ryde, N.; Rix, H. -W.; Walton, N.; Xiang, M.; Zucker,
D.; 4MIDABLE-Lr Team
Bibcode: 2019Msngr.175...30C
Altcode: 2019arXiv190302469C
The mechanisms of the formation and evolution of the Milky Way are
encoded in the orbits, chemistry and ages of its stars. With the
4MOST MIlky way Disk And BuLgE Low-Resolution Survey (4MIDABLE-LR)
we aim to study kinematic and chemical substructures in the Milky Way
disc and bulge region with samples of unprecedented size out to larger
distances and greater precision than conceivable with Gaia alone or any
other ongoing or planned survey. Gaia gives us the unique opportunity
for target selection based almost entirely on parallax and magnitude
range, hence increasing the efficiency in sampling larger Milky Way
volumes with well-defined and effective selection functions.
Title: 4MOST Consortium Survey 2: The Milky Way Halo High-Resolution
Survey
Authors: Christlieb, N.; Battistini, C.; Bonifacio, P.; Caffau, E.;
Ludwig, H. -G.; Asplund, M.; Barklem, P.; Bergemann, M.; Church, R.;
Feltzing, S.; Ford, D.; Grebel, E. K.; Hansen, C. J.; Helmi, A.;
Kordopatis, G.; Kovalev, M.; Korn, A.; Lind, K.; Quirrenbach, A.;
Rybizki, J.; Skúladóttir, Á.; Starkenburg, E.
Bibcode: 2019Msngr.175...26C
Altcode: 2019arXiv190302468C
We will study the formation history of the Milky Way, and the earliest
phases of its chemical enrichment, with a sample of more than 1.5
million stars at high galactic latitude. Elemental abundances of up to
20 elements with a precision of better than 0.2 dex will be derived
for these stars. The sample will include members of kinematically
coherent substructures, which we will associate with their possible
birthplaces by means of their abundance signatures and kinematics,
allowing us to test models of galaxy formation. Our target catalogue
is also expected to contain 30 000 stars at a metallicity of less than
one hundredth that of the Sun. This sample will therefore be almost
a factor of 100 larger than currently existing samples of metal-poor
stars for which precise elemental abundances are available (determined
from high-resolution spectroscopy), enabling us to study the early
chemical evolution of the Milky Way in unprecedented detail.
Title: 4MOST Consortium Survey 4: Milky Way Disc and Bulge
High-Resolution Survey (4MIDABLE-HR)
Authors: Bensby, T.; Bergemann, M.; Rybizki, J.; Lemasle, B.; Howes,
L.; Kovalev, M.; Agertz, O.; Asplund, M.; Barklem, P.; Battistini,
C.; Casagrande, L.; Chiappini, C.; Church, R.; Feltzing, S.; Ford,
D.; Gerhard, O.; Kushniruk, I.; Kordopatis, G.; Lind, K.; Minchev,
I.; McMillan, P.; Rix, H. -W.; Ryde, N.; Traven, G.
Bibcode: 2019Msngr.175...35B
Altcode: 2019arXiv190302470B
The signatures of the formation and evolution of a galaxy are
imprinted in its stars. Their velocities, ages, and chemical
compositions present major constraints on models of galaxy formation,
and on various processes such as the gas inflows and outflows,
the accretion of cold gas, radial migration, and the variability of
star formation activity. Understanding the evolution of the Milky
Way requires large observational datasets of stars via which these
quantities can be determined accurately. This is the science driver
of the 4MOST MIlky way Disc And BuLgE High-Resolution (4MIDABLE-HR)
survey: to obtain high-resolution spectra at < i>R 20 000 and
to provide detailed elemental abundances for large samples of stars
in the Galactic disc and bulge. High data quality will allow us to
provide accurate spectroscopic diagnostics of two million stellar
spectra: precise radial velocities; rotation; abundances of many
elements, including those that are currently only accessible in the
optical, such as Li, s-, and r-process; and multi-epoch spectra for a
sub-sample of stars. Synergies with complementary missions like Gaia
and TESS will provide masses, stellar ages and multiplicity, forming a
multi-dimensional dataset that will allow us to explore and constrain
the origin and structure of the Milky Way.
Title: The GALAH survey: co-orbiting stars and chemical tagging
Authors: Simpson, Jeffrey D.; Martell, Sarah L.; Da Costa, Gary; Casey,
Andrew R.; Freeman, Ken C.; Horner, Jonathan; Ting, Yuan-Sen; Nataf,
David M.; Lewis, Geraint F.; Ness, Melissa K.; Zucker, Daniel B.;
Cottrell, Peter L.; Čotar, Klemen; Asplund, Martin; Bland-Hawthorn,
Joss; Buder, Sven; D'Orazi, Valentina; De Silva, Gayandhi M.; Duong,
Ly; Kos, Janez; Lin, Jane; Lind, Karin; Schlesinger, Katharine J.;
Sharma, Sanjib; Zwitter, Tomaž; Kafle, Prajwal R.; Nordlander, Thomas
Bibcode: 2019MNRAS.482.5302S
Altcode: 2018MNRAS.tmp.2902S; 2018arXiv180405894S
We present a study using the second data release of the GALAH survey
of stellar parameters and elemental abundances of 15 pairs of stars
identified by Oh et al. They identified these pairs as potentially
co-moving pairs using proper motions and parallaxes from Gaia DR1. We
find that 11 very wide (>1 pc) pairs of stars do in fact have similar
Galactic orbits, while a further four claimed co-moving pairs are not
truly co-orbiting. Eight of the 11 co-orbiting pairs have reliable
stellar parameters and abundances, and we find that three of those are
quite similar in their abundance patterns, while five have significant
[Fe/H] differences. For the latter, this indicates that they could be
co-orbiting because of the general dynamical coldness of the thin disc,
or perhaps resonances induced by the Galaxy, rather than a shared
formation site. Stars such as these, wide binaries, debris of past
star formation episodes, and coincidental co-orbiters, are crucial
for exploring the limits of chemical tagging in the Milky Way.
Title: Carbon and oxygen in metal-poor halo stars
Authors: Amarsi, A. M.; Nissen, P. E.; Asplund, M.; Lind, K.; Barklem,
P. S.
Bibcode: 2019A&A...622L...4A
Altcode: 2019arXiv190103592A
Carbon and oxygen are key tracers of the Galactic chemical evolution;
in particular, a reported upturn in [C/O] towards decreasing [O/H]
in metal-poor halo stars could be a signature of nucleosynthesis by
massive Population III stars. We reanalyse carbon, oxygen, and iron
abundances in 39 metal-poor turn-off stars. For the first time, we
take into account 3D hydrodynamic effects together with departures
from local thermodynamic equilibrium (LTE) when determining both the
stellar parameters and the elemental abundances, by deriving effective
temperatures from 3D non-LTE Hβ profiles, surface gravities from Gaia
parallaxes, iron abundances from 3D LTE Fe II equivalent widths, and
carbon and oxygen abundances from 3D non-LTE C I and O I equivalent
widths. We find that [C/Fe] stays flat with [Fe/H], whereas [O/Fe]
increases linearly up to 0.75 dex with decreasing [Fe/H] down to -3.0
dex. Therefore [C/O] monotonically decreases towards decreasing [C/H],
in contrast to previous findings, mainly because the non-LTE effects
for O I at low [Fe/H] are weaker with our improved calculations. Tables 1-4 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/622/L4
Title: VizieR Online Data Catalog: GALAH survey, chemodynamical
analyse with TGAS (Buder+, 2019)
Authors: Buder, S.; Lind, K.; Ness, M. K.; Asplund, M.; Duong, L.;
Lin, J.; Kos, J.; Casagrande, L.; Casey, A. R.; Bland-Hawthorn,
J.; de Silva, G. M.; D'Orazi, V.; Freeman, K. C.; Martell, S. L.;
Schlesinger, K. J.; Sharma, S.; Simpson, J. D.; Zucker, D. B.; Zwitter,
T.; Cotar, K.; Dotter, A.; Hayden, M. R.; Hyde, E. A.; Kafle, P. R.;
Lewis, G. F.; Nataf, D. M.; Nordlander, T.; Reid, W.; Rix, H. -W.;
Skuladottir, A.; Stello, D.; Ting, Y. -S.; Traven, G.; Wyse, R. F. G.;
Galah Collaboration
Bibcode: 2019yCat..36240019B
Altcode:
In the following tables we give stellar parameters, stellar ages,
stellar masses, photometric parameters, astrometric parameters,
kinematical parameters, orbital parameters, and detailed elemental
abundances for Li, C, O, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe,
Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Mo, Ru, Ba, La, Ce, Nd, Sm, and Eu for
7066 main sequence and turn-off, and sub-giant stars observed by the
GALAH survey and overlapping with Gaia DR1 TGAS. (1 data file).
Title: VizieR Online Data Catalog: GALAH carbon-enhanced stars &
CEMP candidates (Cotar+, 2019)
Authors: Cotar, K.; Zwitter, T.; Kos, J.; Munari, U.; Martell, S. L.;
Asplund, M.; Bland-Hawthorn, J.; Buder, S.; de Silva, G. M.; Freeman,
K. C.; Sharma, S.; Anguiano, B.; Carollo, D.; Horner, J.; Lewis, G. F.;
Nataf, D. M.; Nordlander, T.; Stello, D.; Ting, Y. -S.; Tinney, C.;
Traven, G.; Wittenmyer, R. A.; Galah Collaboration
Bibcode: 2019yCat..74833196C
Altcode:
The analysed set of stellar spectra was acquired by the High Efficiency
and Resolution Multi-Element Spectrograph (HERMES), a fibre-fed
multi-object spectrograph on the 3.9m Anglo-Australian Telescope (AAT)
of the Australian Astronomical Observatory. Spectra used in this
study have been taken from multiple different observing programmes
using this spectrograph: the GALactic Archaeology with HERMES (GALAH)
pilot survey (Duong et al., 2018MNRAS.476.5216D), the main GALAH survey
(De Silva et al., 2015MNRAS.449.2604D), the K2-HERMES survey (Wittenmyer
et al. 2016 , AAS Meeting Abstracts #227), and the TESS-HERMES survey
(Sharma et al., 2018MNRAS.473.2004S). Our data set consists of
627708 successfully reduced spectra of 576229 stars observed between
2013 November and 2018 February. (1 data file).
Title: The GALAH survey: velocity fluctuations in the Milky Way
using Red Clump giants
Authors: Khanna, Shourya; Sharma, Sanjib; Bland-Hawthorn, Joss; Hayden,
Michael; Nataf, David M.; Ting, Yuan-Sen; Kos, Janez; Martell, Sarah;
Zwitter, Tomaž; De Silva, Gayandhi; Asplund, Martin; Buder, Sven;
Duong, Ly; Lin, Jane; Simpson, Jeffrey D.; Anguiano, Borja; Horner,
Jonathan; Kafle, Prajwal R.; Lewis, Geraint F.; Nordlander, Thomas;
Wyse, Rosemary F. G.; Wittenmyer, Robert A.; Zucker, Daniel B.
Bibcode: 2019MNRAS.482.4215K
Altcode: 2018arXiv180407217K; 2018MNRAS.tmp.2790K
If the Galaxy is axisymmetric and in dynamical equilibrium, we expect
negligible fluctuations in the residual line-of-sight velocity
field. Recent results using the APOGEE survey find significant
fluctuations in velocity for stars in the mid-plane (|z| <0.25
kpc) out to 5 kpc, suggesting that the dynamical influence of
non-axisymmetric features, i.e. the Milky Way's bar, spiral arms, and
merger events extends out to the Solar neighbourhood. Their measured
power spectrum has a characteristic amplitude of 11 km s-1 on
a scale of 2.5 kpc. The existence of such large-scale streaming motions
has important implications for determining the Sun's motion about the
Galactic Centre. Using Red Clump stars from GALAH and APOGEE, we map
the line-of-sight velocities around the Sun (d < 5 kpc), and |z|
<1.25 kpc from the mid-plane. By subtracting a smooth axisymmetric
model for the velocity field, we study the residual fluctuations
and compare our findings with mock survey generated by GALAXIA. We
find negligible large-scale fluctuations away from the plane. In the
mid-plane, we reproduce the earlier APOGEE power spectrum but with 20
per cent smaller amplitude (9.3 km s-1) after taking into
account a few systematics (e.g. volume completeness). Using a flexible
axisymmetric model the power amplitude is further reduced to 6.3 km
s-1. Additionally, our simulations show that, in the plane,
distances are underestimated for high-mass Red Clump stars which can
lead to spurious power amplitude of about 5.2 km s-1. Taking
this into account, we estimate the amplitude of real fluctuations to
be <4.6 km s-1, about a factor of three less than the
APOGEE result.
Title: Thorium in solar twins: implications for habitability in
rocky planets
Authors: Botelho, R. B.; Milone, A. de C.; Meléndez, J.; Bedell,
M.; Spina, L.; Asplund, M.; dos Santos, L.; Bean, J. L.; Ramírez,
I.; Yong, D.; Dreizler, S.; Alves-Brito, A.; Yana Galarza, J.
Bibcode: 2019MNRAS.482.1690B
Altcode: 2018MNRAS.tmp.2659B; 2018arXiv181010413B
We have investigated the thorium (Th) abundance in a sample of 53 thin
disc solar twins covering a wide range of ages. These data provide
constrains on the mantle energy budget of terrestrial planets that
can be formed over the evolution of the Galaxy's thin disc. We have
estimated Th abundances with an average precision of 0.025 dex (in both
[Th/H] and [Th/Fe]) through comprehensive spectral synthesis of a Th II
line present at 4019.1290 Å, using very high resolution (R = 115 000)
high quality HARPS spectra obtained at the ESO La Silla Observatory. We
have confirmed that there is a large energy budget from Th decay for
maintaining mantle convection inside potential rocky planets around
solar twins, from the Galactic thin disc formation until now, because
the pristine [Th/H]ZAMS is super-solar on average under
a uniform dispersion of 0.056 dex (varying from +0.037 up to +0.138
dex based on linear fits against isochrone stellar age). Comparing to
neodymium (Nd) and europium (Eu), two others neutron-capture elements,
the stellar pristine abundance of Th follows Eu along the Galactic thin
disc evolution, but it does not follow Nd, probably because neodymium
has a significant contribution from the s-process (about 60 per cent).
Title: VizieR Online Data Catalog: GALAH Survey DR2 (Buder+, 2018)
Authors: Buder, S.; Asplund, M.; Duong, L.; Kos, J.; Lind, K.; Ness,
M. K.; Sharma, S.; Bland-Hawthorn, J.; Casey, A. R.; de Silva, G. M.;
D'Orazi, V.; Freeman, K. C.; Lewis, G. F.; Lin, J.; Martell, S. L.;
Schlesinger, K. J.; Simpson, J. D.; Zucker, D. B.; Zwitter, T.; Amarsi,
A. M.; Anguiano, B.; Carollo, D.; Casagrande, L.; Cotar, K.; Cottrell,
P. L.; da Costa, G.; Gao, X. D.; Hayden, M. R.; Horner, J.; Ireland,
M. J.; Kafle, P. R.; Munari, U.; Nataf, D. M.; Nordlander, T.; Stello,
D.; Ting, Y. -S.; Traven, G.; Watson, F.; Wittenmyer, R. A.; Wyse,
R. F. G.; Yong, D.; Zinn, J. C.; Zerjal, M.; GALAH Collaboration
Bibcode: 2019yCat..74784513B
Altcode:
This is the second data release of the GALAH survey. Data for the
GALAH survey are taken with the HERMES spectrograph on the 3.9-metre
Anglo-Australian Telescope (AAT) at Siding Spring Observatory. HERMES
is a fibre-fed high-resolution (R=28000) spectrograph optimized to do
Galactic archaeology from a 4m class telescope, with four discrete
optical wavelength channels covering 4713-4903Å, 5648-5873Å,
6478-6737Å, and 7585-7887Å. (1 data file).
Title: Galactic archaeology with the GALAH survey
Authors: Asplund, M.
Bibcode: 2019gage.confE...1A
Altcode:
No abstract at ADS
Title: VizieR Online Data Catalog: Carbon and oxygen in metal-poor
halo stars (Amarsi+, 2019)
Authors: Amarsi, A. M.; Nissen, P. E.; Asplund, M.; Lind, K.; Barklem,
P. S.
Bibcode: 2019yCat..36229004A
Altcode:
table1.dat contains stellar parameters and abundances. table2.dat
contains line-by-line equivalent widths and abundances for The FeII
lines used in this work. table3.dat contains line-by-line equivalent
widths and abundances for the CI lines used in this work. table4.dat
contains line-by-line equivalent widths and abundances for the OI
lines used in this work. (4 data files).
Title: The GALAH survey: verifying abundance trends in the open
cluster M67 using non-LTE modelling
Authors: Gao, Xudong; Lind, Karin; Amarsi, Anish M.; Buder, Sven;
Dotter, Aaron; Nordlander, Thomas; Asplund, Martin; Bland-Hawthorn,
Joss; de Silva, Gayandhi M.; D'Orazi, Valentina; Freeman, Ken C.; Kos,
Janez; Lewis, Geraint F.; Lin, Jane; Martell, Sarah L.; Schlesinger,
Katharine J.; Sharma, Sanjib; Simpson, Jeffrey D.; Zucker, Daniel B.;
Zwitter, Tomaž; da Costa, Gary; Anguiano, Borja; Horner, Jonathan;
Hyde, Elaina A.; Kafle, Prajwal R.; Nataf, David M.; Reid, Warren;
Stello, Dennis; Ting, Yuan-Sen; Galah Collaboration
Bibcode: 2018MNRAS.481.2666G
Altcode: 2018MNRAS.tmp.2299G; 2018arXiv180406394G
Open cluster members are coeval and share the same initial bulk chemical
composition. Consequently, differences in surface abundances between
members of a cluster that are at different evolutionary stages can be
used to study the effects of mixing and internal chemical processing. We
carry out an abundance analysis of seven elements (Li, O, Na, Mg,
Al, Si, and Fe) in 66 stars belonging to the open cluster M67, based
on high resolution GALAH spectra, 1D MARCS model atmospheres, and
non-local thermodynamic equilibrium (non-LTE) radiative transfer. From
the non-LTE analysis, we find a typical star-to-star scatter in the
abundance ratios of around 0.05 dex. We find trends in the abundance
ratios with effective temperature, indicating systematic differences in
the surface abundances between turn-off and giant stars; these trends
are more pronounced when LTE is assumed. However, trends with effective
temperature remain significant for Al and Si also in non-LTE. Finally,
we compare the derived abundances with prediction from stellar evolution
models including effects of atomic diffusion. We find overall good
agreement for the abundance patterns of dwarfs and sub-giant stars,
but the abundances of cool giants are lower relative to less evolved
stars than predicted by the diffusion models, in particular for Mg.
Title: The GALAH survey: accurate radial velocities and library of
observed stellar template spectra
Authors: Zwitter, Tomaž; Kos, Janez; Chiavassa, Andrea; Buder,
Sven; Traven, Gregor; Čotar, Klemen; Lin, Jane; Asplund, Martin;
Bland-Hawthorn, Joss; Casey, Andrew R.; De Silva, Gayandhi; Duong,
Ly; Freeman, Kenneth C.; Lind, Karin; Martell, Sarah; D'Orazi,
Valentina; Schlesinger, Katharine J.; Simpson, Jeffrey D.; Sharma,
Sanjib; Zucker, Daniel B.; Anguiano, Borja; Casagrande, Luca; Collet,
Remo; Horner, Jonathan; Ireland, Michael J.; Kafle, Prajwal R.; Lewis,
Geraint; Munari, Ulisse; Nataf, David M.; Ness, Melissa; Nordlander,
Thomas; Stello, Dennis; Ting, Yuan-Sen; Tinney, Chris G.; Watson,
Fred; Wittenmyer, Rob A.; Žerjal, Maruša
Bibcode: 2018MNRAS.481..645Z
Altcode: 2018MNRAS.tmp.2178Z; 2018arXiv180406344Z
GALAH is a large-scale magnitude-limited southern stellar spectroscopic
survey. Its second data release (GALAH DR2) provides values of stellar
parameters and abundances of 23 elements for 342 682 stars (Buder
et al.). Here we add a description of the public release of radial
velocities with a typical accuracy of 0.1 km s-1 for 336
215 of these stars, achievable due to the large wavelength coverage,
high resolving power, and good signal-to-noise ratio of the observed
spectra, but also because convective motions in stellar atmosphere and
gravitational redshift from the star to the observer are taken into
account. In the process we derive medians of observed spectra that
are nearly noiseless, as they are obtained from between 100 and 1116
observed spectra belonging to the same bin with a width of 50 K in
temperature, 0.2 dex in gravity, and 0.1 dex in metallicity. Publicly
released 1181 median spectra have a resolving power of 28 000 and trace
the well-populated stellar types with metallicities between -0.6 and
+0.3. Note that radial velocities from GALAH are an excellent match
to the accuracy of velocity components along the sky plane derived
by Gaia for the same stars. The level of accuracy achieved here is
adequate for studies of dynamics within stellar clusters, associations,
and streams in the Galaxy. So it may be relevant for studies of the
distribution of dark matter.
Title: Holistic spectroscopy: complete reconstruction of a wide-field,
multiobject spectroscopic image using a photonic comb
Authors: Kos, Janez; Bland-Hawthorn, Joss; Betters, Christopher H.;
Leon-Saval, Sergio; Asplund, Martin; Buder, Sven; Casey, Andrew R.;
D'Orazi, Valentina; de Silva, Gayandhi; Freeman, Ken; Lewis, Geraint;
Lin, Jane; Martell, Sarah L.; Schlesinger, Katharine; Sharma, Sanjib;
Simpson, Jeffrey D.; Zucker, Daniel; Zwitter, Tomaž; Hayden, Michael;
Horner, Jonathan; Nataf, David M.; Ting, Yuan-Sen
Bibcode: 2018MNRAS.480.5475K
Altcode: 2018MNRAS.tmp.2085K; 2018arXiv180405851K
The primary goal of Galactic archaeology is to learn about the origin
of the Milky Way from the detailed chemistry and kinematics of millions
of stars. Wide-field multifibre spectrographs are increasingly used
to obtain spectral information for huge samples of stars. Some
surveys (e.g. GALAH) are attempting to measure up to 30 separate
elements per star. Stellar abundance spectroscopy is a subtle art that
requires a very high degree of spectral uniformity across each of the
fibres. However, wide-field spectrographs are notoriously non-uniform
due to the fast output optics necessary to image many fibre outputs on
to the detector. We show that precise spectroscopy is possible with
such instruments across all fibres by employing a photonic comb -
a device that produces uniformly spaced spots of light on the CCD to
precisely map complex aberrations. Aberrations are parametrized by a
set of orthogonal moments with ∼100 independent parameters. We then
reproduce the observed image by convolving high-resolution spectral
templates with measured aberrations as opposed to extracting the
spectra from the observed image. Such a forward modelling approach
also trivializes some spectroscopic reduction problems like fibre
cross-talk, and reliably extracts spectra with a resolution ∼2.3
times above the nominal resolution of the instrument. Our rigorous
treatment of optical aberrations also encourages a less conservative
spectrograph design in the future.
Title: The GALAH survey and Gaia DR2: (non-)existence of five sparse
high-latitude open clusters
Authors: Kos, Janez; de Silva, Gayandhi; Buder, Sven; Bland-Hawthorn,
Joss; Sharma, Sanjib; Asplund, Martin; D'Orazi, Valentina; Duong, Ly;
Freeman, Ken; Lewis, Geraint F.; Lin, Jane; Lind, Karin; Martell, Sarah
L.; Schlesinger, Katharine J.; Simpson, Jeffrey D.; Zucker, Daniel B.;
Zwitter, Tomaž; Bedding, Timothy R.; Čotar, Klemen; Horner, Jonathan;
Nordlander, Thomas; Stello, Denis; Ting, Yuan-Sen; Traven, Gregor
Bibcode: 2018MNRAS.480.5242K
Altcode: 2018arXiv180700822K; 2018MNRAS.tmp.2084K
Sparse open clusters can be found at high galactic latitudes where
loosely populated clusters are more easily detected against the lower
stellar background. Because most star formation takes place in the thin
disc, the observed population of clusters far from the Galactic plane is
hard to explain. We combined spectral parameters from the GALAH survey
with the Gaia DR2 catalogue to study the dynamics and chemistry of five
old sparse high-latitude clusters in more detail. We find that four of
them (NGC 1252, NGC 6994, NGC 7772, NGC 7826) - originally classified
in 1888 - are not clusters but are instead chance projections on the
sky. Member stars quoted in the literature for these four clusters are
unrelated in our multidimensional physical parameter space; the quoted
cluster properties in the literature are therefore meaningless. We
confirm the existence of visually similar NGC 1901 for which we provide
a probabilistic membership analysis. An overdensity in three spatial
dimensions proves to be enough to reliably detect sparse clusters,
but the whole six-dimensional space must be used to identify members
with high confidence, as demonstrated in the case of NGC 1901.
Title: VizieR Online Data Catalog: Solar Twins age-chromospheric
activity (Lorenzo-Oliveira+, 2018))
Authors: Lorenzo-Oliveira, D.; Freitas, F.; Melendez, J.; Bedell,
M.; Ramirez, I.; Bean, J.; Asplund, M.; Spina, L.; Dreizler, S.;
Alves-Brito, A.; Casagrande, L.
Bibcode: 2018yCat..36190073L
Altcode:
Our sample was selected from the 88 solar twins presented in Ramirez et
al. (2014A&A...572A..48R). From this sample, we obtained data for
70 stars with the HARPS instrument (Mayor et al., 2003Msngr.114...20M)
at the 3.6 m telescope at the La Silla observatory, to search for
planets around solar twins (program 188.C-0265, Bedell et al.,
2015A&A...581A..34B; Melendez et al., 2015Msngr.161...28M,
2017A&A...597A..34M). Additional data for 12 stars were found in
the ESO archive. (2 data files).
Title: The Solar Twin Planet Search. The age-chromospheric activity
relation
Authors: Lorenzo-Oliveira, Diego; Freitas, Fabrício C.; Meléndez,
Jorge; Bedell, Megan; Ramírez, Iván; Bean, Jacob L.; Asplund, Martin;
Spina, Lorenzo; Dreizler, Stefan; Alves-Brito, Alan; Casagrande, Luca
Bibcode: 2018A&A...619A..73L
Altcode: 2018arXiv180608014L
Context. It is well known that the magnetic activity of solar-type stars
decreases with age, but it is widely debated in the literature whether
there is a smooth decline or if there is an early sharp drop until
1-2 Gyr that is followed by a relatively inactive constant phase.
Aims: We revisited the activity-age relation using time-series
observations of a large sample of solar twins whose precise isochronal
ages and other important physical parameters have been determined.
Methods: We measured the Ca II H and K activity indices using ≈9000
HARPS spectra of 82 solar twins. In addition, the average solar activity
was calculated through asteroids and Moon reflection spectra using
the same instrumentation. Thus, we transformed our activity indices
into the S Mount Wilson scale (SMW), recalibrated the
Mount Wilson absolute flux and photospheric correction equations as a
function of Teff, and then computed an improved bolometric
flux normalized activity index log R'HK (Teff)
for the entire sample.
Results: New relations between activity
and the age of solar twins were derived by assessing the chromospheric
age-dating limits using log R'HK (Teff). We
measured an average solar activity of SMW = 0.1712 ± 0.0017
during solar magnetic cycles 23-24 covered by HARPS observations,
and we also inferred an average of SMW = 0.1694 ± 0.0025
for cycles 10-24, anchored on a sunspot number correlation of S index
versus. We also found a simple relation between the average and the
dispersion of the activity levels of solar twins. This enabled us to
predict the stellar variability effects on the age-activity diagram,
and consequently, to estimate the chromospheric age uncertainties that
are due to the same phenomena. The age-activity relation is still
statistically significant up to ages around 6-7 Gyr, in agreement
with previous works using open clusters and field stars with precise
ages.
Conclusions: Our research confirms that Ca II H &
K lines remain a useful chromospheric evolution tracer until stars
reach ages of at least 6-7 Gyr. We found evidence that for the most
homogenous set of old stars, the chromospheric activity indices seem
to continue to decrease after the solar age toward the end of the main
sequence. Our results indicate that a significant part of the scatter
observed in the age-activity relation of solar twins can be attributed
to stellar cycle modulations effects. The Sun seems to have a normal
activity level and variability for its age. Based on observations
collected at the European Organisation for Astronomical Research in
the Southern Hemisphere under ESO programs 188.C-0265, 183.D-0729,
292.C-5004, 097.C-0571, 092.C-0721, 093.C-0409, 072.C-0488, 183.C-0972,
091.C-0936, 192.C-0852, 196.C-1006, 076.C-0155, 096.C-0499, 185.D-0056,
192.C-0224, 075.C-0332, 090.C-0421, 091.C-0034, 077.C-0364, 089.C-0415,
60.A-9036, 092.C-0832, 295.C-5035, 295.C-5031, 60.A-9700, 289.D-5015,
096.C-0210, 086.C-0284, 088.C-0323, 0100.D-0444, and 099.C-0491.Tables
1 and 2 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/619/A73
Title: The Chemical Homogeneity of Sun-like Stars in the Solar
Neighborhood
Authors: Bedell, Megan; Bean, Jacob L.; Meléndez, Jorge; Spina,
Lorenzo; Ramírez, Ivan; Asplund, Martin; Alves-Brito, Alan; dos
Santos, Leonardo; Dreizler, Stefan; Yong, David; Monroe, TalaWanda;
Casagrande, Luca
Bibcode: 2018ApJ...865...68B
Altcode: 2018arXiv180202576B
The compositions of stars are a critical diagnostic tool for many
topics in astronomy such as the evolution of our Galaxy, the formation
of planets, and the uniqueness of the Sun. Previous spectroscopic
measurements indicate a large intrinsic variation in the elemental
abundance patterns of stars with similar overall metal content. However,
systematic errors arising from inaccuracies in stellar models are known
to be a limiting factor in such studies, and thus it is uncertain to
what extent the observed diversity of stellar abundance patterns is
real. Here we report the abundances of 30 elements with precisions of 2%
for 79 Sun-like stars within 100 pc. Systematic errors are minimized in
this study by focusing on solar twin stars and performing a line-by-line
differential analysis using high-resolution, high-signal-to-noise
spectra. We resolve [X/Fe] abundance trends in galactic chemical
evolution at precisions of 10-3 dex Gyr-1
and reveal that stars with similar ages and metallicities have
nearly identical abundance patterns. Contrary to previous results,
we find that the ratios of carbon-to-oxygen and magnesium-to-silicon
in solar-metallicity stars are homogeneous to within 10% throughout
the solar neighborhood, implying that exoplanets may exhibit much less
compositional diversity than previously thought. Finally, we demonstrate
that the Sun has a subtle deficiency in refractory material relative
to >80% of solar twins (at 2σ confidence), suggesting a possible
signpost for planetary systems like our own.
Title: The age and abundance structure of the stellar populations
in the central sub-kpc of the Milky Way
Authors: Bensby, T.; Feltzing, S.; Gould, A.; Yee, J. C.; Johnson,
J. A.; Asplund, M.; Meléndez, J.; Lucatello, S.; Howes, L. M.
Bibcode: 2018IAUS..334...86B
Altcode: 2017arXiv170705960B
The four main findings about the age and abundance structure of the
Milky Way bulge based on microlensed dwarf and subgiant stars are: (1)
a wide metallicity distribution with distinct peaks at [Fe/H] = -1.09,
-0.63, -0.20, +0.12, +0.41; (2) a high fraction of intermediate-age to
young stars where at [Fe/H] > 0 more than 35 % are younger than 8
Gyr, (3) several episodes of significant star formation in the bulge 3,
6, 8, and 11 Gyr ago; (4) the `knee' in the α-element abundance trends
of the sub-solar metallicity bulge appears to be located at a slightly
higher [Fe/H] (about 0.05 to 0.1 dex) than in the local thick disk.
Title: Inelastic O+H collisions and the O I 777 nm solar
centre-to-limb variation
Authors: Amarsi, A. M.; Barklem, P. S.; Asplund, M.; Collet, R.;
Zatsarinny, O.
Bibcode: 2018A&A...616A..89A
Altcode: 2018arXiv180310531A
The O I 777 nm triplet is a key diagnostic of oxygen abundances
in the atmospheres of FGK-type stars; however, it is sensitive to
departures from local thermodynamic equilibrium (LTE). The accuracy
of non-LTE line formation calculations has hitherto been limited by
errors in the inelastic O+H collisional rate coefficients; several
recent studies have used the Drawin recipe, albeit with a correction
factor SH that is calibrated to the solar centre-to-limb
variation of the triplet. We present a new model oxygen atom that
incorporates inelastic O+H collisional rate coefficients using an
asymptotic two-electron model based on linear combinations of atomic
orbitals, combined with a free electron model based on the impulse
approximation. Using a 3D hydrodynamic STAGGER model solar atmosphere
and 3D non-LTE line formation calculations, we demonstrate that
this physically motivated approach is able to reproduce the solar
centre-to-limb variation of the triplet to 0.02 dex, without any
calibration of the inelastic collisional rate coefficients or other
free parameters. We infer log ɛO = 8.69 ± 0.03 from the
triplet alone, strengthening the case for a low solar oxygen abundance.
Title: The GALAH Survey: second data release
Authors: Buder, Sven; Asplund, Martin; Duong, Ly; Kos, Janez; Lind,
Karin; Ness, Melissa K.; Sharma, Sanjib; Bland-Hawthorn, Joss; Casey,
Andrew R.; de Silva, Gayandhi M.; D'Orazi, Valentina; Freeman, Ken C.;
Lewis, Geraint F.; Lin, Jane; Martell, Sarah L.; Schlesinger, Katharine
J.; Simpson, Jeffrey D.; Zucker, Daniel B.; Zwitter, Tomaž; Amarsi,
Anish M.; Anguiano, Borja; Carollo, Daniela; Casagrande, Luca; Čotar,
Klemen; Cottrell, Peter L.; da Costa, Gary; Gao, Xudong D.; Hayden,
Michael R.; Horner, Jonathan; Ireland, Michael J.; Kafle, Prajwal R.;
Munari, Ulisse; Nataf, David M.; Nordlander, Thomas; Stello, Dennis;
Ting, Yuan-Sen; Traven, Gregor; Watson, Fred; Wittenmyer, Robert A.;
Wyse, Rosemary F. G.; Yong, David; Zinn, Joel C.; Žerjal, Maruša;
Galah Collaboration
Bibcode: 2018MNRAS.478.4513B
Altcode: 2018MNRAS.tmp.1218B; 2018arXiv180406041B
The Galactic Archaeology with HERMES (GALAH) survey is a large-scale
stellar spectroscopic survey of the Milky Way, designed to deliver
complementary chemical information to a large number of stars covered
by the Gaia mission. We present the GALAH second public data release
(GALAH DR2) containing 342 682 stars. For these stars, the GALAH
collaboration provides stellar parameters and abundances for up to
23 elements to the community. Here we present the target selection,
observation, data reduction, and detailed explanation of how the spectra
were analysed to estimate stellar parameters and element abundances. For
the stellar analysis, we have used a multistep approach. We use the
physics-driven spectrum synthesis of Spectroscopy Made Easy (SME)
to derive stellar labels (Teff, log g, [Fe/H], [X/Fe],
vmic, vsin i, A_{K_S}) for a representative training
set of stars. This information is then propagated to the whole
sample with the data-driven method of The Cannon. Special care has
been exercised in the spectral synthesis to only consider spectral
lines that have reliable atomic input data and are little affected by
blending lines. Departures from local thermodynamic equilibrium (LTE)
are considered for several key elements, including Li, O, Na, Mg, Al,
Si, and Fe, using 1D MARCS stellar atmosphere models. Validation tests
including repeat observations, Gaia benchmark stars, open and globular
clusters, and K2 asteroseismic targets lend confidence to our methods
and results. Combining the GALAH DR2 catalogue with the kinematic
information from Gaia will enable a wide range of Galactic Archaeology
studies, with unprecedented detail, dimensionality, and scope.
Title: Stellar ages and masses in the solar neighbourhood: Bayesian
analysis using spectroscopy and Gaia DR1 parallaxes
Authors: Lin, Jane; Dotter, Aaron; Ting, Yuan-Sen; Asplund, Martin
Bibcode: 2018MNRAS.477.2966L
Altcode: 2018MNRAS.477.2606L; 2018MNRAS.tmp..697L; 2018arXiv180310875L
We present a Bayesian implementation of isochrone fitting in
deriving stellar ages and masses, incorporating absolute K magnitude
(M_K) derived from 2MASS photometry and Gaia DR1 parallax and
differentiation between initial bulk metallicity and present-day surface
metallicity, with allowance for incorporating further constraints
(e.g. asteroseismology) when available. As a test, we re-computed
stellar ages and masses of ∼4000 stars in the solar neighbourhood
from six well-studied literature samples using both Hipparcos and
TGAS parallaxes. Our ages are found to be compatible with literature
values but with reduced uncertainties in general. The inclusion of
parallax-based M_K serves as an additional constraint on the derived
quantities, especially when systematic errors in stellar parameters are
underestimated. We reconstructed the age-metallicity relationship in
the solar neighbourhood by re-analysing the Geneva-Copenhagen Survey
with the inclusion of TGAS-parallaxes and initial bulk metallicity
sampling. We found a flat trend for disc stars with ages <11 Gyr
but with smaller scatter at all ages compared to literature.
Title: Detailed chemical compositions of the wide binary HD
80606/80607: revised stellar properties and constraints on planet
formation
Authors: Liu, F.; Yong, D.; Asplund, M.; Feltzing, S.; Mustill, A. J.;
Meléndez, J.; Ramírez, I.; Lin, J.
Bibcode: 2018A&A...614A.138L
Altcode: 2018arXiv180209306L
Differences in the elemental abundances of planet-hosting stars in
binary systems can give important clues and constraints about planet
formation and evolution. In this study we performed a high-precision,
differential elemental abundance analysis of a wide binary system,
HD 80606/80607, based on
high-resolution spectra with high signal-to-noise ratio obtained with
Keck/HIRES. HD 80606 is known to host a giant planet
with the mass of four Jupiters, but no planet has been detected around
HD 80607 so far. We determined stellar parameters as
well as abundances for 23 elements for these two stars with extremely
high precision. Our main results are that (i) we confirmed that the two
components share very similar chemical compositions, but HD
80606 is marginally more metal-rich than HD
80607, with an average difference of +0.013 ± 0.002 dex
(σ = 0.009 dex); and (ii) there is no obvious trend between abundance
differences and condensation temperature. Assuming that this binary
formed from material with the same chemical composition, it is difficult
to understand how giant planet formation could produce the present-day
photospheric abundances of the elements we measure. We cannot
exclude the possibility that HD 80606 might have
accreted about 2.5 to 5 MEarth material onto its surface,
possibly from a planet destabilised by the known highly eccentric
giant. The data presented herein were obtained at the W.M. Keck
Observatory, which is operated as a scientific partnership among the
California Institute of Technology, the University of California and
the National Aeronautics and Space Administration. The Observatory
was made possible by the generous financial support of the W.M. Keck
Foundation.Table A.1 is only available at the CDS via anonymous ftp to
http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/614/A138
Title: The GALAH survey: stellar streams and how stellar velocity
distributions vary with Galactic longitude, hemisphere, and
metallicity
Authors: Quillen, Alice C.; De Silva, Gayandhi; Sharma, Sanjib;
Hayden, Michael; Freeman, Ken; Bland-Hawthorn, Joss; Žerjal, Maruša;
Asplund, Martin; Buder, Sven; D'Orazi, Valentina; Duong, Ly; Kos,
Janez; Lin, Jane; Lind, Karin; Martell, Sarah; Schlesinger, Katharine;
Simpson, Jeffrey D.; Zucker, Daniel B.; Zwitter, Tomaz; Anguiano,
Borja; Carollo, Daniela; Casagrande, Luca; Cotar, Klemen; Cottrell,
Peter L.; Ireland, Michael; Kafle, Prajwal R.; Horner, Jonathan;
Lewis, Geraint F.; Nataf, David M.; Ting, Yuan-Sen; Watson, Fred;
Wittenmyer, Rob; Wyse, Rosemary
Bibcode: 2018MNRAS.478..228Q
Altcode: 2018MNRAS.tmp..840Q; 2018arXiv180202924Q
Using GALAH (GALactic Archaeology with HERMES) survey data of
nearby stars, we look at how structure in the planar (u, v) velocity
distribution depends on metallicity and on viewing direction within the
Galaxy. In nearby stars with distance d ≲ 1 kpc, the Hercules stream
is most strongly seen in higher metallicity stars [Fe/H] > 0.2. The
Hercules stream peak v value depends on viewed galactic longitude,
which we interpret as due to the gap between the stellar stream and
more circular orbits being associated with a specific angular momentum
value of about 1640 km s-1 kpc. The association of the
gap with a particular angular momentum value supports a bar resonant
model for the Hercules stream. Moving groups previously identified in
Hipparcos(HIgh Precision Parallax COllecting Satellite) observations are
easiest to see in stars nearer than 250 pc, and their visibility and
peak velocities in the velocity distributions depends on both viewing
direction (galactic longitude and hemisphere) and metallicity. We
infer that there is fine structure in local velocity distributions
that varies over distances of a few hundred pc in the Galaxy.
Title: Effective temperature determinations of late-type stars based
on 3D non-LTE Balmer line formation
Authors: Amarsi, A. M.; Nordlander, T.; Barklem, P. S.; Asplund, M.;
Collet, R.; Lind, K.
Bibcode: 2018A&A...615A.139A
Altcode: 2018arXiv180402305A
Hydrogen Balmer lines are commonly used as spectroscopic effective
temperature diagnostics of late-type stars. However, reliable
inferences require accurate model spectra, and the absolute accuracy of
classical methods that are based on one-dimensional (1D) hydrostatic
model atmospheres and local thermodynamic equilibrium (LTE) is still
unclear. To investigate this, we carry out 3D non-LTE calculations for
the Balmer lines, performed, for the first time, over an extensive grid
of 3D hydrodynamic STAGGER model atmospheres. For Hα, Hβ, and Hγ we
find significant 1D non-LTE versus 3D non-LTE differences (3D effects):
the outer wings tend to be stronger in 3D models, particularly for
Hγ, while the inner wings can be weaker in 3D models, particularly
for Hα. For Hα, we also find significant 3D LTE versus 3D non-LTE
differences (non-LTE effects): in warmer stars (Teff
≈ 6500 K) the inner wings tend to be weaker in non-LTE models,
while at lower effective temperatures (Teff ≈ 4500 K)
the inner wings can be stronger in non-LTE models; the non-LTE effects
are more severe at lower metallicities. We test our 3D non-LTE models
against observations of well-studied benchmark stars. For the Sun,
we infer concordant effective temperatures from Hα, Hβ, and Hγ;
however the value is too low by around 50 K which could signal residual
modelling shortcomings. For other benchmark stars, our 3D non-LTE
models generally reproduce the effective temperatures to within 1σ
uncertainties. For Hα, the absolute 3D effects and non-LTE effects
can separately reach around 100 K, in terms of inferred effective
temperatures. For metal-poor turn-off stars, 1D LTE models of Hα can
underestimate effective temperatures by around 150 K. Our 3D non-LTE
model spectra are publicly available, and can be used for more reliable
spectroscopic effective temperature determinations. The 3D non-LTE
model spectra is also available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/615/A139
Title: VizieR Online Data Catalog: 3D non-LTE Balmer line formation
(Amarsi+, 2018)
Authors: Amarsi, A. M.; Nordlander, T.; Barklem, P. S.; Asplund, M.;
Collet, R.; Lind, K.
Bibcode: 2018yCat..36150139A
Altcode:
File lineprof.txt: contains emergent total (I) and continuum (Ic)
intensities at specific wavelengths (wl, or wl_air) and viewing angles
(mu), the latter with weights (wmu), for the model atmospheres
with different effective temperatures (Teff), surface gravities
(lgg), and iron abundance ratios ([Fe/H]). If rotational broadening
and instrumental broadening are to be neglected, the normalised
flux can be obtained via Sum(I * mu * wmu) / Sum(Ic * mu * wmu),
at a given wavelength and for a given model atmosphere. File
flux_3d.fits: contains a regular grid of normalised fluxes constructed
by interpolation/extrapolation of the data in lineprof.txt. The fluxes
are given for different effective temperatures (Teff), surface gravities
(lgg), iron abundance ratios ([Fe/H]), projected rotational velocity
(vsini), Gaussian instrumental profile velocity widths (vbroad),
vacuum wavelengths (wl), and lines. (2 data files).
Title: Measuring Oxygen Abundances from Stellar Spectra without
Oxygen Lines
Authors: Ting, Yuan-Sen; Conroy, Charlie; Rix, Hans-Walter; Asplund,
Martin
Bibcode: 2018ApJ...860..159T
Altcode: 2018arXiv180107370T
Oxygen is the most abundant “metal” element in stars and in
the cosmos. But determining oxygen abundances in stars has proven
challenging, because of the shortage of detectable atomic oxygen lines
in their optical spectra as well as observational and theoretical
complications with these lines (e.g., blends, three-dimensional,
non-LTE). Nonetheless, Ting et al. were recently able to demonstrate
that oxygen abundances can be determined from low-resolution (R ≃
2000) optical spectra. Here, we investigate the physical processes
that enable such a measurement for cool stars, such as K-giants. We
show that the strongest spectral diagnostics of oxygen come from the
CNO atomic-molecular network but are manifested in spectral features
that do not involve oxygen. In the outer atmosphere layers, most of
the carbon is locked up in CO, and changes to the oxygen abundance
directly affect the abundances of all other carbon-bearing molecules,
thereby changing the strength of CH, CN, and C2 features
across the optical spectrum. In deeper atmosphere layers, most of the
carbon is in atomic form, and any change in the oxygen abundance has
little effect on the other carbon-bearing molecules. The key physical
effect enabling such oxygen abundance measurements is that spectral
features in the optical arise from both the CO-dominant and the atomic
carbon-dominant regions, providing non-degenerate constraints on both
C and O. Beyond the case at hand, the results show that physically
sound abundances measurements need not be limited to those elements
that have observable lines themselves.
Title: The GALAH survey: properties of the Galactic disc(s) in the
solar neighbourhood
Authors: Duong, L.; Freeman, K. C.; Asplund, M.; Casagrande, L.; Buder,
S.; Lind, K.; Ness, M.; Bland-Hawthorn, J.; De Silva, G. M.; D'Orazi,
V.; Kos, J.; Lewis, G. F.; Lin, J.; Martell, S. L.; Schlesinger, K.;
Sharma, S.; Simpson, J. D.; Zucker, D. B.; Zwitter, T.; Anguiano, B.;
Da Costa, G. S.; Hyde, E.; Horner, J.; Kafle, P. R.; Nataf, D. M.;
Reid, W.; Stello, D.; Ting, Y. -S.; Wyse, R. F. G.
Bibcode: 2018MNRAS.476.5216D
Altcode: 2018arXiv180101514D; 2018MNRAS.tmp..504D
Using data from the GALAH pilot survey, we determine properties of the
Galactic thin and thick discs near the solar neighbourhood. The data
cover a small range of Galactocentric radius (7.9 ≲ R_GC ≲ 9.5 kpc),
but extend up to 4 kpc in height from the Galactic plane, and several
kpc in the direction of Galactic anti-rotation (at longitude 260°
≤ ℓ ≤ 280°). This allows us to reliably measure the vertical
density and abundance profiles of the chemically and kinematically
defined `thick' and `thin' discs of the Galaxy. The thin disc (low-α
population) exhibits a steep negative vertical metallicity gradient,
at d[M/H]/dz = -0.18 ± 0.01 dex kpc-1, which is broadly
consistent with previous studies. In contrast, its vertical α-abundance
profile is almost flat, with a gradient of d[α/M]/dz = 0.008 ± 0.002
dex kpc-1. The steep vertical metallicity gradient of the
low-α population is in agreement with models where radial migration has
a major role in the evolution of the thin disc. The thick disc (high-α
population) has a weaker vertical metallicity gradient d[M/H]/dz =
-0.058 ± 0.003 dex kpc-1. The α-abundance of the thick
disc is nearly constant with height, d[α/M]/dz = 0.007 ± 0.002 dex
kpc-1. The negative gradient in metallicity and the small
gradient in [α/M] indicate that the high-α population experienced
a settling phase, but also formed prior to the onset of major Type
Ia supernova enrichment. We explore the implications of the distinct
α-enrichments and narrow [α/M] range of the sub-populations in the
context of thick disc formation.
Title: Metallicity Variations in the Type II Globular Cluster NGC 6934
Authors: Marino, A. F.; Yong, D.; Milone, A. P.; Piotto, G.; Lundquist,
M.; Bedin, L. R.; Chené, A. -N.; Da Costa, G.; Asplund, M.; Jerjen, H.
Bibcode: 2018ApJ...859...81M
Altcode: 2018arXiv180404158M
The Hubble Space Telescope photometric survey of Galactic globular
clusters (GCs) has revealed a peculiar “chromosome map” for NGC
6934. In addition to a typical sequence, similar to that observed
in Type I GCs, NGC 6934 displays additional stars on the red side,
analogous to the anomalous Type II GCs, as defined in our previous
work. We present a chemical abundance analysis of four red giants in
this GC. Two stars are located on the chromosome map sequence common
to all GCs, and another two lie on the additional sequence. We find (i)
star-to-star Fe variations, with the two anomalous stars being enriched
by ∼0.2 dex. Because of our small-size sample, this difference is
at the ∼2.5σ level. (ii) There is no evidence for variations in
the slow neutron-capture abundances over Fe, at odds with what is
often observed in anomalous Type II GCs, e.g., M 22 and ω Centauri
(iii) no large variations in light elements C, O, and Na, compatible
with locations of the targets on the lower part of the chromosome
map where such variations are not expected. Since the analyzed stars
are homogeneous in light elements, the only way to reproduce the
photometric splits on the sub-giant (SGB) and the red giant (RGB)
branches is to assume that red RGB/faint SGB stars are enhanced in
[Fe/H] by ∼0.2. This fact corroborates the spectroscopic evidence
of a metallicity variation in NGC 6934. The observed chemical pattern
resembles only partially the other Type II GCs, suggesting that NGC
6934 might belong either to a third class of GCs, or be a link between
normal Type I and anomalous Type II GCs. Based on observations
with the NASA/ESA Hubble Space Telescope, obtained at the Space
Telescope Science Institute, which is operated by AURA, Inc., under
NASA contract NAS 5-26555. This paper includes data gathered with the
6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile,
and Gemini Telescope at Canada-France-Hawaii Telescope.
Title: VizieR Online Data Catalog: M67 solar twins chemical
compositions (Liu+, 2016)
Authors: Liu, F.; Asplund, M.; Yong, D.; Melendez, J.; Ramirez, I.;
Karakas, A. I.; Carlos, M.; Marino, A. F.
Bibcode: 2018yCat..74630696L
Altcode:
We observed two solar-type members in M67: M67-1194 and
M67-1315. One of which (M67-1194) has been studied previously by
Oenehag et al. (2011A&A...528A..85O). We obtained high resolution
(R=λ/Δλ=50000), high signal-to-noise ratio (SNR) spectra with the
0.86" slit of the High Resolution Echelle Spectrometer (HIRES) on the
10 m Keck I telescope during January 24-25, 2015. (1 data file).
Title: The benchmark halo giant HD 122563: CNO abundances revisited
with three-dimensional hydrodynamic model stellar atmospheres
Authors: Collet, R.; Nordlund, Å.; Asplund, M.; Hayek, W.;
Trampedach, R.
Bibcode: 2018MNRAS.475.3369C
Altcode: 2017arXiv171208099C
We present an abundance analysis of the low-metallicity benchmark
red giant star HD 122563 based on realistic, state-of-the-art,
high-resolution, three-dimensional (3D) model stellar atmospheres
including non-grey radiative transfer through opacity binning with
4, 12, and 48 bins. The 48-bin 3D simulation reaches temperatures
lower by ∼300-500 K than the corresponding 1D model in the upper
atmosphere. Small variations in the opacity binning, adopted line
opacities, or chemical mixture can cool the photospheric layers by
a further ∼100-300 K and alter the effective temperature by ∼100
K. A 3D local thermodynamic equilibrium (LTE) spectroscopic analysis
of Fe I and Fe II lines gives discrepant results in terms of derived
Fe abundance, which we ascribe to non-LTE effects and systematic errors
on the stellar parameters. We also determine C, N, and O abundances by
simultaneously fitting CH, OH, NH, and CN molecular bands and lines
in the ultraviolet, visible, and infrared. We find a small positive
3D-1D abundance correction for carbon (+0.03 dex) and negative ones for
nitrogen (-0.07 dex) and oxygen (-0.34 dex). From the analysis of the [O
I] line at 6300.3 Å, we derive a significantly higher oxygen abundance
than from molecular lines (+0.46 dex in 3D and +0.15 dex in 1D). We rule
out important OH photodissociation effects as possible explanation for
the discrepancy and note that lowering the surface gravity would reduce
the oxygen abundance difference between molecular and atomic indicators.
Title: The GALAH and TESS-HERMES surveys: high-resolution spectroscopy
of luminous supergiants in the Magellanic Clouds and Bridge
Authors: Simpson, Jeffrey D.; Stello, Dennis; Sharma, Sanjib; Ting,
Yuan-Sen; Nataf, David M.; Da Costa, Gary; Wittenmyer, Robert A.;
Horner, Jonathan; Martell, Sarah L.; Lewis, Geraint F.; De Silva,
Gayandhi M.; Cottrell, Peter L.; Asplund, Martin; Bland-Hawthorn, Joss;
Buder, Sven; D'Orazi, Valentina; Duong, Ly; Freeman, Ken C.; Kos,
Janez; Lin, Jane; Lind, Karin; Schlesinger, Katharine. J.; Zucker,
Daniel B.; Zwitter, Tomaž; Kafle, Prajwal R.; Khanna, Shourya;
Nordlander, Thomas
Bibcode: 2018arXiv180405900S
Altcode:
We report the serendipitous observations of 571 luminous supergiants
in the Magellanic Clouds by the spectroscopic GALAH and TESS-HERMES
surveys: 434 stars in the Large Magellanic Cloud and 137 in the Small
Magellanic Cloud. We also find one star that appears associated with
structured star formation in the Magellanic Bridge. Both of these
surveys are aimed at the local volume of the Galaxy but have simple,
magnitude-limited selection functions that mean they include some
observations of luminous extra-Galactic stars. The surveys determine
stellar parameter and abundances using The Cannon, a data-driven
generative modelling approach. In this work, we explore the results
from The Cannon when it is fed the spectra of these intrinsically
luminous supergiants in the Magellanic Clouds, which are well
outside the normal bounds of The Cannon's training set. We find that,
although the parameters are astrophysically incorrect, the $v\sin i$
and the abundances of lithium, barium, and magnesium are excellent
discriminants of these stars. It shows that in the future, with an
expanded training set, it should be possible to determine accurate
values for these types of stars.
Title: Accurate effective temperatures of the metal-poor benchmark
stars HD 140283, HD 122563, and HD 103095 from CHARA interferometry
Authors: Karovicova, I.; White, T. R.; Nordlander, T.; Lind, K.;
Casagrande, L.; Ireland, M. J.; Huber, D.; Creevey, O.; Mourard, D.;
Schaefer, G. H.; Gilmore, G.; Chiavassa, A.; Wittkowski, M.; Jofré,
P.; Heiter, U.; Thévenin, F.; Asplund, M.
Bibcode: 2018MNRAS.475L..81K
Altcode: 2018arXiv180103274K; 2018MNRAS.tmpL..10K
Large stellar surveys of the Milky Way require validation with reference
to a set of `benchmark' stars whose fundamental properties are well
determined. For metal-poor benchmark stars, disagreement between
spectroscopic and interferometric effective temperatures has called
the reliability of the temperature scale into question. We present
new interferometric measurements of three metal-poor benchmark stars,
HD 140283, HD 122563, and HD 103095, from which we determine their
effective temperatures. The angular sizes of all the stars were
determined from observations with the PAVO beam combiner at visible
wavelengths at the CHARA array, with additional observations of HD
103095 made with the VEGA instrument, also at the CHARA array. Together
with photometrically derived bolometric fluxes, the angular diameters
give a direct measurement of the effective temperature. For HD 140283,
we find θLD = 0.324 ± 0.005 mas, Teff =
5787 ± 48 K; for HD 122563, θLD = 0.926 ± 0.011 mas,
Teff = 4636 ± 37 K; and for HD 103095, θLD =
0.595 ± 0.007 mas, Teff = 5140 ± 49 K. Our temperatures for
HD 140283 and HD 103095 are hotter than the previous interferometric
measurements by 253 and 322 K, respectively. We find good agreement
between our temperatures and recent spectroscopic and photometric
estimates. We conclude some previous interferometric measurements
have been affected by systematic uncertainties larger than their
quoted errors.
Title: The STAGGER-grid: A grid of 3D stellar atmosphere
models. V. Synthetic stellar spectra and broad-band photometry
Authors: Chiavassa, A.; Casagrande, L.; Collet, R.; Magic, Z.; Bigot,
L.; Thévenin, F.; Asplund, M.
Bibcode: 2018A&A...611A..11C
Altcode: 2018arXiv180101895C
Context. The surface structures and dynamics of cool stars are
characterised by the presence of convective motions and turbulent flows
which shape the emergent spectrum.
Aims: We used realistic
three-dimensional (3D) radiative hydrodynamical simulations from
the STAGGER-grid to calculate synthetic spectra with the radiative
transfer code OPTIM3D for stars with different stellar parameters to
predict photometric colours and convective velocity shifts.
Methods: We calculated spectra from 1000 to 200 000 Å with a constant
resolving power of λ/Δλ = 20 000 and from 8470 and 8710 Å (Gaia
Radial Velocity Spectrometer - RVS - spectral range) with a constant
resolving power of λ/Δλ = 300 000.
Results: We used synthetic
spectra to compute theoretical colours in the Johnson-Cousins UBV
(RI)C, SDSS, 2MASS, Gaia, SkyMapper, Strömgren systems,
and HST-WFC3. Our synthetic magnitudes are compared with those obtained
using 1D hydrostatic models. We showed that 1D versus 3D differences
are limited to a small percent except for the narrow filters that
span the optical and UV region of the spectrum. In addition, we
derived the effect of the convective velocity fields on selected Fe
I lines. We found the overall convective shift for 3D simulations
with respect to the reference 1D hydrostatic models, revealing line
shifts of between -0.235 and +0.361 km s-1. We showed a net
correlation of the convective shifts with the effective temperature:
lower effective temperatures denote redshifts and higher effective
temperatures denote blueshifts. We conclude that the extraction
of accurate radial velocities from RVS spectra need an appropriate
wavelength correction from convection shifts.
Conclusions: The
use of realistic 3D hydrodynamical stellar atmosphere simulations has
a small but significant impact on the predicted photometry compared
with classical 1D hydrostatic models for late-type stars. We make
all the spectra publicly available for the community through the
POLLUX database. Tables 5-8 are only available at the CDS and
Table B.1 is also available at the CDS and via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/611/A11
Title: VizieR Online Data Catalog: HD 80606/80607 equivalent widths
(Lui+, 2018)
Authors: Liu, F.; Yong, D.; Asplund, M.; Feltzing, S.; Mustill, A. J.;
Melendez, J.; Ramirez, I.; Lin, J.
Bibcode: 2018yCat..36140138L
Altcode:
We obtained high-resolution (R=86000) spectra of HD 80606/80607
using the 0.4" slit and 'kv408' filter of the High Resolution Echelle
Spectrometer (HIRES) on the 10m Keck I telescope on 1 November 2015. The
spectral wavelength coverage is almost complete from 420 to 860nm. Atomic line data, as well as the equivalent width measurements,
adopted for our analysis. (1 data file).
Title: VizieR Online Data Catalog: Temporal evolution of
neutron-capture elements (Spina+, 2018)
Authors: Spina, L.; Melendez, J.; Karakas, A. I.; Dos Santos, L.;
Bedell, M.; Asplund, M.; Ramirez, I.; Yong, D.; Alves-Brito, A.;
Bean, J. L.; Dreizler, S.
Bibcode: 2018yCat..74742580S
Altcode:
Spectroscopic parameters and abundances for the 79 solar twin stars
analysed in this paper. (4 data files).
Title: The K2-HERMES Survey. I. Planet-candidate Properties from K2
Campaigns 1-3
Authors: Wittenmyer, Robert A.; Sharma, Sanjib; Stello, Dennis; Buder,
Sven; Kos, Janez; Asplund, Martin; Duong, Ly; Lin, Jane; Lind, Karin;
Ness, Melissa; Zwitter, Tomaz; Horner, Jonathan; Clark, Jake; Kane,
Stephen R.; Huber, Daniel; Bland-Hawthorn, Joss; Casey, Andrew R.; De
Silva, Gayandhi M.; D'Orazi, Valentina; Freeman, Ken; Martell, Sarah;
Simpson, Jeffrey D.; Zucker, Daniel B.; Anguiano, Borja; Casagrande,
Luca; Esdaile, James; Hon, Marc; Ireland, Michael; Kafle, Prajwal R.;
Khanna, Shourya; Marshall, J. P.; Saddon, Mohd Hafiz Mohd; Traven,
Gregor; Wright, Duncan
Bibcode: 2018AJ....155...84W
Altcode: 2017arXiv171206774W
Accurate and precise radius estimates of transiting exoplanets
are critical for understanding their compositions and formation
mechanisms. To know the planet, we must know the host star in as
much detail as possible. We present first results from the K2-HERMES
project, which uses the HERMES multi-object spectrograph on the
Anglo-Australian Telescope to obtain R ∼ 28000 spectra of up
to 360 stars in one exposure. This ongoing project aims to derive
self-consistent spectroscopic parameters for about half of K2 target
stars. We present complete stellar parameters and isochrone-derived
masses and radii for 46 stars hosting 57 K2 candidate planets in
Campaigns 1-3. Our revised host-star radii cast severe doubt on three
candidate planets: EPIC 201407812.01, EPIC 203070421.01, and EPIC
202843107.01, all of which now have inferred radii well in excess of
the largest known inflated Jovian planets.
Title: The temporal evolution of neutron-capture elements in the
Galactic discs
Authors: Spina, Lorenzo; Meléndez, Jorge; Karakas, Amanda I.; dos
Santos, Leonardo; Bedell, Megan; Asplund, Martin; Ramírez, Ivan;
Yong, David; Alves-Brito, Alan; Bean, Jacob L.; Dreizler, Stefan
Bibcode: 2018MNRAS.474.2580S
Altcode: 2017arXiv171103643S
Important insights into the formation and evolution of the Galactic
disc(s) are contained in the chemical compositions of stars. We
analysed high-resolution and high signal-to-noise HARPS spectra of 79
solar twin stars in order to obtain precise determinations of their
atmospheric parameters, ages (σ ∼0.4 Gyr) and chemical abundances
(σ <0.01 dex) of 12 neutron-capture elements (Sr, Y, Zr, Ba, La,
Ce, Pr, Nd, Sm, Eu, Gd and Dy). This valuable data set allows us to
study the [X/Fe]-age relations over a time interval of ∼10 Gyr and
among stars belonging to the thin and thick discs. These relations show
that (i) the s-process has been the main channel of nucleosynthesis
of n-capture elements during the evolution of the thin disc; (ii)
the thick disc is rich in r-process elements which suggests that its
formation has been rapid and intensive. In addition, the heavy (Ba,
La, Ce) and light (Sr, Y, Zr) s-process elements revealed details on
the dependence between the yields of AGB stars and the stellar mass
or metallicity. Finally, we confirmed that both [Y/Mg] and [Y/Al]
ratios can be employed as stellar clocks, allowing ages of solar twin
stars to be estimated with an average precision of ∼0.5 Gyr.
Title: The GALAH survey: chemical tagging of star clusters and new
members in the Pleiades
Authors: Kos, Janez; Bland-Hawthorn, Joss; Freeman, Ken; Buder, Sven;
Traven, Gregor; De Silva, Gayandhi M.; Sharma, Sanjib; Asplund, Martin;
Duong, Ly; Lin, Jane; Lind, Karin; Martell, Sarah; Simpson, Jeffrey D.;
Stello, Dennis; Zucker, Daniel B.; Zwitter, Tomaž; Anguiano, Borja;
Da Costa, Gary; D'Orazi, Valentina; Horner, Jonathan; Kafle, Prajwal
R.; Lewis, Geraint; Munari, Ulisse; Nataf, David M.; Ness, Melissa;
Reid, Warren; Schlesinger, Katie; Ting, Yuan-Sen; Wyse, Rosemary
Bibcode: 2018MNRAS.473.4612K
Altcode: 2017arXiv170900794K
The technique of chemical tagging uses the elemental abundances
of stellar atmospheres to 'reconstruct' chemically homogeneous star
clusters that have long since dispersed. The GALAH spectroscopic survey
- which aims to observe one million stars using the Anglo-Australian
Telescope - allows us to measure up to 30 elements or dimensions in the
stellar chemical abundance space, many of which are not independent. How
to find clustering reliably in a noisy high-dimensional space is
a difficult problem that remains largely unsolved. Here, we explore
t-distributed stochastic neighbour embedding (t-SNE) - which identifies
an optimal mapping of a high-dimensional space into fewer dimensions
- whilst conserving the original clustering information. Typically,
the projection is made to a 2D space to aid recognition of clusters by
eye. We show that this method is a reliable tool for chemical tagging
because it can: (i) resolve clustering in chemical space alone, (ii)
recover known open and globular clusters with high efficiency and low
contamination, and (iii) relate field stars to known clusters. t-SNE
also provides a useful visualization of a high-dimensional space. We
demonstrate the method on a data set of 13 abundances measured in
the spectra of 187 000 stars by the GALAH survey. We recover seven
of the nine observed clusters (six globular and three open clusters)
in chemical space with minimal contamination from field stars and
low numbers of outliers. With chemical tagging, we also identify two
Pleiades supercluster members (which we confirm kinematically), one
as far as 6° - one tidal radius away from the cluster centre.
Title: VizieR Online Data Catalog: STAGGER-grid of 3D stellar
models. V. (Chiavassa+, 2018)
Authors: Chiavassa, A.; Casagrande, L.; Collet, R.; Magic, Z.; Bigot,
L.; Thevenin, F.; Asplund, M.
Bibcode: 2018yCat..36110011C
Altcode:
Table B0: RHD simulations' stellar parameters, bolometric magnitude,
and bolometric correction for Johnson-Cousins, 2MASS, SDSS (columns
13 to 17), and Gaia systems Table 4: RHD simulations' stellar
parameters, bolometric magnitude, and bolometric correction for
SkyMapper photometric system, and Stroemgren index b-y, m1=(v-b)-(b-y),
and c1=(u-v)-(v-b) Table 5: RHD simulations' stellar parameters,
bolometric magnitude, and bolometric correction for the HST-WFC3
in VEGA system Table 6: RHD simulations' stellar parameters,
bolometric magnitude, and bolometric correction for the HST-WFC3 in ST
system Table 7: RHD simulations' stellar parameters, bolometric
magnitude, and bolometric correction for the HST-WFC3 in AB system (5 data files).
Title: The GALAH survey: the ancient Galactic thin and thick disks
Authors: Asplund, M.
Bibcode: 2018cdeg.confE..20A
Altcode:
No abstract at ADS
Title: The TESS-HERMES survey data release 1: high-resolution
spectroscopy of the TESS southern continuous viewing zone
Authors: Sharma, Sanjib; Stello, Dennis; Buder, Sven; Kos, Janez;
Bland-Hawthorn, Joss; Asplund, Martin; Duong, Ly; Lin, Jane; Lind,
Karin; Ness, Melissa; Huber, Daniel; Zwitter, Tomaz; Traven, Gregor;
Hon, Marc; Kafle, Prajwal R.; Khanna, Shourya; Saddon, Hafiz; Anguiano,
Borja; Casey, Andrew R.; Freeman, Ken; Martell, Sarah; De Silva,
Gayandhi M.; Simpson, Jeffrey D.; Wittenmyer, Rob A.; Zucker, Daniel B.
Bibcode: 2018MNRAS.473.2004S
Altcode: 2017arXiv170705753S
The Transiting Exoplanet Survey Satellite (TESS) will provide
high-precision time series photometry for millions of stars with
at least a half-hour cadence. Of particular interest are the
circular regions of 12° radius centred around the ecliptic poles
that will be observed continuously for a full year. Spectroscopic
stellar parameters are desirable to characterize and select suitable
targets for TESS, whether they are focused on exploring exoplanets,
stellar astrophysics or Galactic archaeology. Here, we present
spectroscopic stellar parameters (Teff, log g, [Fe/H],
v sin i, vmicro) for about 16 000 dwarf and subgiant
stars in TESS' southern continuous viewing zone. For almost all
the stars, we also present Bayesian estimates of stellar properties
including distance, extinction, mass, radius and age using theoretical
isochrones. Stellar surface gravity and radius are made available
for an additional set of roughly 8500 red giants. All our target
stars are in the range 10 < V < 13.1. Among them, we identify
and list 227 stars belonging to the Large Magellanic Cloud. The data
were taken using the High Efficiency and Resolution Multi-Element
Spectrograph (HERMES; R ∼ 28 000) at the Anglo-Australian Telescope
as part of the TESS-HERMES survey. Comparing our results with the
TESS Input Catalogue (TIC) shows that the TIC is generally efficient
in separating dwarfs and giants, but it has flagged more than 100
cool dwarfs (Teff < 4800 K) as giants, which ought to
be high-priority targets for the exoplanet search. The catalogue can
be accessed via http://www.physics.usyd.edu.au/tess-hermes/, or at
Mikulski Archive for Space Telescopes (MAST).
Title: Spectroscopic binaries in the Solar Twin Planet Search program:
from substellar-mass to M dwarf companions
Authors: dos Santos, Leonardo A.; Meléndez, Jorge; Bedell, Megan;
Bean, Jacob L.; Spina, Lorenzo; Alves-Brito, Alan; Dreizler, Stefan;
Ramírez, Iván; Asplund, Martin
Bibcode: 2017MNRAS.472.3425D
Altcode: 2017arXiv170807465D
Previous studies on the rotation of Sun-like stars revealed that
the rotational rates of young stars converge towards a well-defined
evolution that follows a power-law decay. It seems, however, that some
binary stars do not obey this relation, often by displaying enhanced
rotational rates and activity. In the Solar Twin Planet Search program,
we observed several solar twin binaries, and found a multiplicity
fraction of 42 per cent ± 6 per cent in the whole sample; moreover,
at least three of these binaries (HIP 19911, HIP 67620 and HIP 103983)
clearly exhibit the aforementioned anomalies. We investigated the
configuration of the binaries in the program, and discovered new
companions for HIP 6407, HIP 54582, HIP 62039 and HIP 30037, of which
the latter is orbited by a 0.06 M⊙ brown dwarf in a 1
m long orbit. We report the orbital parameters of the systems with
well-sampled orbits and, in addition, the lower limits of parameters
for the companions that only display a curvature in their radial
velocities. For the linear trend binaries, we report an estimate
of the masses of their companions when their observed separation
is available, and a minimum mass otherwise. We conclude that solar
twin binaries with low-mass stellar companions at moderate orbital
periods do not display signs of a distinct rotational evolution when
compared to single stars. We confirm that the three peculiar stars are
double-lined binaries, and that their companions are polluting their
spectra, which explains the observed anomalies.
Title: Red supergiant stars in NGC 4449, NGC 5055, and NGC 5457
Authors: Chun, Sang-Hyun; Sohn, Yong-Jong; Asplund, Martin; Casagrande,
Luca
Bibcode: 2017IAUS..329..392C
Altcode:
Nearby galaxies are ideal objects for the study of the mechanisms of
galaxy formation and evolution, and massive stars in nearby galaxies
are useful sources to investigate the structures and formation of the
galaxies. It is important to gather the contents of massive stars for
a number of galaxies spanning various metallicities. We focus on the
red supergiants (RSGs) in nearby galaxies NGC 4449, NGC 5055, and
NGC 5457, and the photometric properties of RSGs of three galaxies
were investigated using near-infrared (JHK) imaging data obtained
from WFCAM UKIRT. The (J - K, K)0 CMDs are investigated
and compared with theoretical isochrones (Figure 1). The majority
of RSGs in three galaxies have common age ranges from log(t
yr ) = 6.9 to log(t yr ) = 7.3, and this indicates
that these galaxies have experienced recent star formation within 20
Myr. Spatial correlation of RSGs with H II regions and their colour
distribution were also investigated. For NGC 4449 and NGC 5457, the
RSGs are spatially correlated with the H II regions, which however is
not the case for NGC 5055. We found a similar colour distribution and
a constant peak magnitude of M K = -11.9 for the RSGs in
the three galaxies.
Title: VizieR Online Data Catalog: Abundances of solar twins from
Keck/HIRES (Bedell+, 2017)
Authors: Bedell, M.; Bean, J. L.; Melendez, J.; Mills, S. M.; Fabrycky,
D. C.; Freitas, F. C.; Ramirez, I.; Asplund, M.; Liu, F.; Yong, D.
Bibcode: 2017yCat..18390094B
Altcode:
Over the course of two consecutive nights (2015 July 26-27), we made 22
exposures of Kepler-11 of 1200s each for a coadded result of S/N~260
per pixel in the continuum near 600nm. For these observations, HIRES
was used with a resolution R~67000 and wavelength coverage between
390 and 830nm. We also observed the solar spectrum (via reflection
from Ceres) and nine bright potential Kepler-11 twins with the same
instrumental setup and similar S/N. (2 data files).
Title: VizieR Online Data Catalog: EMBLA survey. Galactic bulge
metal-poor stars (Howes+, 2016)
Authors: Howes, L. M.; Asplund, M.; Keller, S. C.; Casey, A. R.; Yong,
D.; Lind, K.; Frebel, A.; Hays, A.; Alves-Brito, A.; Bessell, M. S.;
Casagrande, L.; Marino, A. F.; Nataf, D. M.; Owen, C. I.; da Costa,
G. S.; Schmidt, B. P.; Tisserand, P.
Bibcode: 2017yCat..74600884H
Altcode:
Ten stars were observed using the MIKE high-resolution spectrograph
on Magellan's 6.5m Clay telescope. The observations took place between
April and June of 2012, and all make use of the full wavelength coverage
offered by MIKE, with the spectra covering (as a minimum) 370-890nm. All
except one star (SMSS J182637.10-342924.2) were configured with a
1.0 arcsec slit, resulting in resolving powers of 22000 in the blue
and 28000 in the red, and were binned by two in both the spatial and
spectral directions. SMSS J182637.10-342924.2 was instead observed in
April as part of a different set of observations, where a slit with
width of 0.35-arcsec and no spatial or spectral binning, was used. This
provided resolving powers of 83000 and 65000, in the blue and red,
respectively. (5 data files).
Title: Chemical evolution of the Galactic bulge as traced by
microlensed dwarf and subgiant stars. VI. Age and abundance structure
of the stellar populations in the central sub-kpc of the Milky Way
Authors: Bensby, T.; Feltzing, S.; Gould, A.; Yee, J. C.; Johnson,
J. A.; Asplund, M.; Meléndez, J.; Lucatello, S.; Howes, L. M.;
McWilliam, A.; Udalski, A.; Szymański, M. K.; Soszyński, I.; Poleski,
R.; Wyrzykowski, Ł.; Ulaczyk, K.; Kozłowski, S.; Pietrukowicz, P.;
Skowron, J.; Mróz, P.; Pawlak, M.; Abe, F.; Asakura, Y.; Bhattacharya,
A.; Bond, I. A.; Bennett, D. P.; Hirao, Y.; Nagakane, M.; Koshimoto,
N.; Sumi, T.; Suzuki, D.; Tristram, P. J.
Bibcode: 2017A&A...605A..89B
Altcode: 2017arXiv170202971B
We present a detailed elemental abundance study of 90 F and G
dwarf, turn-off, and subgiant stars in the Galactic bulge. Based on
high-resolution spectra acquired during gravitational microlensing
events, stellar ages and abundances for 11 elements (Na, Mg, Al,
Si, Ca, Ti, Cr, Fe, Zn, Y and Ba) have been determined. Four main
findings are presented: (1) a wide metallicity distribution with
distinct peaks at [Fe/H] = -1.09, -0.63, -0.20, + 0.12, + 0.41; (2)
ahigh fraction of intermediate-age to young stars where at [Fe/H] >
0 more than 35% are younger than 8 Gyr, and for [Fe/H] ≲ -0.5 most
stars are 10 Gyr or older; (3) several episodes of significant star
formation in the bulge has been identified: 3, 6, 8, and 11 Gyr ago;
(4) tentatively the "knee" in the α-element abundance trends of the
sub-solar metallicity bulge is located at a slightly higher [Fe/H] than
in the local thick disk. These findings show that the Galactic bulge
has complex age and abundance properties that appear to be tightly
connected to the main Galactic stellar populations. In particular,
the peaks in the metallicity distribution, the star formation episodes,
and the abundance trends, show similarities with the properties of the
Galactic thin and thick disks. At the same time, the star formation
rate appears to have been slightly faster in the bulge than in the
local thick disk, which most likely is an indication of the denser
stellar environment closer to the Galactic centre. There are also
additional components not seen outside the bulge region, and that most
likely can be associated with the Galactic bar. Our results strengthen
the observational evidence that support the idea of a secular origin
for the Galactic bulge, formed out of the other main Galactic stellar
populations present in the central regions of our Galaxy. Additionally,
our analysis of this enlarged sample suggests that the (V-I)0
colour of the bulge red clump should be revised to 1.09. Based
on data obtained with the European Southern Observatory telescopes
(Proposal ID:s 87.B-0600, 88.B-0349, 89.B-0047, 90.B-0204, 91.B-0289,
92.B-0626, 93.B-0700, 94.B-0282), the Magellan Clay telescope at the
Las Campanas observatory, and the Keck I telescope at the W.M. Keck
Observatory, which is operated as a scientific partnership among the
California Institute of Technology, the University of California
and the National Aeronautics and Space Administration.Full Tables
A.1 and A.2 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/605/A89
Title: VizieR Online Data Catalog: Spectra of the post-AGB star
J005252.87-722842.9 (Kamath+, 2017)
Authors: Kamath, D.; van Winckel, H.; Wood, P. R.; Asplund, M.;
Karakas, A. I.; Lattanzio, J. C.
Bibcode: 2017yCat..18360015K
Altcode:
We obtained high-resolution optical spectra using the UVES echelle
spectrograph, mounted on the 8m UT2 Kueyen Telescope of the VLT array
at the Paranal Observatory of ESO in Chile. (2 data files).
Title: Non-LTE line formation of Fe in late-type stars - IV. Modelling
of the solar centre-to-limb variation in 3D
Authors: Lind, K.; Amarsi, A. M.; Asplund, M.; Barklem, P. S.;
Bautista, M.; Bergemann, M.; Collet, R.; Kiselman, D.; Leenaarts,
J.; Pereira, T. M. D.
Bibcode: 2017MNRAS.468.4311L
Altcode: 2017arXiv170304027L
Our ability to model the shapes and strengths of iron lines in the solar
spectrum is a critical test of the accuracy of the solar iron abundance,
which sets the absolute zero-point of all stellar metallicities. We use
an extensive 463-level Fe atom with new photoionization cross-sections
for Fe I and quantum mechanical calculations of collisional excitation
and charge transfer with neutral hydrogen; the latter effectively remove
a free parameter that has hampered all previous line formation studies
of Fe in non-local thermodynamic equilibrium (NLTE). For the first
time, we use realistic 3D NLTE calculations of Fe for a quantitative
comparison to solar observations. We confront our theoretical line
profiles with observations taken at different viewing angles across
the solar disc with the Swedish 1-m Solar Telescope. We find that
3D modelling well reproduces the observed centre-to-limb behaviour
of spectral lines overall, but highlight aspects that may require
further work, especially cross-sections for inelastic collisions with
electrons. Our inferred solar iron abundance is log (ɛFe)
= 7.48 ± 0.04 dex.
Title: Spectroscopy and Photometry of Multiple Populations along
the Asymptotic Giant Branch of NGC 2808 and NGC 6121 (M4)
Authors: Marino, A. F.; Milone, A. P.; Yong, D.; Da Costa, G.;
Asplund, M.; Bedin, L. R.; Jerjen, H.; Nardiello, D.; Piotto, G.;
Renzini, A.; Shetrone, M.
Bibcode: 2017ApJ...843...66M
Altcode: 2017arXiv170602278M
We present a photometric and spectroscopic study of multiple populations
along the asymptotic giant branch (AGB) of the intermediate-metallicity
globular clusters (GCs) NGC 2808 and NGC 6121 (M4). Chemical abundances
of O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Fe, Co, Ni, Zn, Y, and Ce in
AGB stars from high-resolution FLAMES+UVES@VLT spectra are reported
for both clusters. Our spectroscopic results have been combined with
multiwavelength photometry from the Hubble Space Telescope UV survey
of Galactic GCs and ground-based photometry, as well as proper motions
derived by combining stellar positions from ground-based images and
Gaia DR1. Our analysis reveals that the AGBs of both clusters host
multiple populations with different chemical compositions. In M4,
we have identified two main populations of stars with different Na/O
content lying on distinct AGBs in the {m}{{F}438{{W}}}
versus {C}{{F}275{{W}},{{F}}336{{W}},{{F}}438{{W}}} and
the V versus {C}{{U},{{B}},{{I}}} pseudo-color-magnitude
diagrams. In the more massive and complex GC NGC 2808, three groups
of stars with different chemical abundances occupy different locations
on the so-called “chromosome map” photometric diagram constructed
for AGB stars. The spectroscopic + photometric comparison of stellar
populations along the AGB and the red giants of this GC suggests that
the AGB hosts stellar populations with a range in helium abundances
from primordial to high contents of Y∼ 0.32. By contrast, from
our data set, there is no evidence for stars with extreme helium
abundance (Y∼ 0.38) on the AGB, suggesting that the most He-rich
stars of NGC 2808 do not reach this phase. Based on observations
collected at the European Organisation for Astronomical Research in
the Southern Hemisphere under ESO programs 093.D-0789 and 094.D-0455
and on observations with the NASA/ESA Hubble Space Telescope, obtained
at the Space Telescope Science Institute, which is operated by AURA,
Inc., under NASA contract NAS 5-26555.
Title: VizieR Online Data Catalog: Abundances of microlensed Bulge
dwarf stars. VI. (Bensby+, 2017)
Authors: Bensby, T.; Feltzing, S.; Gould, A.; Yee; J. C.; Johnson,
J. A.; Asplund, M.; Melendez, J.; Lucatello, S.; Howes, L. M.;
McWilliam, A.; Udalski, A.; Szymanski, M. K.; Soszynski, I.; Poleski,
R.; Wyrzykowski, L.; Ulaczyk, K.; Kozlowski, S.; Pietrukowicz, P.;
Skowron, J.; Mroz, P.; Pawlak; M.; Abe, F.; Asakura, Y.; Bhattacharya,
A.; Bond, I. A.; Bennett, D. P.; Hirao, Y.; Nagakane, M.; Koshimoto,
N.; Sumi, T.; Suzuki, D.; Tristram, P. J.
Bibcode: 2017yCat..36050089B
Altcode:
For each spectral line we give the lower excitation potential,
measured equivalent widths, and derived absolute abundances. We
also give median abundances for each star, normalised to the Sun,
and errors in the median abundances. These tables contain data for
all so far 91 microlensed dwarf stars, and superseeds the tables
in Bensby et al. (2009, Cat. J/A+A/499/737), Bensby et al. (2010,
Cat. J/A+A/512/A41), Bensby et al. (2011, Cat. J/A+A/533/A134), and
Bensby et al. (2013, Cat. J/A+A/549/A147). (2 data files).
Title: Red supergiant stars in NGC 4449, NGC 5055 (M63) and NGC 5457
(M101)
Authors: Chun, Sang-Hyun; Sohn, Young-Jong; Asplund, Martin;
Casagrande, Luca
Bibcode: 2017MNRAS.467..102C
Altcode:
The photometric properties of red supergiants (RSGs) in three nearby
galaxies NGC 4449, NGC 5055 and NGC 5457 were investigated using
near-infrared (JHK) imaging data obtained from WFCAM UKIRT. The
resulting near-infrared photometric catalogue was combined with
optical archive data to remove foreground Galactic stars. We found
that the foreground stars can be separated from the supergiants in
a (I - K, r - I) colour-colour diagram. The (J - K, K)0
colour-magnitude diagrams of the three galaxies are investigated and
compared with theoretical isochrones. The majority of RSGs in the three
galaxies have common age ranges from log (tyr) = 6.9 to log
(tyr) = 7.3, and this indicates that these galaxies have
experienced recent star formation within 20 Myr. For NGC 4449 and NGC
5457, the RSGs are spatially correlated with the H II regions, which,
however, is not the case for NGC 5055. We were not able to identify
a clear metallicity dependence on the colours and the peak absolute
magnitudes of the RSGs in the three galaxies. The inaccuracy of our
photometric data contributes to the unclear metallicity effect on the
colours of RSGs. Instead, we found a similar colour distribution and
a constant peak magnitude of MK = -11.9 for the RSGs in
the three galaxies. Therefore, we note that additional spectroscopy
data for our RSG candidates, including photometry, are necessary to
examine whether the RSG population changes with metallicity.
Title: VizieR Online Data Catalog: Line list for stellar chemical
abundances (Bedell+, 2014)
Authors: Bedell, M.; Melendez, J.; Bean, J. L.; Ramirez, I.; Leite,
P.; Asplund, M.
Bibcode: 2017yCat..17950023B
Altcode:
The five solar spectra used in this analysis were obtained with very
high resolution and signal-to-noise ratios (S/Ns) characteristic of
data used in past stellar abundance analyses. Two spectra were taken
with the Echelle SpectroPolarimetric Device for the Observation of
Stars (ESPaDOnS) instrument (Donati 2003, Solar Polarization (ASP
Conf. Ser. 307), ed. J. Trujillo-Bueno & J. Sanchez Almeida
(San Francisco, CA: ASP), 41) at the 3.6 m Canada-France-Hawaii
Telescope on the night of 2013 March 4. The asteroids Ceres and
Vesta were each observed in "star only" mode at a spectral resolving
power R=81000. The remaining three solar spectra were taken with the
Magellan Inamori Kyocera Echelle (MIKE) spectrograph (Bernstein et
al. 2003SPIE.4841.1694B) at the 6.5 m Magellan Clay telescope. The
asteroid Vesta was observed twice and Iris was observed once during
three separate observing runs spanning January to September of 2011. All
observations were carried out in MIKE's standard setup with the 0.35
arcsec width slit, giving a spectral resolving power of R=83000 on
the blue CCD and 65000 on the red CCD. (1 data file).
Title: Sun-like stars unlike the Sun: Clues for chemical anomaliesof
cool stars
Authors: Adibekyan, V.; Delgado-Mena, E.; Feltzing, S.; González
Hernández, J. I.; Hinkel, N. R.; Korn, A. J.; Asplund, M.; Beck,
P. G.; Deal, M.; Gustafsson, B.; Honda, S.; Lind, K.; Nissen, P. E.;
Spina, L.
Bibcode: 2017AN....338..442A
Altcode: 2017arXiv170105737A
We present a summary of the splinter session "Sun-like stars unlike
the Sun" that was held on June 9, 2016, as part of the Cool Stars
19 conference (Uppsala, Sweden), in which the main limitations
(in the theory and observations) in the derivation of very precise
stellar parameters and chemical abundances of Sun-like stars were
discussed. The most important and most debated processes that can
produce chemical peculiarities in solar-type stars were outlined and
discussed. Finally, in an open discussion between all the participants,
we tried to identify new pathways and prospects toward future solutions
of the currently open questions.
Title: The Influence of Atomic Diffusion on Stellar Ages and Chemical
Tagging
Authors: Dotter, Aaron; Conroy, Charlie; Cargile, Phillip; Asplund,
Martin
Bibcode: 2017ApJ...840...99D
Altcode: 2017arXiv170403465D
In the era of large stellar spectroscopic surveys, there is an emphasis
on deriving not only stellar abundances but also the ages for millions
of stars. In the context of Galactic archeology, stellar ages provide a
direct probe of the formation history of the Galaxy. We use the stellar
evolution code MESA to compute models with atomic diffusion—with
and without radiative acceleration—and extra mixing in the surface
layers. The extra mixing consists of both density-dependent turbulent
mixing and envelope overshoot mixing. Based on these models we argue
that it is important to distinguish between initial, bulk abundances
(parameters) and current, surface abundances (variables) in the
analysis of individual stellar ages. In stars that maintain radiative
regions on evolutionary timescales, atomic diffusion modifies the
surface abundances. We show that when initial, bulk metallicity is
equated with current, surface metallicity in isochrone age analysis,
the resulting stellar ages can be systematically overestimated by up
to 20%. The change of surface abundances with evolutionary phase also
complicates chemical tagging, which is the concept that dispersed star
clusters can be identified through unique, high-dimensional chemical
signatures. Stars from the same cluster, but in different evolutionary
phases, will show different surface abundances. We speculate that
calibration of stellar models may allow us to estimate not only stellar
ages but also initial abundances for individual stars. In the meantime,
analyzing the chemical properties of stars in similar evolutionary
phases is essential to minimize the effects of atomic diffusion in
the context of chemical tagging.
Title: Kepler-11 is a Solar Twin: Revising the Masses and Radii of
Benchmark Planets via Precise Stellar Characterization
Authors: Bedell, Megan; Bean, Jacob L.; Meléndez, Jorge; Mills,
Sean M.; Fabrycky, Daniel C.; Freitas, Fabrício C.; Ramírez, Ivan;
Asplund, Martin; Liu, Fan; Yong, David
Bibcode: 2017ApJ...839...94B
Altcode: 2016arXiv161106239B
The six planets of the Kepler-11 system are the archetypal example of
a population of surprisingly low-density transiting planets revealed
by the Kepler mission. We have determined the fundamental parameters
and chemical composition of the Kepler-11 host star to unprecedented
precision using an extremely high-quality spectrum from Keck-HIRES (R
≃ 67,000, S/N per pixel ≃ 260 at 600 nm). Contrary to previously
published results, our spectroscopic constraints indicate that Kepler-11
is a young main-sequence solar twin. The revised stellar parameters and
new analysis raise the densities of the Kepler-11 planets by between
20% and 95% per planet, making them more typical of the emerging
class of “puffy” close-in exoplanets. We obtain photospheric
abundances of 22 elements and find that Kepler-11 has an abundance
pattern similar to that of the Sun with a slightly higher overall
metallicity. We additionally analyze the Kepler light curves using
a photodynamical model and discuss the tension between spectroscopic
and transit/TTV-based estimates of stellar density.
Title: Asymmetries on red giant branch surfaces from CHARA/MIRC
optical interferometry
Authors: Chiavassa, A.; Norris, R.; Montargès, M.; Ligi, R.; Fossati,
L.; Bigot, L.; Baron, F.; Kervella, P.; Monnier, J. D.; Mourard, D.;
Nardetto, N.; Perrin, G.; Schaefer, G. H.; ten Brummelaar, T. A.;
Magic, Z.; Collet, R.; Asplund, M.
Bibcode: 2017A&A...600L...2C
Altcode: 2017arXiv170302406C
Context. Red giant branch (RGB) stars are very bright objects in
galaxies and are often used as standard candles. Interferometry
is the ideal tool to characterize the dynamics and morphology of
their atmospheres.
Aims: We aim at precisely characterising
the surface dynamics of a sample of RGB stars.
Methods: We
obtained interferometric observations for three RGB stars with the
MIRC instrument mounted at the CHARA interferometer. We looked for
asymmetries on the stellar surfaces using limb-darkening models.
Results: We measured the apparent diameters of HD 197989 (ɛ Cyg)
= 4.61 ± 0.02 mas, HD 189276 (HR 7633) = 2.95 ± 0.01 mas, and HD
161096 (β Oph) = 4.43 ± 0.01 mas. We detected departures from the
centrosymmetric case for all three stars with the tendency of a greater
effect for lower logg of the sample. We explored the causes of this
signal and conclude that a possible explanation to the interferometric
signal is the convection-related and/or the magnetic-related surface
activity. However, it is necessary to monitor these stars with new
observations, possibly coupled with spectroscopy, in order to firmly
establish the cause.
Title: VizieR Online Data Catalog: GALAH semi-automated classification
scheme (Traven+, 2017)
Authors: Traven, G.; Matijevic, G.; Zwitter, T.; Zerjal, M.; Kos, J.;
Asplund, M.; Bland-Hawthorn, J.; Casey, A. R.; de Silva, G.; Freeman,
K.; Lin, J.; Martell, S. L.; Schlesinger, K. J.; Sharma, S.; Simpson,
J. D.; Zucker, D. B.; Anguiano, B.; da Costa, G.; Duong, L.; Horner,
J.; Hyde, E. A.; Kafle, P. R.; Munari, U.; Nataf, D.; Navin, C. A.;
Reid, W.; Ting, Y. -S.
Bibcode: 2017yCat..22280024T
Altcode:
The GALactic Archaeology with HERMES (GALAH) survey was the main
driver for the construction of Hermes (High Efficiency and Resolution
Multi-Element Spectrograph), a fiber-fed multi-object spectrograph
on the 3.9m Anglo-Australian Telescope. Its spectral resolving power
(R) is about 28000, and there is also an R=45000 mode using a slit
mask. Hermes has four simultaneous non-contiguous spectral arms
centered at 4800, 5761, 6610, and 7740Å, covering about 1000Å in
total, including Hα and Hβ lines. About 300000 spectra have been
taken to date, including various calibration exposures. However, we
concentrate on ~210000 spectra recorded before 2016 January 30. We devise a custom classification procedure which is based on two
independently developed methods, the novel dimensionality reduction
technique t-SNE (t-distributed stochastic neighbor embedding; van der
Maaten & Hinton 2008, Journal of Machine Learning Research 9, 2579)
and the renowned clustering algorithm DBSCAN (Ester+ 1996, Proc. 2nd
Int. Conf. on KDD, 226 ed. E. Simoudis, J. Han, and U. Fayyad). (4 data files).
Title: 18 Sco: a solar twin rich in refractory and neutron-capture
elements. Implications for chemical tagging.
Authors: Melendez, J.; Ramirez, I.; Karakas, A. I.; Yong, D.; Monroe,
T. R.; Bedell, M.; Bergemann, M.; Asplund, M.; Tucci, Maia M.; Bean,
J.; Do Nascimento, J. -D., Jr; Bazot, M.; Alves-Brito, A.; Freitas,
F. C.; Castro, M.
Bibcode: 2017yCat..17910014M
Altcode:
No abstract at ADS
Title: The GALAH survey: observational overview and Gaia DR1 companion
Authors: Martell, S. L.; Sharma, S.; Buder, S.; Duong, L.; Schlesinger,
K. J.; Simpson, J.; Lind, K.; Ness, M.; Marshall, J. P.; Asplund, M.;
Bland-Hawthorn, J.; Casey, A. R.; De Silva, G.; Freeman, K. C.; Kos,
J.; Lin, J.; Zucker, D. B.; Zwitter, T.; Anguiano, B.; Bacigalupo,
C.; Carollo, D.; Casagrande, L.; Da Costa, G. S.; Horner, J.; Huber,
D.; Hyde, E. A.; Kafle, P. R.; Lewis, G. F.; Nataf, D.; Navin, C. A.;
Stello, D.; Tinney, C. G.; Watson, F. G.; Wittenmyer, R.
Bibcode: 2017MNRAS.465.3203M
Altcode: 2016arXiv160902822M
The Galactic Archaeology with HERMES (GALAH) survey is a massive
observational project to trace the Milky Way's history of star
formation, chemical enrichment, stellar migration and minor
mergers. Using high-resolution (R ≃ 28 000) spectra, taken with the
High Efficiency and Resolution Multi-Element Spectrograph (HERMES)
instrument at the Anglo-Australian Telescope, GALAH will determine
stellar parameters and abundances of up to 29 elements for up to one
million stars. Selecting targets from a colour-unbiased catalogue
built from 2MASS, APASS and UCAC4 data, we expect to observe dwarfs
at 0.3-3 kpc and giants at 1-10 kpc. This enables a thorough local
chemical inventory of the Galactic thin and thick discs, and also
captures smaller samples of the bulge and halo. In this paper, we
present the plan, process and progress as of early 2016 for GALAH
survey observations. In our first two years of survey observing we
have accumulated the largest high-quality spectroscopic data set at
this resolution, over 200 000 stars. We also present the first public
GALAH data catalogue: stellar parameters (Teff, log(g),
[Fe/H], [α/Fe]), radial velocity, distance modulus and reddening for
10 680 observations of 9860 Tycho-2 stars, 7894 of which are included
in the first Gaia data release.
Title: Using the multi-object adaptive optics demonstrator RAVEN to
observe metal-poor stars in and towards the Galactic Centre
Authors: Lamb, M.; Venn, K.; Andersen, D.; Oya, S.; Shetrone, M.;
Fattahi, A.; Howes, L.; Asplund, M.; Lardière, O.; Akiyama, M.;
Ono, Y.; Terada, H.; Hayano, Y.; Suzuki, G.; Blain, C.; Jackson, K.;
Correia, C.; Youakim, K.; Bradley, C.
Bibcode: 2017MNRAS.465.3536L
Altcode: 2016arXiv161102712L
The chemical abundances for five metal-poor stars in and towards
the Galactic bulge have been determined from the H-band infrared
spectroscopy taken with the RAVEN multi-object adaptive optics science
demonstrator and the Infrared Camera and Spectrograph at the Subaru
8.2-m telescope. Three of these stars are in the Galactic bulge and
have metallicities between -2.1 < [Fe/H] < -1.5, and high [α/Fe]
∼ +0.3, typical of Galactic disc and bulge stars in this metallicity
range; [Al/Fe] and [N/Fe] are also high, whereas [C/Fe] < +0.3. An
examination of their orbits suggests that two of these stars may be
confined to the Galactic bulge and one is a halo trespasser, though
proper motion values used to calculate orbits are quite uncertain. An
additional two stars in the globular cluster M22 show [Fe/H] values
consistent to within 1σ, although one of these two stars has [Fe/H]
= -2.01 ± 0.09, which is on the low end for this cluster. The [α/Fe]
and [Ni/Fe] values differ by 2σ, with the most metal-poor star showing
significantly higher values for these elements. M22 is known to show
element abundance variations, consistent with a multipopulation scenario
though our results cannot discriminate this clearly given our abundance
uncertainties. This is the first science demonstration of multi-object
adaptive optics with high-resolution infrared spectroscopy, and we also
discuss the feasibility of this technique for use in the upcoming era
of 30-m class telescope facilities.
Title: The asteroseismic surface effect from a grid of 3D convection
simulations - I. Frequency shifts from convective expansion of
stellar atmospheres
Authors: Trampedach, Regner; Aarslev, Magnus J.; Houdek, Günter;
Collet, Remo; Christensen-Dalsgaard, Jørgen; Stein, Robert F.;
Asplund, Martin
Bibcode: 2017MNRAS.466L..43T
Altcode: 2016arXiv161102638T
We analyse the effect on adiabatic stellar oscillation frequencies
of replacing the near-surface layers in 1D stellar structure models
with averaged 3D stellar surface convection simulations. The main
difference is an expansion of the atmosphere by 3D convection,
expected to explain a major part of the asteroseismic surface effect,
a systematic overestimation of p-mode frequencies due to inadequate
surface physics. We employ pairs of 1D stellar envelope models and 3D
simulations from a previous calibration of the mixing-length parameter,
α. That calibration constitutes the hitherto most consistent matching
of 1D models to 3D simulations, ensuring that their differences are not
spurious, but entirely due to the 3D nature of convection. The resulting
frequency shift is identified as the structural part of the surface
effect. The important, typically non-adiabatic, modal components of
the surface effect are not included in this analysis, but relegated to
future papers. Evaluating the structural surface effect at the frequency
of maximum mode amplitude, νmax , we find shifts from δν =
-0.8 μHz for giants at log g = 2.2 to - 35 μHz for a (Teff
= 6901 K, log g = 4.29) dwarf. The fractional effect δν(νmax
)/νmax , ranges from -0.1 per cent for a cool dwarf
(4185 K, 4.74) to -6 per cent for a warm giant (4962 K, 2.20).
Title: Discovery of a Metal-poor, Luminous Post-AGB Star that Failed
the Third Dredge-up.
Authors: Kamath, D.; Van Winckel, H.; Wood, P. R.; Asplund, M.;
Karakas, A. I.; Lattanzio, J. C.
Bibcode: 2017ApJ...836...15K
Altcode: 2017arXiv171004368K
Post-asymptotic giant branch (post-AGB) stars are known to be chemically
diverse. In this paper we present the first observational evidence of
a star that has failed the third dredge-up (TDU). J005252.87-722842.9
is an A-type (T eff = 8250 ± 250 K) luminous (8200 ±
700 L ⊙) metal-poor ([Fe/H] = -1.18 ± 0.10) low-mass
(M initial ≈ 1.5-2.0 M ⊙) post-AGB star
in the Small Magellanic Cloud. Through a systematic abundance study,
using high-resolution optical spectra from UVES, we found that this
likely post-AGB object shows an intriguing photospheric composition
with no confirmed carbon-enhancement (upper limit of [C/Fe] < 0.50)
nor enrichment of s-process elements. We derived an oxygen abundance of
[O/Fe] = 0.29 ± 0.1. For Fe and O, we took the effects of nonlocal
thermodynamic equilibrium into account. We could not derive an upper
limit for the nitrogen abundance as there are no useful nitrogen lines
within our spectral coverage. The chemical pattern displayed by this
object has not been observed in single or binary post-AGBs. Based on its
derived stellar parameters and inferred evolutionary state, single-star
nucleosynthesis models predict that this star should have undergone TDU
episodes while on the AGB, and it should be carbon enriched. However,
our observations are in contrast with these predictions. We identify
two possible Galactic analogs that are likely to be post-AGB stars, but
the lack of accurate distances (hence luminosities) to these objects
does not allow us to confirm their post-AGB status. If they have low
luminosities, then they are likely to be dusty post-RGB stars. The
discovery of J005252.87-722842.9 reveals a new stellar evolutionary
channel whereby a star evolves without any TDU episodes.
Title: Are open clusters chemically homogeneous?
Authors: Asplund, Martin
Bibcode: 2017koa..prop....1A
Altcode:
No abstract at ADS
Title: The Gaia-ESO Survey: Calibration strategy
Authors: Pancino, E.; Lardo, C.; Altavilla, G.; Marinoni, S.; Ragaini,
S.; Cocozza, G.; Bellazzini, M.; Sabbi, E.; Zoccali, M.; Donati, P.;
Heiter, U.; Koposov, S. E.; Blomme, R.; Morel, T.; Símon-Díaz, S.;
Lobel, A.; Soubiran, C.; Montalban, J.; Valentini, M.; Casey, A. R.;
Blanco-Cuaresma, S.; Jofré, P.; Worley, C. C.; Magrini, L.; Hourihane,
A.; François, P.; Feltzing, S.; Gilmore, G.; Randich, S.; Asplund, M.;
Bonifacio, P.; Drew, J. E.; Jeffries, R. D.; Micela, G.; Vallenari,
A.; Alfaro, E. J.; Allende Prieto, C.; Babusiaux, C.; Bensby, T.;
Bragaglia, A.; Flaccomio, E.; Hambly, N.; Korn, A. J.; Lanzafame,
A. C.; Smiljanic, R.; Van Eck, S.; Walton, N. A.; Bayo, A.; Carraro,
G.; Costado, M. T.; Damiani, F.; Edvardsson, B.; Franciosini, E.;
Frasca, A.; Lewis, J.; Monaco, L.; Morbidelli, L.; Prisinzano, L.;
Sacco, G. G.; Sbordone, L.; Sousa, S. G.; Zaggia, S.; Koch, A.
Bibcode: 2017A&A...598A...5P
Altcode: 2016arXiv161006480P
The Gaia-ESO survey (GES) is now in its fifth and last year of
observations and has produced tens of thousands of high-quality spectra
of stars in all Milky Way components. This paper presents the strategy
behind the selection of astrophysical calibration targets, ensuring
that all GES results on radial velocities, atmospheric parameters,
and chemical abundance ratios will be both internally consistent and
easily comparable with other literature results, especially from
other large spectroscopic surveys and from Gaia. The calibration
of GES is particularly delicate because of (I) the large space of
parameters covered by its targets, ranging from dwarfs to giants,
from O to M stars; these targets have a large wide of metallicities
and also include fast rotators, emission line objects, and stars
affected by veiling; (II) the variety of observing setups, with
different wavelength ranges and resolution; and (III) the choice of
analyzing the data with many different state-of-the-art methods, each
stronger in a different region of the parameter space, which ensures
a better understanding of systematic uncertainties. An overview
of the GES calibration and homogenization strategy is also given,
along with some examples of the usage and results of calibrators in
GES iDR4, which is the fourth internal GES data release and will form
the basis of the next GES public data release. The agreement between
GES iDR4 recommended values and reference values for the calibrating
objects are very satisfactory. The average offsets and spreads are
generally compatible with the GES measurement errors, which in iDR4 data
already meet the requirements set by the main GES scientific goals. Based on data products from observations made with ESO Telescopes
at the La Silla Paranal Observatory under programme IDs 188.B-3002 and
193.B-0936.Full Table 2 is only available at the CDS via anonymous ftp
to http://cdsarc.u-strasbg.fr
(http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/598/A5
Title: The Galah Survey: Classification and Diagnostics with t-SNE
Reduction of Spectral Information
Authors: Traven, G.; Matijevič, G.; Zwitter, T.; Žerjal, M.; Kos, J.;
Asplund, M.; Bland-Hawthorn, J.; Casey, A. R.; De Silva, G.; Freeman,
K.; Lin, J.; Martell, S. L.; Schlesinger, K. J.; Sharma, S.; Simpson,
J. D.; Zucker, D. B.; Anguiano, B.; Da Costa, G.; Duong, L.; Horner,
J.; Hyde, E. A.; Kafle, P. R.; Munari, U.; Nataf, D.; Navin, C. A.;
Reid, W.; Ting, Y. -S.
Bibcode: 2017ApJS..228...24T
Altcode: 2016arXiv161202242T
Galah is an ongoing high-resolution spectroscopic survey with the goal
of disentangling the formation history of the Milky Way using the fossil
remnants of disrupted star formation sites that are now dispersed around
the Galaxy. It is targeting a randomly selected magnitude-limited
(V ≤ 14) sample of stars, with the goal of observing one million
objects. To date, 300,000 spectra have been obtained. Not all of them
are correctly processed by parameter estimation pipelines, and we need
to know about them. We present a semi-automated classification scheme
that identifies different types of peculiar spectral morphologies in an
effort to discover and flag potentially problematic spectra and thus
help to preserve the integrity of the survey results. To this end,
we employ the recently developed dimensionality reduction technique
t-SNE (t-distributed stochastic neighbor embedding), which enables
us to represent the complex spectral morphology in a two-dimensional
projection map while still preserving the properties of the local
neighborhoods of spectra. We find that the majority (178,483) of
the 209,533 Galah spectra considered in this study represents normal
single stars, whereas 31,050 peculiar and problematic spectra with very
diverse spectral features pertaining to 28,579 stars are distributed
into 10 classification categories: hot stars, cool metal-poor giants,
molecular absorption bands, binary stars, Hα/Hβ emission, Hα/Hβ
emission superimposed on absorption, Hα/Hβ P-Cygni, Hα/Hβ inverted
P-Cygni, lithium absorption, and problematic. Classified spectra with
supplementary information are presented in the catalog, indicating
candidates for follow-up observations and population studies of the
short-lived phases of stellar evolution.
Title: The GALAH survey: the data reduction pipeline
Authors: Kos, Janez; Lin, Jane; Zwitter, Tomaž; Žerjal, Maruška;
Sharma, Sanjib; Bland-Hawthorn, Joss; Asplund, Martin; Casey, Andrew
R.; De Silva, Gayandhi M.; Freeman, Ken C.; Martell, Sarah L.; Simpson,
Jeffrey D.; Schlesinger, Katharine J.; Zucker, Daniel; Anguiano,
Borja; Bacigalupo, Carlos; Bedding, Timothy R.; Betters, Christopher;
Da Costa, Gary; Duong, Ly; Hyde, Elaina; Ireland, Michael; Kafle,
Prajwal R.; Leon-Saval, Sergio; Lewis, Geraint F.; Munari, Ulisse;
Nataf, David; Stello, Dennis; Tinney, C. G.; Traven, Gregor; Watson,
Fred; Wittenmyer, Robert A.
Bibcode: 2017MNRAS.464.1259K
Altcode: 2016arXiv160804391K; 2016MNRAS.tmp.1183K
We present the data reduction procedures being used by the GALactic
Archeology with Hermes (GALAH) survey, carried out with the HERMES
fibre-fed, multi-object spectrograph on the 3.9-m Anglo-Australian
Telescope. GALAH is a unique survey, targeting 1 million stars brighter
than magnitude V = 14 at a resolution of 28 000 with a goal to measure
the abundances of 29 elements. Such a large number of high-resolution
spectra necessitate the development of a reduction pipeline optimized
for speed, accuracy, and consistency. We outline the design and
structure of the IRAF-based reduction pipeline that we developed,
specifically for GALAH, to produce fully calibrated spectra aimed
for subsequent stellar atmospheric parameter estimation. The pipeline
takes advantage of existing IRAF routines and other readily available
software so as to be simple to maintain, testable, and reliable. A
radial velocity and stellar atmospheric parameter estimator code is also
presented, which is used for further data analysis and yields a useful
verification of the reduction quality. We have used this estimator
to quantify the data quality of GALAH for fibre cross-talk level
(≲0.5 per cent) and scattered light (∼5 counts in a typical 20
min exposure), resolution across the field, sky spectrum properties,
wavelength solution reliability (better than 1 km s-1
accuracy), and radial velocity precision.
Title: The solar silicon abundance based on 3D non-LTE calculations
Authors: Amarsi, A. M.; Asplund, M.
Bibcode: 2017MNRAS.464..264A
Altcode: 2016arXiv160907283A
We present 3D non-local thermodynamic equilibrium (non-LTE) radiative
transfer calculations for silicon in the solar photosphere, using an
extensive model atom that includes recent, realistic neutral hydrogen
collisional cross-sections. We find that photon losses in the Si I
lines give rise to slightly negative non-LTE abundance corrections
of the order of -0.01 dex. We infer a 3D non-LTE-based solar silicon
abundance of lg ɛ_{Si{⊙}}=7.51 dex. With silicon commonly chosen
to be the anchor between the photospheric and meteoritic abundances,
we find that the meteoritic abundance scale remains unchanged compared
with the Asplund et al. and Lodders et al. results.
Title: The Solar Twin Planet Search. V. Close-in, low-mass planet
candidates and evidence of planet accretion in the solar twin
HIP 68468
Authors: Meléndez, Jorge; Bedell, Megan; Bean, Jacob L.; Ramírez,
Iván; Asplund, Martin; Dreizler, Stefan; Yan, Hong-Liang; Shi,
Jian-Rong; Lind, Karin; Ferraz-Mello, Sylvio; Galarza, Jhon Yana; dos
Santos, Leonardo; Spina, Lorenzo; Maia, Marcelo Tucci; Alves-Brito,
Alan; Monroe, TalaWanda; Casagrande, Luca
Bibcode: 2017A&A...597A..34M
Altcode: 2016arXiv161009067M; 2016A&A...597A..34M
Context. More than two thousand exoplanets have been discovered to
date. Of these, only a small fraction have been detected around solar
twins, which are key stars because we can obtain accurate elemental
abundances especially for them, which is crucial for studying the
planet-star chemical connection with the highest precision.
Aims: We aim to use solar twins to characterise the relationship between
planet architecture and stellar chemical composition.
Methods:
We obtained high-precision (1 m s-1) radial velocities
with the HARPS spectrograph on the ESO 3.6 m telescope at La Silla
Observatory and determined precise stellar elemental abundances ( 0.01
dex) using spectra obtained with the MIKE spectrograph on the Magellan
6.5 m telescope.
Results: Our data indicate the presence of a
planet with a minimum mass of 26 ± 4 Earth masses around the solar
twin HIP 68468. The planet is more massive than Neptune (17 Earth
masses), but unlike the distant Neptune in our solar system (30 AU),
HIP 68468c is close-in, with a semi-major axis of 0.66 AU, similar to
that of Venus. The data also suggest the presence of a super-Earth with
a minimum mass of 2.9 ± 0.8 Earth masses at 0.03 AU; if the planet is
confirmed, it will be the fifth least massive radial velocity planet
candidate discovery to date and the first super-Earth around a solar
twin. Both isochrones (5.9 ± 0.4 Gyr) and the abundance ratio [Y/Mg]
(6.4 ± 0.8 Gyr) indicate an age of about 6 billion years. The star
is enhanced in refractory elements when compared to the Sun, and the
refractory enrichment is even stronger after corrections for Galactic
chemical evolution. We determined a nonlocal thermodynamic equilibrium
Li abundance of 1.52 ± 0.03 dex, which is four times higher than
what would be expected for the age of HIP 68468. The older age is
also supported by the low log () (-5.05) and low jitter (<1 m
s-1). Engulfment of a rocky planet of 6 Earth masses can
explain the enhancement in both lithium and the refractory elements.
Conclusions: The super-Neptune planet candidate is too massive for in
situ formation, and therefore its current location is most likely the
result of planet migration that could also have driven other planets
towards its host star, enhancing thus the abundance of lithium and
refractory elements in HIP 68468. The intriguing evidence of planet
accretion warrants further observations to verify the existence of
the planets that are indicated by our data and to better constrain
the nature of the planetary system around this unique star.
Title: 3D NLTE analysis of the most iron-deficient star, SMSS0313-6708
Authors: Nordlander, T.; Amarsi, A. M.; Lind, K.; Asplund, M.; Barklem,
P. S.; Casey, A. R.; Collet, R.; Leenaarts, J.
Bibcode: 2017A&A...597A...6N
Altcode: 2016arXiv160907416N; 2016A&A...597A...6N
Context. Models of star formation in the early universe require
a detailed understanding of accretion, fragmentation and radiative
feedback in metal-free molecular clouds. Different simulations predict
different initial mass functions of the first stars, ranging from
predominantly low-mass (0.1-10 M⊙), to massive (10-100
M⊙), or even supermassive (100-1000 M⊙). The
mass distribution of the first stars should lead to unique chemical
imprints on the low-mass second and later generation metal-poor
stars still in existence. The chemical composition of SMSS0313-6708,
which has the lowest abundances of Ca and Fe of any star known,
indicates it was enriched by a single massive supernova.
Aims:
The photospheres of metal-poor stars are relatively transparent in
the UV, which may lead to large three-dimensional (3D) effects as
well as departures from local thermodynamical equilibrium (LTE),
even for weak spectral lines. If 3D effects and departures from LTE
(NLTE) are ignored or treated incorrectly, errors in the inferred
abundances may significantly bias the inferred properties of the
polluting supernovae. We redetermine the chemical composition of
SMSS0313-6708by means of the most realistic methods available, and
compare the results to predicted supernova yields.
Methods:
A 3D hydrodynamical Staggermodel atmosphere and 3D NLTE radiative
transfer were applied to obtain accurate abundances for Li, Na, Mg, Al,
Ca and Fe. The model atoms employ realistic collisional rates, with
no calibrated free parameters.
Results: We find significantly
higher abundances in 3D NLTE than 1D LTE by 0.8 dex for Fe, and 0.5
dex for Mg, Al and Ca, while Li and Na are unaffected to within 0.03
dex. In particular, our upper limit for [Fe/H] is now a factor ten
larger, at [Fe/H] < -6.53 (3σ), than previous estimates based on
⟨ 3D ⟩NLTE (I.e., using averaged 3D models). This higher estimate
is due to a conservative upper limit estimation, updated NLTE data,
and 3D-⟨ 3D ⟩NLTE differences, all of which lead to a higher
abundance determination.
Conclusions: We find that supernova
yields for models in a wide range of progenitor masses reproduce the
revised chemical composition. In addition to massive progenitors of
20-60 M⊙ exploding with low energies (1-2 B, where 1
B = 1051 erg), we also find good fits for progenitors of
10 M⊙, with very low explosion energies (<1 B). We
cannot reconcile the new abundances with supernovae or hypernovae with
explosion energies above 2.5 B, nor with pair-instability supernovae.
Title: Measuring stellar granulation during planet transits
Authors: Chiavassa, A.; Caldas, A.; Selsis, F.; Leconte, J.; Von Paris,
P.; Bordé, P.; Magic, Z.; Collet, R.; Asplund, M.
Bibcode: 2017A&A...597A..94C
Altcode: 2016arXiv160908966C
Context. Stellar activity and convection-related surface structures
might cause bias in planet detection and characterization that use
these transits. Surface convection simulations help to quantify the
granulation signal.
Aims: We used realistic three-dimensional
(3D) radiative hydrodynamical (RHD) simulations from the STAGGER grid
and synthetic images computed with the radiative transfer code OPTIM3D
to model the transits of three prototype planets: a hot Jupiter,
a hot Neptune, and a terrestrial planet.
Methods: We computed
intensity maps from RHD simulations of the Sun and a K-dwarf star at
different wavelength bands from optical to far-infrared that cover
the range of several ground- and space-based telescopes which observe
exoplanet transits. We modeled the transit using synthetic stellar-disk
images obtained with a spherical-tile imaging method and emulated the
temporal variation of the granulation intensity generating random
images covering a granulation time-series of 13.3 h. We measured
the contribution of the stellar granulation on the light curves
during the planet transit.
Results: We identified two types of
granulation noise that act simultaneously during the planet transit:
(i) the intrinsic change in the granulation pattern with timescale
(e.g., 10 min for solar-type stars assumed in this work) is smaller
than the usual planet transit (~hours as in our prototype cases); and
(ii) the fact that the transiting planet occults isolated regions of
the photosphere that differ in local surface brightness as a result
of convective-related surface structures. First, we showed that
our modeling approach returns granulation timescale fluctuations
that are comparable with what has been observed for the Sun. Then,
our statistical approach shows that the granulation pattern of solar
and K-dwarf-type stars have a non-negligible effect of the light curve
depth during the transit, and, consequentially on the determination of
the planet transit parameters such as the planet radius (up to 0.90%
and ~0.47% for terrestrial and gaseous planets, respectively). We also
showed that larger (or smaller) orbital inclination angles with respect
to values corresponding to transit at the stellar center display a
shallower transit depth and longer ingress and egress times, but also
granulation fluctuations that are correlated to the center-to-limb
variation: they increase (or decrease) the value of the inclination,
which amplifies the fluctuations. The granulation noise appears to be
correlated among the different wavelength ranges either in the visible
or in the infrared regions.
Conclusions: The prospects for planet
detection and characterization with transiting methods are excellent
with access to large amounts of data for stars. The granulation has
to be considered as an intrinsic uncertainty (as a result of stellar
variability) on the precise measurements of exoplanet transits of
planets. The full characterization of the granulation is essential for
determining the degree of uncertainty on the planet parameters. In this
context, the use of 3D RHD simulations is important to measure the
convection-related fluctuations. This can be achieved by performing
precise and continuous observations of stellar photometry and radial
velocity, as we explained with RHD simulations, before, after, and
during the transit periods.
Title: Non-LTE line formation of Fe in late-type stars - III. 3D
non-LTE analysis of metal-poor stars
Authors: Amarsi, A. M.; Lind, K.; Asplund, M.; Barklem, P. S.;
Collet, R.
Bibcode: 2016MNRAS.463.1518A
Altcode: 2016arXiv160806390A; 2016MNRAS.tmp.1203A
As one of the most important elements in astronomy, iron abundance
determinations need to be as accurate as possible. We investigate the
accuracy of spectroscopic iron abundance analyses using archetypal
metal-poor stars. We perform detailed 3D non-LTE radiative transfer
calculations based on 3D hydrodynamic STAGGER model atmospheres, and
employ a new model atom that includes new quantum-mechanical neutral
hydrogen collisional rate coefficients. With the exception of the
red giant HD122563, we find that the 3D non-LTE models achieve Fe
I/Fe II excitation and ionization balance as well as not having any
trends with equivalent width to within modelling uncertainties of
0.05 dex, all without having to invoke any microturbulent broadening;
for HD122563 we predict that the current best parallax-based surface
gravity is overestimated by 0.5 dex. Using a 3D non-LTE analysis, we
infer iron abundances from the 3D model atmospheres that are roughly
0.1 dex higher than corresponding abundances from 1D MARCS model
atmospheres; these differences go in the same direction as the non-LTE
effects themselves. We make available grids of departure coefficients,
equivalent widths and abundance corrections, calculated on 1D MARCS
model atmospheres and horizontally and temporally averaged 3D STAGGER
model atmospheres.
Title: The chemical compositions of solar twins in the open cluster
M67
Authors: Liu, F.; Asplund, M.; Yong, D.; Meléndez, J.; Ramírez,
I.; Karakas, A. I.; Carlos, M.; Marino, A. F.
Bibcode: 2016MNRAS.463..696L
Altcode: 2016MNRAS.tmp.1165L; 2016arXiv160803788L
Stars in open clusters are expected to share an identical abundance
pattern. Establishing the level of chemical homogeneity in a given
open cluster deserves further study as it is the basis of the concept
of chemical tagging to unravel the history of the Milky Way. M67 is
particularly interesting given its solar metallicity and age as well as
being a dense cluster environment. We conducted a strictly line-by-line
differential chemical abundance analysis of two solar twins in M67:
M67-1194 and M67-1315. Stellar atmospheric parameters and elemental
abundances were obtained with high precision using Keck/High Resolution
Echelle Spectrometer spectra. M67-1194 is essentially identical to the
Sun in terms of its stellar parameters. M67-1315 is warmer than M67-1194
by ≈150 K as well as slightly more metal-poor than M67-1194 by ≈0.05
dex. M67-1194 is also found to have identical chemical composition to
the Sun, confirming its solar-twin nature. The abundance ratios [X/Fe]
of M67-1315 are similar to the solar abundances for elements with atomic
number Z ≤ 30, while most neutron-capture elements are enriched by
≈0.05 dex, which might be attributed to enrichment from a mixture of
asymptotic giant branch ejecta and r-process material. The distinct
chemical abundances for the neutron-capture elements in M67-1315 and
the lower metallicity of this star compared to M67-1194, indicate that
the stars in M67 are likely not chemically homogeneous. This poses
a challenge for the concept of chemical tagging since it is based on
the assumption of stars forming in the same star-forming aggregate.
Title: Implications of solar wind measurements for solar models
and composition
Authors: Serenelli, Aldo; Scott, Pat; Villante, Francesco L.;
Vincent, Aaron C.; Asplund, Martin; Basu, Sarbani; Grevesse, Nicolas;
Peña-Garay, Carlos
Bibcode: 2016MNRAS.463....2S
Altcode: 2016arXiv160405318S; 2016MNRAS.tmp.1051S
We critically examine recent claims of a high solar metallicity by von
Steiger & Zurbuchen (2016, vSZ16) based on in situ measurements
of the solar wind, rather than the standard spectroscopically inferred
abundances (Asplund et al. 2009, hereafter AGSS09). We test the claim
by Vagnozzi et al. (2016) that a composition based on the solar wind
enables one to construct a standard solar model in agreement with
helioseismological observations and thus solve the decades-old solar
modelling problem. We show that, although some helioseismological
observables are improved compared to models computed with spectroscopic
abundances, most are in fact worse. The high abundance of refractory
elements leads to an overproduction of neutrinos, with a predicted
8B flux that is nearly twice its observed value, and
7Be and CNO fluxes that are experimentally ruled out at high
confidence. A combined likelihood analysis shows that models using the
vSZ16 abundances are worse than AGSS09 despite a higher metallicity. We
also present astrophysical and spectroscopic arguments showing the vSZ16
composition to be an implausible representation of the solar interior,
identifying the first ionization potential effect in the outer solar
atmosphere and wind as the likely culprit.
Title: VizieR Online Data Catalog: Gaia-ESO Survey iDR4 calibrators
(Pancino+, 2017)
Authors: Pancino, E.; Lardo, C.; Altavilla, G.; Marinoni, S.; Ragaini,
S.; Cocozza, G.; Bellazzini, M.; Sabbi, E.; Zoccali, M.; Donati,
P.; Heiter, U.; Koposov, S. E.; Blomme, R.; Morel, T.; Simon-Diaz,
S.; Lobel, A.; Soubiran, C.; Montalban, J.; Valentini, M.; Casey,
A. R.; Blanco-Cuaresma, S.; Jofre, P.; Worley, C. C.; Magrini, L.;
Hourihane, A.; Francois, P.; Feltzing, S.; Gilmore, G.; Randich, S.;
Asplund, M.; Bonifacio, P.; Drew, J. E.; Jeffries, R. D.; Micela,
G.; Vallenari, A.; Alfaro, E. J.; Allende Prieto, C.; Babusiaux,
C.; Bensby, T.; Bragaglia, A.; Flaccomio, E.; Hambly, N.; Korn,
A. J.; Lanzafame, A. C.; Smiljanic, R.; van Eck, S.; Walton, N. A.;
Bayo, A.; Carraro, G.; Costado, M. T.; Damiani, F.; Edvardsson, B.;
Franciosini, E.; Frasca, A.; Lewis, J.; Monaco, L.; Morbidelli, L.;
Prisinzano, L.; Sacco, G. G.; Sbordone, L.; Sousa, S. G.; Zaggia,
S.; Koch, A.; Gaia-ESO Collaboration
Bibcode: 2016yCat..35980005P
Altcode:
List of GES iDR4 calibrators. It can be used to select the iDR4
calibrators from the upcoming ESO Phase 3 public release. The columns
contain: the GES unique identifier of each star (the CName), based on
the object sexagesimal coordinates; the calibration type, which can
be GC or OC for clusters, RV for radial velocity standards, BM for
benchmark stars, or CR for CoRoT targets; the field name; and the
2MASS J and K magnitudes, when available. (1 data file).
Title: Nucleosynthetic history of elements in the Galactic
disk. [X/Fe]-age relations from high-precision spectroscopy
Authors: Spina, L.; Meléndez, J.; Karakas, A. I.; Ramírez, I.;
Monroe, T. R.; Asplund, M.; Yong, D.
Bibcode: 2016A&A...593A.125S
Altcode: 2016arXiv160604842S
Context. The chemical composition of stars is intimately linked to the
formation and evolution of the Galaxy.
Aims: We aim to trace
the chemical evolution of the Galactic disk through the inspection of
the [X/Fe]-age relations of 24 species from C to Eu.
Methods:
Using high-resolution and high signal-to-noise UVES spectra of
nine solar twins, we obtained precise estimates of stellar ages and
chemical abundances. These determinations have been integrated with
additional accurate age and abundance determinations from recent
spectroscopic studies of solar twins existing in the literature,
comprising superb abundances with 0.01 dex precision. Based on this
data set, we outlined the [X/Fe]-age relations over a time interval of
10 Gyr.
Results: We present the [X/Fe] - age relations for 24
elements (C, O, Na, Mg, Al, Si, S, K, Ca, Sc, Ti, V, Cr, Mn, Co, Ni,
Cu, Zn, Y, Ba, La, Ce, Nd, and Eu). Each different class of elements
showed a distinct evolution with time that relies on the different
characteristics, rates, and timescales of the nucleosynthesis sites from
which they are produced. The α-elements are characterized by a [X/Fe]
decrease with time. Strikingly, the opposite behavior is observed for
Ca. The iron-peak elements show an early [X/Fe] increase followed by
a decrease towards the youngest stars. The [X/Fe] for the n-capture
elements decrease with age. We also found that both [Mg/Y] and [Al/Y]
are precise stellar clocks, with [Al/Y] showing the steepest dependence
on age.
Conclusions: Knowledge of the [X/Fe]-age relations
is a gold mine from which we can achieve a great understanding of
the processes that governed the formation and evolution of the Milky
Way. Through the reverse engineering of these relations we will be
able to put strong constraints on the nature of the stellar formation
history, the SNe rates, the stellar yields, and the variety of the
SNe progenitors. Based on observations obtained at the ESO VLT
at Paranal Observatory (Observing program 083.D-0871).
Title: The Gaia-ESO Survey: Hydrogen lines in red giants directly
trace stellar mass
Authors: Bergemann, Maria; Serenelli, Aldo; Schönrich, Ralph; Ruchti,
Greg; Korn, Andreas; Hekker, Saskia; Kovalev, Mikhail; Mashonkina,
Lyudmila; Gilmore, Gerry; Randich, Sofia; Asplund, Martin; Rix,
Hans-Walter; Casey, Andrew R.; Jofre, Paula; Pancino, Elena;
Recio-Blanco, Alejandra; de Laverny, Patrick; Smiljanic, Rodolfo;
Tautvaisiene, Grazina; Bayo, Amelia; Lewis, Jim; Koposov, Sergey;
Hourihane, Anna; Worley, Clare; Morbidelli, Lorenzo; Franciosini,
Elena; Sacco, Germano; Magrini, Laura; Damiani, Francesco;
Bestenlehner, Joachim M.
Bibcode: 2016A&A...594A.120B
Altcode: 2016arXiv160605661B
Red giant stars are perhaps the most important type of stars for
Galactic and extra-galactic archaeology: they are luminous, occur in
all stellar populations, and their surface temperatures allow precise
abundance determinations for many different chemical elements. Yet,
the full star formation and enrichment history of a galaxy can be
traced directly only if two key observables can be determined for large
stellar samples: age and chemical composition. While spectroscopy is a
powerful method to analyse the detailed abundances of stars, stellar
ages are the missing link in the chain, since they are not a direct
observable. However, spectroscopy should be able to estimate stellar
masses, which for red giants directly infer ages provided their chemical
composition is known. Here we establish a new empirical relation between
the shape of the hydrogen line in the observed spectra of red giants
and stellar mass determined from asteroseismology. The relation allows
determining stellar masses and ages with an accuracy of 10-15%. The
method can be used with confidence for stars in the following range
of stellar parameters: 4000 < Teff < 5000 K, 0.5
< log g< 3.5, -2.0 < [Fe/H] < 0.3, and luminosities log
L/LSun < 2.5. Our analysis provides observational evidence
that the Hα spectral characteristics of red giant stars
are tightly correlated with their mass and therefore their age. We
also show that the method samples well all stellar populations with
ages above 1 Gyr. Targeting bright giants, the method allows obtaining
simultaneous age and chemical abundance information far deeper than
would be possible with asteroseismology, extending the possible survey
volume to remote regions of the Milky Way and even to neighbouring
galaxies such as Andromeda or the Magellanic Clouds even with current
instrumentation, such as the VLT and Keck facilities.
Title: VizieR Online Data Catalog: Kepler-10 chemical composition
(Liu+, 2016)
Authors: Liu, F.; Yong, D.; Asplund, M.; Ramirez, I.; Melendez,
J.; Gustafsson, B.; Howes, L. M.; Roederer, I. U.; Lambert, D. L.;
Bensby, T.
Bibcode: 2016yCat..74562636L
Altcode:
We obtained high resolution and high SNR spectra with the
Canada-France-Hawaii Telescope (CFHT), the Hobby-Eberly Telescope (HET)
and the Magellan Clay Telescope. We observed Kepler-10 with the
Echelle SpectroPolarimetric Device for the Observation of Stars at
the CFHT during 2013 June. The spectral revolving power is 68000 and
the spectral range is 3800-8900Å. We also observed Kepler-10
with the High Resolution Spectrograph (HRS) on the HET at McDonald
Observatory during 2011 May. A total integration time of 6.8h was
needed to achieve SNR>350 per pixel. The spectrum has a spectral
resolving power of 60000 and covers 4100-7800Å, with a gap of about
100Å around 6000Å. (4 data files).
Title: VizieR Online Data Catalog: GALAH observational overview
(Martell+, 2017)
Authors: Martell, S. L.; Sharma, S.; Buder, S.; Duong, L.; Schlesinger,
K. J.; Simpson, J.; Lind, K.; Ness, M.; Marshall, J. P.; Asplund, M.;
Bland-Hawthorn, J.; Casey, A. R.; de Silva, G.; Freeman, K. C.; Kos,
J.; Lin, J.; Zucker, D. B.; Zwitter, T.; Anguiano, B.; Bacigalupo,
C.; Carollo, D.; Casagrande, L.; da Costa, G. S.; Horner, J.; Huber,
D.; Hyde, E. A.; Kafle, P. R.; Lewis, G. F.; Nataf, D.; Navin, C. A.;
Stello, D.; Tinney, C. G.; Watson, F. G.; Wittenmyer, R.
Bibcode: 2016yCat..74653203M
Altcode:
Identifiers, positions, derived stellar parameters, radial velocities,
distance moduli and reddenings for stars from the Tycho-2 catalogue
observed by the GALAH Survey. (1 data file).
Title: Nominal Values for Selected Solar and Planetary Quantities:
IAU 2015 Resolution B3
Authors: Prša, Andrej; Harmanec, Petr; Torres, Guillermo; Mamajek,
Eric; Asplund, Martin; Capitaine, Nicole; Christensen-Dalsgaard,
Jørgen; Depagne, Éric; Haberreiter, Margit; Hekker, Saskia; Hilton,
James; Kopp, Greg; Kostov, Veselin; Kurtz, Donald W.; Laskar, Jacques;
Mason, Brian D.; Milone, Eugene F.; Montgomery, Michele; Richards,
Mercedes; Schmutz, Werner; Schou, Jesper; Stewart, Susan G.
Bibcode: 2016AJ....152...41P
Altcode: 2016arXiv160509788P
In this brief communication we provide the rationale for and the
outcome of the International Astronomical Union (IAU) resolution
vote at the XXIXth General Assembly in Honolulu, Hawaii, in 2015,
on recommended nominal conversion constants for selected solar and
planetary properties. The problem addressed by the resolution is a lack
of established conversion constants between solar and planetary values
and SI units: a missing standard has caused a proliferation of solar
values (e.g., solar radius, solar irradiance, solar luminosity, solar
effective temperature, and solar mass parameter) in the literature,
with cited solar values typically based on best estimates at the time
of paper writing. As precision of observations increases, a set of
consistent values becomes increasingly important. To address this, an
IAU Working Group on Nominal Units for Stellar and Planetary Astronomy
formed in 2011, uniting experts from the solar, stellar, planetary,
exoplanetary, and fundamental astronomy, as well as from general
standards fields to converge on optimal values for nominal conversion
constants. The effort resulted in the IAU 2015 Resolution B3, passed at
the IAU General Assembly by a large majority. The resolution recommends
the use of nominal solar and planetary values, which are by definition
exact and are expressed in SI units. These nominal values should be
understood as conversion factors only, not as the true solar/planetary
properties or current best estimates. Authors and journal editors are
urged to join in using the standard values set forth by this resolution
in future work and publications to help minimize further confusion.
Title: The Solar Twin Planet Search. IV. The Sun as a typical rotator
and evidence for a new rotational braking law for Sun-like stars
Authors: dos Santos, Leonardo A.; Meléndez, Jorge; do Nascimento,
José-Dias; Bedell, Megan; Ramírez, Iván; Bean, Jacob L.; Asplund,
Martin; Spina, Lorenzo; Dreizler, Stefan; Alves-Brito, Alan;
Casagrande, Luca
Bibcode: 2016A&A...592A.156D
Altcode: 2016arXiv160606214D
Context. It is still unclear how common the Sun is when compared to
other similar stars in regards to some of its physical properties,
such as rotation. Considering that gyrochronology relations are
widely used today to estimate ages of stars in the main sequence,
and that the Sun is used to calibrate it, it is crucial to assess
whether these procedures are acceptable.
Aims: We analyze the
rotational velocities, limited by the unknown rotation axis inclination
angle, of an unprecedented large sample of solar twins to study the
rotational evolution of Sun-like stars, and assess whether the Sun is a
typical rotator.
Methods: We used high-resolution (R = 115 000)
spectra obtained with the HARPS spectrograph and the 3.6 m telescope
at La Silla Observatory. The projected rotational velocities for 81
solar twins were estimated by line profile fitting with synthetic
spectra. Macroturbulence velocities were inferred from a prescription
that accurately reflects their dependence with effective temperature
and luminosity of the stars.
Results: Our sample of solar twins
include some spectroscopic binaries with enhanced rotational velocities,
and we do not find any nonspectroscopic binaries with unusually high
rotation velocities. We verified that the Sun does not have a peculiar
rotation, but the solar twins exhibit rotational velocities that depart
from the Skumanich relation.
Conclusions: The Sun is a regular
rotator when compared to solar twins with a similar age. Additionally,
we obtain a rotational braking law that better describes the stars in
our sample (v ∝ t-0.6) in contrast to previous, often-used
scalings. Based on observations collected at the European
Organisation for Astronomical Research in the Southern Hemisphere under
ESO programs 188.C-0265, 183.D-0729, 292.C-5004, 077.C-0364, 072.C-0488,
092.C-0721, 093.C-0409, 183.C-0972, 192.C-0852, 091.C-0936, 089.C-0732,
091.C-0034, 076.C-0155, 185.D-0056, 074.C-0364, 075.C-0332, 089.C-0415,
60.A-9036, 075.C-0202, 192.C-0224, 090.C-0421 and 088.C-0323.Full
Table 3 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/592/A156
Title: VizieR Online Data Catalog: The Solar Twin Planet
Search. IV. (dos Santos+, 2016)
Authors: Dos Santos, L. A.; Melendez, J.; Do Nascimento, J. -D. Jr;
Bedell, M.; Ramirez, I.; Bean, J. L.; Asplund, M.; Spina, L.; Dreizler,
S.; Alves-Brito, A.; Casagrande, L.
Bibcode: 2016yCat..35920156D
Altcode:
Ages, the measured projected rotational velocities (vsini) and stellar
parameters of the 81 solar twins and the Sun. The ages of all solar
twins and stellar parameters for HIP68468 were obtained by Tucci Maia et
al. (2016A&A...590A..32T). Stellar parameters for the other solar
twins were obtained by Ramirez et al. (2014A&A...572A..48R). The
vsini were measured by line profile fitting using red spectra from
HARPS (R=115000). Macroturbulence velocities were inferred from the
scaling Eq. 2 in our study. (1 data file).
Title: The EMBLA survey - metal-poor stars in the Galactic bulge
Authors: Howes, Louise M.; Asplund, Martin; Keller, Stefan C.; Casey,
Andrew R.; Yong, David; Lind, Karin; Frebel, Anna; Hays, Austin;
Alves-Brito, Alan; Bessell, Michael S.; Casagrande, Luca; Marino,
Anna F.; Nataf, David M.; Owen, Christopher I.; Da Costa, Gary S.;
Schmidt, Brian P.; Tisserand, Patrick
Bibcode: 2016MNRAS.460..884H
Altcode: 2016arXiv160407834H; 2016MNRAS.tmp..776H
Cosmological models predict the oldest stars in the Galaxy should be
found closest to the centre of the potential well, in the bulge. The
Extremely Metal-poor BuLge stars with AAOmega survey (EMBLA)
successfully searched for these old, metal-poor stars by making
use of the distinctive SkyMapper photometric filters to discover
candidate metal-poor stars in the bulge. Their metal-poor nature was
then confirmed using the AAOmega spectrograph on the Anglo-Australian
Telescope. Here we present an abundance analysis of 10 bulge stars with
-2.8 < [Fe/H] < -1.7 from MIKE/Magellan observations, in total
determining the abundances of 22 elements. Combining these results with
our previous high-resolution data taken as part of the Gaia-ESO Survey,
we have started to put together a picture of the chemical and kinematic
nature of the most metal-poor stars in the bulge. The currently
available kinematic data are consistent with the stars belonging to the
bulge, although more accurate measurements are needed to constrain the
stars' orbits. The chemistry of these bulge stars deviates from that
found in halo stars of the same metallicity. Two notable differences
are the absence of carbon-enhanced metal-poor bulge stars, and the
α element abundances exhibit a large intrinsic scatter and include
stars which are underabundant in these typically enhanced elements.
Title: GRACES observations of young [α/Fe]-rich stars
Authors: Yong, David; Casagrande, Luca; Venn, Kim A.; Chené,
André-Nicolas; Keown, Jared; Malo, Lison; Martioli, Eder; Alves-Brito,
Alan; Asplund, Martin; Dotter, Aaron; Martell, Sarah L.; Meléndez,
Jorge; Schlesinger, Katharine J.
Bibcode: 2016MNRAS.459..487Y
Altcode: 2016MNRAS.tmp..463Y; 2016arXiv160307034Y
We measure chemical abundance ratios and radial velocities in four
massive (I.e. young) [α/Fe]-rich red giant stars using high-resolution
high-S/N spectra from ESPaDOnS fed by Gemini-GRACES. Our differential
analysis ensures that our chemical abundances are on the same scale
as the Alves-Brito et al. (2010) study of bulge, thin, and thick disc
red giants. We confirm that the program stars have enhanced [α/Fe]
ratios and are slightly metal poor. Aside from lithium enrichment in
one object, the program stars exhibit no chemical abundance anomalies
when compared to giant stars of similar metallicity throughout the
Galaxy. This includes the elements Li, O, Si, Ca, Ti, Cr, Ni, Cu,
Ba, La, and Eu. Therefore, there are no obvious chemical signatures
that can help to reveal the origin of these unusual stars. While our
new observations show that only one star (not the Li-rich object)
exhibits a radial velocity variation, simulations indicate that we
cannot exclude the possibility that all four could be binaries. In
addition, we find that two (possibly three) stars show evidence for
an infrared excess, indicative of a debris disc. This is consistent
with these young [α/Fe]-rich stars being evolved blue stragglers,
suggesting their apparent young age is a consequence of a merger or
mass transfer. We would expect a binary fraction of ∼50 per cent or
greater for the entire sample of these stars, but the signs of the
circumbinary disc may have been lost since these features can have
short time-scales. Radial velocity monitoring is needed to confirm
the blue straggler origin.
Title: The Detailed Science Case for the Maunakea Spectroscopic
Explorer: the Composition and Dynamics of the Faint Universe
Authors: McConnachie, Alan; Babusiaux, Carine; Balogh, Michael; Driver,
Simon; Côté, Pat; Courtois, Helene; Davies, Luke; Ferrarese, Laura;
Gallagher, Sarah; Ibata, Rodrigo; Martin, Nicolas; Robotham, Aaron;
Venn, Kim; Villaver, Eva; Bovy, Jo; Boselli, Alessandro; Colless,
Matthew; Comparat, Johan; Denny, Kelly; Duc, Pierre-Alain; Ellison,
Sara; de Grijs, Richard; Fernandez-Lorenzo, Mirian; Freeman, Ken;
Guhathakurta, Raja; Hall, Patrick; Hopkins, Andrew; Hudson, Mike;
Johnson, Andrew; Kaiser, Nick; Koda, Jun; Konstantopoulos, Iraklis;
Koshy, George; Lee, Khee-Gan; Nusser, Adi; Pancoast, Anna; Peng, Eric;
Peroux, Celine; Petitjean, Patrick; Pichon, Christophe; Poggianti,
Bianca; Schmid, Carlo; Shastri, Prajval; Shen, Yue; Willot, Chris;
Croom, Scott; Lallement, Rosine; Schimd, Carlo; Smith, Dan; Walker,
Matthew; Willis, Jon; Colless, Alessandro Bosselli Matthew; Goswami,
Aruna; Jarvis, Matt; Jullo, Eric; Kneib, Jean-Paul; Konstantopoloulous,
Iraklis; Newman, Jeff; Richard, Johan; Sutaria, Firoza; Taylor,
Edwar; van Waerbeke, Ludovic; Battaglia, Giuseppina; Hall, Pat;
Haywood, Misha; Sakari, Charli; Schmid, Carlo; Seibert, Arnaud;
Thirupathi, Sivarani; Wang, Yuting; Wang, Yiping; Babas, Ferdinand;
Bauman, Steve; Caffau, Elisabetta; Laychak, Mary Beth; Crampton,
David; Devost, Daniel; Flagey, Nicolas; Han, Zhanwen; Higgs, Clare;
Hill, Vanessa; Ho, Kevin; Isani, Sidik; Mignot, Shan; Murowinski,
Rick; Pandey, Gajendra; Salmon, Derrick; Siebert, Arnaud; Simons,
Doug; Starkenburg, Else; Szeto, Kei; Tully, Brent; Vermeulen, Tom;
Withington, Kanoa; Arimoto, Nobuo; Asplund, Martin; Aussel, Herve;
Bannister, Michele; Bhatt, Harish; Bhargavi, SS; Blakeslee, John;
Bland-Hawthorn, Joss; Bullock, James; Burgarella, Denis; Chang,
Tzu-Ching; Cole, Andrew; Cooke, Jeff; Cooper, Andrew; Di Matteo, Paola;
Favole, Ginevra; Flores, Hector; Gaensler, Bryan; Garnavich, Peter;
Gilbert, Karoline; Gonzalez-Delgado, Rosa; Guhathakurta, Puragra;
Hasinger, Guenther; Herwig, Falk; Hwang, Narae; Jablonka, Pascale;
Jarvis, Matthew; Kamath, Umanath; Kewley, Lisa; Le Borgne, Damien;
Lewis, Geraint; Lupton, Robert; Martell, Sarah; Mateo, Mario; Mena,
Olga; Nataf, David; Newman, Jeffrey; Pérez, Enrique; Prada, Francisco;
Puech, Mathieu; Recio-Blanco, Alejandra; Robin, Annie; Saunders, Will;
Smith, Daniel; Stalin, C. S.; Tao, Charling; Thanjuvur, Karun; Tresse,
Laurence; van Waerbeke, Ludo; Wang, Jian-Min; Yong, David; Zhao,
Gongbo; Boisse, Patrick; Bolton, James; Bonifacio, Piercarlo; Bouchy,
Francois; Cowie, Len; Cunha, Katia; Deleuil, Magali; de Mooij, Ernst;
Dufour, Patrick; Foucaud, Sebastien; Glazebrook, Karl; Hutchings,
John; Kobayashi, Chiaki; Kudritzki, Rolf-Peter; Li, Yang-Shyang;
Lin, Lihwai; Lin, Yen-Ting; Makler, Martin; Narita, Norio; Park,
Changbom; Ransom, Ryan; Ravindranath, Swara; Eswar Reddy, Bacham;
Sawicki, Marcin; Simard, Luc; Srianand, Raghunathan; Storchi-Bergmann,
Thaisa; Umetsu, Keiichi; Wang, Ting-Gui; Woo, Jong-Hak; Wu, Xue-Bing
Bibcode: 2016arXiv160600043M
Altcode:
MSE is an 11.25m aperture observatory with a 1.5 square degree field of
view that will be fully dedicated to multi-object spectroscopy. More
than 3200 fibres will feed spectrographs operating at low (R ~ 2000 -
3500) and moderate (R ~ 6000) spectral resolution, and approximately
1000 fibers will feed spectrographs operating at high (R ~ 40000)
resolution. MSE is designed to enable transformational science in areas
as diverse as tomographic mapping of the interstellar and intergalactic
media; the in-situ chemical tagging of thick disk and halo stars;
connecting galaxies to their large scale structure; measuring the mass
functions of cold dark matter sub-halos in galaxy and cluster-scale
hosts; reverberation mapping of supermassive black holes in quasars;
next generation cosmological surveys using redshift space distortions
and peculiar velocities. MSE is an essential follow-up facility to
current and next generations of multi-wavelength imaging surveys,
including LSST, Gaia, Euclid, WFIRST, PLATO, and the SKA, and is
designed to complement and go beyond the science goals of other planned
and current spectroscopic capabilities like VISTA/4MOST, WHT/WEAVE,
AAT/HERMES and Subaru/PFS. It is an ideal feeder facility for E-ELT, TMT
and GMT, and provides the missing link between wide field imaging and
small field precision astronomy. MSE is optimized for high throughput,
high signal-to-noise observations of the faintest sources in the
Universe with high quality calibration and stability being ensured
through the dedicated operational mode of the observatory. (abridged)
Title: The Solar Twin Planet Search. III. The [Y/Mg] clock: estimating
stellar ages of solar-type stars
Authors: Tucci Maia, M.; Ramírez, I.; Meléndez, J.; Bedell, M.;
Bean, J. L.; Asplund, M.
Bibcode: 2016A&A...590A..32T
Altcode: 2016arXiv160405733T
Context. Solar twins are stars with similar stellar (surface)
parameters to the Sun that can have a wide range of ages. This provides
an opportunity to analyze the variation of their chemical abundances
with age. Nissen (2015, A&A, 579, A52) recently suggested that the
abundances of the s-process element Y and the α-element Mg could be
used to estimate stellar ages.
Aims: This paper aims to determine
with high precision the Y, Mg, and Fe abundances for a sample of 88
solar twins that span a broad age range (0.3-10.0 Gyr) and investigate
their use for estimating ages.
Methods: We obtained high-quality
Magellan Inamori Kyocera Echelle (MIKE) spectra and determined Y and
Mg abundances using equivalent widths and a line-by-line differential
method within a 1D LTE framework. Stellar parameters and iron abundances
were measured in Paper I of this series for all stars, but a few (three)
required a small revision.
Results: The [Y/Mg] ratio shows a
strong correlation with age. It has a slope of -0.041 ± 0.001 dex/Gyr
and a significance of 41σ. This is in excellent agreement with the
relation first proposed by Nissen (2015). We found some outliers that
turned out to be binaries where mass transfer may have enhanced the
yttrium abundance. Given a precise measurement of [Y/Mg] with typical
error of 0.02 dex in solar twins, our formula can be used to determine
a stellar age with ~0.8 Gyr precision in the 0 to 10 Gyr range. Based on observations obtained at the Clay Magellan Telescopes at
Las Campanas Observatory, Chile and at the 3.6 m Telescope at the La
Silla ESO Observatory, Chile (program ID 188.C-0265).
Title: High-precision analysis of the solar twin HIP 100963
Authors: Yana Galarza, Jhon; Meléndez, Jorge; Ramírez, Ivan; Yong,
David; Karakas, Amanda I.; Asplund, Martin; Liu, Fan
Bibcode: 2016A&A...589A..17Y
Altcode: 2016A&A...589A..17G; 2016arXiv160208008Y
Context. HIP 100963 was one of the first solar twins
identified. Although some high-precision analyses are available, a
comprehensive high-precision study of chemical elements from different
nucleosynthetic sources is still lacking from which to obtain potential
new insights on planets, stellar evolution, and Galactic chemical
evolution (GCE).
Aims: We analyze and investigate the origin
of the abundance pattern of HIP 100963 in detail, in particular the
pattern of the light element Li, the volatile and refractory elements,
and heavy elements from the s- and r-processes.
Methods:
We used the HIRES spectrograph on the Keck I telescope to acquire
high-resolution (R ≈ 70 000) spectra with a high signal-to-noise ratio
(S/N ≈ 400-650 per pixel) of HIP 100963 and the Sun for a differential
abundance analysis. We measured the equivalent widths (EWs) of iron
lines to determine the stellar parameters by employing the differential
spectroscopic equilibrium. We determined the composition of volatile,
refractory, and neutron-capture elements through a differential
abundance analysis with respect to the Sun.
Results: The
stellar parameters we found are Teff = 5818 ± 4 K, log g =
4.49 ± 0.01 dex, vt = 1.03 ± 0.01km s-1, and
[Fe/H] = -0.003 ± 0.004 dex. These low errors allow us to compute a
precise mass (1.03+0.02-0.01 M⊙)
and age (2.0 ± 0.4 Gyr), obtained using Yonsei-Yale isochrones. Using
our [Y/Mg] ratio, we have determined an age of 2.1 ± 0.4 Gyr, in
agreement with the age computed using isochrones. Our isochronal age
also agrees with the age determined from stellar activity (2.4 ± 0.3
Gyr). We study the abundance pattern with condensation temperature
(Tcond) taking corrections by the GCE into account. We
show that the enhancements of neutron-capture elements are explained
by contributions from both the s- and r-process. The lithium abundance
follows the tight Li-age correlation seen in other solar twins.
Conclusions: We confirm that HIP 100963 is a solar twin and demonstrate
that its abundance pattern is about solar after corrections for
GCE. The star also shows enrichment in s- and r-process elements,
as well as depletion in lithium that is caused by stellar evolution.
Title: Atomic diffusion and mixing in old stars. VI. The lithium
content of M30
Authors: Gruyters, Pieter; Lind, Karin; Richard, Olivier; Grundahl,
Frank; Asplund, Martin; Casagrande, Luca; Charbonnel, Corinne; Milone,
Antonino; Primas, Francesca; Korn, Andreas J.
Bibcode: 2016A&A...589A..61G
Altcode: 2016arXiv160301565G
Context. The prediction of the Planck-constrained primordial lithium
abundance in the Universe is in discordance with the observed Li
abundances in warm Population II dwarf and subgiant stars. Among
the physically best motivated ideas, it has been suggested that this
discrepancy can be alleviated if the stars observed today had undergone
photospheric depletion of lithium.
Aims: The cause of this
depletion is investigated by accurately tracing the behaviour of the
lithium abundances as a function of effective temperature. Globular
clusters are ideal laboratories for such an abundance analysis as
the relative stellar parameters of their stars can be precisely
determined.
Methods: We performed a homogeneous chemical
abundance analysis of 144 stars in the metal-poor globular cluster
M30, ranging from the cluster turnoff point to the tip of the red
giant branch. Non-local thermal equilibrium (NLTE) abundances for Li,
Ca, and Fe were derived where possible by fitting spectra obtained
with VLT/FLAMES-GIRAFFE using the quantitative-spectroscopy package
SME. Stellar parameters were derived by matching isochrones to the
observed V vs. V-I colour-magnitude diagram. Independent effective
temperatures were obtained from automated profile fitting of the
Balmer lines and by applying colour-Teff calibrations
to the broadband photometry.
Results: Li abundances of the
turnoff and early subgiant stars form a thin plateau that is broken
off abruptly in the middle of the SGB as a result of the onset of Li
dilution caused by the first dredge-up. Abundance trends with effective
temperature for Fe and Ca are observed and compared to predictions
from stellar structure models including atomic diffusion and ad hoc
additional mixing below the surface convection zone. The comparison
shows that the stars in M30 are affected by atomic diffusion and
additional mixing, but we were unable to determine the efficiency of
the additional mixing precisely. This is the fourth globular cluster
(after NGC 6397, NGC 6752, and M4) in which atomic diffusion signatures
are detected. After applying a conservative correction (T6.0 model)
for atomic diffusion, we find an initial Li abundance of A(Li) = 2.48
± 0.10 for the globular cluster M30. We also detected a Li-rich SGB
star with a Li abundance of A(Li) = 2.39. The finding makes Li-rich mass
transfer a likely scenario for this star and rules out models in which
its Li enhancement is created during the RGB bump phase. Based
on data collected at the ESO telescopes under program 085.D-0375.Full
Tables 1 and 5 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/589/A61
Title: Highlights of IAU Commission 29: Recent Advances and
Perspectives on Stellar Spectroscopy
Authors: Cunha, Katia; Soderblom, David R.; Piskunov, Nikolai; Aoki,
Wako; Asplund, Martin; Carpenter, Kenneth G.; Crowther, Paul; Melendez,
Jorge; Venn, Kimberly; Hill, Vanessa; Yong, David
Bibcode: 2016IAUTA..29..428C
Altcode:
IAU Commission 29 - Stellar Spectra has been one of the IAU commissions
from the onset, until its dissolution at the most recent IAU General
Assembly in Honolulu in 2015. This commission belonged to IAU Division
G (``Stars and Stellar Physics''), the latter committed with fostering
research in stellar astrophysics. Within the general field of stellar
astrophysics, stellar spectroscopy plays a key role, as stellar
spectra are a powerful tool providing a view into the detailed physical
properties of stars and the physical processes occuring within them.
Title: Division G Commission 36: Theory of Stellar Atmospheres
Authors: Puls, Joachim; Hubeny, Ivan; Asplund, Martin; Allard, France;
Allende Prieto, Carlos; Ayres, Thomas R.; Carlsson, Mats; Gustafsson,
Bengt; Kudritzki, Rolf-Peter; Ryabchikova, Tatiana A.
Bibcode: 2016IAUTA..29..453P
Altcode:
Different from previous triennial reports, this report covers the
activities of IAU Commission 36 `Theory of Stellar Atmospheres'
over the past six years†, and will be the last report from the
`old' Commission 36. After the General Assembly in Honolulu (August
2015), a new Commission `Stellar and Planetary Atmospheres' (C.G5,
under Division G, `Stars and Stellar Physics') has come into life,
and will continue our work devoted to the outer envelopes of stars,
as well as extend it to the atmospheres of planets (see Sect. 4).
Title: The Hyades open cluster is chemically inhomogeneous
Authors: Liu, F.; Yong, D.; Asplund, M.; Ramírez, I.; Meléndez, J.
Bibcode: 2016MNRAS.457.3934L
Altcode: 2016arXiv160107354L; 2016MNRAS.tmp...38L
We present a high-precision differential abundance analysis of 16
solar-type stars in the Hyades open cluster based on high-resolution,
high signal-to-noise ratio (S/N ≈ 350-400) spectra obtained from the
McDonald 2.7-m telescope. We derived stellar parameters and differential
chemical abundances for 19 elements (C, O, Na, Mg, Al, Si, S, Ca, Sc,
Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn and Ba) with uncertainties as low
as ∼0.01-0.02 dex. Our main results include: (1) there is no clear
chemical signature of planet formation detected among the sample stars,
I.e. no correlations in abundances versus condensation temperature;
(2) the observed abundance dispersions are a factor of ≈1.5-2 larger
than the average measurement errors for most elements; (3) there are
positive correlations, of high statistical significance, between the
abundances of at least 90 per cent of pairs of elements. We demonstrate
that none of these findings can be explained by errors due to the
stellar parameters. Our results reveal that the Hyades is chemically
inhomogeneous at the 0.02 dex level. Possible explanations for the
abundance variations include (1) inhomogeneous chemical evolution in the
proto-cluster environment, (2) supernova ejection in the proto-cluster
cloud and (3) pollution of metal-poor gas before complete mixing of the
proto-cluster cloud. Our results provide significant new constraints
on the chemical composition of open clusters and a challenge to the
current view of Galactic archaeology.
Title: VizieR Online Data Catalog: Abundance analysis of solar twin
HIP 100963 (Yana Galarza+, 2016)
Authors: Yana Galarza, J.; Melendez, J.; Ramirez, I.; Yong, D.;
Karakas, A. I.; Asplund, M.; Liu, F.
Bibcode: 2016yCat..35890017Y
Altcode:
Stellar abundances [X/H] of HIP 100963 relative to the Sun and
corresponding errors. (1 data file).
Title: The detailed chemical composition of the terrestrial planet
host Kepler-10
Authors: Liu, F.; Yong, D.; Asplund, M.; Ramírez, I.; Meléndez,
J.; Gustafsson, B.; Howes, L. M.; Roederer, I. U.; Lambert, D. L.;
Bensby, T.
Bibcode: 2016MNRAS.456.2636L
Altcode: 2015arXiv151109287L
Chemical abundance studies of the Sun and solar twins have demonstrated
that the solar composition of refractory elements is depleted when
compared to volatile elements, which could be due to the formation
of terrestrial planets. In order to further examine this scenario, we
conducted a line-by-line differential chemical abundance analysis of the
terrestrial planet host Kepler-10 and 14 of its stellar twins. Stellar
parameters and elemental abundances of Kepler-10 and its stellar twins
were obtained with very high precision using a strictly differential
analysis of high quality Canada-France-Hawaii Telescope, Hobby-Eberly
Telescope and Magellan spectra. When compared to the majority of
thick disc twins, Kepler-10 shows a depletion in the refractory
elements relative to the volatile elements, which could be due to
the formation of terrestrial planets in the Kepler-10 system. The
average abundance pattern corresponds to ∼13 Earth masses, while
the two known planets in Kepler-10 system have a combined ∼20 Earth
masses. For two of the eight thick disc twins, however, no depletion
patterns are found. Although our results demonstrate that several
factors [e.g. planet signature, stellar age, stellar birth location and
Galactic chemical evolution (GCE)] could lead to or affect abundance
trends with condensation temperature, we find that the trends give
further support for the planetary signature hypothesis.
Title: VizieR Online Data Catalog: Stellar parameters and abundances
for M30 (Gruyters+, 2016)
Authors: Gruyters, P.; Lind, K.; Richard, F.; Grundahl, O.; Asplund,
M.; Casagrande, L.; Charbonnel, C.; Milone, A.; Primas, F.; Korn, A. J.
Bibcode: 2016yCat..35890061G
Altcode:
Coordinates, photometry and derived effective temperatures for the 144
observed stars in M30. Effective temperatures where derived using three
different temperature scales: a scale based on a Victoria isochrone
(Vandenberg et al., 2014ApJ...794...72V), a scale based on the Alonso
relations (Alonso, 1996A&A...313..873A, 1999A&AS..140..261A)
and a scale based on the Ramirez (2005ApJ...626..465R) and Casagrande
(2010A&A...512A..54C, Cat. J/A+A/512/A54) relations. Additionally,
the derived Hα temperatures are given. (2 data files).
Title: Non-LTE oxygen line formation in 3D hydrodynamic model
stellar atmospheres
Authors: Amarsi, A. M.; Asplund, M.; Collet, R.; Leenaarts, J.
Bibcode: 2016MNRAS.455.3735A
Altcode: 2015arXiv151101155A
The O I 777 nm lines are among the most commonly used diagnostics for
the oxygen abundances in the atmospheres of FGK-type stars. However,
they form in conditions that are far from local thermodynamic
equilibrium (LTE). We explore the departures from LTE of atomic
oxygen, and their impact on O I lines, across the STAGGER-grid of
three-dimensional hydrodynamic model atmospheres. For the O I 777 nm
triplet, we find significant departures from LTE. These departures are
larger in stars with larger effective temperatures, smaller surface
gravities, and larger oxygen abundances. We present grids of predicted
3D non-LTE based equivalent widths for the O I 616 nm, [O I] 630 nm,
[O I] 636 nm, and O I 777 nm lines, as well as abundance corrections
to 1D LTE based results.
Title: First high-precision differential abundance analysis of
extremely metal-poor stars
Authors: Reggiani, Henrique; Meléndez, Jorge; Yong, David; Ramírez,
Ivan; Asplund, Martin
Bibcode: 2016A&A...586A..67R
Altcode: 2015arXiv151203349R
Context. Studies of extremely metal-poor stars indicate that chemical
abundance ratios [X/Fe] have a root mean square scatter as low as
0.05 dex (12%). It remains unclear whether this reflects observational
uncertainties or intrinsic astrophysical scatter arising from physical
conditions in the interstellar medium at early times.
Aims: We
measure differential chemical abundance ratios in extremely metal-poor
stars to investigate the limits of precision and to understand
whether cosmic scatter or observational errors are dominant.
Methods: We used high-resolution (R ~ 95 000) and high signal-to-noise
(S/N = 700 at 5000 Å) HIRES/Keck spectra to determine high-precision
differential abundances between two extremely metal-poor stars through
a line-by-line differential approach. We determined stellar parameters
for the star G64-37 with respect to the standard star G64-12. We
performed EW measurements for the two stars for the lines recognized
in both stars and performed spectral synthesis to study the carbon
abundances.
Results: The differential approach allowed us to
obtain errors of σ(Teff) = 27 K, σ(log g) = 0.06 dex, σ(
[Fe/H] ) = 0.02 dex and σ(vt) = 0.06 km s-1. We
estimated relative chemical abundances with a precision as low as
σ([X/Fe]) ≈ 0.01 dex. The small uncertainties demonstrate that
there are genuine abundance differences larger than the measurement
errors. The observed Li difference cannot be explained by the
difference in mass because the less massive star has more Li.
Conclusions: It is possible to achieve an abundance precision around
≈ 0.01-0.05 dex for extremely metal-poor stars, which opens new
windows on the study of the early chemical evolution of the Galaxy. Table A.1 is also available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/586/A67
Title: The most metal-rich stars: probing exoplanets, stars, the
Milky Way and galaxies
Authors: Asplund, Martin
Bibcode: 2016koa..prop..428A
Altcode:
No abstract at ADS
Title: Measuring the vertical age structure of the Galactic disc
using asteroseismology and SAGA
Authors: Casagrande, L.; Silva Aguirre, V.; Schlesinger, K. J.;
Stello, D.; Huber, D.; Serenelli, A. M.; Schönrich, R.; Cassisi, S.;
Pietrinferni, A.; Hodgkin, S.; Milone, A. P.; Feltzing, S.; Asplund, M.
Bibcode: 2016MNRAS.455..987C
Altcode: 2015arXiv151001376C
The existence of a vertical age gradient in the Milky Way disc
has been indirectly known for long. Here, we measure it directly
for the first time with seismic ages, using red giants observed by
Kepler. We use Strömgren photometry to gauge the selection function
of asteroseismic targets, and derive colour and magnitude limits
where giants with measured oscillations are representative of the
underlying population in the field. Limits in the 2MASS system are
also derived. We lay out a method to assess and correct for target
selection effects independent of Galaxy models. We find that low-mass,
I.e. old red giants dominate at increasing Galactic heights, whereas
closer to the Galactic plane they exhibit a wide range of ages and
metallicities. Parametrizing this as a vertical gradient returns
approximately 4 Gyr kpc-1 for the disc we probe, although
with a large dispersion of ages at all heights. The ages of stars show
a smooth distribution over the last ≃10 Gyr, consistent with a mostly
quiescent evolution for the Milky Way disc since a redshift of about
2. We also find a flat age-metallicity relation for disc stars. Finally,
we show how to use secondary clump stars to estimate the present-day
intrinsic metallicity spread, and suggest using their number count as
a new proxy for tracing the ageing of the disc. This work highlights
the power of asteroseismology for Galactic studies; however, we also
emphasize the need for better constraints on stellar mass-loss, which
is a major source of systematic age uncertainties in red giant stars.
Title: IAU Commission 36 (Theory of Stellar Atmospheres): Hexennial
Report 2009-2015
Authors: Puls, Joachim; Asplund, Martin
Bibcode: 2015arXiv151206972P
Altcode:
This hexennial report covers the activities of IAU Commission 36 --
'Theory of Stellar Atmospheres' -- during the years 2009 to 2015,
and will be the last report from this Commission, being replaced by
Commission C.G5. After outlining the composition of the Organization
Committee(s), we list the scientific meetings held between 2009 and 2015
that were of relevance for our Commission members, and comment on the
establishment and objectives of the new Commission C.G5 ('Stellar and
Planetary Atmospheres') within the re-structuring process of the IAU. In
the main part of the report, we briefly review specific contributions
and achievements within our research field during the last six years,
concentrating on the theoretical aspect, and dividing between late-type
and massive star atmospheres. We also provide a more general overview
of primary research areas, and finish our report with a collection of
useful web links.
Title: HIP 10725: The first solar twin/analogue field blue straggler
Authors: Schirbel, Lucas; Meléndez, Jorge; Karakas, Amanda I.;
Ramírez, Iván; Castro, Matthieu; Faria, Marcos A.; Lugaro, Maria;
Asplund, Martin; Tucci Maia, Marcelo; Yong, David; Howes, Louise;
do Nascimento, José D.
Bibcode: 2015A&A...584A.116S
Altcode: 2015arXiv151001793S
Context. Blue stragglers are easy to identify in globular clusters,
but are much harder to identify in the field. Here we present the
serendipitous discovery of one field blue straggler, HIP 10725,
that closely matches the Sun in mass and age, but with a metallicity
slightly lower than solar.
Aims: We characterise the solar
twin/analogue HIP 10725 to assess whether this star is a blue
straggler.
Methods: We employed spectra with high resolution
(R ~ 105) and high signal-to-noise ratio (330) obtained
with UVES at the VLT to perform a differential abundance analysis of
the solar analogue HIP 10725. Radial velocities obtained by other
instruments were also used to check for binarity. We also studied
its chromospheric activity, age, and rotational velocity.
Results: HIP 10725 is severely depleted in beryllium ([ Be/H ]
≤ -1.2 dex) for its stellar parameters and age. The abundances
relative to solar of the elements with Z ≤ 30 show a correlation
with condensation temperature, and the neutron capture elements
produced by the s-process are greatly enhanced, while the r-process
elements seem normal. We found its projected rotational velocity
(vsini = 3.3 ± 0.1 km s-1) to be significantly higher
than solar and incompatible with its isochrone-derived age. Radial
velocity monitoring shows that the star has a binary companion.
Conclusions: Based on the high s-process element enhancements and low
beryllium abundance, we suggest that HIP 10725 has been polluted by mass
transfer from an AGB star that probably had an initial mass of about 2
M⊙. The radial velocity variations suggest the presence
of an unseen binary companion, probably the remnant of a former AGB
star. Isochrones predict a solar-age star, but this disagrees with the
high projected rotational velocity and high chromospheric activity. We
conclude that HIP 10725 is a field blue straggler, rejuvenated by
the mass-transfer process of its former AGB companion. Based
on observations obtained at the European Southern Observatory (ESO)
Very Large Telescope (VLT) at Paranal Observatory, Chile (observing
programs 083.D-0871, 082.C-0446, 093.D-0807), and complemented with
observations taken at the Observatório Pico dos Dias (OPD), Brazil
(program OP2014A-011).Appendix A is available in electronic form at http://www.aanda.org
Title: VizieR Online Data Catalog: G64-12 and G64-37 linelist and EWs
(Reggiani+, 2016)
Authors: Reggiani, H.; Melendez, J.; Yong, D.; Ramirez, I.; Asplund, M.
Bibcode: 2015yCat..35860067R
Altcode:
The linelist employed in the differential analysis. Includes wavelength,
species, excitation potential, log(gf), and equivalent widths for both
stars analyzed. (1 data file).
Title: PICK2: Planets in Clusters with K2
Authors: Cochran, William D.; Endl, Michael; Johnson, Marshall C.;
Lee, Byeong-Cheol; Park, Chan; Han, Inwoo; Rauer, Heike; Cabrera,
Juan; Csizmadia, Szilard; Paetzold, Martin; Yong, David; Asplund,
Martin; Hatzes, Artie P.
Bibcode: 2015DPS....4741702C
Altcode:
Open clusters are remarkable laboratories for a wide variety of
astrophysical investigations. They comprise the most homogeneous
samples of stars that we can ever hope to find. They are stars that
share the same age, initial chemical composition, distance and dynamical
environment. The fundamental property that distinguishes one star from
another in a cluster is simply the stellar mass. This gives us the
very rare opportunity to conduct well controlled astrophysical studies
of stars, and as a result there is a vast astronomical literature
focused on understanding and characterizing the members of stellar
clusters.We are searching for transiting planets in five open clusters
in the NASA K2 mission Fields 4, 5 and 7. These clusters range in
age from 125My (Pleiades) through the 625My ages of the Hyades and
Praesepe, up to the much older Ruprecht 147 (2.5 Gyr) and M67 (3-5
Gyr) clusters. Examination of the distribution of planetary orbital
parameters as well as the planetary multiplicity, radius and mass
distributions as a function of stellar age (and in comparison with
field stars from both K2 and Kepler) will provide a powerful test of
theories of planetary system formation and dynamical evolution. The
radii of hot Jupiters and Saturns as a function of cluster age will
provide a sensitive test of theories to explain the population of
inflated hot Jupiters.Our team will process the K2 pixel files into
light curves for each target star, and will then search these light
curves for possible planet transit events. We will apply standard
vetting procedures to remove likely false-positives and we will then
model the transit profiles. We will then conduct an extensive set of
ground-based follow-up observations using a wide range of observational
facilities at our disposal. These will include imaging, high resolution
visible and near-IR spectroscopy, precise radial velocity measurement,
and ground-based observations of further transits, as appropriate.
Title: The Galactic chemical evolution of oxygen inferred from 3D
non-LTE spectral-line-formation calculations.
Authors: Amarsi, A. M.; Asplund, M.; Collet, R.; Leenaarts, J.
Bibcode: 2015MNRAS.454L..11A
Altcode: 2015arXiv150804857A
We revisit the Galactic chemical evolution of oxygen, addressing the
systematic errors inherent in classical determinations of the oxygen
abundance that arise from the use of one-dimensional (1D) hydrostatic
model atmospheres and from the assumption of local thermodynamic
equilibrium (LTE). We perform detailed 3D non-LTE radiative-transfer
calculations for atomic oxygen lines across a grid of 3D hydrodynamic
STAGGER model atmospheres for dwarfs and subgiants. We apply our grid
of predicted line strengths of the [O I] 630 nm and O I 777 nm lines
using accurate stellar parameters from the literature. We infer a steep
decay in [O/Fe] for [Fe/H] ≳ -1.0, a plateau [O/Fe] ≈ 0.5 down to
[Fe/H] ≈ -2.5, and an increasing trend for [Fe/H] ≲ -2.5. Our 3D
non-LTE calculations yield overall concordant results from the two
oxygen abundance diagnostics.
Title: Extremely metal-poor stars from the cosmic dawn in the bulge
of the Milky Way
Authors: Howes, L. M.; Casey, A. R.; Asplund, M.; Keller, S. C.; Yong,
D.; Nataf, D. M.; Poleski, R.; Lind, K.; Kobayashi, C.; Owen, C. I.;
Ness, M.; Bessell, M. S.; da Costa, G. S.; Schmidt, B. P.; Tisserand,
P.; Udalski, A.; Szymański, M. K.; Soszyński, I.; Pietrzyński,
G.; Ulaczyk, K.; Wyrzykowski, Ł.; Pietrukowicz, P.; Skowron, J.;
Kozłowski, S.; Mróz, P.
Bibcode: 2015Natur.527..484H
Altcode: 2015arXiv151103930H
The first stars are predicted to have formed within 200 million
years after the Big Bang, initiating the cosmic dawn. A true first
star has not yet been discovered, although stars with tiny amounts
of elements heavier than helium (‘metals’) have been found in
the outer regions (‘halo’) of the Milky Way. The first stars and
their immediate successors should, however, preferentially be found
today in the central regions (‘bulges’) of galaxies, because they
formed in the largest over-densities that grew gravitationally with
time. The Milky Way bulge underwent a rapid chemical enrichment during
the first 1-2 billion years, leading to a dearth of early, metal-poor
stars. Here we report observations of extremely metal-poor stars in
the Milky Way bulge, including one star with an iron abundance about
10,000 times lower than the solar value without noticeable carbon
enhancement. We confirm that most of the metal-poor bulge stars are on
tight orbits around the Galactic Centre, rather than being halo stars
passing through the bulge, as expected for stars formed at redshifts
greater than 15. Their chemical compositions are in general similar
to typical halo stars of the same metallicity although intriguing
differences exist, including lower abundances of carbon.
Title: IAU 2015 Resolution B2 on Recommended Zero Points for the
Absolute and Apparent Bolometric Magnitude Scales
Authors: Mamajek, E. E.; Torres, G.; Prsa, A.; Harmanec, P.;
Asplund, M.; Bennett, P. D.; Capitaine, N.; Christensen-Dalsgaard,
J.; Depagne, E.; Folkner, W. M.; Haberreiter, M.; Hekker, S.; Hilton,
J. L.; Kostov, V.; Kurtz, D. W.; Laskar, J.; Mason, B. D.; Milone,
E. F.; Montgomery, M. M.; Richards, M. T.; Schou, J.; Stewart, S. G.
Bibcode: 2015arXiv151006262M
Altcode:
The XXIXth IAU General Assembly in Honolulu adopted IAU 2015 Resolution
B2 on recommended zero points for the absolute and apparent bolometric
magnitude scales. The resolution was proposed by the IAU Inter-Division
A-G Working Group on Nominal Units for Stellar and Planetary
Astronomy after consulting with a broad spectrum of researchers from
the astronomical community. Resolution B2 resolves the long-standing
absence of an internationally-adopted zero point for the absolute and
apparent bolometric magnitude scales. Resolution B2 defines the zero
point of the absolute bolometric magnitude scale such that a radiation
source with $M_{\rm Bol}$ = 0 has luminosity L$_{\circ}$ = 3.0128e28
W. The zero point of the apparent bolometric magnitude scale ($m_{\rm
Bol}$ = 0) corresponds to irradiance $f_{\circ}$ = 2.518021002e-8
W/m$^2$. The zero points were chosen so that the nominal solar
luminosity (3.828e26 W) adopted by IAU 2015 Resolution B3 corresponds
approximately to $M_{\rm Bol}$(Sun) = 4.74, the value most commonly
adopted in recent literature. The nominal total solar irradiance (1361
W/m$^2$) adopted in IAU 2015 Resolution B3 corresponds approximately to
apparent bolometric magnitude $m_{\rm bol}$(Sun) = -26.832. Implicit
in the IAU 2015 Resolution B2 definition of the apparent bolometric
magnitude scale is an exact definition for the parsec (648000/$\pi$ au)
based on the IAU 2012 Resolution B2 definition of the astronomical unit.
Title: IAU 2015 Resolution B3 on Recommended Nominal Conversion
Constants for Selected Solar and Planetary Properties
Authors: Mamajek, E. E.; Prsa, A.; Torres, G.; Harmanec, P.;
Asplund, M.; Bennett, P. D.; Capitaine, N.; Christensen-Dalsgaard,
J.; Depagne, E.; Folkner, W. M.; Haberreiter, M.; Hekker, S.; Hilton,
J. L.; Kostov, V.; Kurtz, D. W.; Laskar, J.; Mason, B. D.; Milone,
E. F.; Montgomery, M. M.; Richards, M. T.; Schou, J.; Stewart, S. G.
Bibcode: 2015arXiv151007674M
Altcode:
Astronomers commonly quote the properties of celestial objects in
units of parameters for the Sun, Jupiter, or the Earth. The resolution
presented here was proposed by the IAU Inter-Division Working Group
on Nominal Units for Stellar and Planetary Astronomy and passed by the
XXIXth IAU General Assembly in Honolulu. IAU 2015 Resolution B3 adopts
a set of nominal solar, terrestrial, and jovian conversion constants
for stellar and (exo)planetary astronomy which are defined to be
exact SI values. While the nominal constants are based on current best
estimates (CBEs; which have uncertainties, are not secularly constant,
and are updated regularly using new observations), they should be
interpreted as standard values and not as CBEs. IAU 2015 Resolution
B3 adopts five solar conversion constants (nominal solar radius,
nominal total solar irradiance, nominal solar luminosity, nominal
solar effective temperature, and nominal solar mass parameter) and six
planetary conversion constants (nominal terrestrial equatorial radius,
nominal terrestrial polar radius, nominal jovian equatorial radius,
nominal jovian polar radius, nominal terrestrial mass parameter,
and nominal jovian mass parameter).
Title: Using Solar Twins to Explore the Planet-Star Connection with
Unparallelled Precision
Authors: Meléndez, J.; Bean, J. L.; Bedell, M.; Ramírez, I.; Asplund,
M.; Dreizler, S.; Alves-Brito, A.; Spina, L.; Casagrande, L.; Monroe,
T.; Maia, M. T.; Freitas, F.
Bibcode: 2015Msngr.161...28M
Altcode:
This year marks the 20th anniversary of the first definitive
detection of an exoplanet orbiting a Sun-like star by Mayor and
Queloz (1995). Almost 2000 exoplanets have been discovered since this
breakthrough, but many fundamental questions remain open despite the
enormous progress: How common are analogues of the Solar System? How
do planets form and evolve? What is the relationship between stars and
planets? We are observing stars that are near-perfect matches to the
Sun to provide new insights into the above questions, thus exploring
the planet-star connection with unprecedented precision.
Title: The Solar Twin Planet Search. II. A Jupiter twin around a
solar twin
Authors: Bedell, M.; Meléndez, J.; Bean, J. L.; Ramírez, I.; Asplund,
M.; Alves-Brito, A.; Casagrande, L.; Dreizler, S.; Monroe, T.; Spina,
L.; Tucci Maia, M.
Bibcode: 2015A&A...581A..34B
Altcode: 2015arXiv150703998B
Context. With high-precision radial velocity surveys reaching a
sufficiently long time baseline, the domain of long-period planet
detections has recently opened up. The search for Jupiter-like planets
is especially important if we wish to investigate the prevalence
of solar system analogs, but their detection is complicated by the
existence of stellar activity cycles on similar timescales. Radial
velocity data with sufficiently long-term instrumental precision and
robust methods of diagnosing activity are crucial to the detection of
extrasolar Jupiters.
Aims: Through our HARPS survey for planets
around solar twin stars, we have identified a promising Jupiter twin
candidate around the star HIP11915. We characterize this Keplerian
signal and investigate its potential origins in stellar activity.
Methods: We carry out a Markov chain Monte Carlo (MCMC) analysis of
the radial velocity data. To examine the signal's origin, we employ
a variety of statistical tests using activity diagnostics such as
the Ca II H and K lines and line asymmetry tracers.
Results:
Our analysis indicates that HIP11915 hosts a Jupiter-mass planet with
a 3800-day orbital period and low eccentricity. Although we cannot
definitively rule out an activity cycle interpretation, we find that a
planet interpretation is more likely based on a joint analysis of radial
velocity and activity index data.
Conclusions: The challenges of
long-period radial velocity signals addressed in this paper are critical
for the ongoing discovery of Jupiter-like exoplanets. If planetary in
nature, the signal investigated here represents a very close analog to
the solar system in terms of both Sun-like host star and Jupiter-like
planet. Table 3 and Fig. 5 are available in electronic form at http://www.aanda.org
Title: The Surface of Stellar Models - Now with more 3D simulations!
Authors: Trampedach, Regner; Christensen-Dalsgaard, Jørgen; Asplund,
Martin; Stein, Robert F.; Nordlund, Åke
Bibcode: 2015EPJWC.10106064T
Altcode:
We have constructed a grid of 3D hydrodynamic simulations of deep
convective and line-blanketed atmospheres. We have developed a
new consistent method for computing and employing T(τ) relations
from these simulations, as surface boundary conditions for 1D
stellar structure models. These 1D models have, in turn, had their
mixing-length, α, calibrated against the averaged structure of
each of the simulations. Both α and T(τ) vary significantly with
Teff and log g.
Title: The most metal-rich stars: probing exoplanets, stellar
nucleosynthesis, Galactic archaeology and galaxy evolution
Authors: Asplund, Martin
Bibcode: 2015koa..prop..210A
Altcode:
No abstract at ADS
Title: Asteroseismology for Galactic archaeology: bridging two fields
Authors: Casagrande, Luca; Silva Aguirre, Victor; Stello, Dennis;
Huber, Daniel; Serenelli, Aldo; Schlesinger, Katharine J.; Milone,
Antonino; Asplund, Martin
Bibcode: 2015IAUGA..2256260C
Altcode:
Asteroseismology has the capability of precisely determining stellar
properties that would otherwise be inaccessible, such as radii, masses,
and thus ages of field stars. When coupling this information with
classical determinations of stellar parameters, such as metallicities,
effective temperatures, and angular diameters, powerful new diagnostics
for Galactic studies can be obtained. An overview of the ongoing
Strömgren survey for Asteroseismology and Galactic Archaeology (SAGA)
is presented, along with recent results using asteroseismology to
investigate the age structure of the Milky Way disc.
Title: Division II: Commission 12: Solar Radiation and Structure
Authors: Kosovichev, Alexander; Cauzzi, Gianna; Martinez Pillet,
Valentin; Asplund, Martin; Brandenburg, Axel; Chou, Dean-Yi;
Christensen-Dalsgaard, Jorgen; Gan, Weiqun; Kuznetsov, Vladimir D.;
Rovira, Marta G.; Shchukina, Nataliya; Venkatakrishnan, P.
Bibcode: 2015IAUTB..28..109K
Altcode:
The President of C12, Alexander Kosovichev, presented the status of
the Commission and its working Group(s). Primary activities included
organization of international meetings (IAU Symposia, Special Sessions
and Joint Discussion); review and support of proposals for IAU sponsored
meetings; organization of working groups on the Commission topics
to promote the international cooperation; preparation of triennial
report on the organizational and science activities of Commission
members. Commission 12 broadly encompasses topics of solar research
which include studies of the Sun's internal structure, composition,
dynamics and magnetism (through helioseismology and other techniques),
studies of the quiet photosphere, chromosphere and corona, and also
research of the mechanisms of solar radiation, and its variability on
various time scales. Some overlap with topics covered by Commission
10 Solar Activity is unavoidable, and many activities are sponsored
jointly by these two commissions. The Commission website can be found
at http://sun.stanford.edu/IAU-Com12/, with information about related
IAU Symposiums and activities, and links to appropriate web sites.
Title: The Gaia-ESO Survey: Empirical determination of the precision
of stellar radial velocities and projected rotation velocities
Authors: Jackson, R. J.; Jeffries, R. D.; Lewis, J.; Koposov, S. E.;
Sacco, G. G.; Randich, S.; Gilmore, G.; Asplund, M.; Binney, J.;
Bonifacio, P.; Drew, J. E.; Feltzing, S.; Ferguson, A. M. N.;
Micela, G.; Neguerela, I.; Prusti, T.; Rix, H. -W.; Vallenari,
A.; Alfaro, E. J.; Allende Prieto, C.; Babusiaux, C.; Bensby, T.;
Blomme, R.; Bragaglia, A.; Flaccomio, E.; Francois, P.; Hambly, N.;
Irwin, M.; Korn, A. J.; Lanzafame, A. C.; Pancino, E.; Recio-Blanco,
A.; Smiljanic, R.; Van Eck, S.; Walton, N.; Bayo, A.; Bergemann, M.;
Carraro, G.; Costado, M. T.; Damiani, F.; Edvardsson, B.; Franciosini,
E.; Frasca, A.; Heiter, U.; Hill, V.; Hourihane, A.; Jofré, P.; Lardo,
C.; de Laverny, P.; Lind, K.; Magrini, L.; Marconi, G.; Martayan, C.;
Masseron, T.; Monaco, L.; Morbidelli, L.; Prisinzano, L.; Sbordone,
L.; Sousa, S. G.; Worley, C. C.; Zaggia, S.
Bibcode: 2015A&A...580A..75J
Altcode: 2015arXiv150507019J
Context. The Gaia-ESO Survey (GES) is a large public spectroscopic
survey at the European Southern Observatory Very Large Telescope.
Aims: A key aim is to provide precise radial velocities (RVs) and
projected equatorial velocities (vsini) for representative samples
of Galactic stars, which will complement information obtained by the
Gaia astrometry satellite.
Methods: We present an analysis
to empirically quantify the size and distribution of uncertainties
in RV and vsini using spectra from repeated exposures of the same
stars.
Results: We show that the uncertainties vary as simple
scaling functions of signal-to-noise ratio (S/N) and vsini, that the
uncertainties become larger with increasing photospheric temperature,
but that the dependence on stellar gravity, metallicity and age is
weak. The underlying uncertainty distributions have extended tails
that are better represented by Student's t-distributions than by
normal distributions.
Conclusions: Parametrised results are
provided, which enable estimates of the RV precision for almost all GES
measurements, and estimates of the vsini precision for stars in young
clusters, as a function of S/N, vsini and stellar temperature. The
precision of individual high S/N GES RV measurements is 0.22-0.26 km
s-1, dependent on instrumental configuration. Based on
observations collected with the FLAMES spectrograph at VLT/UT2 telescope
(Paranal Observatory, ESO, Chile), for the Gaia- ESO Large Public Survey
(188.B-3002).Full Table 2 is only available at the CDS via anonymous ftp
to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/580/A75
Title: Exploring the vertical age structure of the Galactic disc
Authors: Casagrande, Luca; Silva Aguirre, Victor; Schlesinger,
Katharine J.; Stello, Dennis; Huber, Daniel; Serenelli, Aldo;
Schoenrich, Ralph; Asplund, Martin; Feltzing, Sofia
Bibcode: 2015IAUGA..2256224C
Altcode:
While in external or high-redshift galaxies we can only measure
integrated stellar properties at best, the Milky Way offers us the
unique opportunity to study its individual baryonic components,
including stars. We use oscillations measured in giant stars by the
Kepler satellite to derive stellar ages and explore the vertical age
structure across few kpc of the Milky Way disc. We find that old stars
dominate at increasing Galactic heights, whereas closer to the plane
a rich zoology of ages exists. The age distribution of stars shows
a smooth decline over the last 10 Gyr, which together with a flat
age-metallicity relation is consistent with a quiescent evolution for
the Milky Way disc since a redshift of about two.
Title: The Gaia-ESO Survey: a quiescent Milky Way with no significant
dark/stellar accreted disc
Authors: Ruchti, G. R.; Read, J. I.; Feltzing, S.; Serenelli, A. M.;
McMillan, P.; Lind, K.; Bensby, T.; Bergemann, M.; Asplund, M.;
Vallenari, A.; Flaccomio, E.; Pancino, E.; Korn, A. J.; Recio-Blanco,
A.; Bayo, A.; Carraro, G.; Costado, M. T.; Damiani, F.; Heiter, U.;
Hourihane, A.; Jofré, P.; Kordopatis, G.; Lardo, C.; de Laverny,
P.; Monaco, L.; Morbidelli, L.; Sbordone, L.; Worley, C. C.; Zaggia, S.
Bibcode: 2015MNRAS.450.2874R
Altcode: 2015arXiv150402481R
According to our current cosmological model, galaxies like the Milky Way
are expected to experience many mergers over their lifetimes. The most
massive of the merging galaxies will be dragged towards the disc plane,
depositing stars and dark matter into an accreted disc structure. In
this work, we utilize the chemodynamical template developed in Ruchti
et al. to hunt for accreted stars. We apply the template to a sample
of 4675 stars in the third internal data release from the Gaia-ESO
Spectroscopic Survey. We find a significant component of accreted halo
stars, but find no evidence of an accreted disc component. This suggests
that the Milky Way has had a rather quiescent merger history since
its disc formed some 8-10 billion years ago and therefore possesses
no significant dark matter disc.
Title: An Elemental Assay of Very, Extremely, and Ultra-metal-poor
Stars
Authors: Hansen, T.; Hansen, C. J.; Christlieb, N.; Beers, T. C.;
Yong, D.; Bessell, M. S.; Frebel, A.; García Pérez, A. E.; Placco,
V. M.; Norris, J. E.; Asplund, M.
Bibcode: 2015ApJ...807..173H
Altcode: 2015arXiv150600579H
We present a high-resolution elemental-abundance analysis for a
sample of 23 very metal-poor ([Fe/H] < -2.0) stars, 12 of which
are extremely metal-poor ([Fe/H] < -3.0), and 4 of which are
ultra-metal-poor ([Fe/H] < -4.0). These stars were targeted to
explore differences in the abundance ratios for elements that constrain
the possible astrophysical sites of element production, including
Li, C, N, O, the α-elements, the iron-peak elements, and a number
of neutron-capture elements. This sample substantially increases the
number of known carbon-enhanced metal-poor (CEMP) and nitrogen-enhanced
metal-poor (NEMP) stars—our program stars include eight that are
considered “normal” metal-poor stars, six CEMP-no stars, five
CEMP-s stars, two CEMP-r stars, and two CEMP-r/s stars. One of the
CEMP-r stars and one of the CEMP-r/s stars are possible NEMP stars. We
detect lithium for three of the six CEMP-no stars, all of which are
Li depleted with respect to the Spite plateau. The majority of the
CEMP stars have [C/N] > 0. The stars with [C/N] < 0 suggest
a larger degree of mixing; the few CEMP-no stars that exhibit this
signature are only found at [Fe/H] < -3.4, a metallicity below
which we also find the CEMP-no stars with large enhancements in Na,
Mg, and Al. We confirm the existence of two plateaus in the absolute
carbon abundances of CEMP stars, as suggested by Spite et al. We also
present evidence for a “floor” in the absolute Ba abundances of
CEMP-no stars at A(Ba) ∼ -2.0. Based on observations made with
the European Southern Observatory telescopes.
Title: The Dissimilar Chemical Composition of the Planet-hosting
Stars of the XO-2 Binary System
Authors: Ramírez, I.; Khanal, S.; Aleo, P.; Sobotka, A.; Liu, F.;
Casagrande, L.; Meléndez, J.; Yong, D.; Lambert, D. L.; Asplund, M.
Bibcode: 2015ApJ...808...13R
Altcode: 2015arXiv150601025R
Using high-quality spectra of the twin stars in the XO-2 binary system,
we have detected significant differences in the chemical composition
of their photospheres. The differences correlate strongly with the
elements’ dust condensation temperature. In XO-2N, volatiles are
enhanced by about 0.015 dex and refractories are overabundant by
up to 0.090 dex. On average, our error bar in relative abundance is
0.012 dex. We present an early metal-depletion scenario in which the
formation of the gas giant planets known to exist around these stars are
responsible for a 0.015 dex offset in the abundances of all elements
while 20 M⨁ of non-detected rocky objects that formed
around XO-2S explain the additional refractory-element difference. An
alternative explanation involves the late accretion of at least 20
M⨁ of planet-like material by XO-2N, allegedly as a result
of the migration of the hot Jupiter detected around that star. Dust
cleansing by a nearby hot star as well as age or Galactic birthplace
effects can be ruled out as valid explanations for this phenomenon.
Title: High-Resolution Spectroscopic Study of Extremely Metal-Poor
Star Candidates from the SkyMapper Survey
Authors: Jacobson, Heather R.; Keller, Stefan; Frebel, Anna; Casey,
Andrew R.; Asplund, Martin; Bessell, Michael S.; Da Costa, Gary S.;
Lind, Karin; Marino, Anna F.; Norris, John E.; Peña, José M.;
Schmidt, Brian P.; Tisserand, Patrick; Walsh, Jennifer M.; Yong,
David; Yu, Qinsi
Bibcode: 2015ApJ...807..171J
Altcode: 2015arXiv150403344J
The SkyMapper Southern Sky Survey is carrying out a search for
the most metal-poor stars in the Galaxy. It identifies candidates
by way of its unique filter set which allows for estimation of
stellar atmospheric parameters. The set includes a narrow filter
centered on the Ca ii K 3933 Å line, enabling a robust estimate
of stellar metallicity. Promising candidates are then confirmed
with spectroscopy. We present the analysis of Magellan Inamori
Kyocera Echelle high-resolution spectroscopy of 122 metal-poor
stars found by SkyMapper in the first two years of commissioning
observations. Forty-one stars have [{Fe}/{{H}}]≤slant -3.0. Nine
have [{Fe}/{{H}}]≤slant -3.5, with three at [{Fe}/{{H}}]∼ -4. A
1D LTE abundance analysis of the elements Li, C, Na, Mg, Al, Si,
Ca, Sc, Ti, Cr, Mn, Co, Ni, Zn, Sr, Ba, and Eu shows these stars
have [X/Fe] ratios typical of other halo stars. One star with low
[X/Fe] values appears to be “Fe-enhanced,” while another star
has an extremely large [Sr/Ba] ratio: \gt 2. Only one other star is
known to have a comparable value. Seven stars are “CEMP-no” stars
([{{C}}/{Fe}]\gt 0.7, [{Ba}/{Fe}]\lt 0). 21 stars exhibit mild r-process
element enhancements (0.3≤slant [{Eu}/{Fe}]\lt 1.0), while four stars
have [{Eu}/{Fe}]≥slant 1.0. These results demonstrate the ability
to identify extremely metal-poor stars from SkyMapper photometry,
pointing to increased sample sizes and a better characterization of
the metal-poor tail of the halo metallicity distribution function
in the future. This paper includes data gathered with the 6.5 m
Magellan Telescopes located at Las Campanas Observatory, Chile.
Title: First light results from the High Efficiency and Resolution
Multi-Element Spectrograph at the Anglo-Australian Telescope
Authors: Sheinis, Andrew; Anguiano, Borja; Asplund, Martin; Bacigalupo,
Carlos; Barden, Sam; Birchall, Michael; Bland-Hawthorn, Joss; Brzeski,
Jurek; Cannon, Russell; Carollo, Daniela; Case, Scott; Casey, Andrew;
Churilov, Vladimir; Warrick, Couch; Dean, Robert; De Silva, Gayandhi;
D'Orazi, Valentina; Duong, Ly; Farrell, Tony; Fiegert, Kristin;
Freeman, Kenneth; Gabriella, Frost; Gers, Luke; Goodwin, Michael; Gray,
Doug; Green, Andrew; Heald, Ron; Heijmans, Jeroen; Ireland, Michael;
Jones, Damien; Kafle, Prajwal; Keller, Stefan; Klauser, Urs; Kondrat,
Yuriy; Kos, Janez; Lawrence, Jon; Lee, Steve; Mali, Slavko; Martell,
Sarah; Mathews, Darren; Mayfield, Don; Miziarski, Stan; Muller, Rolf;
Pai, Naveen; Patterson, Robert; Penny, Ed; Orr, David; Schlesinger,
Katharine; Sharma, Sanjib; Shortridge, Keith; Simpson, Jeffrey;
Smedley, Scott; Smith, Greg; Stafford, Darren; Staszak, Nicholas;
Vuong, Minh; Waller, Lewis; de Boer, Elizabeth Wylie; Xavier, Pascal;
Zheng, Jessica; Zhelem, Ross; Zucker, Daniel; Zwitter, Tomaz
Bibcode: 2015JATIS...1c5002S
Altcode:
The High Efficiency and Resolution Multi Element Spectrograph, HERMES,
is a facility-class optical spectrograph for the Anglo-Australian
Telescope (AAT). It is designed primarily for Galactic Archaeology,
the first major attempt to create a detailed understanding of galaxy
formation and evolution by studying the history of our own galaxy,
the Milky Way. The goal of the GALAH survey is to reconstruct the
mass assembly history of the Milky Way through a detailed chemical
abundance study of one million stars. The spectrograph is based at
the AAT and is fed by the existing 2dF robotic fiber positioning
system. The spectrograph uses volume phase holographic gratings to
achieve a spectral resolving power of 28,000 in standard mode and also
provides a high-resolution mode ranging between 40,000 and 50,000 using
a slit mask. The GALAH survey requires an SNR greater than 100 for a
star brightness of V=14 in an exposure time of one hour. The total
spectral coverage of the four channels is about 100 nm between 370
and 1000 nm for up to 392 simultaneous targets within the 2-degree
field of view. HERMES has been commissioned over three runs, during
bright time in October, November, and December 2013, in parallel with
the beginning of the GALAH pilot survey, which started in November
2013. We present the first-light results from the commissioning run
and the beginning of the GALAH survey, including performance results
such as throughput and resolution, as well as instrument reliability.
Title: VizieR Online Data Catalog: Velocity precision in the Gaia-ESO
Survey (Jackson+, 2015)
Authors: Jackson, R. J.; Jeffries, R. D.; Lewis, J.; Koposov, S. E.;
Sacco, G. G.; Randich, S.; Gilmore, G.; Asplund, M.; Binney, J.;
Bonifacio, P.; Drew, J. E.; Feltzing, S.; Ferguson, A. M. N.;
Micela, G.; Neguerela, I.; Prusti, T.; Rix, H. -W.; Vallenari,
A.; Alfaro, E. J.; Allende Prieto, C.; Babusiaux, C.; Bensby, T.;
Blomme, R.; Bragaglia, A.; Flaccomio, E.; Francois, P.; Hambly, N.;
Irwin, M.; Korn, A. J.; Lanzafame, A. C.; Pancino, E.; Recio-Blanco,
A.; Smiljanic, R.; Van Eck, S.; Walton, N.; Bayo, A.; Bergemann, M.;
Carraro, G.; Costado, M. T.; Damiani, F.; Edvardsson, B.; Franciosini,
E.; Frasca, A.; Heiter, U.; Hill, V.; Hourihane, A.; Jof, P.; Lardo,
C.; de Laverny, P.; Lind, K.; Magrini, L.; Marconi, G.; Martayan, C.;
Masseron, T.; Monaco, L.; Morbidelli, L.; Prisinzano, L.; Sbordone,
L.; Sousa, S. G.; Worley, C. C.; Zaggia, S.
Bibcode: 2015yCat..35800075J
Altcode:
The Gaia-ESO Survey (GES) is a large public spectroscopic survey at
the European Southern Observatory Very LargeTelescope. A key aim is
to provide precise radial velocities (RVs) and projected equatorial
velocities (vsini) for representative samples of Galactic stars,
which will complement information obtained by the Gaia astrometry
satellite. We present an analysis to empirically quantify the size
and distribution of uncertainties in RV and vsini using spectra from
repeated exposures of the same stars. We show that the uncertainties
vary as simple scaling functions of signal-to-noise ratio (S/N) and
vsini, that the uncertainties become larger with increasing photospheric
temperature, but that the dependence on stellar gravity, metallicity
and age is weak. The underlying uncertainty distributions have extended
tails that are better represented by Students t-distributions than
by normal distributions. Parametrised results are provided, which
enable estimates of the RV precision for almost all GES measurements,
and estimates of the vsini precision for stars in young clusters,
as a function of S/N, vsini and stellar temperature. The precision of
individual high S/N GES RV measurements is 0.22-0.26km/s, dependent
on instrumental configuration. (1 data file).
Title: Nucleosynthesis in a Primordial Supernova: Carbon and Oxygen
Abundances in SMSS J031300.36-670839.3
Authors: Bessell, Michael S.; Collet, Remo; Keller, Stefan C.; Frebel,
Anna; Heger, Alexander; Casey, Andrew R.; Masseron, Thomas; Asplund,
Martin; Jacobson, Heather R.; Lind, Karin; Marino, Anna F.; Norris,
John E.; Yong, David; Da Costa, Gary; Chan, Conrad; Magic, Zazralt;
Schmidt, Brian; Tisserand, Patrick
Bibcode: 2015ApJ...806L..16B
Altcode: 2015arXiv150503756B
SMSS J031300.36-670839.3 (hereafter SM0313-6708) is a sub-giant halo
star, with no detectable Fe lines and large overabundances of C and
Mg relative to Ca. We obtained Very Large Telescope-Ultraviolet
and Visual Echelle Spectrograph (UVES) spectra extending to 3060
Å showing strong OH A-X band lines enabling an oxygen abundance to
be derived. The OH A-X band lines in SM0313-6708 are much stronger
than the CH C-X band lines. Spectrum synthesis fits indicate an [O/C]
ratio of 0.02 ± 0.175. Our high signal-to-noise ratio UVES data also
enabled us to lower the Fe abundance limit to {{[Fe/H]}< 3D>
,NLTE}\lt -7.52 (3σ). These data support our previous suggestion
that the star formed from the iron-poor ejecta of a single massive
star Population III supernova. Based on observations obtained with
European Southern Observatory (ESO) telescopes (proposal 092.D-0742).
Title: Iron and s-elements abundance variations in NGC 5286:
comparison with `anomalous' globular clusters and Milky Way satellites
Authors: Marino, A. F.; Milone, A. P.; Karakas, A. I.; Casagrande,
L.; Yong, D.; Shingles, L.; Da Costa, G.; Norris, J. E.; Stetson,
P. B.; Lind, K.; Asplund, M.; Collet, R.; Jerjen, H.; Sbordone, L.;
Aparicio, A.; Cassisi, S.
Bibcode: 2015MNRAS.450..815M
Altcode: 2015arXiv150207438M
We present a high-resolution spectroscopic analysis of 62 red giants
in the Milky Way globular cluster (GC) NGC 5286. We have determined
abundances of representative light proton-capture, α, Fe-peak and
neutron-capture element groups, and combined them with photometry of
multiple sequences observed along the colour-magnitude diagram. Our
principal results are: (i) a broad, bimodal distribution in s-process
element abundance ratios, with two main groups, the s-poor and
s-rich groups; (ii) substantial star-to-star Fe variations, with the
s-rich stars having higher Fe, e.g. < [Fe/H]> _{s-rich}} - <
[Fe/H]> _{s-poor}} ∼ 0.2 dex; and (iii) the presence of O-Na-Al
(anti)correlations in both stellar groups. We have defined a new
photometric index, cBVI = (B - V) - (V - I), to maximize
the separation in the colour-magnitude diagram between the two stellar
groups with different Fe and s-element content, and this index is not
significantly affected by variations in light elements (such as the O-Na
anticorrelation). The variations in the overall metallicity present in
NGC 5286 add this object to the class of anomalous GCs. Furthermore,
the chemical abundance pattern of NGC 5286 resembles that observed
in some of the anomalous GCs, e.g. M 22, NGC 1851, M 2, and the more
extreme ω Centauri, that also show internal variations in s-elements,
and in light elements within stars with different Fe and s-elements
content. In view of the common variations in s-elements, we propose
the term s-Fe-anomalous GCs to describe this sub-class of objects. The
similarities in chemical abundance ratios between these objects strongly
suggest similar formation and evolution histories, possibly associated
with an origin in tidally disrupted dwarf satellites.
Title: Testing the chemical tagging technique with open clusters
Authors: Blanco-Cuaresma, S.; Soubiran, C.; Heiter, U.; Asplund,
M.; Carraro, G.; Costado, M. T.; Feltzing, S.; González-Hernández,
J. I.; Jiménez-Esteban, F.; Korn, A. J.; Marino, A. F.; Montes, D.;
San Roman, I.; Tabernero, H. M.; Tautvaišienė, G.
Bibcode: 2015A&A...577A..47B
Altcode: 2015arXiv150302082B
Context. Stars are born together from giant molecular clouds and, if
we assume that the priors were chemically homogeneous and well-mixed,
we expect them to share the same chemical composition. Most of
the stellar aggregates are disrupted while orbiting the Galaxy and
most of the dynamic information is lost, thus the only possibility
of reconstructing the stellar formation history is to analyze the
chemical abundances that we observe today.
Aims: The chemical
tagging technique aims to recover disrupted stellar clusters based
merely on their chemical composition. We evaluate the viability of this
technique to recover co-natal stars that are no longer gravitationally
bound.
Methods: Open clusters are co-natal aggregates that have
managed to survive together. We compiled stellar spectra from 31 old
and intermediate-age open clusters, homogeneously derived atmospheric
parameters, and 17 abundance species, and applied machine learning
algorithms to group the stars based on their chemical composition. This
approach allows us to evaluate the viability and efficiency of the
chemical tagging technique.
Results: We found that stars at
different evolutionary stages have distinct chemical patterns that may
be due to NLTE effects, atomic diffusion, mixing, and biases. When
separating stars into dwarfs and giants, we observed that a few
open clusters show distinct chemical signatures while the majority
show a high degree of overlap. This limits the recovery of co-natal
aggregates by applying the chemical tagging technique. Nevertheless,
there is room for improvement if more elements are included and models
are improved. Based on observations obtained at the Telescope
Bernard Lyot (USR5026) operated by the Observatoire Midi-Pyrénées,
Université de Toulouse (Paul Sabatier), Centre National de la
Recherche Scientifique of France, and on public data obtained from
the ESO Science Archive Facility under requests number 81252 and 81618.
Title: Atomic and molecular data for optical stellar spectroscopy
Authors: Heiter, U.; Lind, K.; Asplund, M.; Barklem, P. S.; Bergemann,
M.; Magrini, L.; Masseron, T.; Mikolaitis, Š.; Pickering, J. C.;
Ruffoni, M. P.
Bibcode: 2015PhyS...90e4010H
Altcode: 2015arXiv150606697H
High-precision spectroscopy of large stellar samples plays a crucial
role for several topical issues in astrophysics. Examples include
studying the chemical structure and evolution of the Milky Way
Galaxy, tracing the origin of chemical elements, and characterizing
planetary host stars. Data are accumulating from instruments that
obtain high-quality spectra of stars in the ultraviolet, optical and
infrared wavelength regions on a routine basis. These instruments
are located at ground-based 2-10 m class telescopes around the world,
in addition to the spectrographs with unique capabilities available at
the Hubble Space Telescope. The interpretation of these spectra requires
high-quality transition data for numerous species, in particular neutral
and singly ionized atoms, and di- or triatomic molecules. We rely
heavily on the continuous efforts of laboratory astrophysics groups
that produce and improve the relevant experimental and theoretical
atomic and molecular data. The compilation of the best available data
is facilitated by databases and electronic infrastructures such as
the NIST Atomic Spectra Database, the VALD database, or the Virtual
Atomic and Molecular Data Centre. We illustrate the current status
of atomic data for optical stellar spectra with the example of the
Gaia-ESO Public Spectroscopic Survey. Data sources for 35 chemical
elements were reviewed in an effort to construct a line list for a
homogeneous abundance analysis of up to 105 stars.
Title: The GALAH survey: scientific motivation
Authors: De Silva, G. M.; Freeman, K. C.; Bland-Hawthorn, J.; Martell,
S.; de Boer, E. Wylie; Asplund, M.; Keller, S.; Sharma, S.; Zucker,
D. B.; Zwitter, T.; Anguiano, B.; Bacigalupo, C.; Bayliss, D.;
Beavis, M. A.; Bergemann, M.; Campbell, S.; Cannon, R.; Carollo, D.;
Casagrande, L.; Casey, A. R.; Da Costa, G.; D'Orazi, V.; Dotter, A.;
Duong, L.; Heger, A.; Ireland, M. J.; Kafle, P. R.; Kos, J.; Lattanzio,
J.; Lewis, G. F.; Lin, J.; Lind, K.; Munari, U.; Nataf, D. M.; O'Toole,
S.; Parker, Q.; Reid, W.; Schlesinger, K. J.; Sheinis, A.; Simpson,
J. D.; Stello, D.; Ting, Y. -S.; Traven, G.; Watson, F.; Wittenmyer,
R.; Yong, D.; Žerjal, M.
Bibcode: 2015MNRAS.449.2604D
Altcode: 2015arXiv150204767D
The Galactic Archaeology with HERMES (GALAH) survey is a large
high-resolution spectroscopic survey using the newly commissioned
High Efficiency and Resolution Multi-Element Spectrograph (HERMES)
on the Anglo-Australian Telescope. The HERMES spectrograph provides
high-resolution (R ∼ 28 000) spectra in four passbands for 392 stars
simultaneously over a 2 deg field of view. The goal of the survey is
to unravel the formation and evolutionary history of the Milky Way,
using fossil remnants of ancient star formation events which have been
disrupted and are now dispersed throughout the Galaxy. Chemical tagging
seeks to identify such dispersed remnants solely from their common and
unique chemical signatures; these groups are unidentifiable from their
spatial, photometric or kinematic properties. To carry out chemical
tagging, the GALAH survey will acquire spectra for a million stars down
to V ∼ 14. The HERMES spectra of FGK stars contain absorption lines
from 29 elements including light proton-capture elements, α-elements,
odd-Z elements, iron-peak elements and n-capture elements from the
light and heavy s-process and the r-process. This paper describes the
motivation and planned execution of the GALAH survey, and presents
some results on the first-light performance of HERMES.
Title: New view on exoplanet transits. Transit of Venus described
using three-dimensional solar atmosphere STAGGER-grid simulations
Authors: Chiavassa, A.; Pere, C.; Faurobert, M.; Ricort, G.; Tanga,
P.; Magic, Z.; Collet, R.; Asplund, M.
Bibcode: 2015A&A...576A..13C
Altcode: 2015arXiv150106207C
Context. An important benchmark for current observational techniques and
theoretical modeling of exoplanet atmospheres is the transit of Venus
(ToV). Stellar activity and, in particular, convection-related surface
structures, potentially cause fluctuations that can affect the transit
light curves. Surface convection simulations can help interpreting the
ToV as well as other transits outside our solar system.
Aims:
We used the realistic three-dimensional (3D) radiative hydrodynamical
(RHD) simulation of the Sun from the Stagger-grid and synthetic images
computed with the radiative transfer code Optim3D to predict the transit
of Venus (ToV) in 2004 that was observed by the satellite ACRIMSAT.
Methods: We computed intensity maps from the RHD simulation of the
Sun and produced a synthetic stellar disk image as an observer would
see, accounting for the center-to-limb variations. The contribution of
the solar granulation was considered during the ToV. We computed the
light curve and compared it to the ACRIMSAT observations as well as
to light curves obtained with solar surface representations carried
out using radial profiles with different limb-darkening laws. We
also applied the same spherical tile imaging method as used for RHD
simulation to the observations of center-to-limb solar granulation with
Hinode.
Results: We explain ACRIMSAT observations of 2004 ToV and
show that the granulation pattern causes fluctuations in the transit
light curve. We compared different limb-darkening models to the RHD
simulation and evaluated the contribution of the granulation to the
ToV. We showed that the granulation pattern can partially explain the
observed discrepancies between models and data. Moreover, we found
that the overall agreement between real and RHD solar granulation
is good, either in terms of depth or ingress/egress slopes of the
transit curve. This confirms that the limb-darkening and granulation
pattern simulated in 3D RHD of the Sun represent well what is imaged
by Hinode. In the end, we found that the contribution of the Venusean
aureole during ToV is ~10-6 times less intense than the
solar photosphere, and thus, accurate measurements of this phenomena
are extremely challenging.
Conclusions: The prospects for
planet detection and characterization with transiting methods are
excellent with access to large a amount of data for stars. Being able
to consistently explain the data of 2004 ToV is a new step forward
for 3D RHD simulations, which are becoming essential for detecting
and characterizing exoplanets. They show that granulation has to
be considered as an intrinsic uncertainty (as a result of stellar
variability) on precise measurements of exoplanet transits of, most
likely, planets with small diameters. In this context, it is mandatory
to obtain a comprehensive knowledge of the host star, including a
detailed study of the stellar surface convection.
Title: Shallow extra mixing in solar twins inferred from Be abundances
Authors: Tucci Maia, M.; Meléndez, J.; Castro, M.; Asplund, M.;
Ramírez, I.; Monroe, T. R.; do Nascimento, J. D., Jr.; Yong, D.
Bibcode: 2015A&A...576L..10T
Altcode: 2015arXiv150307882T
Context. Lithium and beryllium are destroyed at different temperatures
in stellar interiors. As such, their relative abundances offer excellent
probes of the nature and extent of mixing processes within and below the
convection zone.
Aims: We determine Be abundances for a sample
of eight solar twins for which Li abundances have previously been
determined. The analyzed solar twins span a very wide range of age,
0.5-8.2 Gyr, which enables us to study secular evolution of Li and Be
depletion.
Methods: We gathered high-quality UVES/VLT spectra
and obtained Be abundances by spectral synthesis of the Be ii 313 nm
doublet.
Results: The derived beryllium abundances exhibit no
significant variation with age. The more fragile Li, however, exhibits
a monotonically decreasing abundance with increasing age. Therefore,
relatively shallow extra mixing below the convection zone is necessary
to simultaneously account for the observed Li and Be behavior in
the Sun and solar twins. Based on observations obtained at the
European Southern Observatory (ESO) Very Large Telescope (VLT) at
Paranal Observatory, Chile (observing program 083.D-0871).
Title: Gaia-ESO Survey: Analysis of pre-main sequence stellar spectra
Authors: Lanzafame, A. C.; Frasca, A.; Damiani, F.; Franciosini, E.;
Cottaar, M.; Sousa, S. G.; Tabernero, H. M.; Klutsch, A.; Spina, L.;
Biazzo, K.; Prisinzano, L.; Sacco, G. G.; Randich, S.; Brugaletta, E.;
Delgado Mena, E.; Adibekyan, V.; Montes, D.; Bonito, R.; Gameiro,
J. F.; Alcalá, J. M.; González Hernández, J. I.; Jeffries,
R.; Messina, S.; Meyer, M.; Gilmore, G.; Asplund, M.; Binney, J.;
Bonifacio, P.; Drew, J. E.; Feltzing, S.; Ferguson, A. M. N.; Micela,
G.; Negueruela, I.; Prusti, T.; Rix, H. -W.; Vallenari, A.; Alfaro,
E. J.; Allende Prieto, C.; Babusiaux, C.; Bensby, T.; Blomme, R.;
Bragaglia, A.; Flaccomio, E.; Francois, P.; Hambly, N.; Irwin, M.;
Koposov, S. E.; Korn, A. J.; Smiljanic, R.; Van Eck, S.; Walton, N.;
Bayo, A.; Bergemann, M.; Carraro, G.; Costado, M. T.; Edvardsson,
B.; Heiter, U.; Hill, V.; Hourihane, A.; Jackson, R. J.; Jofré, P.;
Lardo, C.; Lewis, J.; Lind, K.; Magrini, L.; Marconi, G.; Martayan,
C.; Masseron, T.; Monaco, L.; Morbidelli, L.; Sbordone, L.; Worley,
C. C.; Zaggia, S.
Bibcode: 2015A&A...576A..80L
Altcode: 2015arXiv150104450L
Context. The Gaia-ESO Public Spectroscopic Survey is obtaining
high-quality spectroscopy of some 100 000 Milky Way stars using the
FLAMES spectrograph at the VLT, down to V = 19 mag, systematically
covering all the main components of the Milky Way and providing the
first homogeneous overview of the distributions of kinematics and
chemical element abundances in the Galaxy. Observations of young open
clusters, in particular, are giving new insights into their initial
structure, kinematics, and their subsequent evolution.
Aims:
This paper describes the analysis of UVES and GIRAFFE spectra acquired
in the fields of young clusters whose population includes pre-main
sequence (PMS) stars. The analysis is applied to all stars in such
fields, regardless of any prior information on membership, and provides
fundamental stellar atmospheric parameters, elemental abundances, and
PMS-specific parameters such as veiling, accretion, and chromospheric
activity.
Methods: When feasible, different methods were used
to derive raw parameters (e.g. line equivalent widths) fundamental
atmospheric parameters and derived parameters (e.g. abundances). To
derive some of these parameters, we used methods that have been
extensively used in the past and new ones developed in the context
of the Gaia-ESO survey enterprise. The internal precision of these
quantities was estimated by inter-comparing the results obtained by
these different methods, while the accuracy was estimated by comparison
with independent external data, such as effective temperature and
surface gravity derived from angular diameter measurements, on a
sample of benchmarks stars. A validation procedure based on these
comparisons was applied to discard spurious or doubtful results and
produce recommended parameters. Specific strategies were implemented to
resolve problems of fast rotation, accretion signatures, chromospheric
activity, and veiling.
Results: The analysis carried out on
spectra acquired in young cluster fields during the first 18 months
of observations, up to June 2013, is presented in preparation of the
first release of advanced data products. These include targets in
the fields of the ρ Oph, Cha I,
NGC 2264, γ Vel, and NGC
2547 clusters. Stellar parameters obtained with the higher
resolution and larger wavelength coverage from UVES are reproduced with
comparable accuracy and precision using the smaller wavelength range
and lower resolution of the GIRAFFE setup adopted for young stars,
which allows us to provide stellar parameters with confidence for the
much larger GIRAFFE sample. Precisions are estimated to be ≈120 K
rms in Teff, ≈0.3 dex rms in log g, and ≈0.15 dex rms in
[Fe/H] for the UVES and GIRAFFE setups.
Title: The Gaia-ESO Survey: A globular cluster escapee in the
Galactic halo
Authors: Lind, K.; Koposov, S. E.; Battistini, C.; Marino, A. F.;
Ruchti, G.; Serenelli, A.; Worley, C. C.; Alves-Brito, A.; Asplund,
M.; Barklem, P. S.; Bensby, T.; Bergemann, M.; Blanco-Cuaresma, S.;
Bragaglia, A.; Edvardsson, B.; Feltzing, S.; Gruyters, P.; Heiter,
U.; Jofre, P.; Korn, A. J.; Nordlander, T.; Ryde, N.; Soubiran,
C.; Gilmore, G.; Randich, S.; Ferguson, A. M. N.; Jeffries, R. D.;
Vallenari, A.; Allende Prieto, C.; Pancino, E.; Recio-Blanco, A.;
Romano, D.; Smiljanic, R.; Bellazzini, M.; Damiani, F.; Hill, V.;
de Laverny, P.; Jackson, R. J.; Lardo, C.; Zaggia, S.
Bibcode: 2015A&A...575L..12L
Altcode: 2015arXiv150203934L
A small fraction of the halo field is made up of stars that share the
light element (Z ≤ 13) anomalies characteristic of second generation
globular cluster (GC) stars. The ejected stars shed light on the
formation of the Galactic halo by tracing the dynamical history of
the clusters, which are believed to have once been more massive. Some
of these ejected stars are expected to show strong Al enhancement at
the expense of shortage of Mg, but until now no such star has been
found. We search for outliers in the Mg and Al abundances of the few
hundreds of halo field stars observed in the first eighteen months of
the Gaia-ESO public spectroscopic survey. One halo star at the base
of the red giant branch, here referred to as 22593757-4648029 is found
to have [ Mg/Fe ] = -0.36 ± 0.04 and [ Al/Fe ] = 0.99 ± 0.08, which
is compatible with the most extreme ratios detected in GCs so far. We
compare the orbit of 22593757-4648029 to GCs of similar metallicity
andfind it unlikely that this star has been tidally stripped with low
ejection velocity from any of the clusters. However, both chemical
and kinematic arguments render it plausible that the star has been
ejected at high velocity from the anomalous GC ω Centauri within
the last few billion years. We cannot rule out other progenitor GCs,
because some may have disrupted fully, and the abundance and orbital
data are inadequate for many of those that are still intact. Based on data acquired by the Gaia-ESO Survey, programme ID
188.B-3002. Observations were made with ESO Telescopes at the La Silla
Paranal Observatory.Appendix A is available in electronic form at http://www.aanda.org
Title: VizieR Online Data Catalog: Photometry and abundances of
NGC1851 stars (Marino+, 2014)
Authors: Marino, A. F.; Milone, A. P.; Yong, D.; Dotter, A.; Da Costa,
G.; Asplund, M.; Jerjen, H.; Mackey, D.; Norris, J.; Cassisi, S.;
Sbordone, L.; Stetson, P. B.; Weiss, A.; Aparicio, A.; Bedin, L. R.;
Lind, K.; Monelli, M.; Piotto, G.; Angeloni, R.; Buonanno, R.
Bibcode: 2015yCat..74423044M
Altcode:
In this paper, we used four distinct photometric data sets. First,
we used Stetson (2000PASP..112..925S) ground-based B, V, R and I
photometry. This photometric catalogue has been established from about
550 images taken at different telescopes, i.e. the Max Planck 2.2m,
the Cerro Tololo Inter-American Observatory (CTIO) 4, 1.5 and 0.9m
telescopes, and the Dutch 0.9m telescope in La Silla. In the present
work, we have complemented the Stetson catalogue with images collected
with the Wide Field Imager (WFI) of the Max Planck 2.2m telescope at
La Silla (WFI@2.2m) through the U filter under the SUrvey of Multiple
pOpulations (SUMO) campaign. Secondly, to study stars in the halo
of NGC 1851, we collected BVI images with WFI@2.2m of a field between
~10 and 35 arcmin to the south of the cluster centre. Photometry
and astrometry for this data set have been obtained by using the
program img2xym_WFI and the procedure described by Anderson et
al. (2006A&A...454.1029A). Third and finally, to investigate
the most crowded central regions, we use Hubble Space Telescope (HST)
F606W and F814W photometry obtained with the Wide Field Channel of the
Advanced Camera for Survey (WFC/ACS) and F275W photometry collected
with the Ultraviolet and Visual Channel of the Wide Field Camera 3
(UVIS/WFC3). (2 data files).
Title: The oldest objects in the Universe: extremely metal-poor
stars in the Galactic bulge (via telecon)
Authors: Asplund, Martin
Bibcode: 2015mwss.confE..55A
Altcode:
No abstract at ADS
Title: The Stagger-grid: A grid of 3D stellar atmosphere
models. IV. Limb darkening coefficients
Authors: Magic, Z.; Chiavassa, A.; Collet, R.; Asplund, M.
Bibcode: 2015A&A...573A..90M
Altcode: 2014arXiv1403.3487M
Aims: We compute the emergent stellar spectra from the UV to
far infrared for different viewing angles using realistic 3D model
atmospheres for a large range in stellar parameters to predict the
stellar limb darkening.
Methods: We have computed full 3D
LTE synthetic spectra based on 3D radiative hydrodynamic atmosphere
models from the Stagger-grid in the ranges: Teff from 4000
to 7000 K, log g from 1.5 to 5.0, and [Fe/H], from -4.0 to +0.5. From
the resulting intensities, we derived coefficients for the standard
limb darkening laws considering a number of often-used photometric
filters. Furthermore, we calculated theoretical transit light curves,
in order to quantify the differences between predictions by the
widely used 1D model atmosphere and our 3D models.
Results:
The 3D models are often found to predict steeper darkening towards
the limb compared to the 1D models, mainly due to the temperature
stratifications and temperature gradients being different in the
3D models compared to those predicted with 1D models based on the
mixing length theory description of convective energy transport. The
resulting differences in the transit light curves are rather small;
however, these can be significant for high-precision observations of
extrasolar transits, and are able to lower the residuals from the fits
with 1D limb darkening profiles.
Conclusions: We advocate the
use of the new limb darkening coefficients provided for the standard
four-parameter non-linear power law, which can fit the limb darkening
more accurately than other choices. Full Table A.1 and the grid
of spectra are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/573/A90,
as well as at http://www.stagger-stars.net
Title: The Stagger-grid: A grid of 3D stellar atmosphere
models. III. The relation to mixing length convection theory
Authors: Magic, Z.; Weiss, A.; Asplund, M.
Bibcode: 2015A&A...573A..89M
Altcode: 2014arXiv1403.1062M
Aims: We investigate the relation between 1D atmosphere models
that rely on the mixing length theory and models based on full 3D
radiative hydrodynamic (RHD) calculations to describe convection in
the envelopes of late-type stars.
Methods: The adiabatic
entropy value of the deep convection zone, sbot,
and the entropy jump, Δs, determined from the 3D RHD models,
were matched with the mixing length parameter, αMLT,
from 1D hydrostatic atmosphere models with identical microphysics
(opacities and equation-of-state). We also derived the mass mixing
length parameter, αm, and the vertical correlation
length of the vertical velocity, C[vz,vz],
directly from the 3D hydrodynamical simulations of stellar subsurface
convection.
Results: The calibrated mixing length parameter
for the Sun is α๏MLT (Sbot)
= 1.98. . For different stellar parameters, αMLT
varies systematically in the range of 1.7 - 2.4. In particular,
αMLT decreases towards higher effective temperature,
lower surface gravity and higher metallicity. We find equivalent
results for α๏MLT (ΔS). In addition, we find
a tight correlation between the mixing length parameter and the inverse
entropy jump. We derive an analytical expression from the hydrodynamic
mean-field equations that motivates the relation to the mass mixing
length parameter, αm, and find that it qualitatively shows
a similar variation with stellar parameter (between 1.6 and 2.4) with
the solar value of α๏m = 1.83.. The vertical
correlation length scaled with the pressure scale height yields 1.71
for the Sun, but only displays a small systematic variation with
stellar parameters, the correlation length slightly increases with
Teff.
Conclusions: We derive mixing length parameters
for various stellar parameters that can be used to replace a constant
value. Within any convective envelope, αm and related
quantities vary strongly. Our results will help to replace a constant
αMLT. Appendices are available in electronic form at http://www.aanda.orgFull
Table A.1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/573/A89
as well as at http://www.stagger-stars.net
Title: The elemental composition of the Sun. III. The heavy elements
Cu to Th
Authors: Grevesse, Nicolas; Scott, Pat; Asplund, Martin; Sauval,
A. Jacques
Bibcode: 2015A&A...573A..27G
Altcode: 2014arXiv1405.0288G
We re-evaluate the abundances of the elements in the Sun from copper
(Z = 29) to thorium (Z = 90). Our results are mostly based on
neutral and singly-ionised lines in the solar spectrum. We use the
latest 3D hydrodynamic solar model atmosphere, and in a few cases
also correct for departures from local thermodynamic equilibrium
(LTE) using non-LTE (NLTE) calculations performed in 1D. In order
to minimise statistical and systematic uncertainties, we make
stringent line selections, employ the highest-quality observational
data and carefully assess oscillator strengths, hyperfine constants
and isotopic separations available in the literature, for every line
included in our analysis. Our results are typically in good agreement
with the abundances in the most pristine meteorites, but there are
some interesting exceptions. This analysis constitutes both a full
exposition and a slight update of the relevant parts of the preliminary
results we presented in Asplund et al. (2009, ARA&A, 47, 481),
including full line lists and details of all input data that we have
employed. Tables 1-3 are available in electronic form at http://www.aanda.org
Title: The elemental composition of the Sun. II. The iron group
elements Sc to Ni
Authors: Scott, Pat; Asplund, Martin; Grevesse, Nicolas; Bergemann,
Maria; Sauval, A. Jacques
Bibcode: 2015A&A...573A..26S
Altcode: 2014arXiv1405.0287S
We redetermine the abundances of all iron group nuclei in the Sun,
based on neutral and singly-ionised lines of Sc, Ti, V, Mn, Fe, Co and
Ni in the solar spectrum. We employ a realistic 3D hydrodynamic model
solar atmosphere, corrections for departures from local thermodynamic
equilibrium (NLTE), stringent line selection procedures and high
quality observational data. We have scoured the literature for
the best quality oscillator strengths, hyperfine constants and
isotopic separations available for our chosen lines. We find log
ɛSc = 3.16 ± 0.04, log ɛTi = 4.93 ± 0.04,
log ɛV = 3.89 ± 0.08, log ɛCr = 5.62 ± 0.04,
log ɛMn = 5.42 ± 0.04, log ɛFe = 7.47 ± 0.04,
log ɛCo = 4.93 ± 0.05 and log ɛNi = 6.20 ±
0.04. Our uncertainties factor in both statistical and systematic errors
(the latter estimated for possible errors in the model atmospheres and
NLTE line formation). The new abundances are generally in good agreement
with the CI meteoritic abundances but with some notable exceptions. This
analysis constitutes both a full exposition and a slight update of the
preliminary results we presented in Asplund et al. (2009, ARA&A,
47, 481), including full line lists and details of all input data
we employed. Tables 1-3 are available in electronic form at http://www.aanda.org
Title: The elemental composition of the Sun. I. The intermediate
mass elements Na to Ca
Authors: Scott, Pat; Grevesse, Nicolas; Asplund, Martin; Sauval,
A. Jacques; Lind, Karin; Takeda, Yoichi; Collet, Remo; Trampedach,
Regner; Hayek, Wolfgang
Bibcode: 2015A&A...573A..25S
Altcode: 2014arXiv1405.0279S
The chemical composition of the Sun is an essential piece of reference
data for astronomy, cosmology, astroparticle, space and geo-physics:
elemental abundances of essentially all astronomical objects are
referenced to the solar composition, and basically every process
involving the Sun depends on its composition. This article, dealing
with the intermediate-mass elements Na to Ca, is the first in a
series describing the comprehensive re-determination of the solar
composition. In this series we severely scrutinise all ingredients
of the analysis across all elements, to obtain the most accurate,
homogeneous and reliable results possible. We employ a highly
realistic 3D hydrodynamic model of the solar photosphere, which has
successfully passed an arsenal of observational diagnostics. For
comparison, and to quantify remaining systematic errors, we repeat
the analysis using three different 1D hydrostatic model atmospheres
(marcs, miss and Holweger & Müller 1974, Sol. Phys., 39, 19) and
a horizontally and temporally-averaged version of the 3D model (⟨ 3D
⟩). We account for departures from local thermodynamic equilibrium
(LTE) wherever possible. We have scoured the literature for the best
possible input data, carefully assessing transition probabilities,
hyperfine splitting, partition functions and other data for inclusion
in the analysis. We have put the lines we use through a very stringent
quality check in terms of their observed profiles and atomic data, and
discarded all that we suspect to be blended. Our final recommended
3D+NLTE abundances are: log ɛNa = 6.21 ± 0.04, log
ɛMg = 7.59 ± 0.04, log ɛAl = 6.43 ± 0.04,
log ɛSi = 7.51 ± 0.03, log ɛP = 5.41 ± 0.03,
log ɛS = 7.13 ± 0.03, log ɛK = 5.04 ± 0.05
and log ɛCa = 6.32 ± 0.03. The uncertainties include both
statistical and systematic errors. Our results are systematically
smaller than most previous ones with the 1D semi-empirical
Holweger & Müller model, whereas the ⟨ 3D ⟩ model returns
abundances very similar to the full 3D calculations. This analysis
provides a complete description and a slight update of the results
presented in Asplund et al. (2009, ARA&A, 47, 481) for Na to
Ca, and includes full details of all lines and input data used. Tables 1-4 and Appendix A are available in electronic form at http://www.aanda.org
Title: Magnesium isotopes in giants in the Milky Way inner disk and
bulge: First results with 3D stellar atmospheres.
Authors: Thygesen, Anders; Sbordone, Luca; Christlieb, Norbert;
Asplund, Martin
Bibcode: 2015AAS...22513303T
Altcode:
The Milky Way bulge is one of the most poorly understood components of
our galaxy and its formation history is still a matter of debate (early
collapse vs. disk instability). All knowledge of its chemical evolution
history has been so far derived by measuring elemental abundances:
no isotopic mixtures have been measured so far in the Bulge. While
quite challenging, isotopic measurements can be accomplished with
present instruments in bulge stars for a few elements, Magnesium being
one of them.Of the three stable Mg isotopes, the most common one,
24Mg, is mainly produced by α capture in SN II, while
the other two, 25Mg and 26Mg, can be produced
efficiently in massive AGB stars, through the 22Ne(α,
n)25Mg(n, γ)26Mg reactions as well as the
Mg-Al chain. Moreover, SN II production of 25Mg and
26Mg increases with increasing progenitor metallicity,
so in older stellar populations, where only the signature of
metal-poor SNe is to be expected, one should not see a significant
25Mg or 26Mg fraction. However, if larger
25Mg/24Mg and 26Mg/24Mg
ratios are observed, relative to what is produced in SNe, this is a
clear sign of an AGB contribution. As such, Mg isotopic ratios are
a very useful probe of AGB pollution onset and chemical enrichment
timescale in a stellar population.Here, we present the first ever
measurements of Mg isotopes in 7 red giant stars in the Milky Way
bulge and inner disk, including two stars in the bulge globular
cluster NGC6522. The isotopic abundances have been derived from high
resolution, high signal-to-noise VLT-UVES spectra using both standard
1D atmospheric models as well as state-of-the-art 3D hydrodynamical
models and spectrosynthesis. The use of 3D atmospheric models impacts
the derived ratios and this work represents the first derivation of
Mg isotopes using full 3D spectrosynthesis. These results yield new
constraints on the proposed formation scenarios of the Milky Way bulge.
Title: The Solar Twin Planet Search. I. Fundamental parameters of
the stellar sample
Authors: Ramírez, I.; Meléndez, J.; Bean, J.; Asplund, M.; Bedell,
M.; Monroe, T.; Casagrande, L.; Schirbel, L.; Dreizler, S.; Teske,
J.; Tucci Maia, M.; Alves-Brito, A.; Baumann, P.
Bibcode: 2014A&A...572A..48R
Altcode: 2014arXiv1408.4130R
Context. We are carrying out a search for planets around a sample
of solar twin stars using the HARPS spectrograph. The goal of this
project is to exploit the advantage offered by solar twins to obtain
chemical abundances of unmatched precision. This survey will enable
new studies of the stellar composition - planet connection.
Aims: We determine the fundamental parameters of the 88 solar twin
stars that have been chosen as targets for our experiment.
Methods: We used the MIKE spectrograph on the Magellan Clay Telescope
to acquire high resolution, high signal-to-noise ratio spectra of
our sample stars. We measured the equivalent widths of iron lines
and used strict differential excitation/ionization balance analysis
to determine atmospheric parameters of unprecedented internal
precision: σ(Teff) = 7 K, σ(log g) = 0.019, σ( [Fe/H]
) = 0.006 dex, σ(vt) = 0.016 km s-1. Reliable
relative ages and highly precise masses were then estimated using
theoretical isochrones.
Results: The spectroscopic parameters
we derived are in good agreement with those measured using other
independent techniques. There is even better agreement if the
sample is restricted to those stars with the most internally precise
determinations of stellar parameters in every technique involved. The
root-mean-square scatter of the differences seen is fully compatible
with the observational errors, demonstrating, as assumed thus far,
that systematic uncertainties in the stellar parameters are negligible
in the study of solar twins. We find a tight activity-age relation
for our sample stars, which validates the internal precision of our
dating method. Furthermore, we find that the solar cycle is perfectly
consistent both with this trend and its star-to-star scatter.
Conclusions: We present the largest sample of solar twins analyzed
homogeneously using high quality spectra. The fundamental parameters
derived from this work will be employed in subsequent work that aims to
explore the connections between planet formation and stellar chemical
composition. Tables 2-4 are available in electronic form at http://www.aanda.org
Title: Improvements to stellar structure models, based on a grid of 3D
convection simulations - II. Calibrating the mixing-length formulation
Authors: Trampedach, Regner; Stein, Robert F.; Christensen-Dalsgaard,
Jørgen; Nordlund, Åke; Asplund, Martin
Bibcode: 2014MNRAS.445.4366T
Altcode: 2014arXiv1410.1559T
We perform a calibration of the mixing length of convection in stellar
structure models against realistic 3D radiation-coupled hydrodynamics
simulations of convection in stellar surface layers, determining
the adiabat deep in convective stellar envelopes. The mixing-length
parameter α is calibrated by matching averages of the 3D simulations
to 1D stellar envelope models, ensuring identical atomic physics
in the two cases. This is done for a previously published grid of
solar-metallicity convection simulations, covering from 4200 to 6900 K
on the main sequence, and from 4300 to 5000 K for giants with log g =
2.2. Our calibration results in an α varying from 1.6 for the warmest
dwarf, which is just cool enough to admit a convective envelope, and
up to 2.05 for the coolest dwarfs in our grid. In between these is a
triangular plateau of α ∼ 1.76. The Sun is located on this plateau
and has seen little change during its evolution so far. When stars
ascend the giant branch, they largely do so along tracks of constant
α, with α decreasing with increasing mass.
Title: The Gaia-ESO Survey: the most metal-poor stars in the
Galactic bulge
Authors: Howes, L. M.; Asplund, M.; Casey, A. R.; Keller, S. C.; Yong,
D.; Gilmore, G.; Lind, K.; Worley, C.; Bessell, M. S.; Casagrande, L.;
Marino, A. F.; Nataf, D. M.; Owen, C. I.; Da Costa, G. S.; Schmidt,
B. P.; Tisserand, P.; Randich, S.; Feltzing, S.; Vallenari, A.;
Allende Prieto, C.; Bensby, T.; Flaccomio, E.; Korn, A. J.; Pancino,
E.; Recio-Blanco, A.; Smiljanic, R.; Bergemann, M.; Costado, M. T.;
Damiani, F.; Heiter, U.; Hill, V.; Hourihane, A.; Jofré, P.; Lardo,
C.; de Laverny, P.; Magrini, L.; Maiorca, E.; Masseron, T.; Morbidelli,
L.; Sacco, G. G.; Minniti, D.; Zoccali, M.
Bibcode: 2014MNRAS.445.4241H
Altcode: 2014arXiv1409.7952H
We present the first results of the EMBLA survey (Extremely
Metal-poor BuLge stars with AAOmega), aimed at finding metal-poor
stars in the Milky Way bulge, where the oldest stars should now
preferentially reside. EMBLA utilizes SkyMapper photometry to
pre-select metal-poor candidates, which are subsequently confirmed
using AAOmega spectroscopy. We describe the discovery and analysis
of four bulge giants with -2.72 ≤ [Fe/H] ≤ -2.48, the lowest
metallicity bulge stars studied with high-resolution spectroscopy to
date. Using FLAMES/UVES spectra through the Gaia-ESO Survey we have
derived abundances of twelve elements. Given the uncertainties, we
find a chemical similarity between these bulge stars and halo stars
of the same metallicity, although the abundance scatter may be larger,
with some of the stars showing unusual [α/Fe] ratios.
Title: NGC 6522: a typical globular cluster in the Galactic bulge
without signatures of rapidly rotating Population III stars
Authors: Ness, Melissa; Asplund, Martin; Casey, Andrew R.
Bibcode: 2014MNRAS.445.2994N
Altcode: 2014arXiv1408.0290N
We present an abundance analysis of eight potential member stars of
the old Galactic bulge globular cluster NGC 6522. The same stars
have previously been studied by Chiappini et al., who found very
high abundances of the slow neutron capture elements compared with
other clusters and field stars of similar metallicity, which they
interpreted as reflecting nucleosynthesis in rapidly rotating,
massive Population III stars. In contrast to their analysis, we do
not find any unusual enhancements of the neutron capture elements Sr,
Y, Ba and Eu and conclude that previous claims result mainly from not
properly accounting for blending lines. Instead, we find NGC 6522 to
be an unremarkable globular cluster with comparable abundance trends
to other Galactic globular clusters at the same metallicity ([Fe/H] =
-1.15 ± 0.16). The stars are also chemically similar to halo and bulge
field stars at the same metallicity, spanning a small range in [Y/Ba]
and with normal α-element abundances. We thus find no observational
evidence for any chemical signatures of rapidly rotating Population
III stars in NGC 6522.
Title: The chemical composition of red giants in 47
Tucanae. I. Fundamental parameters and chemical abundance patterns
Authors: Thygesen, A. O.; Sbordone, L.; Andrievsky, S.; Korotin,
S.; Yong, D.; Zaggia, S.; Ludwig, H. -G.; Collet, R.; Asplund, M.;
Ventura, P.; D'Antona, F.; Meléndez, J.; D'Ercole, A.
Bibcode: 2014A&A...572A.108T
Altcode: 2014arXiv1409.4694T
Context. The study of chemical abundance patterns in globular
clusters is key importance to constraining the different candidates
for intracluster pollution of light elements.
Aims: We aim
at deriving accurate abundances for a wide range of elements in the
globular cluster 47 Tucanae (NGC 104) to add new constraints to the
pollution scenarios for this particular cluster, expanding the range of
previously derived element abundances.
Methods: Using tailored
1D local thermodynamic equilibrium (LTE) atmospheric models, together
with a combination of equivalent width measurements, LTE, and NLTE
synthesis, we derive stellar parameters and element abundances from
high-resolution, high signal-to-noise spectra of 13 red giant stars
near the tip of the RGB.
Results: We derive abundances of a
total 27 elements (O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co,
Ni, Cu, Zn, Y, Zr, Mo, Ru, Ba, La, Ce, Pr, Nd, Eu, Dy). Departures
from LTE were taken into account for Na, Al, and Ba. We find a mean
[Fe/H] = -0.78 ± 0.07 and [ α/ Fe ] = 0.34 ± 0.03 in good agreement
with previous studies. The remaining elements show good agreement with
the literature, but including NLTE for Al has a significant impact on
the behavior of this key element.
Conclusions: We confirm the
presence of an Na-O anti-correlation in 47 Tucanae found by several
other works. Our NLTE analysis of Al shifts the [Al/Fe] to lower values,
indicating that this may be overestimated in earlier works. No evidence
of an intrinsic variation is found in any of the remaining elements. Based on observations made with the ESO Very Large Telescope at
Paranal Observatory, Chile (Programmes 084.B-0810 and 086.B-0237).Full
Tables 2, 5, and 9 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/572/A108Appendix
A is available in electronic form at http://www.aanda.org
Title: VizieR Online Data Catalog: NGC 2808 HB stars abundances
(Marino+, 2014)
Authors: Marino, A. F.; Milone, A. P.; Przybilla, N.; Bergemann,
M.; Lind, K.; Asplund, M.; Cassisi, S.; Catelan, M.; Casagrande, L.;
Valcarce, A. A. R.; Bedin, L. R.; Cortes, C.; D'Antona, F.; Jerjen,
H.; Piotto, G.; Schlesinger, K.; Zoccali, M.; Angeloni, R.
Bibcode: 2014yCat..74371609M
Altcode:
To identify our stellar sample, we use the photometric catalogue of
Momany et al. (2004), which has been obtained from U, B and V images
collected with the Wide-Field Imager (WFI) mounted at the 2.2m ESO-MPI
(Max-Planck-Institut) telescope at La Silla observatory, Chile. Our spectroscopic data consist of FLAMES/GIRAFFE and FLAMES/UVES data
collected under the ESO programme 086.D-0141 (PI: Marino). The GIRAFFE
fibres were used with the HR12 setup, covering the spectral range from
~5820 to ~6140Å with a resolution of ~18700. (6 data files).
Title: The PLATO 2.0 mission
Authors: Rauer, H.; Catala, C.; Aerts, C.; Appourchaux, T.; Benz,
W.; Brandeker, A.; Christensen-Dalsgaard, J.; Deleuil, M.; Gizon,
L.; Goupil, M. -J.; Güdel, M.; Janot-Pacheco, E.; Mas-Hesse,
M.; Pagano, I.; Piotto, G.; Pollacco, D.; Santos, Ċ.; Smith, A.;
Suárez, J. -C.; Szabó, R.; Udry, S.; Adibekyan, V.; Alibert, Y.;
Almenara, J. -M.; Amaro-Seoane, P.; Eiff, M. Ammler-von; Asplund, M.;
Antonello, E.; Barnes, S.; Baudin, F.; Belkacem, K.; Bergemann, M.;
Bihain, G.; Birch, A. C.; Bonfils, X.; Boisse, I.; Bonomo, A. S.;
Borsa, F.; Brandão, I. M.; Brocato, E.; Brun, S.; Burleigh, M.;
Burston, R.; Cabrera, J.; Cassisi, S.; Chaplin, W.; Charpinet, S.;
Chiappini, C.; Church, R. P.; Csizmadia, Sz.; Cunha, M.; Damasso, M.;
Davies, M. B.; Deeg, H. J.; Díaz, R. F.; Dreizler, S.; Dreyer, C.;
Eggenberger, P.; Ehrenreich, D.; Eigmüller, P.; Erikson, A.; Farmer,
R.; Feltzing, S.; de Oliveira Fialho, F.; Figueira, P.; Forveille,
T.; Fridlund, M.; García, R. A.; Giommi, P.; Giuffrida, G.; Godolt,
M.; Gomes da Silva, J.; Granzer, T.; Grenfell, J. L.; Grotsch-Noels,
A.; Günther, E.; Haswell, C. A.; Hatzes, A. P.; Hébrard, G.; Hekker,
S.; Helled, R.; Heng, K.; Jenkins, J. M.; Johansen, A.; Khodachenko,
M. L.; Kislyakova, K. G.; Kley, W.; Kolb, U.; Krivova, N.; Kupka, F.;
Lammer, H.; Lanza, A. F.; Lebreton, Y.; Magrin, D.; Marcos-Arenal,
P.; Marrese, P. M.; Marques, J. P.; Martins, J.; Mathis, S.; Mathur,
S.; Messina, S.; Miglio, A.; Montalban, J.; Montalto, M.; Monteiro,
M. J. P. F. G.; Moradi, H.; Moravveji, E.; Mordasini, C.; Morel, T.;
Mortier, A.; Nascimbeni, V.; Nelson, R. P.; Nielsen, M. B.; Noack,
L.; Norton, A. J.; Ofir, A.; Oshagh, M.; Ouazzani, R. -M.; Pápics,
P.; Parro, V. C.; Petit, P.; Plez, B.; Poretti, E.; Quirrenbach, A.;
Ragazzoni, R.; Raimondo, G.; Rainer, M.; Reese, D. R.; Redmer, R.;
Reffert, S.; Rojas-Ayala, B.; Roxburgh, I. W.; Salmon, S.; Santerne,
A.; Schneider, J.; Schou, J.; Schuh, S.; Schunker, H.; Silva-Valio,
A.; Silvotti, R.; Skillen, I.; Snellen, I.; Sohl, F.; Sousa, S. G.;
Sozzetti, A.; Stello, D.; Strassmeier, K. G.; Švanda, M.; Szabó,
Gy. M.; Tkachenko, A.; Valencia, D.; Van Grootel, V.; Vauclair,
S. D.; Ventura, P.; Wagner, F. W.; Walton, N. A.; Weingrill, J.;
Werner, S. C.; Wheatley, P. J.; Zwintz, K.
Bibcode: 2014ExA....38..249R
Altcode: 2014ExA...tmp...41R; 2013arXiv1310.0696R
PLATO 2.0 has recently been selected for ESA's M3 launch opportunity
(2022/24). Providing accurate key planet parameters (radius, mass,
density and age) in statistical numbers, it addresses fundamental
questions such as: How do planetary systems form and evolve? Are there
other systems with planets like ours, including potentially habitable
planets? The PLATO 2.0 instrument consists of 34 small aperture
telescopes (32 with 25 s readout cadence and 2 with 2.5 s candence)
providing a wide field-of-view (2232 deg 2) and a large
photometric magnitude range (4-16 mag). It focusses on bright (4-11
mag) stars in wide fields to detect and characterize planets down to
Earth-size by photometric transits, whose masses can then be determined
by ground-based radial-velocity follow-up measurements. Asteroseismology
will be performed for these bright stars to obtain highly accurate
stellar parameters, including masses and ages. The combination of
bright targets and asteroseismology results in high accuracy for
the bulk planet parameters: 2 %, 4-10 % and 10 % for planet radii,
masses and ages, respectively. The planned baseline observing strategy
includes two long pointings (2-3 years) to detect and bulk characterize
planets reaching into the habitable zone (HZ) of solar-like stars
and an additional step-and-stare phase to cover in total about 50 %
of the sky. PLATO 2.0 will observe up to 1,000,000 stars and detect
and characterize hundreds of small planets, and thousands of planets
in the Neptune to gas giant regime out to the HZ. It will therefore
provide the first large-scale catalogue of bulk characterized planets
with accurate radii, masses, mean densities and ages. This catalogue
will include terrestrial planets at intermediate orbital distances,
where surface temperatures are moderate. Coverage of this parameter
range with statistical numbers of bulk characterized planets is unique
to PLATO 2.0. The PLATO 2.0 catalogue allows us to e.g.: - complete
our knowledge of planet diversity for low-mass objects, - correlate the
planet mean density-orbital distance distribution with predictions from
planet formation theories,- constrain the influence of planet migration
and scattering on the architecture of multiple systems, and - specify
how planet and system parameters change with host star characteristics,
such as type, metallicity and age. The catalogue will allow us to study
planets and planetary systems at different evolutionary phases. It
will further provide a census for small, low-mass planets. This will
serve to identify objects which retained their primordial hydrogen
atmosphere and in general the typical characteristics of planets
in such low-mass, low-density range. Planets detected by PLATO 2.0
will orbit bright stars and many of them will be targets for future
atmosphere spectroscopy exploring their atmosphere. Furthermore,
the mission has the potential to detect exomoons, planetary rings,
binary and Trojan planets. The planetary science possible with PLATO
2.0 is complemented by its impact on stellar and galactic science via
asteroseismology as well as light curves of all kinds of variable stars,
together with observations of stellar clusters of different ages. This
will allow us to improve stellar models and study stellar activity. A
large number of well-known ages from red giant stars will probe the
structure and evolution of our Galaxy. Asteroseismic ages of bright
stars for different phases of stellar evolution allow calibrating
stellar age-rotation relationships. Together with the results of ESA's
Gaia mission, the results of PLATO 2.0 will provide a huge legacy to
planetary, stellar and galactic science.
Title: Stellar Chemical Abundances: In Pursuit of the Highest
Achievable Precision
Authors: Bedell, Megan; Meléndez, Jorge; Bean, Jacob L.; Ramírez,
Ivan; Leite, Paulo; Asplund, Martin
Bibcode: 2014ApJ...795...23B
Altcode: 2014arXiv1409.1230B
The achievable level of precision on photospheric abundances of stars
is a major limiting factor on investigations of exoplanet host star
characteristics, the chemical histories of star clusters, and the
evolution of the Milky Way and other galaxies. While model-induced
errors can be minimized through the differential analysis of spectrally
similar stars, the maximum achievable precision of this technique
has been debated. As a test, we derive differential abundances of 19
elements from high-quality asteroid-reflected solar spectra taken using
a variety of instruments and conditions. We treat the solar spectra as
being from unknown stars and use the resulting differential abundances,
which are expected to be zero, as a diagnostic of the error in our
measurements. Our results indicate that the relative resolution of
the target and reference spectra is a major consideration, with use
of different instruments to obtain the two spectra leading to errors
up to 0.04 dex. Use of the same instrument at different epochs for
the two spectra has a much smaller effect (~0.007 dex). The asteroid
used to obtain the solar standard also has a negligible effect (~0.006
dex). Assuming that systematic errors from the stellar model atmospheres
have been minimized, as in the case of solar twins, we confirm that
differential chemical abundances can be obtained at sub-0.01 dex
precision with due care in the observations, data reduction, and
abundance analysis.
Title: The make-up of stars
Authors: Asplund, Martin
Bibcode: 2014AIPC.1632...58A
Altcode:
The chemical composition of stars contain vital clues not only about
the stars themselves but also about the conditions prevailing before
their births. As such, stellar spectroscopy plays a key role in
contemporary astrophysics and cosmology by probing cosmic, galactic,
stellar and planetary evolution. In this review I will describe the
theoretical foundations of quantitative stellar spectroscopy: stellar
atmosphere models and spectral line formation. I will focus mainly
on more recent advances in the field, in particular the advent of
realistic time-dependent, 3D, (magneto-)hydrodynamical simulations
of stellar surface convection and atmospheres and non-LTE radiative
transfer relevant for stars like the Sun. I will also discuss some
particular applications of this type of modelling which have resulted
in some exciting break-throughs in our understanding and with wider
implications: the solar chemical composition, the chemical signatures
of planet formation imprinted in stellar abundances, the cosmological
Li problem(s) and where the first stars may be residing today.
Title: The Gaia-ESO Survey: The analysis of high-resolution UVES
spectra of FGK-type stars
Authors: Smiljanic, R.; Korn, A. J.; Bergemann, M.; Frasca, A.;
Magrini, L.; Masseron, T.; Pancino, E.; Ruchti, G.; San Roman,
I.; Sbordone, L.; Sousa, S. G.; Tabernero, H.; Tautvaišienė,
G.; Valentini, M.; Weber, M.; Worley, C. C.; Adibekyan, V. Zh.;
Allende Prieto, C.; Barisevičius, G.; Biazzo, K.; Blanco-Cuaresma,
S.; Bonifacio, P.; Bragaglia, A.; Caffau, E.; Cantat-Gaudin, T.;
Chorniy, Y.; de Laverny, P.; Delgado-Mena, E.; Donati, P.; Duffau,
S.; Franciosini, E.; Friel, E.; Geisler, D.; González Hernández,
J. I.; Gruyters, P.; Guiglion, G.; Hansen, C. J.; Heiter, U.; Hill, V.;
Jacobson, H. R.; Jofre, P.; Jönsson, H.; Lanzafame, A. C.; Lardo, C.;
Ludwig, H. -G.; Maiorca, E.; Mikolaitis, Š.; Montes, D.; Morel, T.;
Mucciarelli, A.; Muñoz, C.; Nordlander, T.; Pasquini, L.; Puzeras,
E.; Recio-Blanco, A.; Ryde, N.; Sacco, G.; Santos, N. C.; Serenelli,
A. M.; Sordo, R.; Soubiran, C.; Spina, L.; Steffen, M.; Vallenari,
A.; Van Eck, S.; Villanova, S.; Gilmore, G.; Randich, S.; Asplund,
M.; Binney, J.; Drew, J.; Feltzing, S.; Ferguson, A.; Jeffries, R.;
Micela, G.; Negueruela, I.; Prusti, T.; Rix, H. -W.; Alfaro, E.;
Babusiaux, C.; Bensby, T.; Blomme, R.; Flaccomio, E.; François, P.;
Irwin, M.; Koposov, S.; Walton, N.; Bayo, A.; Carraro, G.; Costado,
M. T.; Damiani, F.; Edvardsson, B.; Hourihane, A.; Jackson, R.; Lewis,
J.; Lind, K.; Marconi, G.; Martayan, C.; Monaco, L.; Morbidelli, L.;
Prisinzano, L.; Zaggia, S.
Bibcode: 2014A&A...570A.122S
Altcode: 2014arXiv1409.0568S
Context. The ongoing Gaia-ESO Public Spectroscopic Survey is using
FLAMES at the VLT to obtain high-quality medium-resolution Giraffe
spectra for about 105 stars and high-resolution UVES spectra
for about 5000 stars. With UVES, the Survey has already observed
1447 FGK-type stars.
Aims: These UVES spectra are analyzed
in parallel by several state-of-the-art methodologies. Our aim is
to present how these analyses were implemented, to discuss their
results, and to describe how a final recommended parameter scale is
defined. We also discuss the precision (method-to-method dispersion)
and accuracy (biases with respect to the reference values) of the
final parameters. These results are part of the Gaia-ESO second
internal release and will be part of its first public release of
advanced data products.
Methods: The final parameter scale is
tied to the scale defined by the Gaia benchmark stars, a set of stars
with fundamental atmospheric parameters. In addition, a set of open
and globular clusters is used to evaluate the physical soundness
of the results. Each of the implemented methodologies is judged
against the benchmark stars to define weights in three different
regions of the parameter space. The final recommended results are
the weighted medians of those from the individual methods.
Results: The recommended results successfully reproduce the atmospheric
parameters of the benchmark stars and the expected Teff-log
g relation of the calibrating clusters. Atmospheric parameters and
abundances have been determined for 1301 FGK-type stars observed with
UVES. The median of the method-to-method dispersion of the atmospheric
parameters is 55 K for Teff, 0.13 dex for log g and 0.07
dex for [Fe/H]. Systematic biases are estimated to be between 50-100
K for Teff, 0.10-0.25 dex for log g and 0.05-0.10 dex for
[Fe/H]. Abundances for 24 elements were derived: C, N, O, Na, Mg, Al,
Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Mo, Ba, Nd, and
Eu. The typical method-to-method dispersion of the abundances varies
between 0.10 and 0.20 dex.
Conclusions: The Gaia-ESO sample of
high-resolution spectra of FGK-type stars will be among the largest of
its kind analyzed in a homogeneous way. The extensive list of elemental
abundances derived in these stars will enable significant advances in
the areas of stellar evolution and Milky Way formation and evolution. Based on observations made with the ESO/VLT, at Paranal Observatory,
under program 188.B-3002 (The Gaia-ESO Public Spectroscopic Survey, PIs
Gilmore and Randich). Appendices are available in electronic form at http://www.aanda.org
Title: VizieR Online Data Catalog: STAGGER-grid of 3D stellar
models. IV. (Magic+, 2015)
Authors: Magic, Z.; Chiavassa, A.; Collet, R.; Asplund, M.
Bibcode: 2014yCat..35730090M
Altcode: 2014yCat..35739090M
We compute the emergent stellar spectra from the UV to far infrared
for different viewing angles using realistic 3D model atmospheres
for a large range in stellar parameters to predict the stellar limb
darkening. We have computed full 3D LTE synthetic spectra based
on 3D radiative hydrodynamic atmosphere models from the Stagger-grid
in the ranges: Teff from 4000 to 7000K, logg from 1.5 to 5.0, and
[Fe/H], from -4.0 to +0.5. From the resulting intensities at different
wavelength, we derived coefficients for the standard limb darkening laws
considering a number of often-used photometric filters. Furthermore,
we calculated theoretical transit light curves, in order to quantify the
differences between predictions by the widely used 1D model atmosphere
and our 3D models. (1 data file).
Title: VizieR Online Data Catalog: STAGGER-grid of 3D stellar
models. III. (Magic+, 2015)
Authors: Magic, Z.; Weiss, A.; Asplund, M.
Bibcode: 2014yCat..35730089M
Altcode: 2014yCat..35739089M
We investigate the relation between 1D atmosphere models that rely
on the mixing length theory and models based on full 3D radiative
hydrodynamic (RHD) calculations to describe convection in the envelopes
of late-type stars. The adiabatic entropy value of the deep
convection zone, sbot, and the entropy jump, Δs, determined
from the 3D RHD models, are matched with the mixing length parameter,
αMLT, from 1D hydrostatic atmosphere models with identical
microphysics (opacities and equation-of-state). We also derive the mass
mixing length, αm, and the vertical correlation length of
the vertical velocity, C[Vz,Vz], directly from
the 3D hydrodynamical simulations of stellar subsurface convection. (1 data file).
Title: VizieR Online Data Catalog: 47 Tuc red giants chemical
composition (Thygesen+, 2014)
Authors: Thygesen, A. O.; Sbordone, L.; Andrievsky, S.; Korotin,
S.; Yong, D.; Zaggia, S.; Ludwig, H. -G.; Collet, R.; Asplund, M.;
Ventura, P.; D'Antona, F.; Melendez, J.; D'Ercole, A.
Bibcode: 2014yCat..35720108T
Altcode: 2014yCat..35729108T
Table 2 contains linelist of the non-HFS elements. These lines were used
for equivalent width measurements. Sorted by element number. Table 5
contains all the lines used for HFS synthesis. With the exception of
Ba, all lines are split into individual HFS components, including
isotopes. log(gf) values reflect this. Solar isotope mixture is
assumed. Sorted by element number. Table 8 contains the fundamental
stellar parameters. Table 9 contains [Fe/H] as well as abundance ratios
[X/Fe] for all stars. All measurements have an associated uncertainty
sig[X/Fe] and the number of lines used in each individual star. In
cases where no measurement exist, the value "-9.99" is given. (5
data files).
Title: 18 Sco: A Solar Twin Rich in Refractory and Neutron-capture
Elements. Implications for Chemical Tagging
Authors: Meléndez, Jorge; Ramírez, Iván; Karakas, Amanda I.; Yong,
David; Monroe, TalaWanda R.; Bedell, Megan; Bergemann, Maria; Asplund,
Martin; Tucci Maia, Marcelo; Bean, Jacob; do Nascimento, José-Dias,
Jr.; Bazot, Michael; Alves-Brito, Alan; Freitas, Fabrício C.;
Castro, Matthieu
Bibcode: 2014ApJ...791...14M
Altcode: 2014arXiv1406.5244M
We study with unprecedented detail the chemical composition and stellar
parameters of the solar twin 18 Sco in a strictly differential sense
relative to the Sun. Our study is mainly based on high-resolution (R ~
110,000), high signal-to-noise ratio (800-1,000) Very Large Telescope
UVES spectra, which allow us to achieve a precision of about 0.005
dex in differential abundances. The effective temperature and surface
gravity of 18 Sco are T eff = 5823 ± 6 K and log g =
4.45 ± 0.02 dex, i.e., 18 Sco is 46 ± 6 K hotter than the Sun and
log g is 0.01 ± 0.02 dex higher. Its metallicity is [Fe/H] = 0.054
± 0.005 dex, and its microturbulence velocity is +0.02 ± 0.01 km
s-1 higher than solar. Our precise stellar parameters
and differential isochrone analysis show that 18 Sco has a mass
of 1.04 ± 0.02 M ⊙ and that it is ~1.6 Gyr younger
than the Sun. We use precise High Accuracy Radial velocity Planet
Searcher (HARPS) radial velocities to search for planets, but none
are detected. The chemical abundance pattern of 18 Sco displays
a clear trend with condensation temperature, thus showing higher
abundances of refractories in 18 Sco than in the Sun. Intriguingly,
there are enhancements in the neutron-capture elements relative to the
Sun. Despite the small element-to-element abundance differences among
nearby n-capture elements (~0.02 dex), we successfully reproduce the
r-process pattern in the Solar System. This is independent evidence
for the universality of the r process. Our results have important
implications for chemical tagging in our Galaxy and nucleosynthesis in
general. Based on observations obtained at the European Southern
Observatory (ESO) Very Large Telescope (VLT) at Paranal Observatory;
the 3.6 m telescope at La Silla Observatory, Chile (observing programs
083.D-0871 and 188.C-0265); and at the W.M. Keck Observatory, which
is operated jointly by Caltech, the University of California, and NASA.
Title: The halo+cluster system of the Galactic globular cluster
NGC 1851
Authors: Marino, A. F.; Milone, A. P.; Yong, D.; Dotter, A.; Da Costa,
G.; Asplund, M.; Jerjen, H.; Mackey, D.; Norris, J.; Cassisi, S.;
Sbordone, L.; Stetson, P. B.; Weiss, A.; Aparicio, A.; Bedin, L. R.;
Lind, K.; Monelli, M.; Piotto, G.; Angeloni, R.; Buonanno, R.
Bibcode: 2014MNRAS.442.3044M
Altcode: 2014arXiv1406.0944M
NGC 1851 is surrounded by a stellar component that extends more
than 10 times beyond the tidal radius. Although the nature of this
stellar structure is not known, it has been suggested to be a sparse
halo of stars or associated with a stellar stream. We analyse the
nature of this intriguing stellar component surrounding NGC 1851
by investigating its radial velocities and chemical composition, in
particular in comparison with those of the central cluster analysed
in a homogeneous manner. In total we observed 23 stars in the halo
with radial velocities consistent with NGC 1851, and for 15 of them we
infer [Fe/H] abundances. Our results show that (i) stars dynamically
linked to NGC 1851 are present at least up to ∼2.5 tidal radii,
supporting the presence of a halo of stars surrounding the cluster;
(ii) apart from the NGC 1851 radial velocity-like stars, our observed
velocity distribution agrees with that expected from Galactic models,
suggesting that no other substructure (such as a stream) at different
radial velocities is present in our field; (iii) the chemical abundances
for the s-process elements Sr and Ba are consistent with the s-normal
stars observed in NGC 1851; (iv) all halo stars have metallicities,
and abundances for the other studied elements Ca, Mg and Cr, consistent
with those exhibited by the cluster. The complexity of the whole NGC
1851 cluster+halo system may agree with the scenario of a tidally
disrupted dwarf galaxy in which NGC 1851 was originally embedded.
Title: Solar twins in the open cluster M67: chemical signature of
terrestrial planets or natal dust formation?
Authors: Asplund, Martin
Bibcode: 2014koa..prop..367A
Altcode:
No abstract at ADS
Title: The Gaia-ESO Survey: the Galactic thick to thin disc transition
Authors: Recio-Blanco, A.; de Laverny, P.; Kordopatis, G.; Helmi,
A.; Hill, V.; Gilmore, G.; Wyse, R.; Adibekyan, V.; Randich, S.;
Asplund, M.; Feltzing, S.; Jeffries, R.; Micela, G.; Vallenari, A.;
Alfaro, E.; Allende Prieto, C.; Bensby, T.; Bragaglia, A.; Flaccomio,
E.; Koposov, S. E.; Korn, A.; Lanzafame, A.; Pancino, E.; Smiljanic,
R.; Jackson, R.; Lewis, J.; Magrini, L.; Morbidelli, L.; Prisinzano,
L.; Sacco, G.; Worley, C. C.; Hourihane, A.; Bergemann, M.; Costado,
M. T.; Heiter, U.; Joffre, P.; Lardo, C.; Lind, K.; Maiorca, E.
Bibcode: 2014A&A...567A...5R
Altcode: 2014arXiv1403.7568R
Aims: The nature of the thick disc and its relation to the
thin disc is presently an important subject of debate. In fact, the
structural and chemo-dynamical transition between disc populations can
be used as a test of the proposed models of Galactic disc formation
and evolution.
Methods: We used the atmospheric parameters,
[α/Fe] abundances, and radial velocities, which were determined from
the Gaia-ESO Survey GIRAFFE spectra of FGK-type stars (first nine months
of observations) to provide a chemo-kinematical characterisation of
the disc stellar populations. We focussed on a subsample of 1016 stars
with high-quality parameters, covering the volume | Z | < 4.5 kpc
and R in the range 2-13 kpc.
Results: We have identified a thin
to thick disc separation in the [α/Fe] vs. [M/H] plane, thanks to the
presence of a low-density region in the number density distribution. The
thick disc stars seem to lie in progressively thinner layers above the
Galactic plane, as metallicity increases and [α/Fe] decreases. In
contrast, the thin disc population presents a constant value of the
mean distance to the Galactic plane at all metallicities. In addition,
our data confirm the already known correlations between Vφ
and [M/H] for the two discs. For the thick disc sequence, a study of
the possible contamination by thin disc stars suggests a gradient up
to 64 ± 9 km s-1 dex-1. The distributions of
azimuthal velocity, vertical velocity, and orbital parameters are
also analysed for the chemically separated samples. Concerning the
gradients with galactocentric radius, we find, for the thin disc, a
flat behaviour of the azimuthal velocity, a metallicity gradient equal
to -0.058 ± 0.008 dex kpc-1 and a very small positive
[α/Fe] gradient. For the thick disc, flat gradients in [M/H] and
[α/Fe] are derived.
Conclusions: Our chemo-kinematical analysis
suggests a picture where the thick disc seems to have experienced a
settling process, during which its rotation increased progressively
and, possibly, the azimuthal velocity dispersion decreased. At [M/H]
≈ -0.25 dex and [α/Fe]≈ 0.1 dex, the mean characteristics of
the thick disc in vertical distance to the Galactic plane, rotation,
rotational dispersion, and stellar orbits' eccentricity agree with
that of the thin disc stars of the same metallicity, suggesting
a possible connection between these two populations at a certain
epoch of the disc evolution. Finally, the results presented here,
based only on the first months of the Gaia ESO Survey observations,
confirm how crucial large high-resolution spectroscopic surveys
outside the solar neighbourhood are today for our understanding of
the Milky Way history. Based on observations collected with the
FLAMES spectrograph at the VLT/UT2 telescope (Paranal Observatory, ESO,
Chile), for the Gaia-ESO Large Public Survey, programme 188.B-3002.Full
Table 1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/567/A5
Title: Improvements to stellar structure models, based on a grid of
3D convection simulations - I. T(τ) relations
Authors: Trampedach, Regner; Stein, Robert F.; Christensen-Dalsgaard,
Jørgen; Nordlund, Åke; Asplund, Martin
Bibcode: 2014MNRAS.442..805T
Altcode: 2014arXiv1405.0236T
Relations between temperature, T, and optical depth, τ, are often
used for describing the photospheric transition from optically thick
to optically thin in stellar structure models. We show that this is
well justified, but also that currently used T(τ) relations are often
inconsistent with their implementation. As an outer boundary condition
on the system of stellar structure equations, T(τ) relations have an
undue effect on the overall structure of stars. In this age of precision
asteroseismology, we need to re-assess both the method for computing
and for implementing T(τ) relations, and the assumptions they rest
on. We develop a formulation for proper and consistent evaluation
of T(τ) relations from arbitrary 1D or 3D stellar atmospheres,
and for their implementation in stellar structure and evolution
models. We extract radiative T(τ) relations, as described by our
new formulation, from 3D simulations of convection in deep stellar
atmospheres of late-type stars from dwarfs to giants. These simulations
employ realistic opacities and equation of state, and account for
line blanketing. For comparison, we also extract T(τ) relations from
1DMARCSmodel atmospheres using the same formulation. T(τ) relations
from our grid of 3D convection simulations display a larger range of
behaviours with surface gravity, compared with those of conventional
theoretical 1D hydrostatic atmosphere models based on the mixing-length
theory for convection. The 1D atmospheres show little dependence on
gravity. 1D atmospheres of main-sequence stars also show an abrupt
transition to the diffusion approximation at τ ≃ 2.5, whereas the
3D simulations exhibit smooth transitions that occur at the same depth
for M ≃ 0.8 M⊙, and higher in the atmosphere for both
more and less massive main-sequence stars. Based on these results,
we recommend no longer using scaled solar T(τ) relations. Files with
T(τ) relations for our grid of simulations are made available to the
community, together with routines for interpolating in this irregular
grid. We also provide matching tables of atmospheric opacity, for
consistent implementation in stellar structure models.
Title: A high-precision chemical abundance analysis of the HAT-P-1
stellar binary: constraints on planet formation.
Authors: Liu, F.; Asplund, M.; Ramirez, I.; Yong, D.; Melendez, J.
Bibcode: 2014MNRAS.442L..51L
Altcode: 2014arXiv1404.2112L
We present a high-precision, differential elemental abundance
analysis of the HAT-P-1 stellar binary based on high-resolution,
high signal-to-noise ratio Keck/HIRES (High Resolution Echelle
Spectrometer) spectra. The secondary star in this double system is
known to host a transiting giant planet while no planets have yet been
detected around the primary star. The derived metallicities ([Fe/H])
of the primary and secondary stars are identical within the errors:
0.146 ± 0.014 dex (σ = 0.033 dex) and 0.155 ± 0.007 dex (σ =
0.023 dex), respectively. Extremely precise differential abundance
ratios of 23 elements have been measured (mean error of σ([X/Fe])
= 0.013 dex) and are found to be indistinguishable between the two
stars: Δ[X/Fe] (secondary - primary) = +0.001 ± 0.006 dex (σ =
0.008 dex). The striking similarity in the chemical composition of
the two stellar components in HAT-P-1 is contrary to the possible
0.04 dex level difference seen in 16 Cyg A+B, which also hosts a
giant planet, at least three times more massive than the one around
HAT-P-1 secondary star. We conclude that the presence of giant planets
does not necessarily imply differences in the chemical compositions
of the host stars. The elemental abundances of each star in HAT-P-1
relative to the Sun show an identical, positive correlation with the
condensation temperature of the elements; their abundance patterns
are thus very similar to those observed in the majority of solar
twins. In view of the Meléndez et al. interpretation of the peculiar
solar abundance pattern, we conclude that HAT-P-1 experienced less
efficient formation of terrestrial planets than the Sun. This is in
line with the expectation that the presence of close-in giant planets
preventing the formation or survival of terrestrial planets.
Title: Planet transit and stellar granulation detection with
interferometry. Using the three-dimensional stellar atmosphere
Stagger-grid simulations
Authors: Chiavassa, A.; Ligi, R.; Magic, Z.; Collet, R.; Asplund,
M.; Mourard, D.
Bibcode: 2014A&A...567A.115C
Altcode: 2014arXiv1404.7049C
Context. Stellar activity and, in particular, convection-related
surface structures, potentially cause bias in planet detection and
characterisation. In the latter, interferometry can help disentangle
the signal of the transiting planet.
Aims: We used realistic
three-dimensional (3D) radiative hydrodynamical (RHD) simulations
from the Stagger-grid and synthetic images computed with the radiative
transfer code Optim3D to provide interferometric observables to extract
the signature of stellar granulation and transiting planets.
Methods: We computed intensity maps from RHD simulations and produced
synthetic stellar disk images as a nearby observer would see,
thereby accounting for the centre-to-limb variations. We did this
for twelve interferometric instruments covering wavelengths ranging
from optical to infrared. We chose an arbitrary date and arbitrary
star with coordinates, and this ensures observability throughout
the night. This optimisation of observability allows for a broad
coverage of spatial frequencies. The stellar surface asymmetries in
the brightness distribution mostly affect closure phases, because of
either convection-related structures or a faint companion. We then
computed closure phases for all images and compared the system star
with a transiting planet and the star alone. We considered the impact
of magnetic spots with the construction of a hypothetical starspot
image and compared the resulting closure phases with the system star
that has a transiting planet.
Results: We analysed the impact
of convection at different wavelengths. All the simulation depart from
the axisymmetric case (closure phases not equal to 0 or ± π) at all
wavelengths. The levels of asymmetry and inhomogeneity of stellar disk
images reach high values with stronger effects from the 3rd visibility
lobe on. We present two possible targets (Beta Com and Procyon)
either in the visible or in the infrared and find that departures up
to 16° can be detected on the 3rd lobe and higher. In particular,
MIRC is the most appropriate instrument because it combines good
UV coverage and long baselines. Moreover, we explored the impact of
convection on interferometric planet signature for three prototypes
of planets with sizes corresponding to one hot Jupiter, one hot
Neptune, and a terrestrial planet. The signature of the transiting
planet in the closure phase is mixed with the signal due to the
convection-related surface structures, but it is possible to disentangle
it at particular wavelengths (either in the infrared or in the optical)
by comparing the closure phases of the star at difference phases of
the planetary transit. It must be noted that starspots caused by the
magnetic field may pollute the granulation and the transiting planet
signals. However, it is possible to differentiate the transiting planet
signal because the time scale of a planet crossing the stellar disk is
much smaller than the typical rotational modulation of a star.
Conclusions: Detection and characterisation of planets must be based
on a comprehensive knowledge of the host star, and this includes the
detailed study of the stellar surface convection with interferometric
techniques. In this context, RHD simulations are crucial for this
aim. We emphasise that interferometric observations should be pushed
at high spatial frequencies by accumulating observations on closure
phases at short and long baselines.
Title: HIP 114328: a new refractory-poor and Li-poor solar twin
Authors: Meléndez, Jorge; Schirbel, Lucas; Monroe, TalaWanda R.;
Yong, David; Ramírez, Iván; Asplund, Martin
Bibcode: 2014A&A...567L...3M
Altcode: 2014arXiv1406.2385M
Context. The standard solar model fails to predict the very low lithium
abundance in the Sun, which is much lower than the proto-solar nebula
(as measured in meteorites). This Li problem has been debated for
decades, and it has been ascribed either to planet formation or to
secular stellar depletion due to additional mixing below the convection
zone, either during the pre-main sequence and thus possibly linked to
planet formation, or additionally on secular time-scales during the
main sequence. In order to test the evolution of Li, it is important to
find solar twins in a range of ages, i.e., stars with about one solar
mass and metallicity but in different evolutionary stages. Furthermore,
the study of stars similar to the Sun is relevant in relation to the
signature of terrestrial planet formation around the Sun, and for
anchoring photometric and spectroscopic stellar parameter scales.
Aims: We aim to identify and analyse solar twins using high quality
spectra, in order to study Li depletion in the Sun and the possible
relation between chemical abundance anomalies and planet formation.
Methods: We acquired high-resolution (R ~ 110 000), high S/N (~300)
ESO/VLT UVES spectra of several solar twin candidates and the Sun (as
reflected from the asteroid Juno). Among the solar twin candidates
we identify HIP 114328 as a solar twin and perform a differential
line-by-line abundance analysis of this star relative to the Sun.
Results: HIP 114328 has stellar parameters Teff =
5785 ± 10 K, log g = 4.38 ± 0.03, [ Fe/H] = -0.022 ± 0.009, and
a microturbulent velocity 0.05 ± 0.03 km s-1 higher than
solar. The differential analysis shows that this star is chemically
very similar to the Sun. The refractory elements seem slightly more
depleted than in the Sun, meaning that HIP 114328 may be as likely to
form terrestrial planets as the Sun. HIP 114328 is about 2 Gyr older
than the Sun, and is thus the second oldest solar twin analysed at high
precision. It has a Li abundance of A(Li)NLTE ≲ 0.46,
which is about 4 times lower than in the Sun (A(Li)NLTE =
1.07 dex), but close to the oldest solar twin known, HIP 102152.
Conclusions: Based on the lower abundances of refractory elements
when compared to other solar twins, HIP 114328 seems an excellent
candidate to host rocky planets. The low Li abundance of this star
is consistent with its old age and fits very well the emerging
Li-age relation among solar twins of different ages. Based on
observations obtained at the European Southern Observatory (ESO)
Very Large Telescope (VLT) at Paranal Observatory, Chile (observing
program 083.D-0871).Table 1 is available in electronic form at http://www.aanda.org
Title: VizieR Online Data Catalog: T(tau) relations code (Trampedach+,
2014)
Authors: Trampedach, R.; Stein, R. F.; Christensen-Dalsgaard, J.;
Nordlund, A.; Asplund, M.
Bibcode: 2014yCat..74420805T
Altcode:
Radiative T({tau})-relations, in the form of generalised Hopf functions,
computed from a grid of 37, solar metallicity, realistic, 3D convection
simulations with radiative transfer. (6 data files).
Title: Strömgren Survey for Asteroseismology and Galactic
Archaeology: Let the SAGA Begin
Authors: Casagrande, L.; Silva Aguirre, V.; Stello, D.; Huber, D.;
Serenelli, A. M.; Cassisi, S.; Dotter, A.; Milone, A. P.; Hodgkin,
S.; Marino, A. F.; Lund, M. N.; Pietrinferni, A.; Asplund, M.;
Feltzing, S.; Flynn, C.; Grundahl, F.; Nissen, P. E.; Schönrich,
R.; Schlesinger, K. J.; Wang, W.
Bibcode: 2014ApJ...787..110C
Altcode: 2014arXiv1403.2754C
Asteroseismology has the capability of precisely determining stellar
properties that would otherwise be inaccessible, such as radii,
masses, and thus ages of stars. When coupling this information with
classical determinations of stellar parameters, such as metallicities,
effective temperatures, and angular diameters, powerful new diagnostics
for Galactic studies can be obtained. The ongoing Strömgren survey for
Asteroseismology and Galactic Archaeology has the goal of transforming
the Kepler field into a new benchmark for Galactic studies, similar to
the solar neighborhood. Here we present the first results from a stripe
centered at a Galactic longitude of 74° and covering latitude from
about 8° to 20°, which includes almost 1000 K giants with seismic
information and the benchmark open cluster NGC 6819. We describe the
coupling of classical and seismic parameters, the accuracy as well
as the caveats of the derived effective temperatures, metallicities,
distances, surface gravities, masses, and radii. Confidence in the
achieved precision is corroborated by the detection of the first and
secondary clumps in a population of field stars with a ratio of 2 to 1
and by the negligible scatter in the seismic distances among NGC 6819
member stars. An assessment of the reliability of stellar parameters
in the Kepler Input Catalog is also performed, and the impact of
our results for population studies in the Milky Way is discussed,
along with the importance of an all-sky Strömgren survey. Based
on observations made with the Isaac Newton Telescope operated on the
island of La Palma by the Isaac Newton Group in the Spanish Observatorio
del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.
Title: Exploring the Origin of Lithium, Carbon, Strontium, and Barium
with Four New Ultra Metal-poor Stars
Authors: Hansen, T.; Hansen, C. J.; Christlieb, N.; Yong, D.; Bessell,
M. S.; García Pérez, A. E.; Beers, T. C.; Placco, V. M.; Frebel,
A.; Norris, J. E.; Asplund, M.
Bibcode: 2014ApJ...787..162H
Altcode: 2014arXiv1405.5846H
We present an elemental abundance analysis for four newly discovered
ultra metal-poor stars from the Hamburg/ESO survey, with [Fe/H] <=
-4. Based on high-resolution, high signal-to-noise spectra, we derive
abundances for 17 elements in the range from Li to Ba. Three of
the four stars exhibit moderate to large overabundances of carbon,
but have no enhancements in their neutron-capture elements. The
most metal-poor star in the sample, HE 0233-0343 ([Fe/H] = -4.68),
is a subgiant with a carbon enhancement of [C/Fe] = +3.5, slightly
above the carbon-enhancement plateau suggested by Spite et al. No
carbon is detected in the spectrum of the fourth star, but the
quality of its spectrum only allows for the determination of an
upper limit on the carbon abundance ratio of [C/Fe] < +1.7. We
detect lithium in the spectra of two of the carbon-enhanced stars,
including HE 0233-0343. Both stars with Li detections are Li-depleted,
with respect to the Li plateau for metal-poor dwarfs found by Spite
& Spite. This suggests that whatever site(s) produced C either
do not completely destroy lithium, or that Li has been astrated by
early-generation stars and mixed with primordial Li in the gas that
formed the stars observed at present. The derived abundances for the
α elements and iron-peak elements of the four stars are similar to
those found in previous large samples of extremely and ultra metal-poor
stars. Finally, a large spread is found in the abundances of Sr and Ba
for these stars, possibly influenced by enrichment from fast rotating
stars in the early universe. Based on observations made with the
European Southern Observatory (ESO) Telescopes.
Title: The Gaia-ESO Survey: processing FLAMES-UVES spectra
Authors: Sacco, G. G.; Morbidelli, L.; Franciosini, E.; Maiorca, E.;
Randich, S.; Modigliani, A.; Gilmore, G.; Asplund, M.; Binney, J.;
Bonifacio, P.; Drew, J.; Feltzing, S.; Ferguson, A.; Jeffries, R.;
Micela, G.; Negueruela, I.; Prusti, T.; Rix, H. -W.; Vallenari, A.;
Alfaro, E.; Allende Prieto, C.; Babusiaux, C.; Bensby, T.; Blomme,
R.; Bragaglia, A.; Flaccomio, E.; Francois, P.; Hambly, N.; Irwin,
M.; Koposov, S.; Korn, A.; Lanzafame, A.; Pancino, E.; Recio-Blanco,
A.; Smiljanic, R.; Van Eck, S.; Walton, N.; Bergemann, M.; Costado,
M. T.; de Laverny, P.; Heiter, U.; Hill, V.; Hourihane, A.; Jackson,
R.; Jofre, P.; Lewis, J.; Lind, K.; Lardo, C.; Magrini, L.; Masseron,
T.; Prisinzano, L.; Worley, C.
Bibcode: 2014A&A...565A.113S
Altcode: 2014arXiv1403.4865S
The Gaia-ESO Survey is a large public spectroscopic survey that
aims to derive radial velocities and fundamental parameters
of about 105 Milky Way stars in the field and in
clusters. Observations are carried out with the multi-object optical
spectrograph FLAMES, using simultaneously the medium-resolution (R ~
20 000) GIRAFFE spectrograph and the high-resolution (R ~ 47 000) UVES
spectrograph. In this paper we describe the methods and the software
used for the data reduction, the derivation of the radial velocities,
and the quality control of the FLAMES-UVES spectra. Data reduction
has been performed using a workflow specifically developed for this
project. This workflow runs the ESO public pipeline optimizing the
data reduction for the Gaia-ESO Survey, automatically performs sky
subtraction, barycentric correction and normalisation, and calculates
radial velocities and a first guess of the rotational velocities. The
quality control is performed using the output parameters from the ESO
pipeline, by a visual inspection of the spectra and by the analysis
of the signal-to-noise ratio of the spectra. Using the observations
of the first 18 months, specifically targets observed multiple times
at different epochs, stars observed with both GIRAFFE and UVES, and
observations of radial velocity standards, we estimated the precision
and the accuracy of the radial velocities. The statistical error on the
radial velocities is σ ~ 0.4 km s-1 and is mainly due to
uncertainties in the zero point of the wavelength calibration. However,
we found a systematic bias with respect to the GIRAFFE spectra (~0.9 km
s-1) and to the radial velocities of the standard stars (~0.5
km s-1) retrieved from the literature. This bias will be
corrected in the future data releases, when a common zero point for all
the set-ups and instruments used for the survey is be established. Based on observations made with the ESO/VLT, at Paranal Observatory,
under programme 188.B-3002 (The Gaia-ESO Public Spectroscopic Survey).
Title: The Stagger-grid: A grid of 3D stellar atmosphere models -
VI. Surface appearance of stellar granulation
Authors: Magic, Zazralt; Asplund, Martin
Bibcode: 2014arXiv1405.7628M
Altcode:
In the surface layers of late-type stars, stellar convection is
manifested with its typical granulation pattern due to the presence
of convective motions. The resulting photospheric up- and downflows
leave imprints in the observed spectral line profiles. We perform
a careful statistical analysis of stellar granulation and its
properties for different stellar parameters. We employ realistic
3D radiative hydrodynamic (RHD) simulations of surface convection
from the Stagger-grid, a comprehensive grid of atmosphere models
that covers a large parameter space in terms of Teff, logg, and
[Fe/H]. Individual granules are detected from the (bolometric) intensity
maps at disk center with an efficient granulation pattern recognition
algorithm. From these we derive their respective properties: diameter,
fractal dimension (area-perimeter relation), geometry, topology,
variation of intensity, temperature, density and velocity with granule
size. Also, the correlation of the physical properties at the optical
surface are studied. We find in all of our 3D RHD simulations stellar
granulation patterns imprinted, which are qualitatively similar to the
solar case, despite the large differences in stellar parameters. The
granules exhibit a large range in size, which can be divided into two
groups - smaller and larger granules - by the mean granule size. These
are distinct in their properties: smaller granules are regular shaped
and dimmer, while the larger ones are increasingly irregular and more
complex in their shapes and distribution in intensity contrast. This
is reflected in their fractal dimensions, which is close to unity for
the smaller granules, and close to two for larger granules, which is
due to the fragmentation of granules. Stellar surface convection seems
to operate scale-invariant over a large range in stellar parameters,
which translates into a self-similar stellar granulation pattern.
Title: Does SEGUE/SDSS indicate a dual Galactic halo?
Authors: Schönrich, Ralph; Asplund, Martin; Casagrande, Luca
Bibcode: 2014ApJ...786....7S
Altcode: 2014arXiv1403.0937S
We re-examine recent claims of observational evidence for a dual
Galactic halo in SEGUE/SDSS data, and trace them back to improper
error treatment and neglect of selection effects. In particular, the
detection of a vertical abundance gradient in the halo can be explained
as a metallicity bias in distance. A similar bias and the impact of disk
contamination affect the sample of blue horizontal branch stars. These
examples highlight why non-volume complete samples require forward
modeling from theoretical models or extensive bias-corrections. We
also show how observational uncertainties produce the specific
non-Gaussianity in the observed azimuthal velocity distribution
of halo stars, which can be erroneously identified as two Gaussian
components. A single kinematic component yields an excellent fit to
the observed data, when we model the measurement process including
distance uncertainties. Furthermore, we show that sample differences
in proper motion space are the direct consequence of kinematic cuts
and are enhanced when distance estimates are less accurate. Thus,
their presence is neither proof of a separate population nor a measure
of reliability for the applied distances. We conclude that currently
there is no evidence from SEGUE/SDSS that would favor a dual Galactic
halo over a single halo that is full of substructure.
Title: The Gaia-ESO Survey: radial metallicity gradients and
age-metallicity relation of stars in the Milky Way disk
Authors: Bergemann, M.; Ruchti, G. R.; Serenelli, A.; Feltzing, S.;
Alves-Brito, A.; Asplund, M.; Bensby, T.; Gruyters, P.; Heiter, U.;
Hourihane, A.; Korn, A.; Lind, K.; Marino, A.; Jofre, P.; Nordlander,
T.; Ryde, N.; Worley, C. C.; Gilmore, G.; Randich, S.; Ferguson,
A. M. N.; Jeffries, R. D.; Micela, G.; Negueruela, I.; Prusti, T.; Rix,
H. -W.; Vallenari, A.; Alfaro, E. J.; Allende Prieto, C.; Bragaglia,
A.; Koposov, S. E.; Lanzafame, A. C.; Pancino, E.; Recio-Blanco, A.;
Smiljanic, R.; Walton, N.; Costado, M. T.; Franciosini, E.; Hill,
V.; Lardo, C.; de Laverny, P.; Magrini, L.; Maiorca, E.; Masseron,
T.; Morbidelli, L.; Sacco, G.; Kordopatis, G.; Tautvaišienė, G.
Bibcode: 2014A&A...565A..89B
Altcode: 2014arXiv1401.4437B
We study the relationship between age, metallicity, and α-enhancement
of FGK stars in the Galactic disk. The results are based upon the
analysis of high-resolution UVES spectra from the Gaia-ESO large
stellar survey. We explore the limitations of the observed dataset,
i.e. the accuracy of stellar parameters and the selection effects
that are caused by the photometric target preselection. We find that
the colour and magnitude cuts in the survey suppress old metal-rich
stars and young metal-poor stars. This suppression may be as high as
97% in some regions of the age-metallicity relationship. The dataset
consists of 144 stars with a wide range of ages from 0.5 Gyr to 13.5
Gyr, Galactocentric distances from 6 kpcto 9.5 kpc, and vertical
distances from the plane 0 < |Z| < 1.5 kpc. On this basis, we
find that i) the observed age-metallicity relation is nearly flat in
the range of ages between 0 Gyr and 8 Gyr; ii) at ages older than 9
Gyr, we see a decrease in [Fe/H] and a clear absence of metal-rich
stars; this cannot be explained by the survey selection functions;
iii) there is a significant scatter of [Fe/H] at any age; and iv)
[Mg/Fe] increases with age, but the dispersion of [Mg/Fe] at ages >9
Gyr is not as small as advocated by some other studies. In agreement
with earlier work, we find that radial abundance gradients change as
a function of vertical distance from the plane. The [Mg/Fe] gradient
steepens and becomes negative. In addition, we show that the inner disk
is not only more α-rich compared to the outer disk, but also older,
as traced independently by the ages and Mg abundances of stars. Based on observations made with the ESO/VLT, at Paranal Observatory,
under programme 188.B-3002 (The Gaia-ESO Public Spectroscopic Survey).
Title: Towards stellar effective temperatures and diameters at 1
per cent accuracy for future surveys
Authors: Casagrande, L.; Portinari, L.; Glass, I. S.; Laney, D.; Silva
Aguirre, V.; Datson, J.; Andersen, J.; Nordström, B.; Holmberg, J.;
Flynn, C.; Asplund, M.
Bibcode: 2014MNRAS.439.2060C
Altcode: 2014arXiv1401.3754C; 2014MNRAS.tmp..291C
The apparent size of stars is a crucial benchmark for fundamental
stellar properties such as effective temperatures, radii and surface
gravities. While interferometric measurements of stellar angular
diameters are the most direct method to gauge these, they are still
limited to relatively nearby and bright stars, which are saturated
in most of the modern photometric surveys. This dichotomy prevents
us from safely extending well-calibrated relations to the faint
stars targeted in large spectroscopic and photometric surveys. Here,
we alleviate this obstacle by presenting South African Astronomical
Observatory near-infrared JHK observations of 55 stars: 16 of them
have interferometric angular diameters and the rest are in common
with the 2 Micron All Sky Survey (2MASS, unsaturated) data set,
allowing us to tie the effective temperatures and angular diameters
derived via the infrared flux method to the interferometric scale. We
extend the test to recent interferometric measurements of unsaturated
2MASS stars, including giants, and the metal-poor benchmark target
HD122563. With a critical evaluation of the systematics involved, we
conclude that a 1 per cent accuracy in fundamental stellar parameters is
usually within reach. Caution, however, must be used when indirectly
testing a Teff scale via colour relations as well as
when assessing the reliability of interferometric measurements,
especially at submilliarcsec level. As a result, rather different
effective temperature scales can be compatible with a given subset of
interferometric data. We highlight some caveats to be aware of in such
a quest and suggest a simple method to check against systematics in
fundamental measurements. A new diagnostic combination seismic radii
with astrometric distances is also presented.
Title: Global and Nonglobal Parameters of Horizontal-branch Morphology
of Globular Clusters
Authors: Milone, A. P.; Marino, A. F.; Dotter, A.; Norris, J. E.;
Jerjen, H.; Piotto, G.; Cassisi, S.; Bedin, L. R.; Recio Blanco, A.;
Sarajedini, A.; Asplund, M.; Monelli, M.; Aparicio, A.
Bibcode: 2014ApJ...785...21M
Altcode: 2013arXiv1312.4169M
The horizontal-branch (HB) morphology of globular clusters (GCs)
is mainly determined by metallicity. However, the fact that GCs
with almost the same metallicity exhibit different HB morphologies
demonstrates that at least one more parameter is needed to explain
the HB morphology. It has been suggested that one of these should be
a global parameter that varies from GC to GC and the other a nonglobal
parameter that varies within the GC. In this study we provide empirical
evidence corroborating this idea. We used the photometric catalogs
obtained with the Advanced Camera for Surveys of the Hubble Space
Telescope and analyze the color-magnitude diagrams of 74 GCs. The HB
morphology of our sample of GCs has been investigated on the basis of
the two new parameters L1 and L2 that measure the distance between
the red giant branch and the coolest part of the HB and the color
extension of the HB, respectively. We find that L1 correlates with
both metallicity and age, whereas L2 most strongly correlates with
the mass of the hosting GC. The range of helium abundance among the
stars in a GC, characterized by ΔY and associated with the presence
of multiple stellar populations, has been estimated in a few GCs to
date. In these GCs we find a close relationship among ΔY, GC mass, and
L2. We conclude that age and metallicity are the main global parameters,
while the range of helium abundance within a GC is the main nonglobal
parameter defining the HB morphology of Galactic GCs. Based on
observations with the NASA/ESA Hubble Space Telescope, obtained at the
Space Telescope Science Institute, which is operated by AURA, Inc.,
under NASA contract NAS 5-26555.
Title: The M 4 Core Project with HST - II. Multiple stellar
populations at the bottom of the main sequence
Authors: Milone, A. P.; Marino, A. F.; Bedin, L. R.; Piotto, G.;
Cassisi, S.; Dieball, A.; Anderson, J.; Jerjen, H.; Asplund, M.;
Bellini, A.; Brogaard, K.; Dotter, A.; Giersz, M.; Heggie, D. C.;
Knigge, C.; Rich, R. M.; van den Berg, M.; Buonanno, R.
Bibcode: 2014MNRAS.439.1588M
Altcode: 2014arXiv1401.1091M; 2014MNRAS.tmp..278M
The M 4 Core Project with HST is designed to exploit the Hubble
Space Telescope (HST) to investigate the central regions of M 4, the
Globular Cluster closest to the Sun. In this paper we combine optical
and near-infrared photometry to study multiple stellar populations in
M 4. We detected two sequences of M-dwarfs containing ∼38 per cent
(MSI) and ∼62 per cent (MSII) of MS stars
below the main-sequence (MS) knee. We compare our observations with
those of NGC 2808, which is the only other GCs where multiple MSs of
very low-mass stars have been studied to date. We calculate synthetic
spectra for M-dwarfs, assuming the chemical composition mixture inferred
from spectroscopic studies of stellar populations along the red giant
branch, and different helium abundances, and we compare predicted and
observed colours. Observations are consistent with two populations,
one with primordial abundance and another with enhanced nitrogen and
depleted oxygen.
Title: The Gaia-ESO Survey: Abundance ratios in the inner-disk open
clusters Trumpler 20, NGC 4815, NGC 6705
Authors: Magrini, L.; Randich, S.; Romano, D.; Friel, E.; Bragaglia,
A.; Smiljanic, R.; Jacobson, H.; Vallenari, A.; Tosi, M.; Spina, L.;
Donati, P.; Maiorca, E.; Cantat-Gaudin, T.; Sordo, R.; Bergemann, M.;
Damiani, F.; Tautvaišienė, G.; Blanco-Cuaresma, S.; Jiménez-Esteban,
F.; Geisler, D.; Mowlavi, N.; Munoz, C.; San Roman, I.; Soubiran, C.;
Villanova, S.; Zaggia, S.; Gilmore, G.; Asplund, M.; Feltzing, S.;
Jeffries, R.; Bensby, T.; Koposov, S.; Korn, A. J.; Flaccomio, E.;
Pancino, E.; Recio-Blanco, A.; Sacco, G.; Costado, M. T.; Franciosini,
E.; Jofre, P.; de Laverny, P.; Hill, V.; Heiter, U.; Hourihane, A.;
Jackson, R.; Lardo, C.; Morbidelli, L.; Lewis, J.; Lind, K.; Masseron,
T.; Prisinzano, L.; Worley, C.
Bibcode: 2014A&A...563A..44M
Altcode: 2013arXiv1312.6472M
Context. Open clusters are key tools to study the spatialdistribution
of abundances in the disk and their evolution with time.
Aims:
Using the first release of stellar parameters and abundances of the
Gaia-ESO Survey, we analyse the chemical properties of stars in three
old/intermediate-age open clusters, namely NGC 6705, NGC 4815, and
Trumpler 20, which are all located in the inner part of the Galactic
disk at Galactocentric radius RGC ~ 7 kpc. We aim to prove
their homogeneity and to compare them with the field population.
Methods: We study the abundance ratios of elements belonging to
two different nucleosynthetic channels: α-elements and iron-peak
elements. For each element, we analyse the internal chemical homogeneity
of cluster members, and we compare the cumulative distributions of
cluster abundance ratios with those of solar neighbourhood turn-off
stars and of inner-disk/bulge giants. We compare the abundance ratios of
field and cluster stars with two chemical evolution models that predict
different α-enhancement dependences on the Galactocentric distance due
to different assumptions on the infall and star-formation rates.
Results: The main results can be summarised as follows: i) cluster
members are chemically homogeneous within 3σ in all analysed elements;
ii) the three clusters have comparable [El/Fe] patterns within ~1σ,
but they differ in their global metal content [El/H] with NGC 4815
having the lowest metallicity; their [El/Fe] ratios show differences
and analogies with those of the field population, in both the solar
neighbourhood and the bulge/inner disk; iii) comparing the abundance
ratios with the results of two chemical evolution models and with field
star abundance distributions, we find that the abundance ratios of Mg,
Ni, and Ca in NGC 6705 might require an inner birthplace, implying a
subsequent variation in its RGC during its lifetime, which is
consistent with previous orbit determination.
Conclusions: Using
the results of the first internal data release, we show the potential of
the Gaia-ESO Survey through a homogeneous and detailed analysis of the
cluster versus field populations to reveal the chemical structure of our
Galaxy using a completely uniform analysis of different populations. We
verify that the Gaia-ESO Survey data are able to identify the unique
chemical properties of each cluster by pinpointing the composition of
the interstellar medium at the epoch and place of formation. The full
dataset of the Gaia-ESO Survey is a superlative tool to constrain the
chemical evolution of our Galaxy by disentangling different formation
and evolution scenarios. Based on observations collected with
the FLAMES spectrograph at the VLT/UT2 telescope (Paranal Observatory,
ESO, Chile), for the Gaia-ESO Large Public Survey (188.B-3002).
Title: VizieR Online Data Catalog: ARGOS line list λ8395-8830Å
(Freeman+, 2013)
Authors: Freeman, K.; Ness, M.; Wylie-de-Boer, E.; Athanassoula, E.;
Bland-Hawthorn, J.; Asplund, M.; Lewis, G.; Yong, D.; Lane, R.; Kiss,
L.; Ibata, R.
Bibcode: 2014yCat..74283660F
Altcode:
The spectra were acquired with the fibre-fed AAOmega system on the
Anglo-Australian Telescope in 2008-2011 May-August. (1 data file).
Title: The Stagger-grid: A grid of 3D stellar atmosphere models -
V. Fe line shapes, shifts and asymmetries
Authors: Magic, Zazralt; Collet, Remo; Asplund, Martin
Bibcode: 2014arXiv1403.6245M
Altcode:
We present a theoretical study of the effects and signatures of
realistic velocity field and atmospheric inhomogeneities associated
with convective motions at the surface of cool late-type stars on
the emergent profiles of iron spectral lines for a large range in
stellar parameters. We compute 3D spectral line flux profiles under
the assumption of local thermodynamic equilibrium (LTE) by employing
state-of-the-art, time-dependent, 3D, radiative-hydrodynamical
atmosphere models from the Stagger-grid. A set of 35 real unblended,
optical FeI and FeII lines of varying excitation potential are
considered. Additionally, fictitious Fe i and Fe ii lines (5000A
and 0, 2, 4 eV) are used to construct general curves of growth and
enable comparison of line profiles with the same line strength
to illustrate systematical trends stemming from the intrinsic
structural differences among 3D model atmospheres with different
stellar parameters. Theoretical line shifts and bisectors are derived
to analyze the shapes, shifts, and asymmetries imprinted in the full 3D
line profiles emerging self-consistently from the convective simulations
with velocity fields and atmospheric inhomogeneities. We find systematic
variations in line strength, shift, width, and bisectors, that can be
related to the respective physical conditions at the height of the line
formation in the stellar atmospheric environment, in particular the
amplitude of the vertical velocity field. Line shifts and asymmetries
arise due to the presence of convective velocities and the granulation
pattern that are ubiquitously found in observed stellar spectra of
cool stars.
Title: A single low-energy, iron-poor supernova as the source of
metals in the star SMSS J031300.36-670839.3
Authors: Keller, S. C.; Bessell, M. S.; Frebel, A.; Casey, A. R.;
Asplund, M.; Jacobson, H. R.; Lind, K.; Norris, J. E.; Yong, D.;
Heger, A.; Magic, Z.; da Costa, G. S.; Schmidt, B. P.; Tisserand, P.
Bibcode: 2014Natur.506..463K
Altcode: 2014arXiv1402.1517K
The element abundance ratios of four low-mass stars with extremely
low metallicities (abundances of elements heavier than helium)
indicate that the gas out of which the stars formed was enriched
in each case by at most a few--and potentially only one--low-energy
supernova. Such supernovae yield large quantities of light elements
such as carbon but very little iron. The dominance of low-energy
supernovae seems surprising, because it had been expected that the
first stars were extremely massive, and that they disintegrated
in pair-instability explosions that would rapidly enrich galaxies
in iron. What has remained unclear is the yield of iron from the
first supernovae, because hitherto no star has been unambiguously
interpreted as encapsulating the yield of a single supernova. Here we
report the optical spectrum of SMSS J031300.36-670839.3, which shows no
evidence of iron (with an upper limit of 10-7.1 times solar
abundance). Based on a comparison of its abundance pattern with those
of models, we conclude that the star was seeded with material from a
single supernova with an original mass about 60 times that of the Sun
(and that the supernova left behind a black hole). Taken together with
the four previously mentioned low-metallicity stars, we conclude that
low-energy supernovae were common in the early Universe, and that
such supernovae yielded light-element enrichment with insignificant
iron. Reduced stellar feedback both chemically and mechanically from
low-energy supernovae would have enabled first-generation stars to
form over an extended period. We speculate that such stars may perhaps
have had an important role in the epoch of cosmic reionization and
the chemical evolution of early galaxies.
Title: Detailed element abundances of SkyMapper EMP stars: first
results of the high-resolution spectroscopic follow up
Authors: Jacobson, Heather R.; Asplund, Martin; Bessell, Michael S.;
Casey, Andrew R.; Da Costa, Gary S.; Frebel, Anna; Keller, Stefan C.;
Lind, Karin; Norris, John E.; Schmidt, Brian P.; Tisserand, Patrick;
Yong, David
Bibcode: 2014MmSAI..85..227J
Altcode:
The multi band photometry of SkyMapper's Southern Sky Survey is
designed to search for extremely metal-poor (EMP) stars. The best
candidates have been observed with low-resolution spectroscopy
to confirm their low metallicities, and then with high-resolution
spectroscopy to determine their detailed element abundances. So far,
high-resolution Magellan/MIKE spectra have been obtained for over
200 EMP candidates. Here we present the results for the first ∼14
months of this new effort, during which time the photometric candidate
selection has been continuously improved. Of the 50 most recently
observed EMP candidates, roughly half have [Fe/H] < -3, with 3
stars having [Fe/H] < -3.5. Our analysis shows these metal-poor
stars to have typical halo star abundance patterns. These results
clearly demonstrate SkyMapper's capability to find large numbers of
EMP stars which will vastly improve our understanding of the earliest
star formation processes and the onset of chemical evolution.
Title: The First Stars
Authors: Asplund, M.
Bibcode: 2014fegb.confE...5A
Altcode:
No abstract at ADS
Title: Chemical signatures of planets: beyond solar-twins
Authors: Ramírez, I.; Meléndez, J.; Asplund, M.
Bibcode: 2014A&A...561A...7R
Altcode: 2013arXiv1310.8581R
Context. Elemental abundance studies of solar twin stars suggest that
the solar chemical composition contains signatures of the formation of
terrestrial planets in the solar system, namely small but significant
depletions of the refractory elements.
Aims: To test whether
these chemical signatures of planets are real, we study stars which,
compared to solar twins, have less massive convective envelopes
(therefore increasing the amplitude of the predicted effect) or are,
arguably, more likely to host planets (thus increasing the frequency of
signature detections).
Methods: We measure relative atmospheric
parameters and elemental abundances of two groups of stars: a "warm"
late-F type dwarf sample (52 stars), and a sample of "metal-rich"
solar analogs (59 stars). The strict differential approach that we
adopt allows us to determine with high precision (errors ~0.01 dex)
the degree of refractory element depletion in our stars independently
of Galactic chemical evolution. By examining relative abundance ratio
versus condensation temperature plots we are able to identify stars with
"pristine" composition in each sample and to determine the degree of
refractory-element depletion for the rest of our stars. We calculate
what mixture of Earth-like and meteorite-like material corresponds
to these depletions.
Results: We detect refractory-element
depletions with amplitudes up to about 0.15 dex. The distribution of
depletion amplitudes for stars known to host gas giant planets is not
different from that of the rest of stars. The maximum amplitude of
depletion increases with effective temperature from 5650 K to 5950 K,
while it appears to be constant for warmer stars (up to 6300 K). The
depletions observed in solar twin stars have a maximum amplitude that
is very similar to that seen here for both of our samples.
Conclusions: Gas giant planet formation alone cannot explain the
observed distributions of refractory-element depletions, leaving
the formation of rocky material as a more likely explanation of our
observations. More rocky material is necessary to explain the data of
solar twins than metal-rich stars, and less for warm stars. However,
the sizes of the stars' convective envelopes at the time of planet
formation could be regulating these amplitudes. Our results could
be explained if disk lifetimes were shorter in more massive stars,
as independent observations indeed seem to suggest. Nevertheless,
to reach stronger conclusions we will need a detailed knowledge of
extrasolar planetary systems down to at least one Earth mass around a
significant number of stars. Based on observations collected at
the European Organisation for Astronomical Research in the Southern
Hemisphere, Chile, observing proposals 086.D0062 and 087.D0010.Full
Tables 1 and 3-6 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/561/A7
Title: Helium enhanced stars and multiple populations along the
horizontal branch of NGC 2808: direct spectroscopic measurements
Authors: Marino, A. F.; Milone, A. P.; Przybilla, N.; Bergemann,
M.; Lind, K.; Asplund, M.; Cassisi, S.; Catelan, M.; Casagrande, L.;
Valcarce, A. A. R.; Bedin, L. R.; Cortés, C.; D'Antona, F.; Jerjen,
H.; Piotto, G.; Schlesinger, K.; Zoccali, M.; Angeloni, R.
Bibcode: 2014MNRAS.437.1609M
Altcode: 2013MNRAS.tmp.2693M; 2013arXiv1310.4527M
We present an abundance analysis of 96 horizontal branch (HB) stars
in NGC 2808, a globular cluster exhibiting a complex multiple stellar
population pattern. These stars are distributed in different portions
of the HB and cover a wide range of temperature. By studying the
chemical abundances of this sample, we explore the connection between
HB morphology and the chemical enrichment history of multiple stellar
populations. For stars lying on the red HB, we use GIRAFFE and UVES
spectra to determine Na, Mg, Si, Ca, Sc, Ti, Cr, Mn, Fe, Ni, Zn, Y,
Ba and Nd abundances. For colder, blue HB stars, we derive abundances
for Na, primarily from GIRAFFE spectra. We were also able to measure
direct non-local thermodynamic equilibrium He abundances for a subset
of these blue HB stars with temperature higher than ∼9000 K. Our
results show that: (i) HB stars in NGC 2808 show different content
in Na depending on their position in the colour-magnitude diagram,
with blue HB stars having higher Na than red HB stars; (ii) the red
HB is not consistent with a uniform chemical abundance, with slightly
warmer stars exhibiting a statistically significant higher Na content;
and (iii) our subsample of blue HB stars with He abundances shows
evidence of enhancement with respect to the predicted primordial
He content by ΔY = +0.09 ± 0.01 ± 0.05 (internal plus systematic
uncertainty). Our results strongly support theoretical models that
predict He enhancement among second-generation(s) stars in globular
clusters and provide observational constraints on the second-parameter
governing HB morphology.
Title: The GALAH survey
Authors: Anguiano, B.; Freeman, K.; Bland-Hawthorn, J.; De Silva,
G.; Asplund, M.; Carollo, D.; D'Orazi, V.; Keller, S.; Martell, S.;
Sharma, S.; Sneden, C.; de Boer, L. Wylie; Zucker, D.; Zwitter, T.
Bibcode: 2014IAUS..298..322A
Altcode:
HERMES is a new high-resolution multi-object spectrograph on the
Anglo Australian Telescope. The primary science driver for HERMES is
the GALAH survey, GALactic Archaeology with HERMES. We are planning a
spectroscopic survey of about a million stars, aimed at using chemical
tagging techniques to reconstruct the star-forming aggregates that
built up the disk, the bulge and halo of the Galaxy. This project will
benefit greatly from the stellar distances and transverse motions from
the Gaia mission.
Title: ``Old'' versus ``New'' Solar Chemical Composition
Authors: Grevesse, N.; Asplund, M.; Sauval, A. J.; Scott, P.
Bibcode: 2013ASPC..479..481G
Altcode:
We follow the evolution since 1989 of element abundance determinations
in the solar photosphere. We describe how the largely used high
metallicity mixtures (Z = 0.02 to 0.017) of Anders & Grevesse
(1989), Grevesse & Noels (1993) and Grevesse & Sauval (1998)
have been obtained and explain why these mixtures should not be used
anymore. They are to be replaced by the more recent mixture of Asplund
et al. (2009) which results from the first comprehensive and homogeneous
analysis for many decades. We describe the main characteristics of this
work and discuss some impacts of this low Z (Z = 0.0134) mixture. We
also comment on another recent analysis by Caffau et al. (2011) that
leads to somewhat larger metal abundances.
Title: The Stagger-grid: A Grid of 3D Stellar Atmosphere Models
Authors: Magic, Z.; Collet, R.; Asplund, M.
Bibcode: 2013EAS....63..367M
Altcode: 2013arXiv1310.4996M
Theoretical atmosphere models provide the basis for a variety of
applications in astronomy. In simplified one-dimensional (1D) atmosphere
models, convection is usually treated with the mixing length theory
despite its well-known insufficiency, therefore, the superadiabatic
regime is poorly rendered. Due to the increasing computational power
over the last decades, we are now capable to compute large grids of
realistic three-dimensional (3D) hydrodynamical model atmospheres with
the realistic treatment of the radiative transfer. We have computed the
Stagger-grid, a comprehensive grid of 3D atmosphere models for late-type
stars. In the presented contribution, we discuss initial results of
the grid by exploring global properties and mean stratifications of
the 3D models. Furthermore, we also depict the differences to classic
1D atmosphere models.
Title: The Stagger-grid: A grid of 3D stellar atmosphere
models. II. Horizontal and temporal averaging and spectral line
formation
Authors: Magic, Z.; Collet, R.; Hayek, W.; Asplund, M.
Bibcode: 2013A&A...560A...8M
Altcode: 2013arXiv1307.3273M
Aims: We study the implications of averaging methods with
different reference depth scales for 3D hydrodynamical model atmospheres
computed with the Stagger-code. The temporally and spatially averaged
(hereafter denoted as ⟨3D⟩) models are explored in the light
of local thermodynamic equilibrium (LTE) spectral line formation by
comparing spectrum calculations using full 3D atmosphere structures
with those from ⟨3D⟩ averages.
Methods: We explored methods
for computing mean ⟨3D⟩ stratifications from the Stagger-grid
time-dependent 3D radiative hydrodynamical atmosphere models by
considering four different reference depth scales (geometrical depth,
column-mass density, and two optical depth scales). Furthermore,
we investigated the influence of alternative averages (logarithmic,
enforced hydrostatic equilibrium, flux-weighted temperatures). For the
line formation we computed curves of growth for Fe i and Fe ii lines in
LTE.
Results: The resulting ⟨3D⟩ stratifications for the four
reference depth scales can be very different. We typically find that in
the upper atmosphere and in the superadiabatic region just below the
optical surface, where the temperature and density fluctuations are
highest, the differences become considerable and increase for higher
Teff, lower log g, and lower [Fe / H]. The differential
comparison of spectral line formation shows distinctive differences
depending on which ⟨3D⟩ model is applied. The averages over
layers of constant column-mass density yield the best mean ⟨3D⟩
representation of the full 3D models for LTE line formation, while
the averages on layers at constant geometrical height are the least
appropriate. Unexpectedly, the usually preferred averages over layers of
constant optical depth are prone to increasing interference by reversed
granulation towards higher effective temperature, in particular at
low metallicity. Appendix A is available in electronic form
at http://www.aanda.orgMean
⟨3D⟩ models are available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/560/A8
as well as at http://www.stagger-stars.net
Title: VizieR Online Data Catalog: High-precision abundances for
stars with planets (Ramirez+, 2014)
Authors: Ramirez, I.; Melendez, J.; Asplund, M.
Bibcode: 2013yCat..35610007R
Altcode: 2013yCat..35619007R
High-precision stellar parameters and chemical abundances are presented
for 111 stars; 52 of them are late-F type dwarfs and 59 are metal-rich
solar analogs. The atomic linelist employed in the derivation of
chemical abundances is also given. This linelist includes hyperfine
structure parameters for some species. The stars' isochrone masses
and ages are also reported, along with estimates of chromospheric
activity. (5 data files).
Title: A Community Science Case for E-ELT HIRES
Authors: Maiolino, R.; Haehnelt, M.; Murphy, M. T.; Queloz, D.;
Origlia, L.; Alcala, J.; Alibert, Y.; Amado, P. J.; Allende Prieto, C.;
Ammler-von Eiff, M.; Asplund, M.; Barstow, M.; Becker, G.; Bonfils, X.;
Bouchy, F.; Bragaglia, A.; Burleigh, M. R.; Chiavassa, A.; Cimatti,
D. A.; Cirasuolo, M.; Cristiani, S.; D'Odorico, V.; Dravins, D.;
Emsellem, E.; Farihi, J.; Figueira, P.; Fynbo, J.; Gansicke, B. T.;
Gillon, M.; Gustafsson, B.; Hill, V.; Israelyan, G.; Korn, A.; Larsen,
S.; De Laverny, P.; Liske, J.; Lovis, C.; Marconi, A.; Martins, C.;
Molaro, P.; Nisini, B.; Oliva, E.; Petitjean, P.; Pettini, M.; Recio
Blanco, A.; Rebolo, R.; Reiners, A.; Rodriguez-Lopez, C.; Ryde, N.;
Santos, N. C.; Savaglio, S.; Snellen, I.; Strassmeier, K.; Tanvir, N.;
Testi, L.; Tolstoy, E.; Triaud, A.; Vanzi, L.; Viel, M.; Volonteri, M.
Bibcode: 2013arXiv1310.3163M
Altcode:
Building on the experience of the high-resolution community with the
suite of VLT high-resolution spectrographs, which has been tremendously
successful, we outline here the (science) case for a high-fidelity,
high-resolution spectrograph with wide wavelength coverage at the
E-ELT. Flagship science drivers include: the study of exo-planetary
atmospheres with the prospect of the detection of signatures of life
on rocky planets; the chemical composition of planetary debris on the
surface of white dwarfs; the spectroscopic study of protoplanetary and
proto-stellar disks; the extension of Galactic archaeology to the Local
Group and beyond; spectroscopic studies of the evolution of galaxies
with samples that, unlike now, are no longer restricted to strongly
star forming and/or very massive galaxies; the unraveling of the
complex roles of stellar and AGN feedback; the study of the chemical
signatures imprinted by population III stars on the IGM during the
epoch of reionization; the exciting possibility of paradigm-changing
contributions to fundamental physics. The requirements of these science
cases can be met by a stable instrument with a spectral resolution
of R~100,000 and broad, simultaneous spectral coverage extending
from 370nm to 2500nm. Most science cases do not require spatially
resolved information, and can be pursued in seeing-limited mode,
although some of them would benefit by the E-ELT diffraction limited
resolution. Some multiplexing would also be beneficial for some of
the science cases. (Abridged)
Title: High precision differential abundance measurements in globular
clusters: chemical inhomogeneities in NGC 6752
Authors: Yong, David; Meléndez, Jorge; Grundahl, Frank; Roederer,
Ian U.; Norris, John E.; Milone, A. P.; Marino, A. F.; Coelho, P.;
McArthur, Barbara E.; Lind, K.; Collet, R.; Asplund, Martin
Bibcode: 2013MNRAS.434.3542Y
Altcode: 2013MNRAS.tmp.1944Y; 2013arXiv1307.4486Y
We report on a strictly differential line-by-line analysis of
high-quality UVES spectra of bright giants in the metal-poor globular
cluster NGC 6752. We achieved high precision differential chemical
abundance measurements for Fe, Na, Si, Ca, Ti, Cr, Ni, Zn, Y, Zr, Ba,
La, Ce, Pr, Nd, Sm, Eu and Dy with uncertainties as low as ∼0.01
dex (∼2 per cent). We obtained the following main results. (1) The
observed abundance dispersions are a factor of ∼2 larger than the
average measurement uncertainty. (2) There are positive correlations, of
high statistical significance, between all elements and Na. (3) For any
pair of elements, there are positive correlations of high statistical
significance, although the amplitudes of the abundance variations are
small. Removing abundance trends with effective temperature and/or using
a different pair of reference stars does not alter these results. These
abundance variations and correlations may reflect a combination of (a)
He abundance variations and (b) inhomogeneous chemical evolution in the
pre- or protocluster environment. Regarding the former, the current
constraints on ΔY from photometry likely preclude He as being the
sole explanation. Regarding the latter, the nucleosynthetic source(s)
must have synthesized Na, α, Fe-peak and neutron-capture elements and
in constant amounts for species heavier than Si; no individual object
can achieve such nucleosynthesis. We speculate that other, if not all,
globular clusters may exhibit comparable abundance variations and
correlations to NGC 6752 if subjected to a similarly precise analysis.
Title: VizieR Online Data Catalog: STAGGER-grid of 3D stellar
models. II. (Magic+, 2013)
Authors: Magic, Z.; Collet, R.; Hayek, W.; Asplund, M.
Bibcode: 2013yCat..35600008M
Altcode: 2013yCat..35609008M
More (updated) information and data available at:
http://www.stagger-stars.net/ (5 data files).
Title: High Precision Abundances of the Old Solar Twin HIP 102152:
Insights on Li Depletion from the Oldest Sun
Authors: Monroe, TalaWanda R.; Meléndez, Jorge; Ramírez, Iván; Yong,
David; Bergemann, Maria; Asplund, Martin; Bedell, Megan; Tucci Maia,
Marcelo; Bean, Jacob; Lind, Karin; Alves-Brito, Alan; Casagrande,
Luca; Castro, Matthieu; do Nascimento, José-Dias; Bazot, Michael;
Freitas, Fabrício C.
Bibcode: 2013ApJ...774L..32M
Altcode: 2013arXiv1308.5744M
We present the first detailed chemical abundance analysis of the old
8.2 Gyr solar twin, HIP 102152. We derive differential abundances of
21 elements relative to the Sun with precisions as high as 0.004 dex
(lsim1%), using ultra high-resolution (R = 110,000), high S/N UVES
spectra obtained on the 8.2 m Very Large Telescope. Our determined
metallicity of HIP 102152 is [Fe/H] = -0.013 ± 0.004. The atmospheric
parameters of the star were determined to be 54 K cooler than the Sun,
0.09 dex lower in surface gravity, and a microturbulence identical to
our derived solar value. Elemental abundance ratios examined versus
dust condensation temperature reveal a solar abundance pattern for
this star, in contrast to most solar twins. The abundance pattern
of HIP 102152 appears to be the most similar to solar of any known
solar twin. Abundances of the younger, 2.9 Gyr solar twin, 18 Sco,
were also determined from UVES spectra to serve as a comparison for HIP
102152. The solar chemical pattern of HIP 102152 makes it a potential
candidate to host terrestrial planets, which is reinforced by the
lack of giant planets in its terrestrial planet region. The following
non-local thermodynamic equilibrium Li abundances were obtained for HIP
102152, 18 Sco, and the Sun: log epsilon (Li) = 0.48 ± 0.07, 1.62 ±
0.02, and 1.07 ± 0.02, respectively. The Li abundance of HIP 102152 is
the lowest reported to date for a solar twin, and allows us to consider
an emerging, tightly constrained Li-age trend for solar twin stars. Based on observations obtained at the European Southern Observatory
(observing programs 083.D-0871 and 188.C-0265).
Title: The Stagger-grid: A grid of 3D stellar atmosphere
models. I. Methods and general properties
Authors: Magic, Z.; Collet, R.; Asplund, M.; Trampedach, R.; Hayek,
W.; Chiavassa, A.; Stein, R. F.; Nordlund, Å.
Bibcode: 2013A&A...557A..26M
Altcode: 2013arXiv1302.2621M
Aims: We present the Stagger-grid, a comprehensive grid of
time-dependent, three-dimensional (3D), hydrodynamic model atmospheres
for late-type stars with realistic treatment of radiative transfer,
covering a wide range in stellar parameters. This grid of 3D models is
intended for various applications besides studies of stellar convection
and atmospheres per se, including stellar parameter determination,
stellar spectroscopy and abundance analysis, asteroseismology,
calibration of stellar evolution models, interferometry, and extrasolar
planet search. In this introductory paper, we describe the methods
we applied for the computation of the grid and discuss the general
properties of the 3D models as well as of their temporal and spatial
averages (here denoted ⟨3D⟩ models).
Methods: All our models
were generated with the Stagger-code, using realistic input physics for
the equation of state (EOS) and for continuous and line opacities. Our ~
220 grid models range in effective temperature, Teff, from
4000 to 7000 K in steps of 500 K, in surface gravity, log g, from 1.5
to 5.0 in steps of 0.5 dex, and metallicity, [Fe/H], from - 4.0 to +
0.5 in steps of 0.5 and 1.0 dex.
Results: We find a tight scaling
relation between the vertical velocity and the surface entropy jump,
which itself correlates with the constant entropy value of the adiabatic
convection zone. The range in intensity contrast is enhanced at lower
metallicity. The granule size correlates closely with the pressure
scale height sampled at the depth of maximum velocity. We compare the
⟨3D⟩ models with currently widely applied one-dimensional (1D)
atmosphere models, as well as with theoretical 1D hydrostatic models
generated with the same EOS and opacity tables as the 3D models, in
order to isolate the effects of using self-consistent and hydrodynamic
modeling of convection, rather than the classical mixing length theory
approach. For the first time, we are able to quantify systematically
over a broad range of stellar parameters the uncertainties of 1D
models arising from the simplified treatment of physics, in particular
convective energy transport. In agreement with previous findings,
we find that the differences can be rather significant, especially
for metal-poor stars. Appendices A-C are available in electronic
form at http://www.aanda.orgFull
Table C.1 is available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/557/A26
Title: The chemical signatures of planet formation: Kepler stars
with rocky planets
Authors: Asplund, Martin
Bibcode: 2013koa..prop..142A
Altcode:
No abstract at ADS
Title: ARGOS - IV. The kinematics of the Milky Way bulge
Authors: Ness, M.; Freeman, K.; Athanassoula, E.; Wylie-de-Boer, E.;
Bland-Hawthorn, J.; Asplund, M.; Lewis, G. F.; Yong, D.; Lane, R. R.;
Kiss, L. L.; Ibata, R.
Bibcode: 2013MNRAS.432.2092N
Altcode: 2013MNRAS.tmp.1344N; 2013arXiv1303.6656N
We present the kinematic results from our ARGOS spectroscopic survey
of the Galactic bulge of the Milky Way. Our aim is to understand the
formation of the Galactic bulge. We examine the kinematics of about 17
400 stars in the bulge located within 3.5 kpc of the Galactic Centre,
identified from the 28 000 star ARGOS survey. We aim to determine
if the formation of the bulge has been internally driven from disc
instabilities as suggested by its boxy shape, or if mergers have
played a significant role as expected from lambda cold dark matter
simulations. From our velocity measurements across latitudes b =
-5°, - 7.5° and -10° we find the bulge to be a cylindrically
rotating system that transitions smoothly out into the disc. From
observations of 3 fields at b = +10, the kinematics of the bulge
show North-South symmetry about the major axis. Within the bulge,
we find a kinematically distinct metal-poor population ([Fe/H] <
-1.0) that is not rotating cylindrically. The 5 per cent of our stars
with [Fe/H] < -1.0 are a slowly rotating spheroidal population,
which we believe are stars of the metal-weak thick disc and halo
which presently lie in the inner Galaxy. The kinematics of the two
bulge components that we identified in ARGOS Paper III (mean [Fe/H]
≈ -0.25 and [Fe/H] ≈ +0.15, respectively) demonstrate that they
are likely to share a common formation origin and are distinct from
the more metal-poor populations of the thick disc and halo which are
co-located inside the bulge. We do not exclude an underlying merger
generated bulge component but our results favour bulge formation from
instabilities in the early thin disc.
Title: What 3D Hydrodynamical Stellar Model Atmospheres Can Do for
Asteroseismology and Stellar Populations
Authors: Asplund, M.
Bibcode: 2013aspm.confE..11A
Altcode:
No abstract at ADS
Title: VizieR Online Data Catalog: STAGGER-grid of 3D stellar
models. I. (Magic+, 2013)
Authors: Magic, Z.; Collet, R.; Asplund, M.; Trampedach, R.; Hayek,
W.; Chiavassa, A.; Stein, R. F.; Nordlund, A.
Bibcode: 2013yCat..35570026M
Altcode: 2013yCat..35579026M
The 3D model atmospheres presented here were constructed with
a custom version of the Stagger-code, a state-of-the-art,
multipurpose, radiative-magnetohydrodynamics (R-MHD)
code originally developed by Nordlund & Galsgaard (1995,
http://www.astro.ku.dk/~kg/Papers/MHD_code.ps.gz), and continuously
improved over the years by its user community. (1 data file).
Title: The lithium isotopic ratio in very metal-poor stars
Authors: Lind, K.; Melendez, J.; Asplund, M.; Collet, R.; Magic, Z.
Bibcode: 2013A&A...554A..96L
Altcode: 2013arXiv1305.6564L
Context. Un-evolved, very metal-poor stars are the most
important tracers of the cosmic abundance of lithium in the early
universe. Combining the standard Big Bang nucleosynthesis model
with Galactic production through cosmic ray spallation, these stars
at [Fe / H] < - 2 are expected to show an undetectably small
6Li / 7Li isotopic signature. Evidence to the
contrary may necessitate an additional pre-galactic production source
or a revision of the standard model of Big Bang nucleosynthesis. It
would also cast doubts on Li depletion from stellar atmospheres as
an explanation for the factor 3-5 discrepancy between the predicted
primordial 7Li from the Big Bang and the observed value in
metal-poor dwarf/turn-off stars.
Aims: We revisit the isotopic
analysis of four halo stars, two with claimed 6Li-detections
in the literature, to investigate the influence of improved model
atmospheres and line formation treatment.
Methods: For the
first time, a combined 3D, non-local thermodynamic equilibrium
(NLTE) modelling technique for Li, Na, and Ca lines is utilised
to constrain the intrinsic line-broadening and to determine the Li
isotopic ratio. We discuss the influence of 3D NLTE effects on line
profile shapes and assess the realism of our modelling using the Ca
excitation and ionisation balance.
Results: By accounting for
NLTE line formation in realistic 3D hydrodynamical model atmospheres,
we can model the Li resonance line and other neutral lines with a
consistency that is superior to LTE, with no need for additional
line asymmetry caused by the presence of 6Li. Contrary to
the results from 1D and 3D LTE modelling, no star in our sample has a
significant (2σ) detection of the lighter isotope in NLTE. Over a large
parameter space, NLTE modelling systematically reduces the best-fit Li
isotopic ratios by up to five percentage points. As a bi-product, we
also present the first ever 3D NLTE Ca and Na abundances of halo stars,
which reveal significant departures from LTE.
Conclusions: The
observational support for a significant and non-standard 6Li
production source in the early universe is substantially weakened
by our findings. Appendix A is available in electronic form
at http://www.aanda.orgThe
reduced spectra in the region around the Li line
are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/554/A96
Title: How realistic are solar model atmospheres?
Authors: Pereira, T. M. D.; Asplund, M.; Collet, R.; Thaler, I.;
Trampedach, R.; Leenaarts, J.
Bibcode: 2013A&A...554A.118P
Altcode: 2013arXiv1304.4932P
Context. Recently, new solar model atmospheres have been developed
to replace classical 1D local thermodynamical equilibrium (LTE)
hydrostatic models and used to for example derive the solar chemical
composition.
Aims: We aim to test various models against key
observational constraints. In particular, a 3D model used to derive
the solar abundances, a 3D magnetohydrodynamical (MHD) model (with an
imposed 10 mT vertical magnetic field), 1D NLTE and LTE models from
the PHOENIX project, the 1D MARCS model, and the 1D semi-empirical
model of Holweger & Müller.
Methods: We confronted the
models with observational diagnostics of the temperature profile:
continuum centre-to-limb variations (CLVs), absolute continuum fluxes,
and the wings of hydrogen lines. We also tested the 3D models for the
intensity distribution of the granulation and spectral line shapes.
Results: The predictions from the 3D model are in excellent agreement
with the continuum CLV observations, performing even better than
the Holweger & Müller model (constructed largely to fulfil such
observations). The predictions of the 1D theoretical models are worse,
given their steeper temperature gradients. For the continuum fluxes,
predictions for most models agree well with the observations. No
model fits all hydrogen lines perfectly, but again the 3D model comes
ahead. The 3D model also reproduces the observed continuum intensity
fluctuations and spectral line shapes very well.
Conclusions:
The excellent agreement of the 3D model with the observables reinforces
the view that its temperature structure is realistic. It outperforms
the MHD simulation in all diagnostics, implying that recent claims
for revised abundances based on MHD modelling are premature. Several
weaknesses in the 1D hydrostatic models (theoretical and semi-empirical)
are exposed. The differences between the PHOENIX LTE and NLTE models
are small. We conclude that the 3D hydrodynamical model is superior
to any of the tested 1D models, which gives further confidence in the
solar abundance analyses based on it.
Title: VizieR Online Data Catalog: Metal-poor star spectra of the
LiI 670.8nm line (Lind+, 2013)
Authors: Lind, K.; Melendez, J.; Asplund, M.; Collet, R.; Magic, Z.
Bibcode: 2013yCat..35540096L
Altcode: 2013yCat..35549096L
Reduced spectra in the region around the LiI 670.8nm resonance
line. Four stars have been observed: HD19445, HD84937, HD140283 and
G64-12. For each star, wavelength and normalised flux are given. For
the derivation of the Li isotopic ratio, the normalisation has been
further fine-tuned in a spectral interval extending 0.17nm from the
line centre. (4 data files).
Title: A Grid of Three-dimensional Stellar Atmosphere Models of Solar
Metallicity. I. General Properties, Granulation, and Atmospheric
Expansion
Authors: Trampedach, Regner; Asplund, Martin; Collet, Remo; Nordlund,
Åke; Stein, Robert F.
Bibcode: 2013ApJ...769...18T
Altcode: 2013arXiv1303.1780T
Present grids of stellar atmosphere models are the workhorses in
interpreting stellar observations and determining their fundamental
parameters. These models rely on greatly simplified models of
convection, however, lending less predictive power to such models of
late-type stars. We present a grid of improved and more reliable stellar
atmosphere models of late-type stars, based on deep, three-dimensional
(3D), convective, stellar atmosphere simulations. This grid is to be
used in general for interpreting observations and improving stellar
and asteroseismic modeling. We solve the Navier Stokes equations in
3D and concurrent with the radiative transfer equation, for a range
of atmospheric parameters, covering most of stellar evolution with
convection at the surface. We emphasize the use of the best available
atomic physics for quantitative predictions and comparisons with
observations. We present granulation size, convective expansion of the
acoustic cavity, and asymptotic adiabat as functions of atmospheric
parameters.
Title: The SUMO project I. A survey of multiple populations in
globular clusters
Authors: Monelli, M.; Milone, A. P.; Stetson, P. B.; Marino, A. F.;
Cassisi, S.; del Pino Molina, A.; Salaris, M.; Aparicio, A.; Asplund,
M.; Grundahl, F.; Piotto, G.; Weiss, A.; Carrera, R.; Cebrián, M.;
Murabito, S.; Pietrinferni, A.; Sbordone, L.
Bibcode: 2013MNRAS.431.2126M
Altcode: 2013arXiv1303.5187M
We present a general overview and the first results of the SUMO project
(a SUrvey of Multiple pOpulations in Globular Clusters). The objective
of this survey is the study of multiple stellar populations in the
largest sample of globular clusters homogeneously analysed to date. To
this aim we obtained high signal-to-noise (S/N > 50) photometry
for main sequence stars with mass down to ∼0.5 M⊙ in
a large sample of clusters using both archival and proprietary U, B,
V and I data from ground-based telescopes. In this paper, we focus
on the occurrence of multiple stellar populations in 23 clusters. We
define a new photometric index, cU, B, I = (U - B) - (B - I),
which turns out to be very effective for identifying multiple sequences
along the red giant branch (RGB). We found that in the V-cU, B,
I diagram all clusters presented in this paper show broadened
or multimodal RGBs, with the presence of two or more components. We
found a direct connection with the chemical properties of different
sequences, which display different abundances of light elements (O, Na,
C, N and Al). The cU, B, I index is also a powerful tool for
identifying distinct sequences of stars along the horizontal branch and,
for the first time in the case of NGC 104 (47 Tuc), along the asymptotic
giant branch. Our results demonstrate that (i) the presence of more than
two stellar populations is a common feature amongst globular clusters,
as already highlighted in previous work; (ii) multiple sequences
with different chemical contents can be easily identified by using
standard Johnson photometry obtained with ground-based facilities;
(iii) in the study of globular cluster multiple stellar populations
the cU, B, I index is an alternative to spectroscopy,
and has the advantage of larger statistics.
Title: ARGOS - III. Stellar populations in the Galactic bulge of
the Milky Way
Authors: Ness, M.; Freeman, K.; Athanassoula, E.; Wylie-de-Boer, E.;
Bland-Hawthorn, J.; Asplund, M.; Lewis, G. F.; Yong, D.; Lane, R. R.;
Kiss, L. L.
Bibcode: 2013MNRAS.430..836N
Altcode: 2013MNRAS.tmp..635N; 2012arXiv1212.1540N
We present the metallicity results from the ARGOS spectroscopic survey
of the Galactic bulge. Our aim is to understand the formation of the
Galactic bulge: did it form via mergers, as expected from Λ cold
dark matter theory, or from disc instabilities, as suggested by its
boxy/peanut shape, or both? Our stars are mostly red clump giants,
which have a well-defined absolute magnitude from which distances
can be determined. We have obtained spectra for 28 000 stars at
a spectral resolution of R = 11 000. From these spectra, we have
determined stellar parameters and distances to an accuracy of <1.5
kpc. The stars in the inner Galaxy span a large range in [Fe/H],
-2.8 ≤ [Fe/H] ≤ +0.6. From the spatial distribution of the red
clump stars as a function of [Fe/H], we propose that the stars with
[Fe/H] > -0.5 are part of the boxy/peanut bar/bulge. We associate
the lower metallicity stars ([Fe/H] < -0.5) with the thick disc,
which may be puffed up in the inner region, and with the inner
regions of the metal-weak thick disc and inner halo. For the bulge
stars with [Fe/H] > -0.5, we find two discrete populations: (i)
stars with [Fe/H] ≈ -0.25 which provide a roughly constant fraction
of the stars in the latitude interval b = -5° to -10°, and (ii)
a kinematically colder, more metal-rich population with mean [Fe/H]
≈ +0.15 which is more prominent closer to the plane. The changing
ratio of these components with latitude appears as a vertical abundance
gradient of the bulge. We attribute both of these bulge components to
instability-driven bar/bulge formation from the thin disc. We associate
the thicker component with the stars of the early less metal-rich thin
disc, and associate the more metal-rich population concentrated to the
plane with the colder more metal-rich stars of the early thin disc,
similar to the colder and younger more metal-rich stars seen in the
thin disc in the solar neighbourhood today. We do not exclude a weak
underlying classical merger-generated bulge component, but see no
obvious kinematic association of any of our bulge stars with such a
classical bulge component. The clear spatial and kinematic separation
of the two bulge populations (i) and (ii) makes it unlikely that any
significant merger event could have affected the inner regions of the
Galaxy since the time when the bulge-forming instabilities occurred.
Title: Why GN93 should not be used anymore
Authors: Grevesse, N.; Asplund, M.; Sauval, J.; Scott, P.
Bibcode: 2013EPJWC..4301004G
Altcode:
We show why the solar chemical composition of [1] (GN93) and the
similar values of [2] (AG89) and [3] (GS98), characterized by values
of the metallicity of the order of 0.017 to 0.020, largely used in
solar and stellar modeling, are now obsolete. They should be replaced
by the new and more precise results of [4] (AGSS09), with a much lower
metallicity of 0.0134.
Title: ARGOS - II. The Galactic bulge survey
Authors: Freeman, K.; Ness, M.; Wylie-de-Boer, E.; Athanassoula, E.;
Bland-Hawthorn, J.; Asplund, M.; Lewis, G.; Yong, D.; Lane, R.; Kiss,
L.; Ibata, R.
Bibcode: 2013MNRAS.428.3660F
Altcode: 2012MNRAS.428.3660F; 2012arXiv1212.1541F; 2012MNRAS.tmp..296F
We describe the motivation, field locations and stellar selection for
the Abundances and Radial velocity Galactic Origins Survey (ARGOS)
spectroscopic survey of 28 000 stars in the bulge and inner disc of the
Milky Way galaxy across latitudes of b = -5° to -10°. The primary goal
of this survey is to constrain the formation processes of the bulge
and establish whether it is predominantly a merger or instability
remnant. From the spectra (R = 11 000), we have measured radial
velocities and determined stellar parameters, including metallicities
and [α/Fe] ratios. Distances were estimated from the derived stellar
parameters and about 14 000 stars are red giants within 3.5 kpc of
the Galactic Centre. In this paper, we present the observations and
analysis methods. Subsequent papers (III and IV) will discuss the
stellar metallicity distribution and kinematics of the Galactic bulge
and inner disc, and the implications for the formation of the bulge.
Title: The Most Metal-poor Stars. II. Chemical Abundances of 190
Metal-poor Stars Including 10 New Stars with [Fe/H] <= -3.5
Authors: Yong, David; Norris, John E.; Bessell, M. S.; Christlieb,
N.; Asplund, M.; Beers, Timothy C.; Barklem, P. S.; Frebel, Anna;
Ryan, S. G.
Bibcode: 2013ApJ...762...26Y
Altcode: 2012arXiv1208.3003Y
We present a homogeneous chemical abundance analysis of 16 elements
in 190 metal-poor Galactic halo stars (38 program and 152 literature
objects). The sample includes 171 stars with [Fe/H] <= -2.5, of
which 86 are extremely metal poor, [Fe/H] <= -3.0. Our program stars
include 10 new objects with [Fe/H] <= -3.5. We identify a sample
of "normal" metal-poor stars and measure the trends between [X/Fe]
and [Fe/H], as well as the dispersion about the mean trend for this
sample. Using this mean trend, we identify objects that are chemically
peculiar relative to "normal" stars at the same metallicity. These
chemically unusual stars include CEMP-no objects, one star with high
[Si/Fe], another with high [Ba/Sr], and one with unusually low [X/Fe]
for all elements heavier than Na. The Sr and Ba abundances indicate
that there may be two nucleosynthetic processes at lowest metallicity
that are distinct from the main r-process. Finally, for many elements,
we find a significant trend between [X/Fe] versus T eff,
which likely reflects non-LTE and/or three-dimensional effects. Such
trends demonstrate that care must be exercised when using abundance
measurements in metal-poor stars to constrain chemical evolution and/or
nucleosynthesis predictions. This paper includes data gathered
with the 6.5 m Magellan Telescopes located at Las Campanas Observatory,
Chile. Based on observations collected at the European Organisation
for Astronomical Research in the Southern Hemisphere, Chile (proposal
281.D-5015).
Title: The Most Metal-poor Stars. I. Discovery, Data, and Atmospheric
Parameters
Authors: Norris, John E.; Bessell, M. S.; Yong, David; Christlieb,
N.; Barklem, P. S.; Asplund, M.; Murphy, Simon J.; Beers, Timothy C.;
Frebel, Anna; Ryan, S. G.
Bibcode: 2013ApJ...762...25N
Altcode: 2012arXiv1208.2999N
We report the discovery of 34 stars in the Hamburg/ESO Survey for
metal-poor stars and the Sloan Digital Sky Survey that have [Fe/H] <~
-3.0. Their median and minimum abundances are [Fe/H] = -3.1 and -4.1,
respectively, while 10 stars have [Fe/H] < -3.5. High-resolution,
high signal-to-noise spectroscopic data—equivalent widths and
radial velocities—are presented for these stars, together with
an additional four objects previously reported or currently being
investigated elsewhere. We have determined the atmospheric parameters,
effective temperature (T eff), and surface gravity (log g),
which are critical in the determination of the chemical abundances and
the evolutionary status of these stars. Three techniques were used to
derive these parameters. Spectrophotometric fits to model atmosphere
fluxes were used to derive T eff, log g, and an estimate of
E(B - V); Hα, Hβ, and Hγ profile fitting to model atmosphere results
provided the second determination of T eff and log g; and
finally, we used an empirical T eff-calibrated Hδ index,
for the third, independent T eff determination. The three
values of T eff are in good agreement, although the profile
fitting may yield systematically cooler T eff values, by
~100 K. This collective data set will be analyzed in future papers
in the present series to utilize the most metal-poor stars as probes
of conditions in the early universe. This paper includes data
obtained with the ANU 2.3 m Telescope at Siding Spring Observatory,
Australia; the Magellan Clay Telescope at Las Campanas Observatory,
Chile; the Keck I Telescope at the W. M. Keck Observatory, Hawaii, USA;
and the VLT (Kueyen) of the European Southern Observatory, Paranal,
Chile (proposal 281.D-5015).
Title: The SUMO project: a SUrvey of Multiple pOpulations in globular
clusters
Authors: Monelli, M.; Milone, A. P.; Stetson, P. B.; Marino, A. F.;
Cassisi, S.; Del Pino Molina, A.; Salaris, M.; Aparicio, A.; Asplund,
M.; Grundahl, F.; Piotto, G.; Weiss, A.; Carrera, R.; Cebrián, M.;
Murabito, S.; Pietrinferni, A.; Sbordone, L.
Bibcode: 2013MmSAI..84...71M
Altcode:
We present the first results of the SUMO project, aimed at studying
multiple populations in globular clusters. For this purpose we obtained
wide-field photometry in a large sample of clusters using both archival
and proprietary U, B, V, and I data from ground-based telescopes. We
have defined a new photometric index c_U,B,I=(U-B)-(B-I), that we
show is very effective to split multiple sequences along the red
giant branch (RGB). We found a direct connection with the chemical
properties of different sequences, that display different abundances
of light elements.
Title: The Most Metal-poor Stars. III. The Metallicity Distribution
Function and Carbon-enhanced Metal-poor Fraction
Authors: Yong, David; Norris, John E.; Bessell, M. S.; Christlieb,
N.; Asplund, M.; Beers, Timothy C.; Barklem, P. S.; Frebel, Anna;
Ryan, S. G.
Bibcode: 2013ApJ...762...27Y
Altcode: 2012arXiv1208.3016Y
We examine the metallicity distribution function (MDF) and fraction
of carbon-enhanced metal-poor (CEMP) stars in a sample that includes
86 stars with [Fe/H] <= -3.0, based on high-resolution, high
signal-to-noise spectroscopy, of which some 32 objects lie below [Fe/H]
= -3.5. After accounting for the completeness function, the "corrected"
MDF does not exhibit the sudden drop at [Fe/H] = -3.6 that was found in
recent samples of dwarfs and giants from the Hamburg/ESO survey. Rather,
the MDF decreases smoothly down to [Fe/H] = -4.1. Similar results are
obtained from the "raw" MDF. We find that the fraction of CEMP objects
below [Fe/H] = -3.0 is 23% ± 6% and 32% ± 8% when adopting the Beers
& Christlieb and Aoki et al. CEMP definitions, respectively. The
former value is in fair agreement with some previous measurements,
which adopt the Beers & Christlieb criterion. This paper
includes data gathered with the 6.5 m Magellan Telescopes located at
Las Campanas Observatory, Chile. Based on observations collected
at the European Organisation for Astronomical Research in the Southern
Hemisphere, Chile (proposal 281.D-5015).
Title: Chemical evolution of the Galactic bulge as traced by
microlensed dwarf and subgiant stars. V. Evidence for a wide age
distribution and a complex MDF
Authors: Bensby, T.; Yee, J. C.; Feltzing, S.; Johnson, J. A.; Gould,
A.; Cohen, J. G.; Asplund, M.; Meléndez, J.; Lucatello, S.; Han, C.;
Thompson, I.; Gal-Yam, A.; Udalski, A.; Bennett, D. P.; Bond, I. A.;
Kohei, W.; Sumi, T.; Suzuki, D.; Suzuki, K.; Takino, S.; Tristram,
P.; Yamai, N.; Yonehara, A.
Bibcode: 2013A&A...549A.147B
Altcode: 2012arXiv1211.6848B
Based on high-resolution spectra obtained during gravitational
microlensing events we present a detailed elemental abundance analysis
of 32 dwarf and subgiant stars in the Galactic bulge. Combined with
the sample of 26 stars from the previous papers in this series,
we now have 58 microlensed bulge dwarfs and subgiants that have been
homogeneously analysed. The main characteristics of the sample and the
findings that can be drawn are: (i) the metallicity distribution (MDF)
is wide and spans all metallicities between [Fe/H] = -1.9 to +0.6;
(ii) the dip in the MDF around solar metallicity that was apparent in
our previous analysis of a smaller sample (26 microlensed stars) is no
longer evident; instead it has a complex structure and indications of
multiple components are starting to emerge. A tentative interpretation
is that there could be different stellar populations at interplay,
each with a different scale height: the thin disk, the thick disk,
and a bar population; (iii) the stars with [Fe/H] ≲ -0.1 are old
with ages between 10 and 12 Gyr; (iv) the metal-rich stars with [Fe/H]
≳ -0.1 show a wide variety of ages, ranging from 2 to 12 Gyr with a
distribution that has a dominant peak around 4-5 Gyr and a tail towards
higher ages; (v) there are indications in the [α/Fe]-[Fe/H] abundance
trends that the "knee" occurs around [Fe/H] = -0.3to -0.2, which is
a slightly higher metallicity as compared to the "knee" for the local
thick disk. This suggests that the chemical enrichment of the metal-poor
bulge has been somewhat faster than what is observed for the local thick
disk. The results from the microlensed bulge dwarf stars in combination
with other findings in the literature, in particular the evidence that
the bulge has cylindrical rotation, indicate that the Milky Way could be
an almost pure disk galaxy. The bulge would then just be a conglomerate
of the other Galactic stellar populations (thin disk, thick disk,
halo, and ...?), residing together in the central parts of the Galaxy,
influenced by the Galactic bar. Based on data obtained with the
European Southern Observatory telescopes (Proposal ID:s 87.B-0600,
88.B-0349, 89.B-0047, and 90.B-0204), the Magellan Clay telescope at
the Las Campanas observatory, and the Keck I telescope at the W.M. Keck
Observatory, which is operated as a scientific partnership among the
California Institute of Technology, the University of California
and the National Aeronautics and Space Administration.Tables 2-5
are available in electronic form at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr
(130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/549/A147
Title: The Most Metal-poor Stars. IV. The Two Populations with [Fe/H]
<~ -3.0
Authors: Norris, John E.; Yong, David; Bessell, M. S.; Christlieb, N.;
Asplund, M.; Gilmore, Gerard; Wyse, Rosemary F. G.; Beers, Timothy C.;
Barklem, P. S.; Frebel, Anna; Ryan, S. G.
Bibcode: 2013ApJ...762...28N
Altcode: 2012arXiv1211.3157N
We discuss the carbon-normal and carbon-rich populations of Galactic
halo stars having [Fe/H] lsim -3.0, utilizing chemical abundances from
high-resolution, high signal-to-noise model-atmosphere analyses. The
C-rich population represents ~28% of stars below [Fe/H] = -3.1, with the
present C-rich sample comprising 16 CEMP-no stars, and two others with
[Fe/H] ~ -5.5 and uncertain classification. The population is O-rich
([O/Fe] gsim +1.5); the light elements Na, Mg, and Al are enhanced
relative to Fe in half the sample; and for Z > 20 (Ca) there is
little evidence for enhancements relative to solar values. These results
are best explained in terms of the admixing and processing of material
from H-burning and He-burning regions as achieved by nucleosynthesis in
zero-heavy-element models in the literature of "mixing and fallback"
supernovae (SNe); of rotating, massive, and intermediate-mass stars;
and of Type II SNe with relativistic jets. The available (limited)
radial velocities offer little support for the C-rich stars with
[Fe/H] < -3.1 being binary. More data are required before one
could conclude that binarity is key to an understanding of this
population. We suggest that the C-rich and C-normal populations result
from two different gas cooling channels in the very early universe of
material that formed the progenitors of the two populations. The first
was cooling by fine-structure line transitions of C II and O I (to form
the C-rich population); the second, while not well defined (perhaps
dust-induced cooling?), led to the C-normal group. In this scenario,
the C-rich population contains the oldest stars currently observed.
Title: The Infrared Colors of the Sun
Authors: Casagrande, L.; Ramírez, I.; Meléndez, J.; Asplund, M.
Bibcode: 2012ApJ...761...16C
Altcode: 2012arXiv1209.6127C
Solar infrared colors provide powerful constraints on the stellar
effective temperature scale, but they must be measured with both
accuracy and precision in order to do so. We fulfill this requirement
by using line-depth ratios to derive in a model-independent way the
infrared colors of the Sun, and we use the latter to test the zero
point of the Casagrande et al. effective temperature scale, confirming
its accuracy. Solar colors in the widely used Two Micron All Sky
Survey (2MASS) JHKs and WISE W1-4 systems are provided:
(V - J)⊙ = 1.198, (V - H)⊙ = 1.484, (V -
Ks )⊙ = 1.560, (J - H)⊙ = 0.286,
(J - Ks )⊙ = 0.362, (H - Ks
)⊙ = 0.076, (V - W1)⊙ = 1.608, (V -
W2)⊙ = 1.563, (V - W3)⊙ = 1.552, and (V -
W4)⊙ = 1.604. A cross-check of the effective temperatures
derived implementing 2MASS or WISE magnitudes in the infrared flux
method confirms that the absolute calibration of the two systems agrees
within the errors, possibly suggesting a 1% offset between the two, thus
validating extant near- and mid-infrared absolute calibrations. While
2MASS magnitudes are usually well suited to derive \textit {T}_{eff},
we find that a number of bright, solar-like stars exhibit anomalous WISE
colors. In most cases, this effect is spurious and can be attributed to
lower-quality measurements, although for a couple of objects (3% ± 2%
of the total sample) it might be real, and may hint at the presence
of warm/hot debris disks.
Title: The influence of electron collisions on non-LTE Li line
formation in stellar atmospheres
Authors: Osorio, Yeisson; Barklem, Paul; Lind, Karin; Asplund, Martin
Bibcode: 2012JPhCS.388d2018O
Altcode: 2011arXiv1102.1556O
The influence of the uncertainties in the rate coefficient data for
electron-impact excitation and ionization on non-LTE Li line formation
in cool stellar atmospheres is investigated. We examine the electron
collision data used in previous non-LTE calculations and compare them
to our own calculations using the R-matrix with pseudostates (RMPS)
method and to other calculations found in the literature.
Title: Chemical evolution of the Galactic bulge as traced by
microlensed dwarfs and subgiant stars. V. Evidence for a wide age
distribution and a complex MDF.
Authors: Bensby, T.; Yee, J. C.; Feltzing, S.; Johnson, J. A.; Gould,
A.; Cohen, J. G.; Asplund, M.; Melendez, J.; Lucatello, S.; Han, C.;
Thompson, I.; Gal-Yam, A.; Udalski, A.; Benett, D. P.; Bond, I. A.;
Kohei, W.; Sumi, T.; Suzuki, D.; Suzuki, K.; Takino, S.; Tristram,
P.; Yamai, N.; Yonehara, A.
Bibcode: 2012yCat..35490147B
Altcode: 2012yCat..35499147B
For each spectral line we give the lower excitation potential,
measured equivalent widths, and derived absolute abundances. We also
give median abundances for each star, normalised to the Sun, and errors
in the median abundances. These tables contain data for all so far 58
microlensed dwarf stars, and superseeds the tables in Bensby+ (2009,
Cat. J/A+A/499/737), Bensby+ (2010, Cat. J/A+A/512/A41), and Bensby+
(2011, Cat. J/A+A/533/A134). (4 data files).
Title: Non-LTE line formation of Fe in late-type stars - II. 1D
spectroscopic stellar parameters
Authors: Lind, K.; Bergemann, M.; Asplund, M.
Bibcode: 2012MNRAS.427...50L
Altcode: 2012arXiv1207.2454L
We investigate departures from local thermodynamic equilibrium (LTE)
in the line formation of neutral and singly ionized iron lines and
their impact on spectroscopic stellar parameters. The calculations were
performed for an extensive grid of 1D MARCS models of metal-rich and
metal-poor late-type dwarfs and giants. We find that iron abundances
derived from Fe I lines are increasingly underestimated in hotter, lower
surface gravity and more metal-poor stars, in a simple and well-defined
pattern, while LTE is usually a realistic approximation for Fe II
lines. For the vast majority of dwarfs and giants, the perturbed
ionization balance of Fe I and Fe II is the main relevant non-LTE
effect to consider in the determination of spectroscopic parameters,
while for extremely metal-poor stars and hot giant stars significant
impact is seen also on the excitation balance and on the microturbulence
determination from Fe I lines.
Title: Non-LTE line formation of Fe in late-type stars - I. Standard
stars with 1D and <3D> model atmospheres
Authors: Bergemann, Maria; Lind, K.; Collet, R.; Magic, Z.; Asplund, M.
Bibcode: 2012MNRAS.427...27B
Altcode: 2012arXiv1207.2455B
We investigate departures from local thermodynamic equilibrium
(LTE) in the line formation of Fe for a number of well-studied
late-type stars in different evolutionary stages. A new model of
the Fe atom was constructed from the most up-to-date theoretical
and experimental atomic data available so far. Non-LTE (NLTE) line
formation calculations for Fe were performed using 1D hydrostatic MARCS
and MAFAGS-OS model atmospheres, as well as the spatial and temporal
average stratifications from full 3D hydrodynamical simulations of
stellar convection computed using the STAGGER code. It is shown that
the Fe I/Fe II ionization balance can be well established with the 1D
and mean 3D models under NLTE including calibrated inelastic collisions
with H I calculated from Drawin's formulae. Strong low-excitation Fe
I lines are very sensitive to the atmospheric structure; classical 1D
models fail to provide consistent excitation balance, particularly
so for cool metal-poor stars. A better agreement between Fe I lines
spanning a range of excitation potentials is obtained with the mean
3D models. Mean NLTE metallicities determined for the standard stars
using the 1D and mean 3D models are fully consistent. Moreover,
the NLTE spectroscopic effective temperatures and gravities from
ionization balance agree with that determined by other methods,
e.g. the infrared flux method and parallaxes, if one of the stellar
parameters is constrained independently.
Title: Integrating the HERMES spectrograph for the AAT
Authors: Heijmans, Jeroen; Asplund, Martin; Barden, Sam; Birchall,
Michael; Carollo, Daniela; Bland-Hawthorn, Joss; Brzeski, Jurek; Case,
Scott; Churilov, Vladimir; Colless, Matthew; Dean, Robert; De Silva,
Gayandhi; Farrell, Tony; Fiegert, Kristin; Freeman, Kenneth; Gers,
Luke; Goodwin, Michael; Gray, Doug; Heald, Ron; Heng, Anthony; Jones,
Damien; Kobayashi, Chiaki; Klauser, Urs; Kondrat, Yuriy; Lawrence,
Jon; Lee, Steve; Mathews, Darren; Mayfield, Don; Miziarski, Stan;
Monnet, Guy J.; Muller, Rolf; Pai, Naveen; Patterson, Robert; Penny,
Ed; Orr, David; Sheinis, Andrew; Shortridge, Keith; Smedley, Scott;
Smith, Greg; Stafford, Darren; Staszak, Nicholas; Vuong, Minh; Waller,
Lewis; Whittard, Denis; Wylie de Boer, Elisabeth; Xavier, Pascal;
Zheng, Jessica; Zhelem, Ross; Zucker, Daniel
Bibcode: 2012SPIE.8446E..0WH
Altcode:
The High Efficiency and Resolution Multi Element Spectrograph,
HERMES is an optical spectrograph designed primarily for the GALAH,
Galactic Archeology Survey, the first major attempt to create a
detailed understanding of galaxy formation and evolution by studying
the history of our own galaxy, the Milky Way1. The goal of
the GALAH survey is to reconstruct the mass assembly history of the of
the Milky way, through a detailed spatially tagged abundance study of
one million stars in the Milky Way. The spectrograph will be based at
the Anglo Australian Telescope (AAT) and be fed with the existing 2dF
robotic fibre positioning system. The spectrograph uses VPH-gratings
to achieve a spectral resolving power of 28,000 in standard mode and
also provides a high resolution mode ranging between 40,000 to 50,000
using a slit mask. The GALAH survey requires a SNR greater than 100
aiming for a star brightness of V=14. The total spectral coverage
of the four channels is about 100nm between 370 and 1000nm for up to
392 simultaneous targets within the 2 degree field of view. Current
efforts are focused on manufacturing and integration. The delivery date
of spectrograph at the telescope is scheduled for 2013. A performance
prediction is presented and a complete overview of the status of the
HERMES spectrograph is given. This paper details the following specific
topics: The approach to AIT, the manufacturing and integration of the
large mechanical frame, the opto-mechanical slit assembly, collimator
optics and cameras, VPH gratings, cryostats, fibre cable assembly,
instrument control hardware and software, data reduction.
Title: The New Solar Chemical Composition — from Z = 0.02 to Z
= 0.013
Authors: Grevesse, N.; Asplund, M.; Sauval, A. J.; Scott, P.
Bibcode: 2012ASPC..462...41G
Altcode:
We review the current status of our knowledge of the chemical
composition of the sun and present a redetermination of the solar
abundances of all available elements. These new results have recently
been published by Asplund et al. (2009). The basic ingredients of
this work, the main results and their implications are discussed. We
show why the abundances of the main contributors to the metallicity
have decreased and why the old high solar metallicity, Z ∼ 0.02,
is definitely obsolete and should not be used anymore. We also show
why other recent analyzes of the solar composition report solar
metallicities somewhat larger than the one we recommend.
Title: The Origin of the Split Red Clump in the Galactic Bulge of
the Milky Way
Authors: Ness, M.; Freeman, K.; Athanassoula, E.; Wylie-De-Boer, E.;
Bland-Hawthorn, J.; Lewis, G. F.; Yong, D.; Asplund, M.; Lane, R. R.;
Kiss, L. L.; Ibata, R.
Bibcode: 2012ApJ...756...22N
Altcode: 2012arXiv1207.0888N
Near the minor axis of the Galactic bulge, at latitudes b < -5°,
the red giant clump stars are split into two components along the line
of sight. We investigate this split using the three fields from the
ARGOS survey that lie on the minor axis at (l, b) = (0°, -5°), (0°,
-7fdg5), (0°, -10°). The separation is evident for stars with [Fe/H]
> - 0.5 in the two higher-latitude fields, but not in the field
at b = -5°. Stars with [Fe/H] < - 0.5 do not show the split. We
compare the spatial distribution and kinematics of the clump stars with
predictions from an evolutionary N-body model of a bulge that grew from
a disk via bar-related instabilities. The density distribution of the
peanut-shaped model is depressed near its minor axis. This produces
a bimodal distribution of stars along the line of sight through the
bulge near its minor axis, very much as seen in our observations. The
observed and modeled kinematics of the two groups of stars are also
similar. We conclude that the split red clump of the bulge is probably
a generic feature of boxy/peanut bulges that grew from disks, and that
the disk from which the bulge grew had relatively few stars with [Fe/H]
< - 0.5.
Title: Chemically Tagging Disk Fossils: the Case of the Hyades
Supercluster
Authors: De Silva, G. M.; Freeman, K. C.; Bland-Hawthorn, J.;
Asplund, M.
Bibcode: 2012ASPC..458..215D
Altcode:
The Hyades supercluster is a kinematically defined group of stars,
which are located across the Galactic disk. Advocated by Eggen in the
1970's as part of the Hyades open cluster, recent simulations suggest
the Hyades supercluster is a dynamical stream caused by spiral density
waves. We present high resolution elemental abundances of probable
supercluster members. We recover supercluster stars that share a
similar chemical signature as the Hyades open cluster. Our results
support the Hyades supercluster being at least partly the debris of
an originally large star-forming event.
Title: Signatures of an Intermediate-Age Metal-Rich Bulge Population
Authors: Bensby, T.; Feltzing, S.; Gould, A.; Johnson, J. A.; Asplund,
M.; Adén, D.; Meléndez, J.; Cohen, J. G.; Thompson, I.; Lucatello,
S.; Gal-Yam, A.
Bibcode: 2012ASPC..458..203B
Altcode: 2012arXiv1201.2013B
We have determined detailed elemental abundances and stellar ages
for a sample of now 38 microlensed dwarf and subgiant stars in the
Galactic bulge. Stars with sub-solar metallicities are all old and
have enhanced α-element abundances - very similar to what is seen
for local thick disk stars. The metal-rich stars on the other hand
show a wide variety of stellar ages, ranging from 3-4 Gyr to 12 Gyr,
and an average around 7-8 Gyr. The existence of young and metal-rich
stars are in conflict with recent photometric studies of the bulge
which claim that the bulge only contains old stars.
Title: 3D and NLTE Effects on Spectroscopic Parameters of Late-Type
Stars
Authors: Lind, K.; Bergemann, M.; Collet, R.; Asplund, M.; Magic, Z.
Bibcode: 2012ASPC..458..109L
Altcode:
We investigate the impact on spectroscopic effective temperatures
(Teff), surface gravities (log (g)), and metallicites
([Fe/H]) of metal-poor stars, when departures from LTE are taken into
account and the atmospheric model is constructed from realistic 3D,
hydrodynamical simulations. We demonstrate that traditional 1D, LTE
analysis underestimates the values for all three parameters in the
metal-poor subgiant HD140283.
Title: The Oxygen Abundance of the Ultra-metal-poor Star HE 0557-4840
Authors: Norris, John E.; Christlieb, N.; Bessell, M. S.; Asplund,
M.; Eriksson, K.; Korn, A. J.
Bibcode: 2012ApJ...753..150N
Altcode:
We present a high-resolution ultraviolet (UV) spectrum of the
ultra-metal-poor (UMP) carbon-enhanced red giant HE 0557-4840 (T
eff/log g/[Fe/H] = 4900/2.2/-4.8). Combining these data
with earlier observations, the radial velocity is 212.0 ± 0.4 km
s-1, with no evidence of variability during 2006 February
to 2007 December. One-dimensional (1D) LTE model-atmosphere analysis
of UV Fe and CH lines confirms the iron and carbon abundances obtained
previously ([Fe/H] = -4.8 and [C/Fe]1D = +1.7), and places
a more stringent limit on nitrogen abundance of [N/Fe]1D
< +1.0. Analysis of the UV OH lines yields [O/Fe]1D
= +2.3 ± 0.4. When corrections are made for three-dimensional (3D)
effects we obtain [C/Fe]3D = +1.1, [N/Fe]3D <
+0.1, and [O/Fe]3D = +1.4. Comparison of the abundances
of HE 0557-4840 with those of supernova models of Nomoto et al. and
Joggerst et al. suggests that none is able to explain fully the observed
abundance pattern. For HE 0557-4840, the Frebel et al. transition
discriminant D trans(= log(10[C/H] + 0.3 ×
10[O/H]) = -3.4 ± 0.2, consistent with fine-structure
transitions of C II and O I being a major cooling mechanism of
star-forming regions at the earliest times. Of the four stars known
to have [Fe/H] <~ -4.3, three are strongly carbon and oxygen
enhanced. If the suggestion by Caffau et al. that SDSS J102915+172927
([Fe/H] = -4.7) does not belong to the class of C-rich, O-rich, UMP
stars is supported by future similar discoveries, one will need to
consider multiple channels for the production of stars having [Fe/H]
<~ -4.3. Based on observations collected at European Southern
Observatory, Paranal, Chile (proposal 380.D-0040).
Title: The remarkable solar twin HIP 56948: a prime target in the
quest for other Earths
Authors: Meléndez, J.; Bergemann, M.; Cohen, J. G.; Endl, M.;
Karakas, A. I.; Ramírez, I.; Cochran, W. D.; Yong, D.; MacQueen,
P. J.; Kobayashi, C.; Asplund, M.
Bibcode: 2012A&A...543A..29M
Altcode: 2012arXiv1204.2766M
Context. The Sun shows abundance anomalies relative to most solar
twins. If the abundance peculiarities are due to the formation of inner
rocky planets, that would mean that only a small fraction of solar
type stars may host terrestrial planets.
Aims: In this work we
study HIP 56948, the best solar twin known to date, to determine with
an unparalleled precision how similar it is to the Sun in its physical
properties, chemical composition and planet architecture. We explore
whether the abundances anomalies may be due to pollution from stellar
ejecta or to terrestrial planet formation.
Methods: We perform
a differential abundance analysis (both in LTE and NLTE) using high
resolution (R ~ 100 000) high S/N (600-650) Keck HIRES spectra of the
Sun (as reflected from the asteroid Ceres) and HIP 56948. We use precise
radial velocity data from the McDonald and Keck observatories to search
for planets around this star.
Results: We achieve a precision
of σ ≲ 0.003 dex for several elements. Including errors in stellar
parameters the total uncertainty is as low as σ ≃ 0.005 dex (1%),
which is unprecedented in elemental abundance studies. The similarities
between HIP 56948 and the Sun are astonishing. HIP 56948 is only 17
± 7 K hotter than the Sun, and log g, [Fe/H] and microturbulence
velocity are only + 0.02 ± 0.02 dex, +0.02 ± 0.01 dex and +0.01 ±
0.01 km s-1 higher than solar, respectively. Our precise
stellar parameters and a differential isochrone analysis shows that
HIP 56948 has a mass of 1.02 ± 0.02 M⊙ and that it is ~1
Gyr younger than the Sun, as constrained by isochrones, chromospheric
activity, Li and rotation. Both stars show a chemical abundance
pattern that differs from most solar twins, but the refractory elements
(those with condensation temperature Tcond ≳ 1000 K) are
slightly (~0.01 dex) more depleted in the Sun than in HIP 56948. The
trend with Tcond in differential abundances (twins - HIP
56948) can be reproduced very well by adding ~3 M⊕ of a
mix of Earth and meteoritic material, to the convection zone of HIP
56948. The element-to-element scatter of the Earth/meteoritic mix for
the case of hypothetical rocky planets around HIP 56948 is only 0.0047
dex. From our radial velocity monitoring we find no indications of giant
planets interior to or within the habitable zone of HIP 56948.
Conclusions: We conclude that HIP 56948 is an excellent candidate to
host a planetary system like our own, including the possible presence
of inner terrestrial planets. Its striking similarity to the Sun and
its mature age makes HIP 56948 a prime target in the quest for other
Earths and SETI endeavors. Based on observations obtained at the
W.M. Keck Observatory, which is operated jointly by the California
Institute of Technology, the University of California and the National
Aeronautics and Space Administration (NASA). This paper also includes
data taken at the McDonald Observatory of the University of Texas at
Austin and with the European Southern Observatory (ESO) Very Large
Telescope (VLT) at Paranal Observatory, Chile (observing program
083.D-0871).Tables 1-6 and Appendices are available in electronic form
at http://www.aanda.org
Title: VizieR Online Data Catalog: Abundances of M22 subgiants
(Marino+, 2012)
Authors: Marino, A. F.; Milone, A. P.; Sneden, C.; Bergemann, M.;
Kraft, R. P.; Wallerstein, G.; Cassisi, S.; Aparicio, A.; Asplund, M.;
Bedin, R. L.; Hilker, M.; Lind, K.; Momany, Y.; Piotto, G.; Roederer,
I. U.; Stetson, P. B.; Zoccali, M.
Bibcode: 2012yCat..35410015M
Altcode: 2012yCat..35419015M
Ground-based observations were used to analyze the CMD over a wide
spatial field in the B and V bands and to estimate the atmospheric
parameters of the spectroscopic targets. In addition, we used
ground-based U images available for a smaller field, and images taken
with the Advanced Camera for Surveys onboard the HST (ACS/HST) in
the F606W and F814W bands to make our study of the double SGB extend
from the ultraviolet to the infrared spectral regions. The HST ACS/WFC
images were obtained under program GO-10775 (PI Sarajedini). (2
data files).
Title: The double sub-giant branch of NGC 6656 (M 22): a chemical
characterization
Authors: Marino, A. F.; Milone, A. P.; Sneden, C.; Bergemann, M.;
Kraft, R. P.; Wallerstein, G.; Cassisi, S.; Aparicio, A.; Asplund, M.;
Bedin, R. L.; Hilker, M.; Lind, K.; Momany, Y.; Piotto, G.; Roederer,
I. U.; Stetson, P. B.; Zoccali, M.
Bibcode: 2012A&A...541A..15M
Altcode: 2012arXiv1202.2825M
We present an abundance analysis of 101 subgiant branch (SGB) stars
in the globular cluster M 22. Using low-resolution FLAMES/GIRAFFE
spectra we have determined abundances of the neutron-capture strontium
and barium and the light element carbon. With these data we explore
relationships between the observed SGB photometric split in this cluster
and two stellar groups characterized by different contents of iron,
slow neutron-capture process (s-process) elements, and the α element
calcium, which we previously discovered in M 22's red-giant stars. We
show that the SGB stars correlate in chemical composition and the
color-magnitude diagram position. The stars with higher metallicity
and relative s-process abundances define a fainter SGB, while stars
with lower metallicity and s-process content reside on a relatively
brighter SGB. This result has implications for the relative ages of
the two stellar groups of M 22. In particular, it is inconsistent
with a broad spread in ages of the two SGBs. By accounting for the
chemical content of the two stellar groups, isochrone fitting of
the double SGB suggests that their agesare not different by more
than ~300 Myr. Based on data collected at the European Southern
Observatory with the FLAMES/GIRAFFE spectrograph under the program
085.D-0698A.Tables 2 and 3 are available in electronic form at http://www.aanda.org
Title: Commission 29: Stellar Spectra
Authors: Piskunov, Nikolai; Cunha, Katia; Parthasarathy, Mudumba; Aoki,
Wako; Asplund, Martin; Bohlender, David; Carpenter, Kenneth; Melendez,
Jorge; Rossi, Silvia; Smith, Verne; Soderblom, David; Wahlgren, Glenn
Bibcode: 2012IAUTA..28..157P
Altcode:
Commission 29 consists of members of the International Astronomical
Union carrying out theoretical and observational studies of stars
using spectroscopy, developing instrumentation for spectroscopy and
producing and collecting data for interpretation of spectra.
Title: Division Iv: Stars
Authors: Corbally, Christopher; D'Antona, Francesca; Spite, Monique;
Asplund, Martin; Charbonnel, Corinne; Docobo, Jose Angel; Gray,
Richard O.; Piskunov, Nikolai E.
Bibcode: 2012IAUTA..28..147C
Altcode:
This Division IV was started on a trial basis at the General Assembly
in The Hague 1994 and was formally accepted at the Kyoto General
Assembly in 1997. Its broad coverage of ``Stars'' is reflected in
its relatively large number of Commissions and so of members (1266 in
late 2011). Its kindred Division V, ``Variable Stars'', has the same
history of its beginning. The thinking at the time was to achieve
some kind of balance between the number of members in each of the 12
Divisions. Amid the current discussion of reorganizing the number of
Divisions into a more compact form it seems advisable to make this
numerical balance less of an issue than the rationalization of the
scientific coverage of each Division, so providing more effective
interaction within a particular field of astronomy. After all, every
star is variable to a certain degree and such variability is becoming
an ever more powerful tool to understand the characteristics of every
kind of normal and peculiar star. So we may expect, after hearing the
reactions of members, that in the restructuring a single Division will
result from the current Divisions IV and V.
Title: Three-dimensional interferometric, spectrometric, and planetary
views of Procyon
Authors: Chiavassa, A.; Bigot, L.; Kervella, P.; Matter, A.; Lopez,
B.; Collet, R.; Magic, Z.; Asplund, M.
Bibcode: 2012A&A...540A...5C
Altcode: 2012arXiv1201.3264C
Context. Procyon is one of the brightest stars in the sky and one
of our nearest neighbours. It is therefore an ideal benchmark
object for stellar astrophysics studies using interferometric,
spectroscopic, and asteroseismic techniques.
Aims: We use a
new realistic three-dimensional (3D) radiative-hydrodynamical (RHD)
model atmosphere of Procyon generated with the Stagger Code and
synthetic spectra computed with the radiative transfer code Optim3D
to re-analyze interferometric and spectroscopic data from the optical
to the infrared. We provide synthetic interferometric observables
that can be validated using observations.
Methods: We computed
intensity maps from a RHD simulation in two optical filters centered
on 500 and 800 nm (Mark III) and one infrared filter centered on 2.2
μm (Vinci). We constructed stellar disk images accounting for the
center-to-limb variations and used them to derive visibility amplitudes
and closure phases. We also computed the spatially and temporally
averaged synthetic spectrum from the ultraviolet to the infrared. We
compare these observables to Procyon data.
Results: We study the
impact of the granulation pattern on center-to-limb intensity profiles
and provide limb-darkening coefficients in the optical as well as in the
infrared. We show how the convection-related surface structures affect
the visibility curves and closure phases with clear deviations from
circular symmetry, from the 3rd lobe on. These deviations are detectable
with current interferometers using closure phases. We derive new angular
diameters at different wavelengths with two independent methods based
on 3D simulations. We find that θVinci = 5.390 ± 0.03
mas, which we confirm by comparison with an independent asteroseismic
estimation (θseismic = 5.360 ± 0.07 mas. The resulting
Teff is 6591 K (or 6556 K depending on the bolometric
flux used), which is consistent with the value of Teff,IR
= 6621 K found with the infrared flux method. We measure a surface
gravity log g = 4.01 ± 0.03 [cm/s2] that is higher by
0.05 dex than literature values. Spectrophotometric comparisons with
observations provide very good agreement with the spectral energy
distribution and photometric colors, allowing us to conclude that the
thermal gradient in the simulation matches Procyon fairly well. Finally,
we show that the granulation pattern of a planet-hosting Procyon-like
star has a non-negligible impact on the detection of hot Jupiters in
the infrared using interferometry closure phases. It is then crucial
to have a comprehensive knowledge of the host star to directly detect
and characterize hot Jupiters. In this respect, RHD simulations are
very important to achieving this aim.
Title: Commission 12: Solar Radiation and Structure
Authors: Kosovichev, Alexander; Cauzzi, Gianna; Pillet, Valentin
Martinez; Asplund, Martin; Brandenburg, Axel; Chou, Dean-Yi;
Christensen-Dalsgaard, Jorgen; Gan, Weiqun; Kuznetsov, Vladimir D.;
Rovira, Marta G.; Shchukina, Nataliya; Venkatakrishnan, P.
Bibcode: 2012IAUTA..28...81K
Altcode: 2012IAUTB..28...81K
Commission 12 of the International Astronomical Union encompasses
investigations of the internal structure and dynamics of the Sun, mostly
accessible through the techniques of local and global helioseismology,
the quiet solar atmosphere, solar radiation and its variability, and
the nature of relatively stable magnetic structures like sunspots,
faculae and the magnetic network. The Commission sees participation
of over 350 scientists worldwide.
Title: The Gaia-ESO Public Spectroscopic Survey
Authors: Gilmore, G.; Randich, S.; Asplund, M.; Binney, J.; Bonifacio,
P.; Drew, J.; Feltzing, S.; Ferguson, A.; Jeffries, R.; Micela, G.;
Negueruela, I.; Prusti, T.; Rix, H. -W.; Vallenari, A.; Alfaro, E.;
Allende-Prieto, C.; Babusiaux, C.; Bensby, T.; Blomme, R.; Bragaglia,
A.; Flaccomio, E.; François, P.; Irwin, M.; Koposov, S.; Korn, A.;
Lanzafame, A.; Pancino, E.; Paunzen, E.; Recio-Blanco, A.; Sacco,
G.; Smiljanic, R.; Van Eck, S.; Walton, N.; Aden, D.; Aerts, C.;
Affer, L.; Alcala, J. -M.; Altavilla, G.; Alves, J.; Antoja, T.;
Arenou, F.; Argiroffi, C.; Asensio Ramos, A.; Bailer-Jones, C.;
Balaguer-Nunez, L.; Bayo, A.; Barbuy, B.; Barisevicius, G.; Barrado
y Navascues, D.; Battistini, C.; Bellas Velidis, I.; Bellazzini, M.;
Belokurov, V.; Bergemann, M.; Bertelli, G.; Biazzo, K.; Bienayme, O.;
Bland-Hawthorn, J.; Boeche, C.; Bonito, S.; Boudreault, S.; Bouvier,
J.; Brandao, I.; Brown, A.; de Bruijne, J.; Burleigh, M.; Caballero,
J.; Caffau, E.; Calura, F.; Capuzzo-Dolcetta, R.; Caramazza, M.;
Carraro, G.; Casagrande, L.; Casewell, S.; Chapman, S.; Chiappini,
C.; Chorniy, Y.; Christlieb, N.; Cignoni, M.; Cocozza, G.; Colless,
M.; Collet, R.; Collins, M.; Correnti, M.; Covino, E.; Crnojevic,
D.; Cropper, M.; Cunha, M.; Damiani, F.; David, M.; Delgado, A.;
Duffau, S.; Edvardsson, B.; Eldridge, J.; Enke, H.; Eriksson, K.;
Evans, N. W.; Eyer, L.; Famaey, B.; Fellhauer, M.; Ferreras, I.;
Figueras, F.; Fiorentino, G.; Flynn, C.; Folha, D.; Franciosini,
E.; Frasca, A.; Freeman, K.; Fremat, Y.; Friel, E.; Gaensicke, B.;
Gameiro, J.; Garzon, F.; Geier, S.; Geisler, D.; Gerhard, O.; Gibson,
B.; Gomboc, A.; Gomez, A.; Gonzalez-Fernandez, C.; Gonzalez Hernandez,
J.; Gosset, E.; Grebel, E.; Greimel, R.; Groenewegen, M.; Grundahl,
F.; Guarcello, M.; Gustafsson, B.; Hadrava, P.; Hatzidimitriou, D.;
Hambly, N.; Hammersley, P.; Hansen, C.; Haywood, M.; Heber, U.; Heiter,
U.; Held, E.; Helmi, A.; Hensler, G.; Herrero, A.; Hill, V.; Hodgkin,
S.; Huelamo, N.; Huxor, A.; Ibata, R.; Jackson, R.; de Jong, R.;
Jonker, P.; Jordan, S.; Jordi, C.; Jorissen, A.; Katz, D.; Kawata,
D.; Keller, S.; Kharchenko, N.; Klement, R.; Klutsch, A.; Knude,
J.; Koch, A.; Kochukhov, O.; Kontizas, M.; Koubsky, P.; Lallement,
R.; de Laverny, P.; van Leeuwen, F.; Lemasle, B.; Lewis, G.; Lind,
K.; Lindstrom, H. P. E.; Lobel, A.; Lopez Santiago, J.; Lucas, P.;
Ludwig, H.; Lueftinger, T.; Magrini, L.; Maiz Apellaniz, J.; Maldonado,
J.; Marconi, G.; Marino, A.; Martayan, C.; Martinez-Valpuesta, I.;
Matijevic, G.; McMahon, R.; Messina, S.; Meyer, M.; Miglio, A.;
Mikolaitis, S.; Minchev, I.; Minniti, D.; Moitinho, A.; Momany, Y.;
Monaco, L.; Montalto, M.; Monteiro, M. J.; Monier, R.; Montes, D.;
Mora, A.; Moraux, E.; Morel, T.; Mowlavi, N.; Mucciarelli, A.; Munari,
U.; Napiwotzki, R.; Nardetto, N.; Naylor, T.; Naze, Y.; Nelemans, G.;
Okamoto, S.; Ortolani, S.; Pace, G.; Palla, F.; Palous, J.; Parker, R.;
Penarrubia, J.; Pillitteri, I.; Piotto, G.; Posbic, H.; Prisinzano,
L.; Puzeras, E.; Quirrenbach, A.; Ragaini, S.; Read, J.; Read, M.;
Reyle, C.; De Ridder, J.; Robichon, N.; Robin, A.; Roeser, S.; Romano,
D.; Royer, F.; Ruchti, G.; Ruzicka, A.; Ryan, S.; Ryde, N.; Santos,
N.; Sanz Forcada, J.; Sarro Baro, L. M.; Sbordone, L.; Schilbach, E.;
Schmeja, S.; Schnurr, O.; Schoenrich, R.; Scholz, R. -D.; Seabroke, G.;
Sharma, S.; De Silva, G.; Smith, M.; Solano, E.; Sordo, R.; Soubiran,
C.; Sousa, S.; Spagna, A.; Steffen, M.; Steinmetz, M.; Stelzer, B.;
Stempels, E.; Tabernero, H.; Tautvaisiene, G.; Thevenin, F.; Torra,
J.; Tosi, M.; Tolstoy, E.; Turon, C.; Walker, M.; Wambsganss, J.;
Worley, C.; Venn, K.; Vink, J.; Wyse, R.; Zaggia, S.; Zeilinger, W.;
Zoccali, M.; Zorec, J.; Zucker, D.; Zwitter, T.; Gaia-ESO Survey Team
Bibcode: 2012Msngr.147...25G
Altcode:
The Gaia-ESO Public Spectroscopic Survey has begun and will obtain high
quality spectroscopy of some 100000 Milky Way stars, in the field and
in open clusters, down to magnitude 19, systematically covering all the
major components of the Milky Way. This survey will provide the first
homogeneous overview of the distributions of kinematics and chemical
element abundances in the Galaxy. The motivation, organisation and
implementation of the Gaia-ESO Survey are described, emphasising the
complementarity with the ESA Gaia mission. Spectra from the very first
observing run of the survey are presented.
Title: Limb darkening laws for two exoplanet host stars derived
from 3D stellar model atmospheres. Comparison with 1D models and
HST light curve observations
Authors: Hayek, W.; Sing, D.; Pont, F.; Asplund, M.
Bibcode: 2012A&A...539A.102H
Altcode: 2012arXiv1202.0548H
We compare limb darkening laws derived from 3D hydrodynamical model
atmospheres and 1D hydrostatic MARCS models for the host stars of
two well-studied transiting exoplanet systems, the late-type dwarfs
HD 209458 and HD 189733. The
surface brightness distribution of the stellar disks is calculated
for a wide spectral range using 3D LTE spectrum formation and opacity
sampling⋆. We test our theoretical predictions using
least-squares fits of model light curves to wavelength-integrated
primary eclipses that were observed with the Hubble Space Telescope
(HST). The limb darkening law derived from the 3D model of HD 209458 in
the spectral region between 2900 Å and 5700 Å produces significantly
better fits to the HST data, removing systematic residuals that were
previously observed for model light curves based on 1D limb darkening
predictions. This difference arises mainly from the shallower mean
temperature structure of the 3D model, which is a consequence of the
explicit simulation of stellar surface granulation where 1D models
need to rely on simplified recipes. In the case of HD 189733, the
model atmospheres produce practically equivalent limb darkening curves
between 2900 Å and 5700 Å, partly due to obstruction by spectral
lines, and the data are not sufficient to distinguish between the
light curves. We also analyze HST observations between 5350 Å and
10 500 Å for this star; the 3D model leads to a better fit compared
to 1D limb darkening predictions. The significant improvement of fit
quality for the HD 209458 system demonstrates the higher degree of
realism of 3D hydrodynamical models and the importance of surface
granulation for the formation of the atmospheric radiation field of
late-type stars. This result agrees well with recent investigations of
limb darkening in the solar continuum and other observational tests of
the 3D models. The case of HD 189733 is no contradiction as the model
light curves are less sensitive to the temperature stratification
of the stellar atmosphere and the observed data in the 2900-5700
Å region are not sufficient to distinguish more clearly between
the 3D and 1D limb darkening predictions. Full theoretical
spectra for both stars are available in electronic form at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/539/A102,
as well as at www.astro.ex.ac.uk/people/sing.
Title: Simulations of the solar near-surface layers with the CO5BOLD,
MURaM, and Stagger codes
Authors: Beeck, B.; Collet, R.; Steffen, M.; Asplund, M.; Cameron,
R. H.; Freytag, B.; Hayek, W.; Ludwig, H. -G.; Schüssler, M.
Bibcode: 2012A&A...539A.121B
Altcode: 2012arXiv1201.1103B
Context. Radiative hydrodynamic simulations of solar and stellar surface
convection have become an important tool for exploring the structure and
gas dynamics in the envelopes and atmospheres of late-type stars and for
improving our understanding of the formation of stellar spectra.
Aims: We quantitatively compare results from three-dimensional,
radiative hydrodynamic simulations of convection near the solar surface
generated with three numerical codes (CO5BOLD, MURaM,
and Stagger) and different simulation setups in order to investigate
the level of similarity and to cross-validate the simulations.
Methods: For all three simulations, we considered the average
stratifications of various quantities (temperature, pressure, flow
velocity, etc.) on surfaces of constant geometrical or optical depth,
as well as their temporal and spatial fluctuations. We also compared
observables, such as the spatially resolved patterns of the emerging
intensity and of the vertical velocity at the solar optical surface
as well as the center-to-limb variation of the continuum intensity
at various wavelengths.
Results: The depth profiles of the
thermodynamical quantities and of the convective velocities as well as
their spatial fluctuations agree quite well. Slight deviations can be
understood in terms of differences in box size, spatial resolution
and in the treatment of non-gray radiative transfer between the
simulations.
Conclusions: The results give confidence in the
reliability of the results from comprehensive radiative hydrodynamic
simulations.
Title: VizieR Online Data Catalog: HD 209458 and HD 189733 theoretical
spectra (Hayek+, 2012)
Authors: Hayek, W.; Sing, D.; Pont, F.; Asplund, M.
Bibcode: 2012yCat..35390102H
Altcode: 2012yCat..35399102H
Theoretical spectrum computations for the G-type dwarf HD 209458 and
the K-type dwarf HD 189733 are presented, based on 3D hydrodynamical
models of the stellar atmospheres. Surface intensities were computed
in LTE using the SCATE spectrum formation code and cover the wavelength
region between about 910 Angstroem and 20 micron with constant sampling
of R=λ/δ_λ=20,000. The stellar disk was sampled at the disk center
(μ=cos(θ)=1.0) and at angles μ = 0.90, 0.80, 0.70, 0.60, 0.50,
0.40, 0.30, 0.25, 0.20, 0.15, 0.125, 0.1, 0.075, 0.05, 0.025, 0.01
towards the limb. Use integration weights 0.05, 0.1, 0.1, 0.1, 0.1,
0.1, 0.1, 0.075, 0.05, 0.05, 0.0375, 0.025, 0.025, 0.025, 0.025, 0.02,
0.0125 to obtain fluxes. (2 data files).
Title: The detection and treatment of distance errors in kinematic
analyses of stars
Authors: Schönrich, Ralph; Binney, James; Asplund, Martin
Bibcode: 2012MNRAS.420.1281S
Altcode: 2011MNRAS.tmp.2130S; 2011arXiv1111.0204S
We present a new method for detecting and correcting systematic errors
in the distances to stars when both proper motions and line-of-sight
velocities are available. The method, which is applicable for samples
of 200 or more stars that have a significant extension on the sky,
exploits correlations between the measured U, V and W velocity
components that are introduced by distance errors. We deliver a
formalism to describe and interpret the specific imprints of distance
errors including spurious velocity correlations and shifts of mean
motion in a sample. We take into account correlations introduced by
measurement errors, Galactic rotation and changes in the orientation
of the velocity ellipsoid with position in the Galaxy. Tests on
pseudo-data show that the method is more robust and sensitive than
traditional approaches to this problem. We investigate approaches
to characterizing the probability distribution of distance errors,
in addition to the mean distance error, which is the main theme of the
paper. Stars with the most overestimated distances bias our estimate of
the overall distance scale, leading to the corrected distances being
slightly too small. We give a formula that can be used to correct for
this effect. We apply the method to samples of stars from the Sloan
Extension for Galactic Understanding and Exploration (SEGUE) survey,
exploring optimal gravity cuts, sample contamination, and correcting
the used distance relations.
Title: VizieR Online Data Catalog: Elemental abundances in Hyades
supercluster (De Silva+, 2011)
Authors: de Silva, G. M.; Freeman, K. C.; Bland-Hawthorn, J.; Asplund,
M.; Williams, M.; Holmberg, J.
Bibcode: 2012yCat..74150563D
Altcode:
High-resolution and high signal-to-noise ratio spectra of probable
members of the Hyades supercluster were observed using the VLT UV-Visual
Echelle Spectrograph (UVES) at UT2 in the framework of programmes
080.D-0094(A) and 381.B-0045(A). A total of 45 probable member stars
were submitted for service mode observations, using the UVES Red arm
standard setting at 520 nm which provides complete spectral coverage
from 4200 to 6200Å, and employed a 0.8-arcsec slit to achieve a
spectral resolving power of 60000. (3 data files).
Title: The chemical evolution of the Galactic Bulge seen through
micro-lensing events
Authors: Feltzing, S.; Bensby, T.; Meléndez, J.; Adén, D.; Asplund,
M.; Gould, A.; Johnson, J.; Lucatello, S.; Gal-Yam, A.
Bibcode: 2012EPJWC..1906002F
Altcode: 2011arXiv1110.4465F
Galactic bulges are central to understanding galaxy formation and
evolution. Here we report on recent studies using micro-lensing events
to obtain spectra of high resolution and moderately high signal-to-noise
ratios of dwarf stars in the Galactic bulge. Normally this is not
feasible for the faint turn-off stars in the Galactic bulge, but
micro-lensing offers this possibility. Elemental abundance trends
in the Galactic bulge as traced by dwarf stars are very similar to
those seen for dwarf stars in the solar neighbourhood. We discuss the
implications of the ages and metallicity distribution function derived
for the micro-lensed dwarf stars in the Galactic bulge.
Title: Spectral diagnostics of late-type stars: Non-LTE and <3D>
approach
Authors: Bergemann, M.; Lind, K.; Collet, R.; Asplund, M.; Magic, Z.
Bibcode: 2012EPJWC..1905013B
Altcode:
We determine effective temperature, metallicity, and microturbulence for
a number of well-studied late-type stars. We use the new NLTE atomic
model of Fe, and discuss the results for the MARCS models, as well
as for the spatial and temporal averages of full 3D hydrodynamical
simulations of stellar convection. It is shown that, contrary to
the mean 3D models, certain limitations shall be imposed on the line
formation and spectrum synthesis calculations with classical hydrostatic
1D models to obtain physically-realistic results.
Title: Evidence for a vanishing 6Li/7Li isotopic
signature in the metal-poor halo star HD 84937
Authors: Lind, K.; Asplund, M.; Collet, R.; Meléndez, J.
Bibcode: 2012MSAIS..22..142L
Altcode:
The claimed detections of 6Li in the atmospheres of
some metal-poor halo stars have lead to speculative additions
to the standard model of Big Bang nucleosynthesis and the early
Universe, as the inferred abundances cannot be explained by Galactic
cosmic ray production. A prominent example of a so far un-disputed
6Li-detection is that of the metal-poor turn-off star
HD 84937, for which at least three different groups obtain very
similar results. We revisit the lithium isotopic analysis for this
star and two other halo stars, G 64-12 and HD 140283, using spectra
of superiour quality and applying for the first time a combined 3D,
NLTE synthesis to both the Li line and to Ca lines that are used to
constrain the external line broadening. We demonstrate how differential
NLTE effects between the Li and Ca line profiles can lead to spurious
6Li-detections in LTE, compatible with previously reported
values of 6Li/7Li≈5%. With our new analysis
technique, none of the three analysed stars have a significant detection
of 6Li in NLTE. We discuss which further progress is needed
to firmly establish these results.
Title: The cosmological Li problems: Big Bang in crisis perhaps
Authors: Asplund, Martin
Bibcode: 2012cemw.confE...2A
Altcode:
No abstract at ADS
Title: NLTE effects on Fe I/II in the atmospheres of FGK stars and
application to the abundance analysis of their spectra
Authors: Bergemann, Maria; Lind, Karin; Collet, Remo; Asplund, Martin
Bibcode: 2011JPhCS.328a2002B
Altcode: 2011arXiv1109.2601B
We describe the first results from our project aimed at large-scale
calculations of NLTE abundance corrections for important astrophysical
atoms and ions. In this paper, the focus is on Fe which is a proxy
of stellar metallicity and is commonly used to derive effective
temperature and surface gravity. We present a small grid of NLTE
abundance corrections for a sample of Fe I lines and discuss how the
NLTE effects influence the determination of effective temperature,
surface gravity, and metallicity for late-type stars.
Title: The StaggerGrid project: a grid of 3-D model atmospheres for
high-precision spectroscopy
Authors: Collet, Remo; Magic, Zazralt; Asplund, Martin
Bibcode: 2011JPhCS.328a2003C
Altcode: 2011arXiv1110.5475C
In this contribution, we present the STAGGERGRID, a collaborative
project for the construction of a comprehensive grid of time-dependent,
three-dimensional (3-D), hydrodynamic model atmospheres of solar-
and late-type stars with different effective temperatures,
surface gravities, and chemical compositions. We illustrate the
main characteristics of these 3-D models and their effects on the
predicted strengths, wavelength-shifts, and shapes of spectral lines,
highlighting the differences with respect to calculations based on
classical, one-dimensional, hydrostatic models, and discuss some of
their possible applications to elemental abundance analysis of stellar
spectra in the context of large observational surveys.
Title: Effects of Scattering on the Temperature Stratification in
3D Model Atmospheres of Late-Type Stars
Authors: Collet, R.; Hayek, W.; Asplund, M.
Bibcode: 2011ASPC..448..819C
Altcode: 2011csss...16..819C
Three-dimensional (3D) radiative hydrodynamic model atmospheres
of metal-poor late-type stars predict cooler upper photospheric
stratifications than their one-dimensional (1D) counterparts. This
property of 3D model atmospheres affects the determination of
elemental abundances from temperature-sensitive spectral features, with
important consequences for galactic chemical evolution studies. In this
contribution, we investigate the impact of different approximations
of scattering in the solution of the radiative transfer equation on
the temperature stratification of 3D model atmospheres of metal-poor
red giants. We use the BIFROST code to construct 3D model atmospheres
of metal-poor red giants using three different approximations of
scattering. First, we self-consistently solve the radiative transfer
equation for the general case of a source function with a coherent
scattering term; second, we solve the radiative transfer equation
assuming a Planckian source function and neglecting altogether
the contribution of continuum scattering to extinction in the
optically thin layers; third, we assume a Planckian source function
and treat continuum scattering as pure absorption everywhere in the
simulation's domain. We find that the second approach produces very
similar temperature structures with cool upper photospheric layers as
when treating scattering correctly, and at a much lower computational
cost. In contrast, treating scattering as pure absorption leads to
significantly hotter and shallower temperature stratifications.
Title: 3-D hydrodynamical model atmospheres: a tool to correct radial
velocities and parallaxes for Gaia
Authors: Chiavassa, A.; Bigot, L.; Thévenin, F.; Collet, R.;
Jasniewicz, G.; Magic, Z.; Asplund, M.
Bibcode: 2011JPhCS.328a2012C
Altcode: 2011arXiv1111.5515C
Convection plays an essential role in the emerging intensity for
many stars that will be observed by Gaia. Convective-related surface
structures affect the shape, shift, and asymmetry of absorption lines,
the photocentric and photometric variability causing bias in Gaia
measurements. Regarding the importance of Gaia mission and its goals,
it is mandatory to have the best models of the observed stars. 3-D
time-dependent hydrodynamical simulations of surface convection are
crucial to model the photosphere of late type stars in a very realistic
way. These simulations are an important tool to correct the radial
velocities and to better estimate the parallaxes and photometric
variability.
Title: Spectroscopic Microvariability Induced by Convective Motions
Authors: Porter, L.; Asplund, M.
Bibcode: 2011ASPC..448.1013P
Altcode: 2011csss...16.1013P
Convection reaches the atmospheres of cool stars creating detectable
variability in the photometry and spectrum of the star. Current 3D
hydro-dynamical models of dwarfs and red giants simulate only a small
representative volume of the stellar atmosphere, typically covering
some 10 granules horizontally. To derive observable quantities it is
necessary to integrate these 'Box-in-a-star' models over the stellar
disk. The disk-integrated variability caused by convective motions can
be constrained using the statistical properties of spatial and temporal
fluctuations from a time-series of these models. Previously suggested
for white light and photometric centroid (Ludwig 2006), we extend this
method to spectral lines, including the effects of stellar rotation. We
believe a better characterisation of this convective microvariability
would benefit velocity diagnostics for helioseismology, eg NiI 6768 Å,
used by SOHO MDI (Jones 1989) and could be used to remove the 'noise'
induced by convective motions in radial velocity planet searches.
Title: Is the solar spectrum latitude-dependent?. An investigation
with SST/TRIPPEL
Authors: Kiselman, D.; Pereira, T. M. D.; Gustafsson, B.; Asplund,
M.; Meléndez, J.; Langhans, K.
Bibcode: 2011A&A...535A..14K
Altcode: 2011arXiv1108.4527K
Context. In studies of the solar spectrum compared to spectra of solar
twin stars, it has been found that the chemical composition of the Sun
seems to depart systematically from those of the twins. One possible
explanation could be that the effect is caused by the special aspect
angle of the Sun when observed from Earth compared with the aspect
angles of the twins. This means that a latitude dependence of the
solar spectrum, even with the heliocentric angle constant, could
lead to the observed effects.
Aims: We explore a possible
variation in the strength of certain spectral lines that are used
in the comparisons between the composition of the Sun and the twins
at loci on the solar disk with different latitudes but at constant
heliocentric angle.
Methods: We use the TRIPPEL spectrograph at
the Swedish 1-m Solar Telescope on La Palma to record spectra in five
spectral regions to compare different locations on the solar disk at
a heliocentric angle of 45°. Equivalent widths and other parameters
are measured for fifteen different lines representing nine atomic
species. Spectra acquired at different times are used in averaging the
line parameters for each line and observing position.
Results:
The relative variations in equivalent widths at the equator and at
solar latitude ~45° are found to be less than 1.5% for all spectral
lines studied. Translated into elemental abundances as they would be
measured from a terrestrial and a hypothetical pole-on observer, the
difference is estimated to be within 0.005 dex in all cases.
Conclusions: It is very unlikely that latitude effects could cause the
reported abundance difference between the Sun and the solar twins. The
accuracy obtainable in measurements of small differences in spectral
line strengths between different solar disk positions is very high,
and can be exploited in studies of, e.g. weak magnetic fields or
effects of solar activity on atmospheric structure.
Title: Chemical evolution of the Galactic bulge as traced by
microlensed dwarf and subgiant stars. IV. Two bulge populations
Authors: Bensby, T.; Adén, D.; Meléndez, J.; Gould, A.; Feltzing,
S.; Asplund, M.; Johnson, J. A.; Lucatello, S.; Yee, J. C.; Ramírez,
I.; Cohen, J. G.; Thompson, I.; Bond, I. A.; Gal-Yam, A.; Han, C.;
Sumi, T.; Suzuki, D.; Wada, K.; Miyake, N.; Furusawa, K.; Ohmori,
K.; Saito, To.; Tristram, P.; Bennett, D.
Bibcode: 2011A&A...533A.134B
Altcode: 2011arXiv1107.5606B
Based on high-resolution (R ≈ 42 000 to 48 000) and high
signal-to-noise (S/N ≈ 50 to 150) spectra obtained with UVES/VLT, we
present detailed elemental abundances (O, Na, Mg, Al, Si, Ca, Ti, Cr,
Fe, Ni, Zn, Y, and Ba) and stellar ages for 12 new microlensed dwarf and
subgiant stars in the Galactic bulge. Including previous microlensing
events, the sample of homogeneously analysed bulge dwarfs has now
grown to 26. The analysis is based on equivalent width measurements
and standard 1-D LTE MARCS model stellar atmospheres. We also present
NLTE Li abundances based on line synthesis of the 7Li
line at 670.8 nm. The results from the 26 microlensed dwarf and
subgiant stars show that the bulge metallicity distribution (MDF)
is double-peaked; one peak at [Fe/H] ≈ -0.6 and one at [Fe/H] ≈ +
0.3, and with a dearth of stars around solar metallicity. This is in
contrast to the MDF derived from red giants in Baade's window, which
peaks at this exact value. A simple significance test shows that it is
extremely unlikely to have such a gap in the microlensed dwarf star
MDF if the dwarf stars are drawn from the giant star MDF. To resolve
this issue we discuss several possibilities, but we can not settle on a
conclusive solution for the observed differences. We further find that
the metal-poor bulge dwarf stars arepredominantly old with ages greater
than 10 Gyr, while the metal-rich bulge dwarf stars show a wide range
of ages. The metal-poor bulge sample is very similar to the Galactic
thick disk in terms of average metallicity, elemental abundance trends,
and stellar ages. Speculatively, the metal-rich bulge population might
be the manifestation of the inner thin disk. If so, the two bulge
populations could support the recent findings, based on kinematics,
that there are no signatures of a classical bulge and that the Milky Way
is a pure-disk galaxy. Also, recent claims of a flat IMF in the bulge
based on the MDF of giant stars may have to be revised based on the MDF
and abundance trends probed by our microlensed dwarf stars. Based
on observations made with the European Southern Observatory telescopes
(84.B-0837, 85.B-0399, and 86.B-0757). This paper also includes data
gathered with the 6.5 m Magellan Telescopes located at the Las Campanas
Observatory, Chile, and data obtained at the W. M. Keck Observatory,
which is operated as a scientific partnership among the California
Institute of Technology, the University of California and the National
Aeronautics and Space Administration.Tables 4 and 5 are available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/533/A134
Title: VizieR Online Data Catalog: Abundances of microlensed stars
in the Bulge (Bensby+, 2011)
Authors: Bensby, T.; Aden, D.; Melendez, J.; Gould, A.; Feltzing, S.;
Asplund, M.; Johnson, J. A.; Lucatello, S.; Yee, J. C.; Ramirez, I.;
Cohen, J. G.; Thompson, I.; Gal-Yam, A.; Han, C.; Sumi, T.; Suzuki, D.;
Wada, K.; Miyake, N.; Furusawa, K.; Ohmori, K.; Saito, To.; Tristram,
P.; Bennett, D.
Bibcode: 2011yCat..35330134B
Altcode: 2011yCat..35339134B
For each spectral line we give the lower excitation potential, measured
equivalent widths, and derived absolute abundances. We also give
median abundances for each star, normalised to the Sun, and errors
in the median abundances. These tables contain data for the last 12
microlensed dwarf stars. Data for the first 14 microlensed dwarfs can
be found in Bensby et al. (2009, Cat. J/A+A/499/737) and Bensby et
al. (2010, Cat. J/A+A/512/A41). (5 data files).
Title: On the alleged duality of the Galactic halo
Authors: Schönrich, Ralph; Asplund, Martin; Casagrande, Luca
Bibcode: 2011MNRAS.415.3807S
Altcode: 2010arXiv1012.0842S; 2011MNRAS.tmp.1011S
We examine the kinematics of the Galactic halo based on SDSS/SEGUE data
by Carollo et al. We find that their claims of a counter-rotating
halo are the result of substantial biases in distance estimates
(of the order of 50 per cent): the claimed retrograde component,
which makes up only a tiny fraction of the entire sample, prone to
contaminations, is identified as the tail of distance overestimates. The
strong overestimates also result in a lift in the vertical velocity
component, which explains the large altitudes those objects were
claimed to reach. Errors are worst for the lowest metallicity stars,
which explains the metal-poor nature of the artificial component. We
also argue that measurement errors were not properly accounted for
and that the use of Gaussian fitting on intrinsically non-Gaussian
Galactic components invokes the identification of components that are
distorted or even artificial. Our evaluation of the data leads to a
revision of the estimated velocity ellipsoids and does not yield any
reliable evidence for a counter-rotating halo component. If a distinct
counter-rotating halo component exists, then it must be far weaker
than claimed by Carollo et al. Finally, we note that their revised
analysis presented in Beers et al. does not alleviate our main concerns.
Title: The Effect of Scattering on the Temperature Stratification
of 3D Model Atmospheres of Metal-Poor Red Giants
Authors: Collet, Remo; Hayek, Wolfgang; Asplund, Martin
Bibcode: 2011IAUS..271..373C
Altcode:
We study the effects of different approximations of scattering in 3D
radiation-hydrodynamics simulations on the photospheric temperature
stratification of metal-poor red giant stars. We find that assuming a
Planckian source function and neglecting the contribution of scattering
to extinction in optically thin layers provides a good approximation
of the effects of coherent scattering on the photospheric temperature
balance.
Title: High-resolution elemental abundance analysis of the Hyades
supercluster
Authors: de Silva, G. M.; Freeman, K. C.; Bland-Hawthorn, J.; Asplund,
M.; Williams, M.; Holmberg, J.
Bibcode: 2011MNRAS.415..563D
Altcode: 2011MNRAS.tmp..794D; 2011arXiv1103.2588D
The existence of a kinematically defined moving group of stars
centred at U=-40, V=-17 km s-1, referred to as the Hyades
supercluster, has been suggested to be the debris of an originally
large star-forming event, with its core being the present-day Hyades
open cluster. Using high-resolution UV-Visual Echelle Spectrograph
(UVES) spectra, we present the elemental abundances for a range
of alpha, Fe-peak and neutron-capture elements for 26 proposed
supercluster stars. Our results show that the sample stars display
a heterogeneous abundance distribution, with a clump around [Fe/H]
=+0.15. We also calculate stellar radial velocities and U, V, W space
velocities. Enforcing strict chemical and kinematical membership
criteria, we find that four supercluster stars share the Hyades open
cluster abundances and kinematics, while many of the remaining stars
fit the disc field kinematics and abundance range. We discuss our
findings in the context of the Hyades supercluster being a dispersed
star-forming remnant, a stellar stream of purely dynamical origin or a
result of several processes. Based on observations made at the European
Southern Observatory, Paranal, Chile (ESO programmes 080.D-0094(A)
and 381.B-0045(A)).
Title: Sulphur abundances in halo giants from the [S I] line at 1082
nm and the [S I] triplet around 1045 nm
Authors: Jönsson, H.; Ryde, N.; Nissen, P. E.; Collet, R.; Eriksson,
K.; Asplund, M.; Gustafsson, B.
Bibcode: 2011A&A...530A.144J
Altcode: 2011arXiv1104.2148J
Context. It is still debated whether or not the Galactic chemical
evolution of sulphur in the halo follows the flat trend with [Fe/H]
that is ascribed to the result of explosive nucleosynthesis in type
II SNe. It has been suggested that the disagreement between different
investigations of sulphur abundances in halo stars might be owing
to problems with the diagnostics used, that a new production source
of sulphur might be needed in the early Universe, like hypernovae, or
that the deposition of supernova ejecta into the interstellar medium is
time-delayed.
Aims: The aim of this study is to try to clarify
this situation by measuring the sulphur abundance in a sample of halo
giants using two diagnostics: the S i triplet around 1045 nm and the
[S i] line at 1082 nm. The latter of the two is not believed to be
sensitive to non-LTE effects. We can thereby minimize the uncertainties
in the diagnostic used and estimate the usefulness of the triplet for
the sulphur determination in halo K giants. We will also be able to
compare our sulphur abundance differences from the two diagnostics
with the expected non-LTE effects in the 1045 nm triplet previously
calculated by others.
Methods: High-resolution near-infrared
spectra of ten K giants were recorded using the spectrometer CRIRES
mounted at VLT. Two standard settings were used, one covering the S i
triplet and one covering the [S i] line. The sulphur abundances were
individually determined with equivalent widths and synthetic spectra
for the two diagnostics using tailored 1D model atmospheres and relying
on non-LTE corrections from the litterature. Effects of convective
inhomogeneities in the stellar atmospheres are investigated.
Results: The sulphur abundances derived from both the [S i] line and the
non-LTE corrected 1045 nm triplet favor a flat trend for the evolution
of sulphur. In contrast to some previous studies, we saw no "high"
values of [S/Fe] in our sample.
Conclusions: We corroborate
the flat trend in the [S/Fe] vs. [Fe/H] plot for halo stars found in
some previous studies but do not find a scatter or a rise in [S/Fe]
as obtained in other works. We find the sulphur abundances deduced
from the non-LTE corrected triplet to be somewhat lower than the
abundances from the [S i] line, possibly indicating too large non-LTE
corrections. Considering 3D modeling, however, they might instead
be too small. Moreover, we show that the [S i] line can be used as
a sulphur diagnostic down to [Fe/H] ~ -2.3 in giants. Based on
observations collected at the European Southern Observatory, Chile
(ESO program 080.D-0675(A)).
Title: New constraints on the chemical evolution of the solar
neighbourhood and Galactic disc(s). Improved astrophysical parameters
for the Geneva-Copenhagen Survey
Authors: Casagrande, L.; Schönrich, R.; Asplund, M.; Cassisi, S.;
Ramírez, I.; Meléndez, J.; Bensby, T.; Feltzing, S.
Bibcode: 2011A&A...530A.138C
Altcode: 2011arXiv1103.4651C
We present a re-analysis of the Geneva-Copenhagen survey, which
benefits from the infrared flux method to improve the accuracy of the
derived stellar effective temperatures and uses the latter to build a
consistent and improved metallicity scale. Metallicities are calibrated
on high-resolution spectroscopy and checked against four open clusters
and a moving group, showing excellent consistency. The new temperature
and metallicity scales provide a better match to theoretical isochrones,
which are used for a Bayesian analysis of stellar ages. With respect to
previous analyses, our stars are on average 100 K hotter and 0.1 dex
more metal rich, which shift the peak of the metallicity distribution
function around the solar value. From Strömgren photometry we are
able to derive for the first time a proxy for [α/Fe] abundances,
which enables us to perform a tentative dissection of the chemical
thin and thick disc. We find evidence for the latter being composed
of an old, mildly but systematically alpha-enhanced population that
extends to super solar metallicities, in agreement with spectroscopic
studies. Our revision offers the largest existing kinematically
unbiased sample of the solar neighbourhood that contains full
information on kinematics, metallicities, and ages and thus provides
better constraints on the physical processes relevant in the build-up
of the Milky Way disc, enabling a better understanding of the Sun in
a Galactic context. Catalogue (Table 2) is only available at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/530/A138
Title: 3D LTE spectral line formation with scattering in red giant
stars
Authors: Hayek, W.; Asplund, M.; Collet, R.; Nordlund, Å.
Bibcode: 2011A&A...529A.158H
Altcode: 2011arXiv1108.3366H
Aims: We investigate the effects of coherent isotropic continuum
scattering on the formation of spectral lines in local thermodynamic
equilibrium (LTE) using 3D hydrodynamical and 1D hydrostatic model
atmospheres of red giant stars.
Methods: Detailed radiative
transfer with coherent and isotropic continuum scattering is computed
for 3D hydrodynamical and 1D hydrostatic models of late-type stellar
atmospheres using the SCATE code. Opacities are computed in LTE, while
a coherent and isotropic scattering term is added to the continuum
source function. We investigate the effects of scattering by comparing
continuum flux levels, spectral line profiles and curves of growth
for different species with calculations that treat scattering as
absorption.
Results: Rayleigh scattering is the dominant source
of scattering opacity in the continuum of red giant stars. Photons
may escape from deeper, hotter layers through scattering, resulting in
significantly higher continuum flux levels beneath a wavelength of λ
≲ 5000 Å. The magnitude of the effect is determined by the importance
of scattering opacity with respect to absorption opacity; we observe
the largest changes in continuum flux at the shortest wavelengths
and lowest metallicities; intergranular lanes of 3D models are more
strongly affected than granules. Continuum scattering acts to increase
the profile depth of LTE lines: continua gain more brightness than line
cores due to their larger thermalization depth in hotter layers. We
thus observe the strongest changes in line depth for high-excitation
species and ionized species, which contribute significantly to photon
thermalization through their absorption opacity near the continuum
optical surface. Scattering desaturates the line profiles, leading to
larger abundance corrections for stronger lines, which reach -0.5 dex
at 3000 Å for Fe ii lines in 3D with excitation potential χ = 2 eV at
[Fe/H] = -3.0. The corrections are less severe for low-excitation lines,
longer wavelengths, and higher metallicity. Velocity fields increase
the effects of scattering by separating emission from granules and
intergranular lanes in wavelength. 1D calculations exhibit similar
scattering abundance corrections for weak lines, but those for
strong lines are generally smaller compared to 3D models and depend
on the choice of microturbulence.
Conclusions: Continuum
scattering should be taken into account for computing realistic
spectral line profiles at wavelengths λ ≲ 4000 Å in metal-poor
giant stars. Profile shapes are strongly affected by velocity fields
and horizontal inhomogeneities, requiring a treatment based on 3D
hydrodynamical rather than classical 1D hydrostatic model atmospheres.
Title: The influence of electron collisions on non-LTE Li line
formation in stellar atmospheres
Authors: Osorio, Y.; Barklem, P. S.; Lind, K.; Asplund, M.
Bibcode: 2011A&A...529A..31O
Altcode:
The influence of the uncertainties in the rate coefficient data for
electron-impact excitation and ionization on non-LTE Li line formation
in cool stellar atmospheres is investigated. We examine the electron
collision data used in previous non-LTE calculations and compare them to
recent calculations that use convergent close-coupling (CCC) techniques
and to our own calculations using the R-matrix with the pseudostates
(RMPS) method. We find excellent agreement between rate coefficients
from the CCC and RMPS calculations, and reasonable agreement between
these data and the semi-empirical data used in non-LTE calculations
up to now. The results of non-LTE calculations using the old and new
data sets are compared and only small differences found: about 0.01
dex (~2%) or less in the abundance corrections. We therefore conclude
that the influence on non-LTE calculations of uncertainties in the
electron collision data is negligible. Indeed, together with the
collision data for the charge exchange process Li(3s) + H ⇌ Li
+ + H - now available, and barring the existence
of an unknown important collisional process, the collisional data in
general is not a source of significant uncertainty in non-LTE Li line
formation calculations.
Title: Non-LTE calculations for neutral Na in late-type stars using
improved atomic data
Authors: Lind, K.; Asplund, M.; Barklem, P. S.; Belyaev, A. K.
Bibcode: 2011A&A...528A.103L
Altcode: 2011arXiv1102.2160L
Neutral sodium is a minority species in the atmospheres of late-type
stars, and line formation in local thermodynamic equilibrium (LTE) is
often a poor assumption, in particular for strong lines. We present
an extensive grid of non-LTE calculations for several Na I lines in
cool stellar atmospheres, including metal-rich and metal-poor dwarfs
and giants. For the first time, we constructed a Na model atom that
incorporates accurate quantum mechanical calculations for collisional
excitation and ionisation by electrons as well as collisional excitation
and charge exchange reactions with neutral hydrogen. Similar to Li
I, the new rates for hydrogen impact excitation do not affect the
statistical equilibrium calculations, while charge exchange reactions
have a small but non-negligible influence. The presented LTE and non-LTE
curves-of-growth can be interpolated to obtain non-LTE abundances and
abundance corrections for arbitrary stellar parameter combinations and
line strengths. The typical corrections for weak lines are -0.1... -0.2
dex, whereas saturated lines may overestimate the abundance in LTE by
more than 0.5 dex. The non-LTE Na abundances appear very robust with
respect to uncertainties in the input collisional data.
Title: VizieR Online Data Catalog: Geneva-Copenhagen survey
re-analysis (Casagrande+, 2011)
Authors: Casagrande, L.; Schoenrich, R.; Asplund, M.; Cassisi, S.;
Ramirez, I.; Melendez, J.; Bensby, T.; Feltzing, S.
Bibcode: 2011yCat..35300138C
Altcode: 2011yCat..35309138C
We present a re-analysis of the Geneva-Copenhagen survey, benefiting
from the infrared flux method to improve upon the accuracy of the
derived stellar effective temperatures and using the latter to build a
consistent and improved metallicity scale. Metallicities are calibrated
on high-resolution spectroscopy and checked against four open clusters
and a moving group, showing excellent consistency. The new temperature
and metallicity scales provide a better match to theoretical isochrones,
which are used for a Bayesian analysis of stellar ages. With respect
to previous analyses, our stars are on average 100K hotter and 0.1dex
more metal rich, shifting the peak of the metallicity distribution
function around the solar value. From Stromgren photometry we are
able to derive for the first time a proxy for [Fe] abundances, which
enables for a tentative dissection of the chemical thin and thick
disc. We find evidence for the latter being composed of an old, mildly
but systematically alpha-enhanced population extending to super solar
metallicities, in agreement with spectroscopic studies. Our revision
offers the largest existing kinematically unbiased sample of the
solar neighbourhood that contains full information on kinematics,
metallicities and ages and thus provides better constraints on the
physical processes relevant in the build-up of the Milky Way disc,
enabling a better understanding of the Sun in a Galactic context. (1 data file).
Title: The chemical composition of the sun
Authors: Grevesse, N.; Asplund, M.; Sauval, A. J.; Scott, P.
Bibcode: 2011CaJPh..89..327G
Altcode:
No abstract at ADS
Title: Three-dimensional surface convection simulations of metal-poor
stars. The effect of scattering on the photospheric temperature
stratification
Authors: Collet, R.; Hayek, W.; Asplund, M.; Nordlund, Å.; Trampedach,
R.; Gudiksen, B.
Bibcode: 2011A&A...528A..32C
Altcode: 2011arXiv1101.3265C
Context. Three-dimensional (3D) radiative hydrodynamic model atmospheres
of metal-poor late-type stars are characterized by cooler upper
photospheric layers than their one-dimensional counterparts. This
property of 3D model atmospheres can dramatically affect the
determination of elemental abundances from temperature-sensitive
spectral features, with profound consequences on galactic chemical
evolution studies.
Aims: We investigate whether the cool surface
temperatures predicted by 3D model atmospheres of metal-poor stars
can be ascribed to approximations in the treatment of scattering
during the modelling phase.
Methods: We use the Bifrost
code to construct 3D model atmospheres of metal-poor stars and test
three different ways to handle scattering in the radiative transfer
equation. As a first approach, we solve iteratively the radiative
transfer equation for the general case of a source function with
a coherent scattering term, treating scattering in a correct and
consistent way. As a second approach, we solve the radiative transfer
equation in local thermodynamic equilibrium approximation, neglecting
altogether the contribution of continuum scattering to extinction in the
optically thin layers; this has been the default mode in our previous
3D modelling as well as in present Stagger-Code models. As our third
and final approach, we treat continuum scattering as pure absorption
everywhere, which is the standard case in the 3D modelling by the
CO5BOLD collaboration.
Results: For all simulations,
we find that the second approach produces temperature structures
with cool upper photospheric layers very similar to the case in which
scattering is treated correctly. In contrast, treating scattering as
pure absorption leads instead to significantly hotter and shallower
temperature stratifications. The main differences in temperature
structure between our published models computed with the Stagger-
and Bifrost codes and those generated with the CO5BOLD
code can be traced to the different treatments of scattering.
Conclusions: Neglecting the contribution of continuum scattering to
extinction in optically thin layers provides a good approximation
to the full, iterative solution of the radiative transfer equation
in metal-poor stellar surface convection simulations, and at a much
lower computational cost. Our results also demonstrate that the cool
temperature stratifications predicted for metal-poor late-type stars
by previous models by our collaboration are not an artifact of the
approximated treatment of scattering.
Title: Tracing the evolution of NGC 6397 through the chemical
composition of its stellar populations
Authors: Lind, K.; Charbonnel, C.; Decressin, T.; Primas, F.; Grundahl,
F.; Asplund, M.
Bibcode: 2011A&A...527A.148L
Altcode: 2010arXiv1012.0477L
Context. The chemical compositions of globular clusters provide
important information on the star formation that occurred at very
early times in the Galaxy. In particular the abundance patterns of
elements with atomic number z ≤ 13 may shed light on the properties
of stars that early on enriched parts of the star-forming gas with the
rest-products of hydrogen-burning at high temperatures.
Aims:
We analyse and discuss the chemical compositions of a large number of
elements in 21 red giant branch stars in the metal-poor globular cluster
NGC 6397. We compare the derived abundance patterns with theoretical
predictions in the framework of the "wind of fast rotating massive
star"-scenario.
Methods: High-resolution spectra were obtained
with the FLAMES/UVES spectrograph on the VLT. We determined non-LTE
abundances of Na, and LTE abundances for the remaining 21 elements,
including O (from the [OI] line at 630 nm), Mg, Al, α, iron-peak,
and neutron-capture elements, many of which had not been previously
analysed for this cluster. We also considered the influence of possible
He enrichment in the analysis of stellar spectra.
Results:
We find that the Na abundances of evolved, as well as unevolved,
stars in NGC 6397 show a distinct bimodality, which is indicative
of two stellar populations: one primordial stellar generation of
composition similar to field stars, and a second generation that
is polluted with material processed during hydrogen-burning, i.e.,
enriched in Na and Al and depleted in O and Mg. The red giant branch
exhibits a similar bimodal distribution in the Strömgren colour
index cy = c1 - (b - y), implying that there
are also large differences in the N abundance. The two populations
have the same composition for all analysed elements heavier than Al,
within the measurement uncertainty of the analysis, with the possible
exception of [Y/Fe]. Using two stars with almost identical stellar
parameters, one from each generation, we estimate the difference
in He content, ΔY = 0.01 ± 0.06, given the assumption that the
mass fraction of iron is the same for the stars.
Conclusions:
NGC 6397 hosts two stellar populations that have different chemical
compositions of N, O, Na, Mg, and probably Al. The cluster is dominated
(75%) by the second generation. We show that massive stars of the
first generation can be held responsible for the abundance patterns
observed in the second generation long-lived stars of NGC 6397. We
estimate that the initial mass of this globular cluster is at least
ten times higher than its present-day value. Based on data
collected at European Southern Observatory (ESO), Paranal, Chile,
under program IDs 077.A-0018(A) and 281.D-5028(A), as well as data
collected with the Danish 1.54 m at European Southern Observatory
(ESO), La Silla.Tables A.1 and A.2 are only available in electronic
form at http://www.aanda.orgTwo
tables with line equivalent widths, chemical abundances, and stellar
parameters are only available in electronic form at the CDS via
anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/527/A148
Title: The radius and mass of the close solar twin 18 Scorpii derived
from asteroseismology and interferometry
Authors: Bazot, M.; Ireland, M. J.; Huber, D.; Bedding, T. R.;
Broomhall, A. -M.; Campante, T. L.; Carfantan, H.; Chaplin, W. J.;
Elsworth, Y.; Meléndez, J.; Petit, P.; Théado, S.; Van Grootel,
V.; Arentoft, T.; Asplund, M.; Castro, M.; Christensen-Dalsgaard,
J.; Do Nascimento, J. D.; Dintrans, B.; Dumusque, X.; Kjeldsen, H.;
McAlister, H. A.; Metcalfe, T. S.; Monteiro, M. J. P. F. G.; Santos,
N. C.; Sousa, S.; Sturmann, J.; Sturmann, L.; ten Brummelaar, T. A.;
Turner, N.; Vauclair, S.
Bibcode: 2011A&A...526L...4B
Altcode: 2012arXiv1209.0217B
The growing interest in solar twins is motivated by the possibility of
comparing them directly to the Sun. To carry on this kind of analysis,
we need to know their physical characteristics with precision. Our
first objective is to use asteroseismology and interferometry on
the brightest of them: 18 Sco. We observed the star during 12 nights
with HARPS for seismology and used the PAVO beam-combiner at CHARA
for interferometry. An average large frequency separation 134.4 ±
0.3 μHz and angular and linear radiuses of 0.6759 ± 0.0062 mas and
1.010 ± 0.009 R⊙ were estimated. We used these values
to derive the mass of the star, 1.02 ± 0.03 M⊙. Based on observations collected at the European Southern Observatory
(ID 183.D-0729(A)) and at the CHARA Array, operated by Georgia State
University.
Title: VizieR Online Data Catalog: NGC6397 red giants chemical
composition (Lind+, 2011)
Authors: Lind, K.; Charbonnel, C.; Decressin, T.; Primas, F.; Grundahl,
F.; Asplund, M.
Bibcode: 2011yCat..35270148L
Altcode: 2011yCat..35279148L
The tables contain stellar parameters, equivalent widths, and
line-by-line abundances for stars in the metal-poor globular cluster
NGC6397. All abundances are given in logarithmic units relative to
hydrogen, according to A(x)=log(N(x)/N(H))+12, where N(x) is the number
density of element x and N(H) the number density of hydrogen. For
photometric data, Li abundances, and equivalent widths of Fe lines
we refer to Lind et al. (2009, Cat. J/A+A/503/545). Table 2 contains
improved non-LTE Na abundances for the targets presented in Lind et al
(2009,, Cat. J/A+A/503/545). (2 data files).
Title: The New Solar Composition and the Solar Metallicity
Authors: Grevesse, Nicolas; Asplund, Martin; Sauval, A. Jacques;
Scott, Pat
Bibcode: 2011sswh.book...51G
Altcode:
No abstract at ADS
Title: Three-dimensional hydrodynamical simulations of red
giant stars: semi-global models for interpreting interferometric
observations
Authors: Chiavassa, A.; Collet, R.; Casagrande, L.; Asplund, M.
Bibcode: 2010A&A...524A..93C
Altcode: 2010arXiv1009.1745C
Context. Theoretical predictions from models of red giant branch
stars are a valuable tool for various applications in astrophysics
ranging from galactic chemical evolution to studies of exoplanetary
systems.
Aims: We use the radiative transfer code Optim3D
and realistic 3D radiative-hydrodynamical (RHD) surface convection
simulations of red giants to explore the impact of granulation on
interferometric observables. We assess how 3D simulations of surface
convection can be validated against observations.
Methods: We
computed intensity maps for the 3D simulation snapshots in two filters,
the optical at 5000 ± 300 Å and the K band 2.14 ± 0.26 μm FLUOR
filter, corresponding to the wavelength-range of instruments mounted on
the CHARA interferometer. From the intensity maps, we constructed images
of the stellar disks and account for center-to-limb variations. We
then derived interferometric visibility amplitudes and phases. We
study their behavior with position angle and wavelength, and compare
them with CHARA observations of the red giant star HD 214868.
Results: We provide average limb darkening coefficients for different
metallicities and wavelengths ranges. We explain prospects for detecting
and characterizing granulation and center-to-limb variations of red
giant stars with today's interferometers. Regarding interferometric
observables, we find that the effect of convective-related surface
structures depends on metallicity and surface gravity. We provide
theoretical closure-phases that should be incorporated into the analysis
of red giant planet companion closure phase signals. We estimate
3D-1D corrections to stellar radii determination: 3D models are ~3.5%
smaller to ~1% larger in the optical than 1D, and roughly 0.5 to 1.5%
smaller in the infrared. Even if these corrections are small, they are
needed to properly set the zero point of effective temperature scale
derived by interferometry and to strengthen the confidence of existing
red giant catalogs of calibrating stars for interferometry. Finally,
we show that our RHD simulations provide an excellent fit to the red
giant HD 214868 even though more observations are needed at higher
spatial frequencies and shorter wavelength.
Title: Granulation Signatures in the Spectrum of the Very Metal-poor
Red Giant HD 122563
Authors: Ramírez, I.; Collet, R.; Lambert, D. L.; Allende Prieto,
C.; Asplund, M.
Bibcode: 2010ApJ...725L.223R
Altcode: 2010arXiv1011.4077R
A very high resolution (R = λ/Δλ = 200, 000), high signal-to-noise
ratio (S/N ~= 340) blue-green spectrum of the very metal-poor ([Fe/H]
~= -2.6) red giant star HD 122563 has been obtained by us at McDonald
Observatory. We measure the asymmetries and core wavelengths of a set
of unblended Fe I lines covering a wide range of line strength. Line
bisectors exhibit the characteristic C-shape signature of surface
convection (granulation) and they span from about 100 m s-1
in the strongest Fe I features to 800 m s-1 in the
weakest ones. Core wavelength shifts range from about -100 to -900
m s-1, depending on line strength. In general, larger
blueshifts are observed in weaker lines, but there is increasing
scatter with increasing residual flux. Assuming local thermodynamic
equilibrium (LTE), we synthesize the same set of spectral lines using
a state-of-the-art three-dimensional (3D) hydrodynamic simulation
for a stellar atmosphere of fundamental parameters similar to those
of HD 122563. We find good agreement between model predictions and
observations. This allows us to infer an absolute zero point for
the line shifts and radial velocity. Moreover, it indicates that
the structure and dynamics of the simulation are realistic, thus
providing support to previous claims of large 3D-LTE corrections to
elemental abundances and fundamental parameters of very metal-poor
red giant stars obtained with standard 1D-LTE spectroscopic analyses,
as suggested by the hydrodynamic model used here.
Title: Chemical evolution of the Galactic bulge as traced by
microlensed dwarf and subgiant stars. III. Detection of lithium in
the metal-poor bulge dwarf MOA-2010-BLG-285S
Authors: Bensby, T.; Asplund, M.; Johnson, J. A.; Feltzing, S.;
Meléndez, J.; Dong, S.; Gould, A.; Han, C.; Adén, D.; Lucatello,
S.; Gal-Yam, A.
Bibcode: 2010A&A...521L..57B
Altcode: 2010arXiv1009.5792B
Context. To study the evolution of Li in the Galaxy it is necessary
to observe dwarf or subgiant stars. These are the only long-lived
stars whose present-day atmospheric chemical composition reflects
their natal Li abundances according to standard models of stellar
evolution. Although Li has been extensively studied in the Galactic
disk and halo, to date there has only been one uncertain detection of
Li in an unevolved bulge star.
Aims: Our aim with this study
is to provide the first clear detection of Li in the Galactic bulge,
based on an analysis of a dwarf star that has largely retained its
initial Li abundance.
Methods: We performed a detailed elemental
abundance analysis of the bulge dwarf star MOA-2010-BLG-285S using a
high-resolution and high signal-to-noise spectrum obtained with the UVES
spectrograph at the VLT when the object was optically magnified during
a gravitational microlensing event (visual magnification A~550 during
observation). The Li abundance was determined through synthetic line
profile fitting of the 7Li resonance doublet line at 670.8
nm. The results have been corrected for departures from LTE.
Results: MOA-2010-BLG-285S is, at [Fe/H] = -1.23, the most metal-poor
dwarf star detected so far in the Galactic bulge. Its old age (12.5 Gyr)
and enhanced [α/Fe] ratios agree well with stars in the thick disk
at similar metallicities. This star represents the first unambiguous
detection of Li in a metal-poor dwarf star in the Galactic bulge. We
find an NLTE corrected Li abundance of logɛ(Li) = 2.16, which is
consistent with values derived for Galactic disk and halo dwarf stars
at similar metallicities and temperatures.
Conclusions: Our
results show that there are no signs of Li enrichment or production
in the Galactic bulge during its earliest phases. Observations of Li
in other galaxies (ω Cen) and other components of the Galaxy suggest
further that the Spite plateau is universal. Based on observations
carried out at the European Southern Observatory telescopes on Paranal,
Chile, Program ID 085.B-0399.
Title: A possible signature of terrestrial planet formation in the
chemical composition of solar analogs
Authors: Ramírez, I.; Asplund, M.; Baumann, P.; Meléndez, J.;
Bensby, T.
Bibcode: 2010A&A...521A..33R
Altcode: 2010arXiv1008.3161R
Recent studies have shown that the elemental abundances in the
Sun are anomalous when compared to most (about 85%) nearby solar
twin stars. Compared to its twins, the Sun exhibits a deficiency of
refractory elements (those with condensation temperatures TC
≳ 900 K) relative to volatiles (TC ≲ 900 K). This finding
is speculated to be a signature of the planet formation that occurred
more efficiently around the Sun compared with the majority of solar
twins. Furthermore, within this scenario, it seems more likely that
the abundance patterns found are specifically related to the formation
of terrestrial planets. In this work we analyze abundance results from
six large independent stellar abundance surveys to determine whether
they confirm or reject this observational finding. We show that the
elemental abundances derived for solar analogs in these six studies
are consistent with the TC trend suggested as a planet
formation signature. The same conclusion is reached when those results
are averaged heterogeneously. We also investigate the dependency of the
abundances with first ionization potential (FIP), which correlates well
with TC. A trend with FIP would suggest a different origin
for the abundance patterns found, but we show that the correlation
with TC is statistically more significant. We encourage
similar investigations of metal-rich solar analogs and late F-type
dwarf stars, for which the hypothesis of a planet formation signature
in the elemental abundances makes very specific predictions. Finally,
we examine a recent paper that claims that the abundance patterns of two
stars hosting super-Earth like planets contradict the planet formation
signature hypothesis. Instead, we find that the chemical compositions
of these two stars are fully compatible with our hypothesis.
Title: Lithium depletion in solar-like stars: no planet connection
Authors: Baumann, P.; Ramírez, I.; Meléndez, J.; Asplund, M.;
Lind, K.
Bibcode: 2010A&A...519A..87B
Altcode: 2010arXiv1008.0575B
We have determined precise stellar parameters and lithium abundances
in a sample of 117 stars with basic properties very similar to the
Sun. This sample selection reduces biasing effects and systematic errors
in the analysis. We estimate the ages of our sample stars mainly from
isochrone fitting but also from measurements of rotation period and
X-ray luminosity and test the connection between lithium abundance, age,
and stellar parameters. We find strong evidence for increasing lithium
depletion with age. Our sample includes 14 stars that are known to
host planets and it does not support recent claims that planet-host
stars have experienced more lithium depletion than stars without
planets. We find the solar lithium abundance normal for a star of its
age, mass, and metallicity. Furthermore, we analyze published data for
82 stars that were reported to support an enhanced lithium depletion
in planet hosts. We show that those stars in fact follow an age trend
very similar to that found with our sample and that the presence of
giant planets is not related to low lithium abundances. Finally, we
discuss the systematic biases that led to the incorrect conclusion of
an enhanced lithium depletion in planet-host stars.
Title: The chemical composition of the Sun
Authors: Grevesse, N.; Asplund, M.; Sauval, A. J.; Scott, P.
Bibcode: 2010Ap&SS.328..179G
Altcode: 2010Ap&SS.tmp...48G
We present a redetermination of the solar abundances of all available
elements. The new results have very recently been published by
Asplund et al. (Annu. Rev. Astron. Astrophys. 47:481, 2009). The
basic ingredients of this work, the main results and some of their
implications are summarized hereafter.
Title: The solar, exoplanet and cosmological lithium problems
Authors: Meléndez, J.; Ramírez, I.; Casagrande, L.; Asplund, M.;
Gustafsson, B.; Yong, D.; Do Nascimento, J. D.; Castro, M.; Bazot, M.
Bibcode: 2010Ap&SS.328..193M
Altcode: 2009Ap&SS.tmp..221M; 2009arXiv0910.5845M
We review three Li problems. First, the Li problem in the Sun, for which
some previous studies have argued that it may be Li-poor compared to
other Suns. Second, we discuss the Li problem in planet hosting stars,
which are claimed to be Li-poor when compared to field stars. Third,
we discuss the cosmological Li problem, i.e. the discrepancy between
the Li abundance in metal-poor stars (Spite plateau stars) and the
predictions from standard Big Bang Nucleosynthesis. In all three cases
we find that the “problems” are naturally explained by non-standard
mixing in stars.
Title: Radiative transfer with scattering for domain-decomposed 3D
MHD simulations of cool stellar atmospheres. Numerical methods and
application to the quiet, non-magnetic, surface of a solar-type star
Authors: Hayek, W.; Asplund, M.; Carlsson, M.; Trampedach, R.; Collet,
R.; Gudiksen, B. V.; Hansteen, V. H.; Leenaarts, J.
Bibcode: 2010A&A...517A..49H
Altcode: 2010arXiv1007.2760H
Aims: We present the implementation of a radiative
transfer solver with coherent scattering in the new BIFROST
code for radiative magneto-hydrodynamical (MHD) simulations of
stellar surface convection. The code is fully parallelized using
MPI domain decomposition, which allows for large grid sizes and
improved resolution of hydrodynamical structures. We apply the code
to simulate the surface granulation in a solar-type star, ignoring
magnetic fields, and investigate the importance of coherent scattering
for the atmospheric structure.
Methods: A scattering term
is added to the radiative transfer equation, requiring an iterative
computation of the radiation field. We use a short-characteristics-based
Gauss-Seidel acceleration scheme to compute radiative flux divergences
for the energy equation. The effects of coherent scattering are
tested by comparing the temperature stratification of three 3D
time-dependent hydrodynamical atmosphere models of a solar-type star:
without scattering, with continuum scattering only, and with both
continuum and line scattering.
Results: We show that continuum
scattering does not have a significant impact on the photospheric
temperature structure for a star like the Sun. Including scattering in
line-blanketing, however, leads to a decrease of temperatures by about
350 K below log10 τ5000 ⪉ -4. The effect is
opposite to that of 1D hydrostatic models in radiative equilibrium,
where scattering reduces the cooling effect of strong LTE lines in
the higher layers of the photosphere. Coherent line scattering also
changes the temperature distribution in the high atmosphere, where
we observe stronger fluctuations compared to a treatment of lines as
true absorbers.
Title: The chemical composition of solar-type stars in comparison
with that of the Sun
Authors: Gustafsson, Bengt; Meléndez, Jorge; Asplund, Martin;
Yong, David
Bibcode: 2010Ap&SS.328..185G
Altcode: 2010Ap&SS.tmp...36G
The question whether the solar chemical composition is typical for
solar-type stars is analysed by comparing the Sun with different stellar
samples, including a sample of stars with very similar parameters,
solar twins. Although typical in terms of overall metallicity for
stars of solar age and galactic orbit, the solar atmosphere is found to
have abundances, as compared with solar twins, that indicate that its
gas has once been affected by dust formation and dust separation. It
is concluded that this may be related to the formation of the solar
planetary system and its special properties.
Title: Observational evidence for a broken Li Spite plateau and
mass-dependent Li depletion
Authors: Meléndez, J.; Casagrande, L.; Ramírez, I.; Asplund, M.;
Schuster, W. J.
Bibcode: 2010A&A...515L...3M
Altcode: 2010arXiv1005.2944M
We present NLTE Li abundances for 88 stars in the metallicity range
-3.5 < [Fe/H] < -1.0. The effective temperatures are based on the
infrared flux method with improved E(B-V) values obtained mostly from
interstellar Na I D lines. The Li abundances were derived through MARCS
models and high-quality UVES+VLT, HIRES+Keck and FIES+NOT spectra, and
complemented with reliable equivalent widths from the literature. The
less-depleted stars with [Fe/H] < -2.5 and [Fe/H] > -2.5 fall
into two well-defined plateaus of ALi = 2.18 (σ = 0.04) and
ALi = 2.27 (σ = 0.05), respectively. We show that the two
plateaus are flat, unlike previous claims for a steep monotonic decrease
in Li abundances with decreasing metallicities. At all metallicities we
uncover a fine-structure in the Li abundances of Spite plateau stars,
which we trace to Li depletion that depends on both metallicity and
mass. Models including atomic diffusion and turbulent mixing seem to
reproduce the observed Li depletion assuming a primordial Li abundance
ALi = 2.64, which agrees well with current predictions
(ALi = 2.72) from standard Big Bang nucleosynthesis. Adopting
the Kurucz overshooting model atmospheres increases the Li abundance
by +0.08 dex to ALi = 2.72, which perfectly agrees with
BBN+WMAP. Based in part on observations obtained at the W. M. Keck
Observatory, the Nordic Optical Telescope on La Palma, and on data from
the HIRES/Keck archive and the European Southern Observatory ESO/ST-ECF
Science Archive Facility.Table 1 is only available in electronic form
at http://www.aanda.org
Title: Commission 29: Stellar Spectra
Authors: Piskunov, Nikolai; Cunha, Katia; Parthasarathy, Mudumba;
Aoki, Wako; Asplund, Martin; Bohlender, David; Carpenter, Kenneth;
Melendez, Jorge; Parthasarathy, Mudumba; Rossi, Silvia; Smith, Verne;
Soderblom, David; Wahlgren, Glenn
Bibcode: 2010IAUTB..27..193P
Altcode:
The business meeting was attended by 23 members of the Commission. The
meeting started at 16:00 a short report of the activities during the
triennium 2006-2009. The focus of the activities was the sharing
of expertise between spectroscopic techniques in various areas of
astronomical research. In particular, the progress in instrumentation,
detectors, data reduction, data analysis and archiving. The second
activity was the analysis of to IAU meeting proposals followed by
recommendations for improvements and eventually support. The sponsored
symposia included Sponsoring symposia The Ages of Stars and The Disk
Galaxy Evolution in the Cosmological Context. The Commission was also
disseminating information about the Commission activities and relevant
meetings to the Commission members. In this respect the Commission
web page is playing a crucial role.
Title: Commission 36: Theory of Stellar Atmospheres
Authors: Asplund, Martin; Puls, Joachim; Landstreet, John; Allende
Prieto, Carlos; Ayres, Thomas; Berdyugina, Svetlana; Gustafsson,
Bengt; Hubeny, Ivan; Ludwig, Hans Günter; Mashonkina, Lyudmila;
Randich, Sofia
Bibcode: 2010IAUTB..27..197A
Altcode:
The members of the Commission 36 Organizing Committee attending the IAU
General Assembly in Rio de Janeiro met for a business session on August
7. Both members from the previous (2006-2009) and the new (2009-2012)
Organizing Committee partook in the discussions. Past president John
Landstreet described the work he had done over the past three years
in terms of supporting proposed conferences on the topic. He has
also spent significant amount of time establishing an updated mailing
list of all >350 members of the commission, which is unfortunately
not provided automatically by the IAU. Such a list is critical for a
rapid dissemination of information to the commission members and for
a correct and smooth running of elections of IAU officials. Everyone
present thanked John effusively for all of his hard work over the past
three years to stimulate a high level of activity within the discipline.
Title: Lithium in other Suns: no connection between stars and planets
Authors: Meléndez, Jorge; Ramírez, Iván; Asplund, Martin; Baumann,
Patrick
Bibcode: 2010IAUS..268..341M
Altcode:
An unbiased sample of solar twins shows that the Sun has a normal
Li abundance for its age and that a low Li abundance does not imply
the presence of planets. We find a tight correlation between Li and
age, which holds for all stars analyzed in our sample: solar twins,
stars with and without detected giant planets, and stars that may host
terrestrial planets.
Title: Chemical similarities between Galactic bulge and local thick
disk red giants: O, Na, Mg, Al, Si, Ca, and Ti
Authors: Alves-Brito, A.; Meléndez, J.; Asplund, M.; Ramírez, I.;
Yong, D.
Bibcode: 2010A&A...513A..35A
Altcode: 2010arXiv1001.2521A
Context. The formation and evolution of the Galactic bulge and its
relationship with the other Galactic populations is still poorly
understood.
Aims: To establish the chemical differences and
similarities between the bulge and other stellar populations, we
performed an elemental abundance analysis of α- (O, Mg, Si, Ca, and
Ti) and Z-odd (Na and Al) elements of red giant stars in the bulge
as well as of local thin disk, thick disk and halo giants.
Methods: We use high-resolution optical spectra of 25 bulge giants in
Baade's window and 55 comparison giants (4 halo, 29 thin disk and 22
thick disk giants) in the solar neighborhood. All stars have similar
stellar parameters but cover a broad range in metallicity (-1.5 <
[Fe/H] < +0.5). A standard 1D local thermodynamic equilibrium
analysis using both Kurucz and MARCS models yielded the abundances
of O, Na, Mg, Al, Si, Ca, Ti and Fe. Our homogeneous and differential
analysis of the Galactic stellar populations ensured that systematic
errors were minimized.
Results: We confirm the well-established
differences for [α/Fe] at a given metallicity between the local thin
and thick disks. For all the elements investigated, we find no chemical
distinction between the bulge and the local thick disk, in agreement
with our previous study of C, N and O but in contrast to other groups
relying on literature values for nearby disk dwarf stars. For -1.5
< [Fe/H] < -0.3 exactly the same trend is followed by both the
bulge and thick disk stars, with a star-to-star scatter of only 0.03
dex. Furthermore, both populations share the location of the knee
in the [α/Fe] vs. [Fe/H] diagram. It still remains to be confirmed
that the local thick disk extends to super-solar metallicities as is
the case for the bulge. These are the most stringent constraints to
date on the chemical similarity of these stellar populations.
Conclusions: Our findings suggest that the bulge and local thick disk
stars experienced similar formation timescales, star formation rates
and initial mass functions, confirming thus the main outcomes of our
previous homogeneous analysis of [O/Fe] from infrared spectra for nearly
the same sample. The identical α-enhancements of thick disk and bulge
stars may reflect a rapid chemical evolution taking place before the
bulge and thick disk structures we see today were formed, or it may
reflect Galactic orbital migration of inner disk/bulge stars resulting
in stars in the solar neighborhood with thick-disk kinematics. Tables 8-15 are only available in electronic form at the CDS
via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/513/A35
Title: The light elements in the light of 3D and non-LTE effects
Authors: Asplund, Martin; Lind, Karin
Bibcode: 2010IAUS..268..191A
Altcode: 2010arXiv1002.1993A
In this review we discuss possible systematic errors inherent
in classical 1D LTE abundance analyses of late-type stars for
the light elements (here: H, He, Li, Be and B). The advent of
realistic 3D hydrodynamical model atmospheres and the availability
of non-LTE line formation codes place the stellar analyses on a
much firmer footing and indeed drastically modify the astrophysical
interpretations in many cases, especially at low metallicities. For
the Teff-sensitive hydrogen lines both stellar granulation
and non-LTE are likely important but the combination of the two has not
yet been fully explored. A fortuitous near-cancellation of significant
but opposite 3D and non-LTE effects leaves the derived 7Li
abundances largely unaffected but new atomic collisional data should
be taken into account. We also discuss the impact on 3D non-LTE line
formation on the estimated lithium isotopic abundances in halo stars
in light of recent claims that convective line asymmetries can mimic
the presence of 6Li. While Be only have relatively minor
non-LTE abundance corrections, B is sensitive even if the latest
calculations imply smaller non-LTE effects than previously thought.
Title: Observational signatures of lithium depletion in the metal-poor
globular cluster NGC6397
Authors: Lind, Karin; Primas, Francesca; Charbonnel, Corinne; Grundahl,
Frank; Asplund, Martin
Bibcode: 2010IAUS..268..263L
Altcode: 2010arXiv1001.5153L
The “stellar” solution to the cosmological lithium problem proposes
that surface depletion of lithium in low-mass, metal-poor stars can
reconcile the lower abundances found for Galactic halo stars with
the primordial prediction. Globular clusters are ideal environments
for studies of the surface evolution of lithium, with large number
statistics possible to obtain for main sequence stars as well as
giants. We discuss the Li abundances measured for >450 stars in
the globular cluster NGC 6397, focusing on the evidence for lithium
depletion and especially highlighting how the inferred abundances
and interpretations are affected by early cluster self-enrichment and
systematic uncertainties in the effective temperature determination.
Title: Observational signatures for depletion in the Spite plateau:
solving the cosmological Li discrepancy?
Authors: Meléndez, Jorge; Casagrande, Luca; Ramírez, Iván; Asplund,
Martin; Schuster, William J.
Bibcode: 2010IAUS..268..211M
Altcode: 2009arXiv0912.2949M
We present Li abundances for 73 stars in the metallicity range -3.5
< [Fe/H] < -1.0 using improved IRFM temperatures (Casagrande et
al. 2010) with precise E(B-V) values obtained mostly from interstellar
NaI D lines, and high-quality equivalent widths (σEW
~ 3%). At all metallicities we uncover a fine-structure in the Li
abundances of Spite plateau stars, which we trace to Li depletion that
depends on both metallicity and mass. Models including atomic diffusion
and turbulent mixing seem to reproduce the observed Li depletion
assuming a primordial Li abundance ALi = 2.64 dex (MARCS
models) or 2.72 (Kurucz overshooting models), in good agreement with
current predictions (ALi = 2.72) from standard BBN. We are
currently expanding our sample to have a better coverage of different
evolutionary stages at the high and low metallicity ends, in order to
verify our findings.
Title: Chemical similarities between the Galactic bulge and local
thick disk red giant stars: analysis from optical data
Authors: Alves-Brito, Alan; Meléndez, Jorge; Asplund, Martin
Bibcode: 2010IAUS..265..342A
Altcode:
The Galactic structure and composition remain as one of the greatest
open problems in modern astrophysics. We show here that there are
chemical similarities between the Galactic bulge and local thick disk
red giant stars. This finding puts strong constraints on the IMF,
SFR and chemical enrichment timescale of the bulge and thick disk. Our
results are based upon a detailed elemental abundance analysis of 80
high S/N and high resolution optical spectra of giant stars, in the
range -1.5 < [Fe/H] < +0.5.
Title: A Puzzle Involving Galactic Bulge Microlensing Events
Authors: Cohen, Judith G.; Gould, Andrew; Thompson, Ian B.; Feltzing,
Sofia; Bensby, Thomas; Johnson, Jennifer A.; Huang, Wenjin; Meléndez,
Jorge; Lucatello, Sara; Asplund, Martin
Bibcode: 2010ApJ...711L..48C
Altcode: 2009arXiv0911.5081C
We study a sample of 16 microlensed Galactic bulge main-sequence turnoff
region stars for which high-dispersion spectra have been obtained with
detailed abundance analyses. We demonstrate that there is a very strong
and highly statistically significant correlation between the maximum
magnification of the microlensed bulge star and the value of the [Fe/H]
deduced from the high resolution spectrum of each object. Physics
demands that this correlation, assuming it to be real, be the result
of some sample bias. We suggest several possible explanations, but are
forced to reject them all, and are left puzzled. To obtain a reliable
metallicity distribution in the Galactic bulge based on microlensed
dwarf stars, it will be necessary to resolve this issue through the
course of additional observations. Based in part on observations
obtained at the W. M. Keck Observatory, which is operated jointly by
the California Institute of Technology, the University of California,
and the National Aeronautics and Space Administration.
Title: Unprecedented accurate abundances: signatures of other Earths?
Authors: Meléndez, Jorge; Asplund, Martin; Gustafsson, Bengt; Yong,
David; Ramírez, Iván
Bibcode: 2010IAUS..265..412M
Altcode: 2009arXiv0910.0875M
For more than 140 years the chemical composition of our Sun has
been considered typical of solar-type stars. Our highly differential
elemental abundance analysis of unprecedented accuracy (~0.01 dex)
of the Sun relative to solar twins, shows that the Sun has a peculiar
chemical composition with a ≈20% depletion of refractory elements
relative to the volatile elements in comparison with solar twins. The
abundance differences correlate strongly with the condensation
temperatures of the elements. A similar study of solar analogs from
planet surveys shows that this peculiarity also holds in comparisons
with solar analogs known to have close-in giant planets while the
majority of solar analogs without detected giant planets show the solar
abundance pattern. The peculiarities in the solar chemical composition
can be explained as signatures of the formation of terrestrial planets
like our own Earth.
Title: Chemical evolution of the Galactic bulge as traced by
microlensed dwarf and subgiant stars. II. Ages, metallicities,
detailed elemental abundances, and connections to the Galactic
thick disc
Authors: Bensby, T.; Feltzing, S.; Johnson, J. A.; Gould, A.; Adén,
D.; Asplund, M.; Meléndez, J.; Gal-Yam, A.; Lucatello, S.; Sana,
H.; Sumi, T.; Miyake, N.; Suzuki, D.; Han, C.; Bond, I.; Udalski, A.
Bibcode: 2010A&A...512A..41B
Altcode: 2009arXiv0911.5076B
Context. The Bulge is the least understood major stellar population of
the Milky Way. Most of what we know about the formation and evolution
of the Bulge comes from bright giant stars. The underlying assumption
that giants represent all the stars, and accurately trace the chemical
evolution of a stellar population, is under debate. In particular,
recent observations of a few microlensed dwarf stars give a very
different picture of the evolution of the Bulge from that given by the
giant stars.
Aims: We aim to resolve the apparent discrepancy
between Bulge metallicity distributions derived from microlensed
dwarf stars and giant stars. Additionally, we aim to put observational
constraints on the elemental abundance trends and chemical evolution
of the Bulge.
Methods: We perform a detailed elemental abundance
analysis of dwarf stars in the Galactic bulge, based on high-resolution
spectra that were obtained while the stars were optically magnified
during gravitational microlensing events. The analysis method is
the same as for a large sample of F and G dwarf stars in the Solar
neighbourhood, enabling a fully differential comparison between the
Bulge and the local stellar populations in the Galactic disc.
Results: We present detailed elemental abundances and stellar ages
for six new dwarf stars in the Galactic bulge. Combining these with
previous events, here re-analysed with the same methods, we study a
homogeneous sample of 15 stars, which constitute the largest sample to
date of microlensed dwarf stars in the Galactic bulge. We find that the
stars span the full range of metallicities from [Fe/H] = -0.72 to +0.54,
and an average metallicity of < [Fe/H]> = -0.08 ± 0.47, close to
the average metallicity based on giant stars in the Bulge. Furthermore,
the stars follow well-defined abundance trends, that for [Fe/H]<0
are very similar to those of the local Galactic thick disc. This
suggests that the Bulge and the thick disc have had, at least partially,
comparable chemical histories. At sub-solar metallicities we find the
Bulge dwarf stars to have consistently old ages, while at super-solar
metallicities we find a wide range of ages. Using the new age and
abundance results from the microlensed dwarf stars we investigate
possible formation scenarios for the Bulge. Based on observations
made with the European Southern Observatory telescopes, Program IDs
082.B-0453 and 083.B-0265.Table 5 is also available in electronic form
at the CDS and full Table 4 is only available in electronic form at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/512/A41
Title: Elemental abundances in the Galactic bulge from microlensed
dwarf stars
Authors: Bensby, T.; Feltzing, S.; Johnson, J. A.; Gould, A.; Sana,
H.; Gal-Yam, A.; Asplund, M.; Lucatello, S.; Melendez, J.; Udalski,
A.; Kubas, D.; James, G.; Adén, D.; Simmerer, J.
Bibcode: 2010IAUS..265..346B
Altcode: 2009arXiv0908.2779B
We present elemental abundances of 13 microlensed dwarf and subgiant
stars in the Galactic bulge, which constitute the largest sample to
date. We show that these stars span the full range of metallicity from
Fe/H= -0.8 to +0.4, and that they follow well-defined abundance trends,
coincident with those of the Galactic thick disc.
Title: A possible signature of terrestrial planet formation in the
chemical composition of solar twins
Authors: Ramírez, I.; Meléndez, J.; Asplund, M.; Baumann, P.
Bibcode: 2010iac..talk....2R
Altcode: 2010iac..talk..148R
No abstract at ADS
Title: VizieR Online Data Catalog: Abundances in solar analogs
(Ramirez+, 2009)
Authors: Ramirez, I.; Melendez, J.; Asplund, M.
Bibcode: 2010yCat..35089017R
Altcode:
Our sample stars were selected from the Hipparcos catalog (I/239) by
applying constraints on color, based on the color-Teff calibrations by
Ramirez & Melendez (2005ApJ...626..465R), corrected by suspected
zero point errors (Casagrande et al., 2009, submitted), trigonometric
parallaxes, and literature values for [Fe/H] and chromospheric activity,
if available. About 100 stars satisfied our selection criteria
and, given our observational constraints, data for 64 of them were
acquired. We also observed the asteroids Vesta and Ceres as solar
reference. (2 data files).
Title: Precise Li abundances in metal-poor stars: depletion in the
Spite plateau
Authors: Meléndez, J.; Casagrande, L.; Ramírez, I.; Asplund, M.
Bibcode: 2010IAUS..265...71M
Altcode:
We present Li abundances for 73 stars in the metallicity range -3.5
< [Fe/H] < -1.0 using improved IRFM temperatures (Casagrande et
al. 2009) with precise E(B-V) values obtained mostly from interstellar
NaI D lines, and high-quality equivalent widths (σEW
~ 3%). At all metallicities we uncover a fine-structure in the Li
abundances of Spite plateau stars, which we trace to Li depletion
that depends on both metallicity and mass. Models including atomic
diffusion and turbulent mixing seem to reproduce the observed Li
depletion assuming a primordial Li abundance ALi = 2.64 dex
(MARCS models) or 2.72 (Kurucz overshooting models), in good agreement
with current predictions (ALi = 2.72) from standard BBN.
Title: An absolutely calibrated Teff scale from the
infrared flux method. Dwarfs and subgiants
Authors: Casagrande, L.; Ramírez, I.; Meléndez, J.; Bessell, M.;
Asplund, M.
Bibcode: 2010A&A...512A..54C
Altcode: 2010arXiv1001.3142C
Various effective temperature scales have been proposed over the
years. Despite much work and the high internal precision usually
achieved, systematic differences of order 100 K (or more) among
various scales are still present. We present an investigation based
on the infrared flux method aimed at assessing the source of such
discrepancies and pin down their origin. We break the impasse among
different scales by using a large set of solar twins, stars which
are spectroscopically and photometrically identical to the Sun,
to set the absolute zero point of the effective temperature scale
to within few degrees. Our newly calibrated, accurate and precise
temperature scale applies to dwarfs and subgiants, from super-solar
metallicities to the most metal-poor stars currently known. At solar
metallicities our results validate spectroscopic effective temperature
scales, whereas for [Fe/H]⪉ -2.5 our temperatures are roughly 100
K hotter than those determined from model fits to the Balmer lines
and 200 K hotter than those obtained from the excitation equilibrium
of Fe lines. Empirical bolometric corrections and useful relations
linking photometric indices to effective temperatures and angular
diameters have been derived. Our results take full advantage of the
high accuracy reached in absolute calibration in recent years and
are further validated by interferometric angular diameters and space
based spectrophotometry over a wide range of effective temperatures and
metallicities. Table 8 is only available in electronic form at the
CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/512/A54
Title: VizieR Online Data Catalog: Teff and Fbol from Infrared Flux
Method (Casagrande+, 2010)
Authors: Casagrande, L.; Ramirez, I.; Melendez, J.; Bessell, M.;
Asplund, M.
Bibcode: 2010yCat..35120054C
Altcode: 2010yCat..35129054C
Sample stars used and fundamental physical parameters (Teff, Fbol, diam)
derived via IRFM. The apparent bolometric magnitudes (mBol) have been
computed according to Casagrande et al. (2006MNRAS.373...13C), where the
absolute bolometric magnitude of the Sun MBol⊙=4.74. For
each star mBol is obtained using its bolometric flux (Fbol) and
effective temperature (Teff) and therefore it is already corrected for
reddening, if present. Notice however that the observed magnitudes
given here are not: before computing bolometric corrections,
the observed magnitudes should be dereddened using the E(B-V)
given here. The correction into dereddened magnitudes as been done
iteratively, as described in Section 2.1 of the paper. However,
average relations between E(B-V) and various photometric bands can
be found in literature e.g. McCall (2004AJ....128.2144M). Bolometric
corrections in each band can be readily obtained using the dereddened
magnitudes. E.g. BCV=mBol-V0, where BCV is the
bolometric correction in V band, mBol is thw apparent bolometric
magnitude, V0 is the dereddened apparent V magnitude (=Vmag if
E(B-V)=0). Errors have been computed as described in the paper, without
accounting for the uncertainty in E(B-V): changing it by +/-0.01 would
affect Teff by approximately +/-50K. (1 data file).
Title: VizieR Online Data Catalog: Abundances of microlensed stars
in the Bulge (Bensby+, 2010)
Authors: Bensby, T.; Feltzing, S.; Johnson, J. A.; Gould, A.; Aden,
D.; Asplund, M.; Melendez, J.; Gal-Yam, A.; Lucatello, S.; Sana, H.;
Sumi, T.; Miyake, N.; Suzuki, N.; Han, C.; Bond, I.; Udalski, A.
Bibcode: 2010yCat..35120041B
Altcode: 2010yCat..35129041B
For each spectral line we give the lower excitation potential, measured
equivalent widths, and derived absolute abundances. We also give median
abundances for each star, normalised to the Sun, and errors in the
median abundances. (3 data files).
Title: Searching for Signatures of Radial Mixing in The Chemically
Divided Galactic Disks
Authors: Lee, Young S.; Schonrich, R.; Beers, T. C.; Heather, M. L.;
An, D.; Allende Prieto, C.; Asplund, M.; Carollo, D.; Rockosi, C. M.
Bibcode: 2010AAS...21541303L
Altcode: 2010BAAS...42R.250L
The Milky Way's thick disk was originally identified by fitting
the vertical density distribution of stars to a double exponential
profile. Recent investigations have shown that, in addition to being
older, thick disk stars show chemical and kinematical properties
distinct from the thin disk. Most scenarios of thick disk formation
discussed to date emphasize mergers, e.g., heating of a pre-existing
thin disk, accretion of stars from disrupted satellites, or in-situ
formation induced by infalling gas-rich systems. Recently, however,
growing observational and theoretical evidence has suggested that the
thick disk might be the result of the cumulative radial migration
of disk stars over the history of the Galaxy. According to these
models, disk stars move radially over their lifetimes, spreading the
chemical signatures associated with their birth place at a range of
galactocentric distances and giving rise to chemical and kinematical
signatures corresponding to the common thin and thick disk divisions. In
this study we search for observational signatures of radial mixing in
the disk populations based on a large sample of F-and G-type dwarfs
observed by SEGUE-1, divided into thin and thick disk populations
characterized by low (-0.1 <[α/Fe] < +0.2) and high (+0.3 <
[α/Fe] < +0.6) α-abundances, respectively. We also demonstrate
that we are able to determine [α/Fe] with an accuracy of < 0.1
dex down to S/N = 20/1 for the SEGUE stellar spectra. This work
was supported in part by grants PHY 02-16783 and PHY 08-22648:
Physics Frontiers Center / Joint Institute for Nuclear Astrophysics
(JINA), awarded by the U.S. National Science Foundation.
Title: The lithium history of NGC 6397
Authors: Primas, Francesca; Lind, Karin; Charbonnel, Corinne; Grundahl,
Frank; Asplund, Martin
Bibcode: 2010IAUS..266..143P
Altcode:
The primordial lithium abundance inferred from WMAP and standard Big
Bang nucleosysnthesis is approximately three times higher than the
plateau value measured in old metal-poor Population II stars, suggesting
that these stars have undergone atmospheric Li depletion. To constrain
the physics responsible for such depletion, we conducted a homogeneous
analysis of a large sample of stars in the metal-poor globular cluster
NGC 6397, covering all evolutionary phases from below the main-sequence
turnoff to high up the red-giant branch (RGB). The dwarf, turnoff,
and early subgiant stars form a thin abundance plateau, with a sharpe
edge in the middle of the subgiant branch, where Li dilution caused by
the inward extension of the convective envelope starts (the beginning
of the so-called first dredge up). A second steep abundance drop
is seen at the RGB bump, again highlighting the need for the onset
of nonstandard mixing in this evolutionary phase. Moreover, by also
measuring the sodium abundances of the targets, we have gained insight
into the degree of pollution by early cluster self-enrichement, and may
separate highly polluted, Li-poor and Na-rich stars from stars formed
from pristine material. Our observational findings strictly limit both
the extent of lithium surface depletion, which in turn constrains the
efficiency of mixing below the outer convection zone, and the resulting
spread in lithium abundance in metal-poor turn-off stars.
Title: VizieR Online Data Catalog: Abundances of Galactic red giants
(Alves-Brito+, 2010)
Authors: Alves-Brito, A.; Melendez, J.; Asplund, M.; Ramirez, I.;
Yong, D.
Bibcode: 2010yCat..35130035A
Altcode: 2010yCat..35139035A
Line list and equivalent widths (EWs) of a sample of 80 giant stars
in the Galactic bulge, halo, thin- and thick disk. The list includes
lines of [OI], NaI, MgI, AlI, SiI, CaI, TiI, FeI and FeII. The adopted
oscillator strengths (loggfs) and excitation potential (EP) are also
listed. For the bulge stars, the EWs were taken from Fulbrigth et
al. (2006, Cat. <J/ApJ/636/821>, 2007ApJ...661.1152F). Refer to
the paper's text for more detail. (2 data files).
Title: Chemical abundances of 11 bulge stars from high-resolution,
near-IR spectra
Authors: Ryde, N.; Gustafsson, B.; Edvardsson, B.; Meléndez, J.;
Alves-Brito, A.; Asplund, M.; Barbuy, B.; Hill, V.; Käufl, H. U.;
Minniti, D.; Ortolani, S.; Renzini, A.; Zoccali, M.
Bibcode: 2010A&A...509A..20R
Altcode: 2009arXiv0910.0448R
Context. It is debated whether the Milky Way bulge has characteristics
more similar to those of a classical bulge than those of a
pseudobulge. Detailed abundance studies of bulge stars are important
when investigating the origin, history, and classification of the
bulge. These studies provide constraints on the star-formation
history, initial mass function, and differences between stellar
populations. Not many similar studies have been completed because
of the large distance and high variable visual extinction along the
line-of-sight towards the bulge. Therefore, near-IR investigations
can provide superior results.
Aims: To investigate the origin
of the bulge and study its chemical abundances determined from
near-IR spectra for bulge giants that have already been investigated
with optical spectra. The optical spectra also provide the stellar
parameters that are very important to the present study. In particular,
the important CNO elements are determined more accurately in the
near-IR. Oxygen and other α elements are important for investigating
the star-formation history. The C and N abundances are important for
determining the evolutionary stage of the giants and the origin of C
in the bulge.
Methods: High-resolution, near-infrared spectra
in the H band were recorded using the CRIRES spectrometer mounted on
the Very Large Telescope. The CNO abundances are determined from the
numerous molecular lines in the wavelength range observed. Abundances
of the α elements Si, S, and Ti are also determined from the near-IR
spectra.
Results: The abundance ratios [O/Fe], [Si/Fe], and
[S/Fe] are enhanced to metallicities of at least [Fe/H] = -0.3, after
which they decline. This suggests that the Milky Way bulge experienced a
rapid and early burst of star formation similar to that of a classical
bulge. However, a similarity between the bulge trend and the trend of
the local thick disk seems to be present. This similarity suggests that
the bulge could have had a pseudobulge origin. The C and N abundances
suggest that our giants are first-ascent red-giants or clump stars,
and that the measured oxygen abundances are those with which the
stars were born. Our [C/Fe] trend does not show any increase with
[Fe/H], which is expected if W-R stars contributed substantially to
the C abundances. No “cosmic scatter” can be traced around our
observed abundance trends: the measured scatter is expected, given the
observational uncertainties. Based on observations collected at
the European Southern Observatory, Chile (ESO program 079.B-0338(A)).
Title: Improved log(gf) Values Of Selected Lines In Mn I And Mn II
For Studies Of Non-equilibrium Effects In Stellar Photospheres
Authors: Den Hartog, Elizabeth; Lawler, J. E.; Sobeck, J.; Sneden,
C.; Cowan, J. J.; Asplund, M.
Bibcode: 2010AAS...21542403D
Altcode: 2010BAAS...42..330D
The work presents transition probabilities with very low uncertainties
for a selected set of multiplets of Mn I and Mn II. Multiplets are
chosen which are accessible to ground-based observation, are relatively
unblended and unsaturated in stellar spectra and which are amenable
to accurate branching fraction determination. These lab measurements
provide a foundation for studies of non-LTE and 3-dimensional effects in
stellar photospheres. We report on new radiative lifetime measurements
for 22 levels of Mn I from the e8D, z6P,
z6D, z4F, e8S and e6S
multiplets and 3 levels of Mn II from the z5P multiplet using
time-resolved laser-induced fluorescence on a slow atomic beam. New
branching fractions for transitions from these levels, measured using
a Fourier-transform spectrometer, are also reported. When combined,
these measurements yield transition probabilities for 47 transitions
of Mn I and 12 transitions of Mn II. Comparisons are made to data
from the literature and to simple Russell-Saunders or LS theory. Final
recommended values, which are weighted averages of all available modern
measurements and in some cases LS theory, are given for the transition
probabilities. These recommended log(gf) values are accurate to +/-
0.02 dex with high ( 2 sigma) confidence. The companion paper applies
these new lab results to studies of departures from both LTE in Mn I
and Saha equilibrium between Mn I and Mn II on a variety of stellar
photospheres. This research is supported in part by NASA Grant
NNX08AQ09G and NSF Grant AST-0907732.
Title: Accurate abundance patterns of solar twins and analogs. Does
the anomalous solar chemical composition come from planet formation?
Authors: Ramírez, I.; Meléndez, J.; Asplund, M.
Bibcode: 2009A&A...508L..17R
Altcode:
We derive the abundance of 19 elements in a sample of 64 stars with
fundamental parameters very similar to solar, which minimizes the
impact of systematic errors in our spectroscopic 1D-LTE differential
analysis, using high-resolution (R≃60 000), high signal-to-noise ratio
(S/N≃200) spectra. The estimated errors in the elemental abundances
relative to solar are as small as ≃0.025 dex. The abundance ratios
[X/Fe] as a function of [Fe/H] agree closely with previously established
patterns of Galactic thin-disk chemical evolution. Interestingly, the
majority of our stars show a significant correlation between [X/Fe]
and condensation temperature (T_C). In the sample of 22 stars with
parameters closest to solar, we find that, on average, low TC
elements are depleted with respect to high TC elements in
the solar twins relative to the Sun by about 0.08 dex (≃20%). An
increasing trend is observed for the abundances as a function of
TC for 900<T_C<1800 K, while abundances of lower
TC elements appear to be roughly constant. We speculate that
this is a signature of the planet formation that occurred around the Sun
but not in the majority of solar twins. If this hypothesis is correct,
stars with planetary systems like ours, although rare (frequency of
≃15%), may be identified through a very detailed inspection of the
chemical compositions of their host stars. Figure 1 and Tables
1-4 are only available in electronic form at http://www.aanda.org
Title: Oxygen lines in solar granulation. II. Centre-to-limb
variation, NLTE line formation, blends, and the solar oxygen abundance
Authors: Pereira, T. M. D.; Asplund, M.; Kiselman, D.
Bibcode: 2009A&A...508.1403P
Altcode: 2009arXiv0909.2310P
Context: There is a lively debate about the solar oxygen abundance and
the role of 3D models in its recent downward revision. These models
have been tested using high-resolution solar atlases of flux and
disk-centre intensity. Further testing can be done using centre-to-limb
variations.
Aims: Using high-resolution and high S/N observations
of neutral oxygen lines across the solar surface, we seek to test
that the 3D and 1D models reproduce their observed centre-to-limb
variation. In particular we seek to assess whether the latest generation
of 3D hydrodynamical solar model atmospheres and NLTE line formation
calculations are appropriate to derive the solar oxygen abundance.
Methods: We use our recent observations of O i 777 nm, O i 615.81 nm,
[O i] 630.03 nm, and nine lines of other elements for five viewing
angles 0.2≤μ≤ 1 of the quiet solar disk. We compared them with
the predicted line profiles from the 3D and 1D models computed with
the most up-to-date line formation codes and line data and allowing
for departures of LTE. The centre-to-limb variation of the O i 777 nm
lines is also used to obtain an empirical correction for the poorly
known efficiency of the inelastic collisions with H i.
Results:
The 3D model generally reproduces the centre-to-limb observations of
the lines very well, particularly the oxygen lines. From the O i 777 nm
lines we find that the classical Drawin recipe slightly overestimates
H i collisions (S_H≈ 0.85 agrees best with the observations). The
limb observations of the O i 615.82 nm line allow us to identify a
previously unknown contribution of molecules for this line, prevalent
at the solar limb. A detailed treatment of the [O i] 630.03 nm line
that includes the recent nickel abundance shows that the 3D modelling
closely agrees with the observations. The derived oxygen abundances
with the 3D model are 8.68 (777 nm lines), 8.66 (630.03 nm line), and
8.62 (615.82 nm line).
Conclusions: These additional tests have
reinforced the trustworthiness of the 3D model and line formation for
abundance analyses. SST spectra are available in electronic form
at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)
or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/508/1403
Title: Solar Surface Convection
Authors: Nordlund, Åke; Stein, Robert F.; Asplund, Martin
Bibcode: 2009LRSP....6....2N
Altcode:
We review the properties of solar convection that are directly
observable at the solar surface, and discuss the relevant underlying
physics, concentrating mostly on a range of depths from the temperature
minimum down to about 20 Mm below the visible solar surface.
Title: Does the anomalous solar chemical composition come from
planet formation?
Authors: Ramirez, I.; Melendez, J.; Asplund, M.
Bibcode: 2009arXiv0911.1893R
Altcode:
We derive the abundance of 19 elements in a sample of 64 stars with
fundamental parameters very similar to solar, which minimizes the impact
of systematic errors in our spectroscopic 1D-LTE differential analysis,
using high-resolution (R=60,000), high signal-to-noise ratio (S/N=200)
spectra. The estimated errors in the elemental abundances relative
to solar are as small as 0.025 dex. The abundance ratios [X/Fe] as a
function of [Fe/H] agree closely with previously established patterns
of Galactic thin-disk chemical evolution. Interestingly, the majority of
our stars show a significant correlation between [X/Fe] and condensation
temperature (Tc). In the sample of 22 stars with parameters closest
to solar, we find that, on average, low Tc elements are depleted with
respect to high Tc elements in the solar twins relative to the Sun by
about 0.08 dex (20%). An increasing trend is observed for the abundances
as a function of Tc for 900<Tc<1800 K, while abundances of lower
Tc elements appear to be roughly constant. We speculate that this is a
signature of the planet formation that occurred around the Sun but not
in the majority of solar twins. If this hypothesis is correct, stars
with planetary systems like ours, although rare (frequency of 15%),
may be identified through a very detailed inspection of the chemical
compositions of their host stars.
Title: Oxygen lines in solar granulation. I. Testing 3D models
against new observations with high spatial and spectral resolution
Authors: Pereira, T. M. D.; Kiselman, D.; Asplund, M.
Bibcode: 2009A&A...507..417P
Altcode: 2009arXiv0909.2307P
Aims: We seek to provide additional tests of the line formation of
theoretical 3D solar photosphere models. In particular, we set out
to test the spatially-resolved line formation at several viewing
angles, from the solar disk-centre to the limb and focusing on atomic
oxygen lines. The purpose of these tests is to provide additional
information on whether the 3D model is suitable to derive the solar
oxygen abundance. We also aim to empirically constrain the NLTE
recipes for neutral hydrogen collisions, using the spatially-resolved
observations of the O i 777 nm lines.
Methods: Using the Swedish
1-m Solar Telescope we obtained high-spatial-resolution observations of
five atomic oxygen lines (as well as several lines for other species,
mainly Fe i) for five positions on the solar disk. These observations
have a high spatial (sub-arcsecond) and spectral resolution, and
a continuum intensity contrast up to 9% at 615 nm. The theoretical
line profiles were computed using the 3D model, with a full 3D NLTE
treatment for oxygen and LTE for the other lines.
Results:
At disk-centre we find an excellent agreement between predicted
and observed line shifts, strengths, FWHM and asymmetries. At other
viewing angles the agreement is also good, but the smaller continuum
intensity contrast makes a quantitative comparison harder. We use the
disk-centre observations we constrain SH, the scaling factor
for the efficiency of collisions with neutral hydrogen. We find that
SH=1 provides the best match to the observations, although
this method is not as robust as the centre-to-limb line variations to
constrain SH.
Conclusions: Overall there is a very
good agreement between predicted and observed line properties over
the solar granulation. This further reinforces the view that the 3D
model is realistic and a reliable tool to derive the solar oxygen
abundance. 2D spectrograms are available in electronic form at
the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or
via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/507/417
Title: New Solar Composition: The Problem with Solar Models Revisited
Authors: Serenelli, Aldo M.; Basu, Sarbani; Ferguson, Jason W.;
Asplund, Martin
Bibcode: 2009ApJ...705L.123S
Altcode: 2009arXiv0909.2668S
We construct updated solar models with different sets of solar
abundances, including the most recent determinations by Asplund et
al. The latter work predicts a larger (~10%) solar metallicity compared
to previous measurements by the same authors but significantly lower
(~25%) than the recommended value from a decade ago by Grevesse &
Sauval. We compare the results of our models with determinations of the
solar structure inferred through helioseismology measurements. The
model that uses the most recent solar abundance determinations
predicts the base of the solar convective envelope to be located
at R CZ = 0.724 R sun and a surface helium
mass fraction of Y surf = 0.231. These results are in
conflict with helioseismology data (R CZ = 0.713 ± 0.001
R sun and Y surf = 0.2485 ± 0.0035) at 5σ and
11σ levels, respectively. Using the new solar abundances, we calculate
the magnitude by which radiative opacities should be modified in order
to restore agreement with helioseismology. We find that a maximum
change of ~15% at the base of the convective zone is required with a
smooth decrease toward the core, where the change needed is ~5%. The
required change at the base of the convective envelope is about half
the value estimated previously. We also present the solar neutrino
fluxes predicted by the new models. The most important changes brought
about by the new solar abundances are the increase by ~10% in the
predicted 13N and 15O fluxes that arise mostly
due to the increase in the C and N abundances in the newly determined
solar composition.
Title: VizieR Online Data Catalog: Oxygen lines in solar
granulation. II. (Pereira+, 2009)
Authors: Pereira, T. M. D.; Asplund, M.; Kiselman, D.
Bibcode: 2009yCat..35081403P
Altcode:
We obtained solar observations of several lines at several positions
of the solar disk. Data were obtained in May 2007 with the TRIPPEL
spectrograph at the Swedish 1-m Solar Telescope (SST). The spectra
were obtained for three distinct wavelength windows at ~615, 630 and
777nm. Each window covers approx. 1nm. Here we provide the spatially and
temporally averaged spectra. Each spectrum was the average of 50 frames
(mu=1.0) or 25 frames (other positions). The frames were selected by
the highest continuum contrast, and thus are not regularly spaced in
time between the start and end Julian dates. The observations are
given for five positions in the solar disk, ordered by mu, the cosine
of the heliocentric angle. The objective was to study the centre-to-limb
variation of the lines. Active sun regions were avoided. Important
note: the wavelength scales have NOT been corrected for solar rotation
or gravitational redshift. (4 data files).
Title: The Peculiar Solar Composition and Its Possible Relation to
Planet Formation
Authors: Meléndez, J.; Asplund, M.; Gustafsson, B.; Yong, D.
Bibcode: 2009ApJ...704L..66M
Altcode: 2009arXiv0909.2299M
We have conducted a differential elemental abundance analysis of
unprecedented accuracy (~0.01 dex) of the Sun relative to 11 solar twins
from the Hipparcos catalog and 10 solar analogs from planet searches. We
find that the Sun shows a characteristic signature with a ≈20%
depletion of refractory elements relative to the volatile elements in
comparison with the solar twins. The abundance differences correlate
strongly with the condensation temperatures of the elements. This
peculiarity also holds in comparisons with solar analogs known to have
close-in giant planets while the majority of solar analogs found not
to have such giant planets in radial velocity monitoring show the solar
abundance pattern. We discuss various explanations for this peculiarity,
including the possibility that the differences in abundance patterns
are related to the formation of planetary systems like our own, in
particular to the existence of terrestrial planets.
Title: VizieR Online Data Catalog: Equivalent widths of Li, Na, Fe,
Ca in NGC 6397 (Lind+, 2009)
Authors: Lind, K.; Primas, F.; Charbonnel, C.; Grundahl, F.;
Asplund, M.
Bibcode: 2009yCat..35030545L
Altcode:
The tables contain coordinates, photometry, derived stellar parameters,
equivalent widths, and abundances for a large number of dwarfs,
subgiant branch stars, and red giant branch stars in the metal-poor
globular cluster NGC6397. All abundances are given in logarithmic units
relative to hydrogen, according to A(x)=log(N(x)/N(H))+12, where N(x)
is the number density of element x and N(H) the number density of
hydrogen. Table 3 contains only a subset (32) of all targets. The
oscillator strengths adopted are listed in the paper. (3 data
files).
Title: The Barium Isotopic Abundance in the Metal-Poor Star HD140283
Authors: Collet, R.; Asplund, M.; Nissen, P. E.
Bibcode: 2009PASA...26..330C
Altcode: 2008arXiv0811.4586C
We derive the mixture of odd to even barium isotopes in the atmosphere
of the metal-poor subgiant HD140283 from the analysis of the Ba
ii transition at 4554 Å in a high-resolution high signal-to-noise
spectrum of the star. The detailed shape of this spectral line depends
on the relative contributions of odd and even isotopes via isotopic
and hyperfine splitting. We measure the fractional abundance of odd Ba
isotopes by modelling the formation of the Ba ii 4554-Å line profile
with the use of both a classical 1D hydrostatic and a 3D hydrodynamical
model atmosphere of HD140283. We interpret the results in terms of
contributions by the slow (s) and rapid (r) neutron-capture processes
to the isotopic mix. While the result of the 1D analysis of the Ba
ii feature indicates a 64 +/- 36% contribution of the r-process to
the isotopic mix, the 3D analysis points toward a mere 15 +/- 34%
contribution from this process, that is consistent with a solar-like
mixture of barium isotopes.
Title: Testing 3D solar models against observations
Authors: Pereira, Tiago M. D.; Asplund, Martin; Kiselman, Dan
Bibcode: 2009arXiv0909.4121P
Altcode:
We present results from a series of observational tests to 3D and 1D
solar models. In particular, emphasis is given to the line formation
of atomic oxygen lines, used to derive the much debated solar oxygen
photospheric abundance. Using high-quality observations obtained
with the Swedish Solar Telescope (SST) we study the centre-to-limb
variation of the O I lines, testing the models and line formation
(LTE and non-LTE). For the O I 777 nm triplet, the centre-to-limb
variation sets strong constraints in the non-LTE line formation, and
is used to derive an empirical correction factor (S_H) to the classical
Drawin recipe for neutral hydrogen collisions. Taking advantage of the
spatially-resolved character of the SST data, an additional framework
for testing the 3D model and line formation is also studied. From
the tests we confirm that the employed 3D model is realistic and its
predictions agree very well with the observations.
Title: VizieR Online Data Catalog: Oxygen lines in solar
granulation. I. (Pereira+, 2009)
Authors: Pereira, T. M. D.; Kiselman, D.; Asplund, M.
Bibcode: 2009yCat..35070417P
Altcode:
We obtained solar observations of several lines at several positions
of the solar disk. Data were obtained in May 2007 with the TRIPPEL
spectrograph at the Swedish 1-m Solar Telescope (SST). The spectra were
obtained for three distinct wavelength windows at approx 615, 630 and
777nm. Each window covers ~1nm. The spectra are spatially-resolved
in the solar surface, hence are given as 2D spectrograms. One axis
covers the wavelength and the other spatial position. The
observations are given for five positions in the solar disk, ordered
by mu, the cosine of the heliocentric angle. The objective was to
study the centre-to-limb variation of the lines. Active sun regions
were avoided. In total 150 spectrograms are given for each wavelength
window: 50 for the solar disk-centre (mu=1) and 25 for the other four
positions (mu=0.8, 0.6, 0.4, 0.2). The images were selected by continuum
contrast, hence their observed times are not the same for the three
windows. The spectrograms are given as FITS files. Each file
has two Header/Data Units (HDU). The first HDU contains the reduced
spectrogram, a 2D array. The first dimension of the array contains
(FITS NAXIS1) corresponds to wavelength, and the second (FITS NAXIS2)
to spatial coordinate. The second HDU contains the continuum levels
obtained for each spatial point (1D array, length equal to the number
of spatial points in the spectrogram). To obtain the normalized reduced
spectrogram one has to divide each spectrum in the spectrogram by the
corresponding continuum level. The spectrograms have been corrected
for stray light and to minimize noise a Fourier filter has been applied
(details in the paper). Important note: the wavelength scales have
NOT been corrected for solar rotation or gravitational redshift. (3 data files).
Title: The Chemical Composition of the Sun
Authors: Asplund, Martin; Grevesse, Nicolas; Sauval, A. Jacques;
Scott, Pat
Bibcode: 2009ARA&A..47..481A
Altcode: 2009arXiv0909.0948A
The solar chemical composition is an important ingredient in our
understanding of the formation, structure, and evolution of both the
Sun and our Solar System. Furthermore, it is an essential reference
standard against which the elemental contents of other astronomical
objects are compared. In this review, we evaluate the current
understanding of the solar photospheric composition. In particular,
we present a redetermination of the abundances of nearly all available
elements, using a realistic new three-dimensional (3D), time-dependent
hydrodynamical model of the solar atmosphere. We have carefully
considered the atomic input data and selection of spectral lines, and
accounted for departures from local thermodynamic equilibrium (LTE)
whenever possible. The end result is a comprehensive and homogeneous
compilation of the solar elemental abundances. Particularly noteworthy
findings are significantly lower abundances of C, N, O, and Ne compared
to the widely used values of a decade ago. The new solar chemical
composition is supported by a high degree of internal consistency
between available abundance indicators, and by agreement with
values obtained in the Solar Neighborhood and from the most pristine
meteorites. There is, however, a stark conflict with standard models
of the solar interior according to helioseismology, a discrepancy that
has yet to find a satisfactory resolution.
Title: Signatures of intrinsic Li depletion and Li-Na anti-correlation
in the metal-poor globular cluster NGC 6397
Authors: Lind, K.; Primas, F.; Charbonnel, C.; Grundahl, F.;
Asplund, M.
Bibcode: 2009A&A...503..545L
Altcode: 2009arXiv0906.2876L
Context: To alleviate the discrepancy between the prediction of
the primordial lithium abundance in the universe and the abundances
observed in Pop II dwarfs and subgiant stars, it has been suggested
that the stars observable today have undergone photospheric depletion
of lithium.
Aims: To identify the cause of this depletion,
it is important to accurately establish the behaviour of lithium
abundance with effective temperature and evolutionary phase. Stars in
globular clusters are ideal objects for such an abundance analysis,
because relative stellar parameters can be determined precisely.
Methods: We conducted a homogeneous analysis of a very large sample
of stars in the metal-poor globular cluster NGC 6397, covering all
evolutionary phases from below the main sequence turn-off to high up
on the red giant branch. Non-LTE Li abundances or abundance upper
limits were obtained for all stars, and for a sizeable subset of
the targets sodium abundances were also obtained. The Na abundances
were used to distinguish stars formed out of pristine material from
stars formed out of material affected by pollution from a previous
generation of more massive stars.
Results: The dwarf, turn-off,
and early subgiant stars in our sample form a thin abundance plateau,
disrupted in the middle of the subgiant branch by the Li dilution caused
by the first dredge-up. A second steep abundance drop is seen at the
luminosity of the red giant branch bump. The turn-off stars are more
Li-poor, by up to 0.1 dex, than subgiants that have not yet undergone
dredge-up. In addition, hotter dwarfs are slightly more Li-poor than
cooler dwarfs, which may be a signature of the so-called Li dip in
the cluster, commonly seen among Pop I stars. The feature is however
weak. A considerably wide spread in Na abundance confirms that NGC 6397
has suffered from intracluster pollution in its infancy and a limited
number of Na-enhanced and Li-deficient stars strongly contribute to
forming a significant anti-correlation between the abundances of Na
and Li. It is nevertheless seen that Li abundances are unaffected
by relatively high degrees of pollution. Lithium abundance trends
with effective temperature and stellar luminosity are compared to
predictions from stellar structure models including atomic diffusion
and ad-hoc turbulence below the convection zone. We confirm previous
findings that some turbulence, with strict limits to its efficiency,
is necessary for explaining the observations. Based on data
collected at European Southern Observatory (ESO), Paranal, Chile,
under program IDs 077.A-0018(A) and 281.D-5028(A), as well as data
collected with the Danish 1.54 m at European Southern Observatory
(ESO), La Silla. Full Tables 2-4 are only available in electronic form
at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)
or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/503/545
Title: Subaru High-Resolution Spectroscopy of Star G in the Tycho
Supernova Remnant
Authors: Kerzendorf, Wolfgang E.; Schmidt, Brian P.; Asplund, M.;
Nomoto, Ken'ichi; Podsiadlowski, Ph.; Frebel, Anna; Fesen, Robert A.;
Yong, David
Bibcode: 2009ApJ...701.1665K
Altcode: 2009arXiv0906.0982K
It is widely believed that Type Ia supernovae (SNe Ia) originate in
binary systems where a white dwarf accretes material from a companion
star until its mass approaches the Chandrasekhar mass and carbon is
ignited in the white dwarf's core. This scenario predicts that the
donor star should survive the supernova (SNe) explosion, providing
an opportunity to understand the progenitors of SNe Ia. In this
paper, we argue that rotation is a generic signature expected of
most nongiant donor stars that is easily measurable. Ruiz-Lapuente
et al. examined stars in the center of the remnant of SN 1572 (Tycho
SN) and showed evidence that a subgiant star (Star G by their naming
convention) near the remnant's center was the system's donor star. We
present high-resolution (R sime 40, 000) spectra taken with the High
Dispersion Spectrograph on Subaru of this candidate donor star and
measure the star's radial velocity as 79 ± 2 km s-1 with
respect to the local standard of rest and put an upper limit on the
star's rotation of 7.5 km s-1. In addition, by comparing
images that were taken in 1970 and 2004, we measure the proper motion
of Star G to be μ l = -1.6 ± 2.1 mas yr-1 and
μ b = -2.7 ± 1.6 mas yr-1. We demonstrate
that all of the measured properties of Star G presented in this
paper are consistent with those of a star in the direction of Tycho
SN that is not associated with the SN event. However, we discuss an
unlikely, but still viable scenario for Star G to be the donor star,
and suggest further observations that might be able to confirm or
refute it. Based in part on data collected at Subaru telescope,
which is operated by the National Astronomical Observatory of Japan.
Title: How Carbon Enhanced are Carbon-Enhanced Metal-Poor Stars?
Authors: Schuler, Simon C.; Asplund, Martin; Sivarani, Thirupathi;
Smith, Verne V.; Cunha, Katia; Beers, Timothy C.; Margheim, Steven J.
Bibcode: 2009noao.prop...99S
Altcode:
Carbon-Enhanced Metal-Poor (CEMP) stars make up a large fraction of
very metal-poor (VMP) stars in the Galactic halo, and they are proving
to be important to our understanding of a wide range of astrophysical
phenomena. Accurate abundance determinations of these stars are
needed to both fully delineate their formation and evolution, and to
firmly place them into a greater astrophysical context. Our group
has recently demonstrated that CEMP star C abundances derived from
the blue bands of CH and the C_2 Swan system, the principal features
used for this purpose, may be systematically overestimated at [Fe/H]
<=- 3.0. We have also shown that the (lambda) 8727 forbidden [C I]
line is an accurate abundance indicator for CEMP stars. Here we propose
an observational program to obtain Keck/HIRES spectra of six CEMP
stars, four of which have Fe abundances ranging from -4.0 <=[Fe/H]
<=-3.12, in order to derive accurate C abundances of the targets
from the [C I] line. With the proposed observations we will determine
if indeed molecular line-based C abundances of CEMP stars are too high
at very low metallicities and if so, provide empirically determined
corrections for those abundances.
Title: Departures from LTE for neutral Li in late-type stars
Authors: Lind, K.; Asplund, M.; Barklem, P. S.
Bibcode: 2009A&A...503..541L
Altcode: 2009arXiv0906.0899L
We perform non-LTE calculations of lithium in late-type stars for
a wide range of stellar parameters, including quantum mechanical
cross-sections for collisions with neutral hydrogen and the negative
hydrogen ion. Non-LTE abundance corrections for the lithium resonance
line at 670.7 nm and the subordinate line at 610.3 nm, are calculated
using 1D MARCS model atmospheres spanning a grid T_eff = [4000, 8000]
K, log g = [1.0, 5.0], and [Fe/H] = [0.0, -3.0], for lithium abundances
in the range A(Li) = [-0.3, 4.2]. The competing effects of ultraviolet
over-ionization and photon losses in the resonance line govern the
behaviour of the non-LTE effects with stellar parameters and lithium
abundance. The size and sign of the non-LTE abundance corrections
vary significantly over the grid for the 670.7 nm line, but are
typically positive and below 0.15 dex for the 610.3 nm, line. The new
collisional data play a significant role in determining the abundance
corrections. Complete Tables [see full textsee full textsee full
textsee full textsee full text] and [see full textsee full textsee
full textsee full textsee full text] are only available in electronic
form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)
or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/503/541
Title: Granulation in K-type dwarf stars. II. Hydrodynamic simulations
and 3D spectrum synthesis
Authors: Ramírez, I.; Allende Prieto, C.; Koesterke, L.; Lambert,
D. L.; Asplund, M.
Bibcode: 2009A&A...501.1087R
Altcode: 2009arXiv0905.3101R
Aims: To explore the impact of surface inhomogeneities on stellar
spectra, granulation models need to be computed. Ideally, the most
fundamental characteristics of these models should be carefully
tested before applying them to the study of more practical matters,
such as the derivation of photospheric abundances. Our goal is to
analyze the particular case of a K-dwarf.
Methods: We construct a
three-dimensional radiative-hydrodynamic model atmosphere of parameters
T_eff=4820 K, log g=4.5, and solar chemical composition. Using this
model and 3D spectrum synthesis, we computed a number of Fe i and Fe
ii line profiles. The observations presented in the first paper of this
series were used to test the model predictions. The effects of stellar
rotation and instrumental imperfections are carefully taken into account
in the synthesis of spectral lines.
Results: The theoretical
line profiles show the typical signatures of granulation: the lines
are asymmetric, with their bisectors having a characteristic C-shape
and their core wavelengths shifted with respect to their laboratory
values. The line bisectors span from about 10 to 250 m s-1,
depending on line strength, with the stronger features showing larger
span. The corresponding core wavelength shifts range from about -200 m
s-1 for the weak Fe i lines to almost +100 m s-1
in the strong Fe i features. Based on observational results for the Sun,
we argue that there should be no core wavelength shift for Fe i lines
of EW≳100 mÅ. The cores of the strongest lines show contributions
from the uncertain top layers of the model, where non-LTE effects
and the presence of the chromosphere, which are important in real
stars, are not accounted for. The Fe ii lines suffer from stronger
granulation effects due to their deeper formation depth which makes them
experience stronger temperature and velocity contrasts. For example,
the core wavelength shifts of the weakest Fe ii lines are about -600
m s-1. The comparison of model predictions to observed Fe
i line bisectors and core wavelength shifts for our reference star,
HIP 86 400, shows excellent agreement, with the exception of the core
wavelength shifts of the strongest features, for which we suspect
inaccurate theoretical values. Since this limitation does not affect
the predicted line equivalent widths significantly, we consider our
3D model validated for photospheric abundance work.
Title: Experimental and theoretical radiative decay rates for highly
excited ruthenium atomic levels and the solar abundance of ruthenium
Authors: Fivet, V.; Quinet, P.; Palmeri, P.; Biémont, É.; Asplund,
M.; Grevesse, N.; Sauval, A. J.; Engström, L.; Lundberg, H.; Hartman,
H.; Nilsson, H.
Bibcode: 2009MNRAS.396.2124F
Altcode: 2009MNRAS.tmp..738F
The solar photospheric abundance of ruthenium is revised on the basis
of a new set of oscillator strengths derived for RuI transitions with
wavelengths in the spectral range 2250-4710 Å. The new abundance value
(in the usual logarithmic scale where the solar hydrogen abundance
is equal to 12.00), ARu = 1.72 +/- 0.10, is in agreement
with the most recent meteoritic result, ARu = 1.76 +/-
0.03. The accuracy of the transition probabilities, obtained using a
relativistic Hartree-Fock model including core-polarization effects,
has been assessed by comparing the theoretical lifetimes with previous
experimental results. A comparison is also made with new measurements
performed in this work by the time-resolved laser-induced fluorescence
spectroscopy for 10 highly excited odd-parity levels of RuI.
Title: The C/O ratio at low metallicity: constraints on early chemical
evolution from observations of Galactic halo stars
Authors: Fabbian, D.; Nissen, P. E.; Asplund, M.; Pettini, M.;
Akerman, C.
Bibcode: 2009A&A...500.1143F
Altcode: 2008arXiv0810.0281F
Aims: We present new measurements of the abundances of carbon and
oxygen derived from high-excitation C i and O i absorption lines in
metal-poor halo stars, with the aim of clarifying the main sources
of these two elements in the early stages of the chemical enrichment
of the Galaxy.
Methods: We target 15 new stars compared to our
previous study, with an emphasis on additional C/O determinations
in the crucial metallicity range -3 ⪉ [Fe/H]⪉ -2. The stellar
effective temperatures were estimated from the profile of the Hβ
line. Departures from local thermodynamic equilibrium were accounted
for in the line formation for both carbon and oxygen. The non-LTE
effects are very strong at the lowest metallicities but, contrary
to what has sometimes been assumed in the past due to a simplified
assessment, of different degrees for the two elements. In addition,
for the 28 stars with [Fe/H] < -1 previously analysed, stellar
parameters were re-derived and non-LTE corrections applied in the same
fashion as for the rest of our sample, giving consistent abundances
for 43 halo stars in total.
Results: The new observations and
non-LTE calculations strengthen previous suggestions of an upturn in
C/O towards lower metallicity (particularly for [O/H] ⪉ -2). The
C/O values derived for these very metal-poor stars are, however,
sensitive to excitation via the still poorly quantified inelastic
H collisions. While these do not significantly affect the non-LTE
results for C i, they greatly modify the O i outcome. Adopting the
H collisional cross-sections estimated from the classical Drawin
formula leads to [C/O] ≈ 0 at [O/H] ≈ -3. To remove the upturn
in C/O, near-LTE formation for O i lines would be required, which
could only happen if the H collisional efficiency with the Drawin
recipe is underestimated by factors of up to several tens of times,
a possibility which we consider unlikely.
Conclusions: The high
C/O values derived at the lowest metallicities may be revealing the
fingerprints of Population III stars or may signal rotationally-aided
nucleosynthesis in more normal Population II stars. Based on data
collected with the European Southern Observatory's Very Large Telescope
(VLT) at the Paranal, Chile (programmes No. 67.D-0106 and 73.D-0024)
and with the Magellan Telescope at Las Campanas Observatory, Chile.
Title: On and Na abundance patterns in open clusters of the Galactic
disk
Authors: de Silva, G. M.; Gibson, B. K.; Lattanzio, J.; Asplund, M.
Bibcode: 2009A&A...500L..25D
Altcode: 2009arXiv0905.4354D
Aims: A global O-Na abundance anti-correlation is observed in globular
clusters, which is not present in the Galactic field population. Open
clusters are thought to be chemically homogeneous internally. We aim to
explore the O and Na abundance pattern among the open cluster population
of the Galactic disk.
Methods: We combine open cluster abundance
ratios of O and Na from high-resolution spectroscopic studies in the
literature and normalize them to a common solar scale. We compare
the open cluster abundances against the globular clusters and disk
field.
Results: We find that the different environments show
different abundance patterns. The open clusters do not show the
O-Na anti-correlation at the extreme O-depletion/Na-enhancement as
observed in globular clusters. Furthermore, the high Na abundances in
open clusters do not match the disk field stars. If real, it may be
suggesting that the dissolution of present-day open clusters is not a
significant contribution to building the Galactic disk. Large-scale
homogeneous studies of clusters and field will further confirm the
reality of the Na enhancement.
Title: Neutral oxygen spectral line formation revisited with new
collisional data: large departures from LTE at low metallicity
Authors: Fabbian, D.; Asplund, M.; Barklem, P. S.; Carlsson, M.;
Kiselman, D.
Bibcode: 2009A&A...500.1221F
Altcode: 2009arXiv0902.4472F
Aims: A detailed study is presented, including estimates of the
impact on elemental abundance analysis, of the non-local thermodynamic
equilibrium (non-LTE) formation of the high-excitation neutral oxygen
777 nm triplet in model atmospheres representative of stars with
spectral types F to K.
Methods: We have applied the statistical
equilibrium code MULTI to a number of plane-parallel MARCS atmospheric
models covering late-type stars (4500 ≤ T_eff ≤ 6500 K, 2 ≤ log
g ≤ 5 [cgs], and -3.5 ≤ [Fe/H] ≤ 0). The atomic model employed
includes, in particular, recent quantum-mechanical electron collision
data.
Results: We confirm that the O i triplet lines form under
non-LTE conditions in late-type stars, suffering negative abundance
corrections with respect to LTE. At solar metallicity, the non-LTE
effect, mainly attributed in previous studies to photon losses in the
triplet itself, is also driven by an additional significant contribution
from line opacity. At low metallicity, the very pronounced departures
from LTE are due to overpopulation of the lower level (3s ^5S^o) of the
transition. Large line opacity stems from triplet-quintet intersystem
electron collisions, a form of coupling previously not considered or
seriously underestimated. The non-LTE effects generally become severe
for models (both giants and dwarfs) with higher T_eff. Interestingly,
in metal-poor turn-off stars, the negative non-LTE abundance corrections
tend to rapidly become more severe towards lower metallicity. When
neglecting H collisions, they amount to as much as |Δlog ɛ_O|
~ 0.9 dex and ~1.2 dex, respectively at [Fe/H] = -3 and [Fe/H]
= -3.5. Even when such collisions are included, the LTE abundance
remains a serious overestimate, correspondingly by |Δlog ɛ_O| ~ 0.5
dex and ~0.9 dex at such low metallicities. Although the poorly known
inelastic hydrogen collisions thus remain an important uncertainty,
the large metallicity-dependent non-LTE effects seem to point to
a resulting “low” (compared to LTE) [O/Fe] in metal-poor halo
stars.
Conclusions: Our results may be important in solving
the long-standing [O/Fe] debate. When applying the derived non-LTE
corrections, the LTE oxygen abundance inferred from the 777 nm permitted
triplet will be decreased substantially at low metallicity. If the
classical Drawin formula is employed for O+H collisions, the derived
[O/Fe] trend becomes almost flat below [Fe/H] ~ -1, in better agreement
with recent literature estimates generally obtained from other oxygen
abundance indicators. A value of [O/Fe] ⪉ +0.5 may therefore be
appropriate, as suggested by standard theoretical models of type II
supernovae nucleosynthetic yields. If neglecting impacts with H atoms
instead, [O/Fe] decreases towards lower [Fe/H], which would open new
questions. Our tests using ATLAS model atmospheres show that, though
non-LTE corrections for metal-poor dwarfs are smaller (by ~0.2 dex
when adopting efficient H collisions) than in the MARCS case, our
main conclusions are preserved, and that the LTE approach tends to
seriously overestimate the O abundance at low metallicity. However,
in order to finally reach consistency between oxygen abundances from
the different available spectral features, it is of high priority to
reduce the large uncertainty regarding H collisions, to undertake a
full investigation of the interplay of non-LTE and 3D effects, and to
clarify the issue of the temperature scale at low metallicity.
Title: VizieR Online Data Catalog: Neutral Li in late-type stars
non-LTE calculations (Lind+, 2009)
Authors: Lind, K.; Asplund, M.; Barklem, P. S.
Bibcode: 2009yCat..35030541L
Altcode:
Non-LTE abundance corrections and equivalent widths for atmospheric
models in the stellar parameter range Teff=[4000,8000]K,
log(g)=[1.0,5.0], [Fe/H]=[0.0,-3.0], and microturbulence
[1.0,5.0]km/s. The lithium abundance ranges between A(Li)=[-0.3,4.2]. An
IDL-code for interpolation between table-values can be obtained on
request to klind(at)eso.org. (2 data files).
Title: Metal-poor Globular Clusters of the Galactic bulge
Authors: Barbuy, B.; Dias, B.; Alves-Brito, A.; Zoccali, M.; Minniti,
D.; Meléndez, J.; Asplund, M.; Ortolani, S.; Renzini, A.; Hill, V.;
Gómez, A.; Bica, E.
Bibcode: 2009RMxAC..35..150B
Altcode:
We are carrying studies on the metal-poor globular clusters of the
Galactic bulge. These objects appear to be very old, and might be
relics of the first objects in the Galaxy. High resolution observations
carried out with VLT-UVES, VLT-FLAMES and Gemini-PHOENIX are presented,
and the abundance pattern of these globulars is studied.
Title: Stellar abundances tracing the formation of the Galactic Bulge
Authors: Barbuy, Beatriz; Zoccali, Manuela; Ortolani, Sergio; Hill,
Vanessa; Renzini, Alvio; Meléndez, Jorge; Gómez, Anita; Asplund,
Martin; Minniti, Dante; Bica, Eduardo; Alves-Brito, Alan
Bibcode: 2009IAUS..254..153B
Altcode:
The metallicity distribution and abundance ratios of the Galactic
bulge are reviewed. Issues raised by different groups in recent
work, in particular the high metallicity end, a comparison between
the oxygen abundances derived from different indicators, the [OI]
630nm and IR OH lines, and the issue of measuring giants vs. dwarfs,
are discussed. Finally, abundances in bulge globular clusters are
briefly described.
Title: On the Solar Nickel and Oxygen Abundances
Authors: Scott, Pat; Asplund, Martin; Grevesse, Nicolas; Sauval,
A. Jacques
Bibcode: 2009ApJ...691L.119S
Altcode: 2008arXiv0811.0815S
Determinations of the solar oxygen content relying on the neutral
forbidden transition at 630 nm depend upon the nickel abundance,
due to a Ni I blend. Here, we rederive the solar nickel abundance,
using the same ab initio three-dimensional hydrodynamic model of the
solar photosphere employed in the recent revision of the abundances
of C, N, O, and other elements. Using 17 weak, unblended lines of
Ni I together with the most accurate atomic and observational data
available, we find log epsilonNi = 6.17 ± 0.02(statistical)
± 0.05(systematic), a downward shift of 0.06-0.08 dex relative to
previous abundances based on one-dimensional model atmospheres. We
investigate the implications of the new nickel abundance for studies of
the solar oxygen abundance based on the [O I] 630 nm line in the quiet
Sun. Furthermore, we demonstrate that the oxygen abundance implied
by the recent sunspot spectropolarimetric study of Centeno &
Socas-Navarro needs to be revised downward from log epsilonO
= 8.86 ± 0.07 to 8.71 ± 0.10. This revision is based on the new
nickel abundance, the application of the best available gf value for
the 630 nm forbidden oxygen line, and a more transparent treatment of
CO formation. Determinations of the solar oxygen content relying on
forbidden lines now appear to converge around log epsilonO
= 8.7.
Title: Commission 36: Theory of Stellar Atmospheres
Authors: Landstreet, John D.; Asplund, Martin; Spite, Monique;
Balachandran, Suchitra B.; Berdyugina, Svetlana V.; Hauschildt, Peter
H.; Ludwig, Hans G.; Mashonkina, Lyudmila I.; Nagendra, K. N.; Puls,
Joachim; Randich, M. Sofia; Tautvaisiene, Grazina
Bibcode: 2009IAUTA..27..222L
Altcode:
Commission 36 covers the whole field of the physics of stellar
atmospheres. The scientific activity in this large subject has been very
intense during the last triennium and led to the publication of a large
number of papers, which makes a complete report quite impractical. We
have therefore decided to keep the format of the preceding report:
first a list of areas of current research, then Web links for obtaining
further information.
Title: Carbon Abundances Of Three Cemp Stars From High-resolution
Gemini-s/bHROS Spectra Of The [c I] Forbidden Line
Authors: Schuler, Simon C.; Margheim, S. J.; Sivarani, T.; Asplund,
M.; Smith, V. V.; Cunha, K.; Beers, T. C.
Bibcode: 2009AAS...21340608S
Altcode: 2009BAAS...41..199S
We present the results from a LTE analysis of the [C I] Forbidden line
at 8727 angstroms in high-resolution Gemini-S/bHROS spectra of three
Carbon-Enhanced Metal-Poor (CEMP) stars. Carbon abundances of CEMP stars
are primarily derived from CH and C2 features, lines that are expected
to be highly sensitive to photospheric temperature inhomogeneities,
the so-called 3D effects. We find the [C/Fe] ratios based on the [C I]
abundances of the two most Fe-rich stars in our sample (HE 0506-1653:
[Fe/H] = -1.42 and HE 0054-2542: [Fe/H] = -2.66) to be in good agreement
with previously determined molecular line-based values. The [C/Fe]
ratio of the most Fe-poor star in our sample (HE 1005-1439: [Fe/H]
= -3.08), however, is 0.34 dex lower than the published molecular
line-based abundance. This result is in line with expectations
that 3D effects on the molecular lines become more severe toward
lower metallicities. We have carried out 3D LTE calculations for
[C I], and the resulting corrections for all three stars are found
to be modest, suggesting the discrepancy between the [C I] line and
molecular line-based abundances of HE 1005-1439 is due to more severe
3D effects on the molecular lines. S.C.S. is supported by the
NOAO Leo Goldberg Fellowship; NOAO is operated by the Association of
Universities for Research Astronomy (AURA), Inc., under cooperative
agreement with the National Science Foundation (NSF). V.V.S. and
K.C. gratefully acknowledge support from the NSF under grant AST
06-46790. T.C.B. and T.S. acknowledge partial support for this work
from the NSF under grants AST 04-06784, AST 07-07776, and PHY 02-16783;
Physics Frontier Center/Joint Institute for Nuclear Astrophysics (JINA).
Title: Granulation across the HR diagram
Authors: Ramírez, I.; Allende Prieto, C.; Lambert, D. L.; Koesterke,
L.; Asplund, M.
Bibcode: 2009MmSAI..80..618R
Altcode: 2009arXiv0908.4571R
We have obtained ultra-high quality spectra (R=180,000; S/N>300)
with unprecedented wavelength coverage (4400 to 7400 Å) for a
number of stars covering most of the HR diagram in order to test the
predictions of models of stellar surface convection. Line bisectors
and core wavelength shifts are both measured and modeled, allowing
us to validate and/or reveal the limitations of state-of-the-art
hydrodynamic model atmospheres of different stellar parameters. We
show the status of our project and preliminary results.
Title: Accounting for convective blue-shifts in the determination
of absolute stellar radial velocities.
Authors: Allende Prieto, C.; Koesterke, L.; Ramírez, I.; Ludwig,
H. -G.; Asplund, M.
Bibcode: 2009MmSAI..80..622A
Altcode: 2009arXiv0909.0470A
For late-type non-active stars, gravitational redshifts and convective
blueshifts are the main source of biases in the determination of
radial velocities. If ignored, these effects can introduce systematic
errors of the order of ∼ 0.5 km s-1. We demonstrate that
three-dimensional hydrodynamical simulations of solar surface convection
can be used to predict the convective blue-shifts of weak spectral
lines in solar-like stars to ∼ 0.070 km s-1. Using accurate
trigonometric parallaxes and stellar evolution models, the gravitational
redshifts can be constrained with a similar uncertainty, leading to
absolute radial velocities accurate to ∼ 0.1 km s-1.
Title: Abundance analysis of the halo giant HD 122563 with
three-dimensional model stellar atmospheres
Authors: Collet, R.; Nordlund, Å.; Asplund, M.; Hayek, W.;
Trampedach, R.
Bibcode: 2009MmSAI..80..719C
Altcode: 2009arXiv0909.0690C
We present a preliminary local thermodynamic equilibrium (LTE) abundance
analysis of the template halo red giant HD122563 based on a realistic,
three-dimensional (3D), time-dependent, hydrodynamical model atmosphere
of the very metal-poor star. We compare the results of the 3D analysis
with the abundances derived by means of a standard LTE analysis based
on a classical, 1D, hydrostatic model atmosphere of the star. Due to
the different upper photospheric temperature stratifications predicted
by 1D and 3D models, we find large, negative, 3D-1D LTE abundance
differences for low-excitation OH and Fe I lines. We also find trends
with lower excitation potential in the derived Fe LTE abundances
from Fe I lines, in both the 1D and 3D analyses. Such trends may be
attributed to the neglected departures from LTE in the spectral line
formation calculations.
Title: Testing 3D solar models against observations . Center-to-limb
variations of oxygen lines, spatially-resolved line formation and
probing for departures from LTE
Authors: Pereira, T. M. D.; Asplund, M.; Kiselman, D.
Bibcode: 2009MmSAI..80..650P
Altcode:
We present results from a series of observational tests to 3D and 1D
solar models. In particular, emphasis is given to the line formation
of atomic oxygen lines, used to derive the much debated solar oxygen
photospheric abundance. Using high-quality observations obtained
with the Swedish Solar Telescope (SST) we study the center-to-limb
variation of the O I lines, testing the models and line formation
(LTE and non-LTE). For the O I 777 nm triplet, the center-to-limb
variation sets strong constraints in the non-LTE line formation, and
is used to derive an empirical correction factor (SH) to
the classical Drawin recipe for neutral hydrogen collisions. Taking
advantage of the spatially-resolved character of the SST data, an
additional framework for testing the 3D model and line formation is
also studied. From the tests we confirm that the employed 3D model is
realistic and its predictions agree very well with the observations.
Title: Spectroscopic Properties of Granulation in K-type Dwarf Stars
Authors: Ramirez, Ivan; Allende Prieto, C.; Asplund, M.; Koesterke,
L.; Lambert, D. L.
Bibcode: 2009AAS...21340601R
Altcode: 2009BAAS...41..198R
The presence of surface convection in K-type dwarfs is revealed in very
high quality spectra of nine bright stars. The observed asymmetries and
wavelength shifts of the Fe I absorption line profiles are mainly due
to granulation. The bisectors of the strongest Fe I lines have a span
of about 100 m/s and the central wavelengths of the weakest Fe I lines
are shifted by up to -200 m/s. The blueshifts decrease for stronger Fe
I lines, but they become independent of line strength for equivalent
widths larger than about 100 mA. The detection of this "plateau"
in the velocity shifts of the strongest Fe I lines is necessary to
remove the non-negligible uncertainty introduced by granulation in the
determination of absolute radial velocities. Line profiles computed
using a 3D model atmosphere accurately reproduce the observations, with
statistical tests showing an agreement at the 95 % confidence level,
which validates the 3D model for spectroscopic studies of abundances
and fundamental parameters of K-dwarfs. We find that 3D effects reduce
the difference in the iron abundance determined separately from Fe II
and Fe I lines, which is about 0.15 dex for 1D models, by two thirds,
thus alleviating significantly the iron ionization imbalance problem in
K-dwarfs. However, the 3D iron abundances from Fe I lines show a small
dependence with excitation potential, similar to the 1D case, possibly
due to non-LTE effects that have not been taken into account. We also
find that the 3D correction to the effective temperatures of solar
metallicity K-dwarfs derived with the infrared flux method is about +30
K. Finally, we show that the 3D spectrum synthesis of molecular bands
greatly improves the agreement with the observational data compared
to the 1D analysis, which overestimates the abundances derived from
molecular features by a factor of 2.
Title: Commission 12: Solar Radiation and Structure
Authors: Martínez Pillet, Valentin; Kosovichev, Alexander;
Mariska, John T.; Bogdan, Thomas J.; Asplund, Martin; Cauzzi, Gianna;
Christensen-Dalsgaard, Jørgen; Cram, Lawrence E.; Gan, Weiqun; Gizon,
Laurent; Heinzl, Petr; Rovira, Marta G.; Venkatakrishnan, P.
Bibcode: 2009IAUTA..27..104M
Altcode:
Commission 12 encompasses investigations on the internal structure
and dynamics of the Sun, mostly accessible through the techniques of
local and global helioseismology, the quiet solar atmosphere, solar
radiation and its variability, and the nature of relatively stable
magnetic structures like sunspots, faculae and the magnetic network. A
revision of the progress made in these fields is presented. For some
specific topics, the review has counted with the help of experts
outside the Commission Organizing Committee that are leading and/or
have recently presented relevant works in the respective fields. In
this cases the contributor's name is given in parenthesis.
Title: Carbon Abundances of Three Carbon-Enhanced Metal-Poor Stars
from High-Resolution Gemini-S/bHROS Spectra of the λ8727 [C I] Line
Authors: Schuler, Simon C.; Margheim, Steven J.; Sivarani, Thirupathi;
Asplund, Martin; Smith, Verne V.; Cunha, Katia; Beers, Timothy C.
Bibcode: 2008AJ....136.2244S
Altcode: 2008arXiv0809.1377S
We present the results from an analysis of the λ8727 forbidden
[C I] line in high-resolution Gemini-S/bHROS spectra of three
Carbon-Enhanced Metal-Poor (CEMP) stars. Previous derivations of C
abundances in CEMP stars have primarily used the blue bands of CH
and the C2 Swan system, features which are suspected to be
sensitive to photospheric temperature inhomogeneities (the so-called
three-dimensional effects). We find the [C/Fe] ratios based on the [C I]
abundances of the two most Fe-rich stars in our sample (HE 0507-1653:
[Fe/H] = -1.42 and HE 0054-2542: [Fe/H] = -2.66) to be in good agreement
with previously determined values. For the most Fe-deficient star in
our sample (HE 1005-1439: [Fe/H] = -3.08), however, the [C/Fe] ratio is
found to be 0.34 dex lower than the published molecular-based value. We
have carried out three-dimensional local thermodynamic equilibrium (LTE)
calculations for [C I], and the resulting corrections are found to be
modest for all three stars, suggesting that the discrepancy between
the [C I] and molecular-based C abundances of HE 1005-1439 is due to
more severe three-dimensional effects on the molecular lines. Carbon
abundances are also derived from C I high-excitation lines and are found
to be 0.45-0.64 dex higher than the [C I]-based abundances. Previously
published non-LTE (NLTE) C I abundance corrections bring the [C I]
and C I abundances into better agreement; however, targeted NLTE
calculations for CEMP stars are clearly needed. We have also derived
the abundances of nitrogen, potassium, and iron for each star. The
Fe abundances agree well with previously derived values, and the K
abundances are similar to those of C-normal metal-poor stars. Nitrogen
abundances have been derived from resolved lines of the CN red system
assuming the C abundances derived from the [C I] feature. The abundances
are found to be approximately 0.44 dex larger than literature values,
which have been derived from CN blue bands near 3880 and 4215 Å. We
discuss evidence that suggests that analyses of the CN blue system
bands underestimate the N abundances of metal-poor giants.
Title: A new sample of extremely/ultra metal-poor stars
Authors: García Pérez, A. E.; Christlieb, N.; Ryan, S. G.; Beers,
T. C.; Aoki, W.; Asplund, M.; Barklem, P. S.; Bessell, M. S.; Eriksson,
K.; Frebel, A.; Gustafsson, B.; Korn, A. J.; Nordström, B.; Norris,
J. E.
Bibcode: 2008PhST..133a4036G
Altcode:
A sample of 30 very metal-poor stars from the Hamburg-European
Southern Observatory (ESO) objective-prism survey have been observed
at high spectral resolution at the Very Large Telescope (VLT) using the
Ultraviolet and Visual Echelle Spectrograph (UVES). Two of the observed
stars are very interesting not only because of their very low iron
content, approximately four orders of magnitude lower than the solar
value, but also because we detected the neutral lithium resonance line
at 670.8 nm. Hydrogen lines suggest that the two observed stars have
effective temperatures around 6000 6250 K and according to isochrones,
they are either on the main sequence or on the subgiant branch, in
which case they would probably be the most metal-poor dwarfs or warm
subgiants with lithium detections known. These detections would allow
to determine more accurately the slope of the trend of the lithium
abundance with [Fe/H] than was possible with samples of unevolved
stars restricted to higher metallicities.
Title: Abundances in the Galactic bulge
Authors: Barbuy, B.; Alves-Brito, A.; Ortolani, S.; Zoccali, M.;
Hill, V.; Meléndez, J.; Asplund, M.; Bica, E.; Renzini, A.; Gómez,
A.; Minniti, D.
Bibcode: 2008PhST..133a4032B
Altcode:
The metallicity distribution and abundance ratios of the Galactic bulge
are reviewed. Issues raised by recent work of different groups, in
particular the high metallicity end, the overabundance of α-elements in
the bulge relative to the thick disc and the measurement of giants
versus dwarfs, are discussed. Abundances in the old moderately
metal-poor bulge globular clusters are described.
Title: Another forbidden solar oxygen abundance: the [O I] 5577
Å line
Authors: Meléndez, J.; Asplund, M.
Bibcode: 2008A&A...490..817M
Altcode: 2008arXiv0808.2796M
Context: Recent works with improved model atmospheres, line formation,
atomic and molecular data, and detailed treatment of blends have
resulted in a significant downward revision of the solar oxygen
abundance.
Aims: Considering the importance of the Sun as an
astrophysical standard and the current conflict of standard solar models
using the new solar abundances with helioseismological observations we
have performed a new study of the solar oxygen abundance based on the
forbidden [O I] line at 5577.34 Å, not previously considered.
Methods: High-resolution (R > 500 000), high signal-to-noise
(S/N > 1000) solar spectra of the [O I] 5577.34 Å line have been
analyzed employing both three-dimensional (3D) and a variety of 1D
(spatially and temporally averaged 3D, Holweger & Müller, MARCS
and Kurucz models with and without convective overshooting) model
atmospheres.
Results: The oxygen abundance obtained from the
[O I] 5577.3 Å forbidden line is almost insensitive to the input
model atmosphere and has a mean value of log ɛO = 8.71
± 0.02 (σ from using the different model atmospheres). The total
error (0.07 dex) is dominated by uncertainties in the log gf value
(0.03 dex), apparent line variation (0.04 dex) and uncertainties in
the continuum and line positions (0.05 dex).
Conclusions: The
oxygen abundance derived here is close to the 3D-based estimates from
the two other [O I] lines at 6300 and 6363 Å, the permitted O I lines
and vibrational and rotational OH transitions in the infrared. Our
study thus supports a low solar oxygen abundance (log ɛO
≈ 8.7), independent of the adopted model atmosphere.
Title: PREFACE: A Stellar Journey A Stellar Journey
Authors: Asplund, M.
Bibcode: 2008PhST..133a1002A
Altcode:
The conference A Stellar Journey was held in Uppsala, Sweden, 23 27June
2008, in honour of Professor Bengt Gustafsson's 65th birthday. The
choice of Uppsala as the location for this event was obvious given
Bengt's long-standing association with the city stemming back to
his school days. With the exception of a two-year postdoc stint in
Copenhagen, five years as professor at Stockholm University and two
years as director of the Sigtuna foundation, Bengt has forged his
illustrious professional career at Uppsala University. The symposium
venue was Museum Gustavianum, once the main building of the oldest
university in Scandinavia. The title of the symposium is a
paraphrasing of Bengt's popular astronomy book Kosmisk Resa (in
English: Cosmic Journey) written in the early eighties. I think this
aptly symbolizes his career that has been an astronomical voyage
from near to far, from the distant past to the present. The original
book title was modified slightly to reflect that most of his work
to date has dealt with stars in one way or another. In addition
it also gives credit to Bengt's important role as a guiding light
for a very large number of students, colleagues and collaborators,
indeed for several generations of astronomers. For me personally,
the book Kosmisk Resa bears particular significance as it has shaped
my life rather profoundly. Although I had already decided to become
an astronomer, when I first read the book as a 14-year-old I made up
my mind then and there that I would study under Bengt Gustafsson and
work on stars. Indeed I have remained true to this somewhat audacious
resolution. I suspect that a great number of us have similar stories
how Bengt has had a major influence on our lives, whether on the
professional or personal level. Perhaps Bengt's most outstanding
characteristic is his enthralling enthusiasm. This is equally true
whether he is pondering some scientific conundrum, supervising students
or performing in front of an audience, be it an astronomical talk,
student lecture, musical concert or theatre play. Another attribute of
Bengt is his boundless optimism, which not the least has helped many
of his students overcome the unavoidable moments of despair (this
is only true as long as one is aware of the well-known BG factor:
multiply any of Bengt's estimates for the time required to complete a
task by at least a factor of three). His personal traits make working
with Bengt always very enjoyable as well as highly educating. Bengt's
work also extends well beyond the domain of astronomy, including
music, literature, theatre, religion, research ethics, science
policy and science popularization. Bengt is an excellent role model
for a successful scientist with a rich and rewarding life outside of
academia. The symposium A Stellar Journey was divided into five
sessions covering basically the main research areas Bengt has worked on:
Stellar atmospheres, Solar/stellar spectroscopy, Stellar parameters,
Stellar evolution and nucleosynthesis and Stellar populations. In
addition, one afternoon was devoted to a session entitled Anything
but astronomy (see the symposium program), which tried to showcase
Bengt's diverse interests outside of astronomy with talks ranging
from religion and history of science over science popularization
and future studies to literature and music. My task, as chair
of the Scientific Organizing Committee, to put together an exciting
scientific program of invited reviews and talks was made considerably
easier thanks to the excellent suggestions by the other SOC members:
Ann Boesgaard, Sofia Feltzing, John Lattanzio, Andre Maeder, Bertrand
Plez and Monique Spite. I believe in the end we were successful in
achieving our charge, an impression corroborated by the many encouraging
comments from various participants during and after the conference. I am
particularly grateful to Nils Bergvall, Bengt Edvardsson and Bertrand
Plez for their time-consuming efforts in arranging the extraordinary
and greatly appreciated non-astronomical session on Tuesday afternoon;
Sigbritt Ernald provided a rich source of suggestions for suitable
interesting persons to invite for the stimulating and highly enjoyable
oral and musical presentations. While the responsibilities of
the SOC are quite pleasant and frankly not particularly demanding,
the heavy burden with organizing a conference falls squarely with
the Local Organizing Committee, which has to deal with a seemingly
never-ending stream of practicalities and more mundane chores. The main
reason the Stellar Journey conference was such an astounding success
and ran so smoothly is the tireless work by the whole LOC. All of us
owe a great deal of gratitude to Paul Barklem, Nils Bergvall, Norbert
Christlieb, Bengt Edvardsson (Chair), Kjell Eriksson, Ulrike Heiter,
Susanne Höfner, Andreas Korn, Nikolai Piskunov, Bertrand Plez and
Astrid Wachter for their extensive efforts. I'd like to also extend a
special acknowledgement to all of the Uppsala students who helped out
during the reception, registration and various sessions. Last but
not the least, I'd like to thank all of the conference participants for
giving such excellent talks and for providing stimulating discussions
throughout the week. It is telling that essentially everyone invited
to participate in the conference almost immediately accepted while
the very few who declined did so only reluctantly due to other prior
commitments. Bengt is a highly regarded colleague and friend, whom we
all wished to celebrate this special occasion with. This conference
represented merely one brief stop on a marvellous and truly stellar
journey. I dare say that without exception we are all deeply thankful
for having been able to join Bengt Gustafsson on at least some of his
many cosmic adventures during the past decades. We trust that this
exciting odyssey will continue for many years.
Title: Does the Sun have a subsolar metallicity?
Authors: Asplund, Martin
Bibcode: 2008IAUS..252...13A
Altcode:
The solar chemical composition has recently undergone a drastic
revision, in particular in terms of the C, N, O and Ne abundances that
have been lowered by almost a factor of two. In this invited review
I will describe the different compounding reasons for this change (3D
model atmospheres, non-LTE line formation, improved atomic/molecular
data) and discuss some astrophysical implications thereof, which
fall under both good (solar neighborhood) and bad (helioseismology)
news. The most recent literature regarding the solar O abundance is
surveyed and a critical evaluation whether or not these support the
low solar abundance scale is presented. Finally I venture to make some
predictions to what the real solar O abundance may be.
Title: Reality of Moving Groups in the Galaxy and Chemically Tagging
the Galactic Disk
Authors: de Silva, G. M.; Freeman, K. C.; Bland-Hawthorn, J.;
Asplund, M.
Bibcode: 2008ASPC..396...59D
Altcode:
The existence of old dispersed stellar groups within the Milky Way disk
is still controversial. Are they the debris of ancient star-forming
aggregates, or short-lived artifacts of dynamical origin? With detailed
elemental abundance measurements from high quality spectroscopic data,
we show that at least one such old dispersed stellar group is a true
relic of an earlier phase of star formation. The identification of
other such relic structures will provide essential information for
probing the evolutionary history of the Milky Way disk.
Title: Reality of Moving Groups in the Galaxy
Authors: De Silva, G. M.; Freeman, K. C.; Bland-Hawthorn, J.;
Asplund, M.
Bibcode: 2008arXiv0810.3346D
Altcode:
The existence of old dispersed stellar groups within the Milky Way disk
is still controversial. Are they the debris of ancient star-forming
aggregates, or short-lived artifacts of dynamical origin? With detailed
elemental abundance measurements from high quality spectroscopic data,
we show that at least one such old dispersed stellar group is a true
relic of an earlier phase of star formation. The identification of
other such relic structures will provide essential information for
probing the evolutionary history of the Milky Way disk.
Title: Nitrogen Abundances in Giant Stars of the Globular Cluster
NGC 6752
Authors: Yong, David; Grundahl, Frank; Johnson, Jennifer A.; Asplund,
Martin
Bibcode: 2008ApJ...684.1159Y
Altcode: 2008arXiv0806.0187Y
We present N abundances for 21 bright giants in the globular cluster NGC
6752 based on high-resolution UVES spectra of the 3360 Å NH lines. We
confirm that the Strömgren c1 index traces the N abundance
and find that the star-to-star N abundance variation is 1.95 dex, at the
sample's luminosity. We find statistically significant correlations,
but small-amplitude variations, between the abundances of N and α-,
Fe-peak, and s-process elements. Analyses using model atmospheres with
appropriate N, O, Na, and Al abundances would strengthen, rather than
mute, these correlations. If the small variations of heavy elements are
real, then the synthesis of the N anomalies must take place in stars
which also synthesize α-, Fe-peak, and s-process elements. These
correlations offer support for contributions from both asymptotic
giant branch and massive stars to the globular cluster abundance
anomalies. Based on observations made with ESO Telescopes at the
Paranal Observatories under program 65.L-0165(A).
Title: Signatures of Granulation in the Spectra of K-Dwarfs
Authors: Ramírez, I.; Allende Prieto, C.; Lambert, D. L.; Asplund, M.
Bibcode: 2008ASPC..393..255R
Altcode: 2007arXiv0712.0387R
Very high resolution (R>150,000) spectra of a small sample of
nearby K-dwarfs have been acquired to measure the line asymmetries
and central wavelength shifts caused by convective motions present
in stellar photospheres. This phenomenon of granulation is modeled
by 3D hydrodynamical simulations but they need to be confronted with
accurate observations to test their realism before they are used in
stellar abundance studies. We find that the line profiles computed
with a 3D model agree reasonably well with the observations. The line
bisectors and central wavelength shifts on K-dwarf spectra have a
maximum amplitude of only about 200 m s-1 and we have been
able to resolve these granulation effects with a very careful observing
strategy. By computing a number of iron lines with 1D and 3D models
(assuming local thermodynamic equilibrium), we find that the impact of
3D-LTE effects on classical iron abundance determinations is negligible.
Title: 18O and the Origins of HdC and R CrB Stars
Authors: Geballe, T. R.; Clayton, G. C.; Asplund, M.; Herwig, F.;
Fryer, C. L.
Bibcode: 2008ASPC..391...51G
Altcode:
We have detected enormously enhanced 18O and correspondingly
small values of 16O/18O in many hydrogen-deficient
carbon (HdC) stars and R Coronae Borealis (R CrB) stars. The similar
ratios suggest a common origin for the two types of stars. Of the two
leading candidates for the origin of R CrB stars, white dwarf mergers
and final helium flashes, the former appears more likely to produce
this and other observed isotopic anomalies.
Title: Chemical similarities between Galactic bulge and local thick
disk red giant stars
Authors: Meléndez, J.; Asplund, M.; Alves-Brito, A.; Cunha, K.;
Barbuy, B.; Bessell, M. S.; Chiappini, C.; Freeman, K. C.; Ramírez,
I.; Smith, V. V.; Yong, D.
Bibcode: 2008A&A...484L..21M
Altcode: 2008arXiv0804.4124M
Context: The evolution of the Milky Way bulge and its relationship with
the other Galactic populations is still poorly understood. The bulge
has been suggested to be either a merger-driven classical bulge or
the product of a dynamical instability of the inner disk.
Aims:
To probe the star formation history, the initial mass function and
stellar nucleosynthesis of the bulge, we performed an elemental
abundance analysis of bulge red giant stars. We also completed an
identical study of local thin disk, thick disk and halo giants to
establish the chemical differences and similarities between the various
populations.
Methods: High-resolution infrared spectra of 19 bulge
giants and 49 comparison giants in the solar neighborhood were acquired
with Gemini/Phoenix. All stars have similar stellar parameters but
cover a broad range in metallicity. A standard 1D local thermodynamic
equilibrium analysis yielded the abundances of C, N, O and Fe. A
homogeneous and differential analysis of the bulge, halo, thin disk and
thick disk stars ensured that systematic errors were minimized.
Results: We confirm the well-established differences for [O/Fe]
(at a given metallicity) between the local thin and thick disks. For
the elements investigated, we find no chemical distinction between
the bulge and the local thick disk, which is in contrast to previous
studies relying on literature values for disk dwarf stars in the solar
neighborhood.
Conclusions: Our findings suggest that the bulge
and local thick disk experienced similar, but not necessarily shared,
chemical evolution histories. We argue that their formation timescales,
star formation rates and initial mass functions were similar.
Title: Primordial and Pre-Galactic Origins of the Lithium Isotopes
Authors: Asplund, Martin; Meléndez, Jorge
Bibcode: 2008AIPC..990..342A
Altcode:
There are currently two cosmological lithium problems: compared with
predictions from Big Bang Nucleosynthesis and models for Galactic
cosmic ray production, the observed 7Li abundance in
Galactic halo stars is too low while the 6Li content is
too high. Here we report on new Keck/HIRES observations of the two
extremely metal-poor stars G064-012 and G064-37, which both show
distortions of the Li I 670.8 nm line consistent with a significant
(~3σ) presence of 6Li. If confirmed, these are the
lowest metallicity 6Li detections and would suggest a
cosmological or pre-Galactic origin for the isotope. Invoking stellar
Li depletion to solve the above-mentioned 7Li discrepancy
would further increase the inferred initial 6Li abundance
by a factor of ~10. Possible 6Li production scenarios
are decaying/annihilating supersymmetric particles within the first
few minutes of the Big Bang and cosmological cosmic rays from the
first stars, although stellar flare production can not be ruled out
either. Work still remains, however, before one can unequivocally
say that 6Li really has been detected in these and other
halo stars, in particular whether convective atmospheric motions and
non-LTE line formation can mimic the presence of 6Li in
the observed line profiles.
Title: A dedicated northern search for the first stars
Authors: Beers, Timothy; Norris, John; Allende Prieto, Carlos;
Aoki, Wako; Asplund, Martin; Bessell, Michael; Christlieb, Norbert;
Frebel, Anna; Johnson, Jennifer; Melendez, Jorge; Sneden, Christopher;
Yong, David
Bibcode: 2008noao.prop..179B
Altcode:
We propose to continue a northern sky program using high resolution,
moderate S/N spectra to discover the chemically oldest stars - ultra
metal-poor dwarfs and giants drawn from the Hamburg/ESO and SEGUE
surveys. With these data we seek to (1) discover more stars with [Fe/H]
< -4.0 (only three of which are known and all of which our group
has discovered) to constrain the nature of the first stars; (2) measure
the Li abundance for more stars with [Fe/H] < -4.0, to investigate
further the non-detection on this element in the subgiant HE1327-2326
([Fe/H] = -5.4) and its implication for Big Bang Nucleosynthesis;
and (3) discover further r-process enhanced metal-poor stars with
detectable Th and U, for cosmo-chronometric age determinations.
Title: Comparing 3D Solar Model Atmospheres with Observations:
Hydrogen Lines and Centre-to-limb Variations
Authors: Pereira, Tiago M. D.; Asplund, Martin; Trampedach, Regner
Bibcode: 2008psa..conf..313P
Altcode:
Three dimensional hydrodynamical stellar model atmospheres
represent a major step forward in stellar spectroscopy. Making use
of radiative-hydrodynamical convection simulations that contain no
adjustable free parameters, the model atmospheres provide a robust
and realistic treatment of convection. These models have been applied
to several lines in the Sun and other stars, yielding an excellent
agreement with observations (e.g., Asplund et al. (2000) [1]).
Title: [C/O] Observations in Low-[Fe/H] Halo Stars
Authors: Fabbian, D.; Nissen, P. E.; Asplund, M.; Akerman, C. J.;
Pettini, M.
Bibcode: 2008psa..conf...45F
Altcode:
We have observed 15 halo stars to determine the [C/O] behaviour at low
[Fe/H]. Making use of our recent non-LTE calculations, which show
that the high excitation C and O lines used in previous studies in
the literature are affected by very significant departures from LTE,
we aim to obtain accurate [C/O] ratios down to [Fe/H]∼ —3.2, which
will enable us to shed light on the possible presence of an upturn of
[C/O] at low metallicities.
Title: Beyond 1D: spectral line formation with 3D hydrodynamical
model atmospheres of red giants
Authors: Collet, R.; Asplund, M.; Trampedach, R.
Bibcode: 2008MmSAI..79..649C
Altcode: 2007arXiv0711.3186C
We present the results of realistic, 3D, hydrodynamical, simulations
of surface convection in red giant stars with varying effective
temperatures and metallicities. We use the convection simulations as
time-dependent, hydrodynamical, model atmospheres to compute spectral
line profiles for a number of ions and molecules under the assumption
of local thermodynamic equilibrium (LTE). We compare the results with
the predictions of line formation calculations based on 1D, hydrostatic,
model stellar atmospheres in order to estimate the impact of 3D models
on the derivation of elemental abundances. We find large negative
3D-1D LTE abundance corrections (typically -0.5 to -1 dex) for weak
low-excitation lines from molecules and neutral species in the very
low metallicity cases. Finally, we discuss the extent of departures
from LTE in the case of neutral iron spectral line formation.
Title: Sulphur Abundances in Metal-poor Stars
Authors: Nissen, P. E.; Akerman, C.; Asplund, M.; Fabbian, D.;
Pettini, M.
Bibcode: 2008psa..conf...51N
Altcode:
We report on sulphur abundances in halo stars as derived from near-IR
UVES spectra. The importance of removing telluric lines and residual
CCD fringing patterns by using early B-type stars as calibrators is
emphasized. Comparison of data from the weak λ8694.6 and the stronger
λ9212.9, 9237.5 pair of S I lines provides important constraints on
non-LTE effects. We do not confirm the high sulphur abundances reported
by others for some metal-poor stars; our results instead indicate that
sulphur behaves like other typical α-capture elements with a plateau at
[S/Fe] ∼ +0.3 dex in the Galactic halo.
Title: Lithium Isotopic Abundances in Stars
Authors: Nissen, Poul Erik; Asplund, Martin
Bibcode: 2008psa..conf....3N
Altcode:
The Li isotope ratio, 6Li/7Li, in stars can
be determined from the isotopic shift in the Li I 670.8 nm resonance
line. Because of the small effect this however requires truly precision
spectroscopy: spectral resolving power R ≥ 105 and S/N ≥
500. In this review we discuss the method and what one can learn from
Li isotopic abundances in terms of Big-Bang nucleosynthesis, cosmic
ray production of Li, stellar structure, and planet formation. Some
instrumental problems and the need for new instrumentation are briefly
discussed.
Title: Lithium Isotopic Abundances in the Early Galaxy
Authors: Asplund, M.
Bibcode: 2007ASPC..374..119A
Altcode:
The lithium isotopes are potent probes of cosmic, galactic and
stellar evolution. Herein I describe the challenging method used to
derive Li isotopic abundances in metal-poor halo stars and their
associated uncertainties. The results from our VLT-based program
using extraordinarily high-quality spectra points to two cosmological
Li problems: the observed ^7Li abundance is too low while the ^6Li
abundance is too large compared with standard models for Big Bang
nucleosynthesis and Galactic cosmic ray spallation.
Title: Commission 36: Theory of Stellar Atmospheres
Authors: Spite, Monique; Landstreet, John D.; Asplund, Martin; Ayres,
Thomas R.; Balachandran, Suchitra C.; Dravins, Dainis; Hauschildt,
Peter H.; Kiselman, Dan; Nagendra, K. N.; Sneden, Christopher;
Tautvaišiené, Grazina; Werner, Klaus
Bibcode: 2007IAUTB..26..160S
Altcode:
The business meeting of Commission 36 was held during the General
Assembly in Prague on 16 August. It was attended by about 15
members. The issues presented included a review of the work made
by members of Commission 36, and the election of the new Organising
Committee. We note that a comprehensive report on the activities of
the commission during the last triennium has been published in Reports
on Astronomy, Transactions IAU Volume XXVIA. The scientific activity
of the members of the commission has been very intense, and has led
to the publication of a large number of papers.
Title: Three-dimensional hydrodynamical simulations of surface
convection in red giant stars. Impact on spectral line formation
and abundance analysis
Authors: Collet, R.; Asplund, M.; Trampedach, R.
Bibcode: 2007A&A...469..687C
Altcode: 2007astro.ph..3652C
Aims:We investigate the impact of realistic three-dimensional (3D)
hydrodynamical model atmospheres of red giant stars at different
metallicities on the formation of spectral lines of a number of ions
and molecules.
Methods: We carry out realistic, ab initio, 3D,
hydrodynamical simulations of surface convection at the surface of red
giant stars with varying effective temperatures and metallicities. We
use the convection simulations as time-dependent hydrodynamical model
stellar atmospheres to calculate spectral lines of a number of ions (Li
I, O I, Na I, Mg I, Ca I, Fe I, and Fe II) and molecules (CH, NH, and
OH) under the assumption of local thermodynamic equilibrium (LTE). We
carry out a differential comparison of the line strengths computed
in 3D with the results of analogous line formation calculations for
classical, 1D, hydrostatic, plane-parallel marcs model atmospheres in
order to estimate the impact of 3D models on the derivation of elemental
abundances.
Results: The temperature and density inhomogeneities
and correlated velocity fields in 3D models, as well as the differences
between the mean 3D stratifications and corresponding 1D model
atmospheres significantly affect the predicted strengths of spectral
lines. Under the assumption of LTE, the low atmospheric temperatures
encountered in 3D model atmospheres of very metal-poor giant stars
cause spectral lines from neutral species and molecules to appear
stronger than within the framework of 1D models. As a consequence,
elemental abundances derived from these lines using 3D models are
significantly lower than according to 1D analyses. In particular,
the differences between 3D and 1D abundances of C, N, and O derived
from CH, NH, and OH weak low-excitation lines are found to be in the
range -0.5 dex to -1.0 dex for the the red giant stars at [Fe/H]=-3
considered here. At this metallicity, large negative corrections
(about -0.8 dex) are also found, in LTE, for weak low-excitation Fe
I lines. We caution, however, that the neglected departures from LTE
might be significant for these and other elements and comparable to
the effects due to stellar granulation.
Title: Sulphur and zinc abundances in Galactic halo stars revisited
Authors: Nissen, P. E.; Akerman, C.; Asplund, M.; Fabbian, D.; Kerber,
F.; Kaufl, H. U.; Pettini, M.
Bibcode: 2007A&A...469..319N
Altcode: 2007astro.ph..2689N
Aims:Based on a new set of sulphur abundances in very metal-poor stars
and an improved analysis of previous data, we aim at resolving current
discrepancies on the trend of S/Fe vs. Fe/H and thereby gain better
insight into the nucleosynthesis of sulphur. The trends of Zn/Fe and
S/Zn will also be studied.
Methods: High resolution VLT/UVES
spectra of 40 main-sequence stars with -3.3 < [Fe/H] < -1.0 are
used to derive S abundances from the weak λ 8694.6 S I line and the
stronger λ λ 9212.9,9237.5 pair of S I lines. For one star, the S
abundance is also derived from the S I triplet at 1.046 μm recently
observed with the VLT infrared echelle spectrograph CRIRES. Fe and
Zn abundances are derived from lines in the blue part of the UVES
spectra, and effective temperatures are obtained from the profile
of the Hβ line.
Results: Comparison of sulphur abundances
from the weak and strong S I lines provides important constraints on
non-LTE effects. The high sulphur abundances reported by others for
some metal-poor stars are not confirmed; instead, when taking non-LTE
corrections into account, the Galactic halo stars distribute around a
plateau at [S/Fe] ~ +0.2 dex with a scatter of 0.07 dex only. [Zn/Fe]
is close to zero for metallicities in the range -2.0 < [Fe/H]
< -1.0 but increases to a level of [Zn/Fe] ~ +0.1 to +0.2 dex in
the range -2.7 < [Fe/H] < -2.0. At still lower metallicities
[Zn/Fe] rises steeply to a value of [Zn/Fe] ~ +0.5 dex at [Fe/H] =
-3.2.
Conclusions: The trend of S/Fe vs. Fe/H corresponds to
the trends of Mg/Fe, Si/Fe, and Ca/Fe and indicates that sulphur in
Galactic halo stars has been made by α-capture processes in massive
SNe. The observed scatter in S/Fe is much smaller than predicted from
current stochastic models of the chemical evolution of the early Galaxy,
suggesting that either the models or the calculated yields of massive
SNe should be revised. We also examine the behaviour of S/Zn and find
that departures from the solar ratio are significantly reduced at
all metallicities if non-LTE corrections to the abundances of these
two elements are adopted. This effect, if confirmed, would reduce the
usefulness of the S/Zn ratio as a diagnostic of past star-formation
activity, but would bring closer together the values measured in damped
Lyman-alpha systems and in Galactic stars. Based on observations
collected at the European Southern Observatory at Paranal, Chile
(programmes No. 67.D-0106, 73.D-0024 and CRIRES science verification
program 60.A-9072). Table 1 and Appendices are only available in
electronic form at http://www.aanda.org
Title: Sulphur Abundances in Metal-Poor Stars First Result from
CRIRES Science Verification
Authors: Nissen, Poul Erik; Asplund, Martin; Fabbian, Damian; Kerber,
Florian; Käufl, Hans Ulrich; Pettini, Max
Bibcode: 2007Msngr.128...38N
Altcode:
Sulphur is the tenth most abundant element in the Universe and plays an
im-portant role in studies of the chemical enrichment and star formation
history of distant galaxies. Due to the lack of suitable sulphur lines
in the visible part of stellar spectra there is, however, still no
agreement on the abundance of sulphur in Galactic metal poor stars,
and we are therefore uncertain about the nucleosynthetic origin of
sulphur. New observations of infrared sulphur lines with the cryogenic
high resolution infrared echelle spectrograph (CRIRES) at ESO's VLT
are helping to solve this problem.
Title: Uniquely Large Excesses of 18O in HdC and RCB Stars: Evidence
for White Dwarf Mergers
Authors: Clayton, G. C.; Geballe, T. R.; Herwig, F.; Fryer, C.;
Asplund, M.
Bibcode: 2007apn4.confE..83C
Altcode:
No abstract at ADS
Title: The Solar Chemical Composition
Authors: Grevesse, N.; Asplund, M.; Sauval, A. J.
Bibcode: 2007SSRv..130..105G
Altcode: 2007SSRv..tmp..105G
We present our current knowledge of the solar chemical composition
based on the recent significant downward revision of the solar
photospheric abundances of the most abundant metals. These new solar
abundances result from the use of a 3D hydrodynamic model of the solar
atmosphere instead of the classical 1D hydrostatic models, accounting
for departures from LTE, and improved atomic and molecular data. With
these abundances, the new solar metallicity, Z, decreases to Z=0.012,
almost a factor of two lower than earlier widely used values. We
compare our values with data from other sources and analyse a number
of impacts of these new photospheric abundances. While resolving a
number of longstanding problems, the new 3D-based solar photospheric
composition also poses serious challenges for the standard solar model
as judged by helioseismology.
Title: Very Large Excesses of 18O in Hydrogen-deficient
Carbon and R Coronae Borealis Stars: Evidence for White Dwarf Mergers
Authors: Clayton, Geoffrey C.; Geballe, T. R.; Herwig, Falk; Fryer,
Christopher; Asplund, Martin
Bibcode: 2007ApJ...662.1220C
Altcode: 2007astro.ph..3453C
We have found that at least seven hydrogen-deficient carbon (HdC) and R
Coronae Borealis (RCB) stars, have 16O/18O ratios
close to and in some cases less than unity, values that are orders
of magnitude lower than measured in other stars (the solar value is
500). Greatly enhanced 18O is evident in every HdC and RCB
we have measured that is cool enough to have detectable CO bands. The
three HdC stars measured have 16O/18O<1,
lower values than any of the RCB stars. These discoveries are
important clues in determining the evolutionary pathways of HdC
and RCB stars, for which two models have been proposed: the double
degenerate (white dwarf [WD] merger) and the final helium-shell flash
(FF). No overproduction of 18O is expected in the FF
scenario. We have quantitatively explored the idea that HdC and RCB
stars originate in the mergers of CO- and He-WDs. The merger process
is estimated to take only a few days, with accretion rates of 150
Msolar yr-1 producing temperatures at the base
of the accreted envelope of (1.2-1.9)×108 K. Analysis of
a simplified one-zone calculation shows that nucleosynthesis in the
dynamically accreting material may provide a suitable environment for
a significant production of 18O, leading to very low values
of 16O/18O, similar to those observed. We also
find qualitative agreement with observed values of 12C/
13C and with the CNO elemental ratios. H-admixture during the
accretion process from the small H-rich C/O WD envelope may play
an important role in producing the observed abundances. Overall,
our analysis shows that WD mergers may very well be the progenitors
of O18-rich RCB and HdC stars, and that more detailed
simulations and modeling are justified.
Title: Convection and the solar abundances: Does the sun have a
sub-solar metallicity?
Authors: Asplund, Martin
Bibcode: 2007IAUS..239..122A
Altcode:
No abstract at ADS
Title: Commission 36: Theory of Stellar Atmospheres
Authors: Spite, Monique; Landstreet, John; Asplund, M.; Ayres, T.;
Balachandran, S.; Dravins, D.; Hauschildt, P.; Kiselman, D.; Nagendra,
K. N.; Sneden, C.; Tautvaišiené, G.; Werner, K.
Bibcode: 2007IAUTA..26..215S
Altcode:
Commission 36 covers all the physics of stellar atmospheres. The
scientific activity in this large field has been very intense during
the last triennium and led to the publication of a large number of
papers which makes an exhaustive report practically not feasible. As
a consequence we decided to keep the format of the preceding report:
first a list of areas of current research, then web links for obtaining
further information.
Title: Soils Ain't Soils: The Preservation of Solar Wind in Metal
Grains from the Lunar Regolith
Authors: Ireland, T. R.; Holden, P.; Norman, M. D.; Mya, J.;
Asplund, M.
Bibcode: 2007LPI....38.1449I
Altcode:
Oxygen isotopes from two more lunar soils have been analysed. Neither
has an implanted component and all oxygen isotope compositions measured
are normal. Solar wind exposure must be independently ascertained for
each grain.
Title: Commission 12: Solar Radiation & Structure
Authors: Bogdan, Thomas. J.; Martínez Pillet, Valentin; Asplund,
M.; Christensen-Dalsgaard, J.; Cauzzi, G.; Cram, L. E.; Dravins, D.;
Gan, W.; Henzl, P.; Kosovichev, A.; Mariska, J. T.; Rovira, M. G.;
Venkatakrishnan, P.
Bibcode: 2007IAUTA..26...89B
Altcode:
Commission 12 covers research on the internal structure and dynamics
of the Sun, the "quiet" solar atmosphere, solar radiation and its
variability, and the nature of relatively stable magnetic structures
like sunspots, faculae and the magnetic network. There is considerable
productive overlap with the other Commissions of Division II as
investigations move progressively toward the fertile intellectual
boundaries between traditional research disciplines. In large part,
the solar magnetic field provides the linkage that connects these
diverse themes. The same magnetic field that produces the more subtle
variations of solar structure and radiative output over the 11 yr
activity cycle is also implicated in rapid and often violent phenomena
such as flares, coronal mass ejections, prominence eruptions, and
episodes of sporadic magnetic reconnection.The last three years have
again brought significant progress in nearly all the research endeavors
touched upon by the interests of Commission 12. The underlying causes
for this success remain the same: sustained advances in computing
capabilities coupled with diverse observations with increasing levels
of spatial, temporal and spectral resolution. It is all but impossible
to deal with these many advances here in anything except a cursory and
selective fashion. Thankfully, the Living Reviews in Solar Physics; has
published several extensive reviews over the last two years that deal
explicitly with issues relevant to the purview of Commission 12. The
reader who is eager for a deeper and more complete understanding of
some of these advances is directed to http://www.livingreviews.org
for access to these articles.
Title: Chemical Homogeneity in Collinder 261 and Implications for
Chemical Tagging
Authors: De Silva, G. M.; Freeman, K. C.; Asplund, M.; Bland-Hawthorn,
J.; Bessell, M. S.; Collet, R.
Bibcode: 2007AJ....133.1161D
Altcode: 2006astro.ph.11832D
This paper presents abundances for 12 red giants of the old open
cluster Collinder 261 based on spectra from the Very Large Telescope
UVES. Abundances were derived for Na, Mg, Si, Ca, Mn, Fe, Ni, Zr,
and Ba. We find that the cluster has a solar-level metallicity of
[Fe/H]=-0.03 dex. However, most α- and s-process elements were found to
be enhanced. The star-to-star scatter was consistent with the expected
measurement uncertainty for all elements. The observed rms scatter
is as follows: Na=0.07, Mg=0.05, Si=0.06, Ca=0.05, Mn=0.03, Fe=0.02,
Ni=0.04, Zr=0.12, and Ba=0.03 dex. The intrinsic scatter was estimated
to be less than 0.05 dex. Such high levels of homogeneity indicate that
chemical information remains preserved in this old open cluster. We use
the chemical homogeneity we have now established in Cr 261, the Hyades,
and the HR 1614 moving group to examine the uniqueness of the individual
cluster abundance patterns, i.e., chemical signatures. We demonstrate
that the three studied clusters have unique chemical signatures and
discuss how other such signatures may be searched for in the future. Our
findings support the prospect of chemically tagging disk stars to common
formation sites in order to unravel the dissipative history of the
Galactic disk. Based on observations collected during ESO VLT-UT2
Program 73.D-0716A at the European Southern Observatory, Paranal, Chile.
Title: Chemically Tagging the HR 1614 Moving Group
Authors: De Silva, G. M.; Freeman, K. C.; Bland-Hawthorn, J.; Asplund,
M.; Bessell, M. S.
Bibcode: 2007AJ....133..694D
Altcode: 2006astro.ph.10041D
We present abundances for a sample of F, G, and K dwarfs of the HR
1614 moving group based on high-resolution, high signal-to-noise ratio
spectra from the Anglo-Australian Telescope UCLES instrument. Our
sample includes stars from Feltzing and Holmberg, as well as from
Eggen. Abundances were derived for Na, Mg, Al, Si, Ca, Mn, Fe, Ni, Zr,
Ba, Ce, Nd, and Eu. The α, Fe, and Fe-peak element abundances show a
bimodal distribution, with four stars having solar metallicities, while
the remaining 14 stars are metal-rich, [Fe/H]>=0.25 dex. However,
the abundances of these two groups converge for the heavier n-capture
elements. Based on their photometry and kinematics, three of the
four deviating stars are likely nonmembers or binaries. Although
one star cannot be excluded on these grounds, we do expect low-level
contamination from field stars within the HR 1614 moving group's range
of magnitude, color, and space velocities. Disregarding these four
stars, the abundance scatter across the group members for all elements
is low. We find that there is an 80% probability that the intrinsic
scatter does not exceed the following values: Fe, 0.01 dex; Na, 0.08
dex; Mg, 0.02 dex; Al, 0.06 dex; Si, 0.02 dex; Ca, 0.02 dex; Mn, 0.01
dex; Ni, 0.01 dex; Zr, 0.03 dex; Ba, 0.03 dex; Ce, 0.04 dex; Nd, 0.01
dex; and Eu, 0.02 dex. The homogeneity of the HR 1614 group in age and
abundance suggests that it is the remnant of a dispersed star-forming
event. Its kinematical coherence shows that such a dispersing system
need not be significantly perturbed by external dynamical influences
such as Galactic spiral structure or giant molecular clouds, at least
over a period of 2 Gyr.
Title: The Solar Chemical Composition
Authors: Grevesse, N.; Asplund, M.; Sauval, A. J.
Bibcode: 2007coma.book..105G
Altcode:
We present our current knowledge of the solar chemical composition
based on the recent significant downward revision of the solar
photospheric abundances of the most abundant metals. These new solar
abundances result from the use of a 3D hydrodynamic model of the solar
atmosphere instead of the classical 1D hydrostatic models, accounting
for departures from LTE, and improved atomic and molecular data. With
these abundances, the new solar metallicity, Z, decreases to Z=0.012,
almost a factor of two lower than earlier widely used values. We
compare our values with data from other sources and analyse a number
of impacts of these new photospheric abundances. While resolving a
number of longstanding problems, the new 3D-based solar photospheric
composition also poses serious challenges for the standard solar model
as judged by helioseismology.
Title: Evidence that R Coronae Borealis Stars Evolve from a White
Dwarf Merger rather than a Final Helium Shell Flash
Authors: Clayton, Geoffrey C.; Geballe, T. R.; Herwig, F.; Fryer,
C.; Tenenbaum, E.; Asplund, M.
Bibcode: 2006AAS...20916812C
Altcode: 2006BAAS...38.1140C
We have discovered, mainly using Gemini/GNIRS, that several
hydrogen-deficient carbon (HdC) and R Coronae Borealis (RCB) stars,
have 18O/16O ratios close to and sometimes exceeding unity, a value
orders of magnitude greater than measured in other known stars
(the Solar value is 1/500). This discovery is an important step in
determining the evolutionary pathway of HdC and RCB stars in general,
for which two models have been proposed: double degenerate (white dwarf
(WD) merger), and the final helium-shell flash (FF). The FF model for
producing RCB stars has been discredited recently due to a mismatch
of abundances and timescales needed to produce the RCB stars. We have
explored the idea that HdC and RCB stars originate in the merger of
COand He-WDs in the light of the new observations. Understanding the
RCB and HdC stars is a key test for any theory that aims to explain
hydrogen deficiency in post-AGB stars. These new results on the 18O/16O
ratio and our work on the FF star V605 Aql represent an opportunity for
a huge breakthrough. Confirmation of the WD merger scenario, which is
suggested, by both the models and these observations, will allow the use
of RCB and HdC stars as probes for WD merger simulations. The ability to
model the rates of these low-mass WD mergers will help us to understand
the rates of more massive mergers that may make some type Ia supernovae.
Title: The non-LTE line formation of neutral carbon in late-type stars
Authors: Fabbian, D.; Asplund, M.; Carlsson, M.; Kiselman, D.
Bibcode: 2006A&A...458..899F
Altcode: 2006astro.ph..8284F
Aims.We investigate the non-Local Thermodynamic Equilibrium (non-LTE)
line formation of neutral carbon in late-type stars in order to remove
some of the potential systematic errors in stellar abundance analyses
employing C i features.
Methods: .The statistical equilibrium
code MULTI was used on a grid of plane-parallel 1D MARCS atmospheric
models.
Results: .Within the parameter space explored, the
high-excitation C i lines studied are stronger in non-LTE due to
the combined effect of line source function drop and increased line
opacity due to overpopulation of the lower level for the transitions
considered; the relative importance of the two effects depends on
the particular combination of T{eff}, log g, [Fe/H] and
[C/Fe] and on the analysed C i line. As a consequence, the non-LTE
abundance corrections are negative and can be substantially so,
for example ∼ -0.4 dex in halo turn-off stars at [Fe/H]∼ -3. The
magnitude of the non-LTE corrections is rather insensitive to whether
inelastic H collisions are included or not.
Conclusions: .Our
results have implications on studies of nucleosynthetic processes and
on Galactic chemical evolution models. When applying our calculated
corrections to recent observational data, the upturn in [C/O] at low
metallicity might still be present (thus apparently still necessitating
contributions from massive Pop. III stars for the carbon production),
but at a lower level and possibly with a rather shallow trend of ∼
-0.2 dex/dex below [O/H]∼ -1.
Title: The solar chemical composition
Authors: Asplund, Martin; Grevesse, Nicolas; Jacques Sauval, A.
Bibcode: 2006NuPhA.777....1A
Altcode: 2004astro.ph.10214A
We present what we believe to be the best estimates of the chemical
compositions of the solar photosphere and the most pristine meteorites.
Title: Line formation in solar granulation. VII. CO lines and the
solar C and O isotopic abundances
Authors: Scott, P. C.; Asplund, M.; Grevesse, N.; Sauval, A. J.
Bibcode: 2006A&A...456..675S
Altcode: 2006astro.ph..5116S
CO spectral line formation in the Sun has long been a source of
consternation for solar physicists, as have the elemental abundances
it seems to imply. We modelled solar CO line formation using a
realistic, ab initio, time-dependent 3D radiative-hydrodynamic model
atmosphere. Results were compared with space-based observations
from the ATMOS space shuttle experiment. We employed weak
12C16O, 13C16O and
12C18O lines from the fundamental (Δ v =
1) and first overtone (Δ v = 2) bands to determine the solar
carbon abundance, as well as the 12C/13C
and 16O/18O isotopic ratios. A weighted
solar carbon abundance of logɛ_C=8.39 ± 0.05 was found. We
note with satisfaction that the derived abundance is identical to
our recent 3D determination based on C i, [C i], C2 and CH lines,
increasing our confidence in the accuracy of both results. Identical
calculations were carried out using 1D models, but only the 3D
model was able to produce abundance agreement between different
CO lines and the other atomic and molecular diagnostics. Solar
12C/13C and 16O/18O ratios
were measured as 86.8+3.9-3.7 (δ13C
= 30+46-44) and 479+29-28
(δ18O = 41+67-59), respectively. These
values may require current theories of solar system formation, such as
the CO self-shielding hypothesis, to be revised. Excellent agreement
was seen between observed and predicted weak CO line shapes, without
invoking micro- or macroturbulence. Agreement breaks down for the
strongest CO lines however, which are formed in very high atmospheric
layers. Whilst the line asymmetries (bisectors) were reasonably
well reproduced, line strengths predicted on the basis of C and O
abundances from other diagnostics were weaker than observed. The
simplest explanation is that temperatures are overestimated in the
highest layers of the 3D simulation. Thus, our analysis supports
the presence of a COmosphere above the traditional photospheric
temperature minimum, with an average temperature of less than 4000
K. This shortcoming of the 3D model atmosphere is not surprising,
given that it was never intended to properly describe such high layers.
Title: New and improved experimental oscillator strengths in Zr II
and the solar abundance of zirconium
Authors: Ljung, G.; Nilsson, H.; Asplund, M.; Johansson, S.
Bibcode: 2006A&A...456.1181L
Altcode:
Using the Fourier Transform Spectrometer at Lund Observatory, intensity
calibrated spectra of singly ionized zirconium have been recorded and
analyzed. Oscillator strengths for 263 Zr II spectral lines in the
region 2500-5400 Å have been derived by combining new experimental
branching fractions with previously measured radiative lifetimes. The
transitions combine 34 odd parity levels with 29 low metastable levels
between 0 and 2.4 eV. The experimental branching fractions have been
compared with theoretical values and the oscillator strengths with
previously published data when available. The oscillator strengths
have been employed to derive the solar photospheric Zr abundance
based on both 1D and 3D model atmospheres. Based on the seven best
and least perturbed Zr II lines in the solar disk-center spectrum, we
determine the solar Zr abundance to log ɛ_Zr=2.58±0.02 when using a
3D hydrodynamical solar model atmosphere. The new value is in excellent
agreement with the meteoritic Zr abundance.
Title: Isotopic Analysis of the Sun
Authors: Ireland, T. R.; Asplund, M.
Bibcode: 2006M&PSA..41.5176I
Altcode:
No abstract at ADS
Title: Oxygen isotope reservoirs in the solar system
Authors: Ireland, T. R.; Asplund, M.
Bibcode: 2006GeCAS..70Q.278I
Altcode:
No abstract at ADS
Title: Chemically tagging the HR moving group
Authors: de Silva, G.; Freeman, K.; Bland-Hawthorn, J.; Asplund, M.;
Bessell, M.
Bibcode: 2006AAONw.110...13D
Altcode:
No abstract at ADS
Title: The solar model problem: helioseismology vs the new solar
chemical composition
Authors: Asplund, M.
Bibcode: 2006IAUJD..17E...3A
Altcode:
Recently the solar photospheric abundances of C, N and O have been
significantly revised downward as a consequence of 3D hydrodynamical
solar model atmosphere, non-LTE line formation, and improved
atomic/molecular data. While this new solar chemical composition solves
many long-standing problems in astrophysics such as the apparent high
metallicity of the Sun relative to the current-day solar neighbourhood,
it wrecks havoc with standard solar interior models as judged by
helioseismology. In this review I will describe the background of this
solar model problem, the new 3D solar abundance analysis, and possible
solutions to the discrepancy.
Title: An abundance study of the most iron-poor star HE1327-2326
with Subaru/HDS
Authors: Aoki, W.; Frebel, A.; Christlieb, N.; Norris, J. E.; Beers,
T. C.; Minezaki, T.; Barklem, P. S.; Honda, S.; Takada-Hidai, M.;
Asplund, M.; Ryan, S. G.; Tsangarides, S.; Eriksson, K.; Steinhauer,
A.; Deliyannis, C. P.; Nomoto, K.; Fujimoto, M. Y.; Ando, H.; Yoshii,
Y.; Kajino, T.
Bibcode: 2006AIPC..847...53A
Altcode:
We present an elemental abundance analysis of HE 1327-2326, the most
iron-deficient star known, based on a comprehensive investigation of
spectra obtained with the Subaru Telescope. HE 1327-2326 is either
in its main sequence or subgiant phase of evolution, hence it is
essentially unevolved. The chemical abundances of this star have
the following properties, which provide new constraints on models of
nucleosynthesis processes that occurred in first-generation objects: (1)The iron abundance (NLTE) is [Fe/H]= -5.45. This value is 0.2 dex
lower than that of HE 0107-5240, the previously most iron-poor object
known. No object having [Fe/H]= -5 ~ -4 is known to date. (2)This
star, as well as HE 0107-5240, exhibits extremely large overabundances
of carbon relative to solar ratios ([C/Fe]~ +4). (3)HE 1327-2326
exhibits remarkable overabundances of the light elements (N, Na, Mg
and Al), while HE 0107-5240 shows only relatively small excesses of N
and Na. (4)A large overabundance of Sr is found in HE 1327-2326
as compared to other extremely low metallicity stars. (5)The Li
I 6707 Å line, which is detected in the great majority of metal-poor
dwarfs and warm subgiants, is not found in HE 1327-2326. The upper
limit on the Li abundance we determine (log ɛ (Li) < 1.5) is
clearly lower than the expected value from the Spite plateau.
Title: Lithium Isotopic Abundances in Metal-poor Halo Stars
Authors: Asplund, Martin; Lambert, David L.; Nissen, Poul Erik;
Primas, Francesca; Smith, Verne V.
Bibcode: 2006ApJ...644..229A
Altcode: 2005astro.ph.10636A
Very high quality spectra of 24 metal-poor halo dwarfs and subgiants
have been acquired with ESO's VLT/UVES for the purpose of determining
Li isotopic abundances. The derived one-dimensional, non-LTE
7Li abundances from the Li I 670.8 nm line reveal a pronounced
dependence on metallicity but with negligible scatter around this
trend. Very good agreement is found between the abundances from the Li I
670.8 nm line and the Li I 610.4 nm line. The estimated primordial
7Li abundance is 7Li/H=(1.1-1.5)×10-10,
which is a factor of 3-4 lower than predicted from standard big bang
nucleosynthesis with the baryon density inferred from the cosmic
microwave background. Interestingly, 6Li is detected in 9
of our 24 stars at the >=2 σ significance level. Our observations
suggest the existence of a 6Li plateau at the level
of logɛ6Li~0.8 however, taking into account
predictions for 6Li destruction during the pre-main-sequence
evolution tilts the plateau such that the 6Li abundances
apparently increase with metallicity. Our most noteworthy result is the
detection of 6Li in the very metal-poor star LP 815-43. Such
a high 6Li abundance during these early Galactic epochs
is very difficult to achieve by Galactic cosmic-ray spallation and
α-fusion reactions. It is concluded that both Li isotopes have a
pre-Galactic origin. Possible 6Li production channels include
protogalactic shocks and late-decaying or annihilating supersymmetric
particles during the era of big bang nucleosynthesis. The presence of
6Li limits the possible degree of stellar 7Li
depletion and thus sharpens the discrepancy with standard big bang
nucleosynthesis. Based on observations collected at the European
Southern Observatory, Paranal, Chile (observing programs 65.L-0131,
68.D-0091, and 273.D-5043).
Title: The Chemical Compositions of the Extreme Halo Stars
HE 0107-5240 and HE 1327-2326 Inferred from Three-dimensional
Hydrodynamical Model Atmospheres
Authors: Collet, R.; Asplund, M.; Trampedach, R.
Bibcode: 2006ApJ...644L.121C
Altcode: 2006astro.ph..5219C
We investigate the impact of realistic three-dimensional (3D)
hydrodynamical model stellar atmospheres on the determination of
elemental abundances in the carbon-rich, hyper-iron-poor stars HE
0107-5240 and HE 1327-2326. We derive the chemical compositions of the
two stars by means of a detailed 3D analysis of spectral lines under
the assumption of local thermodynamic equilibrium (LTE). The lower
temperatures of the line-forming regions of the hydrodynamical models
cause changes in the predicted spectral line strengths. In particular,
we find the 3D abundances of C, N, and O to be lower by about -0.8 dex
(or more) than estimated from a 1D analysis. The 3D abundances of iron
peak elements are also decreased but by smaller factors (about -0.2
dex). We caution, however, that the neglected non-LTE effects might
actually be substantial for these metals. We finally discuss possible
implications for studies of early Galactic chemical evolution.
Title: Oxygen abundances in metal-poor subgiants as determined from
[O I], O I and OH lines
Authors: García Pérez, A. E.; Asplund, M.; Primas, F.; Nissen,
P. E.; Gustafsson, B.
Bibcode: 2006A&A...451..621G
Altcode: 2005astro.ph.12290G
The debate on the oxygen abundances of metal-poor stars has its
origin in contradictory results obtained using different abundance
indicators. To achieve a better understanding of the problem we
have acquired high quality spectra with the Ultraviolet and Visual
Echelle Spectrograph at VLT, with a signal-to-noise of the order of
100 in the near ultraviolet and 500 in the optical and near infrared
wavelength range. Three different oxygen abundance indicators,
OH ultraviolet lines around 310.0 nm, the [O i] line at 630.03 nm
and the O i lines at 777.1-5 nm were observed in the spectra of 13
metal-poor subgiants with -3.0≤[Fe/H]≤-1.5. Oxygen abundances
were obtained from the analysis of these indicators which was carried
out assuming local thermodynamic equilibrium and plane-parallel
model atmospheres. Abundances derived from O i were corrected for
departures from local thermodynamic equilibrium. Stellar parameters
were computed using T_eff-vs.-color calibrations based on the infrared
flux method and Balmer line profiles, Hipparcos parallaxes and Fe II
lines. [O/Fe] values derived from the forbidden line at 630.03 nm are
consistent with an oxygen/iron ratio that varies linearly with [Fe/H] as
[O/Fe]=-0.09(±0.08)[Fe/H]+0.36(±0.15). Values based on the O i triplet
are on average 0.19±0.22 dex(s.d.) higher than the values based on the
forbidden line while the agreement between OH ultraviolet lines and the
forbidden line is much better with a mean difference of the order of
-0.09±0.25 dex(s.d.). In general, our results follow the same trend
as previously published results with the exception of the ones based
on OH ultraviolet lines. In that case our results lie below the values
which gave rise to the oxygen abundance debate for metal-poor stars.
Title: HE 1327-2326, an Unevolved Star with [Fe/H]<-5.0. I. A
Comprehensive Abundance Analysis
Authors: Aoki, W.; Frebel, A.; Christlieb, N.; Norris, J. E.; Beers,
T. C.; Minezaki, T.; Barklem, P. S.; Honda, S.; Takada-Hidai, M.;
Asplund, M.; Ryan, S. G.; Tsangarides, S.; Eriksson, K.; Steinhauer,
A.; Deliyannis, C. P.; Nomoto, K.; Fujimoto, M. Y.; Ando, H.; Yoshii,
Y.; Kajino, T.
Bibcode: 2006ApJ...639..897A
Altcode: 2005astro.ph..9206A
We present the elemental abundances of HE 1327-2326, the most
iron-deficient star known, determined from a comprehensive analysis
of spectra obtained with the Subaru Telescope High Dispersion
Spectrograph. HE 1327-2326 is either in its main-sequence or
subgiant phase of evolution. Its non-LTE-corrected iron abundance is
[Fe/H]=-5.45, 0.2 dex lower than that of HE 0107-5240, the previously
most iron-poor object known, and more than 1 dex lower than those
of all other metal-poor stars. Both HE 1327-2326 and HE 0107-5240
exhibit extremely large overabundances of carbon ([C/Fe]~+4). The
combination of extremely high carbon abundance with outstandingly
low iron abundance in these objects clearly distinguishes them from
other metal-poor stars. The large carbon excesses in these two stars
are not the result of a selection effect. There also exist important
differences between HE 1327-2326 and HE 0107-5240. While the former
shows remarkable overabundances of the light elements (N, Na, Mg,
and Al), the latter shows only relatively small excesses of N and
Na. The neutron-capture element Sr is detected in HE 1327-2326,
but not in HE 0107-5240 its Sr abundance is significantly higher
than the upper limit for HE 0107-5240. The Li I λ6707 line, which is
detected in most metal-poor dwarfs and warm subgiants having the same
temperature as HE 1327-2326, is not found in this object. The upper
limit of its Li abundance [logɛ(Li)<1.5] is clearly lower than the
Spite plateau value. These data provide new constraints on models of
nucleosynthesis processes in the first-generation objects that were
responsible for metal enrichment at the earliest times. We discuss
possible scenarios to explain the observed abundance patterns. Based on data collected with the Subaru Telescope, which is operated
by the National Astronomical Observatory of Japan.
Title: The Oxygen Abundance of HE 1327-2326
Authors: Frebel, Anna; Christlieb, Norbert; Norris, John E.; Aoki,
Wako; Asplund, Martin
Bibcode: 2006ApJ...638L..17F
Altcode: 2005astro.ph.12543F
From a newly obtained VLT/UVES spectrum, we have determined the
oxygen abundance of HE 1327-2326, the most iron-poor star known to
date. Ultraviolet OH lines yield one-dimensional LTE abundances of
[O/Fe]OH =3.7 (subgiant case) and [O/Fe]OH=3.4
(dwarf case). Using a correction of -1.0 dex to account for
three-dimensional (3D) effects on OH line formation, the abundances
are lowered to [O/Fe]=2.8 and [O/Fe]=2.5, respectively, which we
adopt. Without 3D corrections, the UV OH-based abundance would be in
disagreement with the upper limits derived from the O I triplet lines:
[O/Fe]trip<2.8 (subgiant) and [O/Fe]trip<3.0
(dwarf). We also correct the previously determined carbon and nitrogen
abundances for 3D effects. Knowledge of the O abundance of HE 1327-2326
has implications for the interpretation of its abundance pattern. A
large O abundance is in accordance with HE 1327-2326 being an early
Population II star that formed from material chemically enriched by
a first-generation supernova. Our derived abundances, however, do
not exclude other possibilities such as a Population III scenario. Based on observations collected at the European Southern Observatory,
Paranal, Chile (proposal 075.D-0048).
Title: Getting a handle on the origin of the Galactic Bulge
Authors: Lambert, David L.; Ryde, Nils; Hinkle, Kenneth; Smith, Verne
V.; Gustafsson, Bengt; Edvardsson, Bengt; Asplund, Martin; Johansson,
Sveneric; Wahlin, Rurik
Bibcode: 2006noao.prop..268L
Altcode:
The origin, chemical properties, and evolution history of the
Galactic Bulge remain poorly understood. Abundance ratios of bulge
stars, especially in the [(alpha)/Fe] vs [Fe/H] diagram, serve to
constrain the evolutionary models. Measuring, for instance, a high
(alpha) over-abundance indicates rapid and early star-formation. Thus,
we propose an infrared based study of the (alpha) elements, including
oxygen, of ten stars in two low-extinction windows towards the bulge. We
will also re-investigate the oxygen abundance trends found from optical
spectra of K giants in Baade's window by McWilliam & Rich (2004),
which indicate a surprising cession of oxygen production in the bulge
for metallicities larger than -0.5. The infrared, with lower extinction
and molecular rather than atomic abundance indicators, is a preferred
wavelength region to study abundances in bulge stars.
Title: Ci Non-LTE Spectral Line Formation in Late-Type Stars
Authors: Fabbian, D.; Asplund, M.; Carlsson, M.
Bibcode: 2006cams.book...52F
Altcode:
We present the results from our non-LTE investigation for neutral
carbon, which was carried out to remove potential systematic errors
in stellar abundance analyses. The calculations were performed for
late-type stars and give substantial negative non-LTE abundance
corrections. When applied to observations of extremely metal-poor
stars, which within the LTE framework seem to suggest a possible [C/O]
uprise at low metallicities (Akerman et al. 2004), these improvements
will have important implications, enabling us to understand if the
standard chemical evolution model is adequate, with no need to invoke
signatures by Pop. III stars for the carbon nucleosynthesis.
Title: Chemical Homogeneity in the Hyades
Authors: De Silva, G. M.; Sneden, C.; Paulson, D. B.; Asplund, M.;
Bland-Hawthorn, J.; Bessell, M. S.; Freeman, K. C.
Bibcode: 2006AJ....131..455D
Altcode: 2005astro.ph..9241D
We present an abundance analysis of the heavy elements Zr, Ba,
La, Ce, and Nd for Hyades F-K dwarfs based on high-resolution, high
signal-to-noise ratio spectra from Keck HIRES. The derived abundances
show the stellar members to be highly uniform, although some elements
show a small residual trend with temperature. The rms scatter for each
element for the cluster members is as follows: Zr=0.055, Ba=0.049,
Ce=0.025, La=0.025, and Nd=0.032 dex. This is consistent with the
measurement errors and implies that there is little or no intrinsic
scatter among the Hyades members. Several stars thought to be nonmembers
of the cluster based on their kinematics are found to deviate from the
cluster mean abundances by about 2 σ. Establishing chemical homogeneity
in open clusters is the primary requirement for the viability of
chemically tagging Galactic disk stars to common formation sites in
order to unravel the dissipative history of early disk formation.
Title: The new solar abundances - Part I: the observations
Authors: Asplund, M.; Grevesse, N.; Sauval, A. J.
Bibcode: 2006CoAst.147...76A
Altcode:
The new solar abundances have been derived from analyses of the
photospheric spectrum. They result from the use of a 3D hydrodynamical
model of the solar atmosphere instead of the classical 1D hydrostatic
models, accounting for departures from LTE when possible and improved
atomic and molecular data. The new solar abundances are lower than
previously recommended values and the present solar metallicity, Z,
and Z/X, decrease to Z = 0.0122 and Z/X = 0.0165 respectively, almost
a factor of two lower than earlier widely used values. We briefly
discuss the new results for the most abundant elements, show why they
are trustworthy and discuss some implications (see also Montalban et
al. 2006, Part II).
Title: 3D Hydrodynamical Simulations of Convection in Red-Giants
Stellar Atmospheres
Authors: Collet, R.; Asplund, M.; Trampedach, R.
Bibcode: 2006cams.book..306C
Altcode:
We present preliminary results of 3D hydrodynamical simulations
of surface convection in red giants stars. We investigate the main
differences between static 1D and 3D time-dependent model stellar
atmospheres of red giants for a range of metallicities between solar
and [Fe/H] = -3 focusing in particular on the impact of 3D spectral
line formation on the derivation of stellar abundances.
Title: Chemical abundance patterns of extremely metal-poor stars
Authors: Aoki, Wako; Beers, Timothy C.; Christlieb, Norbert; Frebel,
Anna; Norris, John E.; Honda, Satoshi; Takada-Hidai, Masahide; Asplund,
Martin; Ando, Hiroyasu; Ryan, Sean G.; Tsangarides, Stelios
Bibcode: 2006isna.confE.210A
Altcode: 2006PoS....28E.210A
We have obtained high resolution (R =60,000), high quality (S/N
>100) spectroscopy using Subaru/HDS for 20 candidate extremely
metal-poor stars ([Fe/H]< -3) to determine their chemical abundance
patterns. In the observing program we found HE1327-2326, which has
[Fe/H]= -5.4, the lowest Fe abundance known in normal stars. This
star shows extremely large excesses of C and N, and also excesses
of other light elements (e.g. O, Na). The low iron abundance and the
peculiar abundance pattern provide a signature of the nucleosynthesis
by the first generation stars in the Universe. We also present the
preliminary results for other stars: (1) The iron abundances of our
sample, except for HE 1327-2326, are higher than [Fe/H]= -4. There is
a gap of iron abundance between [Fe/H]= -4 and -5. This would indicate
that the nucleosynthesis, or formation processes that are responsible
for the stars with [Fe/H]< -5 and others are quite different. (2)
Six stars of our sample, including HE1327-2326, show clear excesses
of carbon. Only two of them show excesses of the heavy neutron-capture
element Ba, suggesting a large contribution of AGB nucleosynthesis. The
origin of carbon-excesses in other stars are still unclear, but the
existence of these stars is a remarkable feature only found at the
extremely low metallicity.
Title: Highlights from the Search for Bright Extremely Metal-poor
Stars
Authors: Frebel, A.; Norris, J. E.; Christlieb, N.; Beers, T. C.;
Asplund, M.; Bessell, M. S.; Aoki, W.
Bibcode: 2005AAS...207.6910F
Altcode: 2005BAAS...37.1272F
We present very recent work on bright (10 < B < 14) extremely
metal-poor stars selected from the Hamburg/ESO survey. Detailed
knowledge about the most metal-poor objects found in the halo
of the Galaxy is crucial for a comprehensive understanding of
the early Universe since they are the closest relatives to true
first stars (``Population III" objects). In a sample of 1777 bright
metal-poor candidate stars we identified ∼ 100 star with [Fe/H] <
-2.5. This sample is currently being observed with high-resolution
spectroscopy to reveal any unusual abundance patterns which are
of astrophysical interest (e.g. ultra metal-poor, s- or r-process
enhanced). So far, we have found the bright dwarf or subgiant HE
1327-2326 which has a new low record iron abundance of [Fe/H] =
-5.4. Most characteristically, this star displays huge amounts of CNO
elements with respect to iron ( ∼ 4 dex) as well as an enhancement
of the neutron-capture element Sr. Despite its evolutinary status,
no Li could be detected. The interpretation of the abundance pattern
of HE 1327-2326 challenges the current theoretical understanding of
the first stars. Furthermore, we are searching for stars with strong
enhancement of r-process abundances. Potential abundance measurements
of the the heavy elements Th and U allow the determination of
stellar ages. These are independent lower limits for the age of the
Universe. A.F, J.E.N., M.S.B and M.A. acknowledge funding from the
Australian Research Council. N.C. acknowledges funding from Deutsche
Forschungsgemeinschaft. T.C.B. acknowledges funding from the US National
Science Foundation Physics and Frontiers Center/JINA: Joint Institute
for Nuclear Astrophysics, awarded by the US National Science Foundation.
Title: Lithium Isotopic Abundances in Metal-Poor Stars: A Problem
for Standard Big Bang Nucleosynthesis?
Authors: Nissen, Poul E.; Asplund, Martin; Lambert, David L.; Primas,
Francesca; Smith, Verne V.
Bibcode: 2005Msngr.122...32N
Altcode:
Spectra obtained with VLT/UVES suggest the existence of the Li isotope
in several metal-poor stars at a level that challenges ideas about its
synthesis. The Li abundance is, on the other hand, a factor of three
lower than predicted by standard Big Bang nucleosynthesis theory. Both
problems may be explained if decaying supersymmetric particles affect
the synthesis of light elements in the Big Bang.
Title: Effects of line-blocking on the non-LTE Fe I spectral line
formation
Authors: Collet, R.; Asplund, M.; Thévenin, F.
Bibcode: 2005A&A...442..643C
Altcode: 2005astro.ph..7375C
The effects of background line opacity (line-blocking) in statistical
equilibrium calculations for Fe in late-type stellar atmospheres have
been investigated using an extensive and up-to-date model atom with
radiative data primarily from the iron Project. The background metal
line opacities have been computed using data from the marcs stellar
model atmospheres. While accounting for this line opacity is important
at solar metallicity, the differences between calculations including
and excluding line-blocking at low metallicity are insignificant for
the non-local thermodynamic equilibrium (non-LTE) abundance corrections
for Fe I lines. The line-blocking has no impact on the non-LTE effects
of Fe II lines. The dominant uncertainty in Fe non-LTE calculations
for metal-poor stars is still the treatment of the inelastic H I
collisions, which here have been included using scaling factors to the
classical Drawin formalism, and whether or not thermalisation of the
high Fe I levels to Fe II ground state should be enforced. Without such
thermalisation, the Fe I non-LTE abundance corrections are substantial
in metal-poor stars: about 0.3 dex with efficient (i.e. Drawin-like)
H I collisions and ⪉0.5 dex without. Without both thermalisation and
H I collisions, even Fe II lines show significant non-LTE effects in
such stars.
Title: The solar model problem resurrected
Authors: Asplund, M.; Grevesse, N.; Guedel, M.; Sauval, A. J.
Bibcode: 2005astro.ph.10377A
Altcode:
The new solar composition, when applied to compute a model of the Sun,
leads to serious disagreement between the predictions of the model
and the observations obtained by helioseismology. New measurements of
the coronal Ne/O abundance ratio in nearby stars using X-ray spectra
typically find high values of Ne/O=0.4 rather than 0.15 normally adopted
for the Sun. Drake & Testa (2005) suggest that this high Ne/O ratio
is appropriate also for the Sun, which would bring the solar models
back in agreement with the helioseismological observations. Here we
present arguments why the high Ne/O ratio is unlikely to be applicable
to the Sun.
Title: Trends and Scatter of Abundance Ratios for Metal-poor
Turnoff Stars
Authors: Nissen, P. E.; Asplund, M.; Lambert, D. L.; Primas, F.;
Smith, V. V.
Bibcode: 2005ASPC..336...55N
Altcode:
Trends and scatter of abundances of Li, O, Ca and Fe in metal-poor
stars are discussed with particular emphasis on new results obtained
by analyzing high resolution ESO VLT/UVES spectra of 23 turnoff stars
using effective temperatures derived from the Hα line. Evidence of a
significant cosmic scatter in O/Fe and Ca/Fe at a given metallicity is
found, whereas the scatter in Li/H is very small, i.e. less than 0.03
dex. The results are compared to previous data for halo, thick and
thin disk stars, and to the prediction of the primordial Li abundance
from WMAP.
Title: New Light on Stellar Abundance Analyses: Departures from LTE
and Homogeneity
Authors: Asplund, Martin
Bibcode: 2005ARA&A..43..481A
Altcode:
The information on the chemical compositions of stars encoded in their
spectra plays a central role in contemporary astrophysics. Stellar
element abundances are, however, not observed: to decipher the spectral
fingerprints in terms of abundances requires realistic models for the
stellar atmospheres and the line-formation processes. Still today,
the vast majority of abundance analyses of late-type stars rely on
one-dimensional (1D), hydrostatic model atmospheres and the assumption
of local thermodynamic equilibrium (LTE). In this review possible
systematic errors in studies of F-, G- and K-type stars introduced by
these questionable approximations are discussed. Departures from LTE
are commonplace and often quite severe, in particular for low surface
gravities or metallicities, with minority species and low-excitation
transitions being the most vulnerable. Recently, time-dependent, 3D,
hydrodynamical model atmospheres have started to be employed for stellar
abundance purposes, with large differences compared with 1D modeling
found in particular for metal-poor stars. An assessment of non-LTE
and 3D effects for individual elements as well as on the estimated
stellar parameters is presented.
Title: Chemical abundances in 43 metal-poor stars
Authors: Jonsell, K.; Edvardsson, B.; Gustafsson, B.; Magain, P.;
Nissen, P. E.; Asplund, M.
Bibcode: 2005A&A...440..321J
Altcode: 2005astro.ph..5118J
We have derived abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Fe,
Ni, and Ba for 43 metal-poor field stars in the solar neighbourhood,
most of them subgiants or turn-off-point stars with iron abundances
[Fe/H] ranging from -0.4 to -3.0. About half of this sample has not been
spectroscopically analysed in detail before. Effective temperatures
were estimated from uvby photometry, and surface gravities primarily
from Hipparcos parallaxes. The analysis is differential relative to
the Sun, and was carried out with plane-parallel MARCS models. Various
sources of error are discussed and found to contribute a total error
of about 0.1-0.2 dex for most elements, while relative abundances,
such as [Ca/Fe], are most probably more accurate. For the oxygen
abundances, determined in an NLTE analysis of the 7774 Å triplet
lines, the errors may be somewhat larger. We made a detailed comparison
with similar studies and traced the reasons for the, in most cases,
relatively small differences. Among the results we find that [O/Fe]
possibly increases beyond [Fe/H] = -1.0, though considerably less so
than in results obtained by others from abundances based on OH lines. We
did not trace any tendency toward strong overionization of iron, and
find the excesses, relative to Fe and the Sun, of the α elements Mg,
Si, and Ca to be smaller than those of O. We discuss some indications
that also the abundances of different α elements relative to Fe vary
and the possibility that some of the scatter around the trends in
abundances relative to iron may be real. This may support the idea that
the formation of Halo stars occurred in smaller systems with different
star formation rates. We verify the finding by Gratton et al. (2003b,
A&A, 406, 131) that stars that do not participate in the rotation
of the galactic disk show a lower mean and larger spread in [ α/Fe]
than stars participating in the general rotation. The latter stars also
seem to show some correlation between [ α/Fe] and rotation speed. We
trace some stars with peculiar abundances, among these two Ba stars,
HD 17072 and HD 196944, the
second already known to be rich in s elements. Finally we advocate
that a spectroscopic study of a larger sample of halo stars with
well-defined selection criteria is very important, in order to add to
the very considerable efforts that various groups have already made.
Title: The Solar Chemical Composition
Authors: Asplund, M.; Grevesse, N.; Sauval, A. J.
Bibcode: 2005ASPC..336...25A
Altcode:
We review our current knowledge of the solar chemical composition
as determined from photospheric absorption lines. In particular we
describe the recent significant revisions of the solar abundances as a
result of the application of a time-dependent, 3D hydrodynamical model
of the solar atmosphere instead of 1D hydrostatic models. This has
decreased the metal content in the solar convection zone by almost a
factor of two compared with the widely used compilation by Anders &
Grevesse (1989). While resolving a number of long-standings problems,
the new 3D-based element abundances also pose serious challenges,
most notably for helioseismology.
Title: Lithium isotopic abundances in very metal-poor halo stars
Authors: Asplund, Martin
Bibcode: 2005noao.prop..186A
Altcode:
In our VLT/UVES survey of 6Li and 7Li isotopic abundances in Galactic
halo stars, we have boosted the number of positive 6Li detections in
such stars from the previous single case to at least ten. No doubt
the most exciting result stemming from our program is a detection
of 6Li in LP815-43, one of the most metal-poor stars in our sample
([Fe/H]=-2.7). If high 6Li abundances at low [Fe/H] is a general
feature, it would have important ramifications for light element
production in the early Universe, Li depletion in metal-poor stars, Big
Bang nucleosynthesis and possibly even non-standard particle physics. We
here request Keck/HIRES time to observe a sufficiently large sample of
very metal-poor stars to test whether such a 6Li plateau indeed exists.
Title: Detection of Near-Infrared CO Absorption Bands in R Coronae
Borealis Stars
Authors: Tenenbaum, Emily D.; Clayton, Geoffrey C.; Asplund, Martin;
Engelbracht, C. W.; Gordon, Karl D.; Hanson, M. M.; Rudy, Richard J.;
Lynch, David K.; Mazuk, S.; Venturini, Catherine C.; Puetter, R. C.
Bibcode: 2005AJ....130..256T
Altcode: 2005astro.ph..3497T
R Coronae Borealis (RCB) stars are hydrogen-deficient, carbon-rich,
pulsating, post-asymptotic giant branch stars that experience
massive irregular declines in brightness caused by circumstellar dust
formation. The mechanism of dust formation around RCB stars is not well
understood. It has been proposed that CO molecules play an important
role in cooling the circumstellar gas so that dust may form. We report
on a survey for CO in a sample of RCB stars. We obtained H- and K-band
spectra including the first- and second-overtone CO bands for eight
RCB stars, the RCB-like star DY Per, and the final-helium-flash star FG
Sge. The first- and second-overtone CO bands were detected in the cooler
(Teff<6000 K) RCB stars, Z Umi, ES Aql, SV Sge, and DY
Per. The bands are not present in the warmer (Teff>6000
K) RCB stars, R CrB, RY Sgr, SU Tau, and XX Cam. In addition,
first-overtone bands are seen in FG Sge, a final-helium-flash star
that is in an RCB-like phase at present. Effective temperatures of the
eight RCB stars range from 4000 to 7250 K. The observed photospheric
CO absorption bands were compared to line-blanketed model spectra of
RCB stars. As predicted by the models, the CO bands are strongest in
the coolest RCB stars and not present in the warmest. No correlation
was found between the presence or strength of the CO bands and dust
formation activity in the stars.
Title: Line formation in solar granulation. IV. [O I], O I and OH
lines and the photospheric O abundance
Authors: Asplund, M.; Grevesse, N.; Sauval, A. J.; Allende Prieto,
C.; Kiselman, D.
Bibcode: 2005A&A...435..339A
Altcode:
A&A, 417, 751-768 (2004), DOI:10.1051/0004-6361:20034328
Title: VizieR Online Data Catalog: Chemical abundances in 43
metal-poor stars (Jonsell+, 2005)
Authors: Jonsell, K.; Edvardsson, B.; Gustafsson, B.; Magain, P.;
Nissen, P. E.; Asplund, M.
Bibcode: 2005yCat..34400321J
Altcode:
Data from an analysis of 43 metal-poor field stars with iron abundances
[Fe/H] ranging from -0.4 to -3.0dex are presented here. Photometric
data, stellar velocities, masses, fundamental parameters, spectral
classifications and notations of possible binarity are given. Tables
with line data for O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Fe, Ni and
Ba, equivalent widths and resulting abundances are also given. (4
data files).
Title: Nucleosynthetic signatures of the first stars
Authors: Frebel, Anna; Aoki, Wako; Christlieb, Norbert; Ando, Hiroyasu;
Asplund, Martin; Barklem, Paul S.; Beers, Timothy C.; Eriksson,
Kjell; Fechner, Cora; Fujimoto, Masayuki Y.; Honda, Satoshi; Kajino,
Toshitaka; Minezaki, Takeo; Nomoto, Ken'ichi; Norris, John E.; Ryan,
Sean G.; Takada-Hidai, Masahide; Tsangarides, Stelios; Yoshii, Yuzuru
Bibcode: 2005Natur.434..871F
Altcode: 2005astro.ph..3021F
The chemically most primitive stars provide constraints on the nature
of the first stellar objects that formed in the Universe; elements
other than hydrogen, helium and traces of lithium present within
these objects were generated by nucleosynthesis in the very first
stars. The relative abundances of elements in the surviving primitive
stars reflect the masses of the first stars, because the pathways of
nucleosynthesis are quite sensitive to stellar masses. Several models
have been suggested to explain the origin of the abundance pattern
of the giant star HE0107-5240, which hitherto exhibited the highest
deficiency of heavy elements known. Here we report the discovery of
HE1327-2326, a subgiant or main-sequence star with an iron abundance
about a factor of two lower than that of HE0107-5240. Both stars
show extreme overabundances of carbon and nitrogen with respect to
iron, suggesting a similar origin of the abundance patterns. The
unexpectedly low Li and high Sr abundances of HE1327-2326, however,
challenge existing theoretical understanding: no model predicts the
high Sr abundance or provides a Li depletion mechanism consistent with
data available for the most metal-poor stars.
Title: An Extremely Large Excess of 18O in the
Hydrogen-deficient Carbon Star HD 137613
Authors: Clayton, Geoffrey C.; Herwig, Falk; Geballe, T. R.; Asplund,
Martin; Tenenbaum, Emily D.; Engelbracht, C. W.; Gordon, Karl D.
Bibcode: 2005ApJ...623L.141C
Altcode: 2005astro.ph..3198C
We report the discovery of a uniquely large excess of 18O in
the hydrogen-deficient carbon (HdC) star HD 137613 based on a spectrum
of the first-overtone bands of CO at 2.3-2.4 μm in which three
strong absorption bands of 12C18O are clearly
present. Bands of 12C16O also are present, but no
bands of 13C16O or 12C17O
are seen. We estimate an isotopic ratio 16O/18O
<~ 1. The solar value of this ratio is ~500. Neither He-core burning
nor He-shell flash burning can produce the isotopic ratios of oxygen and
carbon observed in HD 137613. However, a remarkable similarity exists
between the observed abundances and those found in the outer layers of
the broad He shell of early-asymptotic giant branch (AGB) stars, soon
after the end of He-core burning. It is not known how the outer envelope
down to the He shell could be lost, but some mechanism of enhanced mass
loss must be involved. HD 137613 may be a post-early-AGB star with the
outer layers of the former He-burning shell as its photosphere. The
unusual elemental abundances of the HdC stars resemble those of the
R Coronae Borealis (RCB) stars, but HdC stars do not produce clouds
of dust that produce declines in brightness. None of the other RCB or
HdC stars observed show significant 18O.
Title: VizieR Online Data Catalog: Center-to-limb variation of quiet
Sun (Allende+, 2004)
Authors: Allende Prieto, C.; Asplund, M.; Fabiani Bendicho, P.
Bibcode: 2005yCat..34231109A
Altcode:
Solar observations of the center-to-limb variation of several spectral
lines were carried out in October 22-23, 1997, with the Gregory Coude
Telescope (GCT) and its Czerny-Turner echelle spectrograph at the
Observatorio del Teide (Tenerife, Spain). We secured spectra
for 8 spectral setups in 6 different positions across the solar
disk, as summarized in Table 1. Positions #1 to #5 were always
at heliocentric angles theta = 0, 15, 30, 45, and 60 degrees (mu =
cos(theta) = 1.00, 0.97, 0.87, 0.71, and 0.50) along a straight line
crossing the center of the solar disk. Position #6 was also selected
along the same direction, sometimes at theta = 75 degrees and others
at 80 degrees (mu = 0.26 or 0.17). (2 data files).
Title: Line formation in solar granulation. VI. [C I], C I, CH and
C2 lines and the photospheric C abundance
Authors: Asplund, M.; Grevesse, N.; Sauval, A. J.; Allende Prieto,
C.; Blomme, R.
Bibcode: 2005A&A...431..693A
Altcode: 2004astro.ph.10681A
The solar photospheric carbon abundance has been determined from [C
I], C I, CH vibration-rotation, CH A-X electronic and C2
Swan electronic lines by means of a time-dependent, 3D, hydrodynamical
model of the solar atmosphere. Departures from LTE have been considered
for the C I lines. These turned out to be of increasing importance for
stronger lines and are crucial to remove a trend in LTE abundances
with the strengths of the lines. Very gratifying agreement is found
among all the atomic and molecular abundance diagnostics in spite of
their widely different line formation sensitivities. The mean value
of the solar carbon abundance based on the four primary abundance
indicators ([C I], C I, CH vibration-rotation, C2 Swan)
is log ɛC = 8.39 ± 0.05, including our best estimate of
possible systematic errors. Consistent results also come from the CH
electronic lines, which we have relegated to a supporting role due
to their sensitivity to the line broadening. The new 3D based solar C
abundance is significantly lower than previously estimated in studies
using 1D model atmospheres.
Title: Lithium isotopic abundances in metal-poor stars
Authors: Asplund, Martin; Nissen, Poul Erik; Lambert, David L.;
Primas, Francesca; Smith, Verne V.
Bibcode: 2005IAUS..228...53A
Altcode:
We report on a survey of 7Li and 6Li isotopic
abundances in metal-poor halo stars. The spectra of the 24 stars
observed with VLT/UVES are of exceptionally high quality: S/N>400
and resolving power R ≃ 120 000. The 7Li abundances on
our Hα Teff-scale show very small intrinsic scatter and
a pronounced [Fe/H]-dependence. The resulting estimated primordial
7Li abundance is about 0.5 dex lower than predicted from
Big Bang nucleosynthesis and the baryon density inferred by the cosmic
microwave background. Nine of the stars yield a positive detection
(>2σ) of 6Li, which suggests the existence of a
6Li plateau for halo stars. The most interesting result is
the presence of 6Li in the very metal-poor ([Fe/H]=-2.74)
dwarf LP815-43 at the level of 6Li/7Li ≃
0.05±0.02. According to models for stellar Li depletion due to
diffusion or rotationally-induced mixing, a 0.5 dex 7Li
depletion would require an unrealistic high initial 6Li
abundance (log 6Li ≥ 2.0). Simultaneously, the
observed high 6Li abundance at such low [Fe/H] can not be
reconciled with existing models for Galactic cosmic ray spallation and
α-fusion reactions. This opens up exciting prospects of pre-Galactic
6Li production, possibly due to cosmological cosmic rays
or late-decaying massive particles such as the gravitino or neutralino
in the Big Bang.
Title: Globular cluster abundances in the light of 3D hydrodynamical
model atmospheres
Authors: Asplund, Martin
Bibcode: 2005HiA....13..151A
Altcode:
Recently realistic time-dependent 3D hydrodynamical simulations of
stellar surface convection have become feasible. Such 3D hydrodynamical
model atmospheres often show significant differences in their
atmospheric structures compared with existing hydrostatic 1D model
atmospheres which directly propagate to differences in the emergent
spectrum and the inferred interpretations in terms of for example
elemental abundances. In this review I will discuss the impact of the
new generation of 3D model atmospheres on the derived abundances for
globular clusters concentrating on elements of specific importance for
the understanding of the formation and evolution of globular clusters.
Title: Effective temperatures and lithium abundances of halo
turnoff stars
Authors: Nissen, P. E.; Akerman, C.; Asplund, M.; Fabbian, D.;
Pettini, M.
Bibcode: 2005IAUS..228..101N
Altcode:
Effective temperatures of 30 turnoff stars with -3.2 {[Fe/H]{
have been derived from the profiles of Balmer lines in high S/N,
VLT/UVES spectra. While the systematic error of Teff may
be of the order of 100K, the differential values of Teff
are determined with a one-sigma precision of ∼25K. These precise
Teff values are used in a study of the slope and dispersion
of the Li abundance as a function of [Fe/H]. A small, but significant
cosmic dispersion in A(Li) appears to be present exemplified by the
two very metal-poor stars G64-12 and G64-37.
Title: The evolution of the C/O ratio in metal-poor halo stars
Authors: Akerman, C. J.; Carigi, L.; Nissen, P. E.; Pettini, M.;
Asplund, M.
Bibcode: 2005HiA....13Q.578A
Altcode:
Whilst it is known that oxygen is produced in massive stars and is
dispersed into the ISM by type II supernovae the origins and yields of
carbon are less certain. Carbon is produced during helium burning in
both massive intermediate-mass and low-mass stars but the dependence
of the carbon yield on stellar mass and initial composition is not
well known. A reliable determination of the C/O abundance ratio as
a function of the oxygen abundance for main-sequence stars will be
helpful in gaining an understanding of these problems. Previous
studies have measured the C/O ratio for disk stars using forbidden lines
([CI] 8727.1 A [OI] 6300.3 A). In halo main-sequence stars with [Fe/H]
< -1 the forbidden carbon line is too weak to be measured. Tomkin
et al. (1992) use instead four high excitation CI lines around 9100A
together with the oxygen triplet at 7774 A. To test and expand on
their results which hint at interesting features in the trend of [C/O]
we derive C and O abundances for 35 metal-poor halo stars from high
resolution near-IR VLT/UVES spectra. Combined with the previous [C/O]
measurements a more detailed trend with oxygen abundance is derived.
Title: Sulphur and zinc abundances in halo and disk stars
Authors: Nissen, P. E.; Chen, Y. Q.; Asplund, M.; Pettini, M.
Bibcode: 2005HiA....13..587N
Altcode:
Sulphur and zinc are key elements in studies of the chemical evolution
of DLAs because they are undepleted on interstellar dust. It is often
assumed that S is an ""alpha""-element made by Type II supernovae
whereas Zn follows iron in its chemical evolution. If correct the S/Zn
ratio can be used as ""a chemical clock"" to date the star formation
process in DLAs. Recent studies of S/Fe and Zn/Fe in Galactic stars
have however questioned these assumptions. In order to advance
the study of the chemical evolution of S and Zn in our Galaxy we have
obtained high resolution ESO VLT/UVES spectra for 35 halo stars and
the Xinglong 2.16m telescope has been used to observe disk stars. From
a model atmosphere analysis of these spectra including estimates of
3D effects we have derived the trends of S/Fe and Zn/Fe for Galactic
stars in the metallicity range -3.2 < [Fe/H] < +0.2. Preliminary
results suggest that S behaves like an ""alpha""-element whereas Zn
may show small deviations from the trend of iron.
Title: Uncertainties in Stellar Abundance Analyses
Authors: Asplund, Martin
Bibcode: 2005HiA....13..542A
Altcode:
No abstract at ADS
Title: Oxygen abundances in metal-poor subgiants
Authors: García Pérez, A. E.; Asplund, M.; Primas, F.; Nissen,
P. E.; Gustafsson, B.
Bibcode: 2005IAUS..228..257G
Altcode: 2005IAUS..228..257P
There seems to be no consensus on the [O/Fe] values found in
metal-poor stars nor their trend with metallicity: different
indicators give different results. We present here [O/Fe] derived
from three different oxygen abundance indicators ([OI], OI and OH UV
lines) for a sample of thirteen subgiant stars with metallicities
in the range -3≤[Fe/H]≤-1.5. Oxygen and iron abundances were
determined from the analysis of high S/N spectra acquired with
the UVES spectrograph at VLT. We found good agreement between
[O/Fe] estimates based on OH and the estimates based on [Oi]
(mean difference∼-0.09±0.25(s.d.)), although the scatter is not
insignificant. Unfortunately, good agreement is not reached for
the third indicator (mean difference∼0.19±0.22(s.d.)). Our [OI]
and OH-based estimates do not show a well defined linear trend with
metallicity. Another interesting result is that the abundances based
on molecular lines ([O/Fe]∼0.45) are in general lower than previous
published results for turn-off stars even though a lower solar oxygen
abundance (A(O)=8.74) was assumed.
Title: Chemical Abundance Patterns of Extremely Metal-Poor Stars with
[Fe/H]≲ -3.5
Authors: Aoki, W.; Beers, T. C.; Christlieb, N.; Frebel, A.; Norris,
J. E.; Honda, S.; Takada-Hidai, M.; Asplund, M.; Ando, H.; Ryan, S. G.;
Tsangarides, S.; Nomoto, K.; Fujimoto, M. Y.; Kajino, T.; Yoshii, Y.
Bibcode: 2005IAUS..228..195A
Altcode:
We present preliminary results on the chemical abundance patterns of
extremely metal-poor stars obtained during an ongoing observing program
with Subaru/HDS. High-resolution, high signal-to-noise spectra have
been obtained for 14 stars with [Fe/H]≲ -3. Five of them exhibit
clear overabundances of carbon, a remarkable characteristic found
only in the most metal-poor range. One of the carbon-rich stars,
HE 1327-2326, has [Fe/H]NLTE=-5.4, the lowest Fe abundance
known. No stars with {-}5 {[Fe/H] { have yet been found in our program,
suggesting that quite different enrichment processes were responsible
for stars with [Fe/H] { and [Fe/H] {>} {-}4. While neutron-capture
elements are deficient in most of our stars, one star (BS 16550-087)
exhibits large enhancements of its light neutron-capture elements (Sr,
Y and Zr), providing a strong constraint on models for the production
of such elements in the very early Galaxy.
Title: CI non LTE spectral line formation in late-type stars
Authors: Fabbian, D.; Asplund, M.; Carlsson, M.; Kiselman, D.
Bibcode: 2005IAUS..228..255F
Altcode: 2005astro.ph..8063F
We present non-Local Thermodynamic Equilibrium (non-LTE) calculations
for neutral carbon spectral line formation, carried out for a grid
of model atmospheres covering the range of late-type stars. The
results of our detailed calculations suggest that the carbon
non-LTE corrections in these stars are higher than usually adopted,
remaining substantial even at low metallicity. For the most metal-poor
stars in the sample of Akerman et al (2004), the effects are of the
order of ΔlogɛC ≃ -0.35ldots-0.45 (when neglecting H
collisions). Applying our results to those observations, the apparent
[C/O] upturn seen in their LTE analysis is no longer present, thus
revealing no need to invoke contributions from Pop. III stars to the
carbon nucleosynthesis.
Title: The new record holder for the most iron-poor star: HE 1327
2326, a dwarf or subgiant with [Fe/H[=[minus sign]5.4
Authors: Frebel, A.; Aoki, W.; Christlieb, N.; Ando, H.; Asplund, M.;
Barklem, P. S.; Beers, T. C.; Eriksson, K.; Fechner, C.; Fujimoto,
M. Y.; Honda, S.; Kajino, T.; Minezaki, T.; Nomoto, K.; Norris, J. E.;
Ryan, S. G.; Takada-Hidai, M.; Tsangarides, S.; Yoshii, Y.
Bibcode: 2005IAUS..228..207F
Altcode: 2005astro.ph..9658F
We describe the discovery of HE 1327-2326, a dwarf or subgiant with
[Fe/H]=-5.4. The star was found in a sample of bright metal-poor
stars selected from the Hamburg/ESO survey. Its abundance pattern is
characterized by very high C and N abundances. The detection of Sr
which is overabundant by a factor of 10 as compared to iron and the
Sun, suggests that neutron-capture elements had already been produced
in the very early Galaxy. A puzzling Li depletion is observed in this
unevolved star which contradicts the value of the primordial Li derived
from WMAP and other Li studies. Possible scenarios for the origin of
the abundance pattern (Pop. II or Pop. III) are presented as well as
an outlook on future observations.
Title: The Impact of Non-LTE Effects and Granulation Inhomogeneities
on the Derived Iron and Oxygen Abundances in Metal-Poor Halo Stars
Authors: Shchukina, N. G.; Trujillo Bueno, J.; Asplund, M.
Bibcode: 2005ApJ...618..939S
Altcode: 2004astro.ph.10475S
This paper presents the results of a detailed theoretical investigation
of the impact of non-LTE (NLTE) effects and of granulation
inhomogeneities on the derived iron and oxygen abundances in the
metal-poor halo subgiant HD 140283. Our analysis is based on both the
``classical'' one-dimensional stellar atmosphere models and on the
new generation of three-dimensional hydrodynamic models. The NLTE
calculations presented here have been carried out without inelastic
collisions with neutral hydrogen atoms. We find that if NLTE effects
are taken into account when synthesizing the Fe I spectrum in both
types of atmospheric models, then the derived iron abundance turns out
to be very similar in both cases. The emergent spectral line profiles
in both models are very much weaker in NLTE than in LTE because the
UV overionization mechanism produces a very strong underpopulation
of the Fe I levels, in particular in the granular regions of the
three-dimensional model. As a result, the NLTE effects on the derived
iron abundance are very important, amounting to ~0.9 and to ~0.6 dex in
the three- and one-dimensional cases, respectively. On the other hand,
we find that NLTE and three-dimensional effects have to be taken into
account for a reliable determination of the iron abundance from weak Fe
II lines, because the significant overexcitation of their upper levels
in the granular regions tend to produce emission features. As a result,
such Fe II lines are weaker than in LTE and the abundance correction
amounts to ~0.4 dex for the three-dimensional case. We also derive
the oxygen-to-iron abundance ratio in the metal-poor star HD 140283
by using the O I triplet at 7772-7775 Å and the forbidden [O I] line
at 6300 Å. Our results for the oxygen abundance confirm the values
reported in some recent investigations. While the oxygen abundance
derived from the O I IR triplet is not very sensitive to the presence
of granulation inhomogeneities, such three-dimensional effects amount to
~-0.2 dex for the [O I] line. The NLTE abundance correction for the O I
IR triplet turns out to be -0.2 dex, approximately. Interestingly, when
both NLTE and three-dimensional effects are taken into account there
still remain significant discrepancies in the iron abundances derived
from Fe I and Fe II lines, as well as in the oxygen abundances inferred
from the O I and [O I] lines. We conclude that the discrepancies could
be due to uncertainties in the stellar parameters of this metal-poor
star. We argue that adopting Teff~5600 K (instead of
Teff~5700 K) and [Fe/H]~-2.0 (instead of [Fe/H]~-2.5)
substantially reduces the discrepancies in the abundances of iron and
oxygen inferred from several spectral lines. Under such circumstances,
we find [O/Fe]~0.5 at [Fe/H]=-2. Obviously, our tentative conclusion
that the metallicity of this type of metal-poor star is significantly
larger than previously thought may have far-reaching implications in
stellar astrophysics.
Title: 3D hydrodynamical model stellar atmospheres of metal-poor
red giants
Authors: Collet, Remo; Asplund, Martin; Trampedach, Regner
Bibcode: 2005IAUS..228..247C
Altcode:
We investigate the main differences between static 1D and 3D
time-dependent model stellar atmospheres of red giants at very low
metallicities. We focus in particular on the impact of 3D LTE spectral
line formation on the derivation of elemental abundances for the
extremely metal-poor ([Fe/H] ≈-5.3) red giant HE 0107-5240.
Title: The New Solar Chemical Composition
Authors: Grevesse, N.; Asplund, M.; Sauval, A. J.
Bibcode: 2005EAS....17...21G
Altcode:
We present our current knowledge of the solar chemical composition based
on the recent significant downward revision of the solar photospheric
abundances of the most abundant metals very recently reviewed in detail
by Asplund et al. (2005a). These new solar abundances result from the
use of a 3D hydrodynamical model of the solar atmosphere instead of
the classical 1D hydrostatic models, accounting for departures from
LTE, and improved atomic and molecular data. With these abundances,
the new solar metallicity, Z, and Z/X, decrease to Z = 0.012 and Z/X =
0.0165 respectively, almost a factor of 2 lower than earlier widely
used values. While resolving a number of longstanding problems, the new
3D-based solar photospheric composition also poses serious challenges
for the standard solar model.
Title: Chemical abundances in 43 metal-poor stars
Authors: Gustafsson, Bengt; Asplund, Martin; Edvardsson, Bengt;
Jonsell, Karin; Magain, Pierre; Nissen, Poul Erik
Bibcode: 2005IAUS..228..259G
Altcode:
We have derived abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Fe,
Ni and Ba for 43 metal-poor field stars, mostly stars at the turn-off
point and on the subgiant branch, in the interval {-}3.0{[Fe/H]{. The
analysis is differential relative to the Sun. Oxygen abundances,
with consideration of NLTE effects, were derived from the OI 777.4 nm
triplet lines. We find [O/Fe] to gradually increase with decreasing
[Fe/H], though considerably slower than has earlier been obtained from
OH lines in the UV. A scatter in [O,Mg,Ca,Ti/Fe] at a given [Fe/H] is
found and we argue that this scatter is partly real. The deviations from
the mean trends of abundance ratios vs [Fe/H] are found to correlate
in non-trivial ways for different abundances. Similar trends are found
from results of accurate studies by other groups. This seems to give
further evidence for the hypothesis that the stars once formed in
different subsystems, with different star-formation rates.The paper
is in press in A&A, may be obtained as astro-ph/0505118.
Title: Center-to-limb variation of solar line profiles as a test of
NLTE line formation calculations
Authors: Allende Prieto, C.; Asplund, M.; Fabiani Bendicho, P.
Bibcode: 2004A&A...423.1109A
Altcode: 2004astro.ph..5154A; 2004astro.ph..5154P
We present new observations of the center-to-limb variation
of spectral lines in the quiet Sun. Our long-slit spectra are
corrected for scattered light, which amounts to 4-8% of the continuum
intensity, by comparison with a Fourier transform spectrum of the disk
center. Different spectral lines exhibit different behaviors, depending
on their sensitivity to the physical conditions in the photosphere and
the range of depths they probe as a function of the observing angle,
providing a rich database to test models of the solar photosphere and
line formation. We examine the effect of inelastic collisions with
neutral hydrogen in NLTE line formation calculations of the oxygen
infrared triplet, and the Na I λ6160.8 line. Adopting a classical
one-dimensional theoretical model atmosphere, we find that the sodium
transition, formed in higher layers, is more effectively thermalized
by hydrogen collisions than the high-excitation oxygen lines. This
result appears as a simple consequence of the decrease of the ratio
NH/Ne with depth in the solar photosphere. The
center-to-limb variation of the selected lines is studied both under
LTE and NLTE conditions. In the NLTE analysis, inelastic collisions
with hydrogen atoms are considered with a simple approximation or
neglected, in an attempt to test the validity of such approximation. For
the sodium line studied, the best agreement between theory and
observation happens when NLTE is considered and inelastic collisions
with hydrogen are neglected in the rate equations. The analysis of
the oxygen triplet benefits from a very detailed calculation using an
LTE three-dimensional model atmosphere and NLTE line formation. The
χ2 statistics favors including hydrogen collisions with
the approximation adopted, but the oxygen abundance derived in that
case is significantly higher than the value derived from OH infrared
transitions. GCT spectra are only available in electronic form
at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)
or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/423/1109
Title: Line formation in solar granulation. V. Missing UV-opacity
and the photospheric Be abundance
Authors: Asplund, M.
Bibcode: 2004A&A...417..769A
Altcode: 2003astro.ph.12291A
The possibility of unaccounted for opacity sources in the UV for
late-type stars has often been invoked to explain discrepancies
between predicted and observed flux distributions and spectral
line strengths. Such missing UV-opacity could among other things
have a significant impact on abundance determination for elements
whose only relevant spectral features are accessible in this
wavelength region, such as Be. Here, the study by Balachandran
& Bell (\cite{Balachandran98}) is re-visited in the light of a
realistic 3D hydrodynamical solar model atmosphere and the recently
significantly downward revised solar O abundance obtained with the
same model atmosphere. The amount of missing UV-opacity, if any, is
quantified by enforcing that the OH A-X electronic lines around 313
nm produce the same O abundance as the other available diagnostics:
OH vibration-rotation and pure rotation lines in the IR, the forbidden
[O I] 630.0 and 636.3 nm lines and high-excitation, permitted O I
lines. This additional opacity is then applied for the synthesis of the
Be II line at 313.0 nm to derive a solar photospheric Be abundance in
excellent agreement with the meteoritic value, thus re-enforcing the
conclusions of Balachandran & Bell. The about 50% extra opacity
over accounted for opacity sources can be well explained by recent
calculations by the Iron Project for photo-ionization of Fe I.
Title: Line formation in solar granulation. IV. [O I], O I and OH
lines and the photospheric O abundance
Authors: Asplund, M.; Grevesse, N.; Sauval, A. J.; Allende Prieto,
C.; Kiselman, D.
Bibcode: 2004A&A...417..751A
Altcode: 2003astro.ph.12290A
The solar photospheric oxygen abundance has been determined from
[O I], O I, OH vibration-rotation and OH pure rotation lines by
means of a realistic time-dependent, 3D, hydrodynamical model of
the solar atmosphere. In the case of the O I lines, 3D non-LTE
calculations have been performed, revealing significant departures
from LTE as a result of photon losses in the lines. We derive a solar
oxygen abundance of log ɛO = 8.66 ± 0.05. All oxygen
diagnostics yield highly consistent abundances, in sharp contrast
with the results of classical 1D model atmospheres. This low value
is in good agreement with measurements of the local interstellar
medium and nearby B stars. This low abundance is also supported by
the excellent correspondence between lines of very different line
formation sensitivities, and between the observed and predicted line
shapes and center-to-limb variations. Together with the corresponding
down-ward revisions of the solar carbon, nitrogen and neon abundances,
the resulting significant decrease in solar metal mass fraction to Z =
0.0126 can, however, potentially spoil the impressive agreement between
predicted and observed sound speed in the solar interior determined
from helioseismology.
Title: Sulphur and zinc abundances in Galactic stars and damped
Lyα systems
Authors: Nissen, P. E.; Chen, Y. Q.; Asplund, M.; Pettini, M.
Bibcode: 2004A&A...415..993N
Altcode: 2003astro.ph.11529N
High resolution spectra of 34 halo population dwarf and subgiant
stars have been obtained with VLT/UVES and used to derive sulphur
abundances from the λ λ 8694.0, 8694.6 and λ λ 9212.9, 9237.5 S
I lines. In addition, iron abundances have been determined from 19 Fe
II lines and zinc abundances from the λ λ 4722.2, 4810.5 lines. The
abundances are based on a classical 1D, LTE model atmosphere analysis,
but effects of 3D hydrodynamical modelling on the [S/Fe], [Zn/Fe] and
[S/Zn] ratios are shown to be small. We find that most halo stars
with metallicities in the range -3.2 < [Fe/H] < -0.8 have a
near-constant [S/Fe] ≃ +0.3; a least square fit to [S/Fe] vs. [Fe/H]
shows a slope of only -0.04 ± 0.01. Among halo stars with -1.2 <
[Fe/H] < -0.8 the majority have [S/Fe] ≃ +0.3, but two stars
(previously shown to have low α/Fe ratios) have [S/Fe] ≃ 0.0. For
disk stars with [Fe/H] > -1, [S/Fe] decreases with increasing [Fe/H]
. Hence, sulphur behaves like other typical α-capture elements, Mg,
Si and Ca. Zinc, on the other hand, traces iron over three orders
of magnitude in [Fe/H], although there is some evidence for a small
systematic Zn overabundance ([Zn/Fe] ≃ +0.1) among metal-poor disk
stars and for halo stars with [Fe/H] < -2.0. Recent measurements of
S and Zn in ten damped Lyα systems (DLAs) with redshifts between 1.9
and 3.4 and zinc abundances in the range -2.1 < [Zn/H] < -0.15
show an offset relative to the [S/Zn] - [Zn/H] relation in Galactic
stars. Possible reasons for this offset are discussed, including
low and intermittent star formation rates in DLAs. Based on
observations collected at the European Southern Observatory, Chile
(ESO No. 67.D-0106). Table A1 is only available in electronic
form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)
or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/415/993
Title: The evolution of the C/O ratio in metal-poor halo stars
Authors: Akerman, C. J.; Carigi, L.; Nissen, P. E.; Pettini, M.;
Asplund, M.
Bibcode: 2004A&A...414..931A
Altcode: 2003astro.ph.10472A
We report new measurements of carbon and oxygen abundances in 34 F and
G dwarf and subgiant stars belonging to the halo population and spanning
a range of metallicity from [Fe/H] = -0.7 to -3.2 . The survey is based
on observations of four permitted lines of C I near 9100 Å and the O
I,λ 7774 triplet, all recorded at high signal-to-noise ratios with the
UVES echelle spectrograph on the ESO VLT. The line equivalent widths
were analysed with the 1D, LTE, MARCS model atmosphere code to deduce
C and O abundances; corrections due to non-LTE and 3D effects are
discussed. When combined with similar published data for disk stars,
our results confirm the metallicity dependence of the C/O ratio known
from previous stellar and interstellar studies: C/O drops by a factor
of ∼3-4 as O/H decreases from solar to ∼1/10 solar. Analysed
within the context of standard models for the chemical evolution of
the solar vicinity, this drop results from the metallicity dependence
of the C yields from massive stars with mass loss, augmented by the
delayed release of C from stars of low and intermediate mass. The
former is, however, always the dominant factor. Our survey has also
uncovered tentative evidence to suggest that, as the oxygen abundance
decreases below [O/H] = -1, [C/O] may not remain constant at [C/O] =
-0.5, as previously thought, but increase again, possibly approaching
near-solar values at the lowest metallicities ([O/H] ≲ -3). With the
current dataset this is no more than a 3σ effect and it may be due
to metallicity-dependent non-LTE corrections to the [C/O] ratio which
have not been taken into account. However, its potential importance
as a window on the nucleosynthesis by Population III stars is a
strong incentive for future work, both observational and theoretical,
to verify its reality. Based on observations collected at the
European Southern Observatory, Chile (ESO No. 67.D-0106).
Title: Globular cluster abundances in the light of 3D hydrodynamical
model atmospheres
Authors: Asplund, Martin
Bibcode: 2004MmSAI..75..300A
Altcode: 2003astro.ph.10444A
The new generation of 3D hydrodynamical model atmospheres have been
employed to study the impact of a realistic treatment of stellar
convection on element abundance determinations of globular cluster stars
for a range of atomic and molecular lines. Due to the vastly different
temperature structures in the optically thin atmospheric layers in 3D
metal-poor models compared with corresponding hydrostatic 1D models,
some species can be suspected to be hampered by large systematic errors
in existing analyses. In particular, 1D analyses based on minority
species and low excitation lines may overestimate the abundances by
>0.3 dex. Even more misleading may be the use of molecular lines for
metal-poor globular clusters. However, the prominent observed abundance
(anti-)correlations and cluster variations are largely immune to the
choice of model atmospheres.
Title: The future of stellar model atmospheres: macroscopic
nightmares?
Authors: Asplund, M.
Bibcode: 2004EAS....11....3A
Altcode:
Stellar atmospheres represent unique windows for understanding stellar,
galactic and cosmic evolution by being responsible for the emission of
stellar spectra. Much progress has been made over the years in modelling
stellar atmospheres but still the modelling efforts are hampered by
various, often questionable, assumptions and approximations. This review
describes promising avenues for improving the realism of stellar model
atmospheres for hot (spectral types O, B, A), cool (F, G, K) and very
cool (M and later) stars, respectively, in the coming decade. A common
theme will be time-dependent 3D hydrodynamical calculations with a
detailed non-LTE treatment of the radiative transfer. It is argued
that this is fully within the realm of possibility on this time-scale
and indeed will be necessary to complement the expected advances on
the observational side.
Title: Infrared Absorption By Carbon Monoxide in R CrB Type Stars
Authors: Tenenbaum, E.; Clayton, G. C.; Englebracht, C.; Asplund, M.
Bibcode: 2003AAS...20312701T
Altcode: 2003BAAS...35.1413T
R Coronae Borealis (RCB) type stars experience massive irregular
declines caused by circumstellar dust formation. The dust formation
mechanism remains a mystery, and it has been proposed that CO molecules
play a cooling role in the dust formation process. The detection
of the CO first vibrational overtone (Δ v=2) absorption band in
RCB spectra was first reported by Clayton in 1999. We report on the
first attempt to analyze the CO Δ v=2 band in a large survey of RCB
stars. Low-resolution IR spectra of 10 RCB stars, obtained with FSpec
on the 90" telescope at Steward Observatory, were analyzed for the
presence and, if applicable, equivalent widths of CO Δ v=2 absorption
lines. Effective temperatures of the ten stars range from 3500 to
20000 K. We compared the spectra to line-blanketed model spectra of
RCB stars. As predicted by the model, the CO bands are strongest in
the coolest RCB stars. No correlation was found between the presence
of CO bands and lightcurve declines. This project was supported by the
NSF/REU grant AST-0097694 and the Nantucket Maria Mitchell Association.
Title: VizieR Online Data Catalog: FeII, ZNI and SI abundances on
halo stars (Nissen+, 2004)
Authors: Nissen, P. E.; Chen, Y. Q.; Asplund, M.; Pettini, M.
Bibcode: 2003yCat..34150993N
Altcode:
The table gives equivalent widths (in m{AA}) for 19 FeII lines, two
ZnI lines, and four SI lines, as measured in high resolution VLT/UVES
spectra of 34 metal-poor, main sequence and subgiant, halo stars. (2 data files).
Title: Inelastic H+Li and H-+Li+ collisions
and non-LTE Li I line formation in stellar atmospheres
Authors: Barklem, P. S.; Belyaev, A. K.; Asplund, M.
Bibcode: 2003A&A...409L...1B
Altcode: 2003astro.ph..8170B
Rate coefficients for inelastic collisions between Li and H
atoms covering all transitions between the asymptotic states
Li(2s,2p,3s,3p,3d,4s,4p,4d,4f)+H(1s) and Li++H-
are presented for the temperature range 2000-8000 K based on recent
cross-section calculations. The data are of sufficient completeness
for non-LTE modelling of the Li I 670.8 nm and 610.4 nm features in
late-type stellar atmospheres. Non-LTE radiative transfer calculations
in both 1D and 3D model atmospheres have been carried out for test
cases of particular interest. Our detailed calculations show that
the classical modified Drawin-formula for collisional excitation and
de-excitation (Li*+H \rightleftharpoons Li*'+H)
over-estimates the cross-sections by typically several orders of
magnitude and consequently that these reactions are negligible
for the line formation process. However, the charge transfer
reactions collisional ion-pair production and mutual neutralization
(Li*+H \rightleftharpoons Li++H-) are
of importance in thermalizing Li. In particular, 3D non-LTE calculations
of the Li I 670.8 nm line in metal-poor halo stars suggest that 1D
non-LTE results over-estimate the Li abundance by up to about 0.1 dex,
aggrevating the discrepancy between the observed Li abundances and
the primordial Li abundance as inferred by the WMAP analysis of the
cosmic microwave background.
Title: Multi-level 3D non-LTE computations of lithium lines in the
metal-poor halo stars HD 140283 and HD 84937
Authors: Asplund, M.; Carlsson, M.; Botnen, A. V.
Bibcode: 2003A&A...399L..31A
Altcode: 2003astro.ph..2406A
The lithium abundances in metal-poor halo stars are of importance
for cosmology, galaxy evolution and stellar structure. In an attempt
to study possible systematic errors in the derived Li abundances,
the line formation of Li I lines has been investigated by means of
realistic 3D hydrodynamical model atmospheres of halo stars and
3D non-LTE radiative transfer calculations. These are the first
detailed 3D non-LTE computations reported employing a multi-level
atomic model showing that such problems are now computationally
tractable. The detailed computations reveal that the Li I population
has a strong influence from the radiation field rather than the local
gas temperature, indicating that the low derived Li abundances found by
Asplund et al. (\cite{Asplund1999}) are an artifact of their assumption
of LTE. Relative to 3D LTE, the detailed calculations show pronounced
over-ionization. In terms of abundances the 3D non-LTE values are
within 0.05 dex of the 1D non-LTE results for the particular cases of
HD 140283 and HD 84937, which is a consequence of the dominance of the
radiation in determining the population density of Li I. Although 3D
non-LTE can be expected to give results rather close (~+/- 0.1 dex)
to 1D non-LTE for this reason, there may be systematic trends with
metallicity and effective temperature.
Title: New generations of stellar model atmospheres
Authors: Asplund, Martin
Bibcode: 2003astro.ph..2409A
Altcode:
Stellar model atmospheres form the basis for any element abundance
determination and hence are crucial ingredients for studies of stellar,
galactic and cosmic evolution. With recent observational progress with
the advent of 8m-class telescopes and efficient spectrographs, the
dominant source of uncertainty today originates with the assumptions
and approximations in the analyses, emphasizing the great need for
continuing efforts in improving the realism of stellar atmosphere
modelling. In the present contribution I will describe recent
progress in this regard by focussing on three complementary types
of model atmospheres: line-blanketed non-LTE models of hot stars,
3D hydrodynamical models of cool stars and semi-empirical models for
large-scale stellar abundance analyses.
Title: Uncertainties in Stellar Abundance Analyses
Authors: Asplund, Martin
Bibcode: 2003IAUJD..15E...8A
Altcode: 2003astro.ph.10445A
Stellar element abundances are never observed. Instead they are
inferred from observations using models of the stellar atmospheres
and the line-forming processes. Any shortcomings in this modelling
will therefore directly affect the conclusions inferred about the
stellar abundances. For late-type stars the most severe approximations
normally done is the use of 1D hydrostatic model atmospheres with
convection treated with the mixing length ""theory"" and adopting local
thermodynamic equilibrium for the line formation. Recently much progress
have been achieved in both of these areas which I will briefly describe
in the present talk emphasing on those aspects affecting the analyses of
metal-poor halo stars. In addition I will touch upon other uncertainties
in stellar abundance analysis such as transition probabilities.
Title: Globular Cluster Abundances and 3d Model Atmospheres
Authors: Asplund, Martin
Bibcode: 2003IAUJD...4E...7A
Altcode:
Recently realistic time-dependent 3D hydrodynamical simulations of
stellar surface convection have become feasible. Such 3D hydrodynamical
model atmospheres often show significant differences in their
atmospheric structures compared with existing hydrostatic 1D model
atmospheres which directly propagate to differences in the emergent
spectrum and the inferred interpretations in terms of for example
elemental abundances. In this review I will discuss the impact of the
new generation of 3D model atmospheres on the derived abundances for
globular clusters concentrating on elements of specific importance for
the understanding of the formation and evolution of globular clusters.
Title: Radiative Transfer with Very Few Wavelengths
Authors: Trampedach, R.; Asplund, M.
Bibcode: 2003ASPC..293..209T
Altcode: 2003tdse.conf..209T
Our aim is to develop an opacity sampling scheme suitable for 3D
hydrodynamical simulations of convective stellar atmospheres. This
paper presents a feasibility test for the concept.
Title: Radiative Transfer in 3D Model Stellar Atmospheres
Authors: Asplund, M.; Collet, R.
Bibcode: 2003ASPC..293..197A
Altcode: 2003astro.ph..2408A; 2003tdse.conf..197A
Recently 3D hydrodynamical simulations of stellar surface convection
have become feasible thanks to advances in computer technology and
efficient numerical algorithms. Available observational diagnostics
indicate that these models are highly realistic in describing the
topology of stellar granulation and for spectral line formation
purposes. The traditional free parameters (mixing length parameters,
micro- and macroturbulence) always inherent in standard 1D analyses
have thus finally become obsolete. These 3D models can therefore both
shed light on the elusive nature of stellar convection as well as be
employed in element abundance analyses. In the present contribution
we will describe some aspects of the models and possible applications
of them in terms of radiative transfer.
Title: Sulphur and Iron Abundances in Halo Stars
Authors: Nissen, P. E.; Chen, Y. Q.; Asplund, M.; Pettini, M.
Bibcode: 2003IAUS..210P.E51N
Altcode:
No abstract at ADS
Title: Effects of UV Line Blanketing on the Non-LTE Fe I Line
Formation
Authors: Collet, R.; García Pérez, A. E.; Asplund, M.; Thévenin, F.
Bibcode: 2003IAUS..210P..B3C
Altcode:
No abstract at ADS
Title: Non-LTE Determination of Iron and Oxygen Abundances Using 3D
Hydrodynamical Models: the Metal-Poor Star HD140283
Authors: Shchukina, N. G.; Vasiljeva, I. E.; Trujillo Bueno, J.;
Asplund, M.
Bibcode: 2003IAUS..210P.B10S
Altcode:
No abstract at ADS
Title: Stellar Abundance Analyses in the Light of 3D Hydrodynamical
Model Atmospheres
Authors: Asplund, M.
Bibcode: 2003IAUS..210..273A
Altcode: 2003astro.ph..2407A
I describe recent progress in terms of 3D hydrodynamical model
atmospheres and 3D line formation and their applications to stellar
abundance analyses of late-type stars. Such 3D studies remove the free
parameters inherent in classical 1D investigations (mixing length
parameters, macro- and microturbulence) yet are highly successful
in reproducing a large arsenal of observational constraints such as
detailed line shapes and asymmetries. Their potential for abundance
analyses is illustrated by discussing the derived oxygen abundances
in the Sun and in metal-poor stars, where they seem to resolve
long-standing problems as well as significantly alter the inferred
conclusions.
Title: New Generations of Stellar Model Atmospheres (invited review)
Authors: Asplund, M.
Bibcode: 2003ASPC..304..275A
Altcode: 2003cnou.conf..275A
No abstract at ADS
Title: Sulphur and Zinc Abundances in Halo and Disk Stars
Authors: Nissen, Poul Erik; Chen, Yu Qin; Asplund, Martin; Max, Pettini
Bibcode: 2003IAUJD..15E..26N
Altcode:
Sulphur and zinc are key elements in studies of the chemical evolution
of DLAs because they are undepleted on interstellar dust. It is often
assumed that S is an ""alpha""-element made by Type II supernovae
whereas Zn follows iron in its chemical evolution. If correct the S/Zn
ratio can be used as ""a chemical clock"" to date the star formation
process in DLAs. Recent studies of S/Fe and Zn/Fe in Galactic stars
have however questioned these assumptions. In order to advance
the study of the chemical evolution of S and Zn in our Galaxy we have
obtained high resolution ESO VLT/UVES spectra for 35 halo stars and
the Xinglong 2.16m telescope has been used to observe disk stars. From
a model atmosphere analysis of these spectra including estimates of
3D effects we have derived the trends of S/Fe and Zn/Fe for Galactic
stars in the metallicity range -3.2 < [Fe/H] < +0.2. Preliminary
results suggest that S behaves like an ""alpha""-element whereas Zn
may show small deviations from the trend of iron.
Title: The Granulation Fingerprints of Spectral Lines
Authors: Kiselman, D.; Asplund, M.
Bibcode: 2003IAUS..210P.E62K
Altcode:
No abstract at ADS
Title: Freshly Ionized Matter around the Final Helium Shell Flash
ObjectV4334 Sagittarii (Sakurai's Object)
Authors: Kerber, F.; Pirzkal, N.; De Marco, Orsola; Asplund, M.;
Clayton, G. C.; Rosa, M. R.
Bibcode: 2002ApJ...581L..39K
Altcode: 2002astro.ph.11275K
We report on the discovery of recently ionized hydrogen-deficient gas
in the immediate circumstellar environment of the final helium shell
flash star V4334 Sgr (Sakurai's object). On spectra obtained with
FORS2 multiobject spectroscopy, we have found spatially extended (~2")
emission from [N II], [O I], [O II], and very faint Hα and [S II]. In
the [N II] (λλ6548, 6583) lines, we have identified two components
located at velocities -350+/-50 and +200+/-50 km s-1,
relative to V4334 Sgr itself. The full width of the [N II] λ6583
feature at zero intensity corresponds to a velocity spread of ~1500
km s-1. On the basis of the available data, it is not
possible to conclusively determine the mechanism of ionization. Both
photoionization, from a rapidly evolving central star, and shock
excitation, resulting from the collision of the fast ouflows with slower
circumstellar matter, could account for the observed lines. The central
star is still hidden behind strong dust absorption, since only a faint
highly reddened continuum is apparent in the spectra. Theory states
that it will become hotter and will retrace its post-asymptotic giant
branch evolution toward the planetary nebula domain. Our detection
of the ionized ejecta from the very late helium shell flash marks the
beginning of a new phase in this star's amazingly rapid evolution. Based
on observations collected at the European Southern Observatory, Chile,
proposal 67.D-0405.
Title: O/Fe in metal-poor main sequence and subgiant stars
Authors: Nissen, P. E.; Primas, F.; Asplund, M.; Lambert, D. L.
Bibcode: 2002A&A...390..235N
Altcode: 2002astro.ph..5372N
A study of the O/Fe ratio in metal-poor main sequence and subgiant
stars is presented using the \ion{Oi},6300 Å line, the O I 7774 Å
triplet, and a selection of weak Fe Ii lines observed on high-resolution
spectra acquired with the VLT UVES spectrograph. The \ion{Oi line is
detected in the spectra of 18 stars with -2.4 < [Fe/H] < -0.5,
and the triplet is observed for 15 stars with Fe/H ranging from -1.0
to -2.7. The abundance analysis was made first using standard model
atmospheres taking into account non-LTE effects on the triplet: the
\ion{Oi} line and the triplet give consistent results with [O/Fe]
increasing quasi-linearly with decreasing [Fe/H] reaching [O/Fe] =~
+0.7 at [Fe/H] = -2.5. This trend is in reasonable agreement with
other results for [O/Fe] in metal-poor dwarfs obtained using standard
atmospheres and both ultraviolet and infrared OH lines. There is also
broad agreement with published results for [O/Fe] for giants obtained
using standard model atmospheres and the \ion{Oi} line, and the OH
infrared lines, but the O I lines give higher [O/Fe] values which may,
however, fall into place when non-LTE effects are considered. When
hydrodynamical model atmospheres representing stellar granulation in
dwarf and subgiant stars replace standard models, the [O/Fe] from the
\ion{Oi} and Fe Ii lines is decreased by an amount which increases
with decreasing [Fe/H]. These 3D effects on [O/Fe] is compounded by
the opposite behaviour of the \ion{Oi} (continuous opacity effect)
and Fe Ii lines (excitation effect). The [O/Fe] vs. [Fe/H] relation
remains quasi-linear extending to [O/Fe] =~ +0.5 at [Fe/H] = -2.5,
but with a tendency of a plateau with [O/Fe] =~ +0.3 for -2.0 <
[Fe/H] < -1.0, and a hint of cosmic scatter in [O/Fe] at [Fe/H] =~
-1.0. Use of the hydrodynamical models disturbs the broad agreement
between the oxygen abundances from the \ion{Oi} , O I, and OH lines,
but 3D non-LTE effects may serve to erase these differences. The [O/Fe]
values from the \ion{Oi} line and the hydrodynamical model atmospheres
for dwarfs and subgiant stars are lower than the values for giants
using standard model atmospheres and the \ion{Oi}, and O I lines. Based
on observations collected at the European Southern Observatory, Chile
(ESO Nos. 65.L-0131, 65.L-0507, and 67.D-0439).
Title: Sulphur and iron abundances in halo stars
Authors: Nissen, P. E.; Chen, Y. Q.; Asplund, M.; Pettini, M.
Bibcode: 2002astro.ph..7163N
Altcode:
From equivalent widths of the SI lines at 8694 A, Israelian & Rebolo
(2001) and Takada-Hidai et al. (2002) have derived a surprisingly high
sulphur-to-iron ratio ([S/Fe] = 0.5 to 0.7) in six halo stars with
[Fe/H] ~ -2.0 suggesting perhaps that hypernovae made a significant
contribution to the formation of elements in the early Galaxy. To
investigate this problem we have used high-resolution spectra obtained
with the ESO VLT/UVES spectrograph to determine the S/Fe ratio in
19 main-sequence and subgiant stars ranging in [Fe/H] from -3.2 to
-0.7. The sulphur abundances are determined from SI lines at 8694 A and
9212 - 9237 A, and the iron abundances from about 20 FeII lines. S/Fe
ratios as derived from 1D model atmospheres are presented and possible
3D effects are discussed. The initial results from our survey do not
confirm the high values of [S/Fe] quoted above; instead we find that
the ratio [S/Fe] remains constant at about 0.35 dex for metallicities
-3 < [Fe/H] -1.
Title: Sulphur abundances in disk stars: A correlation with silicon
Authors: Chen, Y. Q.; Nissen, P. E.; Zhao, G.; Asplund, M.
Bibcode: 2002A&A...390..225C
Altcode: 2002astro.ph..6075C
We have performed new determinations of sulphur and silicon
abundances for a sample of 26 disk stars based on high-resolution,
high signal-to-noise spectra. The results indicate a solar [S/Fe]
for [Fe/H] >-0.3, below which [S/Fe] increases to ~ 0.25 dex at
[Fe/H] =-1.0. We find that there is a good correlation between [S/H]
and [Si/H], indicating the same nucleosynthetic origin of the two
elements. It seems that the ratio of sulphur to silicon does not depend
on metallicity for [Fe/H] > -1.0. The implications of these results
on models for the nucleosynthesis of alpha -capture elements and the
chemical evolution of the Galaxy are discussed. Based on observations
carried out at National Astronomical Observatories (Xinglong, PR China).
Title: A Reappraisal of the Solar Photospheric C/O Ratio
Authors: Allende Prieto, Carlos; Lambert, David L.; Asplund, Martin
Bibcode: 2002ApJ...573L.137A
Altcode: 2002astro.ph..6089A; 2002astro.ph..6089P
An accurate determination of photospheric solar abundances requires
detailed modeling of the solar granulation and accounting for departures
from local thermodynamical equilibrium (LTE). We argue that the
forbidden C I line at 8727 Å is largely immune to departures from
LTE and can be realistically modeled using LTE radiative transfer
in a time-dependent three-dimensional simulation of solar surface
convection. We analyze the [C I] line in the solar flux spectrum to
derive the abundance logɛ(C)=8.39+/-0.04 dex. Combining this result
with our parallel analysis of [O I] λ6300, we find C/O=0.50+/-0.07,
in agreement with the ratios measured in the solar corona from gamma-ray
spectroscopy and solar energetic particles.
Title: Signatures of Convection in the Spectrum of Procyon:
Fundamental Parameters and Iron Abundance
Authors: Allende Prieto, Carlos; Asplund, Martin; García López,
Ramón J.; Lambert, David L.
Bibcode: 2002ApJ...567..544A
Altcode: 2001astro.ph.11055A; 2001astro.ph.11055P
We have observed the spectrum of Procyon A (F5 IV) from 4559 to 5780
Å with a signal-to-noise ratio of ~103 and a resolving
power of 2×105. We have measured the line bisectors
and relative line shifts of a large number of Fe I and Fe II lines,
comparing them to those found in the solar spectrum. A three-dimensional
hydrodynamical model atmosphere has been computed and is tested against
observations. The model reproduces in detail most of the features
observed, although we identify some room for improvement. At all levels,
the comparison of the three-dimensional time-dependent calculations
with the observed spectral lines shows a much better agreement than for
classical homogeneous models, making it possible to refine previous
estimates of the iron abundance, the projected rotational velocity,
the limb darkening, and the systemic velocity of the Procyon binary
system. The difference between the iron abundance determined with
the three-dimensional model and its one-dimensional counterpart is
<~0.05 dex. We find consistency between the iron abundance derived
from Fe I and Fe II lines, suggesting that departures from LTE in the
formation of the studied lines are relatively small. The scatter in
the iron abundance determined from different lines still exceeds the
expectations from the uncertainties in the atomic data, pointing out
that one or more components in the modeling can be refined further.
Title: V838 Monocerotis - a Newly Discovered, Very Peculiar, Slow
Nova-Like Object
Authors: Rauch, Thomas; Hauschildt, Peter; Asplund, Martin; Gredel,
Roland; Käufl, Hans-Ulrich; Kerber, Florian; Rosa, Michael;
Starrfield, Sumner G.; Wagner, R. Mark; Williams, Robert E.
Bibcode: 2002ASPC..279..345R
Altcode: 2002IAUCo.187..345R; 2002esce.conf..345R
No abstract at ADS
Title: Oxygen line formation in 3D hydrodynamical model atmospheres
Authors: Asplund, Martin
Bibcode: 2002HiA....12..432A
Altcode:
The formation of [O I], O I and OH lines in metal-poor stars has
been studied by means of 3D hydrodynamical model atmospheres. For
O I detailed 3D non-LTE calculations have been performed. While the
influence of 3D model atmospheres is minor for [O I] and O I lines,
the very low temperatures encountered at low metallicities have a
drastic impact on OH. As a result, the derived O abundances are found
to be systematically overestimated in 1D analyses, casting doubts on
the recent claims for a monotonic increase in [O/Fe] towards lower
metallicities.
Title: The Star Too Tough to Die
Authors: Kerber, Florian; Asplund, Martin
Bibcode: 2001S&T...102e..48K
Altcode:
No abstract at ADS
Title: Chemical Abundances from Inversions of Stellar Spectra:
Analysis of Solar-Type Stars with Homogeneous and Static Model
Atmospheres
Authors: Allende Prieto, Carlos; Barklem, Paul S.; Asplund, Martin;
Ruiz Cobo, Basilio
Bibcode: 2001ApJ...558..830A
Altcode: 2001astro.ph..5262P; 2001astro.ph..5262A
Spectra of late-type stars are usually analyzed with static model
atmospheres in local thermodynamic equilibrium (LTE) and a homogeneous
plane-parallel or spherically symmetric geometry. The energy balance
requires particular attention, as two elements that are particularly
difficult to model play an important role: line blanketing and
convection. Inversion techniques are able to bypass the difficulties
of a detailed description of the energy balance. Assuming that the
atmosphere is in hydrostatic equilibrium and LTE, it is possible
to constrain its structure from spectroscopic observations. Among
the most serious approximations still implicit in the method is a
static and homogeneous geometry. In this paper, we take advantage of a
realistic three-dimensional radiative hydrodynamical simulation of the
solar surface to check the systematic errors incurred by an inversion
assuming a plane-parallel horizontally-homogeneous atmosphere. The
thermal structure recovered resembles the spatial and time average
of the three-dimensional atmosphere. Furthermore, the abundances
retrieved are typically within 10% (0.04 dex) of the abundances used
to construct the simulation. The application to a fairly complete data
set from the solar spectrum provides further confidence in previous
analyses of the solar composition. There is only a narrow range of
one-dimensional thermal structures able to fit the absorption lines in
the spectrum of the Sun. With our carefully selected data set, random
errors are about a factor of 2 smaller than systematic errors. A small
number of strong metal lines can provide very reliable results. We
foresee no major difficulties in applying the technique to other
similar stars, and obtaining similar accuracies, using spectra with
λ/δλ~5×104 and a signal-to-noise ratio as low as 30.
Title: Oxygen abundances of halo dwarf and subgiant stars from
VLT/UVES observations of the [O I] λ 6300 line
Authors: Nissen, Poul E.; Primas, Francesca; Asplund, Martin
Bibcode: 2001NewAR..45..545N
Altcode:
The forbidden oxygen line at 6300 Å has been observed with UVES on
the ESO VLT for 13 dwarf and subgiant stars ranging in metallicity
from [Fe/H]≃-0.7 to -1.8. The spectra obtained have a resolution
of R=55 000 and S/ N≃400. After removal of telluric lines, the
equivalent width of the [O I] line could be measured with an accuracy of
0.2 to 0.3 mÅ. Using these data and the equivalent widths of eight weak
Fe II lines, the trend of [O/Fe] with [Fe/H] has been derived. Below
[Fe/H]≃-1.0 the oxygen-to-iron ratio is nearly constant at a level of
[O/Fe]≃0.4 in contradiction to recent results from UV OH lines.
Title: Abundance analyses of cool extreme helium stars
Authors: Pandey, Gajendra; Kameswara Rao, N.; Lambert, David L.;
Jeffery, C. Simon; Asplund, Martin
Bibcode: 2001MNRAS.324..937P
Altcode: 2001astro.ph..1518P
Extreme helium stars (EHes) with effective temperatures from 8000 to
13000K are among the coolest EHes and overlap the hotter R CrB stars in
effective temperature. The cool EHes may represent an evolutionary link
between the hot EHes and the R CrB stars. Abundance analyses of four
cool EHes, BD+1°4381 (FQ Aqr), LS IV -14°109, BD -1°3438 (NO Ser) and
LS IV -1°002 (V2244 Oph), are presented. All these stars show evidence
of H- and He-burning at earlier stages of their evolution. To test for
an evolutionary connection, the chemical compositions of cool EHes are
compared with those of hot EHes and R CrB stars. Relative to Fe, the
N abundance of these stars is intermediate between those of hot EHes
and R CrB stars. For the R CrB stars, the metallicity M derived from
the mean of Si and S appears to be more consistent with the kinematics
than that derived from Fe. When metallicity M derived from Si and S
replaces Fe, the observed N abundances of EHes and R CrB stars fall at
or below the upper limit corresponding to thorough conversion of initial
C and O to N. There is an apparent difference between the composition
of R CrB stars and EHes, the former having systematically higher [N/M]
ratios. The material present in the atmospheres of many R CrB stars is
heavily CN- and ON-cycled. Most of the EHes have only CN-cycled material
in their atmospheres. There is an indication that the CN- and ON-cycled
N in EHes was partially converted to Ne by α-captures. If EHes are
to evolve to R CrB stars, fresh C in EHes has to be converted to N;
the atmospheres of EHes have just sufficient hydrogen to raise the N
abundance to the level of R CrB stars. If Ne is found to be normal in
R CrB stars, the proposal that EHes evolve to R CrB stars fails. The
idea that R CrB stars evolve to EHes is ruled out; the N abundance in
R CrB stars has to be reduced to the level of EHes, as the C/He, which
is observed to be uniform across EHes, has to be maintained. Hence the
inferred [N/M], C/He and [Ne/M] ratios, and the H-abundances of these
two groups indicate that the EHes and the R CrB stars may not be on the
same evolutionary path. The atmospheres of H-deficient stars probably
consist of three ingredients: a residue of normal H-rich material,
substantial amounts of H-poor CN(O)-cycled material, and C- (and O-)
rich material from gas exposed to He-burning. This composition could
be a result of final He-shell flash in a single post-AGB star (FF
scenario), or a merger of two white dwarfs (DD scenario). Although
the FF scenario accounts for Sakurai's object and other stars (e.g.,
the H-poor central stars of planetary nebulae), present theoretical
calculations imply higher C/He and O/He ratios than are observed in
EHes and R CrB stars. Quantitative predictions are lacking for the
DD scenario.
Title: The Forbidden Abundance of Oxygen in the Sun
Authors: Allende Prieto, Carlos; Lambert, David L.; Asplund, Martin
Bibcode: 2001ApJ...556L..63A
Altcode: 2001astro.ph..6360P; 2001astro.ph..6360A
We reexamine closely the solar photospheric line at 6300 Å, which is
attributed to a forbidden line of neutral oxygen and is widely used
in analyses of other late-type stars. We use a three-dimensional
time-dependent hydrodynamical model solar atmosphere that has been
tested successfully against observed granulation patterns and an array
of absorption lines. We show that the solar line is a blend with a
Ni I line, as previously suggested but oftentimes neglected. Thanks
to accurate atomic data on the [O I] and Ni I lines, we are able to
derive an accurate oxygen abundance for the Sun: logɛ(O)=8.69+/-0.05
dex, a value at the lower end of the distribution of previously
published abundances but in good agreement with estimates for the
local interstellar medium and hot stars in the solar neighborhood. We
conclude by discussing the implication of the Ni I blend on oxygen
abundances derived from [O I] λ6300 in disk and halo stars.
Title: On OH line formation and oxygen abundances in metal-poor stars
Authors: Asplund, M.; García Pérez, A. E.
Bibcode: 2001A&A...372..601A
Altcode: 2001astro.ph..4071A
The formation of the UV OH spectral lines has been investigated for a
range of stellar parameters in the light of 3D hydrodynamical model
atmospheres. The low atmospheric temperatures encountered at low
metallicities compared with the radiative equilibrium values enforced
in classical 1D hydrostatic model atmospheres have a profound impact
on the OH line strengths. As a consequence, the derived O abundances
using 3D models are found to be systematically lower by more than 0.6
dex at [Fe/H] =-3.0 compared with previous 1D analyses, casting doubts
on the recent claims for a monotonic increase in [O/Fe] towards lower
metallicities. In fact, taken at face value the resulting 3D LTE trend
is in rough agreement with the conventional [O/Fe] plateau. Caution
must, however, be exercised in view of the remaining assumptions in
the 3D calculations. We have verified that the stellar parameters
remain essentially unchanged with 3D model atmospheres provided
that the infrared flux method (Delta T_eff <~ 20 K), Hipparcos
parallaxes (Delta {log } g <~ 0.05) and Fe ii lines (Delta [Fe/H]
<~ 0.1 dex) are utilised, leaving the 3D O abundances from OH
lines largely intact (Delta [O/H] <~ 0.05 dex). Greater concern
stems from possible departures from LTE in both the line formation
and the molecular equilibrium, which, if present, would increase the
derived O abundances again. Non-LTE line formation calculations with
1D model atmospheres suggest no significant steepening of the [O/Fe]
trend even if the abundance corrections amount to about 0.2 dex for
all investigated stellar parameters. We note, however, that the 3D
case may not necessarily be as metallicity-independent. The apparent
lack of laboratory or theoretical rate coefficients at the relevant
temperatures for the involved molecular reactions unfortunately prevents
a quantitative discussion on the possible effects of non-equilibrium
chemistry.
Title: The lithium isotope ratio in metal-poor stars
Authors: Nissen, P. E.; Asplund, M.
Bibcode: 2001NuPhA.688..402N
Altcode:
No abstract at ADS
Title: Effects of Convection on Line Profiles and Abundances (CD-ROM
Directory: contribs/asplund)
Authors: Asplund, M.
Bibcode: 2001ASPC..223..217A
Altcode: 2001csss...11..217A
No abstract at ADS
Title: Spatially Resolved Solar Lines as Diagnostics of NLTE Effects
(CD-ROM Directory: contribs/kiselman)
Authors: Kiselman, D.; Asplund, M.
Bibcode: 2001ASPC..223..684K
Altcode: 2001csss...11..684K
No abstract at ADS
Title: Observing beryllium with UVES at the VLT
Authors: Primas, Francesca; Asplund, Martin; Nissen, Poul Erik
Bibcode: 2001coev.conf..117P
Altcode:
We present preliminary results of a new analysis of Be abundances in a
large sample of stars, spanning the metallicity range -2.4 ≤[Fe/H]≤
-0.7. The observations were taken with the Ultraviolet and Visible
Echelle Spectrograph (UVES) at the ESO Very Large Telescope (VLT),
which made it possible to obtain very high data quality and measurements
accuracy. The aim of the project is to further investigate the trend
of Be with metallicity, and the possible presence of dispersion. Our
recent detections of very high Be abundances in two of the most
metal-poor stars suggest either a Be plateau or significant scatter
at the lowest metallicities.
Title: Departures from LTE in be Line Formation
Authors: García Perez, A. E.; Asplund, M.; Kiselman, D.
Bibcode: 2001coev.conf..131G
Altcode:
Stellar abundances of Be can be affected by NLTE effects. We have
calculated the NLTE corrections to the LTE abundances obtained
from the Bell doublet at 313.0 and 313.1 nm for a range of stellar
parameters. These lines are not formed in LTE due to over-ionization
and over-excitation but the NLTE corrections are in general small
(~0.1 dex).
Title: R200,000 Spectroscopic Observations of Procyon. The Surface
Convection and Radial Velocity (CD-ROM Directory: contribs/allende2)
Authors: Allende Prieto, C.; Asplund, M.; García López, R. J.;
Lambert, D. L.; Nordlund, Å.
Bibcode: 2001ASPC..223..760A
Altcode: 2001csss...11..760A
No abstract at ADS
Title: Lithium Isotope Ratios in Metal-Poor Halo Stars
Authors: Asplund, Martin; Lambert, David L.; Nissen, Poul Erik;
Primas, Francesca; Smith, Verne V.
Bibcode: 2001coev.conf...95A
Altcode:
Equipped with very high quality observations obtained from VLT/UVES
and the new generation of 3D hydrodynamical model atmospheres, we
have initiated a survey of 6Li/7Li ratios in
metal-poor halo stars. Here we present the first preliminary results of
this investigation, reporting four new likely detections at a similar
level (6Li/7Li = 2 - 5%) to that previously
found for HD 84937, BD +26°3578 and G271-162.
Title: The beryllium abundance in the very metal-poor halo star G
64-12 from VLT/UVES observations
Authors: Primas, F.; Asplund, M.; Nissen, P. E.; Hill, V.
Bibcode: 2000A&A...364L..42P
Altcode: 2000astro.ph..9482P
We report on a new spectroscopic analysis of the very metal deficient
star G 64-12 ([Fe/H]=-3.3), aimed at determining, for the first time,
its beryllium content. The spectra were observed during the Science
Verification of UVES, the ESO VLT Ultraviolet and Visible Echelle
Spectrograph. The high resolution ( ~ 48 000) and high S/N ( ~ 130
per pixel) achieved at the wavelengths of the Be Ii resonance doublet
allowed an accurate determination of its abundance: log N(Be/H) = -13.10
+/- 0.15 dex. The Be abundance is significantly higher than expected
from previous measurements of Be in stars of similar metallicity
(3D and NLTE corrections acting to make a slightly higher value than
an LTE analysis). When compared to iron, the high [Be/Fe] ratio thus
found may suggest a flattening in the beryllium evolutionary trend
at the lowest metallicity end or the presence of dispersion at early
epochs of galactic evolution. Based on observations taken during the
Science Verification of UVES at the VLT/Kueyen telescope, European
Southern Observatory, Paranal, Chile
Title: FG Sagittae (FG Sge)
Authors: Asplund, M.
Bibcode: 2000eaa..bookE2887A
Altcode:
FG Sge (α=20°11'56'', δ=+20°20'04'', epoch = 2000) is a very
peculiar giant star undergoing extremely rapid evolutionary changes
and nucleosynthetic processing. It has evolved at a remarkable pace
over the last century changing among other properties its appearance
from a hot (O-type) star to a luminous, cool (K-type) giant today. FG
Sge is classified as a `born-again giant' currently experiencin...
Title: Line formation in solar granulation. II. The photospheric
Fe abundance
Authors: Asplund, M.; Nordlund, Å.; Trampedach, R.; Stein, R. F.
Bibcode: 2000A&A...359..743A
Altcode: 2000astro.ph..5321A
The solar photospheric Fe abundance has been determined using realistic
ab initio 3D, time-dependent, hydrodynamical model atmospheres. The
study is based on the excellent agreement between the predicted
and observed line profiles directly rather than equivalent widths,
since the intrinsic Doppler broadening from the convective motions and
oscillations provide the necessary non-thermal broadening. Thus, three
of the four hotly debated parameters (equivalent widths, microturbulence
and damping enhancement factors) in the center of the recent solar Fe
abundance dispute regarding Fe i lines no longer enter the analysis,
leaving the transition probabilities as the main uncertainty. Both Fe i
(using the samples of lines of both the Oxford and Kiel studies) and
Fe ii lines have been investigated, which give consistent results:
log epsilon_FeI = 7.44 +/- 0.05 and log epsilon_FeII = 7.45 +/-
0.10. Also the wings of strong Fe i lines return consistent abundances,
log epsilon_FeII = 7.42 +/- 0.03, but due to the uncertainties inherent
in analyses of strong lines we give this determination lower weight
than the results from weak and intermediate strong lines. In view of
the recent slight downward revision of the meteoritic Fe abundance
log epsilon_Fe = 7.46 +/- 0.01, the agreement between the meteoritic
and photospheric values is very good, thus appearingly settling the
debate over the photospheric Fe abundance from Fe i lines.
Title: The effects of numerical resolution on hydrodynamical surface
convection simulations and spectral line formation
Authors: Asplund, M.; Ludwig, H. -G.; Nordlund, Å.; Stein, R. F.
Bibcode: 2000A&A...359..669A
Altcode: 2000astro.ph..5319A
The computationally demanding nature of radiative-hydrodynamical
simulations of stellar surface convection warrants an investigation
of the sensitivity of the convective structure and spectral synthesis
to the numerical resolution and dimension of the simulations, which
is presented here. With too coarse a resolution the predicted spectral
lines tend to be too narrow, reflecting insufficient Doppler broadening
from the convective motions, while at the currently highest affordable
resolution the line shapes have converged essentially perfectly to
the observed profiles. Similar conclusions are drawn from the line
asymmetries and shifts. Due to the robustness of the pressure and
temperature structures with respect to the numerical resolution, strong
Fe lines with pronounced damping wings and H i lines are essentially
immune to resolution effects, and can therefore be used for improved
T_eff and log g determinations even at very modest resolutions. In
terms of abundances, weak Fe i and Fe ii lines show a very small
dependence ( =~ 0.02 dex) while for intermediate strong lines with
significant non-thermal broadening the sensitivity increases (<~ 0.10
dex). Problems arise when using 2D convection simulations to describe
an inherent 3D phenomenon, which translates to inaccurate atmospheric
velocity fields and temperature and pressure structures. In 2D the
theoretical line profiles tend to be too shallow and broad compared with
the 3D calculations and observations, in particular for intermediate
strong lines. In terms of abundances, the 2D results are systematically
about 0.1 dex lower than for the 3D case for Fe i lines. Furthermore,
the predicted line asymmetries and shifts are much inferior in 2D
with discrepancies amounting to ~ 200 m s-1. Given these
shortcomings and computing time considerations it is better to use
3D simulations of even modest resolution than high-resolution 2D
simulations.
Title: Line formation in solar granulation. I. Fe line shapes,
shifts and asymmetries
Authors: Asplund, M.; Nordlund, Å.; Trampedach, R.; Allende Prieto,
C.; Stein, R. F.
Bibcode: 2000A&A...359..729A
Altcode: 2000astro.ph..5320A
Realistic ab-initio 3D, radiative-hydrodynamical convection simulations
of the solar granulation have been applied to Fe i and Fe ii line
formation. In contrast to classical analyses based on hydrostatic 1D
model atmospheres the procedure contains no adjustable free parameters
but the treatment of the numerical viscosity in the construction
of the 3D, time-dependent, inhomogeneous model atmosphere and the
elemental abundance in the 3D spectral synthesis. However, the numerical
viscosity is introduced purely for numerical stability purposes and is
determined from standard hydrodynamical test cases with no adjustments
allowed to improve the agreement with the observational constraints
from the solar granulation. The non-thermal line broadening is mainly
provided by the Doppler shifts arising from the convective flows in
the solar photosphere and the solar oscillations. The almost perfect
agreement between the predicted temporally and spatially averaged
line profiles for weak Fe lines with the observed profiles and the
absence of trends in derived abundances with line strengths, seem to
imply that the micro- and macroturbulence concepts are obsolete in
these 3D analyses. Furthermore, the theoretical line asymmetries and
shifts show a very satisfactory agreement with observations with an
accuracy of typically 50-100 m s-1 on an absolute velocity
scale. The remaining minor discrepancies point to how the convection
simulations can be refined further.
Title: Line formation in solar granulation. III. The photospheric
Si and meteoritic Fe abundances
Authors: Asplund, M.
Bibcode: 2000A&A...359..755A
Altcode: 2000astro.ph..5322A
Using realistic hydrodynamical simulations of the solar surface
convection as 3D, time-dependent, inhomogeneous model atmospheres,
the solar photospheric Si abundance has been determined to be log
epsilon_Si = 7.51+/-0.04. This constitutes a difference of 0.04 dex
compared with previous estimates based on the 1D Holweger-Müller
(1974) model, of which half is attributable to the adopted model
atmosphere and the remaining part to the improved quantum mechanical
broadening treatment. As a consequence, all meteoritic abundances
should be adjusted downwards by the same amount. In particular the
meteoritic Fe abundance will be log epsilon_Fe = 7.46+/-0.01, in good
agreement with the recently determined photospheric Fe abundance
(Asplund et al. 2000b). The existing uncertainties unfortunately
prevent an observational confirmation of the postulated effects of
elemental migration of metals in the Sun.
Title: The continuing saga of Sakurai's object (V4334 Sgr): dust
production and helium line emission
Authors: Tyne, V. H.; Eyres, S. P. S.; Geballe, T. R.; Evans, A.;
Smalley, B.; Duerbeck, H. W.; Asplund, M.
Bibcode: 2000MNRAS.315..595T
Altcode:
We report further UKIRT spectroscopic observations of Sakurai's
object (V4334 Sgr) made in 1999 April/May in the 1-4.75μm range,
and find that the emission is dominated by amorphous carbon at
Td~600K. The estimated maximum grain size is 0.6μm, and the
mass lower limit is 1.7+/-0.2×10-8Msolar
to 8.9+/-0.6×10-7Msolar
for distances of 1.1-8kpc. For 3.8kpc the mass is
2.0+/-0.1×10-7Msolar. We also report strong
Hei emission at 1.083μm, in contrast to the strong absorption in
this line in 1998. We conclude that the excitation is collisional,
and is probably caused by a wind, consistent with the P Cygni profile
observed by Eyres et al. in 1998.
Title: Abundance analysis of extreme helium stars
Authors: Pandey, Gajendra; Kameswara Rao, N.; Lambert, David L.;
Jeffery, C. Simon; Asplund, Martin
Bibcode: 2000BASI...28..303P
Altcode:
High resolution spectra were obtained for a sample of hydrogen-deficient
stars which are hotter than the R CrB stars and cooler among the
extreme helium stars (EHe). We believe that these stars are transition
objects evolving either to EHe stars or R CrB stars. We aim to explore
the evolutionary link between our program stars, R CrB stars and EHe
stars. Distribution of these stars in the log g - log Teff plane shows
similar L/M ratios (??4.0). These objects have an abundance pattern
like R CrB stars and EHe stars.
Title: The lithium isotope ratio in the metal-poor halo star G271-162
from VLT/UVES observations
Authors: Nissen, P. E.; Asplund, M.; Hill, V.; D'Odorico, S.
Bibcode: 2000A&A...357L..49N
Altcode: 2000astro.ph..4251N
A high resolution (lambda /Delta lambda =~ 110 000), very high
S/N (>~ 600) spectrum of the metal-poor turnoff star G
271-162 has been obtained in connection with the commissioning
of UVES at VLT/Kueyen. Using both 1D hydrostatic and 3D hydrodynamical
model atmospheres, the lithium isotope ratio has been estimated
from the Li I,670.8 nm line by means of spectral synthesis. The
necessary stellar line broadening (1D: macroturbulence + rotation,
3D: rotation) has been determined from unblended K I, Ca I and Fe
I lines. The 3D line profiles agree very well with the observed
profiles, including the characteristic line asymmetries. Both the
1D and 3D analyses reveal a possible detection of \element[][6]{Li}
in G 271-162, element [][6]{Li}/element [][7]{Li}
= 0.02+/-0.01 (1sigma ). It is discussed if the smaller amount of
\element[][6]{Li} in G 271-162 than in the similar
halo star HD 84937 could be due to differences in
stellar mass and/or metallicity or whether it may reflect an intrinsic
scatter of \element[][6]{Li}/\element[][7]{Li} in the ISM at a given
metallicity. Based on public data released from the UVES commissioning
at the VLT/Kueyen telescope, ESO, Paranal, Chile
Title: The Eddington Limit, Radiative Instabilities and the Declines
of R Coronae Borealis Stars
Authors: Asplund, Martin
Bibcode: 2000IAUS..177..521A
Altcode:
No abstract at ADS
Title: The Light Elements in the Light of 3D Hydrodynamical Model
Atmospheres
Authors: Asplund, M.
Bibcode: 2000IAUS..198..448A
Altcode:
No abstract at ADS
Title: Oxygen abundances of halo stars from UVES observations of
the λ6300 [OI] line
Authors: Nissen, P. E.; Primas, F.; Asplund, M.
Bibcode: 2000IAUJD...8E..21N
Altcode:
The forbidden oxygen line at 6300 Å has been observed with UVES at
the ESO VLT for 15 turnoff and subgiant stars ranging in metallicity
from [Fe/H] = -0.7 to -1.8. The spectra obtained have a resolution
of R = 55.000 and S/N > 400 with 6 pixels per spectral resolution
bin. After removal of telluric O2 lines by the aid of B-type
calibration spectra, the equivalent width of the [OI] line could be
measured to a precision of 0.2 to 0.3 m Å . Using these data and the
eqivalent widths of 8 weak FeII lines, the trend of [O/Fe] with [Fe/H]
has been derived and is compared with recent results from the UV OH
lines and the OI triplet at 7774 Å .
Title: Oxygen Line Formation in 3D Hydrodynamical Model Atmospheres
Authors: Asplund, M.; Carlsson, M.; Garcia Perez, A. E.; Kiselman, D.
Bibcode: 2000IAUJD...8E...8A
Altcode: 2000astro.ph.11043A
The new generation of realistic 3-dimensional, time-dependent,
hydrodynamical model atmospheres have been applied to the line
formation of {O}{I}, [{O}{I}] and OH lines. Additionally detailed 3D
non-LTE calculations have been performed for {O}{I} in order to study
the influence of temperature inhomogeneities on the line formation
process. Implications in terms of the evolution of oxygen abundance
with metallicity will be discussed, partly based on new VLT/UVES
observations of metal-poor stars.
Title: The R Coronae Borealis stars - atmospheres and abundances
Authors: Asplund, M.; Gustafsson, B.; Lambert, D. L.; Rao, N. K.
Bibcode: 2000A&A...353..287A
Altcode:
An abundance analysis of the H-deficient and He- and C-rich R Coronae
Borealis (R CrB) stars has been undertaken to examine the ancestry of
the stars. The investigation is based on high-resolution spectra and
line-blanketed H-deficient model atmospheres. The models successfully
reproduce the flux distributions and all spectral features, both
molecular bands and high-excitation transitions, with one important
exception, the C i lines. Since photoionization of C i dominates
the continuous opacity, the line strengths of C i are essentially
independent of the adopted carbon abundance and stellar parameters. All
predicted C i lines are, however, much too strong compared with
observations, with a discrepancy in abundance corresponding to 0.6 dex
with little star-to-star scatter. Various solutions of this ``carbon
problem'' have been investigated. A possible solution is that classical
model atmospheres are far from adequate descriptions of supergiants such
as the R CrB stars. We can also not exclude completely, however, the
possibility that the gf-values for the C i lines are in error. This is
supported by the fact that the C ii, [C i] and C_2 lines are reproduced
by the models with no apparent complications. In spite of the carbon
problem, various tests suggest that abundance ratios are little affected
by the uncertainties. Judging by chemical composition, the R CrB stars
can be divided into a homogeneous majority group and a diverse minority,
which is characterized by extreme abundance ratios, in particular as
regards Si/Fe and S/Fe. All stars show evidence of H- and He-burning in
different episodes as well as mild s-process enhancements. Four of the
majority members are Li-rich, while overabundances of Na, Al, Si and
S are attributes of all stars. An anti-correlation found between the
H and Fe abundances of H-deficient stars remains unexplained. These
enigmatic stars are believed to be born-again giants, formed either
through a final He-shell flash in a post-AGB star or through a merger
of two white dwarfs. Owing to a lack of theoretical predictions of
the resulting chemical compositions, identification of the majority
and minority groups with the two scenarios is unfortunately only
preliminary. Furthermore, Sakurai's object and
V854 Cen exhibit aspects of both majority and
minority groups, which may suggest that the division into two groups
is too simplistic.
Title: VizieR Online Data Catalog: The R CrB stars (Asplund+, 2000)
Authors: Asplund, M.; Gustafsson, B.; Lambert, D. L.; Rao, N. K.
Bibcode: 1999yCat..33530287A
Altcode:
Adopted line data, measured equivalent widths and derived elemental
abundances for the individual lines observed in R Coronae Borealis
and Extreme Helium stars. (2 data files).
Title: ISO. Monitoring the mass loss of a very late Helium flash star
Authors: Kerber, F.; Blommaert, J. A. D. L.; Groenewegen, M. A. T.;
Kimeswenger, S.; Käufl, H. U.; Asplund, M.
Bibcode: 1999A&A...350L..27K
Altcode:
We present ISOCAM observations of Sakurai's object (V4334 Sgr) covering
the wavelength range of 4 to 15 mu m in seven filters. The photometry
shows that in the period from February 1997 to February 1998 the flux
over the whole wavelength range has increased by a factor of about
ten. Combined with ground-based data we conclude that this increase is
the result of mass loss from Sakurai's object and the formation of hot
dust around it. Using a spherically symmetric dust radiative transfer
model we obtain a quantitative result of a variable and increasing mass
loss rate reaching some 10(-7) M_⊙/yr, a value not uncommon among
stars during the Asymptotic Giant Branch (AGB) evolution. This is in
agreement with the notion that Sakurai's object is retracing its own
evolutionary history as a consequence of a very late Helium flash. We
conclusively demonstrate that significant mass loss is associated with
such an event and foster the link to the other few known examples of
final Helium flashes. ISO is an ESA project with instruments funded
by ESA Member States (especially the PI countries: France, Germany,
The Netherlands and the United Kingdom) and with the participation of
ISAS and NASA.} observations of dust formation in Sakurai's object
Title: Strong helium 10830-Å absorption in Sakurai's object
(V4334 Sgr)
Authors: Eyres, S. P. S.; Smalley, B.; Geballe, T. R.; Evans, A.;
Asplund, M.; Tyne, V. H.
Bibcode: 1999MNRAS.307L..11E
Altcode:
We report the appearance and evolution during 1998 of strong neutral
helium ^3S-^3P^o absorption at ~10830Å in Sakurai's Object (V4334 Sgr),
which is believed to be a planetary nebula nucleus (PNN) undergoing a
final helium shell-flash. First detected on 1998 March 18, the profile
of the Hei feature is P Cygni-like. The absorption depth has increased
in three subsequent spectra in 1998. If this is owing to a wind, the
profile indicates a wind velocity of ~670+/-50kms^-1. The strong Ci
10690-Å line seen prior to the appearance of the helium feature has
disappeared; however Srii and CN absorption features remain present. We
tentatively identify several new features as Sii. Taken together
with other observations we suggest that the data are consistent with
Sakurai's Object entering a phase in which it seems to have become a
member of the R Coronae Borealis-type class of stars.
Title: 3D hydrodynamical model atmospheres of metal-poor
stars. Evidence for a low primordial Li abundance
Authors: Asplund, Martin; Nordlund, Åke; Trampedach, Regner; Stein,
Robert F.
Bibcode: 1999A&A...346L..17A
Altcode: 1999astro.ph..5059A
Realistic 3-dimensional (3D), radiative hydrodynamical surface
convection simulations of the metal-poor halo stars HD 140283 and
HD 84937 have been performed. Due to the dominance of adiabatic
cooling over radiative heating very low atmospheric temperatures are
encountered. The lack of spectral lines in these metal-poor stars
thus causes much steeper temperature gradients than in classical 1D
hydrostatic model atmospheres where the temperature of the optically
thin layers is determined by radiative equilibrium. The modified
atmospheric structures cause changes in the emergent stellar spectra. In
particular, the primordial Li abundances may have been overestimated
by 0.2-0.35 dex with 1D model atmospheres. However, we caution that
our result assumes local thermodynamic equilibrium (LTE), while the
steep temperature gradients may be prone to e.g. over-ionization.
Title: First Observations of an R Coronae Borealis Star with the
Space Telescope Imaging Spectrograph: RY Sagittarii near Maximum Light
Authors: Clayton, Geoffrey C.; Ayres, T. R.; Lawson, Warrick A.;
Drilling, John S.; Woitke, P.; Asplund, Martin
Bibcode: 1999ApJ...515..351C
Altcode:
We describe the far-UV (1140-1740 Å) spectrum of the hydrogen-deficient
R Coronae Borealis (RCB) star RY Sgr, obtained near maximum light
(pulsational phase ~0.1) by the Space Telescope Imaging Spectrograph
(STIS) on Hubble Space Telescope. The far-UV spectrum shows a
photospheric continuum rising steeply toward longer wavelengths and
two prominent emission features at the shorter wavelengths: C II λ1335
and Cl I λ1351 (the latter is radiatively fluoresced by the 10 times
stronger C II multiplet). We also find evidence for CO A-X 4th-positive
system absorption band heads and possible weak CO fluorescent emissions
pumped by C II λ1335, but the inferred column densities are low (~few
times 1016 cm-2), consistent with formation in
a warm (~5000 K) atmospheric layer. The detection of CO molecules,
if confirmed, would be significant, because they are thought to
play a key role in the dust ejection episodes of RCB stars through
the initiation of ``molecular cooling catastrophes.'' Based on
observations obtained with the NASA/ESA Hubble Space Telescope, which
is operated by STScI for the Association of Universities for Research
in Astronomy Inc. under NASA contract NAS 5-26555.
Title: The rapid evolution of the born-again giant Sakurai's object
Authors: Asplund, M.; Lambert, D. L.; Kipper, T.; Pollacco, D.;
Shetrone, M. D.
Bibcode: 1999A&A...343..507A
Altcode: 1998astro.ph.11208A
The extraordinarily rapid evolution of the born-again giant Sakurai's
object following discovery in 1996 has been investigated. The
evolution can be traced both in a continued cooling of the stellar
surface and dramatic changes in chemical composition on a timescale
of a mere few months. The abundance alterations are the results
of the mixing and nuclear reactions which have ensued due to the
final He-shell flash which occurred during the descent along the
white dwarf cooling track. The observed changes in the H and Li
abundances can be explained by ingestion and burning of the H-rich
envelope and Li-production through the Cameron-Fowler mechanism. The
rapidly increasing abundances of the light s-elements (including Sc)
are consistent with current s-processing by neutrons released from
the concomitantly produced (13) C. However, the possibility that the
s-elements have previously been synthesized during the AGB-phase and
only mixed to the surface in connection with the final He-shell flash
in the pre-white dwarf cannot be convincingly ruled out either. Since
Sakurai's object shows substantial abundance similarities with the R
CrB stars and has recently undergone R CrB-like visual fading events,
the ``birth'' of an R CrB star may have been witnessed for the first
time ever. Sakurai's object thus lends strong support for the suggestion
that at least some of the R CrB stars have been formed through a final
He-shell flash in a post-AGB star.
Title: Confrontation of Stellar Surface Convection Simulations with
Stellar Spectroscopy
Authors: Asplund, M.; Nordlund, Å.; Trampedach, R.
Bibcode: 1999ASPC..173..221A
Altcode: 1999sstt.conf..221A
No abstract at ADS
Title: Sakurai's object -- stellar evolution in real time
Authors: Asplund, M.
Bibcode: 1999IAUS..191..481A
Altcode:
The born-again giant Sakurai's object is currently experiencing
its second stage as an AGB-star. Furthermore, Sakurai's object has
shown an unprecedented rapid stellar evolution since discovery in
1996, both in terms of a continued cooling of the photosphere and
spectacular changes in chemical composition on a time-scale of a
mere few months. The surface cooling and abundance alterations of H,
Li and the s-elements are the direct consequences of the expansion,
mixing and nucleosynthesis which has ensued as a result of a final
He-shell flash occurring while the star was descending the white dwarf
cooling track. Sakurai's object shows striking similarities with the
R CrB stars in both chemical composition and visual variability.
Title: Convection in Metal-Poor Stars as Traced from Spectral Line
Asymmetries
Authors: Allende Prieto, C.; Asplund, M.; García López, R. J.;
Gustafsson, B.; Lambert, D. L.
Bibcode: 1999ASPC..173..205A
Altcode: 1999sstt.conf..205A
No abstract at ADS
Title: EROS variable stars: discovery of a slow nova in the SMC
Authors: de Laverny, P.; Beaulieu, J. P.; Asplund, M.; Kilkenny, D.;
Renault, C.; Ferlet, R.; Marquette, J. B.; Vidal-Madjar, A.; Maurice,
E.; Prevot, L.; Aubourg, E.; Bareyre, P.; Bauer, F.; Brehin, S.;
Coutures, C.; de Kat, J.; Gros, M.; Laurent, B.; Lachieze-Rey, M.;
Lesquoy, E.; Magneville, C.; Milsztajn, A.; Moscoso, L.; Queinnec,
F.; Rich, J.; Spiro, M.; Vigroux, L.; Zylberajch, S.; Ansari, R.;
Cavalier, F.; Moniez, M.
Bibcode: 1998A&A...335L..93D
Altcode:
We report the discovery of a slow nova found in the core of the Small
Magellanic Cloud by the EROS microlensing survey. Nova SMC 1994 is a
classical nova with a DQ Her type lightcurve characterized by a deep
minimum. Low amplitude variations occuring on time-scales of hours and
days are also detected at maximum light. Spectra collected during the
nebular phase indicate that Nova SMC 1994 is similar to Galactic novae
of the same class. Large helium enhancement in the shell is found and
O and N enrichments are suspected. Based on observations collected at
the European Southern Observatory, Chile.
Title: Abundance similarities between the RCrB star V854Cen and the
born-again Sakurai's object
Authors: Asplund, Martin; Gustafsson, Bengt; Kameswara Rao, N.;
Lambert, David L.
Bibcode: 1998A&A...332..651A
Altcode: 1998astro.ph..1068A
The elemental abundances of the mildly hydrogen-deficient R Coronae
Borealis (RCrB) star V854Cen have been estimated. The RCrB stars
have been divided into majority and minority classes judging by their
abundance patterns. Class assignment has previously been unambiguous
but V854Cen has traits of both the minority and majority class. Neither
V854Cen nor the three obvious minority members show any clear abundance
signatures of having been affected by e.g. dust-gas separation as often
observed in post-AGB stars. By chemical composition, V854Cen closely
resembles Sakurai's object, which has probably recently experienced
a final He-shell flash. Therefore V854Cen and Sakurai's object may
share the same evolutionary background, which would add support for
the final-flash scenario as a viable origin of the RCrB stars. Most
of the few differences in abundance ratios between the stars could if
so be attributed to milder H-ingestion in connection with the final
He-shell flash of V854Cen. The identification of either the majority or
the minority group, if any, as final flash objects, remain uncertain,
however, due to the unclear membership status of V854Cen.
Title: The stability of late-type stars close to the Eddington limit
Authors: Asplund, Martin
Bibcode: 1998A&A...330..641A
Altcode: 1997astro.ph.10158A
The opacity-modified Eddington limit has been computed for
hydrogen-deficient model atmospheres. The R Coronae Borealis (RCrB)
stars are found to be located strikingly close to the limit, which
suggests that the unknown trigger mechanism for their visual declines of
the stars are instabilities in connection with the stars encountering
the Eddington limit in their evolution. It also points to a similarity
between the eruptive behaviours of the RCrB stars and the Luminous
Blue Variables (LBVs). Super-Eddington luminosities in hydrostatic
model atmospheres manifest themselves by the presence of gas pressure
inversions. Such inversions are not an artifact of the assumption of
hydrostatic equilibrium but can also be present in hydrodynamical model
atmospheres. Only for very large mass loss rates hardly realized in
supergiants will the inversions be removed. Instabilities may, however,
still be present in such inversions, which is investigated for both
H-rich and H-deficient late-type supergiant model atmospheres. Dynamical
instabilities may occur in surface ionization zones, which might
lead to ejections of gas. A local, non-adiabatic, linear stability
analysis reveals that sound waves can be amplified due to the strong
radiative forces. However, despite the super-Eddington luminosities,
the efficiency of the radiative instabilities is fairly low compared
to for early-type stars with growth rates of 10(-5) s(-1) .
Title: (Erratum) Line-blanketed model atmospheres for R Coronae
Borealis stars and hydrogen-deficient carbon stars.
Authors: Asplund, M.; Gustafsson, B.; Kiselman, D.; Eriksson, K.
Bibcode: 1997A&A...323..286A
Altcode:
Erratum to Astron. Astrophys. 318, 521-534 (1997)
Title: Evolution and variability of the R Coronae Borealis stars
Authors: Asplund, M.
Bibcode: 1997PhDT........20A
Altcode:
The R Coronae Borealis (RCrB) stars are characterized by their severe
hydrogen-deficiency and drastic visual variability. This thesis
is devoted to both these issues using theoretical, numerical and
observational investigations. A large sample of the stars has been
analysed to determine their elemental abundances, which trace both
their ancestry and the history of stellar nucleosynthesis. For the
purpose, line-blanketed, hydrogen-deficient model atmospheres have
been constructed. The peculiar compositions of the stars indicate that
they are in fact born-again giants, for which two explanations have
been proposed: either a merger of two white dwarfs or a final He-shell
flash in a post-AGB star, which briefly re-inflates the star back to
giant dimensions. According to their composition, the stars can be
divided into a homogeneous majority group and a diverse minority, which
might reflect two different evolutionary backgrounds or the effect of
dust-gas separation. The atmospheres bear witness of H- and He-burning
in different phases as well as s-processing, but the high Si/Fe and S/Fe
ratios of in particular the minority remain unexplained. The inability
of the models to reproduce the CI lines suggests that standard model
atmospheres are far from adequate descriptions of supergiants such
as the RCrB stars. An analysis of Sakurai's object, which has likely
recently experienced a final He-shell flash, reveals similarities
with the RCrB stars as regards chemical composition. More spectacular,
the star shows evidence of very rapid evolution and nucleosynthesis,
most notably a decrease in the H abundance and an increase in the Li
and s-element contents within only five months. The star represents an
impressively fast case of stellar evolution very rarely encountered. The
variability of the stars with fadings of up to 8 magnitudes is unique
and not yet explained. It is probably due to obscuration events of
the stars by newly formed dust clouds. Possible instabilities due to
large radiative forces in the stellar atmospheres, which could be the
unknown trigger mechanism for the variability by ejecting condensible
material, are searched for. A connection between such instabilities
and the declines is supported by the proximity of the stars to the
theoretical opacity-modified Eddington limit.
Title: A stellar endgame - the born-again Sakurai's object.
Authors: Asplund, M.; Gustafsson, B.; Lambert, D. L.; Kameswara Rao, N.
Bibcode: 1997A&A...321L..17A
Altcode: 1997astro.ph..4005A
The surface chemical composition of this remarkable star shows that it
is hydrogen-deficient, carbon-rich and enriched in the light s-process
elements. Spectra taken in May and October 1996 indicate a decrease in
the surface hydrogen abundance by 0.7dex in five months along with an
increase in the abundances of Li, Sr, Y and Zr. The abundance changes
are in agreement with the hypothesis of the star being a rapidly
evolving "born-again" AGB star experiencing a final He-shell flash,
similar to FGSge. The ^12^C/^13^C ratio in October is very low, also
suggesting hydrogen ingestion. By chemical composition, Sakurai's
object resembles the R Coronae Borealis (RCrB) stars.
Title: Line-blanketed model atmospheres for R Coronae Borealis stars
and hydrogen-deficient carbon stars.
Authors: Asplund, M.; Gustafsson, B.; Kiselman, D.; Eriksson, K.
Bibcode: 1997A&A...318..521A
Altcode:
We have constructed line-blanketed model atmospheres for the
hydrogen-deficient and carbon-rich R Coronae Borealis (RCrB) stars,
as well as for the similar hydrogen-deficient carbon (HdC) stars and
the cool extreme helium (EHe) stars. Improved continuum opacities have
been used together with realistic line absorption data for atomic
and molecular transitions. The observed dereddened fluxes of R CrB
are compared with the calculated model fluxes and found to agree best
with a model effective temperature of 6900K, while the infrared flux
method gives between 6600 and 6900K, depending on the nature of the
flux excess in the J and H bands compared to the model fluxes. The
excess may correspond to a recently formed dust cloud close to the
star, with a typical temperature around 2000K and a dust mass of
~10^-11^Msun_. The agreement for the ultraviolet flux
distribution is also very satisfactory as seen from IUE spectra of
RCrB. Theoretical broad band photometry is presented and effective
temperatures of RCrB and HdC stars estimated. The constructed
models show a significantly steeper temperature gradient compared
to previously existing models as a result of the line opacity. Due
to the cool surface and high abundance of carbon, molecular bands of
e.g. C_2_ and CO are visible in the spectra even at as high effective
temperatures as 7000K. Furthermore, the high temperatures encountered
at depth explain the observed Hei and CII lines for T_eff_ down to
~7000K. In the inner layers (τ_Ross_ > 3) the models show density
inversions related to the ionization zone of helium. For certain low
gravity models the luminosity exceeds the local Eddington limit and
hence gas pressure inversions occur as well, which could be related
to the decline events of RCrB stars.
Title: Evolution and variability of the R Coronae Borealis stars
Authors: Asplund, Martin
Bibcode: 1997PhDT.......230A
Altcode:
No abstract at ADS
Title: Are the declines of R Coronae Borealis stars caused by super-
Eddington luminosities?
Authors: Asplund, M.; Gustafsson, B.
Bibcode: 1996ASPC...96...39A
Altcode: 1996hds..conf...39A
No abstract at ADS
Title: A non-LTE investigation of carbon in R Coronae Borealis stars
Authors: Asplund, M.; Ryde, N. A. E.
Bibcode: 1996ASPC...96...57A
Altcode: 1996hds..conf...57A
No abstract at ADS
Title: Model atmospheres of cool hydrogen-deficient carbon stars
Authors: Gustafsson, B.; Asplund, M.
Bibcode: 1996ASPC...96...27G
Altcode: 1996hds..conf...27G
No abstract at ADS
Title: Spectroscopy of RY Sagittarii during the 1993 minimum.
Authors: Asplund, Martin
Bibcode: 1995A&A...294..763A
Altcode:
The R Coronae Borealis (RCB) star RY Sgr underwent a deep minimum
({DELTA}V~7.5mag) in 1993. Here medium and low resolution observations
from approximately 35 days into the decline are presented together with
photometry from the early phases until some 100 days thereafter. The
spectra show sharp chromospheric emission lines of Fe, TiII, ScII, BaII
and YII, as well as broad emission from Na D, HeI, K and MgI. In general
the broad lines are stationary or slightly blueshifted relative to the
star. An absorption feature in Na D_2_ corresponds to a radial velocity
of -200km/s. The helium line at 587.6nm is surprisingly weak, which
suggests high optical depths and electron densities. Strong emission
bands due to the Swan bands of C_2_ are found and two extended emission
"bumps" around 390nm and 590nm still lack definite identification. I
also present the first identified forbidden lines in RY Sgr and the
first published detection of [CaII] in a RCB star. Other lines are
tentatively ascribed to [NII] and [CI]. Comparison of calcium line
ratios indicates an electron density of ~10^9^cm^-3^, but it seems like
at least two different regions emit the broad lines: a high density
chromospheric environment and a much less dense nebula-like region.