Author name code: lambert
ADS astronomy entries on 2022-09-14
author:"Lambert, David L."
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Title: Lithium in red giants: the roles of the He-core flash and
the luminosity bump
Authors: Deepak; Lambert, David L.
Bibcode: 2021MNRAS.507..205D
Altcode: 2021arXiv210704624D; 2021MNRAS.tmp.1807D
Lithium abundances for red giants in the GALAH DR3 survey are
studied. The rare examples of Li-enriched stars with abundances A(Li)
≥1.5 are confirmed to be He-core burning stars belonging to or evolved
from the red clump with similar masses and metallicity: M ≃ 1.1 ± 0.2
M⊙ and [Fe/H] ≃ -0.3 ± 0.3. Li enrichment over the Li
abundance present in a star's predecessor at the tip of the red giant
branch likely occurs in all these red clump stars. Examination of the
elemental abundances (C to Eu) in the GALAH catalogue shows no anomalous
abundances in red clump giants and, in particular, no dependence on the
Li abundance, which ranges over at least five dex. Lithium synthesis is
attributed to the He-core flash occurring in stars at the tip of the
red giant branch. Models from the Modules for Experiments in Stellar
Astrophysics (MESA) match the observed evolution of these stars along
the red giant branch and to the red clump but only at the low effective
temperature end of the observed spread of red clump giants. Run of Li
abundance on the red giant branch is fairly well reproduced by MESA
models. A speculation is presented that the series of He-core flashes
not only leads to 7Li synthesis from a star's internal
reservoir of 3He but also may lead to internal restructuring
leading to the observed effective temperature spread of red clump stars
at about a constant luminosity. Giants exhibiting marked Li enrichments
are not found at other evolutionary phases and, in particular, not
directly associated with the luminosity bump on the red giant branch
for which the Li abundance increase does not exceed 0.3 dex.
Title: Lithium abundances and asteroseismology of red giants:
understanding the evolution of lithium in giants based on
asteroseismic parameters
Authors: Deepak; Lambert, David L.
Bibcode: 2021MNRAS.505..642D
Altcode: 2021MNRAS.tmp.1175D; 2021MNRAS.505..642.; 2021MNRAS.505..642L;
2021arXiv210411741D
In this study, we explore the evolution of lithium in giant stars
based on data assembled from the literature on asteroseismology and Li
abundances for giants. Our final sample of 187 giants consists of 44
red giant branch (RGB), 140 core He-burning (CHeB), and three giants
with an unclassified evolutionary phase. For all 187 stars, the seismic
parameters $\nu \rm _{max}$ (frequency of maximum oscillation power)
and Δν (large frequency spacing) are available, while $\Delta \Pi
\rm _{1}$ (the asymptotic gravity-mode period spacing) is available
for a subset of 64. For some of the CHeB giants, mass estimates from
the asteroseismic scaling relations are found to be underestimated
when compared with mass estimates from isochrones based on seismic
data. Whilst most of the Li-rich giants in the sample have masses less
than 1.5 M⊙, they are also present up to and beyond the
maximum mass expected to have suffered a core He-flash, i.e. $M\, \le$
2.25 M⊙: this suggests contributions from other processes
towards Li enrichment. To understand the evolution of giants in the
$\Delta \Pi \rm _{1}\, -\, \Delta \nu$ plane, we use the Modules for
Experiments in Stellar Astrophysics models that show the presence
of mini-He-flashes following the initial strong core He-flash. From
the distribution of A(Li) as a function of Δν, which is similar
to the distribution of A(Li) as a function of luminosity, we find
no indication of Li enrichment near the luminosity bump. Also, A(Li)
trends to ~-1.5 dex near the RGB tip. The data also suggest a decrease
in A(Li) with an increase in $\Delta \Pi \rm _{1}$ for CHeB giants.
Title: The Transition from Diffuse Molecular Gas to Molecular Cloud
Material in Taurus
Authors: Federman, S. R.; Rice, Johnathan S.; Ritchey, A. M.; Kim,
Hwihyun; Lacy, John H.; Goldsmith, Paul F.; Flagey, Nicolas; Mace,
Gregory N.; Lambert, David L.
Bibcode: 2021ApJ...914...59F
Altcode: 2021arXiv210612748F
We study four lines of sight that probe the transition from diffuse
molecular gas to molecular cloud material in Taurus. Measurements of
atomic and molecular absorption are used to infer the distribution
of species and the physical conditions toward stars behind the
Taurus Molecular Cloud (TMC). New high-resolution spectra at
visible and near-IR wavelengths of interstellar Ca II, Ca I, K I,
CH, CH+, C2, CN, and CO toward HD 28975 and HD
29647 are combined with data at visible wavelengths and published CO
results from ultraviolet measurements for HD 27778 and HD 30122. Gas
densities and temperatures are inferred from C2, CN, and CO
excitation and CN chemistry. Our results for HD 29647 are noteworthy
because the CO column density is 1018 cm-2 while
C2 and CO excitation reveals a temperature of 10 K and a
density of ~1000 cm-3, more like conditions found in dark
molecular clouds. Similar results arise from our chemical analysis
for CN through reactions involving observations of CH, C2,
and NH. Enhanced potassium depletion and a reduced CH/H2
column density ratio also suggest the presence of a dark cloud. The
directions toward HD 27778 and HD 30122 probe molecule-rich diffuse
clouds, which can be considered CO-dark gas, while the sight line toward
HD 28975 represents an intermediate case. Maps of dust temperature help
refine the description of the material along the four sight lines and
provide an estimate of the distance between HD 29647 and a clump in the
TMC. An appendix provides results for the direction toward HD 26571;
this star also probes diffuse molecular gas.
Title: Fluorine detection in hot extreme helium stars
Authors: Bhowmick, Anirban; Pandey, Gajendra; Lambert, David L.
Bibcode: 2020JApA...41...40B
Altcode:
The origin and evolution of hydrogen-deficient stars are not yet
adequately understood. Their chemical peculiarities, along with
hydrogen-deficiency, makes them stand out from the rest and sheds
light on their possible origin. Severe fluorine enrichment (of the
order of 800-8000) is one such characteristic feature of a class of
hydrogen deficient stars, mainly the RCBs (R Coronae Borealis stars)
and cool EHes (Extreme Helium stars) which enforces their close
connection. For hot EHes, this relationship with the cooler EHes,
based on their fluorine abundance is unexplored. Here, first estimates
of fluorine abundances in hot EHes are presented and discussed in the
light of their cooler counterparts to try to establish an evolutionary
connection. The relation between these fluorine estimates with the
other elemental abundances observed in these stars plays a pivotal
role to predict the formation and evolution of these exotic stars.
Title: Galactic chemical evolution and chemical tagging with open
clusters
Authors: Reddy, Arumalla B. S.; Giridhar, Sunetra; Lambert, David L.
Bibcode: 2020JApA...41...38R
Altcode:
The article presents the consolidated results drawn from the
chemical composition studies of Reddy et al. (2012, 2013, 2015,
2016) and Reddy & Lambert (2019), who through the high-dispersion
echelle spectra (R =60000 ) of red giant members in a large sample
of Galactic open clusters (OCs), derived stellar parameters and
chemical abundances for 24 elements by either line equivalent widths
or synthetic spectrum analyses. The focus of this article is on the
issues with radial-metallicity distribution and the potential chemical
tags offered by OCs. Results of these studies confirm the lack of an
age-metallicity relation for OCs but argue that such a lack of trend
for OCs arise from the limited coverage in metallicity compared to that
of field stars which span a wide range in metallicity and age. Results
demonstrate that the sample of clusters constituting a steep radial
metallicity gradient of slope -0.052 ± 0.011 dex kpc-1 at
Rgc< 12 kpc are younger than 1.5 Gyr and located close
to the Galactic midplane (|z |< 0.5 kpc). Whereas the clusters
describing a shallow slope of -0.015 ± 0.007 dex kpc-1 at
Rgc> 12 kpc are relatively old with a striking spread in
age and height above the midplane (0.5<|z |< 2.5 kpc). Results of
these studies reveal that OCs and field stars yield consistent radial
metallicity gradients if the comparison is limited to samples drawn
from the similar vertical heights. The computation of Galactic orbits
reveals that the outer disk OCs were actually born inward of 12 kpc
but the orbital eccentricity has taken them to present locations very
far from their birthplaces. Published results for OCs show that the
abundances of the heavy elements La, Ce, Nd and Sm but not so obviously
Y and Eu vary from one cluster to another across a sample all having
about the solar metallicity. For La, Ce, Nd and Sm the amplitudes
of the variations at solar metallicity scale approximately with the
main s-process contribution to solar system material. Consideration
of published abundances of field stars suggest that such a spread
in heavy element abundances is present for the thin and thick disk
stars of different metallicity. This result provides an opportunity
to chemically tag stars by their heavy elements and to reconstruct
dissolved open clusters from the field star population.
Title: Detection of CH+, CH and H2 Molecules
in the Young Planetary Nebula IC 4997
Authors: Rao, N. Kameswara; Lambert, David L.; Reddy, Arumalla B. S.;
García-Hernández, D. A.; Manchado, Arturo; Díaz-Luis, J. J.
Bibcode: 2020PASP..132g4201R
Altcode: 2020arXiv200500903K
We have detected CH+ and CH molecular absorption lines from
the youngcompact planetary nebula IC 4997 from high resolution optical
spectra. A high-resolution infra-red (H and K bands) spectrum provides
detection of H2 emission lines among many other lines. The
H2 lines provide an excitation temperature of 2100 K which
may result from UV fluorescence in the envelope or from shocks formed
at the interface between an expanding outflow of ionized gas and the
neutral envelope ejected when the star was on the AGB. It is suggested
that the CH+ may result from the endothermic reaction C +
H2 → CH+ + H. Intriguingly, CH+
and also CH show a higher expansion velocity than H2
emission suggesting they may be part of the post-shocked gas. * Based
on observations obtained with The Nordic Optical Telescope and The
Harlan J. Smith Telescope.
Title: Abundance analyses of Li-enriched and normal giants in the
GALAH survey
Authors: Deepak; Lambert, David L.; Reddy, Bacham E.
Bibcode: 2020MNRAS.494.1348D
Altcode: 2020arXiv200305381D; 2020MNRAS.494.1348L; 2020MNRAS.tmp..684D
Compositions of lithium-enriched and normal giants among the GALAH
survey are compared. Except for Li, the only detectable abundance
difference between lithium-enriched and normal giants among the
investigated elements from carbon to europium occurs for carbon. Among
Li-rich giants with A(Li) = 1.8-3.1, the C deficiency is very similar
to that reported for the normal giants [with A(Li) < 1.8] where
the slight C deficiency arises from the first dredge-up. Carbon is
slightly underabundant relative to normal giants among the super
Li-rich giants where the Li abundance exceeds A(Li) = 3.2. The C
abundance as well as the 12C/13C ratios from
the literature suggests that the addition of Li to create a Li-rich
giant may occur independently of the abundance changes wrought by
the first dredge-up. The creation of a super Li-rich giant, however,
appears to occur with additional CN-cycle conversion of C to N. The
probability of becoming a Li-rich giant is approximately independent
of a star's mass, although the majority of the Li-rich giants are
found to be low mass (M ≤ 2 M⊙). The frequency of the
occurrence of Li-enriched giants among normal giants is about 1 per
cent and slightly dependent on metallicity ([Fe/H]). Li-enriched and
normal giants are found to have similar projected rotational velocity,
which suggests that Li enrichment in giants is not linked to scenarios
such as mergers and tidal interaction between binary stars.
Title: SALT revisits DY Cen: a rapidly evolving strontium-rich single
helium star
Authors: Jeffery, C. Simon; Rao, N. Kameswara; Lambert, David L.
Bibcode: 2020MNRAS.493.3565J
Altcode: 2020arXiv200203931J; 2020MNRAS.tmp..379J
The hydrogen-deficient star DY Cen has been reported as an R CrB-type
variable, an extreme helium star (with some hydrogen), and as a
single-lined spectroscopic binary. It has been associated with a
dramatic change in visual brightness and colour corresponding to a
change in effective temperature ( Teff) of some 20 000 K in
the last century. To characterize the binary orbit and Teff
changes more precisely, new high-resolution spectroscopy has been
obtained with SALT. The previous orbital period is not confirmed;
previous measurements may have been confused by the presence of
pulsations. Including data from earlier epochs (1987, 2002, and 2010),
self-consistent spectral analyses from all four epochs demonstrate an
increase in Teff from 18 800 to 24 400 K between 1987 and
2015. Line profiles demonstrate that the surface rotation has increased
by a factor of 2 over the same interval. This is commensurate with
the change in Teff and an overall contraction. Rotation
will exceed critical if contraction continues. The 1987 spectrum
shows evidence of a very high abundance of the s-process element
strontium. The very rapid evolution, non-negligible surface hydrogen
and high surface strontium point to a history involving a very late
thermal pulse. Observations over the next 30 yr should look for a
decreasing pulsation period, reactivation of R CrB-type activity as
the star seeks to shed angular momentum and increasing illumination
by emission lines from nebular material ejected in the past.
Title: Science Operations Planning for the OSIRIS-REx Asteroid Sample
Return Mission
Authors: Polit, A. T.; Enos, H. L.; Boynton, W. V.; Lambert, D.;
Westermann, M. M.; Kidd, J. N.; Garcia, R.; Becker, T.; Balram-Knutson,
S. S.; Harshman, K.; Lauretta, D. S.
Bibcode: 2020LPI....51.2430P
Altcode:
The OSIRIS-REx Science Planning Team has developed sophisticated
processes and tools to address the complexities of the mission.
Title: Detection of Fluorine in Hot Extreme Helium Stars
Authors: Bhowmick, Anirban; Pandey, Gajendra; Lambert, David L.
Bibcode: 2020ApJ...891...40B
Altcode: 2020arXiv200107472B
The main objective of this paper is to explore abundances of fluorine
in hot extreme helium stars (EHes). Overabundance of fluorine is a
characteristic feature for cool EHes and R Coronae Borealis stars
and further enforces their close connection. For hot EHes this
relationship with the cooler EHes, based on their fluorine abundance
is unexplored. We present in this paper the first abundance estimates
of fluorine determined from singly ionized fluorine lines (F II)
for 10 hot EHe stars from optical spectra. Fluorine abundances were
determined using the F II lines in two windows centered at 3505 Å
and 3850 Å. Six of the 10 stars show significant enhancement of
fluorine similar to the cool EHes. Two carbon-poor hot EHes show no
signature of fluorine and have a significant low upper limit for
the F abundance. These fluorine abundances are compared with the
other elemental abundances observed in these stars, which provide an
idea about the formation and evolution of these stars. The trends of
fluorine with C, O, and Ne show that significant helium burning after
a CO-He white dwarf merger can account for a majority of the observed
abundances. Predictions from simulations of white dwarf mergers are
discussed in light of the observed abundances.
Title: Unveiling Vela - variability of interstellar lines in the
direction of the Vela supernova remnant - III. Na D and Ca II K
Authors: Kameswara Rao, N.; Lambert, David L.; Reddy, Arumalla B. S.;
Gupta, Ranjan; Muneer, S.; Varghese, Baba; Singh, Harinder P.
Bibcode: 2020MNRAS.493..497K
Altcode: 2020MNRAS.tmp..267R; 2020arXiv200105790K; 2020MNRAS.493..497R
High-resolution optical spectra were obtained in 2017-2019 with The
Southern African Large Telescope of 15 stars in the direction of the
Vela supernova remnant. Interstellar Ca II H & K and Na I D lines
are discussed in this paper. In particular, the line profiles are
compared with profiles at a comparable spectral resolution obtained in
1993-1996 by Cha and Sembach. Ten of the lines of sight show changes
to one or more of the components in that line of sight. Changes
include small changes (1-2 km s-1) in radial velocity
and/or increases/decreases in equivalent width over the two decades
between the periods of observation. Changes are more obvious in the
Ca K line than in the Na D lines. These changes are attributed to
gas disturbed by interactions between the supernova ejecta and the
surrounding interstellar medium. A representative time-scale may be
20-50 yr. Small-scale variations in line profiles across the face of
the remnant suggest, as previously remarked, that a linear scale for
interactions is a small fraction of the 40 pc size of the present
remnant.
Title: Carbon and Oxygen Isotopic Ratios. II. Semiregular Variable
M Giants
Authors: Lebzelter, Thomas; Hinkle, Kenneth H.; Straniero, Oscar;
Lambert, David L.; Pilachowski, Catherine A.; Nault, Kristie A.
Bibcode: 2019ApJ...886..117L
Altcode: 2019arXiv191204386L
Carbon and oxygen isotopic ratios are reported for a sample
of 51 SRb- and Lb-type variable asymptotic giant branch
stars. Vibration-rotation first- and second-overtone CO lines in
1.5-2.5 μm spectra were measured to derive isotopic ratios for
12C/13C, 16O/17O, and
16O/18O. Comparisons with previous measurements
for individual stars and with various samples of evolved stars, as
available in the extant literature, are discussed. Using the oxygen
isotopic ratios, the masses of the SRb stars can be derived. Combining
the masses with Gaia luminosities, the SRb stars are shown to be
antecedents of the Mira variables. The limiting parameters where
plane-parallel, hydrostatic equilibrium model atmospheres can be used
for abundance analysis of M giants are explored.
Title: The chemical composition of HIP 34407/HIP 34426 and other
twin-star comoving pairs
Authors: Ramírez, I.; Khanal, S.; Lichon, S. J.; Chanamé, J.; Endl,
M.; Meléndez, J.; Lambert, D. L.
Bibcode: 2019MNRAS.490.2448R
Altcode: 2019MNRAS.tmp.2375R; 2019arXiv190907460R
We conducted a high-precision elemental abundance analysis of the
twin-star comoving pair HIP 34407/HIP 34426. With mean error of
0.013 dex in the differential abundances (Δ[X/H]), a significant
difference was found: HIP 34407 is more metal rich than HIP 34426. The
elemental abundance differences correlate strongly with condensation
temperature, with the lowest for the volatile elements like carbon
around 0.05 ± 0.02 dex, and the highest up to about 0.22 ± 0.01 dex
for the most refractory elements like aluminium. Dissimilar chemical
composition for stars in twin-star comoving pairs is not uncommon,
thus we compile previously published results like ours and look for
correlations between abundance differences and stellar parameters,
finding no significant trends with average effective temperature,
surface gravity, iron abundance, or their differences. Instead, we
found a weak correlation between the absolute value of abundance
difference and the projected distance between the stars in each
pair that appears to be more important for elements that have a low
absolute abundance. If confirmed, this correlation could be an important
observational constraint for binary star system formation scenarios.
Title: Overview of OSIRIS-REx Thermal Observations
Authors: Emery, J. P.; Rozitis, B.; Christensen, P. R.; Hamilton,
V. E.; Haberle, C.; Simon, A. A.; Reuter, D. C.; Delbo, M.; Lim,
L. F.; Clark, B. E.; Ryan, A.; Chesley, S. R.; Boynton, W. V.; Polit,
A.; Westerman, M.; Becker, T.; Garcia, R.; Lambert, D.; Kidd, J.;
Howell, E. S.; Nolan, M. C.; Enos, H. L.; Lauretta, D. S.
Bibcode: 2019LPICo2189.2113E
Altcode:
We provide an overview of OSIRIS-REx thermal observations along with
some results.
Title: Fluorine Abundances in the Galactic Disk
Authors: Guerço, Rafael; Cunha, Katia; Smith, Verne V.; Hayes,
Christian R.; Abia, Carlos; Lambert, David L.; Jönsson, Henrik;
Ryde, Nils
Bibcode: 2019ApJ...885..139G
Altcode: 2019arXiv190908655G
The chemical evolution of fluorine is investigated in a sample of
Milky Way red giant stars that span a significant range in metallicity
from [Fe/H] ∼ -1.3 to 0.0 dex. Fluorine abundances are derived from
vibration-rotation lines of HF in high-resolution infrared spectra near
2.335 μm. The red giants are members of the thin and thick disk/halo,
with two stars being likely members of the outer disk Monoceros
overdensity. At lower metallicities, with [Fe/H] < -0.4 to -0.5,
the abundance of F varies as a primary element with respect to the
Fe abundance, with a constant subsolar value of [F/Fe] ∼ -0.3 to
-0.4 dex. At larger metallicities, however, [F/Fe] increases rapidly
with [Fe/H] and displays a near-secondary behavior with respect to
Fe. Comparisons with various models of chemical evolution suggest that
in the low-metallicity regime (dominated here by thick-disk stars),
a primary evolution of 19F with Fe, with a subsolar [F/Fe]
value that roughly matches the observed plateau, can be reproduced by
a model incorporating neutrino nucleosynthesis in the aftermath of the
core collapse in Type II supernovae. A primary behavior for [F/Fe]
at low metallicity is also observed for a model including rapidly
rotating low-metallicity massive stars, but this overproduces [F/Fe]
at low metallicity. The thick-disk red giants in our sample span a
large range of galactocentric distance (R g ∼ 6-13.7 kpc)
yet display a roughly constant value of [F/Fe], indicating a very flat
gradient (with a slope of 0.02 ± 0.03 dex kpc-1) of this
elemental ratio over a significant portion of the Galaxy having | Z|
> 300 pc away from the Galaxy midplane.
Title: Oxygen abundance and the N/C versus N/O relation for AFG
supergiants and bright giants
Authors: Lyubimkov, L. S.; Korotin, S. A.; Lambert, D. L.
Bibcode: 2019MNRAS.489.1533L
Altcode: 2019arXiv190704634L
Non-LTE analysis (where LTE is local thermodynamic equilibrium) of
the oxygen abundances for 51 Galactic A-, F- and G-type supergiants
and bright giants is performed. In contrast with carbon and nitrogen,
oxygen does not show any significant systematic anomalies in its
abundances log ɛ(O). There is no marked difference from the initial
oxygen abundance, within the errors, for the log ɛ(O) determination
across the Teff interval from 4500-8500 K and the \log g
interval from 1.2-2.9 dex. This result agrees well with theoretical
predictions for stellar models with rotation. With our new data for
oxygen and our earlier non-LTE determinations of the N and C abundances
for stars from the same sample, we constructed the [N/C] versus
[N/O] relation for 17 stars. This relation is known to be a sensitive
indicator of stellar evolution. A pronounced correlation between [N/C]
versus [N/O] is found; the observed [N/C] increase from 0 to 1.6 dex is
accompanied by a [N/O] increase from 0 to 0.9 dex. When comparing the
observed [N/C] versus [N/O] relation with the theoretical one, we show
that this relation reflects a strong dependence of the evolutionary
changes in CNO abundances on the initial rotation velocities of
stars. Given that the initial rotational velocities of these stars
are expected to satisfy V0 < 150 km s-1,
it is found that they are mostly post-first-dredge-up (post-FDU)
objects. It is important that such initial velocities V0
are typical for about 80 per cent of the stars in question (i.e. stars
with masses 4-19 M\odot). A constancy of the total C+N+O
abundance during stellar evolution is confirmed. The mean value of
log ɛ(C+N + O) = 8.97 ± 0.08 found for AFG supergiants and bright
giants seems to be very close to the initial values of 8.92 (the Sun)
or 8.94 (unevolved B-type main-sequence stars).
Title: A New Near-IR C2 Linelist for an Improved Chemical
Analysis of Hydrogen-deficient, Carbon-rich Giants
Authors: García-Hernández, D. A.; Masseron, T.; Zamora, O.; Manchado,
A.; Rao, N. K.; Reddy, A. B. S.; Lambert, D. L.; Yurchenko, S.;
Tennyson, J.
Bibcode: 2019ASPC..519..147G
Altcode:
Diatomic carbon (C2) is ubiquitous in astronomical
environments, from comets and stars to translucent clouds and
the interstellar medium. In particular, the C2 bands
(mainly the Ballik-Ramsay and Phillips transitions) are an important
source of opacity in the near-IR region of carbon stars such as the
hydrogen deficient carbon-rich (HdC) or R Coronae Borealis (RCB)
stars. Present C2 linelists are still not accurate
enough (e.g., in wavelength positions) to model the near-IR
spectra of HdC and RCB stars, strongly limiting our ability to
properly model their complex spectra and to extract the elemental
(an isotopic, when possible) abundances of key elements like C,
N, O, F, etc. Very recently, a new near-IR C2 linelist
(including both Ballik-Ramsay and Phillips systems, among others)
have been generated by the ExoMol project (Yurchenko et al. 2018; see
<a href='www.exomol.com'>www.exomol.com</a>). The synthetic
spectrum constructed for the benchmark HdC star HD 137613, using this
new C2 linelist, provides an unprecedented match to its
high-resolution (R∼50,000) observed spectrum. The new C2
linelist is thus expected to significantly improve the near-IR chemical
analysis for HdC and RCB stars but also for normal carbon stars (e.g.,
C-rich AGB and dwarf stars) and even Solar System bodies like comets.
Title: The Transition from Diffuse Atomic Gas to Molecular Cloud
in Taurus
Authors: Federman, Steven; Rice, Johnathan S.; Ritchey, Adam; Kim,
Hwihyun; Lacy, John H.; Goldsmith, Paul F.; Flagey, Nicolas; Mace,
Gregory N.; Lambert, David L.
Bibcode: 2019isms.confEWA06F
Altcode:
We study four lines of sight that probe the transition from diffuse
molecular gas to molecular cloud material in Taurus. Measurements of
atomic and molecular absorption are used to infer the distribution of
species and the physical conditions in the direction to stars behind
the Taurus Molecular Cloud. New high-resolution spectra at visible and
near infrared wavelengths of interstellar K I, CH, CH+,
C2, CN, and CO toward HD 28975 and HD 29647 are combined
with published results for HD 27778 and HD 30122. Gas densities and
temperatures are inferred from analyses of C2, CN, and CO
excitation. Our results for HD 29647 are noteworthy in that the CO
column density is 1018 cm-2, our analysis of CO
and C2 excitation reveal a temperature of 10 K and densities
of about 1000 cm-3, and the CO excitation and radiation
temperatures are the same, more like emission-line studies of dark
molecular clouds. Similar results arise from our chemical analysis
leading to CN through reactions involving the observed species CH
and C2. The other directions are typical of molecule-rich
diffuse clouds and can be considered CO-dark gas.
Title: Fluorine Abundances in the Globular Cluster M4
Authors: Guerço, Rafael; Cunha, Katia; Smith, Verne V.; Pereira,
Claudio B.; Abia, Carlos; Lambert, David L.; de Laverny, Patrick;
Recio-Blanco, Alejandra; Jönsson, Henrik
Bibcode: 2019ApJ...876...43G
Altcode: 2019arXiv190310127G
We present chemical abundances for the elements carbon, sodium, and
fluorine in 15 red giants of the globular cluster M4, as well as six
red giants of the globular cluster ω Centauri. The chemical abundances
were calculated in LTE via spectral synthesis. The spectra analyzed are
high-resolution spectra obtained in the near-infrared region around 2.3
μm with the Phoenix spectrograph on the 8.1 m Gemini South Telescope,
the IGRINS spectrograph on the McDonald Observatory 2.7 m Telescope,
and the CRIRES spectrograph on the ESO 8.2 m Very Large Telescope. The
results indicate a significant reduction in the fluorine abundances
when compared to previous values from the literature for M4 and ω
Centauri, due to a downward revision in the excitation potentials of
the HF (1-0) R9 line used in the analysis. The fluorine abundances
obtained for the M4 red giants are found to be anticorrelated with
those of Na, following the typical pattern of abundance variations
seen in globular clusters between distinct stellar populations. In M4,
as the Na abundance increases by ∼+0.4 dex, the F abundance decreases
by ∼-0.2 dex. A comparison with abundance predictions from two sets
of stellar evolution models finds that the models predict somewhat
less F depletion (∼-0.1 dex) for the same increase of +0.4 dex in Na.
Title: Comprehensive abundance analysis of red giants in the open
clusters Stock 2, NGC 2168, 6475, 6991, and 7762
Authors: Reddy, Arumalla B. S.; Lambert, David L.
Bibcode: 2019MNRAS.485.3623R
Altcode: 2019arXiv190202939R; 2019MNRAS.tmp..460R
We have analysed high-dispersion Echelle spectra (R = 60 000) of red
giant members of five open clusters to derive abundances for many
elements from Na to Eu. The [Fe/H] values are -0.06 ± 0.03 for Stock
2, -0.11 ± 0.03 for NGC 2168, -0.01 ± 0.03 for NGC 6475, 0.00 ± 0.03
for NGC 6991, and -0.07 ± 0.03 for NGC 7662. Sodium is enriched in the
giants relative to the abundance expected of main-sequence stars of the
same metallicity. This enrichment of [Na/Fe] by about +0.25 attributed
to the first dredge-up is discussed in the light of theoretical
predictions and recently published abundance determinations. Abundance
ratios [El/Fe] for other elements are with very few exceptions equal
to those of field giants and dwarfs, i.e. [El/Fe] ≃ 0.00 for [Fe/H]
∼0.0. An exception is the overabundance of La, Ce, Nd, and Sm in
NGC 6991 but this is consistent with our previous demonstration that
the abundances of these s-process products vary by about ±0.2 among
clusters of the same [Fe/H], a variation found also among field giants
and dwarfs.
Title: VizieR Online Data Catalog: Visible obs. of GOT C+ Northern
sightlines (Rice+, 2018)
Authors: Rice, J. S.; Federman, S. R.; Flagey, N.; Goldsmith, P. F.;
Langer, W. D.; Pineda, J. L.; Lambert, D. L.
Bibcode: 2019yCat..18580111R
Altcode:
The data at visible wavelengths were taken at the McDonald Observatory
in 2012 December, 2014 July, and 2017 October with the echelle
spectrograph. Table 1 lists the stellar data and observational details
for the seventeen lines of sight. Table 2 gives the results of fitting
the absorption from the CaII, CaI, KI, CH+, CH and CN
species. (2 data files).
Title: Consequences of Refining the Distance to the Supergiant
HD 169454
Authors: Federman, S. R.; Lambert, David L.
Bibcode: 2019RNAAS...3...60F
Altcode: 2019RNAAS...3d..60F
No abstract at ADS
Title: Chemical compositions of giants in the Hyades and Sirius
superclusters
Authors: Ramya, P.; Reddy, Bacham E.; Lambert, David L.
Bibcode: 2019MNRAS.484..125R
Altcode: 2019arXiv190106050R; 2018MNRAS.tmp.3335R
An abundance analysis for 20 elements from Na to Eu is reported for 34 K
giants from the Hyades supercluster and for 22 K giants from the Sirius
supercluster. Observed giants were identified as highly probable members
of their respective superclusters by Famaey et al. Three giants each
from the Hyades and Praesepe open clusters were similarly observed
and analysed. Each supercluster shows a range in metallicity: -0.20
≤ [Fe/H] ≤ +0.25 for the Hyades supercluster and -0.22 ≤ [Fe/H]
≤ +0.15 for the Sirius supercluster with the metal-rich tail of the
metallicity distribution of the Hyades supercluster extending beyond
that of the Sirius supercluster and spanning the metallicity of the
Hyades and Praesepe cluster giants. Relative elemental abundances
[El/Fe] across the supercluster giants are representative of the
Galactic thin disc as determined from giants in open clusters analysed
in a similar way to our approach. Judged by metallicity and age, very
few and likely none of the giants in these superclusters originated
in an open cluster: the pairings include the Hyades supercluster with
the Hyades - Praesepe open clusters and the Sirius supercluster with
the U Ma open cluster. Literature on main-sequence stars attributed to
the two superclusters and the possible relation to the associated open
cluster is reviewed. It is suggested that the Hyades supercluster's
main-sequence population contains few stars from the two associated
open clusters. As suggested by some previous investigations, the Sirius
supercluster, when tightly defined kinematically, appears to be well
populated by stars shed by the U Ma open cluster.
Title: VizieR Online Data Catalog: Ga, Ge, As, Kr, Cd, Sn and Pb
column densities (Ritchey+, 2018)
Authors: Ritchey, A. M.; Federman, S. R.; Lambert, D. L.
Bibcode: 2018yCat..22360036R
Altcode:
The primary aim of our extensive search of the HST/Space Telescope
Imaging Spectrograph (STIS) archive was the identification of sight
lines showing significant absorption from AsIIλ1263, CdIIλ2145,
SnIIλ1400, and PbIIλ1433. In addition to searching for absorption
from As II, Cd II, Sn II, and Pb II, we sought to incorporate available
data on GaII, GeII, and KrI into our analysis so that the abundances
of all seven n-capture elements could be analyzed in a consistent
manner. We also examined the HST/Goddard High-Resolution Spectrograph
(GHRS) data on GeIIλ1237, along with STIS data for the weaker GeII
line at 1602.5λ. (6 data files).
Title: VizieR Online Data Catalog: Abundance analyses of V652 Her
and HD 144941 (Pandey+, 2017)
Authors: Pandey, G.; Lambert, D. L.
Bibcode: 2018yCat..18470127P
Altcode:
High-resolution optical spectra of V652 Her and HD 144941 were
obtained on 2011 May 13 at the coude focus of the W.J. McDonald
Observatory's Harlan J. Smith 2.7m telescope with the Robert
G. Tull cross-dispersed echelle spectrograph at a resolving power of
R=60000. Three thirty-minute exposures were recorded for each of these
stars. (3 data files).
Title: Abundances and Depletions of Neutron-capture Elements in the
Interstellar Medium
Authors: Ritchey, A. M.; Federman, S. R.; Lambert, D. L.
Bibcode: 2018ApJS..236...36R
Altcode: 2018arXiv180301089R
We present an extensive analysis of the gas-phase abundances and
depletion behaviors of neutron-capture elements in the interstellar
medium (ISM). Column densities (or upper limits to the column densities)
of Ga II, Ge II, As II, Kr I, Cd II, Sn II, and Pb II are determined
for a sample of 69 sight lines with high- and/or medium-resolution
archival spectra obtained with the Space Telescope Imaging Spectrograph
on board the Hubble Space Telescope. An additional 59 sight lines with
column density measurements reported in the literature are included
in our analysis. Parameters that characterize the depletion trends
of the elements are derived according to the methodology developed
by Jenkins. (In an appendix, we present similar depletion results
for the light element B.) The depletion patterns exhibited by Ga and
Ge comport with expectations based on the depletion results obtained
for many other elements. Arsenic exhibits much less depletion than
expected, and its abundance in low-depletion sight lines may even
be supersolar. We confirm a previous finding by Jenkins that the
depletion of Kr increases as the overall depletion level increases
from one sight line to another. Cadmium shows no such evidence of
increasing depletion. We find a significant amount of scatter in the
gas-phase abundances of Sn and Pb. For Sn, at least, the scatter may
be evidence of real intrinsic abundance variations due to s-process
enrichment combined with inefficient mixing in the ISM.
Title: The Connection between Different Tracers of the Diffuse
Interstellar Medium: Kinematics
Authors: Rice, Johnathan S.; Federman, S. R.; Flagey, Nicolas;
Goldsmith, Paul F.; Langer, William D.; Pineda, Jorge L.; Lambert,
D. L.
Bibcode: 2018ApJ...858..111R
Altcode: 2018arXiv180406908R
Using visible, radio, microwave, and submillimeter data, we study
several lines of sight toward stars generally closer than 1 kpc on
a component-by-component basis. We derive the component structure
seen in absorption at visible wavelengths from Ca II, Ca I, K I,
CH, CH+, and CN and compare it to emission from H I, CO
and its isotopologues, and C+ from the GOT C+ survey. The
correspondence between components in emission and absorption helps
create a more unified picture of diffuse atomic and molecular gas in
the interstellar medium. We also discuss how these tracers are related
to the CO-dark H2 gas probed by C+ emission and
discuss the kinematic connections among the species observed.
Title: A-type Stellar Abundances: A Corollary to Herschel Observations
of Debris Disks
Authors: Draper, Zachary H.; Matthews, Brenda; Venn, Kim; Lambert,
David; Kennedy, Grant; Sitnova, Tatyana
Bibcode: 2018ApJ...857...93D
Altcode:
In order to assess the relationship between metallicity and exoplanetary
systems, we compare the abundances of AF-type main-sequence stars
with debris disk properties assessed using Herschel observations of
an unbiased survey of nearby stars. Hot stars are not as commonly
observed, given their unique constraints in data reduction, lack of
metal lines, and “astrophysical noise” from rotation speed. Here,
we address that deficiency using new and archival spectra of 83 AF-type
stars. We measure the abundances of a few species in addition to Fe in
order to classify the stars with Ap/Am or Lambda Boo signatures. Lambda
Boo stars have a chemical signature of solar-abundant volatile species
and sub-solar refractory abundances that is hypothesized to be altered
by the pollution of volatiles. Overall, we see no correlation between
debris disks and metallicity, primarily because the sample size is
cut significantly when using only reliable fits to the spectroscopic
data. The abundance measured from the Mg II 4481 blend is a useful
diagnostic because it can be reliably measured at large v·sin(i)
and is found to be lower around stars with bright debris disks. We
find that Lambda Boo stars have brighter debris disks compared to a
bias-free sample of AF stars. The trend with disk brightness and Mg
abundances suggests pollution effects can be significant and used as
a marker for the stability of planetary systems. We explore trends
with other species, such as with the C/O ratios, but are significantly
limited by the low number of reliable detections.
Title: VizieR Online Data Catalog: Abundance ratio for 5 local
stellar associations (Reddy+, 2015)
Authors: Reddy, A. B. S.; Lambert, D. L.
Bibcode: 2018yCat..74541976R
Altcode:
In this paper, we have performed a homogeneous and a comprehensive
abundance analysis using high-resolution spectroscopy. High-resolution
and high signal-to-noise (S/N) spectra of the program stars
were obtained during the nights of 2015 February 10-11 with the
Robert G. Tull coude cross-dispersed echelle spectrograph (Tull et
al. 1995PASP..107..251T) of the 2.7 m Harlan J. Smith reflector at the
McDonald Observatory. We employed a Tektronix 2048x2048 24 μm pixel,
backside illuminated and anti-reflection coated CCD as a detector and
an R2 echelle grating with 52.67 grooves/mm with exposures centred at
5060 Å. (7 data files).
Title: Iota Horologii Is Unlikely to Be an Evaporated Hyades Star
Authors: Ramírez, I.; Yong, D.; Gutiérrez, E.; Endl, M.; Lambert,
D. L.; Do Nascimento, J. -D., Jr.
Bibcode: 2017ApJ...850...80R
Altcode: 2017arXiv171005930R
We present a high-precision chemical analysis of ι Hor (iota
Horologii), a planet-host field star thought to have formed in
the Hyades. Elements with atomic number 6≤slant Z≤slant 30
have abundances that are in excellent agreement with those of the
cluster within the ±0.01 dex (or ≃ 2 % ) precision errors. Heavier
elements show a range of abundances such that about half of the Z>
30 species analyzed are consistent with those of the Hyades, while
the other half are marginally enhanced by 0.03 ± 0.01 dex (≃ 7+/-
2 % ). The lithium abundance, A(Li), is very low compared to the
well-defined A(Li)-{T}{eff} relation of the cluster. For
its {T}{eff}, ι Hor’s lithium content is about half
the Hyades’. Attributing the enhanced lithium depletion to the
planet would require a peculiar rotation rate, which we are unable to
confirm. Our analysis of ι Hor’s chromospheric activity suggests
{P}{rot}=5 days, which is significantly shorter than
previously reported. Models of Galactic orbits place ι Hor hundreds
of parsecs away from the cluster at formation. Thus, we find the claim
of a shared birthplace very difficult to justify.
Title: VizieR Online Data Catalog: Line list for red giants in open
clusters (Reddy+, 2015)
Authors: Reddy, A. B. S.; Giridhar, S.; Lambert, D. L.
Bibcode: 2017yCat..74504301R
Altcode:
Observations were carried out during observing runs in 2011 May and
November, 2012 November and 2013 March using the Robert G. Tull echelle
spectrograph (Tull et al. 1995PASP..107..251T) at the coude focus of the
2.7m Harlan J. Smith telescope located at the McDonald Observatory. On
all occasions we employed a 2048x2048 24μm pixel, backside-illuminated,
anti-reflection coated CCD as a detector and the 52.67 grooves/mm
echelle grating with exposures centred at 5060Å. (2 data files).
Title: VizieR Online Data Catalog: Hercules stream K giants analysis
(Ramya+, 2016)
Authors: Ramya, P.; Reddy, B. E.; Lambert, D. L.; Musthafa, M. M.
Bibcode: 2017yCat..74601356R
Altcode:
Our sample of giants was chosen from Famaey et al. (2005,
Cat. J/A+A/430/165). Spectra of 58 giants in the Hercules stream
were obtained using the Robert G. Tull coude spectrograph at the
Harlan J. Smith Telescope. Observed spectra cover the wavelength range
3800-10000Å. However, beyond ~5800Å, coverage is incomplete because
of gaps between the recorded portions of the spectral orders, which
progressively increase towards redder wavelengths. (9 data files).
Title: Non-local Thermodynamic Equilibrium Abundance Analyses of
the Extreme Helium Stars V652 Her and HD 144941
Authors: Pandey, Gajendra; Lambert, David L.
Bibcode: 2017ApJ...847..127P
Altcode: 2017arXiv170807945P
Optical high-resolution spectra of V652 Her and HD 144941, the two
extreme helium stars with exceptionally low C/He ratios, have been
subjected to a non-LTE abundance analysis using the tools TLUSTY
and SYNSPEC. Defining atmospheric parameters were obtained from a
grid of non-LTE atmospheres and a variety of spectroscopic indicators
including He I and He II line profiles, and the ionization equilibrium
of ion pairs such as C II/C III and N II/N III. The various indicators
provide a consistent set of atmospheric parameters: T eff
= 25,000 ± 300 K, log g = 3.10 ± 0.12(cgs), and ξ = 13 ± 2 km
s-1 are provided for V652 Her, and T eff = 22,000
± 600 K, log g = 3.45 ± 0.15 (cgs), and ξ = 10 km s-1
are provided for HD 144941. In contrast to the non-LTE analyses, the
LTE analyses—LTE atmospheres and an LTE line analysis—with the
available indicators do not provide a consistent set of atmospheric
parameters. The principal non-LTE effect on the elemental abundances is
on the neon abundance. It is generally considered that these extreme
helium stars with their very low C/He ratio result from the merger of
two helium white dwarfs. Indeed, the derived composition of V652 Her
is in excellent agreement with predictions by Zhang & Jeffery, who
model the slow merger of helium white dwarfs; a slow merger results
in the merged star having the composition of the accreted white
dwarf. In the case of HD 144941, which appears to have evolved from
metal-poor stars, a slow merger is incompatible with the observed
composition but variations of the merger rate may account for the
observed composition. More detailed theoretical studies of the merger
of a pair of helium white dwarfs are to be encouraged.
Title: Abundance Analyses of the New R Coronae Borealis Stars:
ASAS-RCB-8 and ASAS-RCB-10
Authors: Hema, B. P.; Pandey, Gajendra; Kamath, Devika; Kameswara Rao,
N.; Lambert, David; Woolf, Vincent M.
Bibcode: 2017PASP..129j4202H
Altcode: 2017arXiv170701268H
Abundance analyses of the two newly discovered R Coronae Borealis (RCB)
stars ASAS-RCB-8 and ASAS-RCB-10 were conducted using high-resolution
optical spectra and model atmospheres. Their chemical compositions place
the pair among the majority class of RCBs. ASAS-RCB-10 is one of the
most N-poor majority RCBs with an above average O abundance. Relative
to ASAS-RCB-10, ASAS-RCB-8 is H poor by 1.6 dex, O-poor by 0.7 dex
but N-rich by 0.8 dex suggesting a higher contamination by CNO-cycled
material.
Title: Solar Twins and the Barium Puzzle
Authors: Reddy, Arumalla B. S.; Lambert, David L.
Bibcode: 2017ApJ...845..151R
Altcode: 2017arXiv170707051R
Several abundance analyses of Galactic open clusters (OCs) have
shown a tendency for Ba but not for other heavy elements (La-Sm)
to increase sharply with decreasing age such that Ba was claimed to
reach [Ba/Fe] ≃ +0.6 in the youngest clusters (ages < 100 Myr)
rising from [Ba/Fe] = 0.00 dex in solar-age clusters. Within the
formulation of the s-process, the difficulty to replicate higher Ba
abundance and normal La-Sm abundances in young clusters is known as the
barium puzzle. Here, we investigate the barium puzzle using extremely
high-resolution and high signal-to-noise spectra of 24 solar twins and
measured the heavy elements Ba, La, Ce, Nd, and Sm with a precision
of 0.03 dex. We demonstrate that the enhanced Ba II relative to La-Sm
seen among solar twins, stellar associations, and OCs at young ages
(<100 Myr) is unrelated to aspects of stellar nucleosynthesis but
has resulted from overestimation of Ba by standard methods of LTE
abundance analysis in which the microturbulence derived from the Fe
lines formed deep in the photosphere is insufficient to represent the
true line broadening imposed on Ba II lines by the upper photospheric
layers from where the Ba II lines emerge. Because the young stars have
relatively active photospheres, Ba overabundances most likely result
from the adoption of a too low value of microturbulence in the spectrum
synthesis of the strong Ba II lines but the change of microturbulence
in the upper photosphere has only a minor affect on La-Sm abundances
measured from the weak lines.
Title: VizieR Online Data Catalog: Elemental abundances of solar
sibling candidates (Ramirez+, 2014)
Authors: Ramirez, I.; Bajkova, A. T.; Bobylev, V. V.; Roederer, I. U.;
Lambert, D. L.; Endl, M.; Cochran, W. D.; MacQueen, P. J.; Wittenmyer,
R. A.
Bibcode: 2017yCat..17870154R
Altcode:
We used the Tull coude spectrograph on the 2.7 m Harlan J. Smith
Telescope at McDonald Observatory (Tull et al. 1995PASP..107..251T) to
observe most of our targets (23). All but three of them were observed
in 2012 December; the others were observed in 2013 March. The rest
of our targets (seven) have too-low declinations to be observed from
McDonald Observatory. Instead, they were observed using the Magellan
Inamori Kyocera Echelle (MIKE) spectrograph on the 6.5 m Telescope at
Las Campanas Observatory (Bernstein et al. 2003SPIE.4841.1694B) in 2013
April. Slit sizes were chosen so that the spectral resolution of the
data is about 60000 in the visible part of the spectrum. We targeted
a S/N per pixel of at least 200 at 6000 Å. Only one of our targets
(HD 46100) has a significantly lower S/N spectrum. (2 data files).
Title: The Origin of B-type Runaway Stars: Non-LTE Abundances as
a Diagnostic
Authors: McEvoy, Catherine M.; Dufton, Philip L.; Smoker, Jonathan
V.; Lambert, David L.; Keenan, Francis P.; Schneider, Fabian R. N.;
de Wit, Willem-Jan
Bibcode: 2017ApJ...842...32M
Altcode: 2017arXiv170803527M
There are two accepted mechanisms to explain the origin of runaway
OB-type stars: the binary supernova (SN) scenario and the cluster
ejection scenario. In the former, an SN explosion within a close
binary ejects the secondary star, while in the latter close multibody
interactions in a dense cluster cause one or more of the stars to be
ejected from the region at high velocity. Both mechanisms have the
potential to affect the surface composition of the runaway star. tlusty
non-LTE model atmosphere calculations have been used to determine
the atmospheric parameters and the C, N, Mg, and Si abundances for a
sample of B-type runaways. These same analytical tools were used by
Hunter et al. for their analysis of 50 B-type open-cluster Galactic
stars (I.e., nonrunaways). Effective temperatures were deduced using
the Si-ionization balance technique, surface gravities from Balmer
line profiles, and microturbulent velocities derived using the
Si spectrum. The runaways show no obvious abundance anomalies when
compared with stars in the open clusters. The runaways do show a spread
in composition that almost certainly reflects the Galactic abundance
gradient and a range in the birthplaces of the runaways in the Galactic
disk. Since the observed Galactic abundance gradients of C, N, Mg,
and Si are of a similar magnitude, the abundance ratios (e.g., N/Mg)
are as obtained essentially uniform across the sample.
Title: Multi-wavelength Study of Diffuse Atomic and Molecular Gas
Authors: Federman, Steven Robert; Rice, Johnathan; Flagey, Nicolas;
Ritchey, Adam M.; Welty, Daniel E.; Goldsmith, Paul; Langer, William;
Pineda, Jorge L.; Lambert, David L.; Lemaire, Jean-Louis
Bibcode: 2017AAS...23021506F
Altcode:
Diffuse atomic and molecular gas is revealed through a combination
of absorption lines against background targets and emission. We
describe a project that combines results on ultraviolet (UV) and
visible absorption with those obtained from the Herschel key program
GOTC+ (Galactic Observations of Terahertz C+) to develop
a comprehensive picture of neutral diffuse gas in the Galaxy. [C
II], H I, and CO emission acquired for the GOTC+ survey reveal
the presence of warm neutral atomic gas, cold neutral atomic gas,
CO-dark H2 gas (molecular gas not seen in CO emission),
and denser molecular gas in different kinematic components. We derive
the component structure (number of clouds and their column densities)
seen in absorption at visible wavelengths from Ca II, Ca I, K I, CH,
CH+, and CN and compare that to the emission from [C II],
H I, and CO and its isotopologues. Absorption lines from additional
atoms (including C I, O I, and Ni II) and molecules (CO) from UV
spectra obtained with the Hubble Space Telescope are used to expand the
kinematic correspondences. Preliminary results on physical conditions
(gas temperature and density) inferred from analyses of CN chemistry
and excitation of neutral and singly-ionized carbon, neutral oxygen,
and CO are also presented.
Title: Unveiling Vela: time variability of interstellar lines in
the direction of the Vela supernova remnant - II. Na D and Ca II
Authors: Kameswara Rao, N.; Lambert, David L.; Reddy, Arumalla B. S.;
Gupta, Ranjan; Muneer, S.; Singh, Harinder P.
Bibcode: 2017MNRAS.467.1186K
Altcode: 2017MNRAS.467.1186R; 2017arXiv170104349K; 2017MNRAS.tmp..142K
In a survey conducted between 2011 and 2012 of interstellar Na I D
line profiles in the direction of the Vela supernova remnant (SNR), a
few lines of sight showed dramatic changes in low-velocity absorption
components with respect to profiles from 1993 to 1994 reported by
Cha & Sembach. Three stars - HD 63578, HD 68217 and HD 76161 -
showed large decrease in strength over the 1993-2012 interval. HD
68217 and HD 76161 are associated with the Vela SNR whereas HD 63578 is
associated with γ2 Velorum wind bubble. Here, we present
high spectral resolution observations of Ca II K lines obtained with
the Southern African Large Telescope towards these three stars along
with simultaneous observations of Na I D lines. These new spectra
confirm that the Na D interstellar absorption weakened drastically
between 1993-1994 and 2011-2012 but show for the first time that the
Ca II K line is unchanged between 1993-1994 and 2015. This remarkable
contrast between the behaviour of Na D and Ca II K absorption lines
is a puzzle concerning gas presumably affected by the outflow from
the SNR and the wind from γ2 Velorum.
Title: VizieR Online Data Catalog: C and O abundances across the
Hertzsprung gap (Adamczak+, 2014)
Authors: Adamczak, J.; Lambert, D. L.
Bibcode: 2017yCat..17910058A
Altcode:
No abstract at ADS
Title: Parsec-scale Variations in the 7Li I/6Li
I Isotope Ratio Toward IC 348 and the Perseus OB 2 Association
Authors: Knauth, D. C.; Taylor, C. J.; Ritchey, A. M.; Federman,
S. R.; Lambert, D. L.
Bibcode: 2017ApJ...835L..16K
Altcode: 2017arXiv170400357K
Measurements of the lithium isotopic ratio in the diffuse interstellar
medium from high-resolution spectra of the Li I λ6708 resonance doublet
have now been reported for a number of lines of sight. The majority
of the results for the 7Li/6Li ratio are similar
to the solar system ratio of 12.2, but the line of sight toward o Per,
a star near the star-forming region IC 348, gave a ratio of about two,
the expected value for gas exposed to spallation and fusion reactions
driven by cosmic rays. To examine the association of IC 348 with cosmic
rays more closely, we measured the lithium isotopic ratio for lines
of sight to three stars within a few parsecs of o Per. One star, HD
281159, has 7Li/6Li ≃ 2 confirming production
by cosmic rays. The lithium isotopic ratio toward o Per and HD 281159
together with published analyses of the chemistry of interstellar
diatomic molecules suggest that the superbubble surrounding IC 348 is
the source of the cosmic rays. Based on observations obtained
with the Hobby-Eberly Telescope, which is a joint project of the
University of Texas at Austin, the Pennsylvania State University,
Ludwig-Maximilians-Universität München, and Georg-August-Universität
Göttingen.
Title: The evolution of the Milky Way: new insights from open clusters
Authors: Reddy, Arumalla B. S.; Lambert, David L.; Giridhar, Sunetra
Bibcode: 2016MNRAS.463.4366R
Altcode: 2016MNRAS.tmp.1394R; 2016arXiv160902619R
We have collected high-dispersion echelle spectra of red giant members
in the 12 open clusters (OCs) and derived stellar parameters and
chemical abundances for 26 species by either line equivalent widths or
synthetic spectrum analyses. We confirm the lack of an age-metallicity
relation for OCs but argue that such a lack of trend for OCs arise
from the limited coverage in metallicity compared to that of field
stars which span a wide range in metallicity and age. We confirm
that the radial metallicity gradient of OCs is steeper (flatter)
for Rgc < 12 kpc (>12 kpc). We demonstrate that the
sample of clusters constituting a steep radial metallicity gradient
of slope -0.052 ± 0.011 dex kpc-1 at Rgc <
12 kpc are younger than 1.5 Gyr and located close to the Galactic
mid-plane (| z| < 0.5 kpc) with kinematics typical of the thin
disc. Whereas the clusters describing a shallow slope of -0.015 ± 0.007
dex kpc-1 at Rgc > 12 kpc are relatively old,
thick disc members with a striking spread in age and height above the
mid-plane (0.5 < | z| < 2.5 kpc). Our investigation reveals that
the OCs and field stars yield consistent radial metallicity gradients if
the comparison is limited to samples drawn from the similar vertical
heights. We argue via the computation of Galactic orbits that all
the outer disc clusters were actually born inwards of 12 kpc but the
orbital eccentricity has taken them to present locations very far from
their birthplaces.
Title: Prospecting for Chemical Tags among Open Clusters
Authors: Lambert, David L.; Reddy, Arumalla B. S.
Bibcode: 2016ApJ...831..202L
Altcode: 2016arXiv160808594L
Determination of the chemical composition of red giants in a large
sample of open clusters (OCs) shows that the abundances of the heavy
elements La, Ce, Nd, and Sm, but not so obviously Y and Eu, vary
from one cluster to another across a sample in which all the clusters
have nearly solar metallicity. For La, Ce, Nd, and Sm the amplitudes
of the variations at solar metallicity scale approximately with the
main s-process contribution to solar system material. Consideration
of published abundances of field stars suggests that such a spread in
heavy-element abundances is present for the thin and thick disk stars
of different metallicities. This new result provides an opportunity
to chemically tag stars by their heavy elements and to reconstruct
dissolved OCs from the field-star population.
Title: HD 179821 (V1427 Aql, IRAS 19114+0002) - a massive post-red
supergiant star?
Authors: Şahin, T.; Lambert, David L.; Klochkova, Valentina G.;
Panchuk, Vladimir E.
Bibcode: 2016MNRAS.461.4071S
Altcode: 2016arXiv160700142S
We have derived elemental abundances of a remarkable star, HD
179821, with unusual composition (e.g. [Na/Fe] = 1.0 ± 0.2 dex) and
extra-ordinary spectral characteristics. Its metallicity at [Fe/H]
= 0.4 dex places it among the most metal-rich stars yet analysed. The
abundance analysis of this luminous star is based on high-resolution and
high-quality (S/N ≈ 120-420) optical echelle spectra from McDonald
Observatory and Special Astronomy Observatory. The data includes five
years of observations over 21 epochs. Standard 1D local thermodynamic
equilibrium analysis provides a fresh determination of the atmospheric
parameters over all epochs: <italic>Teff</italic>
= 7350 ± 200 K, log g= +0.6 ± 0.3, and a microturbulent velocity ξ
= 6.6 ± 1.6 km s-1 and [Fe/H] = 0.4 ± 0.2, and a carbon
abundance [C/Fe] = -0.19 ± 0.30. We find oxygen abundance [O/Fe]
= -0.25 ± 0.28 and an enhancement of 0.9 dex in N. A supersonic
macroturbulent velocity of 22.0 ± 2.0 km s-1 is determined
from both strong and weak Fe I and Fe II lines. Elemental abundances
are obtained for 22 elements. HD 179821 is not enriched in s-process
products. Eu is overabundant relative to the anticipated [X/Fe] ≈
0.0. Some peculiarities of its optical spectrum (e.g. variability in
the spectral line shapes) is noticed. This includes the line profile
variations for H α line. Based on its estimated luminosity, effective
temperature and surface gravity, HD 179821 is a massive star evolving
to become a red supergiant and finally a Type II supernova.
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: Follow-up observations of extremely metal-poor stars identified
from SDSS
Authors: Aguado, D. S.; Allende Prieto, C.; González Hernández,
J. I.; Carrera, R.; Rebolo, R.; Shetrone, M.; Lambert, D. L.;
Fernández-Alvar, E.
Bibcode: 2016A&A...593A..10A
Altcode: 2016arXiv160600604A
Context. The most metal-poor stars in the Milky Way witnessed the
early phases of formation of the Galaxy, and have chemical compositions
that are close to the pristine mixture from Big Bang nucleosynthesis,
polluted by one or few supernovae.
Aims: Only two dozen stars
with ([Fe/H] < -4) are known, and they show a wide range of abundance
patterns. It is therefore important to enlarge this sample. We present
the first results of an effort to identify new extremely metal-poor
stars in the Milky Way halo.
Methods: Our targets have been
selected from low-resolution spectra obtained as part of the Sloan
Digital Sky Survey, and followed-up with medium resolution spectroscopy
on the 4.2 m William Herschel Telescope and, in a few cases, at high
resolution on the 9.2 m Hobby-Eberly Telescope. Stellar parameters
and the abundances of magnesium, calcium, iron, and strontium have
been inferred from the spectra using classical model atmospheres. We
have also derived carbon abundances from the G band.
Results:
We find consistency between the metallicities estimated from SDSS
and those from new data at the level of 0.3 dex. The analysis of
medium resolution data obtained with ISIS on the WHT allows us to
refine the metallicities and in some cases measure other elemental
abundances. Our sample contains 11 new metal-poor stars with [Fe/H] <
-3.0, one of them with an estimated metallicity of [Fe/H] ~ -4.0. We
also discuss metallicity discrepancies of some stars in common with
previous works in the literature. Only one of these stars is found
to be C-enhanced at about [C/Fe] ~ + 1, whereas the other metal-poor
stars show C abundances at the level of [C/Fe] ~ + 0.45. Based
on observations obtained with the Hobby-Eberly Telescope, which is a
joint project of the University of Texas at Austin, the Pennsylvania
State University, Stanford University, Ludwig-Maximilians-Universität
München, and Georg-August-Universität Göttingen.The reduced spectra
as FITS files 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/593/A10
Title: Chemical compositions and kinematics of the Hercules stream
Authors: Ramya, P.; Reddy, Bacham E.; Lambert, David L.; Musthafa,
M. M.
Bibcode: 2016MNRAS.460.1356R
Altcode: 2016MNRAS.tmp..646R; 2016arXiv160404821R
An abundance analysis is reported of 58-K giants identified by Famaey
et al. (2005, A&A, 430, 165) as highly probable members of the
Hercules stream selected from stars north of the celestial equator in
the Hipparcos catalogue. The giants have compositions spanning the
interval [Fe/H] from -0.17 to +0.42 with a mean value of +0.15 and
relative elemental abundances [El/Fe] representative of the Galactic
thin disc. Selection effects may have biased the selection from the
Hipparcos catalogue against the selection of metal-poor stars. Our
reconsideration of the recent extensive survey by Bensby et al. of FG
dwarfs, including metal-poor stars, provides a [Fe/H] distribution for
the Hercules stream, which is similar to that from the 58 giants. It
appears that the stream is dominated by metal-rich stars from the
thin disc. We discuss suggestions in the literature that the stream
includes metal-poor stars from the thick disc.
Title: HD 16771: A lithium-rich giant in the red-clump stage
Authors: Reddy, Arumalla B. S.; Lambert, David L.
Bibcode: 2016A&A...589A..57R
Altcode: 2016arXiv160305309R
Aims: We report the discovery of a young lithium rich giant,
HD 16771, in the core-helium burning phase that does not seem to
fit existing proposals of Li synthesis near the luminosity function
bump or during He-core flash. We aim to understand the nature of
Li enrichment in the atmosphere of HD 16771 by exploring various Li
enhancement scenarios.
Methods: We have collected high-resolution
echelle spectra of HD 16771 and derived stellar parameters and chemical
abundances for 27 elements by either line equivalent widths or synthetic
spectrum analyses.
Results: HD 16771 is a Li-rich (log ɛ(Li)
= + 2.67 ± 0.10 dex) intermediate mass giant star (M = 2.4 ± 0.1
M⊙) with age ~ 0.76 ± 0.13 Gyr and located at the red
giant clump. Kinematics and chemical compositions are consistent with
HD 16771 being a member of the Galactic thin disk population. The
non-detection of 6Li (<3%), a low carbon isotopic ratio
(12C/13C = 12 ± 2), and the slow rotation (vsin
I = 2.8 km s-1) all suggest that lithium might have been
synthesized in this star. On the contrary, HD 16771 with a mass of
2.4 M⊙ has no chance of encountering luminosity function
bump and He-core flash where the possibility of fast deep-mixing
for Li enrichment in K giants has been suggested previously.
Conclusions: Based of the evolutionary status of this star, we discuss
the possibility that 7Li synthesis in HD 16771 is triggered
by the engulfment of close-in planet(s) during the RGB phase.
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: Unveiling Vela - time variability of Na I D lines in the
direction of the Vela supernova remnant
Authors: Rao, N. Kameswara; Muneer, S.; Lambert, David L.; Varghese,
B. A.
Bibcode: 2016MNRAS.455.2529R
Altcode: 2015arXiv151006494K
High-resolution spectral profiles of Na I D lines from the interstellar
medium towards 64 stars in the direction of the Vela supernova
remnant are presented. This survey conducted mostly between 2011
and 12 complements an earlier survey of the same stars by Cha &
Sembach done in the 1993-96 period. The interval of 15-18 yr provides a
base line to search for changes in the interstellar profiles. Dramatic
disappearance of strong absorption components at low radial velocity is
seen towards three stars - HD 63578, HD 68217, HD 76161 - over 15-18 yr;
HD 68217 and HD 76161 are associated with the Vela SNR but HD 63578 is
likely associated with the wind bubble of γ2 Velorum. The
vanishing of these cold neutral clouds in the short time of 15-18 yr
needs some explanation. Other changes are seen in high-velocity Na
D components.
Title: Local associations and the barium puzzle
Authors: Reddy, Arumalla B. S.; Lambert, David L.
Bibcode: 2015MNRAS.454.1976R
Altcode: 2015arXiv150802815R
We have observed high-dispersion echelle spectra of main-sequence stars
in five nearby young associations - Argus, Carina-Near, Hercules-Lyra,
Orion and Subgroup B4 - and derived abundances for elements ranging
from Na to Eu. These are the first chemical abundance measurements for
two of the five associations, while the remaining three associations
are analysed more extensively in our study. Our results support the
presence of chemical homogeneity among association members with a
typical star-to-star abundance scatter of about 0.06 dex or less over
many elements. The five associations show log ɛ(Li) consistent with
their age and share a solar chemical composition for all elements with
the exception of Ba. We find that all the heavy elements (Y, Zr, La,
Ce, Nd, Sm and Eu) exhibit solar ratios, i.e. [X/Fe] ≃ 0, while Ba
is overabundant by about 0.2-0.3 dex. The origin of the overabundance
of Ba is a puzzle. Within the formulation of the s-process, it is
difficult to create a higher Ba abundance without a similar increase in
the s-process contributions to other heavy elements (La-Sm). Given that
Ba is represented by strong lines of Ba II and La-Sm are represented by
rather weak ionized lines, the suggestion, as previously made by other
studies, is that the Ba abundance may be systematically overestimated
by standard methods of abundance analysis perhaps because the upper
reaches of the stellar atmospheres are poorly represented by standard
model atmospheres. A novel attempt to analyse the Ba I line at 5535
Å gives a solar Ba abundance for stars with effective temperatures
hotter than about 5800 K but increasingly subsolar Ba abundances for
cooler stars with apparent Ba deficiencies of 0.5 dex at 5100 K. This
trend with temperature may signal a serious non-local thermodynamical
equilibrium effect on the Ba I line.
Title: Early-type stars observed in the ESO UVES Paranal Observatory
Project - V. Time-variable interstellar absorption
Authors: McEvoy, Catherine M.; Smoker, Jonathan V.; Dufton, Philip L.;
Smith, Keith T.; Kennedy, Michael B.; Keenan, Francis P.; Lambert,
David L.; Welty, Daniel E.; Lauroesch, James T.
Bibcode: 2015MNRAS.451.1396M
Altcode: 2015arXiv150601348M
The structure and properties of the diffuse interstellar medium (ISM)
on small scales, sub-au to 1 pc, are poorly understood. We compare
interstellar absorption lines, observed towards a selection of O-
and B-type stars at two or more epochs, to search for variations over
time caused by the transverse motion of each star combined with changes
in the structure in the foreground ISM. Two sets of data were used: 83
VLT/UVES spectra with approximately 6 yr between epochs and 21 McDonald
observatory 2.7-m telescope echelle spectra with 6-20 yr between
epochs, over a range of scales from ∼0-360 au. The interstellar
absorption lines observed at the two epochs were subtracted and searched
for any residuals due to changes in the foreground ISM. Of the 104
sightlines investigated with typically five or more components in Na
I D, possible temporal variation was identified in five UVES spectra
(six components), in Ca II, Ca I and/or Na I absorption lines. The
variations detected range from 7 per cent to a factor of 3.6 in column
density. No variation was found in any other interstellar species. Most
sightlines show no variation, with 3σ upper limits to changes of the
order 0.1-0.3 dex in Ca II and Na I. These variations observed imply
that fine-scale structure is present in the ISM, but at the resolution
available in this study, is not very common at visible wavelengths. A
determination of the electron densities and lower limits to the total
number density of a sample of the sightlines implies that there is
no striking difference between these parameters in sightlines with,
and sightlines without, varying components.
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: Comprehensive abundance analysis of red giants in the open
clusters NGC 1342, 1662, 1912, 2354 and 2447
Authors: Reddy, Arumalla B. S.; Giridhar, Sunetra; Lambert, David L.
Bibcode: 2015MNRAS.450.4301R
Altcode: 2015arXiv150405508R
We have observed high-dispersion echelle spectra of red giant
members in the five open clusters (OCs) NGC 1342, NGC 1662, NGC
1912, NGC 2354 and NGC 2447 and determined their radial velocities
and chemical compositions. These are the first chemical abundance
measurements for all but NGC 2447. We combined our clusters from
this and previous papers with a sample drawn from the literature for
which we remeasured the chemical abundances to establish a common
abundance scale. With this homogeneous sample of OCs, we study the
relative elemental abundances of stars in OCs in comparison with field
stars as a function of age and metallicity. We find a range of mild
enrichment of heavy (Ba-Eu) elements in young OC giants over field
stars of the same metallicity. Our analysis supports that the youngest
stellar generations in cluster might be underrepresented by the solar
neighbourhood field stars.
Title: The C14N/C15N Ratio in Diffuse Molecular
Clouds
Authors: Ritchey, A. M.; Federman, S. R.; Lambert, D. L.
Bibcode: 2015ApJ...804L...3R
Altcode: 2015arXiv150308221R
We report the first detection of C15N in diffuse
molecular gas from a detailed examination of CN absorption lines in
archival spectra, obtained with the Ultraviolet and Visual Echelle
Spectrograph of the Very Large Telescope of stars probing local diffuse
clouds. Absorption from the C15N isotopologue is confidently
detected (at ≳ 4σ ) in three out of the four directions studied and
appears as a very weak feature between the main 12CN and
13CN absorption components. Column densities for each CN
isotopologue are determined through profile fitting, after accounting
for weak additional line-of-sight components of 12CN,
which are seen in the absorption profiles of CH and CH+ as
well. The weighted mean value of C14N/C15N for the
three sight lines with detections of C15N is 274 ± 18. Since
the diffuse molecular clouds toward our target stars have relatively
high gas kinetic temperatures and relatively low visual extinctions,
their C14N/C15N ratios should not be affected
by chemical fractionation. The mean C14N/C15N
ratio that we obtain should therefore be representative of the
ambient 14N/15N ratio in the local interstellar
medium. Indeed, our mean value agrees well with that derived from
millimeter-wave observations of CN, HCN, and HNC in local molecular
clouds. Based on observations made with the Very Large Telescope
of the European Southern Observatory, Paranal, Chile, under programs
065.I-0526, 071.C-0367, 071.C-0513, 076.C-0431, and 092.C-0019.
Title: Mid-infrared variations of R Coronae Borealis stars
Authors: Rao, N. Kameswara; Lambert, David L.
Bibcode: 2015MNRAS.447.3664R
Altcode: 2014arXiv1412.7623K
Mid-infrared (IR) photometry of R Coronae Borealis stars obtained
from various satellites from Infrared Astronomical Satellite (IRAS)
to Wide-field Infrared Survey Explorer (WISE) has been utilized in
studying the variations of the circumstellar dust's contributions
to the spectral energy distribution of these stars. The variation
of the fractional coverage (R) of dust clouds and their blackbody
temperatures (Td) have been used in trying to understand the
dust cloud evolution over the three decades spanned by the satellite
observations. In particular, it is shown that a prediction R ∝ T_d^4
developed in the paper is satisfied, especially by those stars for
which a single collection of clouds dominates the IR fluxes.
Title: Carbon abundance and the N/C ratio in atmospheres of A-, F-
and G-type supergiants and bright giants
Authors: Lyubimkov, Leonid S.; Lambert, David L.; Korotin, Sergey A.;
Rachkovskaya, Tamara M.; Poklad, Dmitry B.
Bibcode: 2015MNRAS.446.3447L
Altcode: 2014arXiv1411.2722L
Based on our prior accurate determination of fundamental parameters
for 36 Galactic A-, F- and G-type supergiants and bright giants
(luminosity classes I and II), we undertook a non-LTE analysis of
the carbon abundance in their atmospheres. It is shown that the
non-LTE corrections to the C abundances derived from C I lines are
negative and increase with the effective temperature Teff;
the corrections are especially significant for the infrared C I lines
with wavelengths 9060-9660 Å. The carbon underabundance as a general
property of the stars in question is confirmed; a majority of the stars
studied has the carbon deficiency [C/Fe] between -0.1 and -0.5 dex,
with a minimum at -0.7 dex. When comparing the derived C deficiency
with the N excess found by us for the same stars earlier, we obtain
a pronounced N versus C anticorrelation, which could be expected from
predictions of the theory. We found that the ratio [N/C] spans mostly
the range from 0.3 to 1.7 dex. Both these enhanced [N/C] values and the
C and N anomalies themselves are an obvious evidence of the presence
on a star's surface of mixed material from stellar interiors; so, a
majority of programme stars passed through the deep mixing during the
main sequence (MS) and/or the first dredge-up (FD) phase. Comparison
with theoretical predictions including rotationally induced mixing shows
that the stars are either post-MS objects with the initial rotational
velocities V0 = 200-300 km s-1 or post-FD objects
with V0 = 0-300 km s-1. The observed N versus C
anticorrelation reflects a dependence of the C and N anomalies on the
V0 value: on average the higher V0 the greater
the anomalies. It is shown that an absence of detectable lithium in
the atmospheres of the stars, which is accompanied with the observed
N excess and C deficiency, is quite explainable.
Title: On the Binary Helium Star DY Centauri: Chemical Composition
and Evolutionary State
Authors: Pandey, Gajendra; Kameswara Rao, N.; Jeffery, C. Simon;
Lambert, David L.
Bibcode: 2014ApJ...793...76P
Altcode: 2014arXiv1408.3798P
DY Cen has shown a steady fading of its visual light by about one
magnitude in the last 40 yr, suggesting a secular increase in its
effective temperature. We have conducted non-local thermodynamic
equilibrium (LTE) and LTE abundance analyses to determine the star's
effective temperature, surface gravity, and chemical composition
using high-resolution spectra obtained over two decades. The derived
stellar parameters for three epochs suggest that DY Cen has evolved
at a constant luminosity and has become hotter by about 5000 K in
23 yr. We show that the derived abundances remain unchanged for the
three epochs. The derived abundances of the key elements, including F
and Ne, are as observed for the extreme helium stars resulting from
a merger of a He white dwarf with a C-O white dwarf. Thus DY Cen by
chemical composition appears to also be a product of a merger of two
white dwarfs. This appearance seems to be at odds with the recent
suggestion that DY Cen is a single-lined spectroscopic binary.
Title: High-Resolution Optical Spectroscopy of the R Coronae Borealis
Star V532 Ophiuchi at Maximum Light
Authors: Kameswara Rao, N.; Lambert, David L.; Woolf, Vincent M.;
Hema, B. P.
Bibcode: 2014PASP..126..813K
Altcode: 2014arXiv1407.3696K; 2014PASP..126..813R
Not Available Based on observations obtained with the Harlan
J. Smith Telescope of McDonald Observatory of the University of Texas
at Austin.
Title: Searching for Dust around Hyper Metal Poor Stars
Authors: Venn, Kim A.; Puzia, Thomas H.; Divell, Mike; Côté,
Stephanie; Lambert, David L.; Starkenburg, Else
Bibcode: 2014ApJ...791...98V
Altcode: 2014arXiv1407.1449V
We examine the mid-infrared fluxes and spectral energy distributions
for stars with iron abundances [Fe/H] <-5, and other metal-poor
stars, to eliminate the possibility that their low metallicities are
related to the depletion of elements onto dust grains in the formation
of a debris disk. Six out of seven stars examined here show no mid-IR
excesses. These non-detections rule out many types of circumstellar
disks, e.g., a warm debris disk (T <= 290 K), or debris disks with
inner radii <=1 AU, such as those associated with the chemically
peculiar post-asymptotic giant branch spectroscopic binaries and RV Tau
variables. However, we cannot rule out cooler debris disks, nor those
with lower flux ratios to their host stars due to, e.g., a smaller
disk mass, a larger inner disk radius, an absence of small grains,
or even a multicomponent structure, as often found with the chemically
peculiar Lambda Bootis stars. The only exception is HE0107-5240, for
which a small mid-IR excess near 10 μm is detected at the 2σ level;
if the excess is real and associated with this star, it may indicate
the presence of (recent) dust-gas winnowing or a binary system.
Title: Carbon and Oxygen Abundances across the Hertzsprung Gap
Authors: Adamczak, Jens; Lambert, David L.
Bibcode: 2014ApJ...791...58A
Altcode: 2014arXiv1407.2157A
We derived atmospheric parameters and spectroscopic abundances for C
and O for a large sample of stars located in the Hertzsprung gap in the
Hertzsprung-Russell diagram in order to detect chemical peculiarities
and get a comprehensive overview of the population of stars in this
evolutionary state. We have observed and analyzed high-resolution
spectra (R = 60,000) of 188 stars in the mass range 2-5 M ⊙
with the 2.7 m Harlan J. Smith Telescope at the McDonald Observatory
including 28 stars previously identified as Am/Ap stars. We find that
the C and O abundances of the majority of stars in the Hertzsprung gap
are in accordance with abundances derived for local lower-mass dwarfs
but detect expected peculiarities for the Am/Ap stars. The C and O
abundances of stars with T eff < 6500 K are slightly
lower than for the hotter objects but the C/O ratio is constant in the
analyzed temperature domain. No indication of an alteration of the C
and O abundances of the stars by mixing during the evolution across
the Hertzsprung gap could be found before the homogenization of their
atmospheres by the first dredge-up.
Title: VizieR Online Data Catalog: Abundances of red giants in open
clusters (Reddy+, 2013)
Authors: Reddy, A. B. S.; Giridhar, S.; Lambert, D. L.
Bibcode: 2014yCat..74313338R
Altcode:
High-resolution optical spectra of the program stars were obtained
during the nights of 2011 January 12-14 and March 15-18 with the
Robert G. Tull echelle coude spectrograph on the 2.7-m Harlan J. Smith
telescope at the McDonald observatory using a 2048x2048 pixel Tektronix
charge-coupled device as a detector. (2 data files).
Title: Elemental Abundances of Solar Sibling Candidates
Authors: Ramírez, I.; Bajkova, A. T.; Bobylev, V. V.; Roederer,
I. U.; Lambert, D. L.; Endl, M.; Cochran, W. D.; MacQueen, P. J.;
Wittenmyer, R. A.
Bibcode: 2014ApJ...787..154R
Altcode: 2014arXiv1405.1723R
Dynamical information along with survey data on metallicity and in
some cases age have been used recently by some authors to search
for candidates of stars that were born in the cluster where the Sun
formed. We have acquired high-resolution, high signal-to-noise ratio
spectra for 30 of these objects to determine, using detailed elemental
abundance analysis, if they could be true solar siblings. Only two of
the candidates are found to have solar chemical composition. Updated
modeling of the stars' past orbits in a realistic Galactic potential
reveals that one of them, HD 162826, satisfies both chemical and
dynamical conditions for being a sibling of the Sun. Measurements
of rare-element abundances for this star further confirm its solar
composition, with the only possible exception of Sm. Analysis of
long-term high-precision radial velocity data rules out the presence of
hot Jupiters and confirms that this star is not in a binary system. We
find that chemical tagging does not necessarily benefit from studying
as many elements as possible but instead from identifying and carefully
measuring the abundances of those elements that show large star-to-star
scatter at a given metallicity. Future searches employing data products
from ongoing massive astrometric and spectroscopic surveys can be
optimized by acknowledging this fact.
Title: C15N in Diffuse Molecular Clouds
Authors: Federman, Steven Robert; Ritchey, Adam M.; Lambert, David L.
Bibcode: 2014AAS...22422004F
Altcode:
We report the first detection of C15N in absorption
in diffuse molecular gas from a detailed examination of archival
VLT/UVES data covering the CN lines near 3875 Å. Absorption from the
C15N isotopologue is detected in three out of the four
directions studied and appears as a very weak feature between the
main 12CN and 13CN absorption lines. Column
densities for each CN isotopologue are determined through profile
fitting, after accounting for weak additional line-of-sight components,
which are observed in CH and CH+. The weighted mean value
of C14N/C15N for the three sight lines with
detections of C15N is 277±16, in very good agreement with
the terrestrial 14N/15N ratio of 272. Our results
help to clarify the situation regarding the nitrogen isotope ratio in
the solar neighborhood, with important implications for interstellar
chemistry and Galactic chemical evolution.
Title: Dust Around R Coronae Borealis Stars. II. Infrared Emission
Features in an H-poor Environment
Authors: García-Hernández, D. A.; Rao, N. Kameswara; Lambert, D. L.
Bibcode: 2013ApJ...773..107G
Altcode: 2013arXiv1307.0294G
Residual Spitzer/Infrared Spectrograph spectra for a sample of 31 R
Coronae Borealis (RCB) stars are presented and discussed in terms of
narrow emission features superimposed on the quasi-blackbody continuous
infrared emission. A broad ~6-10 μm dust emission complex is seen in
the RCBs showing an extreme H-deficiency. A secondary and much weaker
~11.5-15 μm broad emission feature is detected in a few RCBs with the
strongest ~6-10 μm dust complex. The Spitzer infrared spectra reveal
for the first time the structure within the ~6-10 μm dust complex,
showing the presence of strong C-C stretching modes at ~6.3 and 8.1
μm as well as of other dust features at ~5.9, 6.9, and 7.3 μm, which
are attributable to amorphous carbonaceous solids with little or no
hydrogen. The few RCBs with only moderate H-deficiencies display the
classical "unidentified infrared bands (UIRs)" and mid-infrared features
from fullerene-related molecules. In general, the characteristics of
the RCB infrared emission features are not correlated with the stellar
and circumstellar properties, suggesting that the RCB dust features
may not be dependent on the present physical conditions around RCB
stars. The only exception seems to be the central wavelength of the 6.3
μm feature, which is blueshifted in those RCBs showing also the UIRs,
i.e., the RCBs with the smallest H deficiency.
Title: Hot bottom burning and s-process nucleosynthesis in massive
AGB stars at the beginning of the thermally-pulsing phase
Authors: García-Hernández, D. A.; Zamora, O.; Yagüe, A.;
Uttenthaler, S.; Karakas, A. I.; Lugaro, M.; Ventura, P.; Lambert,
D. L.
Bibcode: 2013A&A...555L...3G
Altcode: 2013arXiv1306.2134G
We report the first spectroscopic identification of massive Galactic
asymptotic giant branch (AGB) stars at the beginning of the thermal
pulse (TP) phase. These stars are the most Li-rich massive AGBs
found to date, super Li-rich AGBs with log ɛ (Li) ~ 3-4. The high
Li overabundances are accompanied by weak or no s-process element
(i.e. Rb and Zr) enhancements. A comparison of our observations
with the most recent hot bottom burning (HBB) and s-process
nucleosynthesis models confirms that HBB is strongly activated
during the first TPs but the 22Ne neutron source needs
many more TP and third dredge-up episodes to produce enough Rb at
the stellar surface. We also show that the short-lived element Tc,
usually used as an indicator of AGB genuineness, is not detected in
massive AGBs, which is in agreement with the theoretical predictions
when the 22Ne neutron source dominates the s-process
nucleosynthesis. Appendix A is available in electronic form at
http://www.aanda.org
Title: Comprehensive abundance analysis of red giants in the open
clusters NGC 2527, 2682, 2482, 2539, 2335, 2251 and 2266
Authors: Reddy, Arumalla B. S.; Giridhar, Sunetra; Lambert, David L.
Bibcode: 2013MNRAS.431.3338R
Altcode: 2013arXiv1303.1104R
We have analysed high-resolution echelle spectra of red giant members
for seven open clusters in the Galactic anticentre direction to explore
their chemical compositions. Cluster membership has been confirmed
by radial velocity. The spread in temperatures and gravities being
very small among the red giants, nearly the same stellar lines were
employed for all stars thereby reducing the abundance errors: the
errors of the average abundance for a cluster were generally in the
0.02-0.05 dex range. Our present sample covers Galactocentric distances
of 8.3-11.3 kpc and an age range of 0.2-4.3 Gyr. A careful comparison
of our results for the cluster NGC 2682 (M67) to other high-resolution
abundance studies in the literature shows general good agreement for
almost all elements in common.
Title: The changing nebula around the hot R Coronae Borealis star
DY Centauri
Authors: Rao, N. Kameswara; Lambert, David L.; García-Hernández,
D. A.; Manchado, Arturo
Bibcode: 2013MNRAS.431..159R
Altcode: 2013arXiv1301.5773K; 2013MNRAS.431..159K; 2013MNRAS.tmp..884K;
2013MNRAS.tmp..884R
Among the distinguishing characteristics of the remarkable hot R
Coronae Borealis star DY Centauri, which was recently found to be a
spectroscopic binary, is the presence of nebular forbidden lines in its
optical spectrum. A compilation of photometry from 1970 to the present
suggests that the star has evolved to higher effective temperatures. A
comparison of spectra from 2010 with earlier spectra has shown that
between 2003 and 2010, the 6717 and 6730 Å emission lines of [S II]
underwent a dramatic change in their fluxes. This suggests that there
was an increase in the nebula's electron density from 290 to 3140
cm-3 between 1989 and 2010, while the stellar temperature
increased from 19 500 to 25 000 K. The nebular radius is about 0.02
pc, which is 60 000 times larger than the semimajor axis of the DY Cen
binary system. The rapid changes of stellar temperature and the nebula's
response to these changes demonstrate stellar evolution in action.
Title: Erratum: Chemical compositions of stars in two stellar streams
from the Galactic thick disc
Authors: Ramya, P.; Reddy, Bacham E.; Lambert, David L.
Bibcode: 2013MNRAS.430.2510R
Altcode: 2013MNRAS.tmp..705R
No abstract at ADS
Title: Atmospheric Composition of Weak G Band Stars: CNO and Li
Abundances
Authors: Adamczak, Jens; Lambert, David L.
Bibcode: 2013ApJ...765..155A
Altcode: 2013arXiv1301.5571A
We determined the chemical composition of a large sample of weak
G band stars—a rare class of G and K giants of intermediate mass
with unusual abundances of C, N, and Li. We have observed 24 weak G
band stars with the 2.7 m Harlan J. Smith Telescope at the McDonald
Observatory and derived spectroscopic abundances for C, N, O, and
Li, as well as for selected elements from Na-Eu. The results show
that the atmospheres of weak G band stars are highly contaminated
with CN-cycle products. The C underabundance is about a factor of 20
larger than for normal giants and the 12C/13C
ratio approaches the CN-cycle equilibrium value. In addition to the
striking CN-cycle signature the strong N overabundance may indicate the
presence of partially ON-cycled material in the atmospheres of the weak
G band stars. The exact mechanism responsible for the transport of the
elements to the surface has yet to be identified but could be induced
by rapid rotation of the main sequence progenitors of the stars. The
unusually high Li abundances in some of the stars are an indicator
for Li production by the Cameron-Fowler mechanism. A quantitative
prediction of a weak G band star's Li abundance is complicated by the
strong temperature sensitivity of the mechanism and its participants. In
addition to the unusual abundances of CN-cycle elements and Li, we
find an overabundance of Na that is in accordance with the NeNa chain
running in parallel with the CN cycle. Apart from these peculiarities,
the element abundances in a weak G band star's atmosphere are consistent
with those of normal giants.
Title: Spectroscopic followup of three bright halo stars selected
from SDSS and GALEX photometry
Authors: Sahin, Timur; Lambert, David L.; Allende Prieto, Carlos
Bibcode: 2013arXiv1303.4853S
Altcode:
We aim to reveal the nature of the Sloan Digital Sky Survey
(SDSS) stars: SDSSJ100921.40+375233.9, SDSSJ015717.04+135535.9, and
SDSSJ171422.43+283657.2, showing apparently high NUV excesses for their
g-z colors, as expected for extremely low-metallicity stars. High
resolution (R=60 000) spectra of the stars with a wide wavelength
coverage were obtained to determine their chemical compositions with
the Tull echelle spectrograph on the 2.7 m telescope at the McDonald
Observatory. We derived the spectroscopic parameters Teff =5820+-125 K,
log g =3.9+-0.2, and vt =1.1+-0.5 km/s for SDSSJ100921.40+375233.9,
Teff=6250+-125 K, log g =3.7+-0.2, and vt =4.0+-0.5 km/s for
SDSSJ015717.04+135535.9, and Teff=6320+-125 K, log g =4.1+-0.3,
and vt =1.5+-0.5 km/s for SDSS J171422.43+283657.2, and elemental
abundances were computed for 21 elements for J100921 and J171422 and
for 19 elements for J015717 for the first time. We find metallicities
of [Fe/H]= -1.30, -0.94, and -0.80 for SDSSJ100921.40+375233.9,
J015717.04+135535.9, and J171422.43+283657.2, respectively. On the
basis of calculated abundance ratios for J171422.43+283657.2 and
J015717.04+135535.9, we also report that these two program stars
have the expected composition of main-sequence halo turnoff stars,
but with low-alpha abundances, i.e., the [alpha/Fe] ratio is ~0.0 for
J171422.43+283657.2 and ~0.1 for J015717.04+135535.9. The latter one
shows typical halo or thick-disk alpha-element abundances, but has a
substantial rotational line broadening and vsini=40 +- 0.5 km/s.
Title: Carbon, nitrogen and oxygen abundances in atmospheres of the
5-11 M⊙ B-type main-sequence stars
Authors: Lyubimkov, Leonid S.; Lambert, David L.; Poklad, Dmitry B.;
Rachkovskaya, Tamara M.; Rostopchin, Sergey I.
Bibcode: 2013MNRAS.428.3497L
Altcode: 2012arXiv1212.0987L; 2012MNRAS.tmp..222L
Fundamental parameters and the carbon, nitrogen and oxygen abundances
are determined for 22 B-type stars with distances d ≤ 600 pc and slow
rotation (v sin i ≤ 66 km s-1). The stars are selected
according to their effective temperatures Teff and surface
gravities log g, namely: Teff is between 15 300 and 24
100 K and log g is mostly greater than 3.75; therefore, stars with
medium masses of 5-11 M⊙ are selected. Theory predicts
for the stars with such parameters that the C, N and O abundances in
their atmospheres should correspond to their initial values. Non-local
thermodynamic equilibrium (non-LTE) analysis of C ii, N ii and O ii
lines is implemented. The following mean C, N and O abundances are
obtained: log ɛ(C) = 8.31 ± 0.13, log ɛ(N) = 7.80 ± 0.12 and log
ɛ(O) = 8.73 ± 0.13. These values are in very good agreement with
recent data on the C, N and O abundances for nearby B stars from other
authors; it is important that different techniques are applied by us
and other authors. When excluding for the stars HR 1810 and HR 2938,
which can be mixed, we obtain the following mean abundances for the
remaining 20 stars: log ɛ(C) = 8.33 ± 0.11, log ɛ(N) = 7.78 ± 0.09
and log ɛ(O) = 8.72 ± 0.12; these values are in excellent agreement
with a present-day cosmic abundance standard (CAS) of Nieva &
Przybilla. The derived mean N and O abundances in unevolved B stars
are very close to the solar photospheric abundances, as well as to the
protosolar ones. However, the mean C abundance is somewhat lower than
the solar one; this small but stable carbon deficiency is confirmed
by other authors. One may suggest two possibilities to explain the
observed C deficiency. First, current non-LTE computations of C ii
lines are still partially inadequate. In this case the C deficiency
is invalid, so one may conclude that the Sun and the local unevolved B
stars have the same metallicity. This would mean that during the Sun's
life (i.e. for the past 4.5 × 109 yr) the metallicity of
the solar neighbourhood has not markedly changed; so, an intensive
enrichment of the solar neighbourhood by metals occurred before
the Sun's birth. Secondly, the C deficiency in the local B stars is
valid; it is supposed that the Sun can migrate during its life from
inner parts of the Galactic disc where it has born, so its observed
chemical composition can differ from the composition of young stars
in its present neighbourhood.
Title: Oxygen Abundances in Nearby FGK Stars and the Galactic Chemical
Evolution of the Local Disk and Halo
Authors: Ramírez, I.; Allende Prieto, C.; Lambert, D. L.
Bibcode: 2013ApJ...764...78R
Altcode: 2013arXiv1301.1582R
Atmospheric parameters and oxygen abundances of 825 nearby FGK
stars are derived using high-quality spectra and a non-local
thermodynamic equilibrium analysis of the 777 nm O I triplet
lines. We assign a kinematic probability for the stars to be
thin-disk (P 1), thick-disk (P 2), and halo
(P 3) members. We confirm previous findings of enhanced
[O/Fe] in thick-disk (P 2 > 0.5) relative to thin-disk
(P 1 > 0.5) stars with [Fe/H] <~ -0.2, as well as a
"knee" that connects the mean [O/Fe]-[Fe/H] trend of thick-disk stars
with that of thin-disk members at [Fe/H] >~ -0.2. Nevertheless,
we find that the kinematic membership criterion fails at separating
perfectly the stars in the [O/Fe]-[Fe/H] plane, even when a very
restrictive kinematic separation is employed. Stars with "intermediate"
kinematics (P 1 < 0.7, P 2 < 0.7) do not
all populate the region of the [O/Fe]-[Fe/H] plane intermediate between
the mean thin-disk and thick-disk trends, but their distribution is
not necessarily bimodal. Halo stars (P 3 > 0.5) show
a large star-to-star scatter in [O/Fe]-[Fe/H], but most of it is
due to stars with Galactocentric rotational velocity V < -200 km
s-1 halo stars with V > -200 km s-1 follow
an [O/Fe]-[Fe/H] relation with almost no star-to-star scatter. Early
mergers with satellite galaxies explain most of our observations, but
the significant fraction of disk stars with "ambiguous" kinematics
and abundances suggests that scattering by molecular clouds and
radial migration have both played an important role in determining
the kinematic and chemical properties of solar neighborhood stars.
Title: Abundance analysis of an extended sample of open clusters:
A search for chemical inhomogeneities
Authors: Reddy, Arumalla B. S.; Giridhar, Sunetra; Lambert, David L.
Bibcode: 2013ASInC...9...77A
Altcode:
We have initiated a program to explore the presence of chemical
inhomogeneities in the Galactic disk using the open clusters as ideal
probes. We have analyzed high-dispersion echelle spectra (R ≥ 55,000)
of red giant members for eleven open clusters to derive abundances
for many elements. The membership to the cluster has been confirmed
through their radial velocities and proper motions. The spread in
temperatures and gravities being very small among the red giants,
nearly the same stellar lines were employed thereby reducing the random
errors. The errors of average abundance for the cluster were generally
in 0.02 to 0.07 dex range. Our present sample covers galactocentric
distances of 8.3 to 11.3 kpc and an age range of 0.2 to 4.3 Gyrs. Our
earlier analysis of four open clusters (Reddy A.B.S. et al., 2012,
MNRAS, 419,1350) indicate that abundances relative to Fe for elements
from Na to Eu are equal within measurement uncertainties to published
abundances for thin disk giants in the field. This supports the view
that field stars come from disrupted open clusters. In the enlarged
sample of eleven open clusters we find cluster to cluster abundance
variations for some s- and r- process elements, with certain elements
such as Zr and Ba showing large variation. These differences mark the
signatures that these clusters had formed under different environmental
conditions (Type II SN, Type Ia SN, AGB stars or a mixture of any of
these) unique to the time and site of formation. These eleven clusters
support the widely held impression that there is an abundance gradient
such that the metallicity [Fe/H] at the solar galactocentric distance
decreases outwards at about -0.1 dex per kpc.
Title: The Hot R Coronae Borealis Star DY Centauri is a Binary
Authors: Rao, N. Kameswara; Lambert, David L.; García-Hernández,
D. A.; Jeffery, C. Simon; Woolf, Vincent M.; McArthur, Barbara
Bibcode: 2012ApJ...760L...3R
Altcode: 2012ApJ...760L...3K; 2012arXiv1210.4199K
The remarkable hot R Coronae Borealis (RCB) star DY Cen is revealed
to be the first and only binary system to be found among the RCB stars
and their likely relatives, including the extreme helium stars and the
hydrogen-deficient carbon stars. Radial velocity determinations from
1982 to 2010 have shown that DY Cen is a single-lined spectroscopic
binary in an eccentric orbit with a period of 39.67 days. It is also
one of the hottest and most H-rich member of the class of RCB stars. The
system may have evolved from a common envelope to its current form.
Title: The Galactic R Coronae Borealis Stars and the Final He-shell
Flash Object V4334 Sgr (Sakurai's Object): A Comparison
Authors: Hema, B. P.; Pandey, Gajendra; Lambert, David L.
Bibcode: 2012arXiv1211.6219H
Altcode:
The high resolution optical spectra of H-deficient stars, R Coronae
Borealis stars and H-deficient carbon stars are analyzed by synthesizing
the C2 Swan bands (0,1), (0,0), and (1,0) using our detailed line-list
and Uppsala model atmosphere, to determine the C-abundances and the
12C/13C ratios which are potential clues to the formation process of
these stars. The C-abundances derived from C2 bands are about the same
for the adopted models constructed with different carbon abundances over
the range 8.5 (C/He = 0.1%) to 10.5 (C/He = 10%). The carbon abundances
derived from C I lines are a factor of four lower than that adopted for
the model atmosphere over the same C/He interval, as reported by Asplund
et al.: 'the carbon problem'. In principle, the carbon abundances
obtained from C2 Swan bands and that adopted for the model atmosphere
can be equated for a particular choice of C/He that varies from star
to star (unlike C I lines). Then, the carbon problem for C2 bands is
eliminated. However, such C/He ratios are in general less than those
of the extreme helium stars, the seemingly natural relatives to the RCB
and HdC stars. The derived carbon abundances and the 12C/13C ratios are
discussed in light of the double degenerate (DD) and the final flash
(FF) scenarios. The carbon abundance and the 12C/13C ratios for the
FF product, Sakurai's Object is derived. The carbon abundance in the
Sakurai's object is 10 times higher than in the RCB star VZ Sgr. On
an average, the carbon abundance in the Sakurai's Object is about 10
to 100 times higher than in RCB stars. The 12C/13C ratio in Sakurai's
Object is 3.4, the equilibrium value, as expected for FF products.
Title: High-resolution Optical Spectroscopy of DY Cen: Diffuse
Interstellar Bands in a Proto-fullerene Circumstellar Environment?
Authors: García-Hernández, D. A.; Kameswara Rao, N.; Lambert,
David L.
Bibcode: 2012ApJ...759L..21G
Altcode: 2012arXiv1210.1165G
We search high-resolution and high-quality VLT/UVES optical spectra
of the hot R Coronae Borealis star DY Cen for electronic transitions
of the C60 molecule and diffuse interstellar bands
(DIBs). We report the non-detection of the strongest C60
electronic transitions (e.g., those at ~3760, 3980, and 4024
Å). The absence of C60 absorption bands may support
recent laboratory results, which show that the ~7.0, 8.5, 17.4, and
18.8 μm emission features seen in DY Cen—and other similar objects
with polycyclic-aromatic-hydrocarbon-like dominated IR spectra—are
attributable to proto-fullerenes or fullerene precursors rather than to
C60. DIBs toward DY Cen are normal for its reddening; the
only exception is the DIB at 6284 Å (possibly also the 7223 Å DIB)
which is found to be unusually strong. We also report the detection of
a new broad (FWHM ~ 2 Å) and unidentified feature centered at ~4000
Å. We suggest that this new band may be related to the circumstellar
proto-fullerenes seen at infrared wavelengths.
Title: Lithium abundance in atmospheres of F- and G-type supergiants
and bright giants
Authors: Lyubimkov, Leonid S.; Lambert, David L.; Kaminsky, Bogdan M.;
Pavlenko, Yakov V.; Poklad, Dmitry B.; Rachkovskaya, Tamara M.
Bibcode: 2012MNRAS.427...11L
Altcode: 2012arXiv1212.6057L
Lithium in the atmosphere of a F or G supergiant reflects the initial
Li abundance and the internal history of the star. During evolution of a
star from the main sequence (MS) to the supergiant phase, lithium may be
destroyed by, for example, rotationally induced mixing in the MS stars
and strongly diluted by development of the supergiant's convective
envelope. In order to probe the connection between atmospheric
Li abundance and evolutionary predictions, we present a non-local
thermodynamic equilibrium abundance analysis of the resonance doublet
Li I at 6707.8 Å for 55 Galactic F and G supergiants and bright
giants (we observed 43 of them, the remaining 12 are added from Luck
and Wepfer's list). The derived lithium abundances log ɛ(Li) may be
considered in three groups, namely: (i) 10 Li-rich giants with log
ɛ(Li) = 2.0-3.2 (all 10 are F-type or A9 stars); (ii) 13 G- to K0-type
stars with Li abundances in the narrow range log ɛ(Li) = 1.1-1.8;
(iii) all other stars provide just upper limits to the Li abundance. The derived Li abundances are compared with theoretical predictions
of 2-15 M⊙ stars (both rotating and non-rotating). Our
results are generally in good agreement with theory. In particular,
the absence of detectable lithium for the majority of programme stars
is explainable. The comparison suggests that the stars may be separated
by mass M into two groups, namely M ≲ 6 M⊙ and M >
6 M⊙. All Li-rich giants and supergiants with log ɛ(Li)
≥ 2.0 have masses M < 6 M⊙; this conclusion follows
not only from our work but also from a scrutiny of published data. 11 of
13 stars with log ɛ(Li) = 1.1-1.8, specifically the stars with M <
6 M⊙, show good agreement with the post-first dredge-up
surface abundance log ɛ(Li) ≈ 1.4 predicted for the non-rotating 2-6
M⊙ stellar models. An absence of Li-rich stars in the range
M > 6 M⊙ agrees with the theoretical prediction that F
and G supergiants and giants with M > 6 M⊙ cannot show
detectable lithium. We note that present theory appears unable to
account for the derived Li abundances for some stars, namely for (i) a
few relatively low-mass Li-rich giants (M < 6 M⊙), whose
high Li abundances accompanied by rather high rotational velocities
or substantial nitrogen excess contradict theoretical predictions;
(ii) the relatively high-mass supergiants HR 461 and HR 8313 (M >
6 M⊙) with the detected abundances log ɛ = 1.3-1.5. It
is possible that the lithium in such stars was synthesized recently.
Title: Chemical compositions of stars in two stellar streams from
the Galactic thick disc
Authors: Ramya, P.; Reddy, Bacham E.; Lambert, David L.
Bibcode: 2012MNRAS.425.3188R
Altcode: 2012arXiv1207.0767R
We present abundances for 20 elements for stars in two stellar streams
identified by Arifyanto & Fuchs: 18 stars from the Arcturus stream
and 26 from a new stream, which we call the AF06 stream, both from the
Galactic thick disc. Results show that both streams are metal poor and
very old (10-14 Gyr) with kinematics and abundances overlapping with
the properties of local field thick-disc stars. Both streams exhibit
a range in metallicity but with relative elemental abundances that are
identical to those of thick-disc stars of the same metallicity. These
results show that neither stream can result from dissolution of an open
cluster. It is highly unlikely that either stream represents tidal
debris from an accreted satellite galaxy. Both streams most probably
owe their origin to dynamical perturbations within the Galaxy.
Title: Lithium Abundances in nearby FGK Dwarf and Subgiant Stars:
Internal Destruction, Galactic Chemical Evolution, and Exoplanets
Authors: Ramírez, I.; Fish, J. R.; Lambert, D. L.; Allende Prieto, C.
Bibcode: 2012ApJ...756...46R
Altcode: 2012arXiv1207.0499R
We derive atmospheric parameters and lithium abundances for 671
stars and include our measurements in a literature compilation of
1381 dwarf and subgiant stars. First, a "lithium desert" in the
effective temperature (T eff) versus lithium abundance
(A Li) plane is observed such that no stars with T
eff ~= 6075 K and A Li ~= 1.8 are found. We
speculate that most of the stars on the low A Li side of
the desert have experienced a short-lived period of severe surface
lithium destruction as main-sequence or subgiant stars. Next, we search
for differences in the lithium content of thin-disk and thick-disk
stars, but we find that internal processes have erased from the
stellar photospheres their possibly different histories of lithium
enrichment. Nevertheless, we note that the maximum lithium abundance
of thick-disk stars is nearly constant from [Fe/H] = -1.0 to -0.1,
at a value that is similar to that measured in very metal-poor halo
stars (A Li ~= 2.2). Finally, differences in the lithium
abundance distribution of known planet-host stars relative to otherwise
ordinary stars appear when restricting the samples to narrow ranges
of T eff or mass, but they are fully explained by age
and metallicity biases. We confirm the lack of a connection between
low lithium abundance and planets. However, we find that no low A
Li planet-hosts are found in the desert T eff
window. Provided that subtle sample biases are not responsible for
this observation, this suggests that the presence of gas giant planets
inhibit the mechanism responsible for the lithium desert.
Title: An upper limit on the sulphur abundance in HE 1327-2326
Authors: Bonifacio, P.; Caffau, E.; Venn, K. A.; Lambert, D. L.
Bibcode: 2012A&A...544A.102B
Altcode: 2012arXiv1207.1806B
Context. Star HE 1327-2326 is a unique object, with the lowest measured
iron abundance ([Fe/H] ~ -6) and a peculiar chemical composition that
includes large overabundances of C, N, and O with respect to iron. One
important question is whether the chemical abundances in this star
reflect the chemical composition of the gas cloud from which it was
formed or if they have been severely affected by other processes,
such as dust-gas winnowing.
Aims: We measure or provide an
upper limit to the abundance of the volatile element sulphur, which
can help to discriminate between the two scenarios.
Methods: We
observed HE 1327-2326 with the high resolution infra-red spectrograph
CRIRES at the VLT to observe the S i lines of Multiplet 3 at 1045
nm.
Results: We do not detect the S i line. A 3σ upper limit
on the equivalent width (EW) of any line in our spectrum is EW <
0.66 pm. Using either one-dimensional static or three-dimensional
hydrodynamical model-atmospheres, this translates into a robust upper
limit of [S/H] < -2.6.
Conclusions: This upper limit does
not provide conclusive evidence for or against dust-gas winnowing,
and the evidence coming from other elements (e.g., Na and Ti) is
also inconclusive or contradictory. The formation of dust in the
atmosphere versus an origin of the metals in a metal-poor supernova
with extensive "fall-back" are not mutually exclusive. It is possible
that dust formation distorts the peculiar abundance pattern created by a
supernova with fall-back, thus the abundance ratios in HE 1327-2326 may
be used to constrain the properties of the supernova(e) that produced
its metals, but with some caution. Based on spectra obtained with
CRIRES at the 8.2 m Antu ESO telescope, programme 386.D-0095.
Title: Two groups within the thick disc of the Milky Way?
Authors: Stanford, Laura M.; Lambert, David L.
Bibcode: 2012MNRAS.424.2118S
Altcode: 2012MNRAS.tmp.3327S
Compositions of F and G dwarf stars in two groups of thick disc stars
are presented. The groups identified by Schuster et al. have mean
characteristics ([Fe/H], V(rot), Age, σW') of (-0.7 dex,
120 km s-1, 12.5 Gyr, 62 km s-1) and (-0.4, 160,
10.0, 45.8). Abundances for 23 elements obtained from high-resolution
spectra are presented for 59 stars in the metal-rich group and 27 stars
in the metal-poor group. The run of abundance ratios [X/Fe] versus
[Fe/H] for the two groups define a single relation for each element
(designated as X) with no intrinsic scatter and without a measurable
discontinuity at -0.6 < [Fe/H] < -0.5, the metallicity at which
the two groups overlap. The relations [X/Fe] versus [Fe/H] are those
determined previously for thick disc stars. It is suggested that these
two groups and the thick disc as a whole have a common origin in terms
of prior chemical evolution.
Title: VizieR Online Data Catalog: Red giants abundances in 4 open
clusters (Reddy+, 2012)
Authors: Reddy, A. B. S.; Giridhar, S.; Lambert, D. L.
Bibcode: 2012yCat..74191350R
Altcode:
Clusters were selected from the New catalogue of optically visible
open clusters and candidates (Dias et al., 2002, Cat. B/ocl). Observations were conducted during 1999 February 6-10 with Tull
echelle coude spectrograph on the 2.7-m Harlan J. Smith telescope at
the McDonald observatory. (2 data files).
Title: The 7Li/6Li Isotope Ratio near the
Supernova Remnant IC 443
Authors: Taylor, C. J.; Ritchey, A. M.; Federman, S. R.; Lambert, D. L.
Bibcode: 2012ApJ...750L..15T
Altcode: 2012arXiv1203.6057T
We present an analysis of 7Li/6Li isotope ratios
along four sight lines that probe diffuse molecular gas near the
supernova remnant IC 443. Recent gamma-ray observations have revealed
the presence of shock-accelerated cosmic rays interacting with the
molecular cloud surrounding the remnant. Our results indicate that the
7Li/6Li ratio is lower in regions more strongly
affected by these interactions, a sign of recent Li production by
cosmic rays. We find that 7Li/6Li ≈7 toward
HD 254755, which is located just outside the visible edge of IC 443,
while 7Li/6Li ≈3 along the line of sight to HD
43582, which probes the interior region of the supernova remnant. No
evidence of 7Li synthesis by neutrino-induced spallation
is found in material presumably contaminated by the ejecta of a
core-collapse supernova. The lack of a neutrino signature in the
7Li/6Li ratios near IC 443 is consistent with
recent models of Galactic chemical evolution, which suggest that the
ν-process plays only a minor role in Li production. Based on
observations obtained with the Hobby-Eberly Telescope, which is a
joint project of the University of Texas at Austin, the Pennsylvania
State University, Stanford University, Ludwig-Maximilians-Universität
München, and Georg-August-Universität Göttingen.
Title: The Galactic R Coronae Borealis Stars: The C2 Swan
Bands, the Carbon Problem, and the 12C/13C Ratio
Authors: Hema, B. P.; Pandey, Gajendra; Lambert, David L.
Bibcode: 2012ApJ...747..102H
Altcode: 2012arXiv1201.1357H
Observed spectra of R Coronae Borealis (RCB) and hydrogen-deficient
carbon (HdC) stars are analyzed by synthesizing the C2
Swan bands (1, 0), (0, 0), and (0, 1) using our detailed line
list and the Uppsala model atmospheres. The (0, 1) and (0, 0)
C2 bands are used to derive the 12C abundance,
and the (1, 0) 12C13C band to determine the
12C/13C ratios. The carbon abundance derived
from the C2 Swan bands is about the same for the adopted
models constructed with different carbon abundances over the range 8.5
(C/He = 0.1%) to 10.5 (C/He = 10%). Carbon abundances derived from C
I lines are about a factor of four lower than the carbon abundance
of the adopted model atmosphere over the same C/He interval, as
reported by Asplund et al., who dubbed the mismatch between adopted and
derived C abundance as the "carbon problem." In principle, the carbon
abundances obtained from C2 Swan bands and that assumed
for the model atmosphere can be equated for a particular choice of
C/He that varies from star to star. Then, the carbon problem for
C2 bands is eliminated. However, such C/He ratios are in
general less than those of the extreme helium stars, the seemingly
natural relatives to the RCB and HdC stars. A more likely solution to
the C2 carbon problem may lie in a modification of the model
atmosphere's temperature structure. The derived carbon abundances and
the 12C/13C ratios are discussed in light of
the double degenerate and the final flash scenarios.
Title: HETDEX: A Magnitude-limited Spectroscopic Sample Of Stars In
The Galaxy Down To V 20
Authors: Allende-Prieto, Carlos; Shetrone, M.; Odewahn, S. C.;
Benedict, G.; Castanheira, B. G.; de Jong, R.; Lambert, D. L.;
MacQueen, P. J.; Marshall, J. L.; McArthur, B. E.; Sneden, C.;
HETDEX Collaboration
Bibcode: 2012AAS...21942407A
Altcode:
Spectroscopic surveys of stars in the Milky Way are growing rapidly in
size and scope, with the ambitious goals of unravelling the Galaxy's
formation and evolution, and finding out whether our galaxy fits
the current paradigm of hierarchical galaxy formation driven by cold
dark matter. These surveys follow target selection algorithms aimed
at extracting the most information out of a coarse sampling of the
stars in the Galaxy, and as result they are seriously biased. HETDEX
will be the first project to change that -- obtaining low-resolution
(R 750) spectra covering 350-550 nm that will render radial velocities
and overall metallicity for a flux-limited sample of > 100,000
stars down to V 20 over 60 square degrees. Questions that we hope to
address include: 1) the incidence of gross chemical peculiarities, 2)
the metallicity distributions of the main Galactic components, and 3)
the frequency of cold substructure over a range of scales. We show
simulated data and explore the performances of our preliminary data
analysis software.
Title: Abundance Patterns of Neutron-Capture Elements in the
Interstellar Medium
Authors: Ritchey, Adam M.; Federman, S. R.; Lambert, D. L.
Bibcode: 2012AAS...21930204R
Altcode:
We present the results of an archival survey of neutron-capture elements
in diffuse interstellar clouds from HST/STIS observations of over
50 Galactic sight lines. Existing measurements of the interstellar
abundances of Kr, Rb, Cd, and Sn have indicated deficiencies in our
understanding of the production of elements beyond the iron peak
via slow and rapid neutron-capture processes. The elements Kr and
Rb, which are primarily synthesized by massive stars through the
weak s-process and the r-process, are found to be underabundant in
interstellar gas compared to expectations based on current knowledge
of dust depletion. At the same time, Cd and Sn, which are produced in
larger part by the main s-process in low-mass AGB stars, exhibit less
depletion than expected. By combining new abundance determinations for
As, Cd, Sn, and Pb with recent surveys of Ga, Ge, Kr, and Rb, our study
seeks to reveal the causes of the inferred deficit in the contribution
from massive stars to the abundances of neutron-capture elements in
the current epoch. We find that while Ga, Ge, and Pb follow normal
depletion patterns, As is significantly overabundant, with an overall
depletion level similar to Sn. Yet, unlike Sn, As is almost entirely
a product of massive-star nucleosynthesis. The ultimate resolution of
these discrepancies will likely involve a deeper understanding of dust
grain depletion than presently exists. This research was funded
by the Space Telescope Science Institute through grant HST-AR-12123.
Title: The Galactic R Coronae Borealis Stars: The C2 Swan Bands,
The Carbon Problem, and The 12C/13C Ratio
Authors: Hema, B.; Pandey, G.; Lambert, D. L.
Bibcode: 2012nuco.confE.195H
Altcode: 2012PoS...146E.195H
No abstract at ADS
Title: Chemical composition of a sample of candidate post-asymptotic
giant branch stars
Authors: Rao, S. Sumangala; Giridhar, Sunetra; Lambert, David L.
Bibcode: 2012MNRAS.419.1254R
Altcode: 2011MNRAS.tmp.1790R
We have derived elemental abundances for a sample of nine IRAS
sources with colours similar to those of post-asymptotic giant branch
(post-AGB) stars. For IRAS 01259+6823, IRAS 05208-2035, IRAS 04535+3747
and IRAS 08187-1905, this is the first detailed abundance analysis
based upon high-resolution spectra. Mild indication of s-processing
for IRAS 01259+6823, IRAS 05208-2035 and IRAS 08187-1905 has been
found and a more comprehensive study of s-process-enhanced objects
IRAS 17279-1119 and IRAS 22223+4327 has been carried out. We
have also made a contemporary abundance analysis of the high Galactic
latitude supergiants BD+39°4926 and HD 107369. The former is heavily
depleted in refractories and estimated [Zn/H] of -0.7 dex most likely
gives initial metallicity of the star. For HD 107369 the abundances
of α and Fe-peak elements are similar to those of halo objects and
moderate deficiency of s-process elements is seen. IRAS 07140-2321,
despite being a short-period binary with a circumstellar shell, does
not exhibit selective depletion of refractory elements. We have
compiled the stellar parameters and abundances for post-AGB stars
with s-process enhancement, those showing significant depletion of
condensable elements and those showing neither. The compilation shows
that the s-process-enhanced group contains a very small number of
binaries, and observed [α/Fe] are generally similar to thick-disc
values. It is likely that they represent AGB evolution of single
stars. The compilation of the depleted group contains a larger
fraction of binaries and generally supports the hypothesis of dusty
discs surrounding binary post-AGB stars inferred via the shape of their
spectral energy distribution and mid-infrared interferometry. IRAS
07140-2321 and BD+39°4926 are difficult to explain with this scenario
and indicate the existence of an additional parameter/condition
needed to explain the depletion phenomenon. However, the conditions
for discernible depletion, minimum temperature of 5000 K and initial
metallicity larger than -1.0 dex found from our earlier work still
serve as useful criteria.
Title: Lithium isotope ratios near the supernova remnant IC 443
Authors: Ritchey, A. M.; Taylor, C. J.; Federman, S. R.; Lambert, D. L.
Bibcode: 2012MSAIS..22..137R
Altcode:
The rapid rise in the 7Li abundance for stars of near
solar metallicity requires the existence of one or more stellar
sources of 7Li. Likely candidates include red giant
and asymptotic giant branch stars, which produce 7Li
via the Cameron-Fowler mechanism, and Type II supernovae, in which
7Li is synthesized by neutrino-induced spallation. Direct
evidence of the neutrino-process remains elusive, yet could be provided
by detailed studies of Li isotope ratios in interstellar gas surrounding
supernova remnants. Here, we present the results of the first such
investigation, based on high-resolution measurements of Li I along
four lines of sight through the supernova remnant IC 443. While our
observations probe material presumably contaminated by the ejecta
of a core-collapse supernova, we find no evidence of 7Li
synthesis by neutrino-induced spallation. Rather, our results indicate
that the abundance of 6Li relative to 7Li has
been enhanced by interactions between shock-accelerated cosmic rays
and the molecular cloud surrounding the remnant. Future observations
will help to establish unequivocally the role that neutrino spallation
plays in 7Li production.
Title: Spectroscopic investigation of SDSS J100921.40 + 375233.9
selected from SDSS and GALEX photometry
Authors: Şahin, Timur; Lambert, David L.; Allende Prieto, Carlos
Bibcode: 2012ASInC...6..265S
Altcode: 2012arXiv1203.1461S; 2012ASInC...6..265C
In this study, we aim to reveal the nature of the Sloan Digital
Sky Survey (SDSS) star: SDSS J100921.40+375233.9, suspected to
have an extremely low metallicity We observed this star at high
spectral resolution and performed an abundance analysis. We derived
the spectroscopic parameters T_{eff} =5820±125 K, log g = 3.9±0.2,
and ξ_t = 1.1±0.5 km s^{-1}. The star is consistent with belonging
to the thick disk.
Title: Comprehensive abundance analysis of red giants in the open
clusters NGC 752, 1817, 2360 and 2506
Authors: Reddy, Arumalla B. S.; Giridhar, Sunetra; Lambert, David L.
Bibcode: 2012MNRAS.419.1350R
Altcode: 2011MNRAS.tmp.1851R; 2011arXiv1109.2678R
We have analysed high-dispersion echelle spectra (R ≳ 50 000) of red
giant members for four open clusters to derive abundances for many
elements. The spread in temperatures and gravities being very small
among the red giants nearly the same stellar lines were employed thereby
reducing the random errors. The errors of average abundance for the
cluster were generally in the range 0.02-0.07 dex. Our present sample
covers Galactocentric distances of 8.3-10.5 kpc. The [Fe/H] values are
-0.02 ± 0.05 for NGC 752, -0.07 ± 0.06 for NGC 2360, -0.11 ± 0.05 for
NGC 1817 and -0.19 ± 0.06 for NGC 2506. Abundances relative to Fe for
elements from Na to Eu are equal within measurement uncertainties to
published abundances for thin-disc giants in the field. This supports
the view that field stars come from disrupted open clusters.
Title: The chemical abundances of open clusters: NGC 752, NGC 1817,
NGC 2360 and NGC 2506
Authors: Reddy, Arumalla B. S.; Giridhar, Sunetra; Lambert, David L.
Bibcode: 2012ASInC...4..197R
Altcode:
Since the Galactic Open Clusters (OCs) provide a sample of stars
homogeneous in age and chemical composition and their distances are
well determined, they were recognized as suitable candidates to study
the chemical evolution of Galaxy. We have analyzed high-dispersion
echelle spectra (Rgeq50,000) of 3-4 red giant members for each open
cluster to derive abundances for a whole range of elements including
light as well as heavy elements. The membership to the cluster has been
confirmed through their radial velocities and proper motions. The spread
in temperatures and gravities being very small, nearly the same stellar
lines were employed thereby reducing the random errors. Most of these
clusters are located in Galactic anti-center direction and we found
[Fe/H] values of -0.02±0.05 for NGC 752, -0.07±0.06 for NGC 2360,
-0.11±0.05 for NGC 1817 and -0.19±0.06 for NGC 2506. Abundances
relative to Fe for elements from Na to Eu are equal within measurement
uncertainties to published abundances for thin disk giants in the
field with the possible exception of mild anomalies for Mn, Cu, Ba,
Ce and Nd. This supports the view that field stars come from disrupted
open clusters.
Title: Nebula around R Corona Borealis
Authors: Kameswara Rao, N.; Lambert, David L.
Bibcode: 2011arXiv1112.6225K
Altcode:
The star R Corona Borealis (R CrB) shows forbidden lines of [O II],
[N II], and [S II] during the deep minimum when the star is fainter
by about 8 to 9 magnitudes from normal brightness, suggesting the
presence of nebular material around it. We present low and high spectral
resolution observations of these lines during the ongoing deep minimum
of R CrB, which started in July 2007. These emission lines show double
peaks with a separation of about 170 km/s. The line ratios of [S II]
and [O II] suggest an electron density of about 100 cm$^{-3}$. We
discuss the physical conditions and possible origins of this low
density gas. These forbidden lines have also been seen in other R
Coronae Borealis stars during their deep light minima and this is a
general characteristic of these stars, which might have some relevance
to their origins.
Title: The Distribution of the Elements in the Galactic Disk. III. A
Reconsideration of Cepheids from l = 30° to 250°
Authors: Luck, R. Earle; Lambert, David L.
Bibcode: 2011AJ....142..136L
Altcode: 2011arXiv1108.1947L
This paper reports on the spectroscopic investigation of 238 Cepheids in
the northern sky. Of these stars, about 150 are new to the study of the
galactic abundance gradient. These new Cepheids bring the total number
of Cepheids involved in abundance distribution studies to over 400. In
this work, we also consider systematics between various studies and also
those which result from the choice of models. We find that systematic
variations exist at the 0.06 dex level both between studies and model
atmospheres. In order to control the systematic effects our final
gradients depend only on abundances derived herein. A simple linear
fit to the Cepheid data from 398 stars yields a gradient d[Fe/H]/dR
G = -0.062 ± 0.002 dex kpc-1 which is in good
agreement with previously determined values. We have also re-examined
the region of the "metallicity island" of Luck et al. With the doubling
of the sample in that region and our internally consistent abundances,
we find that there is scant evidence for a distinct island. We also find
in our sample the first reported Cepheid (V1033 Cyg) with a pronounced
Li feature. The Li abundance is consistent with the star being on its
redward pass toward the first giant branch.
Title: Chemical Compositions of a sample of candidate post-AGB stars
Authors: Sumangala Rao, S.; Giridhar, Sunetra; Lambert, David L.
Bibcode: 2011arXiv1109.1676S
Altcode:
We have derived elemental abundances for a sample of nine IRAS sources
with colours similar to those of post-AGB stars. For IRAS 01259+6823,
IRAS 05208-2035, IRAS 04535+3747 and IRAS 08187-1905 this is the first
detailed abundance analysis based upon high resolution spectra. Mild
indication of s-processing for IRAS 01259+6823, IRAS 05208-2035 and IRAS
08187-1905 have been found and a more comprehensive study of s-process
enhanced objects IRAS 17279-1119 and IRAS 22223+4327 have been carried
out. We have also made a contemporary abundance analysis of the high
galactic latitude supergiants BD+39 4926 and HD 107369. The former
is heavily depleted in refractories and estimated [Zn/H] of -0.7 dex
most likely gives initial metallicity of the star. For HD 107369 the
abundances of alpha and Fe-peak elements are similar to those of halo
objects and moderate deficiency of s-process elements is seen. IRAS
07140-2321 despite being a short period binary with circumstellar shell
does not exhibit selective depletion of refractory elements. We have
compiled the stellar parameters and abundances for post-AGB stars
with s-process enhancement, those showing significant depletion
of condensable elements and those showing neither. The compilation
shows that the s-process enhanced group contains very small number
of binaries, and observed [alpha/Fe] are generally similar to thick
disc values. It is likely that they represent AGB evolution of single
stars.The compilation of depleted group contains larger fraction
of binaries and generally supports the hypothesis of dusty discs
surrounding binary post-AGB stars inferred via the shape of their SED
and mid IR interferometry. IRAS 07140-2321 and BD+39 4926 are difficult
to explain with this scenario and indicate the existence of additional
parameter/condition needed to explain the depletion phenomenon.
Title: Dust around R Coronae Borealis Stars. I. Spitzer/Infrared
Spectrograph Observations
Authors: García-Hernández, D. A.; Rao, N. Kameswara; Lambert,
David L.
Bibcode: 2011ApJ...739...37G
Altcode: 2011ApJ...739...37A; 2011arXiv1107.1185G
Spitzer/infrared spectrograph (IRS) spectra from 5 to 37 μm
for a complete sample of 31 R Coronae Borealis stars (RCBs) are
presented. These spectra are combined with optical and near-infrared
photometry of each RCB at maximum light to compile a spectral
energy distribution (SED). The SEDs are fitted with blackbody flux
distributions and estimates are made of the ratio of the infrared flux
from circumstellar dust to the flux emitted by the star. Comparisons for
29 of the 31 stars are made with the Infrared Astronomical Satellite
(IRAS) fluxes from three decades earlier: Spitzer and IRAS fluxes
at 12 μm and 25 μm are essentially equal for all but a minority
of the sample. For this minority, the IRAS to Spitzer flux ratio
exceeds a factor of three. The outliers are suggested to be stars
where formation of a dust cloud or dust puff is a rare event. A single
puff ejected prior to the IRAS observations may have been reobserved
by Spitzer as a cooler puff at a greater distance from the RCB. RCBs
which experience more frequent optical declines have, in general, a
circumstellar environment containing puffs subtending a larger solid
angle at the star and a quasi-constant infrared flux. Yet, the estimated
subtended solid angles and the blackbody temperatures of the dust show
a systematic evolution to lower solid angles and cooler temperatures
in the interval between IRAS and Spitzer. Dust emission by these RCBs
and those in the LMC is similar in terms of total 24 μm luminosity and
[8.0]-[24.0] color index.
Title: Is the Post-AGB Star SAO 40039 Mildly Hydrogen-Deficient?
Authors: Sumangala Rao, S.; Pandey, Gajendra; Lambert, David L.;
Giridhar, Sunetra
Bibcode: 2011ApJ...737L...7S
Altcode: 2011arXiv1107.1316S; 2011ApJ...737L...7R
We have conducted an LTE abundance analysis for SAO 40039, a warm
post-AGB star whose spectrum is known to show surprisingly strong
He I lines for its effective temperature and has been suspected of
being H-deficient and He-rich. High-resolution optical spectra are
analyzed using a family of model atmospheres with different He/H
ratios. Atmospheric parameters are estimated from the ionization
equilibrium set by neutral and singly ionized species of Fe and Mg,
the excitation of Fe I and Fe II lines, and the wings of the Paschen
lines. On the assumption that the He I lines are of photospheric
and not chromospheric origin, a He/H ratio of approximately unity
is found by imposing the condition that the adopted He/H ratio of
the model atmosphere must equal the ratio derived from the observed
He I triplet lines at 5876, 4471, and 4713 Å, and singlet lines at
4922 and 5015 Å. Using the model with the best-fitting atmospheric
parameters for this He/H ratio, SAO 40039 is confirmed to exhibit
mild dust-gas depletion, i.e., the star has an atmosphere deficient
in elements of high condensation temperature. The star appears to be
moderately metal-deficient with [Fe/H] = -0.4 dex. But the star's
intrinsic metallicity as estimated from Na, S, and Zn, elements
of a low condensation temperature, is [Fe/H]o ~= -0.2
([Fe/H]o refers to the star's intrinsic metallicity). The
star is enriched in N and perhaps O as well, changes reflecting the
star's AGB past and the event that led to He enrichment.
Title: Origin of Lithium Enrichment in K Giants
Authors: Kumar, Yerra Bharat; Reddy, Bacham E.; Lambert, David L.
Bibcode: 2011ApJ...730L..12K
Altcode: 2011arXiv1102.2299B
In this Letter, we report on a low-resolution spectroscopic survey
for Li-rich K giants among 2000 low-mass (M <= 3 M sun)
giants spanning the luminosity range from below to above the luminosity
of the clump. Fifteen new Li-rich giants including four super Li-rich
K giants (log epsilon(Li) >=3.2) were discovered. A significant
finding is that there is a concentration of Li-rich K giants at
the luminosity of the clump or red horizontal branch. This new
finding is partly a consequence of the fact that our low-resolution
survey is the first large survey to include giants well below and
above the red giant branch (RGB) bump and clump locations in the H-R
diagram. Origin of the lithium enrichment may be plausibly attributed to
the conversion of 3He via 7Be to 7Li
by the Cameron-Fowler mechanism but the location for the onset of the
conversion is uncertain. Two possible opportunities to effect this
conversion are discussed: the bump in the first ascent of the RGB and
the He-core flash at the tip of the RGB. The finite luminosity spread
of the Li-rich giants serves to reject the idea that Li enhancement is,
in general, a consequence of a giant swallowing a large planet.
Title: Are C60 Molecules Detectable in Circumstellar
Shells of R Coronae Borealis Stars?
Authors: García-Hernández, D. A.; Kameswara Rao, N.; Lambert, D. L.
Bibcode: 2011ApJ...729..126G
Altcode: 2011arXiv1101.2253G
The hydrogen-poor, helium-rich, and carbon-rich character of the
gas around R Coronae Borealis (RCB) stars has been suggested to be a
site for formation of C60 molecules. This suggestion is
not supported by observations reported here showing that infrared
transitions of C60 are not seen in a large sample of RCB
stars observed with the Infrared Spectrograph on the Spitzer Space
Telescope. The infrared C60 transitions are seen, however,
in emission and blended with polycyclic aromatic hydrocarbon (PAH)
features in spectra of DY Cen and possibly also of V854 Cen, the two
least hydrogen-deficient (hydrogen deficiency of only ~10-100) RCB
stars. The speculation is offered that C60 (and the PAHs) in
the moderately H-deficient circumstellar envelopes may be formed by the
decomposition of hydrogenated amorphous carbon but fullerene formation
is inefficient in the highly H-deficient environments of most RCBs.
Title: The Abundance of Boron in Diffuse Interstellar Clouds
Authors: Ritchey, A. M.; Federman, S. R.; Sheffer, Y.; Lambert, D. L.
Bibcode: 2011ApJ...728...70R
Altcode: 2010arXiv1012.4457R
We present a comprehensive survey of boron abundances in diffuse
interstellar clouds from observations made with the Space Telescope
Imaging Spectrograph (STIS) of the Hubble Space Telescope. Our
sample of 56 Galactic sight lines is the result of a complete search
of archival STIS data for the B II λ1362 resonance line, with each
detection confirmed by the presence of absorption from O I λ1355, Cu
II λ1358, and Ga II λ1414 (when available) at the same velocity. Five
previous measurements of interstellar B II from Goddard High Resolution
Spectrograph observations are incorporated in our analysis, yielding
a combined sample that more than quadruples the number of sight lines
with significant boron detections. Our survey also constitutes the
first extensive analysis of interstellar gallium from STIS spectra and
expands on previously published results for oxygen and copper. The
observations probe both high- and low-density diffuse environments,
allowing the density-dependent effects of interstellar depletion to be
clearly identified in the gas-phase abundance data for each element. In
the case of boron, the increase in relative depletion with line-of-sight
density amounts to an abundance difference of 0.8 dex between the warm
and cold phases of the diffuse interstellar medium. The abundance of
boron in warm, low-density gas is found to be B/H = (2.4 ± 0.6) ×
10-10, which represents a depletion of 60% relative to the
meteoritic boron abundance. Beyond the effects of depletion, our survey
reveals sight lines with enhanced boron abundances that potentially
trace the recent production of 11B, resulting from
spallation reactions involving either cosmic rays or neutrinos. Future
observations will help to disentangle the relative contributions from
the two spallation channels for 11B synthesis. Based
in part on observations made with the NASA/ESA Hubble Space Telescope,
obtained from the Multimission Archive at the Space Telescope Science
Institute (MAST). STScI is operated by the Association of Universities
for Research in Astronomy, Inc., under NASA contract NAS5-26555.
Title: Neon and CNO Abundances for Extreme Helium Stars—A Non-LTE
Analysis
Authors: Pandey, Gajendra; Lambert, David L.
Bibcode: 2011ApJ...727..122P
Altcode: 2010arXiv1011.5035P
A non-LTE (NLTE) abundance analysis was carried out for three extreme
helium stars (EHes): BD+10° 2179, BD-9° 4395, and LS IV+6° 002,
from their optical spectra with NLTE model atmospheres. NLTE TLUSTY
model atmospheres were computed with H, He, C, N, O, and Ne treated
in NLTE. Model atmosphere parameters were chosen from consideration
of fits to observed He I line profiles and ionization equilibria
of C and N ions. The program SYNSPEC was then used to determine
the NLTE abundances for Ne as well as H, He, C, N, and O. LTE neon
abundances from Ne I lines in the EHes: LSE 78, V1920 Cyg, HD 124448,
and PV Tel, are derived from published models and an estimate of the
NLTE correction applied to obtain the NLTE Ne abundance. We show that
the derived abundances of these key elements, including Ne, are well
matched with semi-quantitative predictions for the EHe resulting from
a cold merger (i.e., no nucleosynthesis during the merger) of an He
white dwarf with a C-O white dwarf.
Title: Lithium abundances in the α Per cluster
Authors: Balachandran, Suchitra C.; Mallik, Sushma V.; Lambert,
David L.
Bibcode: 2011MNRAS.410.2526B
Altcode: 2010MNRAS.tmp.1582B; 2010arXiv1009.2323B
Lithium (Li) abundances are presented and discussed for 70 members of
the 50-Myr-old open cluster α Per. More than half of the abundances
are from new high-resolution spectra. The Li abundance in the F-type
stars is equal to its presumed initial abundance, confirming previous
suggestions that pre-main-sequence depletion is ineffective for these
stars. Intrinsic star-to-star scatter in Li abundance among these
stars is comparable to the measurement uncertainties. There is marginal
evidence that the stars of high projected rotational velocity (v sin
i) follow a different abundance versus temperature trend from the slow
rotators. For stars cooler than about 5500 K, the Li abundance declines
steeply with decreasing temperature and there develops a star-to-star
scatter in the Li abundance. This scatter is shown to resemble the
well-documented scatter seen in the 70-Myr-old Pleiades cluster. The
scatter appears to be far less pronounced in the 30-Myr clusters,
which have been studied for Li abundance.
Title: Interstellar CN and CH+ in Diffuse Molecular Clouds:
12C/13C Ratios and CN Excitation
Authors: Ritchey, A. M.; Federman, S. R.; Lambert, D. L.
Bibcode: 2011ApJ...728...36R
Altcode: 2010arXiv1012.1296R
We present very high signal-to-noise ratio absorption-line
observations of CN and CH+ along 13 lines of sight
through diffuse molecular clouds. The data are examined to extract
precise isotopologic ratios of 12CN/13CN and
12CH+/13CH+ in order
to assess predictions of diffuse cloud chemistry. Our results
on 12CH+/13CH+
confirm that this ratio does not deviate from the ambient
12C/13C ratio in local interstellar clouds,
as expected if the formation of CH+ involves nonthermal
processes. We find that 12CN/13CN, however, can be
significantly fractionated away from the ambient value. The dispersion
in our sample of 12CN/13CN ratios is similar to
that found in recent surveys of 12CO/13CO. For
sight lines where both ratios have been determined, the
12CN/13CN ratios are generally fractionated in the
opposite sense compared to 12CO/13CO. Chemical
fractionation in CO results from competition between selective
photodissociation and isotopic charge exchange (ICE). An
inverse relationship between 12CN/13CN and
12CO/13CO follows from the coexistence of CN
and CO in diffuse cloud cores. However, an ICE reaction with CN may
mitigate the enhancements in 12CN/13CN for
lines of sight with low 12CO/13CO ratios. For
two sight lines with high values of 12CO/13CO,
our results indicate that about 50% of the carbon is locked up in CO,
which is consistent with the notion that these sight lines probe
molecular cloud envelopes where the transition from C+
to CO is expected to occur. An analysis of CN rotational excitation
yields a weighted mean value for T 01(12CN)
of 2.754 ± 0.002 K, which implies an excess over the temperature
of the cosmic microwave background (CMB) of only 29 ± 3 mK. This
modest excess eliminates the need for a local excitation mechanism
beyond electron and neutral collisions. The rotational excitation
temperatures in 13CN show no excess over the temperature
of the CMB. Based in part on observations made with the Very
Large Telescope of the European Southern Observatory, Paranal, Chile,
under programs 065.I-0526, 071.C-0367, 071.C-0513, and 076.C-0431.
Title: Nitrogen enrichment in atmospheres of A- and F-type supergiants
Authors: Lyubimkov, Leonid S.; Lambert, David L.; Korotin, Sergey A.;
Poklad, Dmitry B.; Rachkovskaya, Tamara M.; Rostopchin, Sergey I.
Bibcode: 2011MNRAS.410.1774L
Altcode: 2010arXiv1009.0054L
Using new accurate fundamental parameters of 30 Galactic A and F
supergiants, namely their effective temperatures Teff
and surface gravities log g, we implemented a non-LTE analysis of the
nitrogen abundance in their atmospheres. It is shown that the non-LTE
corrections to the N abundances increase with Teff. The
nitrogen overabundance as a general feature of this type of stars is
confirmed. A majority of the stars have a nitrogen excess [N/Fe] between
0.2 and 0.9 dex with the maximum position of the star's distribution on
[N/Fe] between 0.4 and 0.7 dex. The N excesses are discussed in light
of predictions for B-type main sequence (MS) stars with rotationally
induced mixing and for their next evolutionary phase, i.e. A- and F-type
supergiants that have experienced the first dredge-up. Rotationally
induced mixing in the MS progenitors of the supergiants may be a
significant cause of the nitrogen excesses. When comparing our results
with predictions of the theory developed for stars with the mixing, we
find that the bulk of the supergiants (28 of 30) show the N enrichment
that can be expected (i) either after the MS phase for stars with the
initial rotational velocities v0= 200-400 km s-1
(ii) or after the first dredge-up for stars with v0= 50-400
km s-1. The latter possibility is preferred on account
of the longer lifetime for stars on red-blue loops following the
first dredge-up. Two supergiants without a discernible N enrichment,
namely HR 825 and HR 7876, may be post-MS objects with the relatively
low initial rotational velocity of about 100 km s-1. The
suggested range for v0 is approximately consistent with
inferences from the observed projected rotational velocities of B-type
MS stars, progenitors of A and F supergiants.
Title: Interstellar Lithium and Rubidium in the Diffuse Gas Near
IC 443
Authors: Ritchey, Adam M.; Taylor, C. J.; Federman, S. R.; Lambert,
D. L.
Bibcode: 2011AAS...21725623R
Altcode: 2011BAAS...4325623R
We present an analysis of interstellar lithium and rubidium from
observations made with the Hobby-Eberly Telescope at McDonald
Observatory of the Li I λ6707 and Rb I λ7800 absorption lines
along four lines of sight through the supernova remnant IC 443. The
observations probe interstellar material polluted by the ejecta of a
core-collapse (Type II) supernova and can thus be used to constrain
the contribution from massive stars to the synthesis of lithium and
rubidium. Production of 7Li is expected to occur through
neutrino spallation in the helium and carbon shells of the progenitor
star during the terminal supernova explosion, while both 6Li
and 7Li are synthesized via spallation and fusion reactions
involving cosmic rays accelerated by the remnant. Gamma-ray emission
from IC 443 provides strong evidence for the interaction of accelerated
cosmic rays with the ambient atomic and molecular gas. Rubidium is
also produced by massive stars through the weak s-process in the
He- and C-burning shells and the r-process during core collapse. We
examine interstellar 7Li/6Li isotope ratios as
well as Li/K and Rb/K ratios along each line of sight, and discuss
the implications of our results in the context of nucleosynthesis
associated with Type II supernovae.
Title: Abundance analysis of RV Tauri like stars
Authors: Sudhakar, Sumangala Rao; Giridhar, Sunetra; Lambert, David L.
Bibcode: 2011ASInC...3..121S
Altcode:
We have done comprehensive abundance analysis using high resolution
spectra for IRAS01427+4633, IRAS 06165+3158 and IRAS 19135+3937
which occupy the RV Tauri box in the IRAS two colour diagram. We
have also analyzed RV Tauri stars SU Gem, V453 Oph and TX Per. We
find abundance anomalies caused by selective depletion of refractive
elements for SU Gem and IRAS 19135+3937, although the effect is less
distinct for the later. This effect has been observed in some post-AGB
stars and RV Tauri stars of spectroscopic class B. We have done a
detailed abundance analysis for V453 Oph which is the only galactic
RV Tauri star reported to exhibit s-process enhancement. We find
relative enrichment of α elements Mg, Si, Ca and Ti generally seen
in old disk or halo objects and modest s-process enhancement [s/Fe =
0.6]. We find very mild indication of s-processing in IRAS 06165+3158;
a metal-poor object with RV Tauri like colours.
Title: High-resolution optical spectroscopy of the F supergiant
protoplanetary nebula IRAS 18095+2704
Authors: Şahin, T.; Lambert, David L.; Klochkova, V. G.;
Tavolganskaya, N. S.
Bibcode: 2011MNRAS.410..612S
Altcode: 2010arXiv1008.0358S
An abundance analysis is presented for IRAS 18095+2704 (V887 Her),
a post-asymptotic giant branch star and protoplanetary nebula. The
analysis is based on high-resolution optical spectra from the McDonald
Observatory and the Special Astrophysical Observatory. Standard analysis
using a classical Kurucz model atmosphere and the line analysis program
MOOG provides the atmospheric parameters: Teff= 6500 K,
log g=+0.5, microturbulent velocity ξ= 4.7 km s-1 and
[Fe/H]=-0.9. Extraction of these parameters is based on excitation of Fe
I lines, ionization equilibrium between neutral and ions of Mg, Ca, Ti,
Cr and Fe, and the wings of hydrogen Paschen lines. Elemental abundances
are obtained for 22 elements and upper limits for an additional
four elements. These results show that the star's atmosphere has not
experienced a significant number of C- and s-process enriching thermal
pulses. Abundance anomalies as judged relative to the compositions
of unevolved and less-evolved normal stars of a similar metallicity
include Al, Y and Zr deficiencies with respect to Fe of about 0.5
dex. Judged by composition, the star resembles an RV Tauri variable
that has been mildly affected by dust-gas separation reducing the
abundances of the elements of highest condensation temperature. This
separation may occur in the stellar wind. There are indications that
the standard one-dimensional local thermodynamic equilibrium analysis is
not entirely appropriate for IRAS 18095+2704. These include a supersonic
macroturbulent velocity of 23 km s-1, emission in Hα and the
failure of predicted profiles to fit observed profiles of Hβ and Hγ.
Title: Comprehensive abundance studies of four open clusters
Authors: Arumalla, Bala Sudhakara Reddy; Giridhar, Sunetra; Lambert,
David L.
Bibcode: 2011ASInC...3..133A
Altcode:
Galactic open clusters are excellent tools to study the chemical
evolution of Galaxy. They provide a sample of stars homogeneous
in age and chemical composition and their distances are well
determined. We have analyzed high resolution spectra (40,000) of
red giant members for each cluster to derive abundances for a whole
range of elements including light as well as heavy elements. We have
measured equivalent widths for large number of lines for each species
and have used model atmosphere grid developed by Kurucz and Castelli
and 2009 version of spectrum synthesis code. For each cluster 4-5 red
giants are analyzed. The membership to the cluster has been confirmed
through their radial velocities and proper motions. The spread in
temperatures and gravities being very small nearly the same stellar
lines were employed thereby reducing the random errors. The errors of
average abundance for the cluster were generally in 0.02 to 0.07 dex
range. Our present sample covers galactocentric distance range
of 8.8 to 10.98 kpc. Most of these clusters are located in anti-center
direction. NGC 752 exhibits near-solar [Fe/H] of -0.05, NGC 2360 -0.11,
NGC 1817 -0.15 and NGC 2506 -0.32. The cluster to cluster variations
are encountered for alpha elements, Fe-peak elements and for s and
r-process elements. The present sample is quite modest and would be
extended for a larger set of clusters. For each cluster the observed
chemical abundance patterns, when sufficiently different in one or
more elements, offer the possibility to reconstruct now dispersed
stellar aggregates of the protogalactic disk and so improve our basic
understanding of the disk formation process.
Title: Erratum: A search for interstellar anthracene toward the
Perseus anomalous microwave emission region
Authors: Iglesias-Groth, S.; Manchado, A.; Rebolo, R.; González
Hernández, J. I.; García-Hernández, D. A.; Lambert, D. L.
Bibcode: 2010MNRAS.409..880I
Altcode: 2010MNRAS.tmp.1653I
No abstract at ADS
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: The Interstellar 7Li/6Li Ratio in the
Diffuse Gas Near IC 443
Authors: Ritchey, A. M.; Taylor, C. J.; Federman, S. R.; Lambert, D. L.
Bibcode: 2010mwac.meet..T07R
Altcode:
Supernova remnants are believed to be the primary acceleration sites
of Galactic cosmic rays (GCR), which are essential to gas-phase
interstellar chemistry since they are a major source of ionization in
both diffuse and dense environments. The interaction of accelerated
particles with interstellar gas will also synthesize isotopes of the
light elements Li, Be, and B through the spallation of CNO nuclei
(producing all stable LiBeB isotopes) and through α+α fusion
(yielding 6Li and 7Li, only). Type II supernovae
may provide an additional source of 7Li and 11B
during core collapse through neutrino-induced spallation in the
He and C shells of the progenitor star (the ν-process). However,
direct observational evidence for light element synthesis resulting
from cosmic-ray or neutrino-induced spallation is rare. Here, we
examine 7Li/6Li isotope ratios along four lines
of sight through the supernova remnant IC 443 using observations of
the Li I λ6707 doublet made with the Hobby-Eberly Telescope (HET) at
McDonald Observatory. The 7Li/6Li ratio in
the general interstellar medium is expected to be similar to the ratio
of ~12 that characterizes solar system material. A local enhancement
in the cosmic-ray flux will act to lower 7Li/6Li,
yielding a ratio of ~2 when cosmic rays dominate Li synthesis. Gamma-ray
emission from IC 443 provides strong evidence for the interaction
of cosmic rays accelerated by the remnant with the ambient atomic
and molecular gas. Yet this material has also been contaminated
by the ejecta of a Type II supernova, which should be enriched in
7Li. We are seeking 7Li/6Li ratios
that are either higher than the solar system ratio as a result of
the ν-process or lower due to cosmic-ray spallation. Since the
fine structure separation of the Li I doublet is comparable to the
isotope shift (~7 km s-1) and each fine structure line
is further split into hyperfine components, the velocity structure
along the line of sight must be carefully constrained if meaningful
7Li/6Li ratios are to be determined. In our
analysis, the strongest components seen in K I and CH are used to
synthesize the complex Li I profiles. We will discuss the implications
of our results on 7Li/6Li (and Li/K) ratios in
the context of Li production by Type II supernovae.
Title: Surprising Metallicity of a Newly Discovered M79 Post-AGB Star
Authors: Sahin, T.; Lambert, D. L.
Bibcode: 2010ASPC..432..254S
Altcode: 2009arXiv0910.5567S
A detailed chemical composition analysis based on a high-resolution
(R≍35,000) CCD spectrum is presented for a newly discovered post-AGB
star in the globular cluster M79 for the first time. The elemental
abundance results of M79 post-AGB star are found to be [C/Fe] ≍ -0.7,
[O/Fe] = +1.4, [α-process/Fe] ≍ 0.5, and [s-process/Fe] ≍ -0.1. The
surprising result is that the iron abundance of the star is apparently
about 0.6 dex less than that of the cluster’s red giants as reported
by published studies including a recent high-resolution spectroscopic
analysis by Carretta and colleagues.
Title: A search for interstellar anthracene towards the Perseus
anomalous microwave emission region
Authors: Iglesias-Groth, S.; Manchado, A.; Rebolo, R.; González
Hernández, J. I.; García-Hernández, D. A.; Lambert, D. L.
Bibcode: 2010MNRAS.407.2157I
Altcode: 2010arXiv1005.4388I; 2010MNRAS.tmp.1136I
We report the discovery of a new broad interstellar (or circumstellar)
band at 7088.8 +/- 2.0 Å coincident to within the measurement
uncertainties with the strongest band of the anthracene cation
(C14H10+) as measured in gas-phase
laboratory spectroscopy at low temperatures. The band is detected
in the line of sight of star Cernis 52, a likely member of the
very young star cluster IC 348, and is probably associated with
cold absorbing material in an intervening molecular cloud of the
Perseus star-forming region where various experiments have recently
detected anomalous microwave emission. From the measured intensity
and available oscillator strength we find a column density of implying
that ~0.008 per cent of the carbon in the cloud could be in the form
of C14H10+. A similar abundance has
been recently claimed for the naphthalene cation in this cloud. This is
the first location outside the Solar system where specific polycyclic
aromatic hydrocarbons (PAHs) are identified. We report observations
of interstellar lines of CH and CH+ that support a rather
high column density for these species and for molecular hydrogen. The
strength ratio of the two prominent diffuse interstellar bands at
5780 and 5797 Å suggests the presence of a `zeta'-type cloud in the
line of sight (consistent with steep far-ultraviolet extinction and
high molecular content). The presence of PAH cations and other related
hydrogenated carbon molecules which are likely to occur in this type of
clouds reinforces the suggestion that electric dipole radiation from
fast-spinning PAHs is responsible of the anomalous microwave emission
detected towards Perseus.
Title: Manganese Abundances in the Globular Cluster ω Centauri
Authors: Cunha, Katia; Smith, Verne V.; Bergemann, Maria; Suntzeff,
Nicholas B.; Lambert, David L.
Bibcode: 2010ApJ...717..333C
Altcode: 2010arXiv1005.2363C
We present manganese abundances in 10 red giant members of the globular
cluster ω Centauri; eight stars are from the most metal-poor population
(RGB MP and RGB MInt1) while two targets are members of the more
metal-rich groups (RGB MInt2 and MInt3). This is the first time Mn
abundances have been studied in this peculiar stellar system. The
LTE values of [Mn/Fe] in ω Cen overlap those of Milky Way stars in
the metal-poor ω Cen populations ([Fe/H] ~-1.5 to -1.8), however
unlike what is observed in Milky Way halo and disk stars, [Mn/Fe]
declines in the two more metal-rich RGB MInt2 and MInt3 targets. Non-LTE
calculations were carried out in order to derive corrections to the LTE
Mn abundances. The non-LTE results for ω Cen in comparison with the
non-LTE [Mn/Fe] versus [Fe/H] trend obtained for the Milky Way confirm
and strengthen the conclusion that the manganese behavior in ω Cen
is distinct. These results suggest that low-metallicity supernovae
(with metallicities <= -2) of either Type II or Type Ia dominated
the enrichment of the more metal-rich stars in ω Cen. The dominance
of low-metallicity stars in the chemical evolution of ω Cen has
been noted previously in the s-process elements where enrichment from
metal-poor asymptotic giant branch stars is indicated. In addition,
copper, which also has metallicity-dependent yields, exhibits lower
values of [Cu/Fe] in the RGB MInt2 and MInt3 ω Cen populations.
Title: Oxygen Isotopic Ratios in Cool R Coronae Borealis Stars
Authors: García-Hernández, D. A.; Lambert, David L.; Kameswara Rao,
N.; Hinkle, Ken H.; Eriksson, Kjell
Bibcode: 2010ApJ...714..144G
Altcode: 2010arXiv1003.2901A
We investigate the relationship between R Coronae Borealis (RCB)
stars and hydrogen-deficient carbon (HdC) stars by measuring precise
16O/18O ratios for five cool RCB stars. The
16O/18O ratios are derived by spectrum synthesis
from high-resolution (R ~ 50, 000) K-band spectra. Lower limits to the
16O/17O and 14N/15N ratios
as well as Na and S abundances (when possible) are also given. RCB
stars in our sample generally display less 18O than HdC
stars—the derived 16O/18O ratios range from 3
to 20. The only exception is the RCB star WX CrA, which seems to be an
HdC-like star with 16O/18O = 0.3. Our result of
a higher 16O/18O ratio for the RCB stars must
be accounted for by a theory of the formation and evolution of HdC
and RCB stars. We speculate that a late dredge-up of products of He
burning, principally 12C and 16O, may convert an
18O-rich HdC star into an 18O-poor RCB star as
the H-deficient star begins its final evolution from a cool supergiant
to the top of the white dwarf cooling track.
Title: Lithium abundances in the α Persei Cluster
Authors: Mallik, Sushma V.; Balachandran, Suchitra C.; Lambert,
David L.
Bibcode: 2010IAUS..268..339M
Altcode:
As a sequel to the Li observations by Balachandran, Lambert &
Stauffer (1988, 1996) in 35 stars of the 50 Myr old cluster α Persei,
we have obtained and analyzed high resolution spectra of another
51 stars. Following a reconsideration of the cluster membership of
the stars (Prosser 1992, Makarov 2006, Mermilliod et al. 2008, and
Patience et al. 2002), we discuss the Li abundances for 70 stars. With
our larger sample, we reexamine the question of whether the scatter
in Li abundance at a given Teff seen in young clusters at
cool temperatures is real or not.
Title: Light elements - one observer's historical perspective
Authors: Lambert, David L.
Bibcode: 2010IAUS..268....3L
Altcode: 2014arXiv1412.3876L
This essay attempts to provide a historical perspective on some of
the key questions that engaged the attention of participants at the
symposium. In particular, the writer offers and comments on a personal
list of milestones in the literature published between 1957 and 1982.
Title: Boron abundances in diffuse interstellar clouds
Authors: Ritchey, Adam M.; Federman, S. R.; Sheffer, Y.; Lambert, D. L.
Bibcode: 2010IAUS..268..237R
Altcode: 2009arXiv0912.3579R
We present a comprehensive survey of B abundances in diffuse
interstellar clouds from HST/STIS observations along 56 Galactic sight
lines. Our sample is the result of a complete search of archival
STIS data for the B II λ1362 resonance line, with each detection
confirmed by the presence of absorption from other dominant ions at
the same velocity. The data probe a range of astrophysical environments
including both high-density regions of massive star formation as well
as low-density paths through the Galactic halo, allowing us to clearly
define the trend of B depletion onto interstellar grains as a function
of gas density. Many extended sight lines exhibit complex absorption
profiles that trace both local gas and gas associated with either
the Sagittarius-Carina or Perseus spiral arm. Our analysis indicates
a higher B/O ratio in the inner Sagittarius-Carina spiral arm than
in the vicinity of the Sun, which may suggest that B production in
the current epoch is dominated by a secondary process. The average
gas-phase B abundance in the warm diffuse ISM [log ɛ(B) = 2.38±0.10]
is consistent with the abundances determined for a variety of Galactic
disk stars, but is depleted by 60% relative to the solar system
value. Our survey also reveals sight lines with enhanced B abundances
that potentially trace recent production of 11B either by
cosmic-ray or neutrino-induced spallation. Such sight lines will be
key to discerning the relative importance of the two production routes
for 11B synthesis.
Title: Insights into the s-process and r-process as revealed by
globular clusters
Authors: Yong, D.; Karakas, A. I.; Lambert, D. L.; Chieffi, A.;
Limongi, M.
Bibcode: 2010IAUS..265...54Y
Altcode:
We present abundance measurements for a large number of neutron-capture
elements in giant stars of the globular clusters M4, M5, and M13. The
relative abundance ratios differ between all three clusters. For all
clusters, we find that the mean abundances for the elements from
Ba to Hf can be well explained by scaled versions of the solar s-
and r-process abundances, albeit with different mixtures of s- and
r-process material for each clusters.
Title: Accurate fundamental parameters for A-, F- and G-type
Supergiants in the solar neighbourhood
Authors: Lyubimkov, Leonid S.; Lambert, David L.; Rostopchin, Sergey
I.; Rachkovskaya, Tamara M.; Poklad, Dmitry B.
Bibcode: 2010MNRAS.402.1369L
Altcode: 2009MNRAS.tmp.1881L; 2009arXiv0911.1335L
The following parameters are determined for 63 Galactic supergiants
in the solar neighbourhood: effective temperature Teff;
surface gravity logg iron abundance logɛ(Fe) microturbulent parameter
Vt; mass M/Msolar age t and distance d. A
significant improvement in the accuracy of the determination of logg,
and all parameters dependent on it, is obtained through application
of van Leeuwen rereduction of the Hipparcos parallaxes. The typical
error in the logg values is now +/-0.06dex for supergiants with
distances d < 300 pc and +/-0.12dex for supergiants with d between
300 and 700 pc; the mean error in Teff for these stars is
+/-120K. For supergiants with d > 700 pc, parallaxes are uncertain or
unmeasurable, so typical errors in their logg values are 0.2-0.3dex. A new Teff scale for A5-G5 stars of luminosity classes
Ib-II is presented. Spectral subtypes and luminosity classes of several
stars are corrected. Combining the Teff and logg with
evolutionary tracks, stellar masses and ages are determined; a majority
of the sample has masses between 4 and 15Msolar and, hence,
their progenitors were early to middle B-type main-sequence stars. Using FeII lines, which are insensitive to departures from local
thermodynamic equilibrium, the microturbulent parameter Vt
and the iron abundance logɛ(Fe) are determined from high-resolution
spectra. The parameter Vt is correlated with gravity:
Vt increases with decreasing logg. The mean iron abundance
for the 48 supergiants with distances d < 700 pc is logɛ(Fe) =
7.48 +/- 0.09, a value close to the solar value of 7.45 +/- 0.05,
and thus the local supergiants and the Sun have the same metallicity.
Title: High-resolution spectroscopy of the R Coronae Borealis and
Other Hydrogen Deficient Stars
Authors: Rao, N. Kameswara; Lambert, David L.
Bibcode: 2010ASSP...17..177R
Altcode: 2010rasp.book..177R; 2010rast.conf..177R; 2010ASSP...17..177K;
2010arXiv1002.3433K
High-resolution spectroscopy is a very important tool for studying
stellar physics, perhaps, particularly so for such enigmatic objects
like the R Coronae Borealis and related Hydrogen deficient stars that
produce carbon dust in addition to their peculiar abundances. Examples
of how high-resolution spectroscopy is used in the study of these stars
to address the two major puzzles are presented: (i) How are such rare
H-deficient stars created? and (ii) How and where are the obscuring
soot clouds produced around the R Coronae Borealis stars?
Title: Rubidium in the Interstellar Medium
Authors: Walker, Kyle M.; Federman, S. R.; Knauth, David C.; Lambert,
David L.
Bibcode: 2009ApJ...706..614W
Altcode: 2009arXiv0910.2288W
We present observations of interstellar rubidium toward o Per, ζ Per,
AE Aur, HD 147889, χ Oph, ζ Oph, and 20 Aql. Theory suggests that
stable 85Rb and long-lived 87Rb are produced
predominantly by high-mass stars, through a combination of the weak
s- and r-processes. The 85Rb/87Rb ratio was
determined from measurements of the Rb I line at 7800 Å and was
compared to the solar system meteoritic ratio of 2.59. Within 1σ
uncertainties, all directions except HD 147889 have Rb isotope
ratios consistent with the solar system value. The ratio toward
HD 147889 is much lower than the meteoritic value and similar to
that toward ρ Oph A; both lines of sight probe the Rho Ophiuchus
Molecular Cloud. The earlier result was attributed to a deficit of
r-processed 85Rb. Our larger sample suggests instead that
87Rb is enhanced in these two lines of sight. When the total
elemental abundance of Rb is compared to the K elemental abundance,
the interstellar Rb/K ratio is significantly lower than the meteoritic
ratio for all the sight lines in this study. Available interstellar
samples for other s- and r- process elements are used to help interpret
these results.
Title: The Chemical Composition of Cernis 52 (BD+31° 640)
Authors: González Hernández, J. I.; Iglesias-Groth, S.; Rebolo,
R.; García-Hernández, D. A.; Manchado, A.; Lambert, D. L.
Bibcode: 2009ApJ...706..866G
Altcode: 2009ApJ...706..866H; 2009arXiv0910.2310G
We present an abundance analysis of the star Cernis 52 in whose
spectrum we recently reported the naphthalene cation in absorption
at 6707.4 Å. This star is on a line of sight to the Perseus
molecular complex. The analysis of high-resolution spectra using a
χ2-minimization procedure and a grid of synthetic spectra provides the
stellar parameters and the abundances of O, Mg, Si, S, Ca, and Fe. The
stellar parameters of this star are found to be T eff =
8350 ± 200 K, log(g/cm s2)=4.2 ± 0.4 dex. We derived a
metallicity of [Fe/H] = -0.01 ± 0.15. These stellar parameters are
consistent with a star of ~2 M sun in a pre-main-sequence
evolutionary stage. The stellar spectrum is significantly veiled in the
spectral range λλ5150-6730 Å up to almost 55% of the total flux at
5150 Å and decreasing toward longer wavelengths. Using Johnson-Cousins
and Two Micron All Sky Survey photometric data, we determine a distance
to Cernis 52 of 231+135 -85 pc considering the
error bars of the stellar parameters. This determination places the
star at a similar distance to the young cluster IC 348. This together
with its radial velocity, vr = 13.7 ± 1 km s-1,
its proper motion and probable young age support Cernis 52 as a likely
member of IC 348. We determine a rotational velocity of vsin i =
65 ± 5 km s-1 for this star. We confirm that the stellar
resonance line of Li I at 6707.8 Å is unable to fit the broad feature
at 6707.4 Å. This feature should have a interstellar origin and could
possibly form in the dark cloud L1470 surrounding all the cluster IC
348 at about the same distance.
Title: Rb-Rich Asymptotic Giant Branch Stars in the Magellanic Clouds
Authors: García-Hernández, D. A.; Manchado, A.; Lambert, D. L.;
Plez, B.; García-Lario, P.; D'Antona, F.; Lugaro, M.; Karakas, A. I.;
van Raai, M. A.
Bibcode: 2009ApJ...705L..31G
Altcode: 2009arXiv0909.4391G
We present high-resolution (R ~ 60,000) optical spectra of a carefully
selected sample of heavily obscured and presumably massive O-rich
asymptotic giant branch (AGB) stars in the Magellanic Clouds. We
report the discovery of strong Rb I lines at 7800 Å in four Rb-rich
LMC stars at luminosities equal to or greater than the standard
adopted luminosity limit for AGB stars (M bol ~ -7.1),
confirming that "hot bottom burning" may produce a flux excess in
the more massive AGB stars. In the SMC sample, just one of the five
stars with M bol < -7.1 was detected in Rb; the other
stars may be massive red supergiants. The Rb-rich LMC AGB stars might
have stellar masses of at least ~6-7 M sun. Our abundance
analyses show that these Rb-rich stars are extremely enriched in Rb
by up to 103-105 times solar but seem to have
only mild Zr enhancements. The high Rb/Zr ratios, if real, represent a
severe problem for the s-process, even if the 22Ne source
is operational as expected for massive AGB stars; it is not possible
to synthesize copious amounts of Rb without also overproducing Zr. The
solution to the problem may lie with an incomplete present understanding
of the atmospheres of luminous AGB stars.
Title: High-resolution optical spectroscopy of a newly discovered
post-AGB star with a surprising metallicity in the globular cluster
M79
Authors: Şahin, T.; Lambert, David L.
Bibcode: 2009MNRAS.398.1730S
Altcode: 2009MNRAS.tmp.1162S; 2009arXiv0906.3706S; 2009MNRAS.tmp.1270S;
2009MNRAS.tmp.1286S
An abundance analysis based on a high-resolution spectrum is presented
for a newly discovered post-asymptotic giant branch (PAGB) star in
the globular cluster M79. The surprising result is that the iron
abundance of the star is apparently about 0.6 dex less than that of
the cluster's red giants as reported by published studies including
a recent high-resolution spectroscopic analysis by Carretta and
colleagues. Abundances relative to iron appear to be the same for
the PAGB star and the red giants for the 15 common elements. It is
suggested that the explanation for the lower abundances of the PAGB
star may be that its atmospheric structure differs from that of a
classical atmosphere; the temperature gradient may be flatter than
predicted by a classical atmosphere.
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: Isotopic Titanium Abundances in Local M Dwarfs
Authors: Chavez, Joy; Lambert, David L.
Bibcode: 2009ApJ...699.1906C
Altcode: 2009arXiv0905.2762C
Relative abundances of the five stable isotopes of titanium
(46Ti to 50Ti) are measured for 11 M dwarfs
belonging to the thin disk (four stars), thick disk (three stars),
the halo (one star), and either the thick or the thin disk (three
stars). Over the metallicity range of the sample (-1< [Fe/H] <0),
the isotopic ratios are approximately constant at the solar system
ratios. There is no discernible difference between the isotopic ratios
for thin and thick disk stars. Isotopic ratios are in fair accord
with recent calculations of Galactic chemical evolution despite the
fact that such calculations underpredict [Ti/Fe] by about 0.4 dex at
all metallicities.
Title: Ground-Based Observations of Interstellar CN and CH^+ in
Diffuse Molecular Clouds: the ^{12}C/^{13}C Ratio and the Excitation
of ^{13}CN
Authors: Ritchey, Adam M.; Federman, Steven R.; Sheffer, Yaron;
Lambert, David L.
Bibcode: 2009mss..confEWI04R
Altcode:
We present high signal-to-noise ratio observations of optical
transitions in CN and CH^+ for a number of Galactic diffuse clouds. The
data are examined to extract the ^{12}CN/^{13}CN and ^{12}CH^+/^{13}CH^+
ratios along each line of sight in order to assess predictions of
diffuse cloud chemistry. We find a weighted mean ^{12}CH^+/^{13}CH^+
ratio of 74.4 ± 7.6. This result is consistent with the average
^{12}C/^{13}C ratio of 70 ± 7 for local interstellar clouds,
confirming the theoretical expectation that ^{12}CH^+/^{13}CH^+
represents the ambient carbon isotopic ratio. Our sample includes
three sight lines for which previous studies had found much lower
values of ^{12}CH^+/^{13}CH^+ that are not confirmed here. Thus, we
find no evidence for variation in ^{12}C/^{13}C within 1 kpc of the
Sun. The 12-to-13 ratios in both CN and CO, however, show significant
fractionation away from the ambient value due to the opposing effects
of photodissociation and charge exchange reactions. Our ^{12}CN/^{13}CN
measurements are combined with determinations of ^{12}CO/^{13}CO from
the literature to enable a detailed analysis of the effects of chemical
fractionation in diffuse molecular clouds. We find suggestive evidence
for an inverse relationship between ^{12}CN/^{13}CN and ^{12}CO/^{13}CO,
resulting from the physical association of CN and CO in the cores of the
clouds. Additionally, the isotopologic ratios examined here suggest that
about 20 percent of C is locked up in CO in typical diffuse cloud cores,
while up to 85 percent may reside in CO in the central portions of the
Ophiuchus diffuse clouds. Finally, we examine rotational excitation
temperatures in both ^{12}CN and ^{13}CN. Our weighted mean value of
T_{01}(^{12}CN) = 2.754 ± 0.002 K implies an excess over the cosmic
microwave background (CMB) of only 29 ± 3 mK, considerably smaller
than some recent surveys have suggested. This modest excess can be
accounted for if collisional excitation by electrons is occurring
locally in some clouds, with derived electron densities of n_{e} = 0.1
- 0.5 cm^{-3}. Yet, given the dispersion of 134 mK in our individual
T_{01} measurements, the excess may not be physical. There is some
indication of a greater excess in T_{12}(^{12}CN) based on our weighted
mean of 2.847 ± 0.014 K, but the dispersion in these measurements is
also greater (259 mK). The rotational excitation temperature observed
in ^{13}CN, via the R(0), R(1), and P(1) lines, shows no excess over
the CMB.
Title: Ground-based Observations Of Interstellar CN And CH+
In Diffuse Molecular Clouds: 12C/13C Ratios
And CN Excitation
Authors: Federman, Steven Robert; Ritchey, A. M.; Sheffer, Y.; Lambert,
D. L.
Bibcode: 2009AAS...21442503F
Altcode:
We present high-resolution observations of optical transitions
in CN and CH+ for a number of Galactic diffuse
clouds. We extract the 12CN/13CN and
12CH+/13CH+
ratios along each direction in order to assess predictions
of diffuse cloud chemistry. We find a weighted mean
12CH+/13CH+ ratio
of 74.4 ± 7.6. This result is consistent with the average
12C/13C ratio of 70 ± 7 for local
interstellar clouds and confirms theoretical expectations
that 12CH+/13CH+
represents the ambient carbon isotopic ratio. Thus, we find no
evidence for variation in 12C/13C within 1
kpc of the Sun. The isotopologic ratios in CN and CO, however,
show significant fractionation away from the ambient value due
to the opposing effects of photodissociation and charge exchange
reactions. Our 12CN/13CN measurements are
combined with 12CO/13CO ratios from the
literature to study the effects of chemical fractionation in diffuse
molecular clouds. We find evidence for an inverse relationship between
12CN/13CN and 12CO/13CO,
resulting from the physical association of CN and CO in these cloud
cores. The isotopologic ratios suggest that about 20 percent of C
is locked up in CO in typical cores. Finally, we examine rotational
excitation temperatures in 12CN and 13CN. Our
weighted mean value of T01(12CN) = 2.754 ±
0.002 K implies an excess over the cosmic microwave background
(CMB) of only 29 ± 3 mK, considerably smaller than some recent
surveys suggested. This modest excess likely arises from collisional
excitation by electrons occurring locally in some clouds, with electron
densities of 0.1 to 0.5 cm-3. Given the dispersion of
134 mK in our individual T01 measurements, the excess
may not be physical. There is some indication of a greater excess
in T12(12CN), but the dispersion in these
measurements is also greater (259 mK). The rotational excitation
temperature observed in 13CN shows no excess over the CMB.
Title: CNO Abundances of Hydrogen-Deficient Carbon and R Coronae
Borealis Stars: A View of the Nucleosynthesis in a White Dwarf Merger
Authors: García-Hernández, D. A.; Hinkle, K. H.; Lambert, David. L.;
Eriksson, K.
Bibcode: 2009ApJ...696.1733G
Altcode: 2009arXiv0901.3667G
We present high-resolution (R ~ 50, 000) observations of near-IR
transitions of CO and CN of the five known hydrogen-deficient carbon
(HdC) stars and four R Coronae Borealis (RCB) stars. We perform an
abundance analysis of these stars by using spectrum synthesis and
state-of-the-art MARCS model atmospheres for cool hydrogen-deficient
stars. Our analysis confirms reports by Clayton and colleagues
that those HdC stars exhibiting CO lines in their spectrum and the
cool RCB star S Aps are strongly enriched in 18O (with
16O/18O ratios ranging from 0.3 to 16). Nitrogen
and carbon are in the form of 14N and 12C,
respectively. Elemental abundances for CNO are obtained from C I,
C2, CN, and CO lines. Difficulties in deriving the carbon
abundance are discussed. Abundances of Na from Na I lines and S from
S I lines are obtained. Elemental and isotopic CNO abundances suggest
that HdC and RCB stars may be related objects, and that they probably
formed from a merger of an He white dwarf with a C-O white dwarf.
Title: Searching for the metal-weak thick disc in the solar
neighbourhood
Authors: Reddy, B. E.; Lambert, D. L.
Bibcode: 2009IAUS..254P..59R
Altcode:
No abstract at ADS
Title: Frontier Science and Adaptive Optics On Existing and Next
Generation Telescopes
Authors: Frogel, Jay A.; Alcock, Charles; Bolte, Michael; Freedman,
Wendy; Kudritzki, Rolf-Peter; Kulkarni, Shri; Lambert, David; Martin,
Pierre; Silva, David; Smith, William; Strittmatter, Peter
Bibcode: 2009astro2010P..16F
Altcode:
No abstract at ADS
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: VizieR Online Data Catalog: Li abundances for 81 F dwarfs
(Lambert+, 1991)
Authors: Lambert, D. L.; Heath, J. E.; Edvardsson, B.
Bibcode: 2009yCat..72530610L
Altcode:
All observations where made at the W.J. McDonald Observatory with the
coude spectrographs of the 2.1m and 2.7m reflectors. (1 data file).
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: Granulation in K-type dwarf stars. I. Spectroscopic
observations
Authors: Ramírez, I.; Allende Prieto, C.; Lambert, D. L.
Bibcode: 2008A&A...492..841R
Altcode: 2008arXiv0810.5247R
Aims: We seek to detect and quantify the effects of surface
convection (granulation) on the line spectra of K-dwarfs as a first
step towards a rigorous testing of hydrodynamic models for their
atmospheres.
Methods: Very high-resolution (R≃160 000-210
000), high signal-to-noise ratio (S/N⪆300) spectra of nine bright
K-dwarfs were obtained with the 2dcoudé spectrograph on the 2.7 m
telescope at McDonald Observatory to determine wavelength shifts and
asymmetries of Fe i lines. Spectra of the same stars acquired with the
High Resolution Spectrograph (R≃120,000) on the 9.2 m Hobby Eberly
Telescope were used as radial velocity templates to calibrate the
wavelength scale of the 2dcoudé spectra.
Results: The observed
shapes and positions of Fe i lines reveal asymmetries and wavelength
shifts that indicate the presence of granulation. In particular, line
bisectors show characteristic C-shapes while line core wavelengths are
blueshifted by an amount that increases with decreasing equivalent
width (EW). On average, Fe i line bisectors have a span that ranges
from nearly 0 for the weakest lines (residual core flux ⪆0.7) to
about 75 m s-1 for the strongest lines (residual core flux
≃0.3), while wavelength shifts range from about -150 m s-1
in the weakest (EW≃10 mÅ) lines to 0 in the strongest (EW⪆100 mÅ)
features. A more detailed inspection of the bisectors and wavelength
shifts reveals star-to-star differences that are likely associated
with differences in stellar parameters, projected rotational velocity,
and stellar activity. While the first two are understood and confirmed
by our data, the relation to stellar activity, which is based on our
finding that the largest departures from the expected behavior are
seen in the most active stars, requires further investigation. For
the inactive, slow projected rotational velocity stars, we detect,
unequivocally, a plateau in the line-shifts at high EW values (EW⪆100
mÅ), a behavior that had been identified before only in the solar
spectrum. The detection of this plateau allows us to determine the
zero point of the convective blueshifts, which is useful to determine
absolute radial velocities. Thus, we are able to measure such velocities
with a mean uncertainty of about 60 m s-1 for four of our
sample stars.
Title: Heavy Element Abundances in Giant Stars of the Globular
Clusters M4 and M5
Authors: Yong, David; Karakas, Amanda I.; Lambert, David L.; Chieffi,
Alessandro; Limongi, Marco
Bibcode: 2008ApJ...689.1031Y
Altcode: 2008arXiv0808.2505Y
We present a comprehensive abundance analysis of 27 heavy elements
in bright giant stars of the globular clusters M4 and M5 based on
high-resolution, high signal-to-noise ratio spectra obtained with the
Magellan Clay Telescope. We confirm and expand on previous results
for these clusters by showing that (1) all elements heavier than,
and including, Si have constant abundances within each cluster, (2)
the elements from Ca to Ni have indistinguishable compositions in M4
and M5, (3) Si, Cu, Zn, and all s-process elements are approximately
0.3 dex overabundant in M4 relative to M5, and (4) the r-process
elements Sm, Eu, Gd, and Th are slightly overabundant in M5 relative
to M4. The cluster-to-cluster abundance differences for Cu and Zn are
intriguing, especially in light of their uncertain nucleosynthetic
origins. We confirm that stars other than Type Ia supernovae must
produce significant amounts of Cu and Zn at or below the clusters'
metallicities. If intermediate-mass AGB stars or massive stars are
responsible for the Cu and Zn enhancements in M4, the similar [Rb/Zr]
ratios and (preliminary) Mg isotope ratios in both clusters may be
problematic for either scenario. For the elements from Ba to Hf, we
assume that the s- and r-process contributions are scaled versions
of the solar s- and r-process abundances. We quantify the relative
fractions of s- and r-process material for each cluster and show that
they provide an excellent fit to the observed abundances. Based
on observations made with the Magellan Clay Telescope at Las Campanas
Observatory.
Title: Bengt Gustafsson's stellar journey
Authors: Lambert, D. L.
Bibcode: 2008PhST..133a4001L
Altcode:
This essay celebrates Bengt Gustafsson's 65th birthday by commenting
on a selection of Bengt's many significant papers on topics in stellar
astrophysics.
Title: The evolution of carbon, sulphur and titanium isotopes from
high redshift to the local Universe
Authors: Hughes, G. L.; Gibson, B. K.; Carigi, L.; Sánchez-Blázquez,
P.; Chavez, J. M.; Lambert, D. L.
Bibcode: 2008MNRAS.390.1710H
Altcode: 2008MNRAS.tmp.1117H; 2008arXiv0808.3111H
Recent observations of carbon, sulphur and titanium isotopes at
redshifts z~1 and in the local stellar disc and halo have opened a new
window into the study of isotopic abundance patterns and the origin
of the chemical elements. Using our Galactic chemical evolution code
GETOOL, we have examined the evolution of these isotopes within the
framework of a Milky Way-like system. We have three aims in this work:
first, to test the claim that novae are required, in order to explain
the carbon isotope patterns in the Milky Way; secondly, to test the
claim that sulphur isotope patterns at high redshift require an initial
mass function (IMF) biased towards massive stars; and thirdly, to test
extant chemical evolution models against new observations of titanium
isotopes that suggest an anti-correlation between trace-to-dominant
isotopes with metallicity. Based upon our dual-infall galactic chemical
evolution modelling of a Milky Way-like system and the subsequent
comparison with these new and unique data sets, we conclude the
following: novae are not required to understand the evolution
of 12C/13C in the solar neighbourhood;
a massive star-biased IMF is consistent with the low ratios of
12C/13C and 32S/34S seen
in one high-redshift late-type spiral, but the consequent super-solar
metallicity prediction for the interstellar medium in this system seems
highly unlikely; and deficient isotopes of titanium are predicted to
correlate positively with metallicity, in apparent disagreement with
the new data sets; if confirmed, classical chemical evolution models
of the Milky Way (and the associated supernovae nucleosynthetic yields)
may need a substantial overhaul to be made consistent.
Title: The SEGUE Stellar Parameter Pipeline. III. Comparison with
High-Resolution Spectroscopy of SDSS/SEGUE Field Stars
Authors: Allende Prieto, Carlos; Sivarani, Thirupathi; Beers,
Timothy C.; Lee, Young Sun; Koesterke, Lars; Shetrone, Matthew;
Sneden, Christopher; Lambert, David L.; Wilhelm, Ronald; Rockosi,
Constance M.; Lai, David K.; Yanny, Brian; Ivans, Inese I.; Johnson,
Jennifer A.; Aoki, Wako; Bailer-Jones, Coryn A. L.; Re Fiorentin, Paola
Bibcode: 2008AJ....136.2070A
Altcode: 2007arXiv0710.5780A
We report high-resolution spectroscopy of 125 field stars previously
observed as part of the Sloan Digital Sky Survey and its program for
Galactic studies, the Sloan Extension for Galactic Understanding
and Exploration (SEGUE). These spectra are used to measure radial
velocities and to derive atmospheric parameters, which we compare with
those reported by the SEGUE Stellar Parameter Pipeline (SSPP). The SSPP
obtains estimates of these quantities based on SDSS ugriz photometry and
low-resolution (R ~ 2000) spectroscopy. For F- and G-type stars observed
with high signal-to-noise ratios (S/Ns), we empirically determine
the typical random uncertainties in the radial velocities, effective
temperatures, surface gravities, and metallicities delivered by the SSPP
to be 2.4 km s-1, 130 K (2.2 %), 0.21 dex, and 0.11 dex,
respectively, with systematic uncertainties of a similar magnitude
in the effective temperatures and metallicities. We estimate random
errors for lower S/N based on numerical simulations. Based on
observations obtained with the Hobby-Eberly Telescope (a joint project
of the University of Texas at Austin, Pennsylvania State University,
Stanford University, Ludwig-Maximilians-Universität München, and
Georg-August-Universität Göttingen), the W. M. Keck Observatory
(operated as a scientific partnership among the California Institute
of Technology, the University of California and NASA), and the Subaru
Telescope (operated by the National Astronomical Observatory of Japan).
Title: Searching for the metal-weak thick disc in the solar
neighbourhood
Authors: Reddy, Bacham E.; Lambert, David L.
Bibcode: 2008MNRAS.391...95R
Altcode: 2008arXiv0809.0966R; 2008MNRAS.tmp.1207R
An abundance analysis is presented of 60 metal-poor stars drawn from
catalogues of nearby stars provided by Arifyanto et al. and Schuster
et al. In an attempt to isolate a sample of metal-weak thick disc
stars, we applied the kinematic criteria Vrot >=
100kms-1,|ULSR| <= 140kms-1
(LSR - local standard of rest) and |WLSR| <=
100kms-1. 14 stars satisfying these criteria and having
[Fe/H] <= -1.0 are included in the sample of 60 stars. Eight of the
14 have [Fe/H] >= -1.3 and may be simply thick disc stars of slightly
lower than average [Fe/H]. The other six have [Fe/H] from -1.3 to -2.3
and are either metal-weak thick disc stars or halo stars with kinematics
mimicking those of the thick disc. The sample of 60 stars is completed
by eight thick disc stars, 20 stars of a hybrid nature (halo or thick
disc stars) and 18 stars with kinematics distinctive of the halo.
Title: Ultraviolet Survey of CO and H2 in Diffuse Molecular
Clouds: The Reflection of Two Photochemistry Regimes in Abundance
Relationships
Authors: Sheffer, Y.; Rogers, M.; Federman, S. R.; Abel, N. P.;
Gredel, R.; Lambert, D. L.; Shaw, G.
Bibcode: 2008ApJ...687.1075S
Altcode: 2008arXiv0807.0940S
We carried out a comprehensive far-UV survey of 12CO and
H2 column densities along diffuse molecular Galactic sight
lines. This sample includes new measurements of CO from HST spectra
along 62 sight lines and new measurements of H2 from FUSE
data along 58 sight lines. In addition, high-resolution optical data
were obtained at the McDonald and European Southern Observatories,
yielding new abundances for CH, CH+, and CN along 42 sight
lines to aid in interpreting the CO results. These new sight lines were
selected according to detectable amounts of CO in their spectra and
provide information on both lower density (<=100 cm-3)
and higher density diffuse clouds. A plot of log N(CO) versus log
N(H2) shows that two power-law relationships are needed for
a good fit of the entire sample, with a break located at log N(CO ,
cm -2) = 14.1 and log N(H2) = 20.4, corresponding
to a change in production route for CO in higher density gas. Similar
logarithmic plots among all five diatomic molecules reveal additional
examples of dual slopes in the cases of CO versus CH (break at log
N = 14.1, 13.0), CH+ versus H2 (13.1, 20.3),
and CH+ versus CO (13.2, 14.1). We employ both analytical
and numerical chemical schemes in order to derive details of the
molecular environments. In the denser gas, where C2 and CN
molecules also reside, reactions involving C+ and OH are the
dominant factor leading to CO formation via equilibrium chemistry. In
the low-density gas, where equilibrium chemistry studies have failed
to reproduce the abundance of CH+, our numerical analysis
shows that nonequilibrium chemistry must be employed for correctly
predicting the abundances of both CH+ and CO.
Title: Evidence for the Naphthalene Cation in a Region of the
Interstellar Medium with Anomalous Microwave Emission
Authors: Iglesias-Groth, S.; Manchado, A.; García-Hernández, D. A.;
González Hernández, J. I.; Lambert, D. L.
Bibcode: 2008ApJ...685L..55I
Altcode: 2008arXiv0809.0778I
We report high-resolution spectroscopy of the moderately reddened
(AV = 3) early-type star Cernis 52 located in a region of the
Perseus molecular cloud complex with anomalous microwave emission. In
addition to the presence of the most common diffuse interstellar
bands (DIBs) we detect two new interstellar or circumstellar bands
coincident to within 0.01% in wavelength with the two strongest bands
of the naphthalene cation (C10H8+)
as measured in gas-phase laboratory spectroscopy at low temperatures
and find marginal evidence for the third strongest band. Assuming
these features are caused by the naphthalene cation, from the measured
intensity and available oscillator strengths we find that 0.008% of the
carbon in the cloud could be in the form of this molecule. We expect
hydrogen additions to cause hydronaphthalene cations to be abundant
in the cloud and to contribute via electric dipole radiation to the
anomalous microwave emission. The identification of new interstellar
features consistent with transitions of the simplest polycyclic
aromatic hydrocarbon adds support to the hypothesis that this type
of molecules are the carriers of both diffuse interstellar bands and
anomalous microwave emission.
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: Fluorine in R Coronae Borealis Stars
Authors: Pandey, G.; Lambert, D. L.; Rao, N. K.
Bibcode: 2008ASPC..391...35P
Altcode:
Neutral fluorine (F I) lines are identified in the optical spectra
of several R Coronae Borealis stars (RCBs) at maximum light. These
lines provide the first measurement of the fluorine abundance in
these stars. Fluorine is enriched in some RCBs by factors of 800 to
8000 relative to its likely initial abundance. The overabundances of
fluorine are evidence for the synthesis of fluorine. These results are
discussed in the light of the scenario that RCBs are formed by accretion
of an He white dwarf by a C-O white dwarf. Sakurai's object (V4334 Sgr),
a final He-shell flash product, shows no detectable F I lines.
Title: An Eclectic Look at Stellar Compositions
Authors: Lambert, D. L.
Bibcode: 2008ASPC..390..517L
Altcode:
Much effort in stellar spectroscopy is devoted to abundance analyses
of stars which satisfy exactly or broadly the hypothesis that the
composition of the stellar atmosphere is that of the star's natal
cloud. Studies of Galactic chemical evolution, for example, exploit
this hypothesis. This essay, on the contrary, discusses stars for which
the hypothesis demonstrably fails because either the star since birth
has gained products of nucleosynthesis or other than nuclear processes
have operated to change the composition of the atmosphere. This eclectic
look comments on diffusion in HgMn stars and in residents of the Spite
plateau, the H-deficient cool carbon (HdC) stars, and diverse stars
considered to be affected by dust-gas winnowing.
Title: Center-to-Limb Variation of Solar Three-dimensional
Hydrodynamical Simulations
Authors: Koesterke, L.; Allende Prieto, C.; Lambert, D. L.
Bibcode: 2008ApJ...680..764K
Altcode: 2008arXiv0802.2177K
We examine closely the solar center-to-limb variation of continua
and lines and compare observations with predictions from both a
three-dimensional (3D) hydrodynamic simulation of the solar surface
(provided by M. Asplund and collaborators) and one-dimensional (1D)
model atmospheres. Intensities from the 3D time series are derived by
means of the new synthesis code ASSepsilonT, which overcomes limitations
of previously available codes by including a consistent treatment of
scattering and allowing for arbitrarily complex line and continuum
opacities. In the continuum, we find very similar discrepancies between
synthesis and observation for both types of model atmospheres. This
is in contrast to previous studies that used a "horizontal" and
time-averaged representation of the 3D model and found a significantly
larger disagreement with observations. The presence of temperature and
velocity fields in the 3D simulation provides a significant advantage
when it comes to reproducing solar spectral line shapes. Nonetheless,
a comparison of observed and synthetic equivalent widths reveals that
the 3D model also predicts more uniform abundances as a function
of position angle on the disk. We conclude that the 3D simulation
provides not only a more realistic description of the gas dynamics,
but despite its simplified treatment of the radiation transport, it
also predicts reasonably well the observed center-to-limb variation,
which is indicative of a thermal structure free from significant
systematic errors.
Title: Ultraviolet Survey Of
12C16O/13C16O And
12C16O/H2 In Diffuse Molecular Clouds
Authors: Sheffer, Yaron; Rogers, M.; Federman, S. R.; Lambert, D. L.;
Gredel, R.; Abel, N. P.; Shaw, G.
Bibcode: 2008AAS...212.0505S
Altcode: 2008BAAS...40Q.195S
We analyzed archival HST/STIS and FUSE data to extract column
densities of 12CO, 13CO, and H2
along all diffuse molecular sight lines that show evidence of
CO absorption. High-resolution spectra of CH+, CH,
and CN acquired at McDonald Observatory and ESO expanded the
database of results on these species as an aid in interpreting
the UV measurements. The average value of the 12-to-13 carbon
ratio in the solar neighborhood is known to be 70 ± 7 from radio
observations of CO emission and from optical determinations of
the 12CH+/13CH+
ratio. We find that most (17 of 25) sight lines have
12CO/13CO ratios consistent with 12/13 = 70,
with the rest showing significant fractionation. Of the latter, 5
directions have lower 12CO/13CO ratios, which
can be attributed to charge exchange between 12CO and
13C+, while 3 sight lines have higher ratios
due to selective photodissociation effected by self shielding of
12CO. A comparison of 12CO and H2
column densities shows the dependence of the CO/H2 ratio
on physical conditions, notably total gas density. We find that the
CN/CH+ ratio is better than CN/CH as a tracer of total
gas density, owing to the preferential formation of CH+
and CN in lower- or higher-density clouds, respectively. We use both
analytical CN chemistry and numerical modeling with CLOUDY to infer
that many of our sight lines belong to a low-density regime of diffuse
molecular gas, where non-equilibrium chemistry is needed for correctly
predicting CH+ and CO abundances.
Title: Rubidium in the Interstellar Medium
Authors: Walker, Kyle M.; Federman, S. R.; Knauth, D. C.; Lambert,
D. L.
Bibcode: 2008AAS...212.0503W
Altcode: 2008BAAS...40..194W
We present high-resolution observations of interstellar rubidium
toward ο Per, ζ Per, AE Aur, HD 147889, χ Oph, ζ Oph, and 20
Aql to obtain the 85Rb/87Rb isotope ratio
in each direction. Both the stable 85Rb and long-lived
87Rb isotopes are created through the neutron capture s-
and r- processes. Theoretical predictions indicate that 85Rb
is mainly an r-process nuclide, whereas 87Rb is produced
mainly through the s-process. The Rb I line at 7800 Angstroms is
the focus of our study on rubidium in diffuse interstellar gas. The
85Rb/87Rb ratio was compared to the Solar
System meteoritic ratio of 2.59. The ratio toward HD 147889 is much
lower than the meteoritic value, but consistent with the low ratio
toward ρ Oph A measured previously. We attribute these results to a
deficit of r-processed 85Rb in the Rho Ophiuchus Molecular
Cloud. Within the mutual uncertainties, all other lines of sight are
consistent with the ratio for the Solar System.
Title: s-Process Abundances in Globular Clusters: M4 vs. M5 and
NGC 1851
Authors: Yong, David; Grundahl, Frank; Karakas, Amanda; Lambert,
David L.
Bibcode: 2008AIPC.1001..226Y
Altcode:
We present s-process abundances for giant stars in the globular
clusters M4, M5, and NGC 1851. We find that all s-process elements are
overabundant in M4 relative to M5. Curiously, the abundances of Cu and
Zn are also overabundant in M4 which may offer clues to the synthesis
of these elements. For NGC 1851, we find that the abundances of the
s-process elements Zr and La exhibit a large dispersion. The abundances
of Zr and La also appear to have a bimodal distribution reinforcing
the idea that there are two stellar populations in this cluster.
Title: Could the Ultra-Metal-Poor Stars be Chemically Peculiar and
Not Related to the First Stars?
Authors: Venn, K. A.; Lambert, David L.
Bibcode: 2008ApJ...677..572V
Altcode: 2008arXiv0801.0752V
Chemically peculiar stars define a class of stars that show unusual
elemental abundances due to stellar photospheric effects and not due
to natal variations. In this paper, we compare the elemental abundance
patterns of the ultra-metal-poor stars with metallicities [ Fe/H ] ~
- 5 to those of a subclass of chemically peculiar stars. These include
post-AGB stars, RV Tauri variable stars, and the Lambda Bootis stars,
which range in mass, age, binarity, and evolutionary status, yet can
have iron abundance determinations as low as [ Fe/H ] ~ - 5. These
chemical peculiarities are interpreted as due to the separation of
gas and dust beyond the stellar surface, followed by the accretion of
dust-depleted gas. Contrary to this, the elemental abundances in the
ultra-metal-poor stars are thought to represent yields of the most
metal-poor supernovae and, therefore, observationally constrain the
earliest stages of chemical evolution in the universe. Detailed chemical
abundances are now available for HE 1327-2326 and HE 0107-5240, the two
extreme ultra-metal-poor stars in our Galaxy, and for HE 0557-4840,
another ultra-metal-poor star found by the Hamburg/ESO survey. There
are interesting similarities in their abundance ratios to those of
the chemically peculiar stars; e.g., the abundances of the elements
in their photospheres are related to the condensation temperature of
that element. If these three stars are chemically peculiar, then their
CNO abundances suggest true metallicities of [ X/H ] ~ - 2 to -4. It
is important to establish the nature of these stars, since they are
used as tests of the early chemical evolution of the Galaxy.
Title: Dust in R Coronae Borealis stars
Authors: Lambert, David; Rao, N. Kameswara; Garcia-Hernandez, D. A.
Bibcode: 2008sptz.prop50212L
Altcode:
R Coronae Borealis stars (RCBs) provide an unique circumstellar
environment that is hydrogen-deficient, helium-rich and carbon-rich in
which dust condensation occurs. Litle is known about how and where the
dust condensation process, compositions of the dust, and the trigger
for dust formation. The hydrogen-poor carbon-rich and metal-poor (in
some cases) character of the gas may facilitate the formation of dust
species which are not seen in the interstellar medium or in envelopes
of normal stars. Spitzer/IRS spectroscopy offers a great opportunity
to characterize the infrared spectra of RCBs. Surprisingly, Spitzer
has not systematically observed a complete sample of RCB stars in the
previous four cycles and, thus, a comprehensive study of these dusty and
fascinating stars is at present lacking. Completely inadequate spectra
have been obtained from ground-based telescopes, even after nearly four
decades since the discovery of the IR excess of RCB stars. We propose
to obtain a library of Spitzer/IRS spectra of 18 RCB stars. Our goal
is to observe stars across the chemical composition range observed
in RCBs and to extend observations to the coolest RCB stars. These
spectra will be complemented with the existing Spitzer/IRS spectra of 12
warmer RCB stars, creating a complete sample of 30 RCBs observed with
Spitzer. Present knowledge of the dust features in RCBs depends on our
previous ISO spectra of the 3 brightest RCB stars in the 3 to 25 micron
region. A representative inventory of infrared spectra and dust features
in our complete sample of RCB stars will provide important clues to
the composition and dust formation process in these unique stars.
Title: High-resolution spectroscopy of the R Coronae Borealis star
V Coronae Australis
Authors: Rao, N. Kameswara; Lambert, David L.
Bibcode: 2008MNRAS.384..477R
Altcode: 2007arXiv0710.5030K; 2008MNRAS.tmp...38R
Optical high-resolution spectra of the R Coronae Borealis star V CrA
at light maximum and during minimum light are discussed. Abundance
analysis confirms previous results showing that V CrA has the
composition of the small subclass of R Coronae Borealis (RCB) stars
know as `minority' RCBs, i.e. the Si/Fe and S/Fe ratios are 100 times
their solar values. A notable novel result for RCBs is the detection of
the 1-0 Swan system 12C13C bandhead indicating
that 13C is abundant: spectrum synthesis shows that
12C/13C is about 3-4. Absorption-line profiles
are variable at maximum light with some lines showing evidence of
splitting by about 10 kms-1. A spectrum obtained as the
star was recovering from a deep minimum shows the presence of cool
C2 molecules with a rotational temperature of about 1200K,
a temperature suggestive of gas in which carbon is condensing into
soot. The presence of rapidly outflowing gas is shown by blueshifted
absorption components of the NaI D and KI 7698 Å resonance lines. Based on observations obtained with (1) The Blanco 4-m Telescope at
the Cerro Tololo Inter-American Observatory, which is operated by AURA,
Inc., under contract to the National Science Foundation of USA and
(2) The Harlan J. Smith Telescope of the W. J. McDonald Observatory
of the University of Texas at Austin. E-mail: nkrao@iiap.res.in
Title: Rubidium and Lead Abundances in Giant Stars of the Globular
Clusters M4 and M5
Authors: Yong, David; Lambert, David L.; Paulson, Diane B.; Carney,
Bruce W.
Bibcode: 2008ApJ...673..854Y
Altcode: 2007arXiv0710.2367Y
We present measurements of the neutron-capture elements Rb and Pb for
bright giants in the globular clusters M4 and M5. The clusters are of
similar metallicity ([Fe/H] simeq - 1.2) , but M4 is decidedly s-process
enriched relative to M5: [Ba/Fe] = + 0.6 for M4 but 0.0 for M5. The
Rb and Pb abundances were derived by comparing synthetic spectra with
high-resolution, high signal-to-noise ratio spectra obtained with MIKE
on the Magellan Telescope. Abundances of Y, Zr, La, and Eu were also
obtained. In M4, the mean abundances from 12 giants are [Rb/Fe] = 0.39
+/- 0.02 (σ = 0.07), [Rb/Zr] = 0.17 +/- 0.03 (σ = 0.08), and [Pb/Fe]
= 0.30 +/- 0.02 (σ = 0.07). In M5, the mean abundances from two giants
are [Rb/Fe] = 0.00 +/- 0.05 (σ = 0.06), [Rb/Zr] = 0.08 +/- 0.08 (σ =
0.11), and [Pb/Fe] = - 0.35 +/- 0.02 (σ = 0.04). Within the measurement
uncertainties, the abundance ratios [Rb/Fe], [Pb/Fe], and [Rb/X] for
X = Y, Zr, and La are constant from star to star in each cluster, and
none of these ratios are correlated with O or Na abundances. While M4
has a higher Rb abundance than M5, the ratios [Rb/X] are similar in
both clusters, indicating that the nature of the s-products is very
similar for each cluster but the gas from which M4's stars formed had
a higher concentration of these products. Based on observations
made with the Magellan Clay Telescope at Las Campanas Observatory.
Title: Fluorine in R Coronae Borealis Stars
Authors: Pandey, Gajendra; Lambert, David L.; Kameswara Rao, N.
Bibcode: 2008ApJ...674.1068P
Altcode: 2007arXiv0711.2363P
Neutral fluorine (F I) lines are identified in the optical spectra
of several R Coronae Borealis stars (RCBs) at maximum light. These
lines provide the first measurement of the fluorine abundance in these
stars. Fluorine is enriched in some RCBs by factors of 800-8000 relative
to its likely initial abundance. The overabundances of fluorine are
evidence for the synthesis of fluorine. These results are discussed
in the light of the scenario that RCBs are formed by accretion of an
He white dwarf by a C-O white dwarf. Sakurai's object (V4334 Sgr),
a final He-shell flash product, shows no detectable F I lines.
Title: Do R Coronae Borealis stars evolve from white dwarf mergers?
Authors: Lambert, David L.; Kameswara Rao, N.; Hinkle, Kenneth H.;
Garcia-Hernandez, D. A.; Eriksson, Kjell
Bibcode: 2008noao.prop..316L
Altcode:
Phoenix spectra of C_2, CN and CO lines will provide oxygen isotopic
abundance ratios (^16O/^17O/^18O) and CNO abundances for cool R Coronae
Borealis (RCB) stars. The ratios, especially the ^16O/^18O ratio, will
be used to test the two leading scenarios for RCB production. These
observations were prompted by Clayton et al.'s striking discovery of
low ^16O/^18O (<1) ratios for H-deficient carbon (HdC) stars. This
ratio requires the formation of HdC stars by the merger of two white
dwarfs as some ^14N is burnt to ^18O. The HdC are possible immediate
relatives of the RCBs. Yet, our Phoenix observations of the cool RCB
S Aps give a higher ratio (^16O/^18O=16) than for the HdCs perhaps
questioning a direct evolutionary connection between HdC and RCB
stars. Also, our Phoenix CNO abundance analysis of HdCs shows the ^14N
to ^18O conversion is far from complete. In this proposal, we seek to
extend our CNO elemental and isotopic abundance analyses from one RCB
to several in order to explore the evolutionary connection between HdC
and RCB stars and to constrain the nucleosynthesis that occurs during
the cannibalism of a He white dwarf by a C-O white dwarf.
Title: Further spectroscopic studies of FIP effect in semi-regular
and RV Tauri stars
Authors: Kameswara Rao, N.; Reddy, Eswar; Lambert, D. L.
Bibcode: 2008BASIP..25...53K
Altcode: 2008BASI...25S..53K
Rao and Reddy (2005) have earlier showed that the surface elemental
abundances (deficiencies) in RV Tauri stars CE Vir and EQ Cas are
related to the First Ionization Potential (FIP) of the element. Thus
suggesting that elemental abundances are probably controlled by magnetic
fields such that the stellar winds remove the elements that could get
easily ionized by the stellar radiation field. Both CE Vir and EQ Cas
have Teff close to 4200 K and might evolve into hotter RV Tauri (B)
type stars. We intiated a systematic survey of RV Tauri and semiregular
variables brighter than 10.5 with VBT echelle to investigate (i)
what sort of stars would show FIP effect, is it confined to selected
temperature range (around 4000 K)? (ii) Is the effect seen during full
pulsation cycle? How similar is the magnetically controlled stellar
wind to the solar wind? Do these stars possess chromospheres, similar
to sun? We found few other stars that show FIP effect e.g. V Pyx being
one of them. We discuss these abundance patterns.
Title: Emission lines in high resolution spectra of EHe stars
Authors: Pandey, Gajendra; Kameswara Rao, N.; Lambert, D. L.
Bibcode: 2008BASIP..25Q..55P
Altcode: 2008BASI...25Q..55P
The hydrogen-poor stars whose origins and evolution are not yet
understood include hydrogen-deficient carbon stars (HdC), R CrB stars,
Extreme helium (EHe) stars, He-rich sdOs, H-poor central stars of PN
([WC]), and non DA-white dwarfs. Three scenarios are predicted for
the formation of R CrBs/EHes/[WC] stars; fist: involving a merger of
two white dwarfs (DD), second: a He-shell flash in a post-AGB star,
and the third: close-binary evolution. The theory of stellar evolution
predicts that about one-third of all white dwarfs which are of the
non DA variety are the result of either DD scenario or final He-shell
flash scenario making R CrBs/EHes/[WC] stars, an important segment of
mainstream stellar evolution. Most of the EHes show absorption line
spectra except for the hot R CrBs and [WC] stars which show emission
lines. The hot EHes showing emissions overlap with [WC] stars and
the cool EHes with R CrBs in their effective temperatures. We have
obtained high resolution spectra of couple of EHes and R CrBs, to
search for the presence of emission lines to determine the mass-loss
rates and to test the evolutionary connections with [WC] stars
and/or He-rich sdOs. The spectra are from VBT echelle spectrometer
and McDonald. Surface composition of EHes show C/He about 0.01 (by
number) similar to He-rich sdOs, whereas [WC] stars show C/He about 1
(by number). If EHes are to become [WC] stars they have to lose mass
and alter their surface composition.
Title: Fluorine abundances in R CrB and EHe stars
Authors: Pandey, Gajendra; Kameswara Rao, N.; Lambert, D. L.
Bibcode: 2008BASIP..25R..55P
Altcode: 2008BASI...25R..55P
Neutral fluorine lines are identified in the spectra of warm R CrB
stars and cool EHe stars obtained from VBT echelle spectrometer and
McDonald. The overabundance of fluorine in these H-deficient stars
gives us clues to their origin and evolutionary connection. Synthesis
of fluorine is discussed in the light of single-star evolution,
close-binary evolution, and double-degenerate mergers that results in
H-deficiency in these stars.
Title: An abundance survey of the Galactic thick disk
Authors: Reddy, B. E.; Lambert, D. L.; Allende Prieto, C.
Bibcode: 2008mru..conf...69R
Altcode:
No abstract at ADS
Title: Fluorine in R Coronae Borealis and Extreme Helium Stars
Authors: Pandey, Gajendra; Lambert, David L.; Kameswara Rao, N.
Bibcode: 2007arXiv0712.3971P
Altcode:
Neutral fluorine lines are identified in the optical spectra of several
R Coronae Borealis stars (RCBs) at maximum light. These lines provide
the first measurement of the fluorine abundance in these stars. Fluorine
is enriched in some RCBs by factors of 800 to 8000 relative to its
likely initial abundance. The overabundances of fluorine are evidence
for the synthesis of fluorine. These results are discussed in the light
of the scenario that RCBs are formed by accretion of an He white dwarf
by a C-O white dwarf. Sakurai's object (V4334 Sgr), a final He-shell
flash product, shows no detectable neutral fluorine lines.
Title: Searching For Alpha-poor Stars In The Galactic Halo
Authors: For, Bi-Qing; Lambert, D.; Sneden, C.; Ivans, I.
Bibcode: 2007AAS...21110317F
Altcode: 2007BAAS...39Q.922F
It has been known for more than 40 years that metal-poor stars have
chemical compositions that are enriched by alpha-elements (e.g., Mg,
Si, S, Ca and possibly Ti). These elements are overabundant by a factor
of roughly two compared with the Fe-peak elements. A few striking
exceptions have been discovered in recent years, such as BD+80 245,
G4-36, CS 22966-043 and HE 1424-0241. Similarly low-alpha abundance
patterns are also seen in the Sagittarius dSph galaxy. However,
we know almost nothing about what the true occurance frequency
of these alpha-poor stars is and how they form. We are conducting
the first homogeneous spectroscopic survey of suspected metal poor
([Fe/H]<=-0.75) and alpha-poor ([Mg/Fe]<=+0.2) stars in the
Galactic halo. We are obtaining high resolution, high signal-to-noise
data with the 2dCoude spectrograph of the McDonald Observatory 2.7m
telescope. The goal of this survey is to derive atmospheric parameters
Teff, log g and metallicity in a consistent way, and then to perform
a detailed analysis of the elemental abundance ratios, in particular
the abundances of neutron-capture and alpha-elements. Here we present
the preliminary results of this search. This work is supported by NSF
grant AST-0607708.
Title: Titanium Isotope Ratios Measured in Cool Stars
Authors: Chavez, Joy M.; Lambert, D. L.
Bibcode: 2007AAS...211.5912C
Altcode: 2007BAAS...39..843C
This study measures, for the first time, titanium isotope ratios
in low-mass stars and compares them to models of Galactic chemical
evolution. The isotopes of titanium are tracers of the nucleosynthetic
events in the galaxy. 46Ti and 47Ti are the
products of oxygen burning, while 48Ti and 49Ti
are the result of 48Cr and 49Cr decay. Formation
of 50Ti occurs in more rare environments, resulting from
electron capture. Because of these different formation sites, studying
the isotopes provides a look into the nucleosynthetic environments
in the history of the Galaxy. The ratios of the minor (46, 47, 49,
50) isotopes is measured from the isotopic features seen in the TiO
spectra. Using the 2d coude' spectrograph at the 2.7 m telescope at
McDonald Observatory, I observed 12 M dwarf spectra at a resolving
power of 120,000. I selected stars from various Galactic kinematic
population, observing an even mix of thin disk, thick disk and halo
stars. Using spectrum synthesis, I measured the isotopic ratios from
the isotopic features seen in the TiO gamma 0-0 band from 7054 to 7085
Angstroms. I measured these ratios, 46Ti/48Ti
and 50Ti/48Ti, because these are predicted to
increase significantly with metallicity. Comparisons among the minor
isotopes are also valuable since these features are relatively the same
strength. I also fit these ratios: 46Ti/47Ti,
50Ti/47Ti, 49Ti/50Ti. These
stars, ranging in metallicity from -0.8 to 0.0 [Fe/H], seem to show
little trend in the ratios with metallicity.
Title: A Half-Century of Spectroscopic Astrophysics
Authors: Lambert, David L.
Bibcode: 2007AAS...211.7401L
Altcode: 2007BAAS...39R.864L
In this talk, I shall highlight the growth of spectroscopic
astrophysics over the last half century by drawing on examples of
interesting results and challenges in the field of elemental and
isotopic abundance determinations as applied to problems in stellar
evolution and nucleosynthesis. In addition to mapping the growth in
our understanding of stellar atmospheres and spectral line formation,
I hope to show how progress in atomic and molecular spectroscopy has
stimulated the growth of the field and how nuclear astrophysics has
provided challenges and opportunities. Quantitative stellar spectroscopy
is not an exhausted topic; the talk may end with a glimpse of the
future for the next generations of students of the elements and stars.
Title: Obituary: Ralph Robert Robbins, Jr., 1938-2005
Authors: Hemenway, Mary Kay; Jefferys, William H.; Lambert, David L.
Bibcode: 2007BAAS...39.1078H
Altcode:
Ralph Robert Robbins, Jr., died on 2 December 2005, in Kyle,
Texas. His wife, Maria Elena Robbins, his daughters Julia Robbins
Kelso and Stephanie Juarez Balles, his son Matthew Juarez, and five
grandchildren survive him. Bob was on the faculty at the University
of Texas from 1968 until his retirement in 2003. Bob was born
in Wichita, Kansas, on 2 September 1938, the only son of Mildred and
Ralph Robert Robbins, Sr. Guided by his high school's policy to provide
a practical education to children of working-class parents, Bob began
high school with a heavy dose of vocational courses until the results
of a test indicated his special talent in mathematics. He was awarded
a full scholarship to Yale University, graduating magna cum laude in
mathematics in 1960. He won the Warner Prize in Mathematics at Yale
that year. He received his Ph.D. in 1966 with a dissertation entitled
"The Triplet Spectrum of Neutral Helium in Expanding Nebulae" from the
University of California at Berkeley. His interest in college teaching
was ignited at this time through summer teaching positions at San Mateo
California Junior College and the Ohio State University. Following
a year at Texas as a McDonald Observatory Post-doctoral Fellow,
Bob taught for a year in the physics department of the University
of Houston before returning to the University of Texas at Austin
as an Assistant Professor of Astronomy in 1968. He was promoted to
Associate Professor in 1972. Bob's research in the early 1970s on
theoretical studies of helium was of vital importance to astronomers
for over three decades. These pioneering calculations became vital to
observational astronomers in the mid-1990s as interest grew in the
primordial helium produced by the Big Bang. Bob's interest and
influence in education was international in scope. In the summers
1968-1970, he was a government consultant in Mathematics in East
Pakistan (now Bangladesh). He consulted with the government that was
preparing a master plan for technical education. While teaching all the
mathematics instructors of the polytechnic institutes of the country,
he co-authored a textbook "Polytechnic Mathematics." Bob also was active
for many years in Commission 46 of the International Astronomical Union,
including compiling overviews of educational materials available in
English for over a decade and serving on the organizing committee for
several international meetings. In the 1970s, Bob and William
Jefferys refined their view of how introductory astronomy should be
taught — pioneering a "minds-on, hands-on" approach that emphasized
"learning by doing" even in the non-science majors courses. This
innovative work in astronomy education led to several co-authored
books: a general-level textbook (Discovering Astronomy), a book to
accompany upper-division laboratory courses (Modern Astronomy: an
Activities Approach), and a workbook for college teachers (Effective
Astronomy Teaching and Student Reasoning Ability). Bob also popularized
self-paced astronomy courses that demanded in-depth understanding
from students as well as requiring observations of the sky and small
experiments. Bob was named a Piper Professor in 1972, a statewide award
that recognized his teaching excellence. For many years Bob served both
as an American Astronomical Society Shapley Visiting Lecturer and as
a National Science Foundation Chautauqua lecturer, thus bringing his
expertise to colleges and college instructors across the nation. Bob was fascinated with not only how undergraduate students learn,
but also how people of past civilizations learned about astronomy and
used it in their lives and rituals. Bob's colleague William Jefferys
recalled a 1967 Spring Break trip: "We got into Bob's white and purple
Dodge and went to Mexico with a large tent, big enough for the party of
six. We camped on the beach and by the side of the road, got royally
bitten by mosquitoes, suffered a broken spring and flat tire on the
car (both of which were fixed in Mexico, but the tire expired just as
we reentered the US). We also saw many interesting sites, and Bob's
interest in archaeoastronomy may have been kindled or at least renewed
on that trip." In the 1980s, Bob became increasingly interested
in archaeoastronomy. Being part Cherokee, he honored his own ethnic
heritage through his studies and the new courses he developed and
taught. His field research covered sites in central Texas, New Mexico,
Mexico, and Central America. He regaled his colleagues with tales
of his travels through guerilla-infested jungles with a platoon of
soldiers as a very essential escort to get to a site of astronomical
influence. This interest grew to publications in archaeoastronomy
and extended his teaching from the astronomy department to offering
graduate classes in the Institute for Latin American Studies on Archeo-
and Ethno-Astronomy at the University of Texas. As an involved
faculty member, Bob served on education committees of the American
Astronomical Society, the University of Texas Graduate Studies Committee
in Math and Science Education for the College of Education, as well
as departmental and college committees. He served as undergraduate
advisor for two years and chair of the Graduate Admissions Committee
for four years for the Astronomy Department. He took special interest
in preparing astronomy graduate students, both in formal courses and
in mentoring situations, to become better teachers. Bob's final
years of teaching were hampered by the onset of Parkinson's and Lewy
Body diseases that forced his retirement. He met his disability with
courage and dignity. A gentle person who cared deeply about students
and student learning, his friends and family will miss him.
Title: Carbon Stars in the Bulge -- or Beyond It?
Authors: Wahlin, R.; Eriksson, K.; Gustafsson, B. >; Ryde, N.;
Westerlund, B.; Lambert, D. L.
Bibcode: 2007ASPC..378..410W
Altcode:
The carbon stars in the direction of the Bulge were recently proposed
to belong to the Sagittarius system which, with its lower metallicity,
would more easily produce carbon stars. The compositions of the carbon
stars might be used to distinguish between true members of the Bulge and
members of the Sagittarius stream seen through the Bulge. We present
oxygen abundances for a sample of carbon stars in the Sagittarius
dwarf galaxy including its tidal stream, and towards the galactic
Bulge. The abundances were determined from infrared spectra obtained
with the ISAAC spectrometer on VLT (R=1500). We find that the oxygen
abundances of the Bulge carbon stars are compatible with membership
of the Sagittarius stream, but we also discuss possible scenarios that
might explain their abundances if they were true Bulge members.
Title: Hubble Space Telescope Survey of Interstellar
12CO/13CO in the Solar Neighborhood
Authors: Sheffer, Y.; Rogers, M.; Federman, S. R.; Lambert, D. L.;
Gredel, R.
Bibcode: 2007ApJ...667.1002S
Altcode: 2007arXiv0706.3855S
We examine 20 diffuse and translucent Galactic sight lines
and extract the column densities of the 12CO and
13CO isotopologues from their ultraviolet A-X absorption
bands detected in archival Space Telescope Imaging Spectrograph
data with λ/Δλ>=46,000. Five more targets with Goddard
High-Resolution Spectrograph data are added to the sample that
more than doubles the number of sight lines with published Hubble
Space Telescope observations of 13CO. Most sight lines
have 12CO-to-13CO isotopic ratios that
are not significantly different from the local value of 70 for
12C/13C, which is based on millimeter-wave
observations of rotational lines in emission from CO and H2CO
inside dense molecular clouds, as well as on results from optical
measurements of CH+. Five of the 25 sight lines are found
to be fractionated toward lower 12C/13C values,
while three sight lines in the sample are fractionated toward higher
ratios, signaling the predominance of either isotopic charge exchange or
selective photodissociation, respectively. There are no obvious trends
of the 12CO-to-13CO ratio with physical conditions
such as gas temperature or density, yet 12CO/13CO
does vary in a complicated manner with the column density of either
CO isotopologue, owing to varying levels of competition between
isotopic charge exchange and selective photodissociation in the
fractionation of CO. Finally, rotational temperatures of H2
show that all sight lines with detected amounts of 13CO
pass through gas that is on average colder by 20 K than the gas without
13CO. This colder gas is also sampled by CN and C2
molecules, the latter indicating gas kinetic temperatures of only 28 K,
enough to facilitate an efficient charge exchange reaction that lowers
the value of 12CO/13CO.
Title: The Chemical Compositions of the Type II Cepheids-The BL
Herculis and W Virginis Variables
Authors: Maas, Thomas; Giridhar, Sunetra; Lambert, David L.
Bibcode: 2007ApJ...666..378M
Altcode: 2007arXiv0706.2029M
Abundance analyses from high-resolution optical spectra are presented
for 19 type II Cepheids in the Galactic field. The sample includes
both short-period (BL Her) and long-period (W Vir) stars. This is
the first extensive abundance analysis of these variables. The C, N,
and O abundances with similar spreads for the BL Her and W Vir show
evidence for an atmosphere contaminated with 3α process and CN-cycling
products. A notable anomaly of the BL Her stars is an overabundance
of Na by a factor of about 5 relative to their presumed initial
abundances. This overabundance is not seen in the W Vir stars. The
abundance anomalies running from mild to extreme in W Vir stars but
not seen in the BL Her stars are attributed to dust-gas separation
that provides an atmosphere deficient in elements of high condensation
temperature, notably, Al, Ca, Sc, Ti, and s-process elements. Such
anomalies have previously been seen among RV Tau stars which represent
a long-period extension of the variability enjoyed by the type II
Cepheids. Comments are offered on how the contrasting abundance
anomalies of BL Her and W Vir stars may be explained in terms of the
stars' evolution from the blue horizontal branch.
Title: Iron abundances of B-type post-asymptotic giant branch stars
in globular clusters: Barnard29 in M13 and ROA5701 in ωCen
Authors: Thompson, H. M. A.; Keenan, F. P.; Dufton, P. L.; Ryans,
R. S. I.; Smoker, J. V.; Lambert, D. L.; Zijlstra, A. A.
Bibcode: 2007MNRAS.378.1619T
Altcode: 2007MNRAS.tmp..506T; 2007arXiv0705.2196T
High-resolution optical and ultraviolet (UV) spectra of two B-type
post-asymptotic giant branch (post-AGB) stars in globular clusters,
Barnard29 in M13 and ROA5701 in ωCen, have been analysed using model
atmosphere techniques. The optical spectra have been obtained with
FEROS on the ESO 2.2-m telescope and the 2d-Coudé spectrograph on
the 2.7-m McDonald telescope, while the UV observations are from the
Goddard high-resolution spectrograph on the Hubble Space Telescope
(HST). Abundances of light elements (C, N, O, Mg, Al and S) plus Fe have
been determined from the optical spectra, while the UV data provide
additional Fe abundance estimates from FeIII absorption lines in the
1875-1900 Å wavelength region. A general metal underabundance relative
to young B-type stars is found for both Barnard29 and ROA5701. These
results are consistent with the metallicities of the respective
clusters, as well as with previous studies of the objects. The derived
abundance patterns suggest that the stars have not undergone a gas-dust
separation, contrary to previous suggestions, although they may have
evolved from the AGB before the onset of the third dredge-up. However,
the Fe abundances derived from the HST spectra are lower than those
expected from the metallicities of the respective clusters, by 0.5
dex for Barnard29 and 0.8 dex for ROA5701. A similar systematic
underabundance is also found for other B-type stars in environments
of known metallicity, such as the Magellanic Clouds. These results
indicate that the FeIII UV lines may yield abundance values which are
systematically too low by typically 0.6 dex and hence such estimates
should be treated with caution. This paper includes data taken
at the McDonald Observatory of the University of Texas at Austin,
and on the ESO 2.2-m La Silla, programme 0077.D-025(A). E-mail:
h.thompson@qub.ac.uk
Title: Infrared High-Resolution Spectroscopy of Post-AGB Circumstellar
Disks. I. HR 4049: The Winnowing Flow Observed?
Authors: Hinkle, Kenneth H.; Brittain, Sean D.; Lambert, David L.
Bibcode: 2007ApJ...664..501H
Altcode: 2007arXiv0704.1237H
High-resolution infrared spectroscopy in the 2.3-4.6 μm region is
reported for the peculiar A supergiant, single-lined spectroscopic
binary HR 4049. Lines from the CO fundamental and first overtone, OH
fundamental, and several H2O vibration-rotation transitions
have been observed in the near-infrared spectrum. The spectrum of HR
4049 appears principally in emission through the 3 and 4.6 μm region
and in absorption in the 2 μm region. The 4.6 μm spectrum shows a
rich ``forest'' of emission lines. All the spectral lines observed in
the 2.3-4.6 μm spectrum are shown to be circumbinary in origin. The
presence of OH and H2O lines confirm the oxygen-rich nature
of the circumbinary gas, which is in contrast to the previously detected
carbon-rich material. The emission and absorption line profiles show
that the circumbinary gas is located in a thin, rotating layer near
the dust disk. The properties of the dust and gas circumbinary disk
and the spectroscopic orbit yield masses for the individual stars,
MAI~0.58 Msolar and Msecondary~0.34
Msolar. Gas in the disk also has an outward flow with
a velocity of >~1 km s-1. The severe depletion of
refractory elements but near-solar abundances of volatile elements
observed in HR 4049 results from abundance winnowing. The separation
of the volatiles from the grains in the disk and the subsequent
accretion by the star are discussed. Contrary to prior reports,
the HR 4049 carbon and oxygen isotopic abundances are typical AGB
values, 12C/13C=6+9-4
and 16O/17O>200.
Title: Chemical Composition of Several Pulsating Variable Stars of
the λ Boo and δ Sct Types
Authors: Gopka, V.; Yushchenko, A.; Kim, C.; Lambert, D.; Rostopchin,
S.; Kim, S. -L.; Jeon, Y. -B.; Dorokhova, T.; Tarasov, A.; Chernyshova,
I.
Bibcode: 2007ASPC..362..249G
Altcode:
Objects. We present investigation of four pulsating stars: λ Boo,
HD210111, ρ Pup and V2314 Oph. Observations. High resolution
spectroscopic observations of these stars were made with the 2.7 meter
telescope at the McDonald observatory, the VLT and the 2 meter telescope
at the Terskol observatory. Photometric observations of V2314 Oph were
secured using the 1.2- to 0.4-meter telescopes at five observatories,
namely Bohyunsan & Sobak (Korea), Crimea (Ukraine), Maidanak
(Uzbekistan), and Dushak-Erekdag (Turkmenistan). Methods. Chemical
composition was investigated using a spectrum synthesis method for
all elements except iron. A frequency analysis of photometric data
of V2314 Oph was made. Results. λ Boo - We found the abundances of
several light elements, which were not investigated earlier. HD210111 -
upper limits of abundances of La, Ce, and Nd and the abundance of Dy and
Yb are found for the first time. The profiles of lines in the spectrum
are clearly disturbed by pulsation. V2314 Oph appears to be a new λ
Boo type star. Its chemical composition is presented for the first time
as also are the values of several frequencies of light variations. For
ρ Pup, we give a detailed chemical composition for 33 elements. The
abundance pattern of this star is similar to that of δ Sct.
Title: Interplay between Diffusion, Accretion and Nuclear Reactions
in the Atmospheres of Sirius and Przybylski's Star
Authors: Yushchenko, A.; Gopka, V.; Goriely, S.; Lambert, D.; Shavrina,
A.; Kang, Y. W.; Rostopchin, S.; Valyavin, G.; Lee, B. -C.; Kim, C.
Bibcode: 2007ASPC..362...46Y
Altcode: 2006astro.ph.10611Y
The abundance anomalies in chemically peculiar B-F stars are usually
explained by diffusion of chemical elements in the stable atmospheres
of these stars. But it is well known that peculiar stars with similar
temperatures and gravities show very different chemical compositions. We
show that the abundance patterns of several stars can be influenced
by accretion and (or) nuclear reactions in stellar atmospheres. The
first case is one of the hottest Am stars - Sirius. We determined the
abundances of more than 50 chemical elements in the atmosphere of Sirius
A and show that Sirius A was contaminated by s-process enriched matter
from Sirius B (now a white dwarf). The second case is the well known
Przybylski's star. The abundance pattern of this star is the second
most studied one after the Sun with abundances determined for about 60
chemical elements. Spectral lines of radioactive elements with short
decay times were found in the spectrum of this star. We report the
results of our investigation on the stratification of chemical elements
in the atmosphere of Przybylski's star and the new identification of
lines corresponding to short-lived actinides in its spectrum. Possible
explanations of the abundances pattern of Przybylski's star (as
well as HR465 and HD965) can be the natural radioactive decays of
thorium and uranium, the explosion of a companion as a supernova or
the spallation reactions. These three hypotheses and (or) diffusion
can possibly explain the abundance pattern of Przybylski's star and
several similar objects such as HR465 and HD965.
Title: Oxygen abundances in nearby stars. Clues to the formation
and evolution of the Galactic disk
Authors: Ramírez, I.; Allende Prieto, C.; Lambert, D. L.
Bibcode: 2007A&A...465..271R
Altcode: 2007astro.ph..1362R
The abundances of iron and oxygen are homogeneously determined in
a sample of 523 nearby (d<150 pc) FGK disk and halo stars with
metallicities in the range -1.5<[Fe/H]<0.5. Iron abundances were
obtained from an LTE analysis of a large set of Fe I and Fe II lines
with reliable atomic data. Oxygen abundances were inferred from a
restricted non-LTE analysis of the 777 nm O I triplet. We adopted the
infrared flux method temperature scale and surface gravities based
on Hipparcos trigonometric parallaxes. Within this framework, the
ionization balance of iron lines is not satisfied: the mean abundances
from the Fe I lines are systematically lower by 0.06 dex than those
from the Fe II lines for dwarf stars of Teff>5500 K and
[Fe/H]<0.0, and giant stars of all temperatures and metallicities
covered by our sample. The discrepancy worsens for cooler and metal-rich
main-sequence stars. We use the stellar kinematics to compute the
probabilities of our sample stars to be members of the thin disk,
thick disk, or halo of the Galaxy. We find that the majority of the
kinematically-selected thick-disk stars show larger [O/Fe] ratios
compared to thin-disk stars while the rest show thin-disk abundances,
which suggests that the latter are thin-disk members with unusual
(hotter) kinematics. A close examination of this pattern for disk stars
with ambiguous probabilities shows that an intermediate population with
properties between those of the thin and thick disks does not exist,
at least in the solar neighborhood. Excluding the stars with unusual
kinematics, we find that thick-disk stars show slowly decreasing
[O/Fe] ratios from about 0.5 to 0.4 in the -0.8<[Fe/H]<-0.3
range. Using a simple model for the chemical evolution of the thick
disk we show that this trend results directly from the metallicity
dependence of the Type II supernova yields. At [Fe/H]>-0.3, we find
no obvious indication of a sudden decrease (i.e., a "knee") in the
[O/Fe] vs. [Fe/H] pattern of thick-disk stars that would connect the
thick and thin disk trends at a high metallicity. We conclude that Type
Ia supernovae (SN Ia) did not contribute significantly to the chemical
enrichment of the thick disk. In the -0.8<[Fe/H]<+0.3 range,
thin-disk stars show decreasing [O/Fe] ratios from about 0.4 to 0.0
that require a SN Ia contribution. The implications of these results
for studies of the formation and evolution of the Galactic disk are
discussed. Tables 4-6 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/465/271 Partially based
on observations obtained with the Hobby-Eberly Telescope, which is a
joint project of the University of Texas at Austin, the Pennsylvania
State University, Stanford University, Ludwig-Maximilians-Universität
München, and Georg-August-Universität Göttingen; and data from the
UVES Paranal Observatory Project (ESO DDT Program ID 266.D-5655).
Title: Correlations between Lithium and Technetium Absorption Lines
in the Spectra of Galactic S Stars
Authors: Vanture, Andrew D.; Smith, Verne V.; Lutz, Julie; Wallerstein,
George; Lambert, David; Gonzalez, Guillermo
Bibcode: 2007PASP..119..147V
Altcode:
Correlations between the presence of the 6707 Å line of lithium
and the resonance lines of technetium (4238 and 4262 Å) in a large
sample of Galactic S stars are analyzed. Half of the sample stars are
intrinsic S stars (those exhibiting technetium in their spectra),
and 1/3 of these stars also have strong lithium lines in their
spectra. Stars having both lithium and technetium in their spectra
are interpreted as intermediate-mass thermally pulsating asymptotic
giant branch (TP-AGB) stars in which lithium is produced by the
Cameron-Fowler mechanism. The production of lithium is predicted to
occur in high-luminosity (Mbol<=-6) TP-AGB stars by
the hot-bottom burning (HBB) mechanism. Data on the carbon isotope
ratios of stars in our sample agree with the predictions of HBB;
however, oxygen isotope ratios in these stars do not agree with
the predictions of HBB. Furthermore, the available luminosities
for our sample stars are below the minimum value necessary for HBB
to occur in available models. Cool-bottom processing (CBP) is one
possible explanation for the presence of lithium in the spectra of
these stars. Intrinsic S stars having technetium but no lithium in
their spectra are interpreted as lower mass (1.5-3 Msolar)
thermally pulsating AGB stars that have not undergone CBP. Extrinsic S
stars constitute the remaining half of the sample. Carbon and oxygen
isotope ratios, as well as the lack of technetium and lithium in the
spectra of these stars, are consistent with these being low-mass red
giant branch stars (1-2 Msolar), with mass transfer from
a now extinct thermally pulsating AGB star being responsible for the
enhanced abundance of s-process elements.
Title: VizieR Online Data Catalog: Oxygen abundances in nearby stars
(Ramirez+, 2007)
Authors: Ramirez, I.; Allende Prieto, C.; Lambert, D. L.
Bibcode: 2007yCat..34650271R
Altcode:
We provide in Table 4 basic (HIP and HD numbers, V magnitude and
parallax) and kinematic (radial velocities and heliocentric space
velocity) data for our sample stars. The kinematic probabilities of
being a thin-disk, thick-disk, and halo member are also given. Table 5
contains the line data used in our abundance computations as well as the
equivalent widths of the lines measured in the solar spectrum. Stellar
parameters and abundances are given in Table 6. Effective temperatures
were derived using color calibrations based on the infrared flux
method temperature scale while surface gravities were determined from
the Hipparcos parallaxes and estimates of the stellar masses based on
theoretical isochrones. We provide the mean abundance of iron determined
from Fe I and Fe II lines separately and a mean [Fe/H] value obtained
after applying our empirical re-scaling of the Fe I abundances. LTE
and non-LTE oxygen abundances derived from the 777nm OI triplet are
also given. The last three columns of Table 6, if available, provide
our estimates of the stellar ages. (3 data files).
Title: Spectroscopy of the Post-AGB Disk around HR 4049
Authors: Hinkle, Kenneth H.; Brittain, S. D.; Lambert, D. L.
Bibcode: 2006AAS...209.8102H
Altcode: 2006BAAS...38.1006H
High-resolution infrared spectroscopy in the 2.3-4.6 μm region is
reported for the peculiar star HR 4049. HR 4049 has severe depletion
of refractory elements but solar abundances of volatile elements
suggesting a winnowing process. Lines from the CO fundamental
and first overtone, OH fundamental, and several H2O
vibration-rotation transitions have been observed in the near-infrared
spectrum. The spectrum of HR 4049 appears in emission through the
3 and 4.6 μm region and in absorption in the 2 μm region. The
4.6 μm spectrum shows a rich 'forest' of emission lines. All the
spectral lines observed in the 2.3-4.6 μm spectrum are shown to
be circumstellar in origin. The presence of OH and H2O
lines confirm the oxygen-rich nature of the circumstellar gas. HR
4049 has an oxygen-rich circumbinary disk surrounded by a carbon-rich
circumstellar shell. The emission and absorption line profiles show
that the gas is located in a thin, rotating layer near the circumbinary
dust ring. In addition to rotation, gas in the ring is also flowing
outward with a velocity of at least 1 km s-1. A model
is described where the gas is driven from the grains in a winnowing
process producing the observed surface abundances. Contrary to prior
reports, the HR 4049 carbon and oxygen isotopic abundances are typical
for an AGB or post-AGB star. 12C/13C=9±6 and
16O/17O>200. Assuming that the binary orbit
is co-planer with the disk, the mass of the post-AGB star is 0.58
solar mass and the mass of the unseen companion is 0.34 solar mass.
Title: High-Resolution Calibration of the SDSS/SEGUE Spectroscopic
Analysis Pipeline
Authors: Sivarani, T.; Beers, T. C.; Lee, Y.; Krugler, J.; Wilhelm,
R.; Allende Prieto, C.; Sneden, C.; Lambert, D. L.; Shetrone, M.;
Johnson, J.; Ivans, I.; Rockosi, C.; Lai, D.; Morrison, H.; Aoki, W.
Bibcode: 2006AAS...20916810S
Altcode: 2006BAAS...38.1139S
We present a discussion of efforts to obtain external validation of the
estimated atmospheric parameters (Teff, log g, [Fe/H]) obtained from
medium-resolution (R = 2000) SDSS spectroscopy and ugriz photometry,
which are being employed for both the completed SDSS-I and the
ongoing SEGUE survey. The SDSS/SEGUE spectroscopic pipeline makes
use of a number of methods for the estimation of each parameter, with
estimated internal errors on the order of σ(Teff) = 150 K, σ(log g)
= 0.4 dex, and σ([Fe/H]) = 0.3 dex. Over the course of the past two
years, we have obtained over 100 high-resolution optical spectra of
SDSS/SEGUE stars using the HET, KECK and SUBARU telescopes. For the
KECK/HIRES spectra, which have R = 40000, we have performed standard
high-resolution analyses to estimate the stellar parameters. For the
HET and KECK-ESI data, which have R = 15000 and R = 5000, respectively,
we have performed synthetic spectra matching in order to to estimate
the stellar parameters. We find that the derived stellar parameters
agree well with the SDSS/SEGUE pipeline estimates for the temperature
range 5000 K < Teff < 6500K; the errors are of the order of the
internal errors expected from the SDSS/SEGUE pipeline. For effective
temperatures in the range 4000 K to 5000 K the estimated parameters
from the high-resolution spectroscopy exhibit offsets relative to the
SDSS/SEGUE pipeline values on the order of ΔTeff = 200 K, Δlogg =
0.8 dex, and Δ[Fe/H] = 0.4 dex. Similar offsets exist for stars with T
> 6500 K. The main reason for these offsets appears to arise due to
varying microturbulence, for which the medium-resolution SDSS spectra
are not sensitive. We also have performed external checks on pipline
radial velocities. We find that the errors in radial velocities are
on the order of 7 km/s for stars, which is at the expected level.
Title: Fundamental parameters and abundances of metal-poor stars:
the SDSS standard BD +17 4708
Authors: Ramírez, I.; Allende Prieto, C.; Redfield, S.; Lambert, D. L.
Bibcode: 2006A&A...459..613R
Altcode: 2006astro.ph..8559R
The atmospheric parameters and iron abundance of the Sloan Digital
Sky Survey (SDSS) spectrophotometric standard star BD +17 4708
are critically examined using up-to-date Kurucz model atmospheres,
LTE line formation calculations, and reliable atomic data. We find
Teff=6141 ± 50 K, log g=3.87 ± 0.08, and [Fe/H]=-1.74
± 0.09. The line-of-sight interstellar reddening, bolometric flux,
limb-darkened angular diameter, stellar mass, and the abundances
of Mg, Si, and Ca are also obtained: E(B-V)=0.010 ± 0.003,
fbol=(4.89±0.10) × 10-9 erg cm-2
s-1, θ=0.1016 ± 0.0023 mas, M=0.91 ± 0.06~M_⊙,
[Mg/Fe]=0.40 ± 0.10, [Si/Fe]=0.35 ± 0.11, [Ca/Fe]=0.36 ± 0.11. This
star is a unique example of a moderately metal-poor star for which the
effective temperature (Teff) can be accurately constrained
from the observed spectral energy distribution (corrected for
reddening). Such analysis leads to a value that is higher than most
spectroscopic results previously reported in the literature (~5950
K). Interstellar reddening was estimated using various prescriptions,
including an analysis of interstellar lines. The surface gravity of the
star was inferred from the fitting of the wings of the Mg I b lines. We
used transition probabilities measured in the laboratory and reliable
damping constants for unblended Fe lines to derive the iron abundance
using both Fe I and Fe II lines. We find that the ionization balance
of Fe lines is satisfied only if a low Teff (~5950 K)
is adopted. The mean iron abundance we obtain from the Fe II lines
corresponds to A_Fe=5.77 ± 0.09 ([Fe/H]=-1.74 for our derived
AFe,⊙=7.51) while that from the Fe I lines is A_Fe=5.92
± 0.11, and therefore with our preferred Teff (6141 K),
the discrepancy between the mean iron abundance from Fe I and Fe II
lines cannot be explained by overionization by UV photons as the main
non-LTE effect. Interestingly, the Fe I excitation balance is satisfied
with a Teff only slightly warmer than our preferred solution
and not with the lower value of 5950 K. We also comment on non-LTE
effects and the importance of inelastic collisions with neutral H
atoms in the determination of oxygen abundances in metal-poor stars
from the 7774 Å O I triplet.
Title: The Nature of Interstellar Gas toward the Pleiades Revealed
in Absorption Lines
Authors: Ritchey, A. M.; Martinez, M.; Pan, K.; Federman, S. R.;
Lambert, D. L.
Bibcode: 2006ApJ...649..788R
Altcode: 2006astro.ph..6644R
We present high-resolution, high signal-to-noise ratio absorption-line
observations of CN, Ca II, Ca I, CH+, and CH along 20 lines
of sight toward members of the Pleiades. The acquired data enable the
most detailed study to date of the interaction between cluster stars and
the surrounding interstellar gas. Total equivalent widths are consistent
with previous investigations, except where weaker features are detected
owing to our greater sensitivity. Mean b-values for the molecular
species indicate that toward most of the Pleiades, CH is associated with
the production of CH+ rather than CN. An analysis of radial
velocities reveals a kinematic distinction between ionized atomic gas
and molecular and neutral gas. Molecular components are found with
velocities in the local standard of rest of either ~+7 or ~+9.5 km
s-1, with the higher velocity components being associated
with the strongest absorption. Atomic gas traced by Ca II shows a strong
central component at vLSR~+7 km s-1, exhibiting
velocity gradients indicative of cloud-cluster interactions. Gas density
estimates derived from measured CH/CH+ column density ratios
show good agreement with those inferred from H2 rotational
populations, yielding typical values of n~50 cm-3. Our models
do not include the important time-dependent effects on CH+
formation, which may ultimately be needed to extract physical conditions
in these clouds.
Title: VizieR Online Data Catalog: Elemental abundances for 176 stars
(Reddy+, 2006)
Authors: Reddy, B. E.; Lambert, D. L.; Allende Prieto, C.
Bibcode: 2006yCat..73671329R
Altcode:
High-resolution spectra of the program stars were obtained during the
period 2002 December-2004 June at the Harlan J. Smith 2.7-m telescope
of the W.J. McDonald Observatory, using the 2dcoude echelle spectrometer
with a 2048x2048 Tektronix CCD as detector. (2 data files).
Title: RCoronae Borealis at the 2003 light minimum
Authors: Kameswara Rao, N.; Lambert, David L.; Shetrone, Matthew D.
Bibcode: 2006MNRAS.370..941K
Altcode: 2006MNRAS.370..941R; 2006astro.ph..5218K; 2006MNRAS.tmp..631K
A set of five high-resolution optical spectra of R CrB obtained in
2003 March is discussed. At the time of the first spectrum (March 8),
the star was at V = 12.6, a decline of more than six magnitudes. By
March 31, the date of the last observation, the star at V = 9.3 was on
the recovery to maximum light (V = 6). The 2003 spectra are compared
with the extensive collection of spectra from the 1995-1996 minimum
presented previously. Spectroscopic features common to the two minima
include the familiar ones also seen in spectra of other R Coronae
Borealis stars (RCBs) in decline: sharp emission lines of neutral
and singly ionized atoms, broad emission lines including HeI, [NII]
6583 Å, Na D and CaII H & K lines, and blueshifted absorption
lines of Na D, and KI resonance lines. Prominent differences between
the 2003 and 1995-1996 spectra are seen. The broad Na D and Ca H
& K lines in 2003 and 1995-1996 are centred approximately on
the mean stellar velocity. The 2003 profiles are fit by a single
Gaussian, but in 1995-1996 two Gaussians separated by about 200 km
s-1 were required. However, the HeI broad emission lines
are fit by a single Gaussian at all times; the emitting He and Na-Ca
atoms are probably not colocated. The C2 Phillips 2-0
lines were detected as sharp absorption lines and the C2
Swan band lines as sharp emission lines in 2003, but in 1995-1996
the Swan band emission lines were broad and the Phillips lines were
undetected. The 2003 spectra show CI sharp emission lines at minimum
light with a velocity changing in 5 d by about 20 km s-1
when the velocity of `metal' sharp lines is unchanged; the CI emission
may arise from shock-heated gas. Reexamination of spectra obtained
at maximum light in 1995 shows extended blue wings to strong lines
with the extension dependent on a line's lower excitation potential;
this is the signature of a stellar wind, also revealed by published
observations of the HeI 10830 Å line at maximum light. Changes in
the cores of the resonance lines of AlI and Na D (variable blueshifts)
and the CaII infrared (IR) lines (variable blueshifts and redshifts)
suggest complex flow patterns near the photosphere. The spectroscopic
differences at the two mimima show the importance of continued scrutiny
of the declines of R CrB (and other RCBs). Thorough understanding of
the outer atmosphere and circumstellar regions of R CrB will require
such continued scrutiny. Based on observations obtained with the
Hobby-Eberly Telescope, which is a joint project of the University of
Texas at Austin, the Pennsylvania State University, Stanford University,
Ludwig-Maximilians-Universität München and Georg-August-Universität
Göttingen. E-mail: dll@anchor.as.utexas.edu (DLL)
Title: Water Vapor on Supergiants: The 12 μm TEXES Spectra of
μ Cephei
Authors: Ryde, N.; Richter, M. J.; Harper, G. M.; Eriksson, K.;
Lambert, D. L.
Bibcode: 2006ApJ...645..652R
Altcode: 2006astro.ph..3384R
Several recent papers have argued for warm, semidetached, molecular
layers surrounding red giant and supergiant stars, a concept known as
a MOLsphere. Spectroscopic and interferometric analyses have often
corroborated this general picture. Here we present high-resolution
spectroscopic data of pure rotational lines of water vapor at 12 μm
for the supergiant μ Cep. This star has often been used to test the
concept of molecular layers around supergiants. Given the prediction of
an isothermal, optically thick water vapor layer in local thermodynamic
equilibrium around the star (MOLsphere), we expected the 12 μm lines
to be in emission or at least in absorption but filled in by emission
from the molecular layer around the star. Our data, however, show the
contrary; we find definite absorption. Thus, our data do not easily fit
into the suggested isothermal MOLsphere scenario. The 12 μm lines,
therefore, put new, strong constraints on the MOLsphere concept and
on the nature of water seen in signatures across the spectra of early
M supergiants. We also find that the absorption is even stronger
than that calculated from a standard, spherically symmetric model
photosphere without any surrounding layers. A cool model photosphere,
representing cool outer layers, is, however, able to reproduce the
lines, but this model does not account for water vapor emission at
6 μm. Thus, a unified model for water vapor on μ Cep appears to be
lacking. It does seem necessary to model the underlying photospheres
of these supergiants in their whole complexity. The strong water vapor
lines clearly reveal inadequacies of classical model atmospheres.
Title: VLT UVES Observations of Interstellar Molecules and Diffuse
Bands in the Magellanic Clouds
Authors: Welty, D. E.; Federman, S. R.; Gredel, R.; Thorburn, J. A.;
Lambert, D. L.
Bibcode: 2006ApJS..165..138W
Altcode: 2006astro.ph..3332W
We discuss the abundances of interstellar CH, CH+, and
CN in the Magellanic Clouds, derived from spectra of seven SMC
and 13 LMC stars obtained (mostly) with the VLT UVES. CH and/or
CH+ have now been detected toward three SMC and nine LMC
stars; CN is detected toward Sk 143 (SMC) and Sk -67 2 (LMC). These
data represent nearly all the optical detections of these molecular
species in interstellar media beyond the Milky Way. In the LMC, the
CH/H2 ratio is comparable to that found for diffuse Galactic
molecular clouds in four sight lines but is lower by factors of 2.5-4.0
in two others. In the SMC, the CH/H2 ratio is comparable
to the local Galactic value in one sight line but is lower by factors
of 10-15 in two others. The abundance of CH in the Magellanic Clouds
thus appears to depend on local physical conditions and not just on
metallicity. In both the SMC and the LMC, the observed relationships
between the column density of CH and those of CN, CH+,
Na I, and K I are generally consistent with the trends observed in
our Galaxy. Using existing data for the rotational populations
of H2 in these sight lines, we estimate temperatures,
radiation field strengths, and local hydrogen densities for the
diffuse molecular gas. The inferred temperatures range from about
45 to 90 K, the radiation fields range from about 1 to 900 times
the typical local Galactic field, and the densities (in most cases)
lie between 100 and 600 cm-3. Densities estimated from the
observed N(CH), under the assumption that CH is produced via steady
state gas-phase reactions, are considerably higher than those derived
from H2. Much better agreement is found by assuming that
the CH is made via the (still undetermined) process(es) responsible
for the observed CH+. A significant fraction of the CH and
CH+ in diffuse molecular material in the SMC and LMC may
be produced in photon-dominated regions. The excitation temperature
obtained from the populations of the two lowest CN rotational levels
toward Sk -67 2 is quite consistent with the temperature of the cosmic
microwave background radiation measured with COBE. Toward most
of our targets, the UVES spectra also reveal absorption at velocities
corresponding to the Magellanic Clouds ISM from several of the strongest
of the diffuse interstellar bands (DIBs; at 5780, 5797, and 6284 Å). On
average, the three DIBs are weaker by factors of 7-9 (LMC) and about 20
(SMC), compared to those typically observed in Galactic sight lines with
similar N(H I), presumably due to the lower metallicities and stronger
radiation fields in the LMC and SMC. The three DIBs are also weaker (on
average, but with some exceptions), by factors of order 2-6, relative
to E(B-V), N(Na I), and N(K I) in the Magellanic Clouds. The detection
of several of the so-called C2 DIBs toward Sk 143 and Sk -67
2 with strengths similar to those in comparable Galactic sight lines,
however, indicates that no single, uniform scaling factor (e.g., one
related to metallicity) applies to all DIBs (or for all sight lines)
in the Magellanic Clouds. Based on observations collected at
the European Southern Observatory, Chile, under programs 67.C-0281,
70.D-0164, 72.C-0064, 72.C-0682, and 74.D-0109.
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: Elemental abundance survey of the Galactic thick disc
Authors: Reddy, Bacham E.; Lambert, David L.; Allende Prieto, Carlos
Bibcode: 2006MNRAS.367.1329R
Altcode: 2006MNRAS.tmp..343R; 2005astro.ph.12505R
We have performed an abundance analysis for F- and G- dwarfs of the
Galactic thick-disc component. A sample of 176 nearby (d<= 150pc)
thick-disc candidate stars was chosen from the Hipparcos catalogue and
subjected to a high-resolution spectroscopic analysis. Using accurate
radial velocities combined with the Hipparcos astrometry, kinematics
(U, V and W) and Galactic orbital parameters were computed. We
estimate the probability for a star to belong to the thin disc,
the thick disc or the halo. With a probability P>= 70 per cent
taken as certain membership, we assigned 95 stars to the thick disc,
13 to the thin disc, and 20 to the halo. The remaining 48 stars in the
sample cannot be assigned with reasonable certainty to one of the three
components. Abundances of C, O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr,
Mn, Fe, Co, Ni, Cu, Zn, Y, Ba, Ce, Nd and Eu have been obtained. The
abundances for the thick-disc stars are compared with those for the
thin-disc members from Reddy et al. The ratios of α-elements (O, Mg,
Si, Ca and Ti) to iron for thick-disc stars show a clear enhancement
compared to thin-disc members in the range -0.3 < [Fe/H] <
-1.2. There are also other elements - Al, Sc, V, Co, and possibly Zn -
which show enhanced ratios to iron in the thick disc relative to the
thin disc. The abundances of Na, Cr, Mn, Ni and Cu (relative to Fe) are
very similar for thin- and thick-disc stars. The dispersion in abundance
ratios [X/Fe] at given [Fe/H] for thick-disc stars is consistent with
the expected scatter due to measurement errors, suggesting a lack of
`cosmic' scatter. A few stars classified as members of the thick
disc by our kinematic criteria show thin-disc abundances. These stars,
which appear older than most thin-disc stars, are also, on average,
younger than the thick-disc population. They may have originated early
in the thin-disc history, and been subsequently scattered to hotter
orbits by collisions. The thick disc may not include stars with [Fe/H]
> -0.3. The observed compositions of the thin and thick discs seem
to be consistent with the models of galaxy formation by hierarchical
clustering in a Lambda cold dark matter (ΛCDM) universe.
Title: Testing Rotational Mixing Predictions with New Boron Abundances
in Main-Sequence B-Type Stars
Authors: Mendel, J. T.; Venn, K. A.; Proffitt, C. R.; Brooks, A. M.;
Lambert, D. L.
Bibcode: 2006ApJ...640.1039M
Altcode: 2005astro.ph.12084M
New boron abundances for seven main-sequence B-type stars are
determined from HST STIS spectroscopy around the B III 2066 Å
line. Boron abundances provide a unique and critical test of stellar
evolution models that include rotational mixing, since boron is
destroyed in the surface layers of stars through shallow mixing long
before other elements are mixed from the stellar interior through deep
mixing. The stars in this study are all on or near the main sequence
and are members of young Galactic clusters. They show no evidence of
mixing with gas from H-burning layers from their CNO abundances. Boron
abundances range from 12+log(B/H)<=1.0 to 2.2. The boron abundances
are compared to the published values of the stellar nitrogen abundances
[all have 12+log(N/H)<=7.8] and to their host cluster ages (4-16 Myr)
to investigate the predictions from models of massive star evolution
with rotational mixing effects. We find that the variations in boron
and nitrogen are generally within the range of the predictions from the
stellar evolution models with rotation (where predictions for models
with rotation rates from 0 to 450 km s-1 and μ-barriers
are examined), especially given their age and mass ranges. Three stars
(of 34 B-type stars with detailed boron abundance determinations)
deviate from the model predictions, showing either much larger boron
depletions than can be explained by the rotating model predictions or
a spectroscopic mass that is lower than expected, given the rotating
model predictions for its age and abundances. The results from these
three stars suggest that rotational mixing could be more efficient
than that currently modeled at the highest rotation rates.
Title: Rubidium and Lead Abundances in Giant Stars of the Globular
Clusters M13 and NGC 6752
Authors: Yong, David; Aoki, Wako; Lambert, David L.; Paulson, Diane B.
Bibcode: 2006ApJ...639..918Y
Altcode: 2005astro.ph.11413Y
We present measurements of the neutron-capture elements Rb and Pb in
five giant stars of the globular cluster NGC 6752 and Pb measurements in
four giants of the globular cluster M13. The abundances were derived by
comparing synthetic spectra with high-resolution, high signal-to-noise
ratio spectra obtained using HDS on the Subaru telescope and MIKE
on the Magellan telescope. The program stars span the range of the
O-Al abundance variation. In NGC 6752, the mean abundances are
[Rb/Fe]=-0.17+/-0.06 (σ=0.14), [Rb/Zr]=-0.12+/-0.06 (σ=0.13),
and [Pb/Fe]=-0.17+/-0.04 (σ=0.08). In M13 the mean abundance is
[Pb/Fe]=-0.28+/-0.03 (σ=0.06). Within the measurement uncertainties,
we find no evidence for star-to-star variation for either Rb or Pb
within these clusters. None of the abundance ratios [Rb/Fe], [Rb/Zr],
or [Pb/Fe] are correlated with the Al abundance. NGC 6752 may have
slightly lower abundances of [Rb/Fe] and [Rb/Zr] compared to the small
sample of field stars at the same metallicity. For M13 and NGC 6752 the
Pb abundances are in accord with predictions from a Galactic chemical
evolution model. If metal-poor intermediate-mass asymptotic giant
branch stars did produce the globular cluster abundance anomalies,
then such stars do not synthesize significant quantities of Rb or
Pb. Alternatively, if such stars do synthesize large amounts of Rb or
Pb, then they are not responsible for the abundance anomalies seen in
globular clusters. Based in part on data collected at the Subaru
Telescope, which is operated by the National Astronomical Observatory
of Japan, and on observations made with the Magellan Clay Telescope
at Las Campanas Observatory.
Title: An Analysis of Ultraviolet Spectra of Extreme Helium Stars
and New Clues to Their Origins
Authors: Pandey, Gajendra; Lambert, David L.; Jeffery, C. Simon; Rao,
N. Kameswara
Bibcode: 2006ApJ...638..454P
Altcode: 2005astro.ph.10161P
Abundances of about 18 elements including the heavy elements Y and
Zr are determined from Hubble Space Telescope Space Telescope Imaging
Spectrograph ultraviolet spectra of seven extreme helium stars (EHes):
LSE 78, BD +10 2179, V1920 Cyg, HD 124448, PV Tel, LS IV-1 2, and
FQ Aqr. New optical spectra of BD +10 2179, V1920 Cyg, and HD 124448
were analyzed, and published line lists of LSE 78, HD 124448, and PV
Tel were analyzed afresh. The abundance analyses are done using LTE
line formation and LTE model atmospheres especially constructed for
these EHes. The stellar parameters derived from an EHe's UV spectrum
are in satisfactory agreement with those derived from its optical
spectrum. Adopted abundances for the seven EHes are from a combination
of the UV and optical analyses. Published results for an additional 10
EHes provide abundances obtained in a nearly uniform manner for a total
of 17 EHes, the largest sample on record. The initial metallicity
of an EHe is indicated by the abundance of elements from Al to Ni;
Fe is adopted to be the representative of initial metallicity. Iron
abundances range from approximately solar to about 1/100 solar. Clues
to EHe evolution are contained within the H, He, C, N, O, Y, and Zr
abundances. Two novel results are (1) the O abundance for some stars is
close to the predicted initial abundance yet the N abundance indicates
almost complete conversion of initial C, N, and O to N by the CNO
cycles; and (2) three of the seven stars with UV spectra show a strong
enhancement of Y and Zr attributable to an s-process. The observed
compositions are discussed in light of expectations from accretion of
an He white dwarf by a C-O white dwarf. Qualitative agreement seems
likely except that a problem may be presented by those stars in which
the O abundance is close to the initial O abundance. Based on
observations obtained with the NASA/ESA Hubble Space Telescope, which
is operated by the Association of Universities for Research in Astronomy
(AURA), Inc., under NASA contract NAS 5-26555.
Title: The HdC stars as recently merged white dwarf binaries
Authors: Hinkle, Kenneth; Lambert, David; Smith, Verne; Lebzelter,
Thomas
Bibcode: 2006noao.prop..391H
Altcode:
The hydrogen-deficient carbon star HD 137613 has been reported
by Clayton et al. (2005) to have the extraordinary isotopic ratio
^16O/^18O ~ 0.8. The solar system ratio is ~500 and carbon stars
typically have yet larger ratios. The explanation proposed for the
^16O/^18O value observed in HD 137613 is that the HdC stars are recently
merged white dwarf binaries. The observed supergiant HdC star is a
transient post-merger phase. If so, we have the rare opportunity to see
helium-burning shell products in a low gravity stellar environment. To
test this model we propose to measure the CNO elemental abundances
for HD 137613 as well as the other four hydrogen- deficient carbon
stars. Comparison of the measure abundances with models will lead to
considerable insight into stellar mergers and nucleosynthesis.
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: Mg Isotope Ratios in Giant Stars of the Globular Clusters
M13 and M71
Authors: Yong, David; Aoki, Wako; Lambert, David L.
Bibcode: 2006ApJ...638.1018Y
Altcode: 2005astro.ph.10591Y
We present Mg isotope ratios in four red giants of the globular
cluster M13 and one red giant of the globular cluster M71
based on high-resolution, high signal-to-noise ratio spectra
obtained with HDS on the Subaru Telescope. We confirm earlier
results by Shetrone that for M13 the ratio varies from
(25Mg+26Mg)/24Mg~=1
in stars with the highest Al abundance to
(25Mg+26Mg)/24Mg~=0.2 in stars with
the lowest Al abundance. However, we separate the contributions
of all three isotopes and find a considerable spread in the
ratio 24Mg:25Mg:26Mg, with values
ranging from 48:13:39 to 78:11:11. As in NGC 6752, we find a positive
correlation between 26Mg and Al, an anticorrelation between
24Mg and Al, and no correlation between 25Mg and
Al. In M71, our one star has a Mg isotope ratio of 70:13:17. For both
clusters, even the lowest ratios of 25Mg/24Mg
and 26Mg/24Mg exceed those observed in
field stars at the same metallicity, a result also found in
NGC 6752. The contribution of 25Mg to the total Mg
abundance is constant within a given cluster and between clusters with
25Mg/(24Mg+25Mg+26Mg)~=0.13.
For M13 and NGC 6752, the ranges of the Mg isotope ratios are similar
and both clusters show the same correlations between Al and Mg isotopes,
suggesting that the same process is responsible for the abundance
variations in these clusters. While existing models fail to reproduce
all the observed abundances, we continue to favor the scenario in
which two generations of asymptotic giant branch (AGB) stars produce
the observed abundances. A first generation of metal-poor AGB stars
pollutes the entire cluster and is responsible for the large ratios of
25Mg/24Mg and 26Mg/24Mg
observed in cluster stars with compositions identical to field stars
at the same metallicity. Differing degrees of pollution by a second
generation of AGB stars of the same metallicity as the cluster provides
the star-to-star scatter in Mg isotope ratios. Based on data
collected at the Subaru Telescope, which is operated by the National
Astronomical Observatory of Japan.
Title: Carbon stars in local group dwarf galaxies: C and O abundances
Authors: Wahlin, R.; Eriksson, K.; Gustafsson, B.; Hinkle, K. H.;
Lambert, D. L.; Ryde, N.; Westerlund, B.
Bibcode: 2006MmSAI..77..955W
Altcode: 2006astro.ph..5244W
We present abundances of carbon and oxygen as well as abundance
ratios 12C/13C for a sample of carbon stars
in the LMC, SMC, Carina, Sculptor and Fornax dwarf galaxies. The
overall metallicities in these dwarf galaxies are lower than in the
galactic disc. The observations cover most of the AGB and we discuss
the abundance patterns in different regions along the AGB. The
abundances are determined from infrared spectra obtained with the
ISAAC spectrometer on VLT (R=1500) and the Phoenix Spectrometer on
Gemini South (R=50000). The synthetic spectra used in the analysis
were computed with MARCS model atmospheres. We find that the oxygen
abundance is decreasing with decreasing overall metallicity of the
system while the C/O ratio at a given evolutionary phase is increasing
with decreasing oxygen abundance. Based on observations collected
at the European Southern Observatory, Paranal, Chile (ESO Programme
70.D-0414 & 072.D-0501)
Title: Rubidium and lead abundances in globular clusters .
Authors: Yong, D.; Aoki, W.; Carney, B. W.; Grundahl, F.; Lambert,
D. L.; Nissen, P. E.; Paulson, D. B.
Bibcode: 2006MmSAI..77..991Y
Altcode:
We present a brief and biased summary of key star-to-star abundance
variations recently observed in globular clusters and some possible
explanations for these variations. Measurements of the neutron-capture
elements rubidium (Rb) and lead (Pb) in the globular clusters M 13
and NGC 6752 are then presented along with preliminary measurements
in M 4 and M 5. The abundance ratios [Rb/Zr] and [Pb/Fe] are used to
test the globular cluster AGB pollution scenario and to gain insight
into AGB nucleosynthesis.
Title: Heaviest s-process elements in the atmospheres of barium stars
Authors: Gopka, Vera F.; Yushchenk, Alexander; Lambert, David; Drake,
Natalia; Rostopchin, Sergey
Bibcode: 2006isna.confE.105G
Altcode: 2006PoS....28E.105G
The detailed chemical abundance patterns of barium stars HD204075
and HD101013 are used for investigations of heaviest s-process
elements. Special attention is devoted to elements with Z>70, up to
Pb. Spectrum synthesis method is used for abundance calculations. High
resolu- tion spectra were obtained at 2.7 meter telescope of McDonald
observatory (spectral resolution R=60,000, signal to noise ratio
S/N>400) and VLT (R=80,000, S/N>400). CNO and Fe abun- dances are
found for HD204075 and HD101013. Heavy (Z≥64) elements abundances
are found for HD204075. The results of previous investigations of
HD204075 and our data is in good aggre- ment with s-process enriched
pattern. Our estimates show that the abundances of Z≥64 elements in
HD101013 are significantly higher than in HD204075.
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: 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: Abundances of AGB stars in the LMC and SMC: A Work in Progress
Authors: McSaveney, J. A.; Wood, P.; Lattanzio, J. C.; Hinkle, K.;
Lambert, D. L.
Bibcode: 2005ASPC..336..339M
Altcode:
In order to calibrate stellar evolution and nucleosynthesis models,
a selection of highly evolved AGB stars in the LMC and SMC have
been observed to determine element abundances. These stars are
more evolved than those studied by Smith et al.(2002). They require
the use of dynamical atmospheres and pulsation models to determine
the abundances. We present the data so far and detail some of the
approaches started.
Title: Infrared Spectroscopy of Evolved, Interacting Binary Stars
Authors: Hinkle, K. H.; Fekel, F. C.; Joyce, R. R.; Smith, V. V.;
Lambert, D. L.
Bibcode: 2005ASPC..336..173H
Altcode:
Two interacting binary systems, V2116 Oph and HR 4049, are
discussed. These systems both are evolved and contain disks but are
otherwise very different. Both cases illustrate the role the measurement
of cosmic abundances can have in understanding the evolutionary history
of stellar systems.
Title: Observations of Rotational Mixing in 10 to 40
M⊙. Stars
Authors: Venn, K. A.; Lambert, D. L.
Bibcode: 2005ASPC..336...93V
Altcode:
The surface abundances of carbon, nitrogen, and oxygen in massive stars
are now recognized to be affected by rotational mixing, even during
the main-sequence phase. Stellar evolution scenarios that include
rotational effects have broader implications for stellar masses,
lifetimes, and supernova yields, thus it is important to constrain
observationally these new model predictions further. One unique and
powerful constraint is provided by the surface abundance of boron,
which is depleted through exposure to hot gas lying just below the
stellar surface when rotationally mixed. Boron depletions are larger
and occur earlier than nitrogen or other enrichments that require gas to
be mixed from the stellar interior up to the surface. Boron abundances
in main-sequence B-type stars are reviewed, and discussed relative to
nitrogen enrichments, stellar masses, and ages (when the stars are in
clusters). Two observational tests to study the nucleosynthesis of
boron from main-sequence B-stars are also briefly discussed because
of this element's unique position (with lithium and beryllium) at
the intersection of stellar astrophysics, cosmic ray nucleosynthesis,
and primordial nucleosynthesis.
Title: The Magnesium Abundance In 52 B Stars: A Test Of Metallicity
Authors: Lyubimkov, L. S.; Rostopchin, S. I.; Rachkovskaya, T. M.;
Poklad, D. B.; Lambert, D. L.
Bibcode: 2005ASPC..336..335L
Altcode:
From high-resolution spectra a non-LTE analysis of the mg 4481.2
Å feature is implemented for 52 nearby early and medium B stars
on the main sequence (MS). The magnesium abundance is determined;
it is found that log \varepsilon(Mg) = 7.67 ± 0.21 on average. It
is shown that uncertainties in the microturbulent parameter ťare the
main source of errors in log \varepsilon(Mg). When using 36 stars with
the most reliable ťvalues derived from ol and nl lines, we obtain the
mean abundance log \varepsilon(Mg) = 7.59 ± 0.15. The latter value
is precisely confirmed for several hot B stars from an analysis of
the mg 7877 Å weak line. The derived abundance log \varepsilon(Mg)
= 7.59 ± 0.15 is in excellent agreement with the solar magnesium
abundance log \varepsilonsun(Mg) = 7.55 ± 0.02, as well
as with the proto-Sun abundance log \varepsilonps(Mg) =
7.62 ± 0.02. Thus, it is confirmed that the Sun and the B-type MS
stars in our neighborhood have the same metallicity.
Title: The Revised Solar Abundance of Oxygen
Authors: Allende Prieto, C.; Lambert, D. L.
Bibcode: 2005LPICo1278....9A
Altcode:
No abstract at ADS
Title: Li Abundance Survey in Galactic Thin Disk
Authors: Lambert, D. L.; Reddy, B. E.
Bibcode: 2005ASPC..336..347L
Altcode:
Lithium abundances for a sample of 451 F and G dwarfs including 181 new
stars all belonging to the Galactic thin disk are discussed. Lithium
abundances, metallicities ([Fe/H]), masses, and ages are determined
(Lambert & Reddy 2004). The field stars span a larger range in
[Fe/H] than the open clusters for which [Fe/H] ≃ 0.0±0.2. The
initial Li from which stars formed has been traced from stars for
which astration of lithium is believed to be unimportant.
Title: On the Origin of Sulfur
Authors: Ryde, N.; Lambert, D. L.
Bibcode: 2005ASPC..336..355R
Altcode: 2005astro.ph.10136R
We present our work on the halo evolution of sulfur, based on
observations of the S I lines around 9220 Å for ten stars for which
the S abundance was obtained previously from much weaker S I lines at
8694 Å. We cannot confirm the rise and the high [S/Fe] abundances for
low [Fe/H], as claimed in the literature from analysis of the 8694 Å
lines. The reasons for claims of an increase in [S/Fe] with decreasing
[Fe/H] are probably twofold: uncertainties in the measurements of the
weak 8694 Å lines, and systematic errors in metallicity determinations
from Fe I lines. The near-infrared sulfur triplet at 9212.9, 9228.1,
and 9237.5 Å are preferred for an abundance analysis of sulfur for
metal-poor stars. Our work was presented in full by Ryde & Lambert
(2004).
Title: Green --- Not grey
Authors: Lambert, D. L.
Bibcode: 2005ASPC..336..289L
Altcode:
A miscellany of thoughts gathered before, during and after the meeting
is assembled here. I attempt to illustrate the extraordinary range in
observing tools that has become available since I took my first steps in
1960 towards the field of cosmic abundances. Serendipity is highlighted
as a source of particular delight for observers. A commentary on the
apparent discrepancies between the 6Li and 7Li
abundances of metal-poor dwarfs on the Spite plateau is presented to
show the breadth of disciplines that may be gathered under the umbrella
represented by a single problem in spectroscopic astrophysics involving
cosmic abundances.
Title: Li-Rich K Giants: A Few New Cases
Authors: Reddy, Bacham E.; Lambert, David L.
Bibcode: 2005BASI...33Q.374R
Altcode:
No abstract at ADS
Title: Abundances in giant stars of the globular cluster NGC 6752
Authors: Yong, D.; Grundahl, F.; Nissen, P. E.; Jensen, H. R.; Lambert,
D. L.
Bibcode: 2005A&A...438..875Y
Altcode: 2005astro.ph..4283Y
Recent theoretical yields and chemical evolution models demonstrate that
intermediate-mass AGB stars cannot reproduce the observed abundance
distributions of O, Na, Mg, and Al. As a further observational test
of this finding, we present elemental abundance ratios [X/Fe] for 20
elements in 38 bright giants of the globular cluster NGC 6752 based on
high-resolution, high signal-to-noise spectra obtained with UVES on the
VLT. This is the most complete spectroscopic analysis of this cluster in
terms of the number of elements considered and the number of stars in
the sample. The stars span more than 1000 K in effective temperature
and more than 3 visual magnitudes along the red giant branch. None
of the abundance ratios [X/Fe] show a correlation with evolutionary
status. For Si and heavier elements, the small scatter in [X/Fe] may be
attributable to the measurement uncertainties. Our mean abundance ratios
[X/Fe] are in good agreement with previous studies of this cluster
and are also consistent with other globular clusters and field stars
at the same metallicity. The mean abundance ratios [Ba/Eu] and [La/Eu]
exhibit values, in agreement with field stars at the same metallicity,
that lie approximately midway between the pure r-process and the solar
(s-process + r-process) mix, indicating that AGB stars have played a
role in the chemical evolution of the proto-cluster gas. For the first
time, we find possible evidence for an abundance variation for elements
heavier than Al in this cluster. We find a correlation between [Si/Fe]
and [Al/Fe] which is consistent with the abundance anomalies being
synthesized via proton captures at high temperatures. Leakage from the
Mg-Al chain into 28Si may explain the Si excess in stars
with the highest [Al/Fe]. We identify correlations between [Y/Fe] and
[Al/Fe], [Zr/Fe] and [Al/Fe], and [Ba/Fe] and [Al/Fe] suggesting that Y,
Zr, and Ba abundances may increase by about 0.1 dex as Al increases by
about 1.3 dex. While the correlations are statistically significant,
the amplitudes of the variations are small. If the small variations in
Y, Zr, and Ba are indeed real, then the synthesis of the Al anomalies
must have taken place within an unknown class of stars that also ran
the s-process.
Title: Abundance Analyses of Field RV Tauri Stars. VI. An Extended
Sample
Authors: Giridhar, Sunetra; Lambert, David L.; Reddy, Bacham E.;
Gonzalez, Guillermo; Yong, David
Bibcode: 2005ApJ...627..432G
Altcode: 2005astro.ph..3344G
An abundance analysis is presented and discussed for a sample of 14 RV
Tauri stars. The present abundance data and those from our previous
papers and by other workers are combined in an attempt to further
understanding of the dust-gas separation process that afflicts many RV
Tauri variables. We propose that a star's intrinsic (i.e., initial)
metallicity is given by the photospheric zinc abundance. Variables
warmer than about 5000 K and with an initial metallicity [Fe/H]>=-1
are affected by dust-gas separation. Variables of all metallicities and
cooler than about Teff~=5000 K are unaffected by dust-gas
separation. The RV Tauri variables show a spread in their C abundances,
with the lower boundary of the points in the C versus Zn plane falling
close to the predicted trend for giants after the first dredge-up. The
upper boundary is inhabited by a few stars that are carbon-rich. The
O abundances in the mean follow the predicted trend from unevolved
stars, in line with the expectation that photospheric O abundance is
unaffected by the first dredge-up. An evolutionary scenario involving
mass loss by a first-ascent or early-AGB red giant, the primary star
of a binary, is sketched.
Title: Three Li-rich K Giants: IRAS 12327-6523, 13539-4153, and
17596-3952
Authors: Reddy, Bacham E.; Lambert, David L.
Bibcode: 2005AJ....129.2831R
Altcode: 2005astro.ph..3253R
We report on spectroscopic analyses of three K giants previously
suggested to be Li-rich: IRAS 12327-6523, 13539-4153, and
17596-3952. High-resolution optical spectra and the LTE model
atmospheres are used to derive the stellar parameters (Teff,
logg, [Fe/H]), elemental abundances, and the isotopic ratio
12C/13C. IRAS 13539-4153 shows an extremely
high Li abundance of logɛ(Li)~4.2, a value 10 times greater than the
present Li abundance in the local interstellar medium. This is the third
highest Li abundance yet reported for a K giant. IRAS 12327-6523 shows
a Li abundance of logɛ(Li)~1.4. IRAS 17596-3952 is a rapidly rotating
(Vsini~35 km s-1) K giant with logɛ(Li)~2.2. Infrared
photometry shows the presence of an IR excess, suggesting mass loss. A
comparison is made between these three stars and previously recognized
Li-rich giants.
Title: VLT/UVES Observations of Molecules and Diffuse Bands in the
ISM of the Magellanic Clouds
Authors: Welty, D. E.; Federman, S. R.; Gredel, R.; Lambert, D. L.;
Thorburn, J. A.
Bibcode: 2005AAS...206.3815W
Altcode: 2005BAAS...37..492W
We report some initial results on the abundances of interstellar CH,
CH+, and CN in the Magellanic Clouds, derived from high S/N spectra of
5 SMC and 9 LMC stars obtained with the VLT/UVES. We detect CH and/or
CH+ toward 2 SMC and 8 LMC stars, and detect CN toward one of the LMC
stars. To our knowledge, these are the first reported detections of
these molecular species in the ISM of the Magellanic Clouds, apart
from those of CH and CH+ toward SN 1987A. The column densities now
available for CH, H2, K I, and Na I indicate that all those species are
typically less abundant in the Magellanic Clouds than in our Galaxy,
presumably due to the lower metallicities and generally stronger ambient
radiation fields there. The relationships among those four species,
however, appear to be similar to those observed in the Galactic ISM,
except that Na I/H2, K I/H2, and CH/H2 are generally lower in the
SMC. Toward most of our targets, the UVES spectra also reveal
absorption at velocities corresponding to the Magellanic Clouds ISM
from several of the typically strongest of the enigmatic diffuse
interstellar bands (e.g., those at 5780, 5797, and 6284 A). In most
cases, the Magellanic Clouds DIBs are weaker, for a given N(H), than
those typically observed in our Galaxy (again presumably due to the
lower metallicities and stronger radiation fields) --- but they are
also weaker, relative to Na I, than in the Milky Way. We comment
briefly on the implications of these data for models of diffuse cloud
chemistry in low-metallicity systems and for the properties of the
(still unidentified) carriers of the DIBs. This work has been
supported by NASA LTSA grant NAG5-11413 to the University of Chicago.
Title: Surface abundances of light elements for a large sample
of early B-type stars - IV. The magnesium abundance in 52 stars -
a test of metallicity
Authors: Lyubimkov, L. S.; Rostopchin, S. I.; Rachkovskaya, T. M.;
Poklad, D. B.; Lambert, D. L.
Bibcode: 2005MNRAS.358..193L
Altcode: 2005MNRAS.tmp..141L; 2005astro.ph..1389L
From high-resolution spectra a non-local thermodynamic equilibrium
analysis of the MgII 4481.2-Åfeature is implemented for 52 early
and medium local B stars on the main sequence (MS). The influence
of the neighbouring line AlIII 4479.9-Åis considered. The magnesium
abundance is determined; it is found that logɛ(Mg) = 7.67 +/- 0.21 on
average. It is shown that uncertainties in the microturbulent parameter
Vt are the main source of errors in logɛ(Mg). When using
36 stars with the most reliable Vt values derived from
OII and NII lines, we obtain the mean abundance logɛ(Mg) = 7.59 +/-
0.15. The latter value is precisely confirmed for several hot B stars
from an analysis of the MgII 7877-Åweak line. The derived abundance
logɛ(Mg) = 7.59 +/- 0.15 is in excellent agreement with the solar
magnesium abundance logɛsolar (Mg) = 7.55 +/- 0.02, as
well as with the proto-Sun abundance logɛps(Mg) = 7.62 +/-
0.02. Thus, it is confirmed that the Sun and the B-type MS stars in
our neighbourhood have the same metallicity.
Title: Carbon stars in local group dwarf galaxies: C &
O abundances
Authors: Wahlin, R.; Eriksson, K.; Gustafsson, B.; Hinkle, K. H.;
Lambert, D. L.; Ryde, N.; Westerlund, B.
Bibcode: 2005ESASP.560.1017W
Altcode: 2005csss...13.1017W
No abstract at ADS
Title: Oxygen, sodium and iron abundances in the Hyades
Authors: Allende Prieto, C.; Yong, D.; Lambert, D. L.
Bibcode: 2005ESASP.560..389A
Altcode: 2005csss...13..389A
No abstract at ADS
Title: Far Ultraviolet Spectroscopic Explorer Measurements of
Interstellar Fluorine
Authors: Federman, S. R.; Sheffer, Yaron; Lambert, David L.; Smith,
V. V.
Bibcode: 2005ApJ...619..884F
Altcode: 2004astro.ph.10362F
The source of fluorine is not well understood, although core-collapse
supernovae, Wolf-Rayet stars, and asymptotic giant branch stars have
been suggested. A search for evidence of the ν-process during Type
II supernovae is presented. Absorption from interstellar F I is
seen in spectra of HD 208440 and HD 209339A acquired with the Far
Ultraviolet Spectroscopic Explorer. In order to extract the column
density for F I from the line at 954 Å, absorption from H2
has to be modeled and then removed. Our analysis indicates that for
H2 column densities less than about 3×1020
cm-2, the amount of F I can be determined from λ954. For
these two sight lines, there is no clear indication for enhanced F
abundances resulting from the ν-process in a region shaped by past
supernovae. Based on observations made with the NASA/CNES/CSA Far
Ultraviolet Spectroscopic Explorer (FUSE), which is operated for NASA
by the Johns Hopkins University under NASA contract NAS 5-32985.
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: Oxygen in galactic disk stars: non-LTE abundances from the
777 nm O I triplet
Authors: Ramirez, Ivan; Allende Prieto, Carlos; Lambert, David L.
Bibcode: 2005IAUS..228..271R
Altcode: 2005astro.ph..6744R
Oxygen abundances for a large sample of dwarf and giant stars
kinematically selected to be part of the Galactic thin and thick disks
have been determined from a non-LTE analysis of the O I triplet lines
at 777 nm. The abundance analysis was performed using the infrared
flux method temperature scale, trigonometric surface gravities, and
accurate atomic data. Within this framework, the ionization balance of
iron lines could not be satisfied and so we adopted the iron abundances
from Fe II lines only given that they are relatively less sensitive
to changes in the atmospheric parameters. We show the resulting [O/Fe]
vs. [Fe/H] relationship and briefly discuss its implications.
Title: Phoenix Spectra of Carbon Stars in the LMC
Authors: Wahlin, Rurik; Eriksson, Kjell; Gustafsson, Bengt; Hinkle,
Kenneth; Lambert, David; Ryde, Nils; Westerlund, Bengt
Bibcode: 2005hris.conf..439W
Altcode:
We present high-resolution, IR-spectra of Carbon stars in the LMC
obtained with the Phoenix spectrometer on the Gemini South 8-meter
telescope. This is part of an ongoing project where CNO abundances
and 12C/13C ratios of Carbon Stars are determined in Local-Group
dwarf galaxies of different metallicities. The spectra obtained so
far cover two 20 cm 1 wide spectral regions in the H and K bands. The
bands contain lines from CN, C2, and CO, with 12C and 13C isotopes, and
several atomic lines. The spectra are analyzed with synthetic spectra
of model atmospheres from the MARCS spherical-model-atmosphere code.
Title: Testing Rotational Mixing in Massive Stars with Boron
Abundances in Main-Sequence B-type Stars.
Authors: Mendel, J. T.; Venn, K. A.; Proffitt, C.; Brooks, A. M.;
Lambert, D. L.
Bibcode: 2004AAS...205.1302M
Altcode: 2004BAAS...36S1358M
Boron's role is crucial in verifying the new stellar evolution models
of massive stars that include rotation because its surface abundance
is depleted at an observable level long before CNO-elements are
mixed upwards from the interior to the surface. While most stars
with boron depletions do show nitrogen enrichments, Venn et al
(2002) found 2 boron-poor stars without nitrogen enhancements;
furthermore, they showed that the depletion levels of these 12-13
solar mass stars were uncharacteristically high. In this poster, we
present new boron abundances for seven main-sequence B-type stars
from HST STIS spectroscopy. These target stars are all members of
OB associations, and they have normal, unenriched surface nitrogen
abundances, but suggestively weak B III line strengths from archival
IUE spectroscopy. Five stars could be studied in fine detail, while
the rotational velocities for two stars were so large that we could
only estimate their abundances. For all seven targets, the boron
abundances, nitrogen abundances, stellar parameters, and ages are
all in very good agreement with predictions from the Maeder &
Meynet (2000) and Heger & Langer (2000) stellar models, assuming
rotational velocities between 200 and 300 km/s.
Title: RCoronae Borealis stars at minimum light - UW Cen
Authors: Kameswara Rao, N.; Reddy, Bacham E.; Lambert, David L.
Bibcode: 2004MNRAS.355..855K
Altcode: 2004astro.ph..9211K; 2004MNRAS.tmp..486K; 2004astro.ph..9211R;
2004MNRAS.355..855R
Two high-resolution optical spectra of the R Coronae Borealis (R CrB)
star UW Cen in decline are discussed. A spectrum from mid-1992 when the
star had faded by 3mag shows just a few differences with the spectrum
at maximum light. The ubiquitous sharp emission lines seen in R CrB at
a similar drop below maximum light are absent. In contrast, a spectrum
from mid-2002 when the star was 5mag below maximum light shows an
array of sharp emission lines and a collection of broad emission
lines. Comparisons are made with spectra of R CrB obtained during
the deep 1995-1996 minimum. The many common features are discussed in
terms of a torus-jet geometry.
Title: Lithium in Very Metal-poor Dwarf Stars - Problems for Standard
Big Bang Nucleosynthesis?
Authors: Lambert, David L.
Bibcode: 2004AIPC..743..206L
Altcode: 2004astro.ph.10418L
The standard model of primordial nucleosynthesis by the Big
Bang as selected by the WMAP-based estimate of the baryon density
(Ωbh2) predicts an abundance of 7Li that is a
factor of three greater than the generally reported abundance for stars
on the Spite plateau, and an abundance of 6Li that is about
a thousand times less than is found for some stars on the plateau. This
review discusses and examines these two discrepancies. They can likely
be resolved without major surgery on the standard model of the Big
Bang. In particular, stars on the Spite plateau may have depleted
their surface lithium abundance over their long lifetime from the
WMAP-based predicted abundances down to presently observed abundances,
and synthesis of 6Li (and 7Li) via α + α fusion
reactions may have occurred in the early Galaxy. Yet, there remain
fascinating ways in which to remove the two discrepancies involving
aspects of a new cosmology, particularly through the introduction of
exotic particles.
Title: Galactic Abundance Gradient in Boron
Authors: Semler, D.; Venn, K. A.; Lambert, D. L.
Bibcode: 2004AAS...205.2103S
Altcode: 2004BAAS...36R1376S
We present B III stellar abundances in five main sequence B-stars with
different galactocentric distances from HST UV STIS spectroscopy. The
boron gradient is of interest because the present-day interstellar
boron abundance is dominated by spallation reactions between galactic
cosmic rays and interstellar oxygen atoms. Knowing the present-day
oxygen gradient is near -0.07 dex/kpc, then a determination of a
boron gradient allows us to examine spallation reactions and the
galactic cosmic ray flux with distance. Based on the low nitrogen
abundances, the program stars (LS 5130, NGC 6231-295, NGC 884-2361,
S 285-6, and S 289-2) are thought to be unmixed with CNO-cycled gas,
and thus their stellar boron abundances should be representative of
the present-day boron in the interstellar medium at each galactocentric
location. However, while enriched nitrogen is an indicator that boron
depletion has occurred, unenriched nitrogen levels do not guarantee
undepleted boron levels for a star. Two stars have well determined
boron abundances, which yield a boron abundance gradient of -0.06
dex/kpc. Due to low S/N or a lack of a boron feature, upper limits
are set for three additional stars. The most simple interpretation
of this nearly linear B/O gradient is that the formation of boron and
the galactic cosmic ray flux is similar throughtout the Galactic disk.
Title: Oxygen In The Galactic Disk: Non-LTE Abundances From The 777
nm O I Triplet
Authors: Ramirez, I.; Allende Prieto, C.; Lambert, D. L.
Bibcode: 2004AAS...205.5212R
Altcode: 2004BAAS...36.1424R
Oxygen abundances for a large sample of dwarf stars in the Galactic thin
and thick disks are determined from a non-LTE analysis of the oxygen
triplet lines at 777 nm. Kinematic criteria are employed to determine
whether a star belongs to the thin or thick disk. Temperatures are
obtained from photometric calibrations based on the infrared flux
method and surface gravities from Hipparcos parallaxes and stellar
evolution calculations. High resolution spectra from the HET and the
2.7 m telescopes at McDonald Observatory, and the VLTI-UVES archive are
used. Metallicities are derived from relatively unblended Fe I and Fe
II lines for which reliable laboratory gf values are available. Oxygen
abundances are obtained from the triplet lines at 777 nm and a
restricted non-LTE analysis, i.e. spectrum synthesis was performed
with non-LTE level populations on an LTE atmospheric structure. We
confirm previous studies that suggest higher oxygen abundances in
the thick disk than in the thin disk although our preliminary results
favor a smooth transition instead of two completely separate trends,
i.e. thick disk stars with intermediate and relatively lower oxygen
abundances are also found.
Title: The Hobby-Eberly Telescope: performance upgrades, status,
and plans
Authors: Booth, John A.; Adams, Mark T.; Barker, Edwin S.; Bash,
Frank N.; Fowler, James R.; Good, John M.; Hill, Gary J.; Kelton,
Philip W.; Lambert, David L.; MacQueen, Phillip J.; Palunas, Povilas;
Ramsey, Lawrence W.; Wesley, Gordon L.
Bibcode: 2004SPIE.5489..288B
Altcode:
The Hobby-Eberly Telescope (HET) is a fixed-elevation, 9.2-m telescope
with a spherical primary mirror and a tracker at prime focus to follow
astronomical objects. The telescope was constructed for $13.9M over
the period 1994-1997. A series of extensive engineering upgrades
and corrective actions have been completed recently, resulting in
significantly improved delivered image quality and increased operational
efficiency. The telescope's Spherical Aberration Corrector (SAC) optics
were recoated with a highly reflective and durable broadband coating at
Lawrence Livermore National Laboratory. The software mount model that
maintains optical alignment of the SAC with the 11-m primary mirror
array was recalibrated and improved. The acquisition and guiding optics
for both the High Resolution Spectrograph (HRS) and the Low Resolution
Spectrograph (LRS) were reworked and improved, allowing for better focus
and SAC alignment monitoring and control. Recoating of the primary
mirror segment array was begun. Telescope images of 0.82 arcseconds
have been recorded for sustained periods in preliminary testing
following the engineering upgrade, an improvement of 50% over previous
best performance. Additional engineering upgrades are scheduled to
consolidate these performance gains and to continue improving delivered
image quality, throughput, and telescope operational efficiency. The
HET is now capable of the science performance for which it was designed.
Title: HD 153720 - A SB2 system with twin metallic-line components
Authors: Yushchenko, A. V.; Gopka, V. F.; Khokhlova, V. L.; Lambert,
D. L.; Kim, C.; Kang, Y. W.
Bibcode: 2004A&A...425..171Y
Altcode:
We report the results of abundance determinations for the components
of the SB2 star HD 153720 from high resolution (R=60 000) echelle high
signal-to-noise spectra of the wavelength region 3595-10 260 Å taken
with the 2.7 m telescope of the McDonald Observatory We found the values
of the atmospheric parameters of the primary to be effective temperature
Teff = 7425 K and surface gravity log g,= 4.0 cgs, and of
the secondary to be Teff = 7125 K and log g,= 3.9 cgs. The
microturbulent velocity is vmicro= 2.7 km s-1
for both components, and the projected rotational velocity is v sin
i ,= 15 km s-1 also for both components. The abundances
of about 20 elements were determined with the method of spectrum
synthesis. The components of HD 153720 are metallic-line stars. Possible
inconsistencies between old and new measurements of radial velocities
may be explained by the existence of third body in this system. A
review of recent high resolution spectral observations of eight A4-F1
binaries shows that only one of these systems can be classified as
normal. Based on observations obtained at the 2.7-m telescope of
the McDonald Observatory. The data are only available in electronic
form at http://www.edpsciences.org
Title: The R Coronae Borealis stars: carbon abundances from forbidden
carbon lines
Authors: Pandey, Gajendra; Lambert, David L.; Rao, N. Kameswara;
Gustafsson, Bengt; Ryde, Nils; Yong, David
Bibcode: 2004MNRAS.353..143P
Altcode: 2004MNRAS.tmp..228P; 2004astro.ph..5600P
Spectra of several R Coronae Borealis (RCB) stars at maximum light
have been examined for the [CI] 9850- and 8727-Åabsorption lines. The
9850-Åline is variously blended with an FeII and CN lines, but positive
identifications of the [CI] line are made for RCrB and SUTau. The
8727-Åline is detected in the spectrum of the five stars observed
in this wavelength region. Carbon abundances are derived from the
[CI] lines using the model atmospheres and atmospheric parameters
used by Asplund et al. Although the observed strength of a CI
line is constant from cool to hot RCB stars, the strength is lower
than predicted by an amount equivalent to a factor of 4 reduction
of the gf-value of a line. Asplund et al. dubbed this `the carbon
problem' and discussed possible solutions. The [CI] 9850-Åline
seen clearly in RCrB and SUTau confirms the magnitude of the carbon
problem revealed by the CI lines. The [CI] 8727-Åline measured in
five stars shows an enhanced carbon problem. The gf-value required
to fit the observed [CI] 8727-Åline is a factor of 15 less than the
well-determined theoretical gf-value. We suggest that the carbon problem
for all lines may be alleviated to some extent by a chromospheric-like
temperature rise in these stars. The rise far exceeds that predicted
by our non-local thermodynamic equilibrium calculations, and requires
a substantial deposition of mechanical energy.
Title: Li Enrichment, Mass Loss, and CN Abundances in High Rotating
K Giants
Authors: Drake, N. A.; de La Reza, R.; da Silva, L.; Lambert, D. L.
Bibcode: 2004IAUS..215..242D
Altcode:
No abstract at ADS
Title: S4N: A spectroscopic survey of stars in the solar
neighborhood. The Nearest 15 pc
Authors: Allende Prieto, C.; Barklem, P. S.; Lambert, D. L.; Cunha, K.
Bibcode: 2004A&A...420..183A
Altcode: 2004astro.ph..3108P; 2004astro.ph..3108A
We report the results of a high-resolution spectroscopic survey of all
the stars more luminous than M_V = 6.5 mag within 14.5 pc from the
Sun. The Hipparcos catalog's completeness limits guarantee that our
survey is comprehensive and free from some of the selection effects in
other samples of nearby stars. The resulting spectroscopic database,
which we have made publicly available, includes spectra for 118 stars
obtained with a resolving power of R ≃ 50 000, continuous spectral
coverage between ∼ 362-921 nm, and typical signal-to-noise ratios
in the range 150-600. We derive stellar parameters and perform a
preliminary abundance and kinematic analysis of the F-G-K stars
in the sample. The inferred metallicity ([Fe/H]) distribution is
centered at about -0.1 dex, and shows a standard deviation of 0.2
dex. A comparison with larger samples of Hipparcos stars, some of
which have been part of previous abundance studies, suggests that
our limited sample is representative of a larger volume of the local
thin disk. We identify a number of metal-rich K-type stars which
appear to be very old, confirming the claims for the existence of
such stars in the solar neighborhood. With atmospheric effective
temperatures and gravities derived independently of the spectra, we
find that our classical LTE model-atmosphere analysis of metal-rich
(and mainly K-type) stars provides discrepant abundances from neutral
and ionized lines of several metals. This ionization imbalance could
be a sign of departures from LTE or inhomogeneous structure, which
are ignored in the interpretation of the spectra. Alternatively,
but seemingly unlikely, the mismatch could be explained by systematic
errors in the scale of effective temperatures. Based on transitions of
majority species, we discuss abundances of 16 chemical elements. In
agreement with earlier studies we find that the abundance ratios to
iron of Si, Sc, Ti, Co, and Zn become smaller as the iron abundance
increases until approaching the solar values, but the trends reverse
for higher iron abundances. At any given metallicity, stars with a low
galactic rotational velocity tend to have high abundances of Mg, Si,
Ca, Sc, Ti, Co, Zn, and Eu, but low abundances of Ba, Ce, and Nd. The
Sun appears deficient by roughly 0.1 dex in O, Si, Ca, Sc, Ti, Y,
Ce, Nd, and Eu, compared to its immediate neighbors with similar iron
abundances. Based on observations made with the 2.7 m telescope at
the McDonald Observatory of the University of Texas at Austin (Texas),
and the 1.52 m telescope at the European Southern Observatory (La
Silla, Chile) under the agreement with the CNPq/Observatorio Nacional
(Brazil). Tables 3-5 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/420/183
Title: Surface abundances of light elements for a large sample of
early B-type stars - III. An analysis of helium lines in spectra of
102 stars
Authors: Lyubimkov, L. S.; Rostopchin, S. I.; Lambert, D. L.
Bibcode: 2004MNRAS.351..745L
Altcode:
Non-local thermodynamic equilibrium analysis of He I lines in spectra of
102 B stars is implemented in order to derive the helium abundance He/H,
the microturbulent parameter Vt and the projected rotation
velocity v sini. A simultaneous determination of He/H and Vt
for the stars is effected by analysing equivalent widths of the 4471-
and 4922-Å lines primarily as indicators of He/H and the 4713-, 5016-,
5876- and 6678-Å lines primarily as indicators of Vt. The
rotation velocities v sini are found from profiles of the same
lines. It is shown that, when Vt > 7 km s-1,
the Vt(He I) values determined from He I lines are
systematically overestimated as compared with the Vt(OII,
NII) values derived from OII and NII lines. This discrepancy is
especially appreciable for hot evolved B giants with Vt(He I)
= 16-23 km s-1 and may indicate a failure of classical model
atmospheres to represent the strong He I lines for these stars. Two programme stars, HR 1512 and 7651, are found to be helium-weak
stars. The remaining 100 stars are divided into three groups according
to their masses M. The microturbulent parameter Vt(He I)
is low for all stars of group A (M= 4.1-6.9 Msolar) and for
all stars with the relative ages t/tMS < 0.8 of group
B (M= 7.0-11.2 Msolar). Their Vt(He I) values
are within the 0 to 5 km s-1 range, as a rule; the mean
value is Vt= 1.7 km s-1. Only evolved giants of
group B, which are close to the termination of the main-sequence (MS)
evolutionary phase (t/tMS > 0.8), show Vt(He
I) up to 11 km s-1. The helium abundance He/H is correlated
with the relative age t/tMS in both groups; the averaged
He/H enhancement during the MS phase is 26 per cent. For group C,
containing the most massive stars (M= 12.4-18.8 Msolar), the
Vt(He I) values display a correlation with t/tMS,
varying from 4 to 23 km s-1. The He/H determination for
hot evolved B giants of the group with Vt(He I) > 15
km s-1 depends on a choice between the Vt(He I)
and Vt(OII, NII) scales. The mean He/H enrichment by 67 per
cent during the MS phase is found, if the abundances He/H are based on
the Vt(OII, NII) scale; however, two evolved giants with
especially high v sini, HR 7446 and 7993, show the He/H enhancement
by about a factor of 2.5. When using the same Vt scale,
we found a trend of He/H with projected rotational velocities v sini
a large dispersion for v sini > 150 km s-1 can result
from differences in masses M. A comparison with the stellar model
computations with rotationally induced mixing shows that the observed
helium enrichment during the MS phase can be explained by rotation with
initial velocities 250-400 km s-1. The He/H distribution on
M and v sini based on the Vt(OII, NII) scale seems to be in
better agreement with the theory than one based on the Vt(He
I) scale. The mean value He/H = 0.10 derived for stars in the zero age
main sequence (ZAMS) vicinity can be adopted as the typical initial
helium abundance for early B stars in the solar neighbourhood.
Title: The chemical composition and circumstellar environment of
the variable star QY Sge
Authors: Goswami, Aruna; Kameswara Rao, N.; Lambert, D. L.
Bibcode: 2004ASPC..310..430G
Altcode: 2004vslg.conf..430G; 2004IAUCo.193..430G
Chemical composition studies of the variable star QY Sge show abundance
anomalies suggestive of the pattern exhibited by the warmer RV Tau
variables. Abundance analysis indicates a near-solar atmosphere with
highly condensable elements depleted by several factors. Evidence of
broad Na D emission features in its spectrum, a characteristic feature
of R CrB stars taken at minimum, however, raises the question of its
spectral classification. We address this question through a comparative
analysis of its spectrum with those of γ Cyg, 89 Her and R CrB taken at
minimum, in addition to abundance analysis. We also discuss a possible
physical scenario of the circumstellar environment accounting for the
characteristics of the distinct spectroscopic features.
Title: Boron Benchmarks for the Galactic Disk
Authors: Boesgaard, Ann Merchant; McGrath, Elizabeth J.; Lambert,
David L.; Cunha, Katia
Bibcode: 2004ApJ...606..306B
Altcode:
Sixteen Population I solar-type dwarfs have been selected to ascertain
the baseline B abundance in the Galactic disk for a range of a factor of
4 in metallicity: from [Fe/H] of -0.5 to +0.1. All the stars selected
are undepleted in Be, which ensures that they have also retained their
full initial abundance of B. Evaluation of the trend of B with Fe
provides a means to study the evolution of B in the Galactic disk. We
observed 16 bright stars around the B I 2497 Å line, using the STIS
echelle spectrograph on HST. New observations of Li and Be in some
stars were made, and previous abundance studies of Li and Be in these
stars were reevaluated using revised parameters and a modified spectral
synthesis code for consistency with the B measurements. Abundances of
B were calculated by spectrum synthesis with the revised MOOG code,
which accounts for the increased opacity in the UV due to metals;
the LTE B abundances were then corrected for non-LTE effects. Four
additional stars with undepleted Be have HST B observations, which
increase our sample to 20. For these disk stars there is a shallow slope
for B versus Fe and Be versus Fe, such that as Fe increases by a factor
of 4, B and Be increase by 1.7 times. The slope for BLTE
versus Fe is 0.31+/-0.09, for BNLTE versus Fe 0.40+/-0.12,
and for Be versus Fe 0.38+/-0.14. We have estimated the effect of
additional UV opacity from Mg and find that an increase of 0.3 dex
in Mg results in a higher B abundances by 0.1 dex for all the disk
stars. Individual stars are not consistently above (or below) the mean
in both B and Be, implying that the star-to-star differences are not
due to variations in the elemental content of the ``natal'' clouds. We
find that the trend of B abundance with [Fe/H] is consistent with
the general trend observed in halo stars. If we connect the halo and
disk stars, then an increase in the Fe abundance by 103 is
accompanied by increases of 100 times in B and 550 times in Be. However,
fitting two separate relations for the disk and the halo stars results
in a somewhat steeper slope for Be for the halo stars (1.08+/-0.07)
relative to the disk stars (0.38+/-0.14). This is the case for B also
in LTE, with Bhalo (0.90+/-0.07) versus Bdisk
(0.32+/-0.12). However, the NLTE B abundance increases more slowly
for halo stars than the Be abundance does; since this is not predicted
by light-element synthesis or depletion, we suggest that a full NLTE
analysis would be preferable to making the (small) corrections to the
LTE abundances. Some of the lowest metallicity stars are thought to
have only upper limits on the B abundance; if that is the case, the
NLTE B slope is steeper, nearing 1.0. The abundance of B in the disk
stars is observed to be a factor of ~15+7-5 more
than the abundance of Be in these stars, a result consistent with the
predictions of Galactic cosmic-ray (GCR) spallation, B/Be=15+/-5. The
upper envelope for Li versus Fe yields Li/B and Li/Be ratios that,
when coupled with models and predictions, indicate that 20%-45%
of Li might be produced by GCRs. While there is no evidence to
support the production of B by neutrino spallation, we cannot rule
it out. Based on observations obtained with the NASA/ESA Hubble
Space Telescope (HST) through the Space Telescope Science Institute,
which is operated by the Association of Universities for Research in
Astronomy, Inc., under NASA contract NAS5-26555.
Title: VizieR Online Data Catalog: Masses, ages and metallicities
of F-G dwarfs (Lambert+, 2004)
Authors: Lambert, D. L.; Reddy, B. E.
Bibcode: 2004yCat..73490757L
Altcode:
Lithium abundances are presented for a total of 451 F-G dwarfs. The
aim of this survey of Lithium abundance is to document the astration
of Li as a function of stellar mass, age, and metallicity. These data
are given in table1.dat, which includes 157 stars for which the Li
abundance is determined for the first time. Almost all stars belonging
to thin disc population. (1 data file).
Title: Lithium abundances of the local thin disc stars
Authors: Lambert, David L.; Reddy, Bacham E.
Bibcode: 2004MNRAS.349..757L
Altcode: 2004astro.ph..1259L
Lithium abundances are presented for a sample of 181 nearby F and G
dwarfs with accurate Hipparcos parallaxes. The stars are on circular
orbits about the Galactic centre and, hence, are identified as belonging
to the thin disc. This sample is combined with two published surveys
to provide a catalogue of lithium abundances, metallicities ([Fe/H]),
masses, and ages for 451 F-G dwarfs, almost all belonging to the thin
disc. The lithium abundances are compared and contrasted with published
lithium abundances for F and G stars in local open clusters. The
field stars span a larger range in [Fe/H] than the clusters for which
[Fe/H]~= 0.0 +/- 0.2. The initial (i.e. interstellar) lithium abundance
of the solar neighbourhood, as derived from stars for which astration
of lithium is believed to be unimportant, is traced from logɛ(Li) =
2.2 at [Fe/H]=-1 to logɛ(Li) = 3.2 at +0.1. This form for the evolution
is dependent on the assumption that astration of lithium is negligible
for the stars defining the relation. An argument is advanced that this
latter assumption may not be entirely correct, and, the evolution of
lithium with [Fe/H] may be flatter than previously supposed. A sharp
Hyades-like Li dip is not seen among the field stars and appears to
be replaced by a large spread among lithium abundances of stars more
massive than the lower mass limit of the dip. Astration of lithium by
stars of masses too low to participate in the Li dip is discussed. These
stars show little to no spread in lithium abundance at a given [Fe/H]
and mass.
Title: The Interstellar Rubidium Isotope Ratio toward ρ Ophiuchi A
Authors: Federman, S. R.; Knauth, David C.; Lambert, David L.
Bibcode: 2004ApJ...603L.105F
Altcode: 2004astro.ph..1601F
The isotope ratio 85Rb/87Rb places constraints on
models of the nucleosynthesis of heavy elements, but there is no precise
determination of the ratio for material beyond the solar system. We
report the first measurement of the interstellar Rb isotope ratio. Our
measurement of the Rb I line at 7800 Å for the diffuse gas toward ρ
Oph A yields a value of 1.21+/-0.30 (1 σ) that differs significantly
from the meteoritic value of 2.59. The Rb/K elemental abundance ratio
for the cloud also is lower than that seen in meteorites. Comparison
of the 85Rb/K and 87Rb/K ratios with meteoritic
values indicates that the interstellar 85Rb abundance
in this direction is lower than the solar system abundance. We
attribute the lower abundance to a reduced contribution from the
r-process. Interstellar abundances for Kr, Cd, and Sn are consistent
with much less r-process synthesis for the solar neighborhood compared
to the amount inferred for the solar system.
Title: Magnesium Isotope Ratios in Hyades Stars
Authors: Yong, David; Lambert, David L.; Allende Prieto, Carlos;
Paulson, Diane B.
Bibcode: 2004ApJ...603..697Y
Altcode: 2003astro.ph.12054Y
Using classical model atmospheres and an LTE analysis, Mg
isotope ratios 24Mg:25Mg:26Mg
are measured in 32 Hyades dwarfs covering effective temperatures
4000K<=Teff<=5000K. We find no significant trend
in any isotope ratio versus Teff, and the mean isotope
ratio is in excellent agreement with the solar value. We determine
stellar parameters and Fe abundances for 56 Hyades dwarfs covering
4000K<=Teff<=6200K. For stars warmer than 4700 K,
we derive a cluster mean value of [Fe/H]=0.16+/-0.02 (σ=0.1),
in good agreement with previous studies. For stars cooler than
4700 K, we find that the abundance of Fe from ionized lines
exceeds the abundance of Fe from neutral lines. At 4700 K,
[Fe/H]II-[Fe/H]I~=0.3dex, while at 4000 K
[Fe/H]II-[Fe/H]I~=1.2dex. This discrepancy
between the Fe abundance from neutral and ionized lines likely reflects
inadequacies in the model atmospheres and the presence of non-LTE or
other effects. Despite the inability of the models to reproduce the
ionization equilibrium for Fe, the Mg isotope ratios appear immune to
these problems and remain a powerful tool for studying Galactic chemical
evolution. 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: VizieR Online Data Catalog: Spectroscopic survey in solar
neighborhood (Allende Prieto+ 2004)
Authors: Allende Prieto, C.; Barklem, P. S.; Lambert, D. L.; Cunha, K.
Bibcode: 2004yCat..34200183A
Altcode:
Tables with kinematic data and chemical abundances for the sample. The
atomic line data are also provided. The data in FITS are available
in the internet from the project site S4N (Spectrsocopic Survey of
Stars in the Solar Neighborhood) at http://hebe.as.utexas.edu/s4n/
and at its mirror http://www.astro.uu.se/~s4n/ (5 data files).
Title: A high-resolution spectral analysis of the suspected
spectroscopic binary HD 165553
Authors: Goswami, A.; Rao, N. K.; Lambert, D. L.
Bibcode: 2004Obs...124...47G
Altcode:
No abstract at ADS
Title: On the Galactic chemical evolution of sulfur
Authors: Ryde, N.; Lambert, D. L.
Bibcode: 2004A&A...415..559R
Altcode: 2003astro.ph.12070R
Sulfur abundances have been determined for ten stars to resolve a debate
in the literature on the Galactic chemical evolution of sulfur in the
halo phase of the Milky Way. Our analysis is based on observations of
the S I lines at 9212.9, 9228.1, and 9237.5 Å for stars for which
the S abundance was obtained previously from much weaker S I lines
at 8694.0 and 8694.6 Å. In contrast to the previous results showing
[S/Fe] to rise steadily with decreasing [Fe/H], our results show that
[S/Fe] is approximately constant for metal-poor stars ([Fe/H]⪉ -1)
at [S/Fe] ≃ +0.3. Thus, sulfur behaves in a similar way to the
other \alpha elements, with an approximately constant [S/Fe] for
metallicities lower than [Fe/H]≃ -1. We suggest that the reason
for the earlier claims of a rise of [S/Fe] is partly due to the use
of the weak S I 8694.0 and 8694.6 Å lines and partly uncertainties
in the determination of the metallicity when using Fe I lines. The S
I 9212.9, 9228.1, and 9237.5 Å lines are preferred for an abundance
analysis of sulfur for metal-poor stars.
Title: Abundances of Neutron-Capture Elements in the Hot Extreme
Helium Stars V1920 Cygni and HD 124448
Authors: Pandey, Gajendra; Lambert, David L.; Rao, N. Kameswara;
Jeffery, C. Simon
Bibcode: 2004ApJ...602L.113P
Altcode: 2004astro.ph..1263P
Analysis of Hubble Space Telescope Space Telescope Imaging Spectrograph
ultraviolet spectra of two hot extreme helium (EHe) stars, V1920
Cyg and HD 124448, provides the first measurements of abundances
of neutron-capture elements for EHe stars. Although the two stars
have similar abundances for elements up through the iron group, they
differ strikingly in their abundances of heavier elements: V1920 Cyg
is enriched by a factor of 30 in light neutron-capture elements (Y/Fe
and Zr/Fe) relative to HD 124448. These differences in abundances of
neutron-capture elements among EHe stars are exhibited by the R CrB
stars and are evidence supporting the view that there is an evolutionary
connection between these two groups of hydrogen-deficient stars. Also,
the abundances of Y and Zr in V1920 Cyg provide evidence that at least
one EHe star went through an s-process synthesis episode in its earlier
evolution. Based on observations obtained with the NASA/ESA Hubble
Space Telescope, which is operated by the Association of Universities
for Research in Astronomy, Inc., under NASA contract NAS5-26555.
Title: Mg Isotopic Ratios in Giant Stars of the Globular Cluster
NGC 6752
Authors: Yong, D.; Grundahl, F.; Lambert, D. L.; Nissen, P. E.;
Shetrone, M. D.
Bibcode: 2004oee..sympE..61Y
Altcode:
We have measured Mg isotopic ratios in 20 bright red giants in the
globular cluster NGC 6752 based on high-resolution (R ∼110,000),
high signal-to-noise spectra obtained with UVES on the VLT. We find a
variation in the ratio 24Mg:25Mg:26Mg
with values ranging from 53:9:39 to 83:10:7. We combined our sample
with 21 RGB bump stars (Grundahl et al. 2002) and measured the
abundances of O, Na, Mg, Al, and Fe. The abundances of the samples
are consistent and exhibit the usual anticorrelations between O-Na
and Mg-Al. We found a positive correlation between 26Mg
and Al, a mild anticorrelation between 24Mg and Al, and
no correlation between 25Mg and Al. Neither the elemental
nor isotopic abundances show a dependence on evolutionary status and,
as Gratton et al. (2001) have shown, main sequence stars display the
abundance variations. This strongly suggests that the star-to-star
abundance variations are a result of varying degrees of pollution with
intermediate mass AGB stars being likely polluters. The composition
of the ambient and processed material can be inferred from the
extremes of the abundance variations. The least contaminated stars
(lowest Na and Al and highest O and Mg abundances) have a Mg isotopic
ratio around 80:10:10 and a composition ([O/Fe], [Na/Fe], [Mg/Fe],
[Al/Fe]) ≍(0.6 ,-0.1, 0.5, 0.0). The most polluted stars have a Mg
isotopic ratio around 60:10:30 and a composition ([O/Fe], [Na/Fe],
[Mg/Fe], [Al/Fe]) ≍(-0.1, 0.6, 0.3, 1.2). The least polluted stars
have abundances of 25Mg and 26Mg relative to
24Mg that are considerably higher than predicted for ejecta
from Z = 0 supernovae. Zero metallicity AGB stars may be responsible
for these higher abundances. Our measured Mg isotopic ratios reveal
another layer to the globular cluster star-to-star abundance variations
that demands extensions of our present theoretical knowledge of stellar
nucleosynthesis by giant stars.
Title: 6Li: A Clue for Planet Accretion in Stars
Authors: Reddy, B. E.; Lambert, D. L.
Bibcode: 2004oee..sympE..50R
Altcode:
Using high quality (S/N ≥ 350) and very high resolution spectra
(R≅ 125,000) we have searched for 6Li in stars hosting
planets. For this study we have chosen a sample of 15 stars out
of which 9 are known to have planets, one is a binary, and 5 are
not known to have planets. From detailed profile-fitting analysis
of Li resonance line at 6700Å we find no significant amount of
6Li relative to 7Li in any of the planet hosting
stars (6Li/7Li <∼0.03).
Title: Observational aspects of stellar nucleosynthesis
Authors: Lambert, David L.
Bibcode: 2004cmpe.conf...81L
Altcode:
After several introductory sections, the author discusses two issues
of nucleosynthesis not addressed by the other lecturers: the origins
of Li, Be, and B; the s-process.
Title: The Rise of the s-Process in the Galaxy
Authors: Simmerer, J.; Sneden, C.; Woolf, V.; Lambert, D. L.
Bibcode: 2004oee..sympE..53S
Altcode:
Throughout the history of the Galaxy, the production of
neutron-capture elements (those with Z>30) has been dictated
mainly by two nucleosynthetic processes: the s-process and the
r-process. Elements generated by the s(low)-process are believed
to be formed in the He-burning regions of low to intermediate mass
stars, while r(apid)-process elements likely originate in massive
star supernovae. In the most metal-poor stars, those elements with
large s-process components are deficient with respect to those with
large r-process components. This is consistent with the expected
nucleosynthetic output from the massive stars that probably dominated
the element forming processes early on in the Galaxy. Typically,
the measurement of the s-/r-process has been carried out with the
elements Ba and Eu, since the former is produced almost entirely in
the s-process and the latter in the r-process. Here, instead of Ba,
we measure the s-process element La, since new and highly accurate
atomic data have become available for La and Eu, making the results
much more precise than they have been.
Title: Fluorine Abundances in the LMC and the Galaxy
Authors: Cunha, K.; Smith, V. V.; Lambert, D. L.
Bibcode: 2004oee..sympE..12C
Altcode:
To date, fluorine abundances have only been measured in a sample
of asymptotic giant branch stars and in a few K- and M-giants with
near-solar metallicities in our Galaxy. The behavior of fluorine versus
metallicity has yet to be probed. In this work we discuss the first
results for fluorine abundances measured outside of the Milky Way and
in stars with metallicities significantly lower than solar. The sample
consists of 9 red giants from the Large Magellanic Cloud and 2 red
giants from the Galactic globular cluster ω Centauri. The fluorine
abundances are derived from vibration-rotation transitions of HF
using infrared spectra obtained with the Phoenix spectrograph on the
Gemini South 8.1m telescope. The behavior of fluorine abundances with
metallicity may suggest that Wolf-Rayet stars are an important source
of fluorine production.
Title: Elemental Abundances in the Galactic Disk
Authors: Reddy, B. E.; Tomkin, J.; Lambert, D. L.; Allende Prieto, C.
Bibcode: 2004oee..sympE..49R
Altcode:
Here, we discussed our recent results of elemental abundance survey
of Galactic disk based on 181 F- and G-type dwarfs (published by
Reddy et al. 2003, MNRAS, 340, 304). Using high-resolution and high
signal-to-noise spectra we obtained quantitative abundances for 27
elements: C, N, O, Na, Mg, Al, Si, S, K, Ca, Sc, Ti, V, Cr, Mn, Co,
Ni, Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd, and Eu. For the entire sample we
have determined kinematic (U,V,W) and the orbital parameters (peri-
and apo- Galactic distances). The alpha-elements -- O, Mg,
Si, Ca, and Ti -- show [α/Fe] to increase slightly with decreasing
[Fe/H]. Heavy elements with dominant contributions at solar metallicity
from the s-process show [s/Fe] to decrease slightly with decreasing
[Fe/H]. Scatter in [X/Fe] at a fixed [Fe/H] is entirely attributable
to the small measurement errors, after excluding the few thick disk
stars and the s-process enriched CH subgiants. Tight limits are set on
`cosmic' scatter. If a weak trend with [Fe/H] is taken into account,
the composition of a thin disk star expressed as [X/Fe] is independent
of the star's age and birthplace for elements contributed in different
proportions by massive stars (Type II SN), exploding white dwarfs
(Type Ia SN), and asymptotic red giant branch stars. By combining
our sample with published studies, we deduced properties of thin and
thick disk stars. Thick disk stars are primarily identified by their
VLSR in the range - 40 to -100 km s-1. These
are very old stars with origins in the inner Galaxy and metallicities
[Fe/H] <∼-0.4. At the same [Fe/H], the sampled thin disk stars
have VLSR ∼0 km s-1, and are generally younger
with a birthplace at about the Sun's Galactocentric distance. In the
range -0.35 ≥ [Fe/H] ≥ -0.70, well represented by present thin
and thick disk samples, [X/Fe] of the thick disk stars is greater
than that of thin disk stars for Mg, Al, Si, Ca, Ti, and Eu. [X/Fe]
is very similar for the thin and thick disk for -- notably -- Na, and
iron-group elements. Barium ([Ba/Fe]) may be underabundant in thick
relative to thin disk stars. These results extend previous ideas about
composition differences between the thin and thick disk.
Title: Isotopic abundance analysis of field and cluster stars
Authors: Yong, D.; Lambert, D. L.
Bibcode: 2003AAS...203.9902Y
Altcode: 2003BAAS...35.1368Y
Our understanding of the evolution of the Galaxy is built in part on
the interpretation of observed abundance ratios in stars of different
metallicity. While elemental abundances may be easier to measure,
different stellar sites and nucleosynthetic processes may be responsible
for the production of the individual isotopes. Therefore, isotope ratios
may provide a more detailed insight into the chemical evolution of the
Galaxy. We conducted a search for cool metal-poor stars from which
we measured Mg isotope ratios to study the chemical history of the
Galaxy. Our data are in fair agreement with predictions that assume the
isotopes are the product of massive stars. We find an intrinsic scatter
at all metallicities which may be due to ejecta from AGB stars. To
gauge non-LTE effects and inadequacies in the model atmospheres,
we measured Mg isotope ratios in the Hyades open cluster. While the
model atmospheres did not reproduce ionization equilibrium for Fe,
the Mg isotope ratios were immune to these problems. We have also
used isotope ratios to study globular cluster chemical evolution. Every
well studied Galactic globular cluster shows star-to-star differences in
and correlations between the light elements. The mechanism responsible
for these variations remains poorly understood. We measured Mg isotope
ratios in the giant stars of globular cluster NGC 6752. Varying degrees
of pollution by AGB stars of the same generation as the observed stars
may explain our measured isotopic and elemental abundances. This
research was supported by the Robert A. Welch Foundation of Houston,
Texas.
Title: Magnesium Isotopic Abundance Ratios in Cool Stars
Authors: Yong, David; Lambert, David L.; Ivans, Inese I.
Bibcode: 2003ApJ...599.1357Y
Altcode: 2003astro.ph..9079Y
From high-resolution spectra of 61 cool dwarfs and giants, Mg isotopic
abundance ratios 24Mg:25Mg:26Mg are
derived from spectral synthesis of the MgH A-X lines near 5140 Å. Our
sample spans the range -2.5<=[Fe/H]<=0.1, including the first
measurements of Mg isotope ratios in stars with metallicities below
[Fe/H]=-2.0. We confirm the decrease in 25Mg/24Mg
and 26Mg/24Mg with decreasing [Fe/H], as predicted
by recent models of Galactic chemical evolution in which the Mg isotopes
are produced in massive stars. A subset of kinematically identified
thin-disk stars have Mg isotope ratios in excellent agreement with the
predictions. Within the measurement uncertainties, these thin-disk stars
show no scatter about the predictions. Several of our stars are likely
members of the thick disk, and their high Mg isotopic ratios may reflect
the nucleosynthetic history of the thick disk, which is distinct from
the predictions for, and observations of, the thin disk. For thick-disk
and halo stars we find a scatter in 25Mg/24Mg and
26Mg/24Mg exceeding our measurement uncertainties
and increasing with increasing metallicity. Our data suggest that
an additional source of 25Mg and 26Mg is
required. Intermediate-mass asymptotic giant branch stars are likely
candidates.
Title: A High-Resolution Spectrum of the R Coronae Borealis Star
V2552 Ophiuchi
Authors: Rao, N. Kameswara; Lambert, David L.
Bibcode: 2003PASP..115.1304R
Altcode: 2003astro.ph..8447R; 2003astro.ph..8447K
Photometry and low-resolution spectroscopy have added V2552 Oph
to the rare class of R Coronae Borealis variables. We confirm this
classification of V2552 Oph through a comparison of our high-resolution
optical spectrum of this star and that of R CrB and other F-type
members of the class. We show that V2552 Oph most closely resembles
Y Mus and FH Sct, stars in which Sr, Y, and Zr are enhanced.
Title: S4N: A Spectroscopic Survey of Stars in the Solar
Neighborhood
Authors: Lambert, D. L.; Allende Prieto, C.; Cunha, K.
Bibcode: 2003csss...12..875L
Altcode:
We are using the McDonald 2.7m and ESO 1.52m telescopes to
obtain spectra of nearby stars at high-resolution, high S/N, and
with complete optical coverage. The sample includes all stars in the
Hipparcos catalog brighter than MV = 6.5 (∼ K2 V) within
a 12770 pc3 sphere centered at the Sun. The survey is 78 %
complete. The database will be publicly released in approximately 1
year. We plan to: 1) Provide homogeneous radial velocities with the
accuracy required to exploiting in full the accurate proper motions
and parallaxes determined by Hipparcos (0.1 < σ (v) < 1.0 km
s-1); 2) Provide homogeneous chemical abundances for a
large (> 30) number of elements with an accuracy of 0.04 dex; 3)
Determine the fundamental stellar parameters for the sample using an
array of different methods. We discuss potential applications.
Title: Erratum: ``An Ultra-High-Resolution Survey of the
Interstellar 7Li/6Li Isotope Ratio in the
Solar Neighborhood'' (ApJ, 586,
268 [2003])
Authors: Knauth, David C.; Federman, S. R.; Lambert, David L.
Bibcode: 2003ApJ...594..664K
Altcode:
An error occurred in Table 10 because author corrections were not
transferred faithfully during the production process. The corrected
table appears below. The Press sincerely regrets this error.
Title: Fluorine Abundances in the Large Magellanic Cloud and ω
Centauri: Evidence for Neutrino Nucleosynthesis?
Authors: Cunha, Katia; Smith, Verne V.; Lambert, David L.; Hinkle,
Kenneth H.
Bibcode: 2003AJ....126.1305C
Altcode: 2003astro.ph..5303C
The behavior of fluorine with metallicity has not yet been probed in
any stellar population. In this work, we present the first fluorine
abundances measured outside of the Milky Way from a sample of red
giants in the Large Magellanic Cloud (LMC), as well the Galactic
globular cluster ω Centauri. The fluorine abundances are derived
from vibration-rotation transitions of HF using infrared spectra
obtained with the Phoenix spectrograph on the Gemini South 8.1 m
telescope. It is found that the abundance ratio of F/O declines as the
oxygen abundance decreases. The values of F/O are especially low in
the two ω Cen giants; this very low value of F/O probably indicates
that 19F synthesis in asymptotic giant branch (AGB) stars
is not the dominant source of fluorine in stellar populations. The
observed decline in F/O with lower O abundances is in qualitative
agreement with what is expected if 19F is produced via H-
and He-burning sequences in very massive stars, with this fluorine
then ejected in high mass-loss rate Wolf-Rayet winds. A quantitative
comparison of observations with this process awaits results from more
detailed chemical evolution models incorporating the yields from
Wolf-Rayet winds. Perhaps of more significance is the quantitative
agreement between the Galactic and LMC results with predictions from
models in which 19F is produced from neutrino nucleosynthesis
during core collapse in supernovae of Type II. The very low values
of F/O in ω Cen are also in agreement with neutrino nucleosynthesis
models if the ``peculiar'' star formation history of ω Cen, with
two to four distinct episodes of star formation, is considered. Based on observations obtained at the Gemini Observatory, which is
operated by the Association of Universities for Research in Astronomy,
Inc., under a cooperative agreeement with the NSF on behalf of the
Gemini partnership: the National Science Foundation (United States),
the Particle Physics and Astronomy Research Council (United Kingdom),
the National Research Council (Canada), CONICYT (Chile), the Australian
Research Council (Australia), CNPq (Brazil), and CONICET (Argentina).
Title: Non-LTE Model Atmospheres for Late-Type Stars. I. A Collection
of Data for Light Neutral and Singly Ionized Atoms
Authors: Allende Prieto, Carlos; Lambert, David L.; Hubeny, Ivan;
Lanz, Thierry
Bibcode: 2003ApJS..147..363A
Altcode: 2003astro.ph..3559A; 2003astro.ph..3559P
With the goal of producing a reliable set of model atoms and singly
ionized ions for use in building NLTE model atmospheres, we have
combined measured energy levels, critically compiled line transition
probabilities, and resonance-averaged calculations of photoionization
cross sections. A majority of the elements from Li to Ca are
considered, covering most of the important species in late-type
atmospheres. These include elements that contribute free electrons
and/or continuous opacity in the ultraviolet (e.g., Mg and Si), as well
as trace elements whose abundance determinations rely on ultraviolet
lines (e.g., B from B I lines). The new data complement and, for the
species in common, supersede a previous collection of model atoms
originally designed for use in studies of early-type stars.
Title: Finding Cool Subdwarfs Using a V-J Reduced Proper-Motion
Diagram: Stellar Parameters for 91 Candidates
Authors: Yong, David; Lambert, David L.
Bibcode: 2003PASP..115..796Y
Altcode: 2003astro.ph..6076Y
We present the results of a search for cool subdwarfs for
which our candidates were drawn from a V-J reduced proper-motion
diagram constructed by Salim & Gould. Kinematic (U, V, and W)
and self-consistent stellar parameters (Teff, logg,
[Fe/H], and ξt) are derived for 91 candidate subdwarfs
based on high-resolution spectra. The observed stars span 3900
K<Teff< 6200 K and -2.63<[Fe/H]<0.25 including
only three giants (logg<4.0). Of the sample, 77 stars have MgH lines
present in their spectra. With more than 56% of our candidate subdwarfs
having [Fe/H]<=-1.5, we show that the V-J reduced proper-motion
diagram readily identifies metal-poor stars.
Title: Non-LTE Model Atmospheres for Late-Type Stars. II. Restricted
Non-LTE Calculations for a Solar-like Atmosphere
Authors: Allende Prieto, Carlos; Hubeny, Ivan; Lambert, David L.
Bibcode: 2003ApJ...591.1192A
Altcode: 2003astro.ph..3560A; 2003astro.ph..3560P
We test our knowledge of the atomic opacity in the solar UV
spectrum. Using the atomic data compiled in the first paper in
this series from modern, publicly available databases, we perform
calculations that are compared with space-based observations of
the Sun. At wavelengths longer than about 2600 Å, LTE modeling can
reproduce quite closely the observed fluxes; uncertainties in the atomic
line data account fully for the differences between calculated and
observed fluxes. At shorter wavelengths, departures from LTE appear
to be important, since our LTE and restricted non-LTE calculations
differ. Analysis of visible/near-IR Na I and O I lines, two species
that produce a negligible absorption in the UV, shows that observed
departures from LTE for these species can be reproduced very accurately
with restricted (fixed atmospheric structure) non-LTE calculations.
Title: Further Evidence for Chemical Fractionation from Ultraviolet
Observations of Carbon Monoxide
Authors: Federman, S. R.; Lambert, David L.; Sheffer, Yaron; Cardelli,
Jason A.; Andersson, B. -G.; van Dishoeck, Ewine F.; Zsargó, J.
Bibcode: 2003ApJ...591..986F
Altcode: 2003astro.ph..4170F
Ultraviolet absorption from interstellar 12CO and
13CO was detected toward ρ Oph A and χ Oph. The
measurements were obtained at medium resolution with the Goddard
High Resolution Spectrograph on the Hubble Space Telescope. Column
density ratios, N(12CO)/N(13CO), of 125+/-23
and 117+/-35 were derived for the sight lines toward ρ Oph
A and χ Oph, respectively. A value of 1100+/-600 for the ratio
N(12C16O)/N(12C18O) toward
ρ Oph A was also obtained. Absorption from vibrationally excited
H2 (v''=3) was clearly seen toward this star as
well. The ratios are larger than the isotopic ratios for carbon and
oxygen appropriate for ambient interstellar material. Since for both
carbon and oxygen the more abundant isotopomer is enhanced, selective
isotopic photodissociation plays the key role in the fractionation
process for these directions. The enhancement arises because the more
abundant isotopomer has lines that are more optically thick, resulting
in more self-shielding from dissociating radiation. A simple argument
involving the amount of self-shielding [from N(12CO)] and
the strength of the ultraviolet radiation field permeating the gas
(from the amount of vibrationally excited H2) shows that
selective isotopic photodissociation controls the fractionation seen in
these two sight lines, as well as the sight line to ζ Oph. Based
on observations obtained with the NASA/ESA Hubble Space Telescope
through the Space Telescope Science Institute, which is operated
by the Association of Universities for Research in Astronomy, Inc.,
under NASA contract NAS5-26555.
Title: VizieR Online Data Catalog: [X/Fe] of Galactic disc F and G
dwarfs (Reddy+, 2003)
Authors: Reddy, B. E.; Tomkin, J.; Lambert, D. L.; Allende Prieto, C.
Bibcode: 2003yCat..73400304R
Altcode:
All the observations were made at the Harlan J. Smith 2.7-m telescope
at McDonald Observatory, using the 2dcoude echelle spectrometer
(Tull et al., 1995PASP..107..251T) with a 2048x2048 pixel Tektronix
charge-coupled device (CCD) as detector. (3 data files).
Title: Nucleosynthesis in FG Sge
Authors: Arnone, E.; Gallino, R.; Lambert, D. L.; Straniero, O.
Bibcode: 2003NuPhA.718..536A
Altcode:
We present an attempt of interpretation of the sudden appearance of
an extremely unusual chemical composition of FG Sge.
Title: Mg isotopic ratios in giant stars of the globular cluster
NGC 6752
Authors: Yong, D.; Grundahl, F.; Lambert, D. L.; Nissen, P. E.;
Shetrone, M. D.
Bibcode: 2003A&A...402..985Y
Altcode: 2003astro.ph..3057Y
Mg isotopic abundance ratios are measured in 20 bright red giants
in globular cluster NGC 6752 based on very high-resolution
(R ~ 110 000), high signal-to-noise spectra obtained with
UVES on the VLT. There is a considerable spread in the ratio
24Mg:25Mg:26Mg with values ranging
from 53:9:39 to 83:10:7. We measured the abundances of O, Na, Mg,
Al, and Fe combining our sample with 21 RGB bump stars (Grundahl et
al. \cite{grundahl02}). The abundances of the samples are consistent
and exhibit the usual anticorrelations between O-Na and Mg-Al. A
positive correlation is found between 26Mg and Al, a mild
anticorrelation is found between 24Mg and Al, while no
correlation is found between 25Mg and Al. None of the
elemental or isotopic abundances show a dependence on evolutionary
status and, as shown by Gratton et al. (\cite{gratton01}), the abundance
variations exist even in main sequence stars. This strongly suggests
that the star-to-star abundance variations are a result of varying
degrees of pollution with intermediate mass AGB stars being likely
polluters. Consideration of the extremes of the abundance variations
provides the composition of the ambient material and the processed
material. In the least contaminated stars (lowest Na and Al and
highest O and Mg abundances), we infer a Mg isotopic ratio around
80:10:10 and a composition ([O/Fe], [Na/Fe], [Mg/Fe], [Al/Fe]) =~
(0.6, -0.1, 0.5, 0.0). In the most polluted stars, we find a Mg
isotopic ratio around 60:10:30 and a composition ([O/Fe], [Na/Fe],
[Mg/Fe], [Al/Fe]) =~ (-0.1, 0.6, 0.3, 1.2). Even for the least polluted
stars, the abundances of 25Mg and 26Mg relative
to 24Mg are considerably higher than predicted for ejecta
from Z=0 supernovae. Zero metallicity AGB stars may be responsible for
these higher abundances. Our measured Mg isotopic ratios reveal another
layer to the globular cluster star-to-star abundance variations that
demands extensions of our present theoretical knowledge of stellar
nucleosynthesis by giant stars. Based on observations obtained
with the ESO Very Large Telescope UVES spectrograph for programmes
67.D-0145 and 65.L-0165.
Title: Interstellar Fluorine toward Stars in Cep OB2
Authors: Federman, S. R.; Sheffer, Yaron; Lambert, David L.; Smith,
V. V.
Bibcode: 2003AAS...202.2909F
Altcode: 2003BAAS...35..738F
Massive stars, through their terminal supernova explosions, seed
interstellar clouds with newly synthesized elements. In order to
understand the details of chemical evolution in a site of star
formation, the interstellar material toward stars in Cep OB2 was
studied via absorption lines seen in FUSE spectra. A search for the F
I resonance lines at 951 and 954 Å toward HD 208440 and HD 209339A was
conducted to help resolve the origin of this element: is F synthesized
primarily in Type II supernovae, whose effects should be revealed in
a region of ongoing massive star formation, or in asymptotic giant
branch stars? Syntheses of H2 Lyman bands near 1060 Å were
used to remove H2 absorption in the vicinity of λ 954,
the stronger of the two F I lines. In the process, we determined
the maximium H2 column density before H2
absorption becomes black in this wavelength region. Our upper limits
on λ 951 are consistent with the measures from the 954 Å line. The
inferred F abundances are similar to the abundance derived for the
gas toward δ Sco from measurements with the Copernicus satellite. Further comparisons among elemental abundance ratios were performed
to discern the presence of enhanced F in an environment shaped by
past SNe II. First, we obtained the elemental abundance of Cl (from
FUSE spectra of Cl I and II) to determine the expected amount of F
depletion onto grains. Then, we derived the elemental abundances of N
I and O I from FUSE and HST spectra, respectively, because these two
elements show modest amounts of depletion and are synthesized through
other processes. Our results indicate that the F abundance and the F/O
and F/N elemental abundance ratios are not enhanced for the two sight
lines studied to date. This research was supported by NASA grant
NAG5-10305 and by the STScI grant associated with the program GO-08693.
Title: Minute steps on the quest of the s-process
Authors: Gallino, R.; Arnone, E.; Cristallo, S.; Masera, S.; Travaglio,
C.; Lambert, D. L.; Lugaro, M.; Käppeler, F.; van Winckel, H.;
Reyniers, M.; Straniero, O.; Davis, A. M.
Bibcode: 2003NuPhA.718..181G
Altcode:
No abstract at ADS
Title: Water vapor in the outer atmospheres of red giants probed by
high-resolution, mid-infrared observations
Authors: Ryde, Nils; Lacy, John H.; Richter, Matthew J.; Lambert,
David L.; Greathouse, Thomas K.
Bibcode: 2003ASSL..283..227R
Altcode: 2003mlps.work..227R
Here, we report on our detection of water vapor in the mid-infrared
(11-12 microns) spectrum of the K1.5 giant. Arcturus (α Boo) obtained
with the high-resolution, infrared spectrograph TEXES. The detection
is presented in detail in Ryde et al. 2002 ApJ. We are successful
in modeling several resolved, rotational lines of water vapor and
vibration-rotational (1.5-microns) and rotational lines of OH with a
modified MARCS photosphere.
Title: The chemical compositions of Galactic disc F and G dwarfs
Authors: Reddy, Bacham E.; Tomkin, Jocelyn; Lambert, David L.;
Allende Prieto, Carlos
Bibcode: 2003MNRAS.340..304R
Altcode: 2002astro.ph.11551R
Photospheric abundances are presented for 27 elements from carbon to
europium in 181 F and G dwarfs from a differential local thermodynamic
equilibrium (LTE) analysis of high-resolution and high signal-to-noise
ratio spectra. Stellar effective temperatures (Teff)
were adopted from an infrared flux method calibration of Strömgren
photometry. Stellar surface gravities (g) were calculated from Hipparcos
parallaxes and stellar evolutionary tracks. Adopted Teff and
g values are in good agreement with spectroscopic estimates. Stellar
ages were determined from evolutionary tracks. Stellar space motions
(U, V, W) and a Galactic potential were used to estimate Galactic
orbital parameters. These show that the vast majority of the stars
belong to the Galactic thin disc. Relative abundances expressed
as [X/Fe] generally confirm previously published results. We give
results for C, N, O, Na, Mg, Al, Si, S, K, Ca, Sc, Ti, V, Cr, Mn,
Co, Ni, Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd and Eu. The α elements - O,
Mg, Si, Ca and Ti - show [α/Fe] to increase slightly with decreasing
[Fe/H]. Heavy elements with dominant contributions at solar metallicity
from the s-process show [s/Fe] to decrease slightly with decreasing
[Fe/H]. Scatter in [X/Fe] at a fixed [Fe/H] is entirely attributable
to the small measurement errors, after excluding the few thick disc
stars and the s-process-enriched CH subgiants. Tight limits are set on
`cosmic' scatter. If a weak trend with [Fe/H] is taken into account,
the composition of a thin disc star expressed as [X/Fe] is independent
of the star's age and birthplace for elements contributed in different
proportions by massive stars (Type II supernovae), exploding white
dwarfs (Type Ia supernovae) and asymptotic red giant branch stars. By combining our sample with various published studies, comparisons
between thin and thick disc stars are made. In this composite sample,
thick disc stars are primarily identified by their VLSR
in the range -40 to -100 km s-1. These are very old stars
with origins in the inner Galaxy and metallicities [Fe/H]<=-0.4. At
the same [Fe/H], the sampled thin disc stars have VLSR~ 0 km
s-1, and are generally younger with a birthplace at about the
Sun's Galactocentric distance. In the range -0.35 >=[Fe/H]>=-0.70,
well represented by present thin and thick disc samples, [X/Fe] of
the thick disc stars is greater than that of thin disc stars for Mg,
Al, Si, Ca, Ti and Eu. [X/Fe] is very similar for the thin and thick
disc for - notably - Na and iron-group elements. Barium ([Ba/Fe]) may
be underabundant in thick relative to thin disc stars. These results
extend previous ideas about composition differences between the thin
and thick disc.
Title: An Ultra-high-Resolution Survey of the Interstellar
7Li/6Li Isotope Ratio in the Solar Neighborhood
Authors: Knauth, David C.; Federman, S. R.; Lambert, David L.
Bibcode: 2003ApJ...586..268K
Altcode: 2002astro.ph.12233K
In an effort to probe the extent of variations in the
interstellar 7Li/6Li ratio seen previously,
ultra-high-resolution (R~360,000), high signal-to-noise spectra
of stars in the Perseus OB2 and Scorpius OB2 associations were
obtained. These measurements confirm our earlier findings of an
interstellar 7Li/6Li ratio of about 2 toward ο
Per, the value predicted from models of Galactic cosmic-ray spallation
reactions. Observations of other nearby stars yield limits consistent
with the isotopic ratio of ~12 seen in carbonaceous chondrite
meteorites. If this ratio originally represented the gas toward ο
Per, then to decrease the original isotope ratio to its current value
an order of magnitude increase in the Li abundance is expected, but
it is not seen. The elemental K/Li ratio is not unusual, although
Li and K are formed via different nucleosynthetic pathways. Several
proposals to account for the low 7Li/6Li ratio
were considered, but none seems satisfactory. Analysis of the Li and K
abundances from our survey highlighted two sight lines where depletion
effects are prevalent. There is evidence for enhanced depletion toward
X Per, since both abundances are lower by a factor of 4 when compared
to other sight lines. Moreover, a smaller Li/H abundance is observed
toward 20 Aql, but the K/H abundance is normal, suggesting enhanced Li
depletion (relative to K) in this direction. Our results suggest that
the 7Li/6Li ratio has not changed significantly
during the last 4.5 billion years and that a ratio of ~12 represents
most gas in the solar neighborhood. In addition, there appears to be
a constant stellar contribution of 7Li, indicating that
one or two processes dominate its production in the Galaxy.
Title: A Spectral Analysis of HD 165553
Authors: Goswami, Aruna; Kameswara Rao, N.; Lambert, D. L.
Bibcode: 2003BASI...31..341G
Altcode:
High resolution spectra of HD 165553, a star reported to be a
spectroscopic binary of spectral type F8 Ib are analysed. The stellar
parameters - effective temperature, surface gravity and microturbulence
are determined using model atmospheres. A detail chemical composition
study indicates a near-solar composition for HD 165553. Comparison of
its spectrum with that of Cyg, a normal supergiant of spectral type
F8 Iab indicates that the star is of a later spectral type; a spectral
type G Iab seems more likely for HD 165553.
Title: Carbon Stars in the Local Group -- Detailed Abundance Analysis
of Carbon Stars in the LMC
Authors: Lambert, David L.; Eriksson, Kjell; Gustafsson, Bengt;
Hinkle, Kenneth H.; Ryde, Nils; Wahlin, Rurik; Westerlund, Bengt
Bibcode: 2003noao.prop..265L
Altcode:
Using the Phoenix on Gemini we propose to observe a sample of carbon
stars in the LMC in four different wavelength regions at high spectral
resolution and with high S/N. The spectra will provide CO, CN, and
C_2 and atomic lines from which elemental and isotopic C, N, and O
abundances and metal abundances will be derived by an approach similar
to that previously used for Galactic field carbon stars (Lambert et
al. 1986). We will then be able to calibrate lower resolution spectra
of carbon stars in other Local Group galaxies. The observational study
of carbon stars is a key to understanding late evolutionary stages
and nucleosynthesis of low mass stars.
Title: VizieR Online Data Catalog: Stellar parameters for 134 cool
subdwarfs (Yong+, 2003)
Authors: Yong, D.; Lambert, D. L.
Bibcode: 2003yCat..61150022Y
Altcode:
Table 1 contains the list of candidates observed at McDonald Observatory
on the 2.7m Harlan J. Smith telescope and on the 9.2m Hobby-Eberly
telescope (HET) between 1999 November and 2002 April. The 2.7m data
were obtained using the cross-dispersed echelle spectrometer (Tull et
al., 1995PASP..107..251T) at the coude f/32.5 focus with a resolving
power of either 30000 or 60000. The detector was a Tektronix CCD with
24{mu}m2 pixels in a 2048x2048 format. For this setting,
the spectral coverage was from 3800 to 8900{AA} with gaps between the
orders beyond 5800{AA}. The HET data were taken with the Upgraded Fiber
Optic Echelle spectrograph (Harlow et al., 1996AAS...189.4207H) at a
resolving power of 11000 on a 1024x1024 CCD. The spectral coverage was
from 4500 to 9000{AA} with gaps between the orders beyond 7300{AA}. (1 data file).
Title: Magnesium Isotope Ratios in NGC 6752 Red Giant Stars
Authors: Grundahl, F.; Nissen, P. E.; Yong, D.; Lambert, D. L.;
Briley, M.
Bibcode: 2003ASPC..296..383G
Altcode: 2003nhgc.conf..383G
No abstract at ADS
Title: A Search for Cool Subdwarfs: Stellar Parameters for 134
Candidates
Authors: Yong, David; Lambert, David L.
Bibcode: 2003PASP..115...22Y
Altcode: 2002astro.ph..9347Y
The results of a search for cool subdwarfs are presented. Kinematic
(U, V, and W) and stellar parameters (Teff, logg,
[Fe/H], and ξt) are derived for 134 candidate subdwarfs
based on high-resolution spectra. The observed stars span 4200
K<Teff<6400 K and -2.70<[Fe/H]<0.25 including
only eight giants (logg<4.0). Of the sample, 100 stars have MgH
bands present in their spectra. The targets were selected by their
large reduced proper motion, by the offset from the solar-metallicity
main sequence, or from the literature. We confirm the claims made by
Ryan that the NLTT catalog is a rich source of subdwarfs and verify
the success of the reduced proper-motion constraint in identifying
metal-poor stars. Based in part on observations obtained with the
Hobby-Eberly Telescope, which is a joint project of the University of
Texas at Austin, the Pennsylvania State University, Stanford University,
Ludwig-Maximillians-Universität München, and Georg-August-Universität
Göttingen.
Title: What does the Unexpected Detection of Water Vapor in Arcturus'
Atmosphere Tell us?
Authors: Ryde, N.; Lambert, D. L.; Richter, M. J.; Lacy, J. H.;
Greathouse, T. K.
Bibcode: 2003ASPC..293..214R
Altcode: 2003tdse.conf..214R; 2002astro.ph.10181R
In this talk we presented and discussed our unexpected detection
of water vapor in the disk-averaged spectrum of the K2IIIp red
giant Arcturus [for details, see Ryde et al. (2002)]. Arcturus,
or alpha Bootes is, with its effective temperature of 4300 K, the
hottest star yet to show water vapor features. We argue that the
water vapor is photospheric and that its detection provides us with
new insights into the outer parts of the photosphere. We are not
able to model the water vapor with a standard, one-component, 1D,
radiative-equilibrium, LTE model photosphere, which probably means we
are lacking essential physics in such models. However, we are able to
model several OH lines of different excitation and the water-vapor
lines satisfactorily after lowering the temperature structure of
the very outer parts of the photosphere at log tau(500)=-3.8 and
beyond compared to a flux-constant, hydrostatic, standard marcs model
photosphere. Our new semi-empirical model is consistently calculated
from the given temperature structure. We will discuss some possible
reasons for a temperature decrease in the outer-most parts of the
photosphere and the assumed break-down of the assumptions made in
classical model-atmosphere codes. In order to understand the outer
photospheres of these objects properly, we will, most likely, need
3D hydrodynamical models of red giants also taking into account full
non-LTE and including time-dependent effects of, for example, acoustic
wave heating sensitive to thermal instabilities.
Title: Lithium Enrichment in High Rotating K Giants
Authors: Drake, N. A.; de La Reza, R.; da Silva, L.; Lambert, D. L.
Bibcode: 2003IAUS..210P.D20D
Altcode:
No abstract at ADS
Title: Detection of Water Vapor in Arcturus (K2IIIp)
Authors: Ryde, N.; Lacy, J. H.; Richter, M. J.; Lambert, D. L.;
Greathouse, T. K.
Bibcode: 2003IAUS..210P.E67R
Altcode:
No abstract at ADS
Title: NLTE Line Formation in Late-Type Stellar Atmospheres
Authors: Allende Prieto, C.; Hubeny, I.; Lambert, D. L.; Lanz, T.
Bibcode: 2003IAUS..210P.A24A
Altcode:
No abstract at ADS
Title: High-Resolution Studies of Diffuse Interstellar Gas
Authors: Federman, Steven R.; Knauth, David C.; Lambert, David L.;
Pan, Kaike
Bibcode: 2003IAUJD..20E..10F
Altcode:
We describe two recent projects undertaken at McDonald Observatory whose
success required high-resolution measurements. First high-resolution
spectra revealed a 7Li/6Li ratio of about 2 in gas toward o
Persei a value consistent with expectations of Galactic cosmic ray
spallation but much lower than the meteoritic value (12.3). In order
to probe the extent in the variation of this ratio we performed an
ultra-high-resolution survey. The line of sight toward o Per remains
the only one with an isotope ratio different from the meteoritic
value but this sight line shows no other indication of an enhanced Li
abundance. Second through a high-resolution study of gas seen toward
stars in rho Oph Cep OB2 and Cep OB3 we gleaned information about the
structure of the diffuse material along the line of sight. Line widths
(b-values) and column densities yielded the various distributions
among species for individual velocity components. For instance CN
resides in the densest central portion of a diffuse cloud while Ca+
is much more widely distributed. Moreover gas containing CH arises
from two sources: CH associated with dense gas containing CN and CH
arising from the synthesis of CH+ in less dense material.
Title: Chemical Abundances in 12 Red Giants of the Large Magellanic
Cloud from High-Resolution Infrared Spectroscopy
Authors: Smith, Verne V.; Hinkle, Kenneth H.; Cunha, Katia; Plez,
Bertrand; Lambert, David L.; Pilachowski, Catherine A.; Barbuy,
Beatriz; Meléndez, Jorge; Balachandran, Suchitra; Bessell, Michael
S.; Geisler, Douglas P.; Hesser, James E.; Winge, Claudia
Bibcode: 2002AJ....124.3241S
Altcode: 2002astro.ph..8417S
High-resolution infrared spectra (λ/Δλ=50,000) have been obtained for
12 red giant members of the Large Magellanic Cloud (LMC) with the Gemini
South 8.3 m telescope and Phoenix spectrometer. Two wavelength regions,
at 15540 and 23400 Å, were observed. Quantitative chemical abundances
of carbon (both 12C and 13C), nitrogen, and oxygen
were derived from molecular lines of CO, CN, and OH, while sodium,
scandium, titanium, and iron abundances were obtained from neutral
atomic lines. The 12 LMC red giants span a metallicity range from
[Fe/H]=-1.1 to [Fe/H]=-0.3. It is found that values for both [Na/Fe] and
[Ti/Fe] in the LMC giants fall below their corresponding Galactic values
(at these same [Fe/H] abundances) by about ~0.1-0.5 dex; this effect is
similar to abundance patterns found in the few dwarf spheroidal galaxies
with published abundances. The program red giants all show evidence of
first dredge-up mixing of material exposed to the CN cycle, that is,
low 12C/13C ratios and lower 12C with
higher 14N abundances. The carbon and nitrogen trends are
similar to what is observed in samples of Galactic red giants, although
the LMC red giants seem to show smaller 12C/13C
ratios for a given stellar mass. This relatively small difference in the
carbon isotope ratios between LMC and Galactic red giants could be due
to increased extra mixing in stars of lower metallicity, as suggested
previously in the literature. Comparisons of the oxygen-to-iron ratios
in the LMC and the Galaxy indicate that the trend of [O/Fe] versus
[Fe/H] in the LMC falls about 0.2 dex below the Galactic trend. Such
an offset can be modeled as due to an overall lower rate of supernovae
per unit mass in the LMC relative to the Galaxy, as well as a slightly
lower ratio of supernovae of Type II to supernovae of Type Ia. Based on
observations obtained at the Gemini Observatory, which is operated by
the Association of Universities for Research in Astronomy, Inc., under a
cooperative agreement with the NSF on behalf of the Gemini partnership:
the National Science Foundation (US), the Particle Physics and Astronomy
Research Council (UK), the National Research Council (Canada), CONICYT
(Chile), the Australian Research Council (Australia), CNPq (Brazil),
and CONICET (Argentina).
Title: Detection of Water Vapor in the Photosphere of Arcturus
Authors: Ryde, N.; Lambert, D. L.; Richter, M. J.; Lacy, J. H.
Bibcode: 2002ApJ...580..447R
Altcode: 2002astro.ph..7368R
We report detections of pure rotation lines of OH and H2O in
the K1.5 III red giant star Arcturus (α Bootis) using high-resolution,
infrared spectra covering the regions 806-822 cm-1 (12.2-12.4
μm) and 884-923 cm-1 (10.8-11.3 μm). Arcturus is the
hottest star yet to show water vapor features in its disk-averaged
spectrum. We argue that the water vapor lines originate from the
photosphere, albeit in the outer layers. We are able to predict the
observed strengths of OH and H2O lines satisfactorily
after lowering the temperature structure of the outermost parts of
the photosphere (logτ500=-3.8 and beyond) compared to a
flux-constant, hydrostatic, standard MARCS model photosphere. Our new
model is consistently calculated including chemical equilibrium and
radiative transfer from the given temperature structure. Possible
reasons for a temperature decrease in the outermost parts of the
photosphere and the assumed breakdown of the assumptions made in
classical model atmosphere codes are discussed.
Title: Macroturbulent and rotational broadening in the spectra of
B-type supergiants
Authors: Ryans, R. S. I.; Dufton, P. L.; Rolleston, W. R. J.; Lennon,
D. J.; Keenan, F. P.; Smoker, J. V.; Lambert, D. L.
Bibcode: 2002MNRAS.336..577R
Altcode:
The absorption-line spectra of early B-type supergiants show
significant broadening that implies that an additional broadening
mechanism (characterized here as `macroturbulence') is present in
addition to rotational broadening. Using high-resolution spectra
with signal-to-noise ratios of typically 500, we have attempted to
quantify the relative contributions of rotation and macroturbulence,
but even with data of this quality significant problems were
encountered. However, for all our targets, a model where macroturbulence
dominates and rotation is negligible is acceptable; the reverse scenario
leads to poor agreement between theory and observation. Additionally,
there is marginal evidence for the degree of broadening increasing with
line strength, possibly a result of the stronger lines being formed
higher in the atmosphere. Acceptable values of the projected rotational
velocity are normally less than or equal to 50 km s-1, which
may also be a typical upper limit for the rotational velocity. Our
best estimates for the projected rotational velocity are typically
10-20 km s-1 and hence compatible with this limit. These
values are compared with those predicted by single star evolutionary
models, which are initially rapidly rotating. It is concluded that
either these models underestimate the rate of rotational breaking or
some of the targets may be evolving through a blue loop or are binaries.
Title: A search for 6Li in stars with planets
Authors: Reddy, Bacham E.; Lambert, David L.; Laws, Chris; Gonzalez,
Guillermo; Covey, Kevin
Bibcode: 2002MNRAS.335.1005R
Altcode: 2002astro.ph..5268R
Using very high-resolution (R~ 125000) and high-quality (signal-to-noise
ratio >= 350) spectra, we have searched for 6Li in
stars hosting extrasolar planets. From detailed profile-fitting
of the LiI resonance line at 6707.7 Å, we find no significant
amount of 6Li relative to 7Li for any of eight
planet-bearing stars (6Li/7Li <= 0.0-0.03)
with strong LiI lines. In particular, we do not confirm the presence
of 6Li with 6Li/7Li = 0.13 reported by
Israelian et al. for HD 82943, a star with two known planets. Several of
the eight stars plus HD 219542 A, the planetless primary of a binary,
have been identified in the literature as possible recipients of
accreted terrestrial material. For all of the planet-hosting stars
and an additional five planetless stars, we find no 6Li.
Title: The isotopic mixture of barium in the metal-poor subgiant
HD 140283
Authors: Lambert, David L.; Allende Prieto, Carlos
Bibcode: 2002MNRAS.335..325L
Altcode: 2002astro.ph..5376L
Analyses of the abundances of neutron-capture elements have led to the
belief that these elements in metal-poor stars are r-process products
with relative abundances closely resembling those found in the Solar
system. This picture was challenged by Magain, who found that a pure
r-process mix of the barium isotopes was inconsistent with the mix of
odd to even barium isotopes derived from analysis of the BaII line
at 4554 Å in the spectrum of the metal-poor subgiant HD 140283. In
this paper, we address Magain's challenge using new high-resolution
high signal-to-noise spectra of HD 140283, and find, in contrast to
his result, that a solar-like r-process isotopic mixture provides a
fair fit to the observed 4554-Å profile.
Title: High resolution spectroscopy of QY Sge.
Authors: Kameswara Rao, N.; Goswami, A.; Lambert, D. L.
Bibcode: 2002BASI...30..671K
Altcode:
No abstract at ADS
Title: The Lemaître-Schwarzschild Problem Revisited
Authors: Füzfa, A.; Gerard, J. -M.; Lambert, D.
Bibcode: 2002GReGr..34.1411F
Altcode: 2001gr.qc.....9097F
The Lemaître and Schwarzschild analytical solutions for a relativistic
spherical body of constant density are linked together through the use
of the Weyl quadratic invariant. The critical radius for gravitational
collapse of an incompressible fluid is shown to vary continuously from
9/8 of the Schwarzschild radius to the Schwarzschild radius itself
while the internal pressures become locally anisotropic.
Title: Ultraviolet Detection of Interstellar
12C17O and the CO Isotopomeric Ratios toward
X Persei
Authors: Sheffer, Yaron; Lambert, David L.; Federman, S. R.
Bibcode: 2002ApJ...574L.171S
Altcode: 2002astro.ph..6449S
We report the detection of fully resolved absorption lines of
A-X bands from interstellar 12C17O and
12C18O, through high-resolution spectroscopy
of X Persei with the Space Telescope Imaging Spectrograph.3 The first
ultraviolet measurement of an interstellar 12C17O
column density shows that its isotopomeric ratio is
12C16O/12C17O=8700+/-3600.
Simultaneously, the second ultraviolet detection of interstellar
12C18O establishes its isotopomeric ratio
at 3000+/-600. These ratios are about five times higher than local
ambient oxygen isotopic ratios in the ISM. Such severe fractionation
of rare species shows that both 12C17O and
12C18O are destroyed by photodissociation,
whereas 12C16O avoids destruction through
self-shielding. This is to be contrasted with our ratio of
12C16O/13C16O=73+/-12 toward
X Per, which is indistinguishable from 12C/13C,
the result of a balance between the photodissociation of
13C16O and its preferential formation via the
isotope exchange reaction between CO and C+.
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: New Clues to the Origin of the Extreme Helium Stars
Authors: Lambert, David
Bibcode: 2002hst..prop.9417L
Altcode: 2002hst..prop.5765L
The extreme helium stars {EHes} are H-poor supergiants whose
origins are not yet understood despite thorough analyses of optical
spectra. This proposal seeks STIS echelle spectra for 7 stars from
which novel data on their chemical compositions will be obtained to
pin down key abundances. First, even the EHe's initial metallicity is
uncertain; certain abundance ratios - e.g., Ca/S, Ti/S, and Fe/S -
imply alterations of surface abundances among elements from Na to
Ni resulting from fractionation or diffusive separation, possibly
the result of winnowing of dust grains from gas. The zinc abundance
measurable only from UV spectra will be a powerful clue to the
true metallicity because it is known not to be removed by such
winnowing. Second, elements affected by the s-process, the last of
the major nucleosynthetic processes for which surface abundances are
unknown for EHes, will be studied. The new abundances will be used to
probe the evolutionary origins of these peculiar stars by comparisons
with theoretical scenarios involving a merger of white dwarfs or a final
He-shell flash in a low mass white dwarf, and with observed abundances
for R Coronae Borealis stars that would seem to be close relatives
of the EHes. Spectrophotometric observations of EHes obtained with GO
8603 will give accurate estimates of effective temperature and surface
gravity that will be used in our abundance determinations.
Title: Boron in the Small Magellanic Cloud: A Novel Test of
Light-Element Production
Authors: Brooks, A. M.; Venn, K. A.; Lambert, D. L.; Lemke, M.; Cunha,
K.; Smith, V. V.
Bibcode: 2002ApJ...573..584B
Altcode: 2002astro.ph..4026B
Hubble Space Telescope Space Telescope Imaging Spectrograph (STIS)
observations of the B III resonance line at λ2066 have been obtained
and analyzed for two Small Magellanic Cloud (SMC) B-type stars. While
boron is not detected in either star, upper limits to the boron
abundance are set, with 12+log(B/H)<=1.6 for both AV 304 and NGC
346-637. The upper limits are consistent with the relationship between
boron and oxygen previously reported for Galactic disk stars. The SMC
upper limits are discussed in light of that galaxy's star formation
history, present oxygen abundance, and present cosmic-ray flux. The
UV spectrum has also been used to determine the iron-group abundances
in the SMC stars. For AV 304, [Fe/H]=-0.6+/-0.2, from both an absolute
and a differential analysis (with respect to the Galactic B-type star
HD 36591). This is consistent with results from A-F supergiants in the
SMC. A lower iron abundance is found for NGC 346-637, [Fe/H]=-1.0+/-0.3,
but this is in good agreement with the supergiant iron abundances in
NGC 330, another young SMC cluster. We propose that NGC 346-637 might
be an unrecognized binary, however, which complicates its spectral
analysis. Based on observations made with the NASA/ESA Hubble Space
Telescope, obtained at the Space Telescope Science Institute, which is
operated by the Association of Universities for Research in Astronomy,
Inc., under NASA contract NAS5-26555. These observations are associated
with proposal GO 07400.
Title: High-resolution spectroscopy of QY Sge: an obscured RV Tauri
variable?
Authors: Kameswara Rao, N.; Goswami, Aruna; Lambert, David L.
Bibcode: 2002MNRAS.334..129K
Altcode: 2002astro.ph..3411K; 2002MNRAS.334..129R; 2002astro.ph..3411R
The first high-resolution optical spectra of QY Sge are presented and
discussed. Menzies & Whitelock, on the basis of photometry and
low-resolution spectra, suggested that this G0I supergiant was obscured
by dust and seen only by scattered light from a circumstellar reflection
nebula. The new spectra confirm and extend this picture. Photospheric
lines are unusually broad indicating scattering of photons from dust
in the stellar wind. The presence of very broad, NaD emission lines
is confirmed. Sharp emission lines from low levels of abundant neutral
metal atoms are reported for the first time. An abundance analysis of
photospheric lines shows that the stellar atmosphere is of approximately
solar composition but with highly condensable (e.g. Sc and Ti) elements
depleted by factors of 5-10.
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: Surface abundances of light elements for a large sample of
early B-type stars - II. Basic parameters of 107 stars
Authors: Lyubimkov, Leonid S.; Rachkovskaya, Tamara M.; Rostopchin,
Sergey I.; Lambert, David L.
Bibcode: 2002MNRAS.333....9L
Altcode:
Effective temperatures Teff, surface gravities logg
and interstellar extinctions AV are found for 107 B
stars. Distances d of the stars, which are based on the derived
Teff, logg and AV values, show good agreement
with those obtained from the Hipparcos parallaxes. Comparing the
Teff and logg values with evolutionary computations,
we infer masses, radii, luminosities, ages and relative ages of
the stars. Empirical relations between the Teff and
logg parameters, on the one hand, and the photometric indices Q,
[c1] and β, on the other hand, are constructed; these
relations give a fast method for the Teff and logg
estimation of early and medium B stars. Inclusion of the infrared
J, H and K colours into the Teff, logg and AV
determination shows that (i) the Teff and logg parameters
are altered only slightly; (ii) the AV value is rather
sensitive to these colours, so an accuracy better than 0.05mag in the
JHK data is necessary for precise AV evaluation.
Title: High-Resolution Measurements of Intersystem Bands of Carbon
Monoxide toward X Persei
Authors: Sheffer, Yaron; Federman, S. R.; Lambert, David L.
Bibcode: 2002ApJ...572L..95S
Altcode: 2002astro.ph..5082S
In an echelle spectrum of X Per acquired with the Space Telescope
Imaging Spectrograph, we have identified individual rotational
lines of 11 triplet-singlet (intersystem) absorption bands of
12CO. Four bands provide first detections for interstellar
clouds. From a comparison with the ζ Oph sight line, we find that
X Per is obscured by a higher 12CO column density of
1.4×1016 cm-2. Together with the high spectral
resolution of 1.3 km s-1, this allows (1) an improved
measurement of previously published interstellar f-values for seven
bands and (2) an extraction of the first astrophysical oscillator
strengths for d-X (8-0), (9-0), and (10-0), as well as for e-X
(12-0). The 13CO d-X (12-0) band, previously suspected to
exist toward ζ Oph, is now readily resolved and modeled. Our derived
intersystem f-values for 12CO include a few mild (<=34%)
disagreements with recent predictions from a perturbation analysis
calculated for the interstellar excitation temperature. Overall, the
comparison confirms the superiority of employing multiple singlet levels
in the calculations of mixing coefficients over previous single-level
predictions. Based on observations obtained with the NASA/ESA Hubble
Space Telescope through the Space Telescope Science Institute, which is
operated by the Association of Universities for Research in Astronomy,
Inc., under NASA contract NAS5-26555.
Title: Rapidly Rotating Lithium-rich K Giants: The New Case of the
Giant PDS 365
Authors: Drake, Natalia A.; de la Reza, Ramiro; da Silva, Licio;
Lambert, David L.
Bibcode: 2002AJ....123.2703D
Altcode: 2002astro.ph..2158D
PDS 365 is a newly detected, rapidly rotating (vsini=20 km
s-1), single, low-mass giant star that with HD 233517 and HD
219025 forms a remarkable ensemble of single K giants with the unique
properties of rapid rotation, very strong Li lines, an asymmetrical Hα
profile, and a large far-infrared excess. Their vsini values are between
18 and 23 km s-1, and their LTE Li abundances, logɛ(Li), are
between 2.9 and 3.9. Detailed analysis of PDS 365 reveals it to be a ~1
Msolar giant with a value of 12C/13C
approximately equal to 12. A clear relation between high rotational
velocities and very high Li abundances for K giant stars is found
only when asymmetrical Hα profiles and large far-infrared excesses
are present. If we consider single K giants, we find that among rapid
(vsini>=8 km s-1) rotators, a very large proportion
(~50%) are Li-rich giants. This proportion is in contrast with a very
low proportion (~2%) of Li-rich stars among the much more common slowly
rotating K giants. This striking difference is discussed in terms of
proposed mechanisms for Li enrichment.
Title: The outer atmosphere of the M-type supergiant alpha Orionis:
K I 7699 Åemission
Authors: Plez, B.; Lambert, D. L.
Bibcode: 2002A&A...386.1009P
Altcode: 2002astro.ph..3209P
Spatially-resolved high-resolution long-slit spectra of Betelgeuse's
circumstellar shell are described for a spectral window centered on
the 7699 Å resonance line of neutral potassium. The K I emission
from resonance fluorescent scattering of photospheric photons which
is mapped out to 50 arcsec from the star is approximately spherically
symmetric with a brightness decreasing as r-2.36 +/- 0.03,
where r is the radial distance from the star. Our measurements together
with the earlier theoretical interpretation by Rodgers & Glassgold
suggest that the mass loss rate is about 2 x 10-6 M_sun
y-1. The K I emission is far from homogeneous: intensity
inhomogeneities are seen down to the seeing limit of about 1 arcsec and
the velocity resolution of about 2 km s-1. There is clear
evidence for a thin shell of 50 arcsec radius. This is identified with
the weaker circumstellar absorption component known as S2. Estimates are
made of the density of K atoms in this shell ( =~ 6 x 10-5
cm-3).
Title: Water in Arcturus' Atmosphere
Authors: Ryde, N.; Lambert, D. L.; Richter, M. J.; Lacy, J. H.
Bibcode: 2002AAS...200.7807R
Altcode: 2002BAAS...34..779R
We report on a detection of water vapor in the K1.5III red-giant star
Arcturus (α Bootis) using high-resolution, infrared spectra covering
the regions 806-822 cm-1 (12.2-12.4 μ m) and 884-925
cm-1 (10.8-11.3 μ m). Arcturus is the hottest star yet
to have shown water-vapor features in its disk-averaged spectrum. We
argue that the water vapour lines originate from the photosphere
of the star. In calculating the synthetic spectra, we find that no
existing water-vapor line list has wavelength assignments sufficiently
accurate for our high-resolution spectra. Therefore, we assembled
a new water line-list based on laboratory measurement found in the
literature. The photosphere of Arcturus is modeled with the MARCS
model-atmosphere code with atmospheric parameters from a detailed
study of Arcturus based on the entire mid-infrared, low-resolution
Infrared Space Observatory spectrum (Decin et al. 1997). Using a
photospheric model based on these parameters, we are able to model
several OH lines of different excitation and the water-vapor lines
satisfactorily first after lowering the temperature structure of the
very outer parts of the photosphere at τ 500=-3.8 and
beyond compared to a flux-constant, hydrostatic, standard MARCS model
photosphere. Our new model is consistently calculated from the given
temperature structure. Possible reasons for a temperature decrease in
the outer-most parts of the photosphere and the assumed break-down
of the assumptions made in classical model-atmosphere codes will
be discussed. This work was supported by the Swedish Foundation for
International Cooperation in Research and Higher Education, Stiftelsen
Blanceflor Boncompagni-Ludovisi, née Bildt, and the Robert A. Welch
Foundation of Houston, Texas
Title: Boron in Solar-Type Galactic Disk Stars
Authors: McGrath, E. J.; Boesgaard, A. M.; Lambert, D. L.; Cunha, K.
Bibcode: 2002AAS...200.0714M
Altcode: 2002BAAS...34..652M
This is the first study of the abundance of boron in Population I
solar-type stars that are undepleted in beryllium. The requirement that
the stars be undepleted in Be ensures that they have also retained their
full initial abundance of boron, and thus provides a means to study the
evolution of B in the Galactic disk. Using the STIS echelle spectrograph
onboard HST, we observed sixteen bright stars around the B I 2497
Å line. Ten of these stars had corresponding Keck HIRES data which
was used to determine spectroscopic temperatures and new metallicity
values. Previous abundance studies of Li and Be in these stars were
reevaluated using these revised parameters for consistency. Boron
abundances were calculated by fitting the data to a modified spectral
synthesis code which accounts for the increased opacity in the UV due
to metals, and were then corrected for non-LTE effects. We find that
the trend of boron abundance with metallicity is consistent with the
general trend observed in halo stars, although there may be a slight
flattening of the slope in the disk. In addition, the abundance of
B is observed to be a factor of ~15 more than the abundance of Be in
these stars. This work was funded by HST grant GO-087701.
Title: Spectroscopic Study of IRAS 19285+0517 (PDS 100): A Rapidly
Rotating Li-Rich K Giant
Authors: Reddy, Bacham E.; Lambert, David L.; Hrivnak, Bruce J.;
Bakker, Eric J.
Bibcode: 2002AJ....123.1993R
Altcode: 2001astro.ph.12259R
We report on photometry and high-resolution spectroscopy for IRAS
19285+0517. The spectral energy distribution based on visible and
near-infrared photometry and far-infrared fluxes shows that the
star is surrounded by dust at a temperature of Td~250
K. Spectral line analysis shows that the star is a K giant with a
projected rotational velocity of vsini=9+/-2 km s-1. We
determined the atmospheric parameters: Teff=4500 K,
logg=2.5, ξt=1.5 km s-1, and [Fe/H]=0.14
dex. The LTE abundance analysis shows that the star is Li-rich
[logɛ(Li)=2.5+/-0.15], but with essentially normal C, N, O, and
metal abundances. Spectral synthesis of molecular CN lines yields
the carbon isotopic ratio 12C/13C=9+/-3,
a signature of post-main-sequence evolution and dredge-up on the
red giant branch (RGB). Analysis of the Li resonance line at 6707
Å for different 6Li/7Li ratios shows that
the Li profile can be best fitted with a predicted profile for pure
7Li. Far-infrared excess, high Li abundance, and rapid
rotation suggest that a planet has been swallowed or, perhaps, that
an instability in the RGB outer layers triggered a sudden enrichment
of Li and caused mass loss.
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: Convective Wavelength Shifts in the Spectra of Late-Type Stars
Authors: Allende Prieto, Carlos; Lambert, David L.; Tull, Robert G.;
MacQueen, Phillip J.
Bibcode: 2002ApJ...566L..93A
Altcode: 2002astro.ph..1355P; 2002astro.ph..1355A
We present ultrahigh-resolution spectra for a set of nearby F-G-K
stars on, or close to, the main sequence. The wavelength shifts of
stellar lines relative to their laboratory wavelengths are measured for
more than a thousand Fe I lines per star, finding a clear correlation
with line depth. The observed patterns are interpreted as convective
blueshifts that become more prominent for weaker lines, which are formed
in deeper atmospheric layers. A morphological sequence with spectral
type or effective temperature is apparent. Two K giant stars have also
been studied. The velocity span between weak and strong lines for these
stars is larger than for the dwarfs and subgiants of similar spectral
types. Our results show that convective wavelength shifts may seriously
compromise the accuracy of absolute spectroscopic radial velocities
but that an empirical correction may be applied to measured velocities.
Title: An independent view?
Authors: Lambert, David L.
Bibcode: 2002HiA....12..445L
Altcode:
The current dispute over the oxygen abundance in metal-poor stars has
been viewed from a distance by this observer who would claim a measure
of independence despite an intermittent interest in oxygen abundance
determinations over 3 decades. This summary attempts to persuade all
participants whether they advocate a "high" or "low" oxygen abundance
or are simply bemused by the dispute that in resolving the present
disagreements we shall learn not only about the oxygen abundance of
these oldest Galactic stars but shall achieve a deeper understanding
of the atmospheres of the stars.
Title: A Spectroscopic Search for Massive Thorne-Zytkow Objects
Authors: Kuchner, M. J.; Vakil, D.; Smith, V. V.; Lambert, D. L.;
Plez, B.; Phinney, E. S.
Bibcode: 2002ASPC..263..131K
Altcode: 2002scmc.conf..131K
No abstract at ADS
Title: Spectroscopic Analysis of Two Carbon-rich Post-Asymptotic
Giant Branch Stars
Authors: Reddy, Bacham E.; Lambert, David L.; Gonzalez, G.; Yong, David
Bibcode: 2002ApJ...564..482R
Altcode: 2001astro.ph..9068R
The chemical compositions of the C-rich post-asymptotic giant branch
(pAGB) stars IRAS 05113+1347 and IRAS 22272+5424 are determined
from high-resolution optical spectra using standard LTE model
atmosphere-based techniques. The stars are C, N, and s-process enriched,
suggesting efficient operation of the third dredge-up in the AGB star
following a first dredge-up that increased the N abundance. Lithium is
present with an abundance requiring Li manufacture. With this pair,
abundance analyses are now available for 11 C-rich pAGBs. A common
history is indicated and, in particular, the s-abundances, especially
the relative abundances of light to heavy s-process elements, follow
recent predictions for the third dredge-up in AGB stars.
Title: Observation And Modelling Of Stratospheric Filaments During
The Pico3 Campaign
Authors: Cammas, J. -P.; Mascart, P.; Ancellet, G.; Lambert, D.;
Peuch, V. -H.; Nédelec, P.
Bibcode: 2002EGSGA..27.4942C
Altcode:
The Meso-NHC model (Meso-scale Non-Hydrostatic and Chemical model)
is used to study a Stratosphere - Troposhere Exchange process during
the formation of strato- spheric filaments consecutive to planetary
wave breaking events. We use a grid-nested simulation with horizontal
resolutions of 30 km and 10 km, with a vertical resolu- tion of 300
m. The model is initialised with ARPEGE (Météo-France) analyses for
meteorological variables and with MOCAGE (Météo-France) analyses for
chemical variables. The data set used to evaluate the performances of
the model is the PICO3 data set gathered during an airborne campaign
over NW Africa with the french jet aircraft equiped with in-situ
measurements of O3 and CO and an airborne O3 lidar. Results from a
simulation of a case study will be described.
Title: Boron Abundances in B-Type Stars: A Test of Rotational
Depletion during Main-Sequence Evolution
Authors: Venn, K. A.; Brooks, A. M.; Lambert, David L.; Lemke, M.;
Langer, N.; Lennon, D. J.; Keenan, F. P.
Bibcode: 2002ApJ...565..571V
Altcode: 2001astro.ph..8263V
Boron abundances have been derived for seven main-sequence B-type
stars from Hubble Space Telescope STIS spectra around the B III
λ2066 line. In two stars, boron appears to be undepleted with
respect to the presumed initial abundance. In one star, boron is
detectable but is clearly depleted. In the other four stars, boron
is undetectable, implying depletions of 1-2 dex. Three of these four
stars are nitrogen enriched, but the fourth shows no enrichment
of nitrogen. Only rotationally induced mixing predicts that boron
depletions are unaccompanied by nitrogen enrichments. The inferred
rate of boron depletion from our observations is in good agreement
with these predictions. Other boron-depleted nitrogen-normal
stars are identified from the literature. In addition, several
boron-depleted nitrogen-rich stars are identified, and while all
fall on the boron-nitrogen trend predicted by rotationally induced
mixing, a majority have nitrogen enrichments that are not uniquely
explained by rotation. The spectra have also been used to determine
iron group (Cr, Mn, Fe, and Ni) abundances. The seven B-type stars
have near-solar iron group abundances, as expected for young stars in
the solar neighborhood. We have also analyzed the halo B-type star PG
0832+676. We find [Fe/H]=-0.88+/-0.10, and the absence of the B III
line gives the upper limit [B/H]<-2.5. These and other published
abundances are used to infer the star's evolutionary status as a
post-asymptotic giant branch star. Based on observations made with
the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope
Science Institute, which is operated by the Association of Universities
for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These
observations are associated with proposal GO 07400.
Title: The Rise of the S-process
Authors: Simmerer, J. A.; Sneden, C.; Woolf, V. M.; Lambert, D. L.
Bibcode: 2001AAS...199.9110S
Altcode: 2001BAAS...33Q1438S
Throughout the history of the Galaxy, the composition of neutron-capture
elements (those with atomic numbers greater than 30) has been
dictated mainly by two nucleosynthetic processes: the s-process and
the r-process. Elements generated by the s(low)-process are believed
to be formed in the He-burning of low to intermediate mass stars,
while r(apid)-process elements likely originate in massive star
supernovae. In the most metal-poor stars, those elements with large
s-process components are deficient with respect to those with large
r-process components. This is consistent with expected nucleosynthetic
output from the massive stars that probably dominated the element
forming processes early on in the Galaxy. Typically the measurement
of the s-/r-process has been carried out with the elements Ba and Eu,
since the former is produced almost entirely in the s-process and
the latter in the r-process. Here we use the s-process element La to
measure the s-process, since new and highly accurate atomic data have
become available for La and Eu, making the results much more precise
than they have been. Our sample includes 200 stars in the range range
-2.5<[Fe/H]<-1, for which we have gathered new high resolution
(R ~60,000) and signal-to-noise (S/N>100) spectra, and from which
we derive La/Eu. We have also derived La/Eu from the data of Woolf et
al. (1995) in order to cover a higher metallicity range. Preliminary
results indicate that La/Eu rises steadily, if not entirely smoothly,
over the range -2>[Fe/H]>0, with the s-process apparently
beginning to "turn on" near [Fe/H] ~-1.8. The higher metallicity data
of Woolf et al. indicates that the rise to the solar La/Eu is gradual,
but may show evidence of scatter.
Title: Boron in the Small Magellanic Cloud: A Novel Test of Light
Element Formation
Authors: Brooks, A. M.; Venn, K. A.; Lambert, D. L.; Lemke, M.; Cunha,
K.; Smith, V. V.
Bibcode: 2001AAS...199.5405B
Altcode: 2001BAAS...33.1382B
Hubble Space Telescope STIS observations of the B 3 resonance line at
2066 Å have been obtained and analyzed for two Small Magellanic Cloud
(SMC) B-type stars. Boron is not detected in either star. However,
upper limits to the boron abundance are set, with 12+log(B/H) <= 1.6
for both AV 304 and NGC 346-637. These results suggest that boron may
scale quadratically with oxygen (B α O2) in the SMC, as is
expected for a pure cosmic-ray spallation standard model. However, the
results are also consistent with the scaling law B α O1.4
found for F and G dwarfs in the disk of the Galaxy by Smith etal
(2001). Also, mixing due to rapid-rotation could have depleted boron
in our SMC B-star targets. The UV spectrum of AV 304 has also been
used to determine an iron-group abundance, [Fe/H]=-0.6+/-0.2, from
both an absolute and a differential analysis, with respect to the
Galactic B-star HD 36591. This is consistent with results from the A-F
supergiants in the SMC. Support for proposal GO#08161 was provided by
NASA through a grant from the Space Telescope Science Institute.
Title: Boron Abundances in Main Sequence B-type Stars: A Test of
Rotational Depletion during Main Sequence Evolution
Authors: Venn, K. A.; Brooks, A. M.; Lambert, D. L.; Lemke, M.;
Langer, N.; Lennon, D. J.; Keenan, F. P.
Bibcode: 2001AAS...19913703V
Altcode: 2001BAAS...33.1512V
Boron abundances have been derived for seven main sequence B-type stars
from HST STIS spectra around the BIII 2066 A line. Boron abundances
range from normal to severly depleted. One boron depleted star shows no
nitrogen enrichment, which is an abundance pattern uniquely predicted
from the rotationally-induced mixing models, e.g., Heger and Langer
2000. Other stars show boron depletions that correlate with nitrogen
enrichments; this pattern is predicted by rotationally-induced mixing,
but also by other theories. The inferred rate of boron depletion (i.e.,
boron versus age) from our observations is also in good agreement with
the predictions. Based on observations made with the NASA/ESA Hubble
Space Telescope, obtained at the Space Telescope Science Institute,
which is operated by the Association of Universities for Research in
Astronomy, Inc., under NASA contract NAS 5-26555. These observations
are associated with proposal GO-7400.
Title: Boron and Iron in AV 304: A B-dwarf in the SMC
Authors: Brooks, A. M.; Venn, K. A.; Lambert, D. L.; Lemke, M.
Bibcode: 2001AAS...198.9303B
Altcode: 2001BAAS...33.1179B
An upper limit in the boron abundance in AV 304 is determined as a
test of cosmic ray spallation as the production of boron. Boron is
determined from the B III resonance line at 2066 A from HST STIS
data. AV 304 does not show signs of mixing or mass loss, which can
destroy the fragile boron atom. The abundance othe boron seed nucleus,
oxygen, is also well known in this star, and O is approximately the
same from location to location in the SMC. Thus, the boron abundance
from AV 304 should be representative of the abundance in ththe entire
galaxy. We find an upper limit of 12+log(B/H)=1.7. This boron upper
limit is lower than the oxygen depletion relative to the solar
neighborhood by 0.3 dex. This is unlike the Galactic studies that
suggest that boron scales linearly with oxygen. Additionally, the
numerous Fe-group elements in the UV spectrum allows for a detailed
Fe-group abundance determination. We find 12+log(Fe/H)=0.7+/-0.1,
primarily from Fe III lines. The abundance is in excellent agreement
with determinations from Fe I and Fe II lines in A-K supergiants in
the SMC, and supports that O and Fe have the same underabundance in
the SMC. We appreciate support for this project from NASA GO-08661,
and Clare Boothe Luce research funds.
Title: A high resolution spectroscopic study of XX Ophiuchi
Authors: Goswami, Aruna; Rao, N. K.; Lambert, D. L.
Bibcode: 2001BASI...29..295G
Altcode:
The star XX Oph has been known to exhibit peculiar spectral
variabilities since the work of Merrill in 1924. A high resolution
spectroscopic study of the XX Oph spectra taken in July 1996 and later
in June 1997 also exhibit distinctly different line profiles in several
spectral regions, the most pronounced variations being in the sodium D
and H? profiles. We have estimated the displacement velocities of the
strong emission line profiles and their absorption components whenever
possible and made an attempt to examine possible physical scenarios
that can account for its peculiar variability.
Title: Physical Conditions in the Foreground Gas of Reflection
Nebulae: NGC 2023, vdB 102, and NGC 7023
Authors: Knauth, David C.; Federman, S. R.; Pan, K.; Yan, M.; Lambert,
David L.
Bibcode: 2001ApJS..135..201K
Altcode: 2001astro.ph..3151K
High-resolution optical spectra of HD 37903 and HD 147009, which
illuminate the reflection nebulae NGC 2023 and vdB 102, were obtained
for comparison with our results for HD 200775 and NGC 7023. Ground-based
measurements of the molecules CH, C2, and CN and the
atoms Na I and K I were analyzed to extract physical conditions in
the foreground cloud. Estimates of the gas density, gas temperature,
and flux of ultraviolet radiation were derived and were compared with
the results from infrared and radio studies of the main molecular
cloud. The conditions are similar to those found in studies of diffuse
clouds. The foreground material is less dense than the gas in the
molecular cloud behind the star(s). The gas temperature was set at 40
K, the temperature determined for the foreground gas in NGC 7023. The
flux of ultraviolet radiation was found to be less intense than in the
molecular material behind the star(s). The column densities of Na I
and K I were reproduced reasonably well when the extinction curve for
the specific line of sight was adopted. We obtained NEWSIPS data from
the IUE archive for HD 37903 and HD 200775. The ultraviolet data on
C I and CO allow extraction of the physical conditions by alternate
methods. General agreement among the various diagnostics was found,
leading to self-consistent pictures of the foreground photodissociation
regions. An appendix describes checks on the usefulness of IUE NEWSIPS
data for interstellar studies. Equivalent widths are compared with
a previous analysis of IUE observations for interstellar gas toward
20 Aql. Excellent agreement is found with NEWSIPS results having
smaller errors. A comparison of NEWSIPS data for C I toward X Per
with data acquired with the Hubble Space Telescope shows similar
levels of agreement in equivalent widths and that the derived column
densities from IUE results are accurate to better than a factor of 2
for absorption lines of moderate strength.
Title: Nucleosynthesis and Mixing on the Asymptotic Giant
Branch. III. Predicted and Observed s-Process Abundances
Authors: Busso, Maurizio; Gallino, Roberto; Lambert, David L.;
Travaglio, Claudia; Smith, Verne V.
Bibcode: 2001ApJ...557..802B
Altcode: 2001astro.ph..4424B
We present the results of s-process nucleosynthesis calculations
for asymptotic giant branch (AGB) stars of different metallicities
and different initial stellar masses (1.5 and 3 Msolar),
and we present comparisons of them with observational constraints from
high-resolution spectroscopy of evolved stars over a wide metallicity
range. The computations were based on previously published stellar
evolutionary models that account for the third dredge-up phenomenon
occurring late on the AGB. Neutron production is driven by the
13C(α,n)16O reaction during the interpulse
periods in a tiny layer in radiative equilibrium at the top of the He-
and C-rich shell. The neutron source 13C is manufactured
locally by proton captures on the abundant 12C; a few protons
are assumed to penetrate from the convective envelope into the radiative
layer at any third dredge-up episode, when a chemical discontinuity
is established between the convective envelope and the He- and C-rich
zones. A weaker neutron release is also guaranteed by the marginal
activation of the reaction 22Ne(α,n)25Mg during
the convective thermal pulses. Owing to the lack of a consistent model
for 13C formation, the abundance of 13C burnt
per cycle is allowed to vary as a free parameter over a wide interval
(a factor of 50). The s-enriched material is subsequently mixed with
the envelope by the third dredge-up, and the envelope composition
is computed after each thermal pulse. We follow the changes in the
photospheric abundance of the Ba-peak elements (heavy s [hs]) and that
of the Zr-peak ones (light s [ls]), whose logarithmic ratio [hs/ls] has
often been adopted as an indicator of the s-process efficiency (e.g.,
of the neutron exposure). Our model predictions for this parameter
show a complex trend versus metallicity. Especially noteworthy is
the prediction that the flow along the s-path at low metallicities
drains the Zr and Ba peaks and builds an excess at the doubly magic
208Pb, which is at the termination of the s-path. We
then discuss the effects on the models of variations in the crucial
parameters of the 13C pocket, finding that they are not
critical for interpreting the results. The theoretical predictions
are compared with published abundances of s-elements for AGB giants
of classes MS, S, SC, post-AGB supergiants, and for various classes of
binary stars, which supposedly derive their composition by mass transfer
from an AGB companion. This is done for objects belonging both to the
Galactic disk and to the halo. The observations in general confirm the
complex dependence of neutron captures on metallicity. They suggest
that a moderate spread exists in the abundance of 13C
that is burnt in different stars. Although additional observations
are needed, it seems that a good understanding has been achieved of
s-process operation in AGB stars. Finally, the detailed abundance
distribution including the light elements (CNO) of a few s-enriched
stars at different metallicities are examined and satisfactorily
reproduced by model envelope compositions.
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: Ultraviolet Spectroscopy of R Coronae Borealis Stars --
Broad Lines from an Accretion Disc?
Authors: Lambert, David
Bibcode: 2001hst..prop.9228L
Altcode:
STIS spectra of three R Coronae Borealis {RCB} stars will provide novel
data on hot gas near these stars; such data can be obtained only from
HST. RCBs are hydrogen-deficient and fade at unpredictable times as a
carbon soot cloud obscures the star. Optical spectra taken when a star
has faded reveal an emission line spectrum containing sharp {FWHM 15
km s^-1} and broad {FWHM 250 km s^-1} lines. The latter are of much
higher excitation than the former. For R CrB, it has been suggested
that the broad lines arise from an accretion disk around a compact
secondary. These optical lines are visible only during the infrequent
extreme fadings of a RCB. Although IUE spectra reveal high-excitation
emission lines at maximum light, the IUE spectra lack the spectral
resolution to distinguish broad from sharp lines. STIS spectra will
resolve the broad-line from a sharp-line component, and, in the case,
of R CrB, where repeat visits are requested, be used to search for
velocity variations as the companion orbits the RCB. In addition,
the line intensity ratios will provide new estimates of the physical
conditions of the gas emitting the broad lines. This proposal may help
to answer the question - How are RCBs formed? And this answer may show
that, although RCBs are rare, many low mass stars evolve through the
RCB on their path to extinction as a white dwarf.
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: Infrared Space Observatory Spectra of R Coronae Borealis
Stars. I. Emission Features in the Interval 3-25 Microns
Authors: Lambert, David L.; Rao, N. Kameswara; Pandey, Gajendra;
Ivans, Inese I.
Bibcode: 2001ApJ...555..925L
Altcode: 2001astro.ph..3400L
Infrared Space Observatory 3-25 μm spectra of the R Coronae Borealis
stars V854 Cen, R CrB, and RY Sgr are presented and discussed. Sharp
emission features coincident in wavelength with the well-known
unidentified emission features are present in the spectrum of V854
Cen but not in the spectra of R CrB and RY Sgr. Since V854 Cen is
not particularly hydrogen-poor and has 1000 times more hydrogen than
the other stars, the emission features are probably from a carrier
containing hydrogen. There is a correspondence between the features
and the emission from laboratory samples of hydrogenated amorphous
carbon. A search for C60 in emission or absorption proved
negative. Amorphous carbon particles account for the broad emission
features seen between 6 and 14 μm in the spectrum of each star. Based
on observations with ISO, an ESA project with instruments funded by
ESA member states (especially the PI countries: France, Germany, the
Netherlands, and the UK) and with the participation of ISAS and NASA.
Title: Line identification in the Ca II K spectral region of
sharp-lined B-type stars
Authors: Lehner, N.; Trundle, C.; Keenan, F. P.; Sembach, K. R.;
Lambert, D. L.
Bibcode: 2001A&A...370..996L
Altcode:
Previous Ca Ii K observations of the B-type star HD 83206 have revealed
putative high-velocity interstellar clouds (HVCs) at Local Standard of
Rest (LSR) velocities of -80 and -110 kms-1. Similar results
were also found for the sightline towards HD 135485. In this article,
we show that these absorption lines are in fact due to stellar S Ii
features. As the Ca Ii K absorption line in B-type stars is often
used to assess the presence and distance of HVCs, we also present a
very high quality spectrum of HD 83206 in the Ca Ii K region ( ~ +/-
4 Å or +/- 300 kms-1), so that in the future confusion
between stellar lines and HVC features may be avoided.
Title: Chemical Compositions of Four Metal-poor Giant Stars
Authors: Giridhar, Sunetra; Lambert, David L.; Gonzalez, Guillermo;
Pandey, Gajendra
Bibcode: 2001PASP..113..519G
Altcode: 2001astro.ph..2307G
We present the chemical compositions of four K giants (CS 22877-1,
CS 22166-16, CS 22169-35, and BS 16085-0050) that have [Fe/H] in the
range -2.4 to -3.1. Metal-poor stars with [Fe/H]<-2.5 are known to
exhibit considerable star-to-star variations of many elements. This
quartet confirms this conclusion. CS 22877-1 and CS 22166-16 are
carbon-rich. There is significant spread of [α/Fe] within our samples,
where [α/Fe] is computed from the mean of the [Mg/Fe] and [Ca/Fe]
ratios. BS 16085-0050 is remarkably α-enriched with a mean [α/Fe]
of +0.7, but CS 22169-35 is α-poor. The aluminum abundance also shows
a significant variation over the sample. A parallel and unsuccessful
search among high-velocity late-type stars for metal-poor stars is
described.
Title: The Primordial Lithium Abundance
Authors: Vargas-Ferro, O.; Smith, V. V.; Lambert, D. L.; Hobbs, L. M.
Bibcode: 2001AAS...198.4401V
Altcode: 2001BAAS...33..845V
Lithium abundances are presented for a sample of 23 halo dwarf and
subgiant stars. The abundances are derived from high signal-to-noise
(S/N ~ 400), high-resolution (R = 120,000) spectra obtained at McDonald
Observatory. The program stars span the metallicity range of [Fe/H] =
-3.0 to -1.0 and abundances ( or upper limits) are also determined for
the minor isotope 6Li. The 6Li abundances are used
to constrain possible stellar mixing and Li destruction, as well as the
contribution to the lithium abundance from cosmic-ray synthesis. The
primordial lithium abundance is estimated by an extrapolation to zero
Fe abundance. This research is supported, by part, by the Texas Advanced
Research Program (003661-0003-1999) and the National Science Foundation
(AST99-87374).
Title: Chemical compositions of metal-poor stars - dreams and
nightmares
Authors: Lambert, D. L.
Bibcode: 2001NuPhA.688...29L
Altcode:
No abstract at ADS
Title: Emission-line spectra of XX Ophiuchi in 1996 and 1997
Authors: Goswami, A.; Rao, N. K.; Lambert, D. L.
Bibcode: 2001Obs...121...97G
Altcode:
No abstract at ADS
Title: (Teff, log g, [Fe/H]) Classification of
Low-Resolution Stellar Spectra using Artificial Neural Networks
(CD-ROM Directory: contribs/snider)
Authors: Snider, S.; Qu, Y.; Allende Prieto, C.; von Hippel, T.;
Beers, T. C.; Sneden, C.; Lambert, D. L.; Rossi, S.
Bibcode: 2001ASPC..223.1344S
Altcode: 2001csss...11.1344S
No abstract at ADS
Title: Chemical Compositions of Asymptotic Giant Branch Stars -
A Tool for Understanding the Evolution of Cool Stars and Stellar
Systems (CD-ROM Directory: contribs/lambert1)
Authors: Lambert, D. L.
Bibcode: 2001ASPC..223..163L
Altcode: 2001csss...11..163L
No abstract at ADS
Title: An Analysis of the K I λ7698 Line Profile in the Halo Turnoff
Star HD 84937 and Its Implications for Lithium Isotopic Studies
Authors: Smith, Verne V.; Vargas-Ferro, Omar; Lambert, David L.;
Olgin, John G.
Bibcode: 2001AJ....121..453S
Altcode:
The line profile of the resonance line of K I at 7698 Å has been
analyzed in the halo turnoff star HD 84937, using a high-resolution
(λ/Δλ=110,000), high signal-to-noise ratio (S/N=550) spectrum. Three
different groups have reported detecting 6Li in this star,
based on a red asymmetry in the Li I λ6707 line profile (6Li
displays an isotopic shift of about 0.15 Å to the red, relative to
7Li, in this line). It is possible, however, that convection
could introduce this red asymmetry by mass motions of 7Li in
the star's atmosphere. At the metallicity of HD 84937, the K I resonance
line at 7698 Å is expected to have a similar line strength to the Li
I λ6707 feature, and both these lines are resonance transitions. In
addition, both potassium and lithium have similar first ionization
potentials. The result of these similarities is that the Li I and
K I lines are formed at nearly identical regions in the atmosphere
of HD 84937. This study presents a line profile analysis of the K I
line, which has negligible isotopic splitting and is effectively a
single-component line, in HD 84937. Any possible convective motions of
sufficient magnitude to produce a spurious detection of 6Li
should also produce detectable asymmetries in the K I line. No such
asymmetries are found here, strengthening the case that the previously
reported detections of 6Li in HD 84937 are real.
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: From Brightness and Colour to Size and Temperature (CD-ROM
Directory: contribs/lambert2)
Authors: Lambert, D. L.; Allende Prieto, C.
Bibcode: 2001ASPC..223..821L
Altcode: 2001csss...11..821L
No abstract at ADS
Title: Betelgeuse Circumstellar Shell: K I 7699Å Emission (CD-ROM
Directory: contribs/plez)
Authors: Plez, B.; Lambert, D. L.
Bibcode: 2001ASPC..223.1632P
Altcode: 2001csss...11.1632P
No abstract at ADS
Title: The Chemical Compositions of the SRD Variable Stars. III. KK
Aquilae, AG Aurigae, Z Aurigae, W Leo Minoris, and WW Tauri
Authors: Giridhar, Sunetra; Lambert, David L.; Gonzalez, Guillermo
Bibcode: 2000PASP..112.1559G
Altcode: 2000astro.ph..8428G
Chemical compositions are derived from high-resolution spectra for
five field SRd variables. These supergiants not previously analyzed
are shown to be metal poor: KK Aql with [Fe/H]=-1.2, AG Aur with
[Fe/H]=-1.8, Z Aur with [Fe/H]=-1.4, W LMi with [Fe/H]=-1.1, and WW Tau
with [Fe/H]=-1.1. Their compositions are, except for two anomalies,
identical to within the measurement errors to the compositions of
subdwarfs, subgiants, and less evolved giants of the same [Fe/H]. One
anomaly is an s-process enrichment for KK Aql, the first such enrichment
reported for an SRd variable. The second and more remarkable anomaly
is a strong lithium enrichment for W LMi, also a first for field SRd
variables. The Li I λ6707 profile is not simply that of a photospheric
line but includes strong absorption from redshifted gas, suggesting,
perhaps, that lithium enrichment results from accretion of Li-rich
gas. This potential clue to lithium enrichment is discussed in light
of various proposals for lithium synthesis in evolved stars.
Title: Light-Element Abundance Patterns in the Orion
Association. I.Hubble Space Telescope Observations of Boron in
G Dwarfs
Authors: Cunha, Katia; Smith, Verne V.; Parizot, Etienne; Lambert,
David L.
Bibcode: 2000ApJ...543..850C
Altcode: 2000astro.ph..5437C
The boron abundances for two young solar-type members of the Orion
association, BD -6°1250 and HD 294297, are derived from Hubble
Space Telescope STIS spectra of the B I transition at 2496.771
Å. The best-fit boron abundances for the target stars are 0.13 and
0.44 dex lower than the solar meteoritic value of logɛ(B)=2.78. An
anticorrelation of boron and oxygen is found for Orion when these
results are added to previous abundances obtained for four B-type stars
and the G-type star BD -5°1317. An analysis of the uncertainties in the
abundance calculations indicates that the observed anticorrelation is
probably real. The B versus O relation observed in the Orion association
does not follow the positive correlation of boron versus oxygen that
is observed for the field stars with roughly solar metallicity. The
observed anticorrelation can be accounted for by a simple model in which
two poorly mixed components of gas (supernova ejecta and boron-enriched
ambient medium) contribute to the new stars that form within the
lifetime of the association. This model predicts an anticorrelation
for Be as well, at least as strong as for boron.
Title: Ultraviolet Spectroscopy of R Coronae Borealis Stars --
Broad Lines from an Accretion Disc?
Authors: Lambert, David
Bibcode: 2000hst..prop.8615L
Altcode: 2000hst..prop.4951L
STIS spectra of three R Coronae Borealis {RCB} stars will provide novel
data on hot gas near these stars; such data can be obtained only from
HST. RCBs are hydrogen-deficient and fade at unpredictable times as a
carbon soot cloud obscures the star. Optical spectra taken when a star
has faded reveal an emission line spectrum containing sharp {FWHM 15
km s^-1} and broad {FWHM 250 km s^-1} lines. The latter are of much
higher excitation than the former. For R CrB, it has been suggested
that the broad lines arise from an accretion disk around a compact
secondary. These optical lines are visible only during the infrequent
extreme fadings of a RCB. Although IUE spectra reveal high-excitation
emission lines at maximum light, the IUE spectra lack the spectral
resolution to distinguish broad from sharp lines. STIS spectra will
resolve the broad-line from a sharp-line component, and, in the case,
of R CrB, where repeat visits are requested, be used to search for
velocity variations as the companion orbits the RCB. In addition,
the line intensity ratios will provide new estimates of the physical
conditions of the gas emitting the broad lines. This proposal may help
to answer the question - How are RCBs formed? And this answer may show
that, although RCBs are rare, many low mass stars evolve through the
RCB on their path to extinction as a white dwarf.
Title: The Interstellar Isotopic Ratio of Boron toward Omicron Persei
and Nearby Sight Lines
Authors: Lambert, David
Bibcode: 2000hst..prop.8622L
Altcode: 2000hst..prop.4958L
The isotopic ratio 11B/10B will be determined for diffuse
interstellar material along lines of sight to o Persei, 40 Persei,
Zeta Persei, and X Persei that pass close to the star- forming
region IC 348. High-resolution spectra of the Li I 6707A line
toward o and Zeta Per show remarkably different isotopic ratios for
lithium. Particularly striking is the ratio 7Li/6Li 3 for o Per while
Zeta Per shows a quasi-solar { 10} ratio. The significance of the very
low ratio for o Per is that it is essentially the value predicted for
production by relativistic cosmic rays through spallation reactions;
it is the only interstellar or stellar measurement that approaches
this theoretical value. This discovery provides a novel opportunity to
measure the isotopic B ratio of gas with a Li concentration dominated
by spallation induced by relativistic cosmic rays. Feasibility of
isotopic measurements has been demonstrated by our GHRS observations
of the interstellar B II 1362A resonance line that provided the
first extra-solar measurement of 11B/10B. Comparison of the observed
and predicted isotopic B {and Li} ratios will test the relative
importance of B synthesis by cosmic rays and Type II supernovae,
and test proposals that invoke high-fluxes of high-energy particles
in star-forming regions as major players in light element synthesis.
Title: Surface abundances of light elements for a large sample
of early B-type stars - I. Spectral observations of 123 stars;
measurements of hydrogen and helium lines; infrared photometry
Authors: Lyubimkov, L. S.; Lambert, D. L.; Rachkovskaya, T. M.;
Rostopchin, S. I.; Tarasov, A. E.; Poklad, D. B.; Larionov, V. M.;
Larionova, L. V.
Bibcode: 2000MNRAS.316...19L
Altcode:
High-resolution spectral observations of 123 B0-B5 stars in the
main sequence evolutionary phase were obtained at two observatories,
namely the McDonald Observatory (McDO) and the Crimean Astrophysical
Observatory (CrAO). Accurate equivalent widths W of two Balmer lines,
Hβ and Hγ, and ten Hei lines were obtained for all the stars, as well
as of the Heiiλ4686 line for the hottest ones. A careful analysis of
the measured equivalent widths was performed. It is shown that there
is a very good agreement between the W values derived from the McDO and
CrAO spectra for 14 common stars. A comparison with published data leads
to the conclusion that the W values measured earlier by some authors
for strong Hei lines are very likely to be underestimated. Infrared
photometric observations in the J, H, and K bands were performed for
70 programme stars. All these data will be used in other papers: in
particular for the Teff and logg determination and for the
He, C, N and O abundance analyses.
Title: The Galactic Abundance Gradients of Boron and Iron
Authors: Lambert, David
Bibcode: 2000hst..prop.8621L
Altcode: 2000hst..prop.4957L
This proposal aims to provide the first measurement of the Galactic
abundance gradients for Boron and Iron. Boron abundances will be
obtained for 5 B-type stars {with Galactocentric distances between
4-15 kpc} from the BIII 2066 Angstrom line. Optical spectroscopy of
these {and other B-type} stars has yielded abundance gradients of -0.07
dex/kpc for N & the Alpha-elements {O, Mg, Si}. Determination of
Boron abundances require UV spectra and HST/STIS. It is significant
that stellar nucleosynthesis which is the leading source of oxygen
{via Type II SN} is unlikely to be a major contributor to B synthesis
{spallation being the leading candidate}. Hence, a measurement of
the B abundance gradient provides novel information on the gradient
of cosmic ray flux in the Galaxy. The same STIS spectra will also
provide FeIII lines that will be used to obtain the first estimate
of the present abundance gradient for iron {thought to originate
predominantly in Type I SN}. Recent advances in modelling the chemical
evolution of the Galactic disk have led to definite predictions of the
spatial variation of the Alpha/Fe ratio in competing Galaxy formation
scenarios, viz. the biased infall and biased outflow models. This study
should yield differential Fe abundances accurate to +/-0.1 dex - which
will allow a Alpha/Fe gradient to be compared directly with theory,
as a critical test of formation models.
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: Newly synthesized lithium in the interstellar medium
Authors: Knauth, D. C.; Federman, S. R.; Lambert, David L.; Crane, P.
Bibcode: 2000Natur.405..656K
Altcode:
Astronomical observations of elemental and isotopic abundances
provide the means to determine the source of elements and to reveal
their evolutionary pathways since the formation of the Galaxy some 15
billion years ago. The abundance of lithium is particularly interesting
because, although some of it is thought to be primordial, most results
from spallation reactions (in which Galactic cosmic rays break apart
larger nuclei in the interstellar medium). Spallation reactions are
crucial for the production of other light elements, such as beryllium
and boron, so observations of lithium isotopic abundances can be used
to test model predictions for light-element synthesis in general. Here
we report observations of 7Li and 6Li abundances
in several interstellar clouds lying in the direction of the star ο
Persei. We find the abundance ratio 7Li/6Li to
be about 2, which is significantly lower than the average Solar System
value of 12.3 (refs 6, 7). An abundance ratio of 2 is clear evidence
that the observed lithium must have resulted entirely from spallation,
confirming a basic tenet of light-element synthesis. The total lithium
abundance, however, is not enhanced as expected.
Title: The atmospheric parameters and chemical composition of early
B-type giants in h and chi Persei
Authors: Vrancken, M.; Lennon, D. J.; Dufton, P. L.; Lambert, D. L.
Bibcode: 2000A&A...358..639V
Altcode:
Atmospheric parameters and surface chemical compositions are presented
for eight stars, classified as B1 or B2 but with a range of luminosity
classes, in the northern double cluster h and chi Persei. Echelle
spectroscopy (covering the wavelength region 3900 to 4700 Ä) and
grating spectroscopy (of the Balmer, Hγ and Hβ lines) were analysed
using non-LTE synthetic spectra based on LTE line-blanketed atmosphere
structures. High microturbulences are found in our sample, and this
quantity must be included in the computation of the non-LTE level
populations; its effect is generally to decrease the derived metal
abundances by typically 0.1 dex but by up to 0.4 dex. Our absolute
abundances are in reasonable agreement with those previously found
for main sequence B-type stars, while we find some evidence for
small abundance variations (particularly for nitrogen) within our
sample. One star (BD+56 678) appears to be a spectrum variable and at
two epochs shows a highly enriched nitrogen spectrum. Our atmospheric
parameters imply that two stars have previously been mis-identified as
main sequence objects and a distance modulus, at the higher end of the
values previously deduced. The observational HR diagram is consistent
with stellar evolutionary models that explicitly include the effects
of rotation.
Title: Lines of Circumstellar C2, CN, and CH+
in the Optical Spectra of Post-AGB Stars
Authors: Bakker, Eric J.; Lambert, David L.; van Dishoeck, Ewine F.
Bibcode: 2000IAUS..177..217B
Altcode:
No abstract at ADS
Title: High-resolution optical spectroscopy of the sharp-lined B-type
star HD83206
Authors: Lehner, N.; Dufton, P. L.; Lambert, D. L.; Ryans, R. S. I.;
Keenan, F. P.
Bibcode: 2000MNRAS.314..199L
Altcode:
Very-high-resolution (R~160000) spectroscopic observations are
presented for the early B-type star, HD83206. Because it has very
sharp metal lines, this star affords an opportunity to test theories
of model atmospheres and line formation. Non-LTE model atmosphere
calculations have been used to estimate the atmospheric parameters and
absolute metal abundances (C, N, O, Mg and Si); an LTE analysis was
also undertaken to investigate the validity of this simpler approach
and to estimate an iron abundance. For the non-LTE calculations,
there is excellent agreement with observations of the Balmer lines Hα
and Hδ and the lines of Siii and Siiii for atmospheric parameters of
Teff~=21700+/-600K and logg~=4.00+/-0.15dex. The agreement
is less convincing for the LTE calculations, and a higher gravity is
deduced. Careful comparison of the metal line profiles with non-LTE
calculations implies that the projected rotational and microturbulent
velocities have maximum values of ~=5 and ~=2kms-1,
respectively. The latter value is smaller than has often been adopted in
LTE model atmosphere analyses of main-sequence stars. Non-LTE absolute
metal abundances are estimated, and a comparison with those for
normal B-type stars (deduced using similar non-LTE techniques) shows
no significant differences. A comparison of the abundances deduced
using non-LTE and LTE calculations implies systematic differences
of 0.1-0.2dex, showing the importance of using a non-LTE approach
when accurate absolute abundances are required. Its location in the
Hertzsprung-Russell diagram and normal metal abundance lead us to
conclude that HD83206 is probably a main-sequence B-type star. As such,
it is among the sharpest-lined young B-type star discovered to date.
Title: The Near-Ultraviolet Continuum of Late-Type Stars
Authors: Allende Prieto, Carlos; Lambert, David L.
Bibcode: 2000AJ....119.2445A
Altcode: 2000astro.ph..1508P; 2000astro.ph..1508A
Analyses of the near-ultraviolet continuum of late-type stars have led
to controversial results regarding the performance of state-of-the-art
model atmospheres. The release of the homogeneous International
Ultraviolet Explorer (IUE) final archive and the availability of the
high-accuracy Hipparcos parallaxes provide an opportunity to revisit
this issue, as accurate stellar distances make it possible to compare
observed absolute fluxes with the predictions of model atmospheres. The
near-UV continuum is highly sensitive to Teff and [Fe/H],
and once the gravity is constrained from the parallax, these parameters
may be derived from the analysis of low-dispersion, long-wavelength
(2000-3000 Å) IUE spectra for stars previously studied by Alonso,
Arribas, & Martínez-Roger using the Infrared Flux Method (IRFM). A
second comparison is carried out against the stars spectroscopically
investigated by Gratton, Carretta, & Castelli. It is shown that
there is a good agreement between Teff values obtained
from the IRFM and those from the near-UV continuum, and a remarkable
correspondence between observed and synthetic fluxes for stars with 4000
K<=Teff<=6000 K of any metallicity and gravity. These
facts suggest that model atmospheres provide an adequate description
of the near-UV continuum forming region and that the opacities involved
are essentially understood.
Title: Lithium Isotope Ratios for Interstellar Clouds toward ζ and
o Persei
Authors: Knauth, D. C.; Federman, S. R.; Lambert, D. L.; Crane, P.
Bibcode: 2000AAS...196.4006K
Altcode: 2000BAAS...32..738K
As part of a study on the variation in the 7Li/6Li
ratio, high signal to noise, high resolution spectroscopy of Li I (λ
6708) and K I (λ 4044) were obtained toward ζ and o Per. The lithium
isotope shift is approximately the same as its fine structure splitting
( ~ 0.158 Angstroms), resulting in a blend of the 7Li and
6Li lines. Use of the K I line as a velocity template allowed
for a straightforward determination of the lithium isotope ratio. The
K I line at λ 4044 is a suitable template because it is of comparable
strength to the Li I lines. Our high resolution observations show
remarkably disparate isotope ratios: 7Li/6Li =
10.6 +/- 2.9 toward ζ Per and 3.6 +/- 0.6 and 1.7 +/- 0.3 toward o
Per. While the results for ζ Per are consistent with the meteoritic
value, the ratios for o Per's clouds suggest recent Galactic cosmic ray
spallation. This is the first unambiguous evidence for an interstellar
7Li/6Li ratio that differs dramatically from
the Solar System value. The low ratios indicate a higher flux of
cosmic rays toward o Per than toward ζ Per. A higher flux of cosmic
rays toward o Per was suggested earlier in a study of OH and HD
chemistry (Federman, Weber, & Lambert 1996, ApJ, 463,181). The
total lithium abundance and the K/Li ratio are useful in placing the
7Li/6Li ratio into context. We obtained total
Li abundances of (12.2 +/- 2.2) x 10-10 toward ζ Per and
(9.8 +/- 3.5) x 10-10 toward o Per. The columns of K I and
Li I yielded K/Li ratios that revealed no discernable trend. Since a
Li isotope ratio ~ 2 toward o Per suggests newly processed lithium,
the comparable total Li abundances and K/Li ratios are unexpected.
Title: Boron and Iron in Two B-dwarfs: A Test of Rotation in Massive
Star Evolution
Authors: Brooks, A. M.; Venn, K. A.; Lambert, D. L.; Lemke, M.;
Langer, N.
Bibcode: 2000AAS...196.4010B
Altcode: 2000BAAS...32..738B
We have used HST STIS spectra to determine boron and iron abundances
in two well-studied B-stars. The boron abundances are used to search
for evidence of rotational mixing while these stars are still on
the main-sequence. New stellar evolution models (Heger et al. 2000)
that include rotational mixing predict rapid depletion of boron
from the surface before significant enrichments in nitrogen occur
(both being affected by mixing with hotter gas from the H-burning
layers). Examination of the new boron abundances, particularly with
respect to nitrogen, suggest that rotation has affected the chemistry
of one star, but not the other. In addition, we have calculated Fe-group
abundances in these stars, which were previously unavailable, or highly
uncertain, from optical spectroscopy.
Title: Evidence for Newly Synthesized Lithium in Interstellar Space
Authors: Knauth, David C.; Federman, Steven R.; Lambert, David L.;
Crane, Phillipe
Bibcode: 2000astro.ph..4315K
Altcode:
As a part of a study on the variation in the 7Li/6Li ratio,
high signal to noise, high resolution spectroscopy of Li I (6708
Angstroms) and K I (4044 Angstroms) were obtained toward zeta and o
Per. The lithium isotope shift is approximately the same as its fine
structure splitting (0.158 Angstroms), resulting in a blend of the 7Li
and 6Li lines. Use of the K I line as a velocity template allowed a
straightforward determination of the lithium isotopic ratio. Our high
resolution observations show remarkably disparate isotope ratios:
7Li/6Li = 1 0.6 +/- 2.9 toward zeta Per and 3.6 +/- 0.6 and 1.7 +/-
0.3 toward o Per. While the results toward zeta Per are consistent
with the meteoritic value, the ratio toward o Per's clouds suggest
recent Galactic cosmic ray spallation. This is the first clear and
unambiguous evidence for an interstellar 7Li/6Li ratio that differs
dramatically from the Solar System value. The low ratio indicates a
higher cosmic ray flux toward o Per than toward zeta Per. A higher
flux of cosmic rays toward o Per was suggested earlier in a study of
OH and HD chemistry (Federman, Weber, & Lambert 1996, ApJ 463,
181). The total lithium abundances and the K/Li ratio are useful in
placing the 7Li/6Li ratio into context. We obtained total lithium
abundances of (12.2 +/- 2.2) x 10^(-10) toward zeta Per and (9.8 +/-
3.5) x 10^(-10) toward o Per. The columns of K I and Li I yielded K/Li
ratios that revealed no discernable trend. Since a Li isotope ratio
~2 toward o Per suggests newly processed lithium, the comparable total
Li abundances and K/Li ratios are unexpected.
Title: High-resolution spectroscopy of V854 Cen in decline -
absorption and emission lines of C2 molecules
Authors: Kameswara Rao, N.; Lambert, David L.
Bibcode: 2000MNRAS.313L..33K
Altcode: 2000MNRAS.313L..33R; 2000astro.ph..2237R; 2000astro.ph..2237K
High-resolution optical spectra of the R Coronae Borealis (RCB) star
V854 Centauri in the early stages of a decline show, in addition to the
features reported for other RCBs in decline, narrow absorption lines
from the C2 Phillips system. The low rotational temperature,
Trot=1150K, of the C2 ground electronic state
suggests the cold gas is associated with the developing shroud of carbon
dust. These absorption lines were not seen at a fainter magnitude on
the rise from minimum light, nor at maximum light. This is the first
detection of cold gas around an RCB star.
Title: The Isotopic Abundances of Magnesium in Stars
Authors: Gay, Pamela L.; Lambert, David L.
Bibcode: 2000ApJ...533..260G
Altcode: 1999astro.ph.11217G
Isotopic abundance ratios
24Mg:25Mg:26Mg are derived for 20 stars
from high-resolution spectra of the MgH A-X 0-0 band at 5140 Å. With
the exception of the weak G-band giant HR 1299, the stars are dwarfs
that sample the metallicity range -1.8<[Fe/H]<0.0. The abundance
of 25Mg and 26Mg relative to the dominant isotope
24Mg decreases with decreasing [Fe/H] in fair accord with
predictions from a recent model of Galactic chemical evolution in which
the Mg isotopes are synthesized by massive stars. Several stars appear
especially enriched in the heavier Mg isotopes, suggesting contamination
by material from the envelopes of intermediate-mass asymptotic giant
branch stars.
Title: Georges Lemaitre: une étoile qui n'état pas double.
Authors: Lambert, D.
Bibcode: 2000C&T...116...46L
Altcode:
No abstract at ADS
Title: The Chemical Evolution of the Globular Cluster ω Centauri
(NGC 5139)
Authors: Smith, Verne V.; Suntzeff, Nicholas B.; Cunha, Katia; Gallino,
Roberto; Busso, Maurizio; Lambert, David L.; Straniero, Oscar
Bibcode: 2000AJ....119.1239S
Altcode:
We present abundances for 22 chemical elements in 10 red giant members
of the massive Galactic globular cluster ω Centauri. The spectra
are of relatively high spectral resolution and signal-to-noise. Using
these abundances plus published literature values, abundance trends
are defined as a function of the standard metallicity indicator
iron. The lowest metallicity stars in ω Cen have [Fe/H]~-1.8, and
the initial abundance distribution in the cluster is established
at this metallicity. The stars in the cluster span a range of
[Fe/H]~-1.8 to -0.8. At the lowest metallicity, the heavy-element
abundance is found to be well characterized by a scaled solar system
r-process distribution, as found in other stellar populations at this
metallicity. As iron increases, the s-process heavy-element abundances
increase dramatically. Comparisons of the s-process increases with
recent stellar models finds that s-process nucleosynthesis in 1.5-3
Msolar asymptotic giant branch stars (AGB) fits well the
heavy-element abundance distributions. In these low-mass AGB stars,
the dominant neutron source is 13C(α,n)16O. A
comparison of the Rb/Zr abundance ratios in ω Cen finds that these
ratios are consistent with the 13C source. The reason ω
Cen displays such a large s-process component is possibly due to the
fact that in such a relatively low-mass stellar system, AGB ejecta,
because of their low velocity winds, are more efficiently retained
in the cluster relative to the much faster moving Type II supernova
ejecta. Significant s-process enrichment relative to Fe, from the
lower mass AGB stars, would require that the cluster was active in
star formation for quite a long interval of time, of the order of 2-3
Gyr. The AGB ejecta were mixed with the retained fraction of Type II
supernova ejecta and with the residual gas of initial composition. The
analysis of α-rich elements shows that no significant amounts
of Type Ia supernova debris were retained by the cluster. In this
context, interpretation of the low and constant observed [Cu/Fe]~-0.6
(derived here for the first time in this cluster) finds a plausible
interpretation.
Title: Abundance Analyses of Field RV Tauri Stars. V. DS Aquarii,
UY Arae, TW Camelopardalis, BT Librae, U Monocerotis, TT Ophiuchi,
R Scuti, and RV Tauri
Authors: Giridhar, Sunetra; Lambert, David L.; Gonzalez, Guillermo
Bibcode: 2000ApJ...531..521G
Altcode: 1999astro.ph..9081G
Abundance analyses are presented and discussed for eight RV Tauri
variables. The RVB star UY Ara shows the abundance anomalies seen
in other RVB stars, namely, elements that condense into grains at
high temperature are underabundant, but elements of low condensation
temperature are much less underabundant. This pattern is ascribed
to a separation of dust from gas with accretion of gas but not dust
by the atmosphere. Abundances for two RVC stars with earlier results
for other RVC stars show that these intrinsically metal-poor stars do
not show effects of dust-gas separation. Analyses of five RVA stars
show that these cooler stars are very largely unaffected by dust-gas
separation. It is proposed that the deeper convective envelope of cooler
stars dilutes anomalies resulting from dust-gas separation. Possible
sites for dust formation and dust-gas separation-the dusty wind off
the RV Tauri variable or a dusty circumbinary disk-are reviewed and
observational tests suggested.
Title: A Uniform Analysis of Boron in F and G Disk Dwarfs fromHubble
Space Telescope Archival Spectra
Authors: Cunha, Katia; Smith, Verne V.; Boesgaard, Ann M.; Lambert,
David L.
Bibcode: 2000ApJ...530..939C
Altcode:
The boron abundance is derived for 14 near-solar metallicity F and
G dwarfs from the archived data set of spectra obtained with the
Hubble Space Telescope Goddard High Resolution Spectrograph in the
region of the B I resonance line near 2497 Å. These abundances
are derived in a uniform way with respect to recent work on solar
boron. The synthetic spectra of the B I region were calculated by
means of an improved linelist to fit the spectra of the stars spanning
a range in Teff between 5650 and 6700 K and metallicity
between [Fe/H]=-0.75 and +0.15. The synthetic spectra were computed
considering all major sources of metal opacities and, in particular,
an updated lower value of Mg I b-f opacity at 2500 Å was used in
the calculations. Adopting Li and Be abundances from the literature,
significant B depletions (~0.3-0.5 dex) are found only for the two stars
with the most extreme Li depletions (>=2.5 dex) and Be depletions
(>=1.5 dex), although the trend of B versus Be indicates that mild
B depletions may exist in many of the stars. These results are in
concordance with the Boesgaard et al. conclusion that a slow mixing
in the outer envelope is responsible for depletions of Li, Be, and
B. Stars with less severe Li and Be depletions exhibit roughly solar
[B/Fe] ratios. A comparison of the boron abundances from the disk stars
(with undepleted boron) with metal-poor halo dwarfs reveals that B is
linearly related to Fe over the entire range of metallicities from
[Fe/H]~-2.5 to 0.1. The B/Be ratio found for stars with near-solar
metallicities and no Li depletion is B/Be=27+/-5, equal to the solar
ratio (B/Be=23).
Title: CO Imaging of Late-Type Circumstellar Shells
Authors: Gustafsson, Bengt; Eriksson, Kjell; Lambert, David L.;
Olofsson, Hans; Ryde, Nils; Schoier, Fredrik L.
Bibcode: 2000noao.prop..293G
Altcode:
Microwave emission lines and optical resonance lines have been used
to image circumstellar shells on the sky. Now it is possible to
image resonance scattering from infrared vibration-rotational carbon
monoxide lines (see Ryde et al. A& A 347, L35, 1999). Infrared CO is
formed closer to the star than microwave CO and provides complementary
information. Infrared CO mapping is especially powerful because many
CO lines of differing excitation are present, allowing the extraction
of excitation temperature and abundance from the measured column
densities. Previous on-star observations have led to the detection
of multiple velocity components in the CO lines, formed in different
parts of the circumstellar shell. We have found in an earlier observing
run with this method that the shell of CO gas around Mira (4 arcsec-10
arcsec from the star) is spherically symmetric and homogeneous. But we
also trace from the data a region close to the star devoid of gas or
at least of CO (Ryde et al. ApJ, soon to be submitted). Each CO line
can be used to image the circumstellar outflow at different stellar
radii. Information on the velocity structure and the development of
clumps in the flow will be extracted. The present proposal focuses on
the study of shells around carbon stars for which we have complementary
mm and optical data. We will furthermore for the first time map detached
shells with this method.
Title: Model Photospheres for Late-Type Stars from the Inversion
of High-Resolution Spectroscopic Observations: Groombridge 1830 and
ɛ Eridani
Authors: Allende Prieto, Carlos; García López, Ramón J.; Lambert,
David L.; Ruiz Cobo, Basilio
Bibcode: 2000ApJ...528..885A
Altcode: 1999astro.ph..7368P; 1999astro.ph..7368A
An inversion technique to recover LTE one-dimensional model photospheres
for late-type stars, which was previously applied to the Sun by Allende
Prieto et al. in 1998, is now employed to reconstruct, semiempirically,
the photospheres of cooler dwarfs: the metal-poor Groombridge 1830 and
the active star of solar metallicity ɛ Eridani. The model atmospheres
we find reproduce satisfactorily all the considered weak-to-moderate
neutral lines of metals, satisfying in detail the excitation equilibrium
of iron, the wings of strong lines, and the slope of the optical
continuum. The retrieved models show a slightly steeper temperature
gradient than flux-constant model atmospheres in the layers where
logτ<=-0.5. We argue that these differences should reflect missing
ingredients in the flux-constant models and point to granular-like
inhomogeneities as the best candidate. The iron ionization equilibrium
is well satisfied by the model for Gmb 1830, but not for ɛ Eri, for
which a discrepancy of 0.2 dex between the logarithmic iron abundance
derived from neutral and singly ionized lines may signal departures from
LTE. The chemical abundances of calcium, titanium, chromium, and iron
derived with the empirical models from neutral lines do not differ much
from previous analyses based on flux-constant atmospheric structures.
Title: Compositions of Highly-evolved Stars
Authors: Lambert, David L.
Bibcode: 2000IAUJD...5E...2L
Altcode:
Aspects of the chemical compositions of highly-evolved stars will
be discussed. Emphasis will be placed on the more evolved stars
- AGB and post-AGB stars. Indicators of mixing to be discussed
will be selected from the following: Li, C,N, and O including the
12C/13C ratio, and the s-process.
Title: The Interstellar Lithium Isotope Ratio Toward Per OB2
Authors: Knauth, D. C.; Ferderman, S. R.; Lambert, D. L.; Crane, P.
Bibcode: 2000IAUS..198..338K
Altcode:
No abstract at ADS
Title: Boron abundance of the Orion B-star HD 35299 : B III as a
test of non-LTE
Authors: Lemke, M.; Cunha, K.; Lambert, D. L.
Bibcode: 2000LIACo..35..223L
Altcode: 2000ghgc.conf..223L
No abstract at ADS
Title: Summary
Authors: Lambert, David L.
Bibcode: 2000IAUJD...8E...6L
Altcode:
An attempt will be made to summarize the results presented at this
Joint Discussion. In addition to highlighting evidence in favour of
a particular relation between oxygen and iron abundances, remaining
areas of dispute will be listed.
Title: Selective Depletion of Elements in Stellar Atmospheres:
A Unified Picture?
Authors: Bakker, Eric J.; Gonzalez, Guillermo; Lambert, David L.
Bibcode: 2000IAUS..177..523B
Altcode:
No abstract at ADS
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: Division IV: Stars: (Etoiles)
Authors: Cram, Lawrence; Barbuy, Beatriz; Gerbaldi, Michele; Lambert,
David; Pallavicini, Roberto; Zahn, Jean-Paul; Zinnecker, Hans
Bibcode: 2000IAUTA..24..173C
Altcode:
No abstract at ADS
Title: The 1995-96 decline of R Coronae Borealis: high-resolution
optical spectroscopy
Authors: Kameswara Rao, N.; Lambert, David L.; Adams, Mark T.; Doss,
David R.; Gonzalez, Guillermo; Hatzes, Artie P.; James, C. Renée;
Johns-Krull, C. M.; Luck, R. Earle; Pandey, Gajendra; Reinsch, Klaus;
Tomkin, Jocelyn; Woolf, Vincent M.
Bibcode: 1999MNRAS.310..717K
Altcode: 1999astro.ph..7099R; 1999astro.ph..7099K; 1999MNRAS.310..717R
A set of high-resolution optical spectra of R CrB acquired before,
during and after its 1995-96 decline is discussed. All of the
components reported from earlier declines are seen. This novel data
set provides new information on these components including several
aspects not previously seen in declines of R CrB and other R Coronae
Borealis stars. In the latter category is the discovery that the
onset of the decline is marked by distortions of absorption lines
of high-excitation lines, and quickly followed by emission in these
and in low-excitation lines. This `photospheric trigger' implies that
dust causing the decline is formed close to the star. These emission
lines fade quickly. After 1995 November 2, low-excitation narrow
(FWHM ~12kms-1) emission lines remain. These appear to be
a permanent feature, slightly blueshifted from the systemic velocity,
and unaffected by the decline except for a late and slight decrease
of flux at minimum light. The location of the warm dense gas providing
these lines is uncertain. Absorption lines unaffected by overlying sharp
emission are greatly broadened, weakened and redshifted at the faintest
magnitudes when scattered light from the star is a greater contributor
than direct light transmitted through the fresh soot cloud. A few broad
lines (FWHM ~=300kms-1) are seen at and near minimum light
with approximately constant flux: prominent among these are the Hei
triplet series, Nai D and [Nii] lines. These lines are blueshifted by
about 30kms-1 relative to the systemic velocity, with no
change in velocity over the several months for which the lines were
seen. It is suggested that these lines, especially the Hei lines,
arise from an accretion disc around an unseen compact companion which
may be a low-mass white dwarf. If so, R CrB is similar to the unusual
post-asymptotic giant branch star 89 Her.
Title: (Teff,log g,[Fe/H]) Classification of Low-Resolution Stellar
Spectra using Artificial Neural Networks
Authors: Snider, Shawn; Qu, Yuan; Allende Prieto, Carlos; von Hippel,
Ted; Beers, Timothy C.; Sneden, Chistopher; Lambert, David L.
Bibcode: 1999astro.ph.12404S
Altcode:
New generation large-aperture telescopes, multi-object spectrographs,
and large format detectors are making it possible to acquire very
large samples of stellar spectra rapidly. In this context, traditional
star-by-star spectroscopic analysis are no longer practical. New
tools are required that are capable of extracting quickly and with
reasonable accuracy important basic stellar parameters coded in the
spectra. Recent analyses of Artificial Neural Networks (ANNs) applied to
the classification of astronomical spectra have demonstrated the ability
of this concept to derive estimates of temperature and luminosity. We
have adapted the back-propagation ANN technique developed by von
Hippel et al. (1994) to predict effective temperatures, gravities
and overall metallicities from spectra with resolving power ~ 2000
and low signal-to-noise ratio. We show that ANN techniques are very
effective in executing a three-parameter (Teff,log g,[Fe/H]) stellar
classification. The preliminary results show that the technique is
even capable of identifying outliers from the training sample.
Title: Spectroscopic Observations of Convective Patterns in the
Atmospheres of Metal-poor Stars
Authors: Allende Prieto, Carlos; García López, Ramón J.; Lambert,
David L.; Gustafsson, Bengt
Bibcode: 1999ApJ...526..991A
Altcode: 1999astro.ph..7046A; 1999astro.ph..7046P
Convective line asymmetries in the optical spectrum of two metal-poor
stars, Gmb 1830 and HD 140283, are compared to those observed for solar
metallicity stars. The line bisectors of the most metal-poor star, the
subgiant HD 140283, show a significantly larger velocity span that the
expectations for a solar-metallicity star of the same spectral type
and luminosity class. The enhanced line asymmetries are interpreted
as the signature of the lower metal content, and therefore opacity,
in the convective photospheric patterns. These findings point out the
importance of the three-dimensional convective velocity fields in the
interpretation of the observed line asymmetries in metal-poor stars and,
in particular, urge caution when deriving isotopic ratios from observed
line shapes and shifts using one-dimensional model atmospheres. The
mean line bisector of the photospheric atomic lines is compared with
those measured for the strong Mg I b1 and b2
features. The upper parts of the bisectors are similar, and-assuming
they overlap-the bottom ends of the stronger lines, which are formed
higher in the atmosphere, go much farther to the red. This is in
agreement with the expected decreasing of the convective blueshifts
in upper atmospheric layers, and is compatible with the high-velocity
redshifts observed in the chromosphere, transition region, and corona
in late-type stars.
Title: A Consistency Test of Spectroscopic Gravities for Late-Type
Stars
Authors: Allende Prieto, Carlos; García López, Ramón J.; Lambert,
David L.; Gustafsson, Bengt
Bibcode: 1999ApJ...527..879A
Altcode: 1999astro.ph..7155P; 1999astro.ph..7155A
Chemical analyses of late-type stars are usually carried out
following the classical recipe: LTE line formation and homogeneous,
plane-parallel, flux-constant, and LTE model atmospheres. We review
different results in the literature that have suggested significant
inconsistencies in the spectroscopic analyses, pointing out the
difficulties in deriving independent estimates of the stellar
fundamental parameters and hence, detecting systematic errors. The
trigonometric parallaxes measured by the Hipparcos mission provide
accurate appraisals of the stellar surface gravity for nearby
stars, which are used here to check the gravities obtained from the
photospheric iron ionization balance. We find an approximate agreement
for stars in the metallicity range -1.0<=[Fe/H]<=0, but the
comparison shows that the differences between the spectroscopic and
trigonometric gravities decrease toward lower metallicities for more
metal-deficient dwarfs (-2.5<=[Fe/H]<=-1.0), which casts a shadow
upon the abundance analyses for extreme metal-poor stars that make use
of the ionization equilibrium to constrain the gravity. The comparison
with the strong-line gravities derived by Edvardsson and Fuhrmann
confirms that this method provide systematically larger gravities than
the ionization balance. The strong-line gravities get closer to the
physical ones for the stars analyzed by Fuhrmann, but they are even
further away than the iron ionization gravities for the stars of lower
gravities in Edvardsson's sample. The confrontation of the deviations
of the iron ionization gravities in metal-poor stars, reported here
with departures from the excitation balance found in the literature,
show that they are likely to be induced by the same physical mechanism.
Title: Optical observations of three Galactic halo stars: evidence
for cloudlets in intermediate- and high-velocity interstellar clouds
Authors: Lehner, N.; Sembach, K. R.; Lambert, D. L.; Ryans, R. S. I.;
Keenan, F. P.
Bibcode: 1999A&A...352..257L
Altcode:
Very high resolution (R ~ 160000) absorption line measurements of the
interstellar Ca Ii K and Na I D lines and medium resolution (R ~ 50000)
measurements of the interstellar Ti Ii (3384 Ä) line towards three
Galactic halo stars are presented. The data have signal-to-noise
ratios of ~ 90-240. The sightlines studied clearly show several
intermediate-high velocity interstellar clouds with local standard
of rest velocities in the range ~ - 40 to -110 \km. Two different
methods have been used to analyze these data. Line profile fitting
allows us to model multiple components for the different high-velocity
clouds separated by only a few km. The close proximity of the lines in
velocity space indicates that the cloudlets are related. Conversion
of the absorption profiles to apparent optical depth profiles also
allows us to examine the column densities and their ratios as a
function of velocity. Variations in N(ion {Ca}{ii})/N(ion {Na}i),
N(ion {Ca}{ii})/N(ion {Ti}{ii}) and N(ion {Ti}{ii})/N(ion {Na}i)
with cloud velocity are discussed.
Title: Fundamental parameters of nearby stars from the comparison with
evolutionary calculations: masses, radii and effective temperatures
Authors: Allende Prieto, C.; Lambert, D. L.
Bibcode: 1999A&A...352..555A
Altcode: 1999astro.ph.11002P; 1999astro.ph.11002A
The Hipparcos mission has made it possible to constrain the positions
of nearby field stars in the colour-magnitude diagram with very
high accuracy. These positions can be compared with the predictions
of stellar evolutionary calculations to provide information on the
basic parameters of the stars: masses, radii, effective temperatures,
ages, and chemical composition. The degeneracy between mass, age,
and metallicity is not so large as to prevent a reliable estimate of
masses, radii and effective temperatures, at least for stars of solar
metallicity. The evolutionary models of Bertelli et al. (1994) predict
those parameters finely, and furthermore, the applied transformation
from the theoretical (log g- T_eff) to the observational (M_v-B-V)
plane is precise enough to derive radii with an uncertainty of ~ 6%,
masses within 8%, and T_effs within ~ 2% for a certain range of the
stellar parameters. This is demonstrated by means of comparison with
the measurements in eclipsing binaries and the InfraRed Flux Method. The
application of the interpolation procedure in the theoretical isochrones
to the stars within 100 pc from the Sun observed with Hipparcos
provides estimates for 17,219 stars. Table~1 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/Abstract.html
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: The Chemical Compositions of the SRD Variable Stars. II. WY
Andromedae, VW Eridani, and UW Librae
Authors: Giridhar, Sunetra; Lambert, David L.; Gonzalez, Guillermo
Bibcode: 1999PASP..111.1269G
Altcode: 1999astro.ph..7389G
Chemical compositions are derived from high-resolution spectra for three
stars classed as SRd variables in the General Catalogue of Variable
Stars. These stars are shown to be metal-poor supergiants: WY And with
[Fe/H]=-1.0, VW Eri with [Fe/H]=-1.8, and UW Lib with [Fe/H]=-1.2. Their
compositions are identical to within the measurement errors to the
compositions of subdwarfs, subgiants, and less evolved giants of the
same [Fe/H]. The stars are at the tip of the first giant branch or
in the early stages of evolution along the asymptotic giant branch
(AGB). There is no convincing evidence that these SRd variables are
experiencing thermal pulsing and the third dredge-up on the AGB. The
SRd variables appear to be at the cool limit of the sequence of RV
Tauri variables.
Title: VizieR Online Data Catalog: Fundamental parameters of stars
(Allende Prieto+, 1999)
Authors: Allende Prieto, C.; Lambert, D. L.
Bibcode: 1999yCat..33520555A
Altcode:
The Hipparcos mission has made it possible to constrain the positions
of nearby field stars in the colour-magnitude diagram with very
high accuracy. These positions can be compared with the predictions
of stellar evolutionary calculations to provide information on the
basic parameters of the stars: masses, radii, effective temperatures,
ages, and chemical composition. The degeneracy between mass, age,
and metallicity is not so large as to prevent a reliable estimate
of masses, radii and effective temperatures, at least for stars of
solar metallicity. The evolutionary models of Bertelli et al. (1994,
Cat. <J/A+AS/106/275>) predict those parameters finely,
and furthermore, the applied transformation from the theoretical
log(g)-Teff to the observational Mv-B-V plane
is precise enough to derive radii with an uncertainty of ~6%, masses
within 8%, and Teffs within ~2% for a certain range of the stellar
parameters. This is demonstrated by means of comparison with the
measurements in eclipsing binaries and the InfraRed Flux Method. The
application of the interpolation procedure in the theoretical isochrones
to the stars within 100pc from the Sun observed with Hipparcos provides
estimates for 17,219 stars included in this Table. (1 data file).
Title: Physical Conditions in the Photodissociation Regions of Two
Reflection Nebulae: NGC 2023 and vdB 102
Authors: Knauth, D. C.; Federman, S. R.; Lambert, D. L.
Bibcode: 1999AAS...19410904K
Altcode:
We obtained high resolution optical spectra of the illuminating stars
in two reflection nebulae, NGC 2023 and vdB 102. Such observations probe
the photodissociation regions (PDRs) in front of the stars. Ground-based
measurements of the atoms, Na I and K I, and the molecules, CH, CN,
and C_2, were analyzed to extract the physical conditions present
in each PDR. Estimates of the gas density, gas temperature and flux
of ultraviolet radiation were derived and compared with the results
from infrared and radio studies. The conditions derived are similar to
those found in these previous studies. The foreground material is less
dense than the gas in the molecular cloud behind the star(s). The gas
temperature was set at 30 K since the temperature had a negligible
effect on the chemistry and since this is the temperature inferred
for the foreground PDR toward HD 200775, the illuminating source
of NGC 7023. The flux of ultraviolet radiation was found to be less
intense than in the molecular material. The columns of Na I and K I
were reproduced when the extinction curve for the line of sight was
adopted. Future studies should include the effects of the specific
extinction curve when modeling reflection nebulae and their associated
photodissociation regions.
Title: Rubidium in Metal-deficient Disk and Halo Stars
Authors: Tomkin, Jocelyn; Lambert, David L.
Bibcode: 1999ApJ...523..234T
Altcode: 1999astro.ph..5164T
We report the first extensive study of stellar Rb
abundances. High-resolution spectra have been used to determine, or set
upper limits on, the abundances of this heavy element and the associated
elements Y, Zr, and Ba in 44 dwarfs and giants with metallicities
spanning the range -2.0<[Fe/H]<0.0. In metal-deficient stars
Rb is systematically overabundant relative to Fe; we find an average
[Rb/Fe] of +0.21 for the 32 stars with [Fe/H]<-0.5 and measured
Rb. This behavior contrasts with that of Y, Zr, and Ba, which, with
the exception of three new CH stars (HD 23439A and B and BD +5°3640),
are consistently slightly deficient relative to Fe in the same stars;
excluding the three CH stars, we find that the stars with [Fe/H]<-0.5
have average [Y/Fe], [Zr/Fe], and [Ba/Fe] of -0.19 (24 stars), -0.12
(28 stars), and -0.06 (29 stars), respectively. The different behavior
of Rb on the one hand and Y, Zr, and Ba on the other can be attributed
in part to the fact that in the Sun and in these stars Rb has a large
r-process component while Y, Zr, and Ba are mostly s-process elements
with only small r-process components. In addition, the Rb s-process
abundance is dependent on the neutron density at the s-processing
site. Published observations of Rb in s-process enriched red giants
indicate a higher neutron density in the metal-poor giants. These
observations imply a higher s-process abundance for Rb in metal-poor
stars. The calculated combination of the Rb r-process abundance, as
estimated for the stellar Eu abundances, and the s-process abundance,
as estimated for red giants, accounts satisfactorily for the observed
run of [Rb/Fe] with [Fe/H].
Title: Isotopic lithium abundances in five metal-poor disk stars
Authors: Nissen, P. E.; Lambert, D. L.; Primas, F.; Smith, V. V.
Bibcode: 1999A&A...348..211N
Altcode: 1999astro.ph..6306N
High resolution (R =~ 110 000), very high S/N spectra centered on the
6707.8 Ä Li I line have been obtained with the ESO Coudé Echelle
Spectrometer for five, metal-poor (-0.8 < [Fe/H] < -0.6) disk
stars in the turnoff region of the HR-diagram. The instrumental
and stellar atmospheric line broadening have been determined from
two unblended iron lines and used in a model atmosphere synthesis
of the profile of the Li I line as a function of the lithium
isotope ratio. This has led to a detection of \element[][6]{Li}
in HD 68284 and HD 130551
with element [][6]{Li}/element [][7]{Li} =~ 0.05, whereas the other
stars, HR 2883, HR 3578 and
HR 8181, have \element[][6]{Li}/\element[][7]{Li}
close to zero. By comparing T_eff -values and absolute magnitudes
based on Hipparcos parallaxes with recent stellar evolutionary tracks,
the masses of the stars have been derived. It is shown that the two
stars with \element[][6]{Li} present have a significantly higher
mass, {cal M}/{cal M}_⊙ =~ 1.05, than the other three stars for
which values between 0.85 and 1.0 {cal M}_⊙ are obtained. The
results are discussed in terms of models for the galactic evolution
of the light elements and depletion of the lithium isotopes in
stellar envelopes. It is shown that the measured \element[][6]{Li}
abundances are in agreement with standard cosmic ray production of
\element[][6]{Li} in the galactic disk and a moderate depletion (0.5
dex) in the stars. Recent models for the evolution of \element[][6]{Li}
including alpha + alpha fusion reactions and predicting a high lithium
isotopic ratio, element [][6]{Li}/element [][7]{Li} =~ 0.3 at [Fe/H]
= -0.6, require a high degree of \element[][6]{Li} depletion ( =~
1.0 dex) to fit the observations. Furthermore, these models imply
a \element[][7]{Li} abundance about 0.2 dex higher than observed
for metal-poor disk stars. Based on observations carried out at the
European Southern Observatory, La Silla, Chile
Title: Mercury Elemental and Isotopic Abundances in Mercury-Manganese
Stars
Authors: Woolf, Vincent M.; Lambert, David L.
Bibcode: 1999ApJ...521..414W
Altcode:
Hg II abundances have been determined for 42 mercury-manganese (HgMn)
stars by fitting synthetic spectra to observed spectra of the 3984
Å Hg II line. Twenty of the stars had lines sharp enough to allow
their Hg isotopic abundance mixes to be estimated. The Hg abundance is
reported for more HgMn stars here than in any other single work. No
correlation was found between Hg II abundance and Teff
or the mean central wavelength of HgMn λ3984 stars. The mean
central wavelength of λ3984 , an indicator of the Hg isotopic mix,
is loosely correlated with Teff: stars with primarily
heavy Hg isotopes tend to be cooler, although one star, 46 Aql,
has almost pure 204Hg and Teff in about the
middle of the temperature range for HgMn stars. We find that there
is no evidence that any of the HgMn stars have 196Hg or
198Hg. For the very sharp-lined stars, the 204Hg
abundance decreases with increasing Teff. No correlation is
seen between the mean central wavelength and the surface gravity. No
correlation was found between the projected rotational velocity and
the Hg II abundance or the central wavelength of λ3984, although
this result may be biased by the selection of stars with low reported
vsini. Hg I λ4358 was measured at high spectral resolution for seven
HgMn stars. The isotopic shifts are too small, and the hyperfine
components are too weak to allow unambiguous isotopic abundance
ratios to be found. Hg I abundances correlate fairly well with
Hg II abundances. Some of the Hg isotopic mixtures are difficult
to explain using only diffusion. HR 7245 has approximately equal
abundances of 199Hg, 200Hg, 202Hg,
and 204Hg but very little 201Hg, and 11 Per has
Hg that is mostly 199Hg and 204Hg. Calculations
show that hyperfine splitting of 201Hg changes the radiative
forces it feels compared with other isotopes, which may alter diffusion
of that isotope enough to explain its absence in HR 7245, but we
have found no possible explanation for the Hg isotopic mix found in
11 Per. These are the first very high resolution measurements of Hg
II λ3984 for HR 7245 and 11 Per. Although diffusion may be acting
in HgMn stars, either there are one or more other mechanisms acting
to help produce the overabundances and isotopic mixtures seen or our
understanding of diffusion is lacking on some important point.
Title: Preliminary results on the circumstellar envelopes of alpha
ORI and R Leo from CO 4.6 micron line emission
Authors: Ryde, N.; Gustafsson, B.; Hinkle, K. H.; Eriksson, K.;
Lambert, D. L.; Olofsson, H.
Bibcode: 1999A&A...347L..35R
Altcode:
CO 4.6 mu m vibration-rotational lines are detected in fluorescent
emission from the inner regions of the Betelgeuse (alpha
Orionis) and R Leonis stellar winds. The
spatially and spectrally resolved 1-0 R(1), R(2), and R(3) line profiles
are found to be highly useful probes of circumstellar shells. The
current data sample only a few regions of the circumstellar shells of
the program stars. However, now it should be possible to obtain envelope
maps and absolute flux estimates, allowing new independent estimates
of mass loss rates. This will open up new possibilities in the study
of the structure and dynamics of stellar winds around red giants. The
temperature 4arcsec away from alpha Ori is found to be 38(+6}_{-5} {K)
. For R Leo the temperature 4arcsec North is derived to be 24(+3}_{-2}
{K) and 4arcsec South 35(+7}_{-4} {K) .
Title: Intereclipse Spectroscopic Snapshot of epsilon Aurigae with
the Hubble Space Telescope
Authors: Sheffer, Yaron; Lambert, David L.
Bibcode: 1999PASP..111..829S
Altcode: 1999astro.ph..5129S
A single-epoch low-resolution Goddard High Resolution Spectrograph
spectrum of the eclipsing binary epsilon Aurigae was obtained
while the secondary was orbiting toward eclipse by the primary. The
spectrum as recorded between 1175 and 1461 Å is rich with emission and
absorption lines which include stellar and interstellar components. The
emission-line profiles have the appearance of double-peaked emission
with a stronger red component at a radial velocity of +108 km s^-1, an
overlying unresolved absorption component at -20 km s^-1, and a weaker
blue emission bump at ~-92 km s^-1. We compare these observational
results with known orbital properties of the epsilon Aur binary system
and propose that the emission originates at the inner radius of the disk
surrounding the enigmatic secondary. We interpret the kinematic data
as a possible means to uncover the underlying stellar masses, and we
speculate about the binary's relationship to other ``high-mass'' models.
Title: The Boron Abundance of the Orion G-Dwarf Member BD -05°1317
Authors: Cunha, Katia; Smith, Verne V.; Lambert, David L.
Bibcode: 1999ApJ...519..844C
Altcode:
The boron abundance is derived for the young Orion solar-type member
BD -05°1317 from Hubble Space Telescope Goddard High Resolution
Spectrograph spectra of the B I resonance lines near 2497 Å. The
abundance of logɛ(B)=2.1+/-0.2 is ~0.6-0.7 dex below solar. As this
young pre-main-sequence star has an undepleted lithium abundance,
such a low boron abundance in a near-solar metallicity star is
unexpected. No simple explanation apparently accounts for the low boron
abundance observed for this star. A comparison of the boron and oxygen
abundances in BD -05°1317 with those of other near-solar metallicity
disk stars suggests that there might be a large scatter (~0.8 dex)
in the boron abundance at a given oxygen abundance. Such a scatter
also has been reported in the literature for beryllium at a given
metallicity. Based on observations obtained with the NASA/ESA
Hubble Space Telescope through Space Telescope Science Institute,
which is operated by the Association of Universities for Research in
Astronomy, Inc., under NASA contract NAS-5-26555.
Title: Three Very Young HGMN Stars in the Orion OB1 Association
Authors: Woolf, Vincent M.; Lambert, David L.
Bibcode: 1999ApJ...520L..55W
Altcode: 1999astro.ph..5233W
We report the detection of three mercury-manganese stars in the Orion
OB1 association. HD 37886 and BD -0°984 are in the approximately
1.7 million year old Orion OB1b. HD 37492 is in the approximately 4.6
million year old Orion OB1c. Orion OB1b is now the youngest cluster
with known HgMn star members. This places an observational upper limit
on the timescale needed to produce the chemical peculiarities seen
in mercury-manganese stars, which should help in the search for the
cause or causes of the peculiar abundances in HgMn and other chemically
peculiar upper main-sequence stars.
Title: Further Evidence for Chemical Fractionation from Ultraviolet
Observations of Interstellar Carbon Monoxide
Authors: Federman, S. R.; Lambert, David L.; Sheffer, Yaron; Cardelli,
Jason A.; Andersson, B. -G.; van Dishoeck, Ewine F.; Zsargo, J.
Bibcode: 1999AAS...194.7109F
Altcode: 1999BAAS...31Q.944F
Ultraviolet absorption from interstellar (12) CO and (13) CO was
detected toward rho Oph A and chi Oph. The measurements were obtained
at medium resolution with the Goddard High Resolution Spectrograph
on the Hubble Space Telescope. Equivalent widths were converted into
column densities through the use of f-values from Chan et al. (1993,
Chem. Phys., 170, 123). Column density ratios, N((12) CO)/N((13) CO),
of 125 +/- 23 and 117 +/- 35 were derived for the sight lines toward
rho Oph A and chi Oph, respectively. A value of 1000 +/- 500 for
the ratio N((12) C(16) O)/N((12) C(18) O) toward rho Oph A was also
obtained. These ratios are larger than the isotopic ratios for carbon
and oxygen appropriate for the ambient material. Since for both carbon
and oxygen the more abundant isotopic variant is enhanced, selective
isotope photodissociation plays the key role in the fractionation
process. The enhancement arises because the more abundant variant has
lines that are more optically thick, resulting in more self shielding
from dissociating radiation. A simple argument involving the amount
of self shielding (from N((12) CO)) and the strength of the UV field
permeating the gas (from the amount of vibrationally excited H_2 seen
in our spectra) shows that selective isotope photodissociation does
control the fractionation seen in these two sight lines, as well as
the sight line to zeta Oph.
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: The spectrum of the cool R Coronae Borealis variable Z Ursae
Minoris at minimum
Authors: Goswami, A.; Rao, N. K.; Lambert, D. L.
Bibcode: 1999Obs...119...22G
Altcode:
No abstract at ADS
Title: Observation and Analysis of High-Resolution Optical Line
Profiles in Comet Hyakutake (C/1996 B2)
Authors: Combi, M. R.; Cochran, A. L.; Cochran, W. D.; Lambert, D. L.;
Johns-Krull, C. M.
Bibcode: 1999ApJ...512..961C
Altcode:
Very high resolution (R~200,000) and high signal-to-noise echelle
spectra were obtained of comet Hyakutake (C/1996 B2) using the 2D coudé
spectrograph on the 2.7 m telescope at W. J. McDonald Observatory during
1996 in late March and early April. Doppler resolved profiles are
presented for individual lines of the major optical neutral species:
CN, C2, NH2, O(1D) at 6300 Å,
and H Balmer-α at 6563 Å. They are consistent with the expected
expansion of a water-dominated cometary coma. Because of the small
aperture and the small geocentric distance of the comet, the profiles
of CN, C2, and NH2 are totally shaped by the
outflowing hydrodynamic coma. The NH2 is the narrowest of
the group because of the very short lifetime of the NH2
parent (NH3). The profile of C2 is somewhat
broadened, compared with NH2, because of the relatively
larger contribution of C2 radicals farther from the nucleus
where the bulk outflow speed is larger. Any exothermic ejection
speed they receive upon their production would be quenched. Although
the profile of CN is broader than C2, this is due to the
fact that most of the CN lines are blends of two closely spaced but
nearly equal strength components. Because O(1D) atoms in
the region samples are produced mainly by the photodissociation of
water which results in a prompt emission photon, the line retains
contributions of both the basic coma expansion velocity and the 1.6
km s-1 exothermal ejection speed of the O(1D)
atoms. The H Balmer-α line is complicated by a chance coincidence
of a line of H2O+ and/or NH2 and by
optical depth effects in solar Lyβ which are primarily responsible
for the Balmer-α excitation. However, the width of the line wings is
consistent with other comet observations, including Hyakutake itself,
and the production by dissociation of H2O and OH and partial
thermalization. We have successfully reproduced these data using a
hybrid kinetic/hydrodynamic and Monte Carlo approach which include the
important physical/chemical processes which can shape the spectral
lines. Because the model includes no adjustable fitting parameters,
the model-data agreement indicates that the underlying assumptions
and calculated coma outflow speeds are quite reasonable.
Title: DZ Andromedae : A search for the spectral evidence of its
possible RCB nature
Authors: Goswami, Aruna; Kameswara Rao, N.; Lambert, David L.
Bibcode: 1999BASI...27..129G
Altcode:
No abstract at ADS
Title: Sodium in Faint Stars of NGC 6752
Authors: Briley, M. M.; Smith, V. V.; Suntzeff, N. B.; Bell, R. A.;
Hesser, J. E.; Lambert, D. L.; Smith, G. H.
Bibcode: 1999AAS...19312407B
Altcode: 1999BAAS...31Q.669B
Spectra of the Na I D-lines in two subgiant stars (MV
+2.2) of the globular cluster NGC 6752 are presented. These stars
are of similar brightness and color and are known to possess differing
abundances of C and N at their surfaces. Our spectra show that they also
exhibit differences in Na I line strengths, with abundance differences
of Δ [Na/Fe] = 0.3. The Na abundances correlate with CN band strength,
as is also the case for the more luminous NGC 6752 members. This result
requires the mechanism responsible for a significant component of the Na
differences (as well as the C and N variations) observed in the bright
giants to be in operation before the NGC 6752 stars evolve appreciably
up the red giant branch. Additional spectra of three main-sequence stars
(MV = +5.8) further suggest these abundance differences
are actually in place well below the main-sequence turn-off.
Title: Physical conditions in the photodissociation regions of two
reflection nebulae: NGC 2023 and vdB 102.
Authors: Knauth, D. C.; Federman, S. R.; Lambert, D. L.
Bibcode: 1999BAAS...31R1243K
Altcode:
No abstract at ADS
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: Neural Network Techniques Applied to Low Resolution Spectra
of Halo Stars
Authors: Qu, Y.; Snider, S.; von Hippel, T.; Sneden, C.; Lambert,
D. L.; Beers, T. C.; Rossi, S.
Bibcode: 1998AAS...193.4409Q
Altcode: 1998BAAS...30.1316Q
Recent large surveys of Galactic halo stars have uncovered kinematically
and chemically diverse substructures that contain vital clues to the
early evolution of the Galaxy. As extant spectroscopic sample sizes
grow into the thousands, traditional star-by-star chemical composition
analyses simply will not be able to keep pace. New analytical tools
must be found that can attack the large spectroscopic databases
in a partially or fully automated fashion (thus providing useful
astrophysical data nearly in ``real-time") without sacrificing
information content. Here, for a variety of halo-population stars,
we present preliminary results of applying an artificial neural
network code to low resolution (Requiv lambda /delta lambda ~ 2000)
spectra in the wavelength range 3800--5000 Angstroms. We have adapted
the back-propogation neural network technique originally devised
for stellar spectral classification (von Hippel et al. 1994, MNRAS,
269, 97) to predict effective temperatures, gravities, and overall
metallicities from spectra that are being gathered by Beers and
colleagues (e.g. 1992, AJ, 103, 1987). First results demonstrate that
with properly trained neural networks, the T_eff and [Fe/H] values
may be predicted to typically +/-50K and +/-0.2 dex, respectively,
for stars with well-determined parameters from the literature. We will
discuss these trends, as well as additional studies of the application
to log g predictions, and experiments that focus in on individual
abundance ratios (principally [C/Fe], [Ba/Fe], and [Sr/Fe]).
Title: Abundance Analyses of Field RV Tauri Stars. IV. AD Aquilae,
DS Aquarii, V360 Cygni, AC Herculis, and V453 Ophiuchi
Authors: Giridhar, Sunetra; Lambert, David L.; Gonzalez, Guillermo
Bibcode: 1998ApJ...509..366G
Altcode:
Abundance analyses are presented and discussed for five RV Tauri
variables. Three stars--DS Aqr, V360 Cyg, and V453 Oph--are RV C stars
by spectroscopic classification, i.e., metal lines are weak. They
are shown to be metal poor with [Fe/H] from -1.0 to -2.2 with normal
relative abundances of other elements. By contrast, AD Aql and AC Her
are RV B stars with an odd abundance pattern: elements that condense
into grains at a high temperatures are underabundant (i.e., [Fe/H]
= -2.1 for AD Aql) but elements with a low condensation temperatures
are much less underabundant (i.e., [S/H] = 0.0 and [Zn/H] = -0.1 for
AD Aql). This abundance pattern is ascribed to a separation of dust
and gas in the upper atmosphere of the star. The present analyses with
previously published results are used to investigate the systematics
of the dust-gas separation in RV Tauri variables. The process is
apparently inoperative in stars with an initial metallicity of about
[Fe/H] <~ -1.0 RV C stars and similar variables in globular clusters
are immune to the dust-gas separation. The process achieves more severe
effects in RV B than in RV A stars. The strength of the abundance
anomalies attributed to dust-gas separation is not correlated with
reported infrared excesses. After correction for the effects of the
dust-gas separation, there is no strong evidence from the abundances
that evolution along the AGB and experience of the third dredge-up
preceded the formation of the majority of the RV Tauri variables.
Title: Ultra High Resolution Spectroscopy of K I and CA II in B5
Authors: Andersson, B. -G.; Wannier, P. G.; Lambert, D. L.
Bibcode: 1998AAS...193.6508A
Altcode: 1998BAAS...30.1341A
We present ultrahigh resolution spectroscopic observations of K I
(R=350,000) and Ca II (R=130,000) towards stars in the molecular cloud
B5. Even though this is a kinematically simple sightline, intersecting
only one molecular cloud, the lineshapes are still complex. Further,
the relative velocity structure between tracers, such as mm-wave CO,
21cm HI and optical absorption lines show significant offsets. We show
decompositions of the optical lines and discuss the variation in the
column density ratios K I/Ca II for the resolved velocity components.
Title: The Circumstellar Shell of the
Post-Asymptotic Giant Branch Star HD 56126:
12C12C/12C13C Isotope
Ratio and 12C16O Column Density
Authors: Bakker, Eric J.; Lambert, David L.
Bibcode: 1998ApJ...508..387B
Altcode: 1998astro.ph..4231B
We have made the first detection of circumstellar absorption lines
of the 12C13C A 1Πu-X
1Σ+g (Phillips) system 1-0 band
and the 12C16O X 1Σ+
first-overtone 2-0 band in the spectrum of the post-AGB star HD 56126
(IRAS 07134+1005). All current detections of circumstellar molecular
absorption lines toward HD 56126 (12C2,
12C13C, 12C14N,
13C14N, and 12C16O)
yield the same heliocentric velocity of VCSE =
77.6 +/- 0.4 km s-1. The 12C2,
12C13C, and 12C16O lines
give rotational temperatures and integrated column densities of
Trot = 328 +/- 37 K, log Nint = 15.34 +/- 0.10
cm-2, Trot = 256 +/- 30 K, log Nint =
13.79 +/- 0.12 cm-2, and Trot = 51 +/- 37 K, log
Nint = 18.12 +/- 0.13 cm-2, respectively. The
rotational temperatures are lower for molecules with a higher
permanent dipole moment. Derived relative column densities ratios
are 12C2/12C13C = 36 +/-
13 and 12C16O/(12C2
+ 12C13C) = 606 +/- 230. Combined with
data from a previous paper, we find relative column densities
of 12C16O/(12C14N
+ 13C14N) = 475 +/- 175 and
12C14N/13C14N
= 38 +/- 2. Under chemical equilibrium conditions,
12C13C is formed twice as easily as
12C2. The isotopic exchange reaction for
12C2 is too slow to significantly alter
the 12C2/12C13C
ratio, and the 12C2 to
12C13C ratio is a good measure of half
the carbon isotope ratio: 12C/13C = 2
× 12C2/12C13C =
72 +/- 26. This is in agreement with our prediction that the
isotopic exchange reaction for 12C14N
is efficient and our observation in Paper III of
12C14N/13C14N = 38 +/-
2. A fit of the C2 excitation model of van Dishoeck &
Black to the relative population distribution of C2
yields nc σ/I = 3.3 +/- 1.0 × 10-14. At r
~= 1016 cm, this translates into nc = 1.7
× 107 cm-3 and Ṁ~=2.5×10-4
M⊙ yr-1.
Title: Spectra of Cool Stars in the J Band (1.0-1.3 μm) at Medium
Resolution
Authors: Joyce, Richard R.; Hinkle, Kenneth H.; Wallace, Lloyd;
Dulick, Michael; Lambert, David L.
Bibcode: 1998AJ....116.2520J
Altcode:
A spectroscopic survey of 103 cool S-, C-, and M-type stars was
undertaken with the Kitt Peak cryogenic spectrograph on the 1.3 m
telescope to make a detailed search for new molecular bands in the
1.0-1.3 μm J-band region. While the spectra have high signal-to-noise
ratios and good repeatability, no strong new features were found. Higher
resolution spectra of a small sample of representative stars observed
with the 4 m Fourier transform spectrometer were invoked in order
to identify the features in these spectra. With few exceptions, the
details of these spectra are well understood. Laboratory spectra were
obtained to aid in the identification of some weak features. Spectral
features from dominant lines of Ti, Fe, Al, Si, Mn, Na, and K, and
molecular bands due to TiO, TiS, ZrO, ZrS, VO, H_2O, and CN, have been
identified in the spectra. Several weak unidentified bands are found.
Title: Isotopic Lithium Abundances in Nine Halo Stars
Authors: Smith, Verne V.; Lambert, David L.; Nissen, Poul E.
Bibcode: 1998ApJ...506..405S
Altcode:
High-resolution echelle spectra of the 6707.8 Å Li I absorption line
in spectra of metal-poor halo dwarfs and subgiants are analyzed for
the isotopic fractions of 6Li and 7Li. Positive
detections of 6Li are reported for two stars, HD 84937 and
BD +26° 3578, and tight upper limits to the 6Li fraction
are obtained for an additional seven stars. Two stars, HD 116064 and
BD +26° 2606, were found to be double-lined spectroscopic binaries
and were rejected from the analysis. Elemental Li abundances were also
derived for the nine program stars: the Li abundance is identical across
the sample (excluding the spectroscopic binaries) to within +/-0.04 dex
in log ɛ(Li). Two processes involving high-energy particles (cosmic
rays) are considered as origins of the 6Li: spallation
reactions (e.g., O + p --> 6Li) and α-α fusion
reactions. The contribution of spallation reactions may be assessed
empirically using the published Be and B abundances. The observed
6Li/Be ratio is significantly in excess of that expected
from spallation. In view of the fact that the surface 6Li
abundance has almost certainly been somewhat depleted by exposure to
warm protons, the conclusion is that α-α reactions produced most
of the observed 6Li. Consequences of this conclusion are
sketched. Based on observations carried out at the European
Southern Observatory, La Silla, Chile, and McDonald Observatory,
University of Texas.
Title: Is DZ Andromedae an R Coronae Borealis variable?
Authors: Goswami, A.; Rao, N. K.; Lambert, D. L.
Bibcode: 1998Obs...118..213G
Altcode:
No abstract at ADS
Title: Spectra of Cool Stars in the J Band (1.0-1.3 micrometer)
at Medium Resolution
Authors: Joyce, Richard R.; Hinkle, Kenneth H.; Wallace, Lloyd;
Dulick, Michael; Lambert, David L.
Bibcode: 1998STIN...9917985J
Altcode:
A spectroscopic survey of 103 cool S-, C-, and M-type stars was
undertaken with the Kitt Peak cryogenic spectrograph (CRSP) on the
1.3-m telescope to make a detailed search for new molecular bands
in the 1.0-1.3 micrometer J-band region. While the spectra have
high signal-to-noise (S/N) and good repeatability, no strong new
features were found. Higher-resolution spectra of a small sample
of representative stars observed with the 4-m Fourier transform
spectrometer (FTS) were invoked in order to identify the features
in these spectra. With few exceptions, the details of these spectra
are well understood. Laboratory spectra were obtained to aid in
the identification of some weak features. Spectral features from
dominant lines of Ti, Fe, Al, Si, Mn, Na, and K, and molecular bands
due to TiO, TiS, ZrO, ZrS, VO, H2O, and CN have been identified in
the spectra. Several weak unidentified bands are found.
Title: Spectral variability of the binary HR 4049
Authors: Bakker, Eric J.; Lambert, David L.; Van Winckel, Hans;
McCarthy, James K.; Waelkens, Christoffel; Gonzalez, Guillermo
Bibcode: 1998A&A...336..263B
Altcode: 1998astro.ph..2120B
The C I, Na I D, and Hα lines of the post-AGB binary HR 4049 have
been studied. Na I D variability results from a photospheric absorption
component ([Na/H]=-1.6+/-0.2) which follows the velocity of the primary
and a stationary, non-photospheric component. An emission component
is attributed to the circumbinary disc, and an absorption component
to mass-loss from the system with a velocity of 5.3+/-0.5 km s(-1)
. The Hα profile varies with the orbital period. The two strong shell
type emission peaks are identified as from one single broad emission
feature with an absorption centered around -7.5 km s(-1) . The intensity
variations are largely attributed to a differential amount of reddening
towards the Hα emitting region and the stellar continuum. The radial
velocities suggest that the Hα emission moves in phase with the
primary, but with a slightly lower velocity amplitude. From this we
infer that the Hα emission comes from outside the orbit of the primary,
but still gravitationally bound to the primary. Hα also shows a weak
emission feature at -21.3+/-3.5 km s(-1) , which originates from the
circumbinary disc and a weak absorption feature at -7.5+/-1.6 km s(-1)
due to absorption by the circumbinary disc. We propose two competing
models that could account for the observed velocity and intensity
variations of the Hα profile. Model I: light from the primary reflects
on a localized spot near the inner radius of the circumbinary disc
which is closest to the primary. Model II: Hα emission originates
in the outer layers of the extended atmosphere of the primary due to
activity. These activities are locked to the position of the primary
in its orbit. We discuss the similarities of variability and shape of
the Hα emission of HR 4049 with those of early type T-Tauri stars
(e.g SU Aur). Based on observations obtained at the McDonald, ESO,
CTIO, and La Palma observatories.
Title: The Circumstellar Shell of the Post-Asymptotic Giant Branch
Star HD 56126: The 12CN/13CN Isotope Ratio
and Fractionation
Authors: Bakker, Eric J.; Lambert, David L.
Bibcode: 1998ApJ...502..417B
Altcode: 1997astro.ph.11173B
We have detected circumstellar absorption lines of the 12CN
and 13CN violet and red system in the spectrum of
the post-AGB star HD 56126. From a synthetic spectrum analysis,
we derive a Doppler broadening parameter of b = 0.51 +/- 0.04
km s-1, 12CN/13CN = 38 +/- 2,
and a lower limit of 2000 on 12CN/14CN and
12C14N/12C15N. A simple
chemical model has been computed of the circumstellar shell surrounding
HD 56126 that takes into account the gas-phase ion-molecule reaction
between CN and C+. From this we infer that this reaction
leads to isotopic fractionation of CN. Taking into account the isotopic
exchange reaction and the observed 12CN/13CN,
we find 12C/13C ~ 67 (for Tkin = 25
K). Our analysis suggests that 12CN has a somewhat higher
rotational temperature than 13CN: Trot = 11.5
+/- 0.6 and 8.0 +/- 0.6 K, respectively. We identify possible causes
for this difference in excitation temperature, among which is the N"
dependence of the isotopic exchange reaction.
Title: The Chemical Compositions of the SRd Variable Stars. I. XY
Aquarii, RX Cephei, AB Leonis, and SV Ursae Majoris
Authors: Giridhar, Sunetra; Lambert, David L.; Gonzalez, Guillermo
Bibcode: 1998PASP..110..671G
Altcode:
Chemical compositions are derived from high-resolution spectra for four
stars classed as SRd variables in the General Catalogue of Variable
Stars. Two stars-XY Aquarii and RX Cephei-are of solar metallicity
and most likely not variable stars. Their spectroscopic effective
temperatures and surface gravities correspond to the spectral types G0
V for XY Aqr and G8 III for RX Cep. Two stars are undisputed variables
and shown here to be metal-poor supergiants: AB Leonis with [Fe/H]
~=-1.6 and SV Ursae Majoris with [Fe/H] ~=-1.4. The metallicities and
high radial velocities show them to be halo stars.
Title: Boron in Very Metal Poor Stars
Authors: Garcia Lopez, Ramon J.; Lambert, David L.; Edvardsson, Bengt;
Gustafsson, Bengt; Kiselman, Dan; Rebolo, Rafael
Bibcode: 1998ApJ...500..241G
Altcode: 1998astro.ph..1167G; 1998astro.ph..1167L
We have observed the B I 2497 A line to derive the boron abundances
of two very metal-poor stars selected to help in tracing the origin
and evolution of this element in the early Galaxy: BD +23 3130 and
HD 84937. The observations were conducted using the Goddard High
Resolution Spectrograph on board the Hubble Space Telescope. A
very detailed abundance analysis via spectral synthesis has been
carried out for these two stars, as well as for two other metal-poor
objects with published spectra, using both Kurucz and OSMARCS model
photospheres, and taking into account consistently the NLTE effects
on the line formation. We have also re-assessed all published boron
abundances of old disk and halo unevolved stars. Our analysis shows
that the combination of high effective temperature (Teff > 6000 K,
for which boron is mainly ionized) and low metallicity ([Fe/H]<-1)
makes it difficult to obtain accurate estimates of boron abundances
from the B I 2497 A line. This is the case of HD 84937 and three other
published objects (including two stars with [Fe/H] ~ -3), for which only
upper limits can be established. BD +23 3130, with [Fe/H] ~ -2.9 and
logN(B)_NLTE=0.05+/-0.30, appears then as the most metal-poor star for
which a firm measurement of the boron abundance presently exists. The
evolution of the boron abundance with metallicity that emerges from
the seven remaining stars with Teff < 6000 K and [Fe/H]<-1,
for which beryllium abundances were derived using the same stellar
parameters, shows a linear increase with a slope ~ 1. Furthermore, the
B/Be ratio found is constant at a value ~ 20 for stars in the range
-3<[Fe/H]<-1. These results point to spallation reactions of
ambient protons and alpha particles with energetic particles enriched
in CNO as the origin of boron and beryllium in halo stars.
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: VizieR Online Data Catalog: Radial velocities of HR 4049
(Bakker+ 1998)
Authors: Bakker, E. J.; Lambert, D. L.; van Winckel, H.; McCarthy,
J. K.; Waelkens, C.; Gonzalez, G.
Bibcode: 1998yCat..33360263B
Altcode:
The C I, Na I D, and Hα lines of the post-AGB binary HR 4049 have
been studied. Na I D variability results from a photospheric absorption
component ([Na/H]=-1.6+/-0.2) which follows the velocity of the primary
and a stationary, non-photospheric component. An emission component
is attributed to the circumbinary disc, and an absorption component
to mass-loss from the system with a velocity of 5.3+/-0.5km/s. The
Hα profile varies with the orbital period. The two strong shell type
emission peaks are identified as from one single broad emission feature
with an absorption centered around -7.5km/s. The intensity variations
are largely attributed to a differential amount of reddening towards the
Hα emitting region and the stellar continuum. The radial velocities
suggest that the Hα emission moves in phase with the primary, but
with a slightly lower velocity amplitude. From this we infer that the
Hα emission comes from outside the orbit of the primary, but still
gravitationally bound to the primary. Hα also shows a weak emission
feature at -21.3+/-3.5km/s, which originates from the circumbinary
disc and a weak absorption feature at -7.5+/-1.6km/s due to absorption
by the circumbinary disc. We propose two competing models that could
account for the observed velocity and intensity variations of the Hα
profile. Model I: light from the primary reflects on a localized spot
near the inner radius of the circumbinary disc which is closest to the
primary. Model II: Hα emission originates in the outer layers of the
extended atmosphere of the primary due to activity. These activities
are locked to the position of the primary in its orbit. We discuss
the similarities of variability and shape of the Hα emission of HR
4049 with those of early type T-Tauri stars (e.g SU Aur). (9
data files).
Title: The 11B/10B Ratio of Local Interstellar
Diffuse Clouds
Authors: Lambert, David L.; Sheffer, Yaron; Federman, S. R.; Cardelli,
Jason A.; Sofia, Ulysses J.; Knauth, David C.
Bibcode: 1998ApJ...494..614L
Altcode:
The isotopic ratio 11B/10B of gas in diffuse
interstellar clouds toward ζ Oph, κ Ori, and δ Sco is measured
using HST/Goddard High Resolution Spectrograph echelle spectra
of the B II 1362 Å line. To within the errors of measurement,
the three lines of sight give identical results for a mean value of
11B/10B = 3.4 +/- 0.7, a value quite similar to
the solar system ratio of 4.05. These results show that the latter
value is not highly anomalous and that a ratio higher than 2.5, as
predicted for boron produced from spallation reactions controlled
by high-energy cosmic rays, most probably requires a general
explanation. The observed ratio is consistent with additional boron
production either by spallation by low-energy (``Orion'') cosmic rays
or by neutrino-induced spallation of carbon in Type II supernovae. The
total abundance of B in the diffuse clouds is a factor of 5 less than
the meteoritic value. This depletion of B is consistent with that
found for Cu and Ga, two elements with a condensation temperature
similar to B. Based on observations obtained with the NASA/ESA
Hubble Space Telescope through the Space Telescope Science Institute,
which is operated by the Association of Universities for Research in
Astronomy, Inc., under NASA contract NAS4-26555.
Title: FG Sagittae: A Newborn R Coronae Borealis Star?
Authors: Gonzalez, Guillermo; Lambert, David L.; Wallerstein, George;
Rao, N. Kameswara; Smith, Verne V.; McCarthy, James K.
Bibcode: 1998ApJS..114..133G
Altcode:
We have monitored FG Sge's spectroscopic changes since the time just
prior to its dramatic fading in 1992 August. The most significant
qualitative changes in the spectrum include large variations in the
strength of the C2 molecular bands and the gradual appearance
of broad blueshifted high-velocity (~200 km s-1 relative
to the photosphere) absorption components of the Na I D lines. During
the deep minima of 1994 May and 1996 June, an emission-line spectrum
temporarily appeared superimposed on a weak continuum; in addition to
the previously reported nebular emission lines, the spectra displayed
the C2 and rare earth element lines in emission. Much of
the behavior exhibited by FG Sge since 1992 resembles that seen in R
CrB stars, including the photometric behavior, the evolution of the
Na I D line profiles, variations of the C2 band strengths,
and the appearance of narrow emission lines. The results of our
abundance analysis (using model atmospheres with a solar He/H ratio)
indicate that the carbon abundance is currently greater than that
determined by Langer et al., who reported on the dramatic increase
in the abundances of the rare earth elements in FG Sge. We derive
higher relative abundances of the rare earths ([Me/Fe] ~ 3) than
either Langer et al. or Kipper & Kipper, which we attribute to
some enhancement of these elements since ~1970. We confirm previous
claims that the relative scandium abundance is high ([Sc/Fe] ~ 1) in
FG Sge and suggest that it is the result of neutron captures by the
light elements leading up to 45Sc. The Hα profile of
FG Sge is very similar to that of V854 Cen, a R CrB star deficient in
H by 2-3 dex. This is the first evidence pointing toward H-deficiency
in the atmosphere of FG Sge, which further strengthens its link
with the R CrB class. Additional study is required before we can say
definitively whether or not its atmosphere is H deficient. Based in
part on observations collected at the Kitt Peak National Observatory,
National Optical Astronomy Observatories (NOAO), which is operated by
the Association of Universities for Research in Astronomy Inc. (AURA)
under cooperative agreement with the National Science Foundation.
Title: Chemical composition of the CP Hg-Mn components of
approximately equal mass in the SB2 system 46 Draconis
Authors: Tsymbal, V. V.; Kotchukhov, O. P.; Khokhlova, V. L.; Lambert,
D. L.
Bibcode: 1998AstL...24...90T
Altcode: 1998PAZh...24..116T
We have performed the most complete (to date) atmospheric-abundance
analysis of the components of approximately equal mass in the SB2
system 46 Dra using the high-resolution, S/N = > 200 CCD spectra
obtained with the echelle spectrograph of the 2.7-m McDonald Observatory
telescope. The abundances of 25 elements were determined from lines in
the wide spectral range 3800 to 9000 A. The rotation of the components
is shown to be synchronized and coaxial with the orbital motion. The
chemical anomalies of both components were found to be generally
similar: an underabundance of He, C, N, O, and Al; a nearly solar
abundance of iron-peak elements; and considerable overabundances
of P, Mn, Ga, Sr, Y, Zr, Ba, Pt, Au, and Hg, which increase with
increasing atomic number. However, we found significant differences
in the abundances of some elements in components A and B, similar to
those that were previously detected in the analogous SB2 system ARAur:
an underabundance of Al and Ni in component A with a smaller anomaly
or a normal abundance of these two elements in component B. Component
A shows a considerably greater overabundance of Ga and considerably
smaller overabundances of Sr and Pt than component B does.There are
also differences between the systems themselves: in contrast to AR Aur,
in which only component A exhibits great overabundances of Y, Ba, and
Hg, these elements are equally greatly enhanced in both components of
46 Dra. The most striking difference between components A and B of 46
Dra, which are similar in all physical parameters, is the difference
in the isotopic composition of mercury which was first detected by
Cowley and Aikman (1975) and confirmed in this study. It is concluded
that the abundance difference between the components could arise after
the synchronization of the rotation and the arrival of the stars at
the main sequence.
Title: The B11/B10 Ratio in Interstellar Space
Authors: Federman, S. R.; Lambert, D. L.; Sheffer, Y.; Cardelli, J. A.
Bibcode: 1998ASPC..143..302F
Altcode: 1998sigh.conf..302F
No abstract at ADS
Title: Boron in Lithium- and Beryllium-Deficient F Stars
Authors: Boesgaard, Ann Merchant; Deliyannis, Constantine P.; Stephens,
Alex; Lambert, David L.
Bibcode: 1998ASPC..154..903B
Altcode: 1998csss...10..903B
The Goddard High Resolution Spectrograph (GHRS) has been used with the
Hubble Space Telescope (HST) to observe the B 1 region at 2497 AA in
nine F and G dwarfs of approximately solar metallicity. The stars were
selected because they have a variety of Li and Be deficiencies. Most
of the nine stars were newly observed at 3131 AA for Be 2 and 6708 AA
for Li 1 at high spectral resolution and high signal-to-noise ratios at
the Keck I 10-m telescope, the Canada-France-Hawaii 3.6-m telescope and
the University of Hawaii 2.2-m telescope. Spectrum synthesis has been
used to determine the Li and Be abundances or upper limits, as well
as B abundances in our nine program stars and in five other stars from
the HST archive. Corrections to the B and Li abundances due to non-LTE
effects have been applied. The stars originate from the region on the
ZAMS of the Li (and Be) dip. In spite of large deficiencies in Li and
Be, we find a striking uniformity in the B abundances, i.e. there
is no B dip. For the coolest and most evolved star in our sample,
zeta Her A, the B abundance is a factor of three lower than the mean
for the other stars. This star also has the largest Be deficiency
(more than a factor of 60) and the largest Li deficiency (more than
a factor of 500). These data, together with other studies of the Li
dip, argue strongly against diffusion and mass loss and in favor of
slow mixing as the cause of the Li and Be dip and the absence of a
B dip. Six stars with [Fe/H] from -0.75 to +0.15 have Be abundances
ranging from the maximum of the sample to a factor of four (0.6 dex)
below the maximum yet these stars have a B/Be ratio that is constant
to within +/-0.10 dex and that is close to the predictions of galactic
cosmic ray spallation of 10-15. This indicates that the galactic cosmic
ray production of B and Be is not uniform relative to the production
of elements such as Fe by nucleosynthesis in stars.
Title: Boron in Lithium- and Beryllium-deficient F Stars
Authors: Boesgaard, Ann Merchant; Deliyannis, Constantine P.; Stephens,
Alex; Lambert, David L.
Bibcode: 1998ApJ...492..727B
Altcode:
The Goddard High Resolution Spectrograph (GHRS) has been used with the
Hubble Space Telescope (HST) to observe the B I region at 2497 Å in
nine F and G dwarfs of approximately solar metallicity. The stars were
selected because they have a variety of Li and Be deficiencies. Most
of the nine stars were newly observed at high spectral resolution
and high signal-to-noise ratios at the Keck I 10 m telescope, the
Canada-France-Hawaii 3.6 m telescope, and the University of Hawaii 2.2
m telescope at 3131 Å for Be II and 6708 Å for Li I. With spectrum
synthesis we have determined the abundances of B in our nine program
stars and in five other stars from the HST archive. The stellar
parameters we have used have been determined in a self-consistent
way for the program stars and the archive stars. Spectrum synthesis
has also been used to determine the Li and Be abundances or upper
limits. Corrections to the B and Li abundances due to non-LTE effects
have been applied. The stars originate from the region on the
ZAMS of the Li (and Be) dip. In spite of large deficiencies in Li
and Be, we find a striking uniformity in the B abundances, i.e.,
there is no B dip. In all cases the Li deficiency is greater than the
Be deficiency. For the coolest and most evolved star in our sample,
ζ Her A, the B abundance is 0.6 dex lower than the mean for the other
stars. This star also has the largest Be deficiency (more than a factor
of 80) and the largest Li deficiency (more than a factor of 600). These
data, together with other studies of the Li dip, argue strongly against
diffusion and mass loss and in favor of slow mixing as the cause of the
Li and Be dip and the absence of a B dip. Six stars with [Fe/H]
from -0.75 to +0.15 have Be abundances ranging from the maximum of
the sample to a factor of 4 below the maximum, yet these stars have a
B/Be ratio that is constant to within +/-0.10 dex and that is close
to the predictions of Galactic cosmic-ray spallation of 10-15. The
Be range for four stars with solar metallicity is still a factor of
2, and yet the B/Be ratio is constant to within +/-0.03 dex. These
results imply that the Galactic cosmic-ray production of B and Be
is not uniform relative to the production of elements such as Fe by
stellar nucleosynthesis. Based on observations obtained with the
NASA/ESA Hubble Space Telescope through the Space Telescope Science
Institute which is operated by the Association of Universities for
Research in Astronomy, Inc., under NASA contract NAS5-26555.
Title: The B5 Molecular Cloud Halo: The Cool Atomic and Molecular
Medium
Authors: Wannier, P.; Andersson, B. -G.; Penprase, B. E.; Federman,
S.; Lambert, D.
Bibcode: 1998ASPC..143..285W
Altcode: 1998sigh.conf..285W
No abstract at ADS
Title: Chemical Evolution of the Orion Association. IV. The Oxygen
and Iron Abundances of F and G Stars
Authors: Cunha, Katia; Smith, Verne V.; Lambert, David L.
Bibcode: 1998ApJ...493..195C
Altcode:
Oxygen and iron abundances are derived for a sample of pre-main-sequence
F and G stars of the Orion association. Results for association members
are compared with results published previously for main-sequence B
stars in the association. The abundances reveal that the F and G stars
exhibit the pattern of abundances shown by the main-sequence B stars:
the stars have a single iron abundance, but there is a star-to-star
variation of oxygen abundance. Oxygen-rich and oxygen-poor stars are
roughly segregated on the sky.
Title: A Retrospective Introduction
Authors: Lambert, D. L.
Bibcode: 1998HiA....11...94L
Altcode:
No abstract at ADS
Title: A Brief History of Noncommutative Space-Time
Authors: Heller, M.; Lambert, D.; Madore, J.
Bibcode: 1998AcC....24...51H
Altcode:
No abstract at ADS
Title: Differential Calculi on Generalized Clifford Algebras
Authors: Kpamegan, A. B.; Lambert, D.
Bibcode: 1998AcC....24...87K
Altcode:
No abstract at ADS
Title: Chemical Abundance Trends Among RV Tauri Stars
Authors: Gonzalez, G.; Lambert, D. L.
Bibcode: 1998ASPC..135...34G
Altcode: 1998hcsp.conf...34G
We have obtained high resolution spectra of 9 field and 3 globular
cluster RV Tau stars. Employing LTE abundance analyses, we have
discovered that the chemical abundances of the photospheres of the field
RV Tau stars correlate with condensation temperature. The globular
cluster RV Tau stars do not display this pattern (except possibly
V1 in Omega Cen), but instead display the products of CNO cycling in
their photospheres. We discuss possible u sources of these trends.
Title: The rise and fall of the NaMgAl stars.
Authors: Tomkin, J.; Edvardsson, B.; Lambert, D. L.; Gustafsson, B.
Bibcode: 1997A&A...327..587T
Altcode: 1997astro.ph..7208T
We have made new abundance determinations for a sample of NaMgAl
stars. These stars, which are a subgroup of the nearby metal-rich
field F and G disk dwarfs, were first identified by Edvardsson
et al. (1993A&A...275..101E) on the basis of their apparent
enrichment in Na, Mg and Al relative to other elements. The discovery
of a planetary companion to the nearby solar type star 51 Peg (Mayor
& Queloz, 1995Natur.378..355M) combined with Edvardsson et al.'s
earlier identification of 51 Peg as a NaMgAl star highlighted the
group's potential importance. Our new analysis, which uses new spectra
of higher resolution and better wavelength coverage than the analysis
of Edvardsson et al., shows that the Na, Mg and Al abundances of the
NaMgAl stars are indistinguishable from those of non-NaMgAl stars with
otherwise similar properties. The group thus appears to be spurious. Our
study, which includes 51 Peg, also provides the most complete set
of abundances for this star available to date. The new Fe abundance,
[Fe/H]=+0.20+/-0.07, of 51 Peg confirms earlier measurements of its
metal richness. Abundances for 19 other elements, including C, N and O,
reveal a fairly uniform enrichment similar to that of Fe and show no
evidence of abnormality compared to other metal rich stars of similar
spectral type.
Title: Probing the Photodissociation Region toward HD 200775
Authors: Federman, S. R.; Knauth, D. C.; Lambert, David L.
Bibcode: 1997ApJ...489..758F
Altcode:
The illuminating source of the photodissociation region associated with
the reflection nebula NGC 7023 is HD 200775. We probed the foreground
atomic and molecular material through diagnostics observed in absorption
against the background star. Ground-based measurements of Na I, K I,
and Ca II and of the molecules CH, CH+, C2,
and CN were analyzed in order to extract the physical conditions
for this material. In particular, estimates for gas density, gas
temperature, and the flux of ultraviolet radiation were derived and
compared with information obtained from maps of radio emission. The
foreground material has lower density than the other portions of the
photodissociation region; the observed excitation of C2,
the observed column of C2, and the columns of neutral sodium
and potassium are reproduced when the extinction curve derived for
this line of sight is adopted. Future models of the NGC 7023 nebula
should include the effects associated with this extinction curve. The
observed CN column density is larger than our predicted amount; an
additional contribution from the background molecular cloud is inferred.
Title: Synthesis of the elements in stars: forty years of progress
Authors: Wallerstein, George; Iben, Icko, Jr.; Parker, Peter;
Boesgaard, Ann Merchant; Hale, Gerald M.; Champagne, Arthur E.; Barnes,
Charles A.; Käppeler, Franz; Smith, Verne V.; Hoffman, Robert D.;
Timmes, Frank X.; Sneden, Chris; Boyd, Richard N.; Meyer, Bradley S.;
Lambert, David L.
Bibcode: 1997RvMP...69..995W
Altcode:
Forty years ago Burbidge, Burbidge, Fowler, and Hoyle combined
what we would now call fragmentary evidence from nuclear physics,
stellar evolution and the abundances of elements and isotopes in the
solar system as well as a few stars into a synthesis of remarkable
ingenuity. Their review provided a foundation for forty years of
research in all of the aspects of low energy nuclear experiments and
theory, stellar modeling over a wide range of mass and composition, and
abundance studies of many hundreds of stars, many of which have shown
distinct evidence of the processes suggested by B2FH. In
this review we summarize progress in each of these fields with emphasis
on the most recent developments.
Title: VizieR Online Data Catalog: Abundances of 9 solar-type stars
(Tomkin+ 1997)
Authors: Tomkin, J.; Edvardsson, B.; Lambert, D. L.; Gustafsson, B.
Bibcode: 1997yCat..33270587T
Altcode:
Line identifications, measured equivalent widths and derived chemical
abundances in 9 solar-type dwarf stars, which are identified by their
Bright Star (HR, (Cat. <V/50>)) numbers. (1 data file).
Title: McDonald Observatory High Spectral Resolution Observations
of Comet Hale-Bopp
Authors: Cochran, A. L.; Barker, E. S.; Cochran, W. D.; Lambert, D. L.
Bibcode: 1997DPS....29.3721C
Altcode: 1997BAAS...29.1050C
We observed comet Hale-Bopp with the 2DCoude spectrograph on the 2.7m
telescope at McDonald Observatory. This is a cross-dispersed echelle
spectrograph located at the coude focus. It is capable of working in
two different resolution regimes: the lower spectral resolving power
is R=60,000; the higher spectral resolving power is R=180,000. Comet
Hale-Bopp was observed with this spectrograph on 4 nights in fall
1996 with R=60,000. It was observed an additional 17 nights from 21
February through 7 April 1997 using the R=180,000 mode on 8 nights
and the R=60,000 mode on 9 nights. The R=180,000 observations were
obtained on 28 February through 3 March when the comet was at ~ 1.1
(pre-perihelion) and 1.5au heliocentric and geocentric distances
respectively. Hale-Bopp was also observed at R=180,000 on 4 through
7 April when the comet was at ~ 0.9 (post-perihelion) and 1.4au
heliocentric and geocentric distances. The R=60,000 observations were
obtained on 21 through 23 February, 15 and 16 March, and 26 through
29 March, all pre-perihelion. In the R=60,000 mode, the spectral
coverage is complete from ~ 3800--5800 Angstroms. From 5800--10,000
Angstroms the spectral coverage is broken by increasing interorder
gaps. In the R=180,000 mode, spectral coverage is much more limited,
with 14--20 spectral orders of approximately 20 Angstroms each. Thus,
in the higher spectral resolving power regime, specific molecular
features were targeted. In this regime, individual molecular lines
could be fully resolved and thus we measure the velocity broadening of
the various species. On all nights, the slit was placed at different
locations in the coma so that differences can be studied between the
dustier and less dusty regions of the coma. We will show the effect on
the line width of different regions of the coma and of different epochs
in the comet's passage. In addition, these spectra will be useful for
the study of isotope ratios in the coma, particularly (12) C/(13) C.
Title: Abundance Analyses of Type II Cepheids in Globular Clusters
Authors: Gonzalez, Guillermo; Lambert, David L.
Bibcode: 1997AJ....114..341G
Altcode:
We have determined the photospheric compositions of five luminous F-G
variables in globular clusters: V11 in M2, V42 in M5, V84 in M5, V2 in
M10, and V17 in M28, three of which are classified as RV Tau variable
stars. Unlike the recent findings that the photospheres of field RV
Tau variables have been altered by a gas-dust separation process,
none of these stars, except possibly V2 in M10, show such signs. We
suggest that either a smaller carbon abundance in the photosphere
of a globular cluster RV Tau star (compared to its field analogues)
might be a factor in the gas-dust separation process due to the lack
of sufficient carbon grain formation, or the stellar winds and their
efficacy as dust-grain separators is influenced by the metallicity of
the stellar envelope which, unlike the photosphere, is never subject
to alteration by a dust-gas separation. Our analysis is most complete
for V84, for which we have estimated the abundances of 19 chemical
elements. Compared to the other giants in M5, this star displays a
very large excess of Na and a deficit of O. This finding is consistent
with a recently proposed mechanism of Na production in the ON-cycling
region of metal-poor RGB stars. The value of [Al/Fe] for V84 is also
high (also consistent with ON-cycling), but a comparison with the
other cluster giants cannot be performed until Al is measured in their
spectra. The s-process elements are not significantly enhanced in the
atmosphere of V84 relative to the other cluster members.
Title: On the Hydrogen Deficient Nature of Z UMi
Authors: Goswami, A.; Rao, N. K.; Lambert, D. L.; Gonzalez, G.
Bibcode: 1997PASP..109..796G
Altcode:
Z Ursa Minoris was classified by Benson et al. (1994) a a R Coronae
Borealis (RCB) variable star from its light variations. Hydrogen
deficiency, which is a defining feature of RCB stars, was not
established. To investigate this aspect we have obtained high
resolution spectra in both blue (4200-4630\AA) and red (5050-7950\AA)
regions. Lines of the CH molecule (G band) at about 4300\AA, which
are present in spectra of N-type carbon stars are weak or absent in
the spectrum of Z UMi indicating its hydrogen deficient nature and
membership of the rare class of RCB variables. (SECTION: Stars)
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: Abundance Analyses of Field RV Tauri Variables. III. DY
Aquilae, SS Geminorum, CT Orionis, and CE Virginis
Authors: Gonzalez, Guillermo; Lambert, David L.; Giridhar, Sunatra
Bibcode: 1997ApJ...481..452G
Altcode:
Analyses of the photospheric compositions of the four field RV
Tauri stars, DY Aql, SS Gem, CT Ori, and CE Vir, indicate that to
varying degrees they have experienced fractionation processes that
have preferentially depleted their atmospheres of elements with high
condensation temperatures. This corroborates our previous studies,
which showed similar patterns in five other field RV Tauri stars. Two stars in our sample, DY Aql and CE Vir, were found to have strong
Li I resonance lines, with corresponding lithium abundances near log
ɛ(Li) = 0.0; this is not significantly different from that found in
less evolved M giants. These are also the coolest stars displaying a
correlation of photospheric abundances with condensation temperatures.
Title: Abundance Analyses of the Field RV Tauri Variables: EP Lyrae,
DY Orionis, AR Puppis, and R Sagittae
Authors: Gonzalez, Guillermo; Lambert, David L.; Giridhar, Sunetra
Bibcode: 1997ApJ...479..427G
Altcode:
Analyses of the photospheric compositions of the four field RV
Tauri stars, EP Lyr, DY Ori, AR Pup, and R Sge, indicate that to
varying degrees they have experienced fractionation processes that
have preferentially depleted their atmospheres of elements with high
condensation temperatures. The depletion, as indicated by, for instance,
[S/Fe], is greatest for DY Ori, [S/Fe] = 2.5, and least for R Sge,
[S/Fe] = 0.9. The initial composition, presumably indicated by the
sulfur abundance, was nearly solar for AR Pup, R Sge, and DY Ori, while
it was about 0.6 dex less than solar for EP Lyr. This implies that
the RV Tauri stars as a group may not be as metal-poor as previously
thought--they are instead ``metal-depleted.'' The field RV Tauri's are
not halo stars, but probably belong to the thick disk. This brings
to seven the number of type II Cepheids that show such a trend; the
other three are IW Car and V1 in ω Cen, RV Tauri stars, and ST Pup,
a W Virginis star. The 12C/13C ratios for
EP Lyr and DY Ori are 9 +/- 1 and 6 +/- 3, respectively, indicating
that CN-cycled material has been mixed with their surface layers. This
is consistent with the general consensus that RV Tau stars are in a
post-AGB evolutionary stage. There is also evidence that EP Lyr has
a stellar mass companion, but additional observations are required
to calculate an orbit; hence, EP Lyr could be a link to the group
of metal-depleted, high-latitude A-F supergiants, all of which are
binaries.
Title: The Spectrum of the Cool R Coronae Borealis Variable S Apodis
in a Deep Decline
Authors: Goswami, Aruna; Rao, N. K.; Lambert, D. L.; Smith, V. V.
Bibcode: 1997PASP..109..270G
Altcode:
A high resolution spectrum (5575 - 8875\AA) of the cool R Coronae
Borealis variable S Apodis in its 1993 deep decline is discussed. Narrow
or chromospheric emission lines of Na I, K I, Ca II, and Ba II and
broad emission lines of He I 7065\AA and Na I D are seen, as expected
from published reports of warmer RCBs in decline. The surprise of the
S Aps spectrum is the considerable blue shift of the broad emissions
component to the Na D lines. The blue shift may result from lines
formed in a bipolar flow which is obscured asymmetrically by soot
clouds along the line of sight. (SECTION: Stars)
Title: Boron Abundances of B Stars of the Orion Association
Authors: Cunha, Katia; Lambert, David L.; Lemke, Michael; Gies,
Douglas R.; Roberts, Lewis C.
Bibcode: 1997ApJ...478..211C
Altcode:
The boron abundance of four B-type stars from the Orion association has
been determined from Goddard High Resolution Spectrograph (GHRS)/Hubble
Space Telescope (HST) spectra covering the B II 1362 Å resonance
line. After correction for large non-LTE effects, the mean boron
abundance is similar to the meteoritic abundance, but a factor of 4
(0.6 dex) greater than published abundances of boron in interstellar
gas. This difference in boron abundance between young stars and gas
is unexplained. The Orion stars were selected by their oxygen
abundances: two are enriched in oxygen by about 60% relative to the
others. Analysis of the GHRS spectra shows that the O-rich stars are
deficient in boron by about 250% (0.4 dex) relative to the O-poor
stars. Then, if the differences in oxygen abundance reflect differing
levels of contamination of the natal clouds with (O-rich) ejecta
of local Type II supernovae, the ejecta were not enriched in boron
synthesized by the ν-process. Based on observations obtained
with the NASA/ESA Hubble Space Telescope through the Space Telescope
Science Institute, which is operating the Association of Universities
for research in Astronomy, Inc., under NASA contract NAS5-26555.
Title: Division IV: Stars. Introduction to Division IV's commission
reports.
Authors: Lambert, D. L.
Bibcode: 1997IAUTA..23..277L
Altcode:
Commissions 26: Double & multiple stars, 29: Stellar spectra,
35: Stellar constitution, 36: Theory of stellar atmospheres, 45:
Stellar classification.
Title: High-resolution spectroscopy of R CrB - pulsations, shells
and mass loss
Authors: Rao, N. Kameswara; Lambert, David L.
Bibcode: 1997MNRAS.284..489R
Altcode:
High spectral resolution observations obtained in 1994 and spanning
three pulsation cycles of R CrB are discussed along with available UBV
photometric observations for the same epochs. Model atmosphere based
analyses of the spectra at pulsation light maximum and minimum show
the atmosphere to be cooler by 500 K at minimum. Radial velocities
of high- and low-excitation lines at maximum light show, on one
occasion, a marked velocity difference. Weak blueshifted Hα emission
is seen in spectra at the phase of minimum light. In addition to a
photospheric component, the Na i D lines show absorption components
from circumstellar gas. One strong component not seen in 1990 or early
1993 may be a result of gas ejected during the late-1933 deep decline.
Title: Chemical Composition of Approximately Equal Mass Hg-Mn
Components of the SB2 System 46 Draconis
Authors: Tsymbal, V. V.; Kotchoukhov, O. P.; Lambert, D. L.; Khokhlova,
V. L.
Bibcode: 1997OAP....10...78T
Altcode:
We report results of the most complete up to date elemental
abundance analysis of approximately equal mass Hg-Mn components of
chemically-peculiar SB2 system 46 Dra. The high-dispersion S/N >=
200 CCD spectrum were obtained with the echelle spectrograph of the
McDonald Observatory 2.7-m reflector. Lines in the wide spectral region
of 3800-9000 Angstroms were identified and the chemical composition
of each component was determined for 25 elements. Chemical anomalies
of both components are found to be roughly similar: He, C, N, O
and Al deficiency, nearly normal abundance of iron-peak elements,
large excesses of P, Mn, Ga, Sr, Y, Zr, Ba, Pt, Au and Hg which show a
common trend with atomic number. However we found significant abundance
differences between the components especially for Ne, Al, S, V, Mn,
Ni, Ga, Sr, Zr and Pt.
Title: Isotopic Carbon Abundances in M71
Authors: Briley, Michael M.; Smith, Verne V.; King, Jeremy; Lambert,
David L.
Bibcode: 1997AJ....113..306B
Altcode:
High resolution echelle spectra of the 8005 Angstroms CN bands are
presented for five bright giants in the globular cluster M71 (C1951
+186, NGC 6838). An analysis of the (13) CN feature included in
this region confirms the results of \cite{briley94a}; that the M71
red giants evince low (12}C/({13)) C ratios and that these ratios
are correlated with CN band strengths (CN-strong stars having lower
(12}C/({13)) C ratios). This finding is consistent with the theory
that the star-to-star CN band strength variations, as well as the
oxygen and possibly sodium differences observed in M71, are related
to the CN(O)-cycle of hydrogen burning. (One asymptotic giant branch
candidate is also included in the present sample, which exhibits both
weak-CN band strength and a low (12}C/({13)) C ratio.) Examination of
published data on CN band strengths and (12}C/({13)) C ratios among
the more metal-poor clusters implies a metallicity dependence in
the efficiency of the underlying mechanism responsible for the low
(12}C/({13)) C ratios. A likely candidate appears to be the mixing
of CN(O)-processed material into the stellar atmospheres, although a
primordial source of CN-processing cannot be ruled out.
Title: Sodium abundance variations in main-sequence stars of the
globular cluster 47 Tucanae
Authors: Briley, Michael M.; Smith, Verne V.; Suntzeff, Nicholas B.;
Lambert, David L.; Bell, Roger A.; Hesser, James E.
Bibcode: 1996Natur.383..604B
Altcode:
GALACTIC globular clusters were once thought to be chemically
homogeneous, having formed quite rapidly from relatively small
condensations of primordial gas29. In many clusters,
significant star-to-star variations in light-element abundances have
been observed1-4 in evolved giant stars. These variations
have been attributed to the presence at the stellar surfaces of
nucleosynthesis products generated deep within the stars. But other
observations13 have suggested that some of this variability
was established earlier in the stars' lifetimes, perhaps as a result of
inhomogeneities in the gas cloud from which the cluster formed. Here
we report the observation of variations in the sodium abundances of
unevolved (main-sequence) stars in the cluster 47 Tucanae. Although
these variations are similar to those observed in evolved cluster stars,
they cannot be explained by mixing, in the framework of current models
of stellar evolution. This indicates either that the gas out of which
47 Tuc formed was chemically inhomogeneous, or that some mechanism
for altering the surface element abundances of stars operates while
they are still on the main sequence.
Title: Lithium in Lower Main-Sequence Stars of the alpha Persei
Cluster: Erratum
Authors: Balachandran, Suchitra; Lambert, David L.; Stauffer, John R.
Bibcode: 1996ApJ...470.1243B
Altcode:
No abstract at ADS
Title: Detection of Quiescent Extreme Ultraviolet Emission from
the Very Low Mass Dwarf van Biesbroeck 8: Evidence for a Turbulent
Field Dynamo
Authors: Drake, Jeremy J.; Stern, Robert A.; Stringfellow, Guy;
Mathioudakis, Mihalis; Laming, J. Martin; Lambert, David L.
Bibcode: 1996ApJ...469..828D
Altcode:
We report the detection of quiescent EUV emission from the very low
mass dwarf VB 8 by the Extreme Ultraviolet Explorer (EUVE) in the
Lexan/B band (65-190 Å). We interpret this emission in terms of a
hot coronal plasma and combine this information with previous X-ray
detections to estimate the quiescent plasma temperature and emission
measure. The combined observations made by Einstein, ROSAT, and EUVE
between 1979 and 1994 are consistent with a quiescent coronal plasma
temperature of (2-6) x 106 degrees and indicate the same
emission measure to within a factor of about 2. The nonflaring corona
of VB 8 then appears relatively constant over timescales of more than
10 yr. Our results are consistent with the picture of a turbulently
driven or distributive dynamo for VB 8, rather than with a large-scale
field dynamo which appears to dominate the solar corona. Evidence from
X-ray and optical data concerning the long-term coronal variability of
the more active stars of higher mass also points toward the idea that
active late-type stars in general are dominated by a turbulent dynamo.
Title: The emission-line spectrum of the hot R Coronae Borealis star
MV SGR
Authors: Pandey, Gajendra; Kameswara Rao, N.; Lambert, David L.
Bibcode: 1996MNRAS.282..889P
Altcode:
Spectra of MV Sgr obtained at CTIO in 1992 May show many emission
lines in the red. Most of the emission lines show two components with a
minimum centred at the stellar velocity. Species represented include H,
HeI, TiII and FeII. Of special interest is emission in the LiI 6707-A
resonance doublet. [OI] and [NII] emission indicate the presence of a
nebula around the star. The radial velocity of the absorption lines
(AlIII, SiIII, NII and CII) and FeII emission lines agrees with the
radial velocity given by Jeffery et al.
Title: Study of the air-sea interactions at the mesoscale: the
SEMAPHORE experiment
Authors: Eymard, L.; Planton, S.; Durand, P.; Le Visage, C.; Le Traon,
P. Y.; Prieur, L.; Weill, A.; Hauser, D.; Rolland, J.; Pelon, J.;
Baudin, F.; Bénech, B.; Brenguier, J. L.; Caniaux, G.; de Mey, P.;
Dombrowski, E.; Druilhet, A.; Dupuis, H.; Ferret, B.; Flamant, C.;
Flamant, P.; Hernandez, F.; Jourdan, D.; Katsaros, K.; Lambert, D.;
Lefèvre, J. M.; Le Borgne, P.; Le Squere, B.; Marsoin, A.; Roquet,
H.; Tournadre, J.; Trouillet, V.; Tychensky, A.; Zakardjian, B.
Bibcode: 1996AnGeo..14..986E
Altcode:
The SEMAPHORE (Structure des Echanges Mer-Atmosphère, Propriétés des
Hétérogénéités Océaniques: Recherche Expérimentale) experiment
has been conducted from June to November 1993 in the Northeast Atlantic
between the Azores and Madeira. It was centered on the study of the
mesoscale ocean circulation and air-sea interactions. The experimental
investigation was achieved at the mesoscale using moorings, floats,
and ship hydrological survey, and at a smaller scale by one dedicated
ship, two instrumented aircraft, and surface drifting buoys, for
one and a half month in October-November (IOP: intense observing
period). Observations from meteorological operational satellites as
well as spaceborne microwave sensors were used in complement. The
main studies undertaken concern the mesoscale ocean, the upper
ocean, the atmospheric boundary layer, and the sea surface, and first
results are presented for the various topics. From data analysis and
model simulations, the main characteristics of the ocean circulation
were deduced, showing the close relationship between the Azores front
meander and the occurrence of Mediterranean water lenses (meddies), and
the shift between the Azores current frontal signature at the surface
and within the thermocline. Using drifting buoys and ship data in the
upper ocean, the gap between the scales of the atmospheric forcing and
the oceanic variability was made evident. A 2 °C decrease and a 40-m
deepening of the mixed layer were measured within the IOP, associated
with a heating loss of about 100 W m-2. This evolution was shown to be
strongly connected to the occurrence of storms at the beginning and the
end of October. Above the surface, turbulent measurements from ship and
aircraft were analyzed across the surface thermal front, showing a 30%
difference in heat fluxes between both sides during a 4-day period, and
the respective contributions of the wind and the surface temperature
were evaluated. The classical momentum flux bulk parameterization was
found to fail in low wind and unstable conditions. Finally, the sea
surface was investigated using airborne and satellite radars and wave
buoys. A wave model, operationally used, was found to get better results
compared with radar and wave-buoy measurements, when initialized using
an improved wind field, obtained by assimilating satellite and buoy wind
data in a meteorological model. A detailed analysis of a 2-day period
showed that the swell component, propagating from a far source area,
is underestimated in the wave model. A data base has been created,
containing all experimental measurements. It will allow us to pursue
the interpretation of observations and to test model simulations in
the ocean, at the surface and in the atmospheric boundary layer, and to
investigate the ocean-atmosphere coupling at the local and mesoscales.
Title: Lines of Circumstellar C2, CN, and CH+ in the Optical Spectra
of Post-Agb Stars
Authors: Bakker, Eric J.; Lambert, David L.; van Dishoeck, Ewine F.
Bibcode: 1996astro.ph..9030B
Altcode:
Recent optical spectra of post-AGB stars show the presence of C2, CN,
and CH+ originating in the circumstellar shell. We present here new,
higher resolution spectra which provide constraints on the physical
parameters and information on the line profiles. An empirical curve of
growth for the C2 Phillips and CN Red system lines in the spectrum of
HD 56126 yields b = 0.50 (+0.59, -0.23) km/s. CH+ (0,0) emission lines
in the spectrum of the Red Rectangle have been resolved with a FWHM
approx 8.5 pm 0.8 km/s. The circumstellar CN lines of IRAS 08005--2356
are resolved into two separate components with a velocity separation
of Delta v = 5.7 pm 2.0 km/s. The line profiles of CN of HD 235858
have not been resolved.
Title: Spectral Variations of DY Cen
Authors: Giridhar, Sunetra; Rao, N. Kameswara; Lambert, David L.
Bibcode: 1996JApA...17...23G
Altcode:
Two high resolution spectra of the hot RCrB star DY Cen in the red
region are compared. The photospheric absorption lines show a radial
velocity variation of 12 kms-1 between 1989 July and 1992 May. Emission
components to some CII lines present in 1989 are almost entirely
absent in 1992. Nebular forbidden lines of [OI], [NII] and [SII]
appear unchanged from 1989 to 1992
Title: The boron isotope ratio in the interstellar medium
Authors: Federman, S. R.; Lambert, David L.; Cardelli, Jason A.;
Sheffer, Yaron
Bibcode: 1996Natur.381..764F
Altcode:
OBSERVATIONS of the abundances of elements provide insight into
their production and distribution. The production of light elements
(in particular, lithium, beryllium and boron) is dominated by
spallation reactions1, in which cosmic rays break
apart more massive nuclei. Models2,3 suggest that the
11B/10B ratio should be about 2.5, but the
observed ratio in the Solar System is about 4 (refs 4,5). This has
led to the suggestion5 that the pre-solar nebula was
subjected to bombardment by low-energy Galactic cosmic rays, leading
to an overproduction of 11B (ref. 6). Until now, it has
not been possible to measure the 11B/10B ratio
in the interstellar medium, because the lines are very weak. Here we
present a spectroscopic measurement of the 11B/10B
ratio in the interstellar gas lying between the Earth and the star δ
Scorpii, made using the Hubble Space Telescope. Our measured ratio,
3.4+1.3-0.6, is comparable to the meteoritic
value5, but somewhat lower. Further measurements will be
needed to establish whether the ratio reported here is characteristic
of the interstellar medium in general.
Title: Cosmic Ray--induced Chemistry toward Perseus OB2
Authors: Federman, S. R.; Weber, Jody; Lambert, David L.
Bibcode: 1996ApJ...463..181F
Altcode:
New measurements of absorption from interstellar OH at 3078 and
3081 Å are presented for three directions toward the Perseus OB2
association. The measured equivalent widths are in excellent agreement
with previous determinations for ο and ζ Per. Our measurements also
provide stringent upper limits for the line of sight to ζ Per. The
available data on λ3078 toward ο and ζ Per with published equivalent
widths for the (0, 0) band of the D-X electronic transition near 1222
Å are used to determine the oscillator strength for the D-X band;
the value agrees with theory. The first ground-based detections
of absorption from interstellar Ti II λ3072 are discussed in
an appendix. Cosmic-ray ionization followed by ion-molecule
reactions is found to be the primary means of producing OH and HD
in the environment probed by our observations. Our OH data are used
in conjunction with a simple but adequate chemical model to obtain
estimates of the cosmic-ray ionization rate. These estimates then
yield a value for the local interstellar D/H ratio of (1.5±0.5) x
10-5 from available observations of HD that is consistent
with more direct measures. Furthermore, the derived rate allows us to
place limits on the production of NH through gas-phase processes.
Title: High-Resolution Observations of Comet Hyakutake (1996 B2):
O ((1) D)
Authors: Cochran, A. L.; Lambert, D. L.; Cochran, W. D.
Bibcode: 1996AAS...188.6208C
Altcode: 1996BAAS...28..927C
We obtained observations of comet Hyakutake (1996B2) with the 2DCoude
spectrograph on the McDonald Observatory 2.7-m telescope on 30
March 1996 UT. The observations were at a nominal resolving power of
185,000. The spectra included the O((1) D) (6300 Angstroms) emission
line from the comet. The doppler shift was sufficient to separate
clearly the cometary emission line from the telluric oxygen line. The
spectrograph entrance slit subtended 0.34x8.2arcsec on the sky. A ThAr
line had a width of approximately 3 pixels with this setup (FWHM=0.034
Angstroms), while the cometary emission line was clearly resolved at ~
6 pixels. The O((1) D) emission arises from the photodissociation of
H2O, the dominant parent ice. The branching ratio to produce
the oxygen ((1) D) is approximately 7% of the photodissociations. The
production of the oxygen emission line is by prompt emission. Thus,
the width of the 6300 Angstroms O((1) D) line is a direct measure of
the gas outflow velocity of the coma. We will present our observations
of this emission line along with modeling of the data to derive the
outflow velocity. These observations represent a unique opportunity
to study a comet at such high spectral resolving power in order to
accurately measure the line width.
Title: The Boron Isotope Ratio in Interstellar Space
Authors: Federman, S. R.; Lambert, D. L.; Cardelli, J. A.; Sheffer, Y.
Bibcode: 1996AAS...188.0710F
Altcode: 1996BAAS...28Q.833F
We derived the (11) B/(10) B ratio along the sight lines toward
two stars, kappa Ori and delta Sco, from spectra acquired with the
Goddard High Resolution Spectrograph on HST. These interstellar
ratios, which are the first determinations beyond the Solar System,
were based on analysis of absorption from the weak resonance line
of B II at 1362 Angstroms. The interstellar value obtained from our
analysis is similar for the two sight lines -- namely, 4 +/- 1. The
interstellar value agrees with the boron isotope ratio of 4.05 +/-
0.05 for the Solar System. Our findings are consistent with detailed
models of light element nucleosynthesis, which include the effects of
spallation from cosmic ray protons on interstellar CNO, from enhanced
fluxes of low energy C and O nuclei on interstellar protons, and from
neutrinos on (12) C during a supernova explosion. Particular models
predict a constant isotope ratio from the time the Solar System formed
to the present. Furthermore, our analysis of the B II line yielded an
isotope shift of 13.7 +/- 3.5 m Angstroms which agrees with the shift
of 13.3 m Angstroms obtained from large-scale quantal computations.
Title: High-Resolution Observations of Interstellar C 2 Toward
zeta Ophiuchi
Authors: Sembach, Kenneth R.; Danks, Anthony C.; Lambert, David L.
Bibcode: 1996ApJ...460L..61S
Altcode:
We present high-resolution ( lambda / Delta lambda ~ 540,000)
absorption-line observations of two weak C2 lines in the 2--0 band
of the Phillips system in the direction of zeta Ophiuchi. These
high signal-to-noise ratio (S/N ~ 230--380) data were obtained at
the McDonald Observatory 2.7 m telescope using the coude echelle
spectrograph in double-pass mode. The C2 line profiles are resolved
into two components, having a spacing of ~1.14 km s-1, as has been
seen for other molecular species such as CN, CO, and CH. Unlike these
molecules, however, the strengths of the two narrow C2 components
are very similar. We briefly discuss the implications these results
have for understanding the chemical behavior of diatomic molecules in
diffuse interstellar clouds.
Title: The abundance of boron in evolved A- and B-type stars.
Authors: Venn, K. A.; Lambert, D. L.; Lemke, M.
Bibcode: 1996A&A...307..849V
Altcode: 1995astro.ph..8001V
Boron abundances in A- and B-type stars may be a successful way to
track evolutionary effects in these hot stars. The light elements
- Li, Be, and B - are tracers of exposure to temperatures more
moderate than those in which the H-burning CN-cycle operates. Thus,
any exposure of surface stellar layers to deeper layers will affect
these light element abundances. Li and Be are used in this role
in investigations of evolutionary processes in cool stars, but are
not observable in hotter stars. An investigation of boron, however,
is possible through the BII 1362A resonance line. We have gathered
high resolution spectra from the IUE database of A- and B-type
stars near 10Msun_ for which nitrogen abundances have
been determined (by Gies & Lambert and Venn). The BII 1362A
line is blended throughout the temperature range of this program,
requiring spectrum syntheses to recover the boron abundances. For no
star could we synthesize the 1362A region using the meteoritic/solar
boron abundance of logɛ(B)=2.88 (Anders & Grevesse); a lower boron
abundance was necessary which may reflect evolutionary effects (e.g.,
mass loss or mixing near the main-sequence), the natal composition
of the star forming regions, or a systematic error in the analyses
(e.g., non-LTE effects). Regardless of the initial boron abundance, and
despite the possibility of non-LTE effects, it seems clear that boron
is severely depleted in some stars. It may be that the nitrogen and
boron abundances are anticorrelated, as would be expected from mixing
between the H-burning and outer stellar layers. If, as we suspect, a
residue of boron is present in the A-type supergiants, we may exclude
a scenario in which mixing occurs continuously between the surface and
the deep layers operating the CN-cycle. Further exploitation of the
BII 1362A line as an indicator of the evolutionary status of A- and
B-type stars will require a larger stellar sample to be observed with
higher signal-to-noise as attainable with the Hubble Space Telescope.
Title: The Chemical Composition of Field RR Lyrae Stars. I. Iron
and Calcium
Authors: Lambert, David L.; Heath, James E.; Lemke, Michael; Drake,
Jeremy
Bibcode: 1996ApJS..103..183L
Altcode:
Iron and calcium abundances for 18 local field RR Lyrae stars
are obtained from high-resolution spectra taken near minimum
light. Abundance analyses are presented using model atmospheres defined
by published photometry. Analyses were also undertaken using model
atmospheres chosen to fit the excitation equilibrium of Fe I and the
ionization equilibrium of iron. Systematic differences between the two
analyses are discussed. Contributions of non-LTE effects are assessed
quantitatively. The Fe abundance is given most reliably by Fe II lines
analyzed with the photometric models, and the Ca abundance is probably
best given by combining this Fe abundance with the Ca/ Fe ratio given
by the photometric (or the spectroscopic) model atmospheres and the
Ca I and Fe I lines. The Ca/Fe ratio of these RR Lyrae stars follows
the well-known variation of [Ca/Fe] with [Fe/H] found for dwarfs and
giants; most notably, the metal-rich ([Fe/H] ≃ 0) RR Lyrae stars
do not have an anomalous Ca/Fe ratio. New calibrations are presented
of the δS - [Fe/ H] and Mv - [Fe/H] relations. Appendices
provide critical evaluations of published gf-values for the Fe I and
Fe ii lines used in this analysis.
Title: Observational evidence for evolutionary links
Authors: Lambert, D.
Bibcode: 1996ASPC...96..443L
Altcode: 1996hds..conf..443L
No abstract at ADS
Title: Hydrogen-deficient nature of Z UMi
Authors: Goswami, A.; Rao, N. K.; Gonzalez, G.; Lambert, D. L.
Bibcode: 1996ASPC...96...58G
Altcode: 1996hds..conf...58G
No abstract at ADS
Title: Spectral variations of DY CEN
Authors: Giridhar, S.; Rao, N. K.; Lambert, D. L.
Bibcode: 1996ASPC...96..171G
Altcode: 1996hds..conf..171G
No abstract at ADS
Title: Spectrum of S APS at deep minimum
Authors: Rao, N. K.; Goswami, A.; Smith, V. V.; Lambert, D. L.
Bibcode: 1996ASPC...96...59R
Altcode: 1996hds..conf...59R
No abstract at ADS
Title: MV SGR - the emission line spectrum
Authors: Pandey, G.; Rao, N. K.; Lambert, D. L.
Bibcode: 1996ASPC...96..167P
Altcode: 1996hds..conf..167P
No abstract at ADS
Title: The boron isotope ratio in interstellar space.
Authors: Federman, S. R.; Lambert, D. L.; Cardelli, J. A.; Sheffer, Y.
Bibcode: 1996BAAS...28..833F
Altcode:
No abstract at ADS
Title: R CR B pulsation and mass loss
Authors: Rao, N. K.; Lambert, D. L.
Bibcode: 1996ASPC...96...60R
Altcode: 1996hds..conf...60R
No abstract at ADS
Title: Surface composition of the RCB stars - refinement of a few
mere facts
Authors: Rao, N. K.; Lambert, D. L.
Bibcode: 1996ASPC...96...43R
Altcode: 1996hds..conf...43R
No abstract at ADS
Title: A Fine Abundance Analysis of Four Stars in the gamma Per
Cluster- a Cautionary Tale
Authors: Gonzalez, Guillermo; Lambert, David L.
Bibcode: 1996AJ....111..424G
Altcode:
High-resolution spectra of the F5 I β supergiant α Per and three
dwarfs belonging to the α Per cluster were obtained in order to search
for systematic differences in the abundances. Using LTE analyses of
the spectroscopic data we have found that [Fe/H] is about 0.3-0.5
dex smaller for α Per as compared to the dwarfs, which we ascribe
primarily to non-LTE effects in the analysis of α Per. If this result
is confirmed, then it will be necessary to correct LTE abundance
analyses that have been performed on supergiants. Surprisingly, our
estimate for the mean value of [Fe/H] for the dwarfs is 0.17±0.06 dex;
this value is significantly larger than the accepted value for the
cluster, about [Fe/H]=0.04. While we have not been able to determine
the source of this discrepancy, there is some evidence that it is due
to chromospheric activity.
Title: Carbon Isotopes in M71 Giants - CNO, Mixing, and Metallicity
Authors: Briley, M. M.; Smith, V. V.; King, J. R.; Lambert, D. L.
Bibcode: 1995AAS...187.8208B
Altcode: 1995BAAS...27.1405B
High resolution echelle spectra of the 8005 Angstroms CN feature in
five M71 bright red giants are presented. A synthetic spectrum analysis
of the (13) CN feature in this region yields (12}C/({13)) C ratios
considerably lower than those expected from standard first dredge-up
models for all five stars. The low ratios imply substantial exposure
of envelope material to the CN and/or CNO-cycle of H-burning. This is
a well known contradiction between theory and observation in the case
of evolved low mass stars and thought to be the result of some "extra"
mixing process operating after the first dredge-up phase of red giant
evolution. The (12}C/({13)) C ratios are also found to be correlated
with CN band strengths (CN-strong stars having lower (12}C/({13))
C ratios) and anticorrelated with O abundances (O-poor stars having
lower (12}C/({13)) C ratios). This is entirely consistent with the
suggestion that the star-to-star CN band strength variations, and
to a lesser extent O abundance differences, observed in M71 and other
globular cluster bright red giants are associated with H-burning via the
CN(O)-cycle. A comparison with (12}C/({13)) C ratios observed in more
metal-poor cluster giants reveals a trend of decreasing (12}C/({13))
C ratios with decreasing metallicity. This suggests a metallicity
dependence to the efficiency of any underlying mixing mechanism and a
natural explanation for the smaller star-to-star variations in [O/Fe]
and [Na/Fe] seen in M71 by Sneden et al. (1994, AJ, 107, 1773) when
compared to its more metal-poor counterparts (M3, M13, M10, etc.). One
asymptotic giant branch candidate is included in the present sample,
which exhibits both weak-CN band strength and a low (12}C/({13))
C ratio. This work was partially supported by a grant from the Fund
for Astrophysical Research.
Title: The Chemical Composition of Omega Centauri.I.Heavy-Element
Abundances of Seven Warm Giants
Authors: Smith, Verne V.; Cunha, Katia; Lambert, David L.
Bibcode: 1995AJ....110.2827S
Altcode:
We derive abundances for a range of elements (O, Ca, Sc, Ti, Fe,
Ni, Y, Ba, La, and Eu) in seven giant stars in the massive Galactic
globular cluster ω Centauri. These giant stars have similar stellar
parameters (Teff=4000-4500 K and log g =0.5-t.5) but
they sample metallicities from [Fe/H]= -2.2 up to - t.3. As in other
metal-poor populations, we find that the α elements (O, Ca, and Ti) are
overabundant relative to Fe, by +0.2-0.3 dex. The Ni/Fe and Sc/Fe ratios
are indistinguishable from solar. As found by previous investigators,
the s-process elements (Y, Ba, and La) show a dramatic increase in
abundance with increasing [Fe/H]: the slope of the trend of [s/Fe]
with [Fe/H] is approximately 3. For the first time, Eu abundances
are determined in a number of ω Cen stars. We find a remarkable
deficiency in [Eu/Fe] in most of the ω Cen stars when compared to
field stars. Although Eu is usually identified with the r process,
we argue that the Eu abundances in ω Cen can be explained largely
as s process in origin. The implications for this type of chemical
evolution in ω Cen, relative to most of the metal-poor populations
studied previously, are discussed.
Title: The r-Process Element Europium in Galactic Disk F and G
Dwarf Stars
Authors: Woolf, Vincent M.; Tomkin, Jocelyn; Lambert, David L.
Bibcode: 1995ApJ...453..660W
Altcode:
Abundances of the r-process element Eu have been derived for 81 nearby
field F and G disk dwarfs. Galactic orbital properties and abundances
of 15 other elements have previously been derived for these stars
by Edvardsson et al. The average logarithmic abundance ratio [Eu/Fe]
increases from -0.1 to 0.4 with decreasing Fe abundance over the range
-0.9 ≤ [Fe/H] ≤ +0.3. Scatter in [Eu/Fe] at a given [Fe/H] is
consistent with observational and analysis uncertainties in [Eu/Fe]. The Eu abundances from this study and the published Ba abundances show
[Eu/Ba] to increase with stellar age. This is interpreted as indicating
a change in the relative number of r-process and s-process sites
over the history of the Galaxy or a change in the efficiency of the
sites. Thus we cannot assume that the ratio of r-process to s-process
contributions to heavy element abundances has remained constant, even
recently. The Th/Nd stellar chronometer depends on this ratio being
constant; thus, the variation in [Eu/Ba] reported here may indicate
that the Th/Nd chronometer needs revision. The variation of [Eu/Fe]
with [Fe/H] is found to most closely resemble the variations of oxygen
and the α elements which are thought to be produced primarily in
Type II supernovae. When compared to theoretical models for Galactic
r-process nucleosynthesis, the abundance trend found for the stars we
have studied corresponds most closely to models in which the r-process
site is Type II supernovae. Although this correspondence has previously
been reported, in the metallicity range observed in this study the
Eu abundances reported here correlate more closely to the predictions
based on Type II supernovae models than previous data have.
Title: Chemical Evolution of the Orion Association. III. The Lithium
Abundance of F and G Stars
Authors: Cunha, Katia; Smith, Verne V.; Lambert, David L.
Bibcode: 1995ApJ...452..634C
Altcode:
We derive lithium abundances for a sample of 25 late F to early G dwarfs
in the direction of the Orion association from spectra obtained with
the McDonald Observatory's 2.1 m telescope plus a Cassegrain cross-
dispersed echelle spectrometer at a spectral resolution of 60,000. Iron
abundances are also derived for the slowly rotating stars. A kinematical
discussion, combined with information on rotation and X-ray emission
for the stars, led us to conclude that 10 stars in our sample are
members of the Ic and Id subgroups of Orion, while two are probable
members of the Ib subgroup, with the remaining stars being field stars
in the direction of Orion. The Li abundances obtained for the seven
members of the Ic subgroup with υ sin i > 20 km s-1
show a small scatter, comparable to our uncertainties in the abundance
determinations themselves. The mean non-LTE Li abundance for the
rapidly rotating Ic members is log ɛ(Li) = 3.2±0.1 very close to the
solar system meteoritic value of 3.3. If the Orion interstellar gas
is representative of local Galactic gas, there is apparently little
evidence of an increase in the Li abundance over the last 5 Gyr.
Title: In situ synthesis of ^6^Li by galactic cosmic rays in halo
stars.
Authors: Lambert, D. L.
Bibcode: 1995A&A...301..478L
Altcode:
An evaluation is made of the proposal that galactic cosmic rays
decelerated in envelopes of halo stars provide for nucleosynthesis
of ^6^Li and other light nuclides at observable levels. It is argued
that while this mode of nucleosynthesis is unimportant for Be and
B, it may just possibly provide for observable amounts of ^6^Li in
extremely metal-poor stars near the main sequence turnoff.
Title: The Chemical Composition of Red Giants. IV. The Neutron
Density at the s-Process Site
Authors: Lambert, David L.; Smith, Verne V.; Busso, Maurizio; Gallino,
Roberto; Straniero, Oscar
Bibcode: 1995ApJ...450..302L
Altcode:
Rubidium abundances are determined from the Rb 1 7800 A line via
synthetic spectra for a sample of M, MS, and S giants. The Rb abundance
increases with increasing s-process enrichment. A ratio Rb/Sr ≃
0.05 is derived for the s-processed material from the He-burning
shell. Thanks to the branch in the s-process path at 85Kr
the Rb/Sr ratio may be used to determine the neutron density at the
time of s-processing. The derived ratio is consistent with predicted
neutron densities for operation of the s-process during the interpulse
intervals in low-mass asymptotic giant branch (AGB) stars but clearly
inconsistent with much higher neutron densities predicted for the
running of the s-process in the He-shell thermal pulses of intermediate
mass AGB stars and probably also of low-mass AGB stars. Zirconium
isotopic abundances are determined from ZrO bandheads near 6925 Å
via synthetic spectra for a sample of S stars. No evidence is found
for the isotope 96Zr whose synthesis is controlled by the
branch in the s-process path at 95Zr. This observation
shows that the observed stars are not intermediate mass stars with
massive (MC ≳ 1 Msun) cores. The absence of
96Zr sets an upper limit on the neutron density at the
s-process site which is higher than and, therefore, consistent with
the limit set by the Rb abundances in related stars.
Title: Boron Abundances in Orion and Boron Production in Type II
Supernovae
Authors: Lambert, David
Bibcode: 1995hst..prop.6077L
Altcode: 1995hst..prop.2550L
The Orion OB1 association comprises four subgroups of differing
ages. The youngest stars show higher oxygen abundances than the oldest
stars. This enrichment has been shown to be due to contamination of the
natal gas by oxygen- rich ejecta from supernovae. The boron abundance
will be derived from the B II 1362 Angstrom line for three stars in the
Orion OB1 association having different oxygen abundances. A positive
correlation of the boron and oxygen abundance will, if present,
indicate that boron, as ^11B, is synthesized by the supernovae held
responsible for the oxygen abundances. This will be the first direct
evidence for ^11B production by supernovae.
Title: High-Resolution Spectroscopy with HST - Final GTO Observations
of Stars.
Authors: Lambert, David
Bibcode: 1995hst..prop.6289L
Altcode:
This proposal concludes GTO observations by D. L. Lambert using the
GHRS. Four problems are addressed. (1) The ultraviolet spectrum of
Eps Aur will be obtained from 1190-1450A with G140L. IUE observations
show that in this interval the spectrum is emitted by the enigmatic
secondary and not the A-type supergiant. These observations will provide
the first detailed spectrum of the secondary. (2) Two high galactic
latitude B stars will be observed at 1360A with G160M to obtain the
boron abundance. These stars are too far from the galactic plane to
have been born in the plane and, therefore, the boron abundance will
refer to their sites of formation, presumably gas clouds far from the
plane. (3) Theta Uma will be observed at 2090A with ECH-B in an attempt
to obtain the 10B/11B isotopic ratio from the B I 2089A resonance
line. (4) Interstellar CO bands in Zeta Oph will be observed with
ECH-A to high S/N in order to define the line profiles, to search for
weak high rotational lines and to confirm the isotopic ratios derived
previously from G160M spectra.
Title: A Very High Resolution Survey of Interstellar CH and CH +
Authors: Crane, Philippe; Lambert, David L.; Sheffer, Yaron
Bibcode: 1995ApJS...99..107C
Altcode:
We report the results of a survey at very high spectral resolution
of interstellar CH and CH+ in diffuse clouds toward 20
bright stars, and medium-resolution observations to determine radial
velocities. The high-resolution observations [(λ/δλ) ∼ 500,000]
resolve all the CH+ and all the CH lines. Most of the CH
lines show multiple overlapping components at this resolution. It
is often possible to associate a weak broad CH component with a
CH+ component of similar radial velocity and width. The
implications of these results for CH and CH+ formation
scenarios are discussed.
Title: Nucleosynthesis and Mixing on the Asymptotic Giant
Branch. II. Carbon and Barium Stars in the Galactic Disk
Authors: Busso, M.; Lambert, D. L.; Beglio, L.; Gallino, R.; Raiteri,
C. M.; Smith, V. V.
Bibcode: 1995ApJ...446..775B
Altcode:
We study the role played by nucleosynthesis processes in thermal
pulses and by mixing episodes (the third dredge-up) in determining
the abundances of intrinsic and extrinsic asymptotic giant branch
(AGB) stars. This is done by comparing results from AGB models
with observations of s-process and CNO nuclei in C stars (N-type)
and in various classes of Ba stars (Ba dwarfs, CH subgiants, and Ba
II giants) with metallicities typical of the disk population. The
complementary information coming from abundances of Li and Mg isotopes
is also discussed. According to a generally accepted scenario, the
main neutron source at the origin of s-process nucleosynthesis is
assumed to be the reaction 13C(α, n)16O; a
minor contribution derives also from the marginal activation of the
reaction 22Ne(α, n)25Mg at the end of each
flash. Making use of the latest neutron- capture cross sections and
parameterizing the amount of 13C burnt per pulse, we compute
the nucleosynthesis occurring in the He shell and the dredge-up of
material to the surface according to recent AGB models. Using envelope
abundances after the first dredge-up derived from observations of
first-ascent red giants and ad opting standard prescriptions for mass
loss, we succeed in fitting the photospheric compositions of C and
Ba stars within their uncertainties. Our results confirm that C stars
(N-type) are evolutionary descendants of normal (Tc-rich) S stars and
are characterized by the same spread in mean neutron exposures (0.2-0.4
mbarn-1). As for the binary Ba stars, their abundances
are compatible with the from an AGB primary component to a dwarf or
giant secondary. We show that several constraints, including the Mg
isotope ratios and the neutron density derived from the Rb/Sr ratio,
require that s-processing occur in low-mass AGB stars but exclude the
possibility that barium stars derive from primaries of intermediate
mass (3 ≤ M/Msun ≤ 8) efficiently burning the neutron
source 22Ne. The s-process enriched binary Ba giants show
mean neutron exposures covering a wider range, reaching higher values
(up to 1.0 mbarn-1) than for normal (single) C stars. An
inverse correlation of the mean neutron exposure with metallicity is
also present. Hence, the higher efficiency in s-processing shown by
several Ba stars is interpreted as an indication that the metallicity
range they cover is larger than for intrinsic AGB stars commonly
observed. In fact, if the amount of primary 13C burnt
is roughly constant for the studied stars, their effectiveness in
producing neutron-rich nuclei must increase (nonlinearly) toward
lower metal contents. In this scenario the exponential distributions
of neutron exposures provided by low-mass AGB stars can account well
for the s-process abundances observed in Population I AGB stars,
with no need to invoke strong single neutron exposures, as sometimes
suggested in the past.
Title: Vibrationally Excited H 2, HCl, and NO + in the Diffuse Clouds
toward zeta Ophiuchi
Authors: Federman, S. R.; Cardell, Jason A.; van Dishoeck, Ewine F.;
Lambert, David L.; Black, J. H.
Bibcode: 1995ApJ...445..325F
Altcode:
Absorption lines from vibrationally excited H2 and from HCl were
detected in the ultraviolet spectrum of Zeta Oph with the Hubble
Space Telescope (HST). Improved upper limits on NO(+) absorption were
obtained as well. The data were analyzed with an updated version of
a chemical model for diffuse clouds (van Dishoeck & Black 1986)
as a guide to understanding this gaseous environment. The comparisons
suggest that the flux of ultraviolet radiation impinging on the cloud
surface is approximately 1-2 times the average interstellar radiation
field, which is lower than once believed.
Title: The discovery of high-velocity flares in NV and the detection
of carbon in the double degenerate binary GP COM
Authors: Marsh, T. R.; Wood, Janet H.; Horne, Keith; Lambert, D.
Bibcode: 1995MNRAS.274..452M
Altcode:
We present time-resolved ultraviolet spectra of the ultrashort-period
binary GP Com taken with the Hubble Space Telescope. During
our observations GP Com displayed spectacular variability in the
dominant NV emission line which showed three large flares in 13h of
observations. We isolate the flare spectrum which reveals CIV emission
at a level of 0.094 times the NV flux; this is the first detection of
carbon in GP Com. We obtain a 3sigma upper limit of 0.015 upon the
ratio of SiIV to NV emission, supporting evidence from optical data
that heavy elements are under-abundant relative to nitrogen in GP
Com. There are many other features in the spectrum that we have been
unable to identify. We suggest that the flare emission could come
from irradiation of the accretion disc in GP Com or from variable
mass loss in a wind. Subtraction of the flare spectrum followed by
phase-folding on the 46-min orbital period of GP Com reveals the
ultraviolet counterpart to the `S'-wave known from optical data. The
`S'-wave is seen in NV, CIV, NI 1493, and a line at 1335A, which may
be CII 1335.
Title: Carbon in Field F and G Disk Dwarfs
Authors: Tomkin, Jocelyn; Woolf, Vincent M.; Lambert, David L.;
Lemke, Michael
Bibcode: 1995AJ....109.2204T
Altcode:
We have determined C abundances from observations of the 7100 Å C I
lines in 105 field disk F and U main-sequence stars. We use the results
to investigate the enrichment of C in the Galactic disk over the range
-0.8≤[Fe/H]≤+0.2. A moderate enrichment of C in metal-deficient
stars, such that [C/Fe]∼+0.20±0.05 at [Fe/H]=-0.8, is found. This
is consistent with the results of earlier investigations based on
more limited samples of stars. With the aid of ages and galactocentric
distances for the same stars determined by Edvardsson et al. (1993),
we examine the relation between stellar age and C abundance. For
stars in the same range of galactocentric distance, we find only a
weak correlation between the stars' C abundances and their ages. The
moderate enrichment of C in metal-deficient disk stars is qualitatively
similar to that seen for O and the a elements. We compare the behavior
of the stellar [C/Fe], [0/Fe], and [a/Fe] abundances as functions of
metallicity (using O and α element abundances from Edvardsson et al.),
with the predictions of Timmes et al. `s [ApJS (in press) (1995)]
new models of Galactic chemical evolution. The comparison confirms
Timmes et al. `s conclusion that, with regard to the variation of these
abundances with metallicity, the best agreement between observation and
theory is provided by models in which the iron yields of II supernovae
are reduced by a factor of 2 below the (uncertain) value adopted for
their standard models. A similar comparison of the [C/O] and [C/α]
abundances, which are much less sensitive to the Type II supernovae
iron yields, as functions of metallicity, shows substantial agreement
of observation and theory.
Title: The Demise of the Metal Poor Disk?: Spectroscopic Iron
Abundances
Authors: Ryan, Sean G.; Lambert, David L.
Bibcode: 1995AJ....109.2068R
Altcode:
High resolution spectra of metal-poor disk giants initially believed to
have [Fe/II]<-1.0 have yielded generally higher abundances than had
been claimed on the basis of DDO photometry. Although good agreement
has been found for giants identified chemically and kinematically
with the halo, most of the stars in our sample that were previously
identified with the metal-poor disk are found to have abundances
[Fe/H]>-1.0, typical of thick disk stars which their kinematics
also match. Although we cannot convincingly explain the errors in
the DDO abundances, we conclude that the disk does not contribute as
significantly to the stellar population of the galaxy at [Fe/H]<-1.0
as might have been thought.
Title: The High-Resolution Cross-Dispersed Echelle White Pupil
Spectrometer of the McDonald Observatory 2.7-m Telescope
Authors: Tull, Robert G.; MacQueen, Phillip J.; Sneden, Christopher;
Lambert, David L.
Bibcode: 1995PASP..107..251T
Altcode:
A new high-resolution cross-dispersed echelle spectrometer has
been installed at the coude focus of the McDonald Observatory 2.7-m
telescope. Its primary goal was to simultaneously gather spectra over
as much of the spectral range 3400A to 1 micron as practical, at a
resolution R = lambda/delta-lambda =~ 60,000 with signal-to-noise ratio
of ~100 for stars down to magnitude 11, using 1-hour exposures. In the
instrument as built, two exposures are all that are needed to cover
the full range. Featuring a white-pupil design, fused silica prism
ross disperser, and folded Schmidt camera with a Tektronix 2048 X 2048
CCD used at either of two foci, it has been in regularly-scheduled
operation since April 1992. Design details and performance will be
described. (SECTION: Astronomical Instrumentation)
Title: A Survey of Lithium in the Red Giants of the Magellanic Clouds
Authors: Smith, Verne V.; Plez, Bertrand; Lambert, David L.; Lubowich,
D. A.
Bibcode: 1995ApJ...441..735S
Altcode:
A spectroscopic search for the Li 1 6707 A resonance line has been
carried out in 112 red giants from both the Small and Large Magellanic
Clouds. The spectra are a mixture of high- (R = λ/{DELTA}λ = 18,000)
and low-resolution (R = 4000) data, and the stars surveyed consist
of spectral types M, S, and C. Most of these stars have absolute
bolometric magnitude, M_bol_, determinations available from various
published investigations. The Li I line is detected in 35 of these
red giants (29 S stars and six C stars). All stars with a measurable
Li I feature are asymptotic giant branch (AGB) stars with the majority
(26) being luminous S stars within the narrow luminosity range of -7.2
<~M_bol_ <~ 6.0(M_bol_ = -6.52 +/- 0.38 in this subset of the
stars). Abundance estimates of lithium in these stars fall in the range
of log ɛ(Li)~1.0-4.0. The presence of Li in these highly evolved AGB
stars is ascribed to hot-bottom convective envelope (HBCE) burning and
a comparison of the Li abundances derived here with published models
of HBCE shows reasonably good agreement.
Title: Emission Line Spectrum of the Hot R-Coronae Type Star
Mv-Sagittarius
Authors: Pandey, G.; Rao, N. K.; Lambert, D. L.
Bibcode: 1995JApAS..16..327P
Altcode:
No abstract at ADS
Title: Hubble Space Telescope Observations of C 2 Molecules in
Diffuse Interstellar Clouds
Authors: Lambert, David L.; Sheffer, Yaron; Federman, S. R.
Bibcode: 1995ApJ...438..740L
Altcode:
Interstellar C2 F-X (1342 A) and D-X (2313 A) bands in the spectrum of
zeta Oph were detected using the Goddard High-Resolution Spectrograph
(GHRS) on the Hubble Space Telescope (HST). The total C2 column density
is (1.79 +/- 0.06) 1013/sq cm for an adopted f-value of
0.0545 for the 2313 A band of the Mulliken (D-X) system. Relative
f-values for the 0-0 F-X, 0-0 D-X, and 2-0 A-X (Phillips) bands
are derived by combining ultraviolet and near-infrared spectra:
f00FX/f00DX = 1.83 +/- 0.18
and f20AX/f00DX = 0.0226 +/-
0.0029. For the Mulliken system, lines are detected up to a rotational
level J double prime = 24. The relative populations along the rotational
ladder are shown to be consistent with the physical and environmental
conditions suggested by other diagnostics. Interstellar C2 molecules
were detected towards zeta Per (N(C2) = (0.80 +/- 0.23) 1013)
but not towards Beta1, pi, and omega1 Sco(N(C2)
less than or equal to 0.17 x 1013/sq cm.
Title: Line asymmetries in the metal-poor star HD 140283
Authors: Allende Prieto, C.; García López, R. J.; Lambert, D. L.;
Gustafsson, B.
Bibcode: 1995IAUS..176P.107A
Altcode:
No abstract at ADS
Title: Lithium abundances for a sample of F and G stars in the
Orion association.
Authors: Cunha, K.; Smith, V. V.; Lambert, D. L.
Bibcode: 1995MmSAI..66..371C
Altcode:
No abstract at ADS
Title: The Chemical Composition of the RV Tauri Variable IW Carinae
Authors: Giridhar, Sunetra; Rao, N. Kameswara; Lambert, David L.
Bibcode: 1994ApJ...437..476G
Altcode:
Analysis of the RV Tauri star IW Carinae shows a photospheric
composition unlike that reported previously for a few other RV Tau
stars but resembling that of certain post-asymptotic giant branch
stars (post-AGB) stars. IW Car is carbon-rich: several lines of
C I are detected and suggest C/O greater than or = 1. The star is
generally metal poor. The composition of (Fe/H) approximately -1.0,
(Ca/H) approximately = -1.9 but (Zn/H) approximately 0.0 reflects that
of gas of solar metallicity from which easily condensable elements
have condensed into dust grains and been removed from the star's
photosphere. Separation of gas and dust may have occurred in the
present or recent stellar wind of IW Car. These characteristics also
suggest that RV Tauri stars are post-AGB objects.
Title: Sodium in Weak G-Band Giants
Authors: Drake, Jeremy J.; Lambert, David L.
Bibcode: 1994ApJ...435..797D
Altcode:
Sodium abundances have been determined for eight weak G-band giants
whose atmospheres are greatly enriched with products of the CN-cycling
H-burning reactions. Systematic errors are minimized by comparing
the weak G-band giants to a sample of similar but normal giants. If,
further, Ca is selected as a reference element, model atmosphere-related
errors should largely be removed. For the weak-G-band stars (Na/Ca) =
0.16 +/- 0.01, which is just possibly greater than the result (Na/Ca) =
0.10 /- 0.03 from the normal giants. This result demonstrates that the
atmospheres of the weak G-band giants are not seriously contaminated
with products of ON cycling.
Title: Boron in the extreme Population II star HD 140283 and the
production of light elements in the Early Galaxy
Authors: Edvardsson, B.; Gustafsson, B.; Johansson, S. G.; Kiselman,
D.; Lambert, D. L.; Nissen, P. E.; Gilmore, G.
Bibcode: 1994A&A...290..176E
Altcode: 1994astro.ph..3002E
Using observations of the 2496.7A Bi line with the HST GHRS at a
nominal resolving power of 90,000, we have found the abundance of
boron of HD140283 to be logɛ_B_(=12+log(N_B_/N_H_))=0.34+/-0.20. This
result is found when a significant non-LTE effect in the formation of
the Bi line is taken into account. The resulting N_B_/N_Be_ ratio is
about 17 (in the range 9-34), which is in very good agreement with
what is expected from spallation by cosmic rays. We conclude that
this origin of Be and B in the Early Galaxy is the most probable of
recently suggested formation mechanisms.
Title: Intersystem Transitions of Interstellar Carbon Monoxide toward
zeta Ophiuchi
Authors: Federman, S. R.; Cardelli, Jason A.; Sheffer, Yaron; Lambert,
David L.; Morton, D. C.
Bibcode: 1994ApJ...432L.139F
Altcode:
Absorption from seven intersystem (triplet-singlet) transitions of
interstellar (12)CO were detected in ultraviolet spectra of zeta
Oph. The observed equivalent widths are approximately consistent with
the transitions' predicted f-values and the (12) CO column density
derived from the weakest of the observed A-X bands. These unsaturated
intersystem transitions provide the opportunity to measure the (12)CO
column density for heavily reddened (dense) sight lines. Laboratory
measurements of oscillator strengths more precise than available ones
will be needed to derive accurate column densities.
Title: The lithium isotope ratio in metal-poor stars.
Authors: Nissen, P. E.; Lambert, D. L.; Smith, V. V.
Bibcode: 1994Msngr..76...36N
Altcode:
In the present article the scientific reasons for studying the lithium
isotope ratio in stars are briefly reviewed, and the reduction and
analysis of recent observations of the Li I 6707.8 Aresonance line
in spectra of metal-poor stars are discussed in some detail. The aim
and prospects of obtaining similar observations for fainter and more
interesting stars with the ESO VLT are also touched upon.
Title: Chemical Evolution of the Orion Association. II. The Carbon,
Nitrogen, Oxygen, Silicon, and Iron Abundances of Main-Sequence
B Stars
Authors: Cunha, Katia; Lambert, David L.
Bibcode: 1994ApJ...426..170C
Altcode:
Carbon, nitrogen, oxygen, and silicon abundances are presented from
local thermodynamic equilibrium (LTE) and non-LTE analyses of C II,
N II, and Si III lines in the spectra of 18 main-sequence B stars
from the four subgroups comprising the Orion association. Iron LTE
abundances from Fe III lines are also presented. The C, N, and Fe
abundances show no significant variations across the subgroups, but the
O and Si abundances are found to be higher for some of the youngest
stars that are collocated on the sky and at a common distance. The O
and Si abundances are correlated. Although such a correlation may in
part reflect measurement errors, it is suggested that the enrichment
of young stars in O and Si arose because they were formed from regions
of the molecular cloud enriched with the ejecta of Type II supernovae,
which are predicted to be rich in O and Si but not in C and N. With
the exception of one star, we see no evidence for CN-cycled material on
the stars' surfaces. The stellar abundances agree, within the expected
uncertainties, with published nebular analyses that show Orion to be
slightly underabundant in C, N, and O relative to the Sun.
Title: Boron Abundances in Early Type Stars
Authors: Venn, K. A.; Lambert, D. L.; Lemke, M.
Bibcode: 1994AAS...184.3115V
Altcode: 1994BAAS...26..910V
Boron is a trace element in hot stars which can be observed from the B
II resonance line at 1362 Angstroms. We have used IUE archival spectra
to examine the B abundances in early type stars. The abundances of
boron in A and B-type stars were originally calculated by Boesgaard
& Heacox (1978 ApJ 226, 888) from Copernicus spectra as a method of
testing the predictions of galactic cosmic ray spallation reactions. We
are primarily interested in the effects of stellar evolution on
B. Boesgaard & Heacox do not report any relationship between
evolutionary state and the B abundance, however there are very few
evolved stars in their sample and the few studied have very large
uncertainties in B. Boron is destroyed by protons at temperatures
above about 4 million K, thus the stellar surface B abundance is a
sensitive monitor of evolutionary processes, such as mass loss and
mixing, which would lead to large losses in the surface B. Gies &
Lambert (1992 ApJ 387, 673) found evidence of CNO-cycled gas in some
slightly evolved B-type stars, suggesting that some mixing may occur
in massive stars near the main-sequence. We examine the B abundances
in these stars for evidence of a boron-nitrogen relationship.
Title: Chemical Transitions for Interstellar C 2 and CN in Cloud
Envelopes
Authors: Federman, S. R.; Strom, C. J.; Lambert, D. L.; Cardelli,
Jason A.; Smith, V. V.; Joseph, C. L.
Bibcode: 1994ApJ...424..772F
Altcode:
Observations were made of absorption from CH, C2, and CN toward
moderately reddened stars in Sco, OB2, Ceo OB3, and Taurus/Auriga. For
these directions, most of the reddening is associated with a
single cloud complex, for example, the rho Ophiuchus molecular
cloud, and as a result, the observations probe moderately dense
material. When combined with avaliable data for nearby directions,
the survey provides the basis for a comprehensive analysis of the
chemistry for these species. The chemical transitions affecting C2
and CN in cloud envelopes were analyzed. The depth into a cloud at
which a transition takes place was characterized by tauuv,
the grain optical depth at 1000 A. One transition at tauuv
approx. = 2, which arises from, the conversion of C(+) into CO, affects
the chemistries for both molecules because of the key role this ion
plays. A second one involving production terms in the CN chemistry
occurs at tauuv of approx. = 3; neutral reactions which C2
and CH is more important at larger values for tauuv. The
transition from photodissociation to chemical destruction takes place
at tauuv approx. = 4.5 for C2 and CN. The observational
data for stars in Sco OB2, Cep OB3, and Taurus/Auriga were studied
with chemical rate equations containing the most important production
and destruction mechanisms. Because the sample of stars in Sco OB2
includes sight lines with Av ranging from 1-4 mag, sight
lines dominated by photochemistry could be analyzed separately from
those controlled by gas-phase destruction. The analysis yielded values
for two poorly known rate constants for reactions involved in the
production of CN; the reactions are C2 + N yields CN + C and C(+) +
NH yields all products. The other directions were analyzed with the
inferred values. The predicted column densities for C2 and CN agree
with the observed values to better than 50%, and in most instances
20%. When combining the estimates for density and temperature derived
from chemical modeling and molecular excitation for a specific cloud,
such as the rho Ophiuchus molecular cloud, the portion of the cloud
envelope probed by C2 and CN absorption was found to be in pressure
equilibrium.
Title: Isotopic Carbon Ratios among M71 Bright Red Giants
Authors: Briley, Michael M.; Smith, Verne V.; Lambert, David L.
Bibcode: 1994ApJ...424L.119B
Altcode:
We present high signal-to-noise, high-resolution spectra of 8005 A
CN-12 and CN-13 lines in two groups of CN strong/weak M71 (C1951+186,
NGC 6838) bright giants chosen for their different (O/Fe) and (Na/Fe)
abundances, as well as CN band strengths. These abundance variations in
M71, as well as similar star-to-star differences in (O/Fe) and (Na/Fe)
seen in other clusters (e.g., M92, M15, M13, M3, and M5), have been
suggested to result from differing degrees of deep mixing. Our analysis
of the present observations with synthetic spectra yields C-12/C-13
ratios ranging from 4.9 to 8.9; the CN-strong/O-poor stars exhibit
slightly lower ratios. This C-12/C-13 difference between the two groups
may conceivably be the result of differing degrees of the dredge-up.
Title: Fluorescent K i 7699 Angstrom Emission from Circumstellar
Shells of Red Giants: Evidence for Highly Asymmetric Winds
Authors: Plez, Bertrand; Lambert, David L.
Bibcode: 1994ApJ...425L.101P
Altcode:
Potassium atoms in the circumstellar shells of R Aql, V Hya, g Her,
and R Leo are detected through fluorescent emission at 7699 A at
angular distances of up to several seconds of arc from the star. As
traced by the 7699 A emission, the shells are highly asymmetric.
Title: High-Resolution Spectroscopy of V1853 Cygni (LS II +34 degrees
26): Birth of a Planetary Nebula?
Authors: Smith, Verne V.; Lambert, David L.
Bibcode: 1994ApJ...424L.123S
Altcode:
High-resolution optical spectra are discussed for the high-latitude
B-supergiant V1853 Cyg (LS II + 34 deg 26), which has been
identified recently as a hot post-asymptotic giant branch (AGB)
star with far-infrared Infrared Astronomical Satellite (IRAS) colors
similar to those of dusty planetary nebulae. Spectra obtained on
eight nights between 1993 August and November reveal strong emission
lines of H-alpha, beta, and gamma, as well as a variety of profiles
(absorption, emission, P Cygni) for the He I lines. A photospheric
spectrum of absorption lines, fairly typical of B1-2 supergiants, is
present, but the lines are asymmetric and their shapes and equivalent
widths vary significantly on a night-to-night basis. The velocity of
the absorption lines varies by approximately 40 km/s. Emission lines
from permitted (C II, N II, Si II, and Fe III) and forbidden (N II),
(O I), (S II), and (Fe II) transitions are visible at a constant radial
velocity over the observing interval. This object may be in the process
of becoming a planetary nebula.
Title: The Carbon Underabundance of the Secondary of V356 Sagittarii
Authors: Tomkin, Jocelyn; Lambert, David L.
Bibcode: 1994PASP..106..365T
Altcode:
We report observations of visual and near-infrared C I, N I, and O I
lines in the A2 II secondary of V356 Sgr made during a total eclipse
of the primary. We confirm the weakness of the secondary's C I lines
first seen in ultraviolet observations. Based on a marginal detection
of the 9100A C I lines we estimate that relative to a standard star
(HR 7145; A0 II) of similar spectral type the [C/Fe] abundance ratio of
the secondary is -1.7 +/- 0.3 dex. The secondary is not significantly
underabundant in N or O. We interpret the C poorness of the secondary
as a result of mass transfer, which has removed its outer layers and
exposed its CN-processed interior. (SECTION: Stars)
Title: The R Coronae Borealis stars - a few mere facts.
Authors: Lambert, David L.; Rao, N. Kameswara
Bibcode: 1994JApA...15...47L
Altcode:
This review presents a selection of recent highlights of observations of
R Coronae Borealis (RCB) variables. Emphasis is placed on an abundance
analysis of a complete sample (18 stars) of the warm galactic RCBs. It
is shown that 14 of the 18 have very similar compositions: the iron
mass fraction ranges about a factor of 3 around the solar value
(assuming C/He=3%) but abundance ratios X/Fe for elements from Na to
Ba show little variation. By contrast, the other 4 stars are deficient
in iron but not in Na, Si, S and some other elements. With for example,
(Si/Fe) approximately equal to 2, the quartet is indeed 'peculiar'. One
of the quartet, V854 Cen shows depletions of elements (other than CNO)
similar to the depletions seen in interstellar medium corresponding
to average log n (Htot)=1.5. Scenarios for creating RCB
from normal single and double stars are summarized.
Title: V356 Sagittarii - Mass Transfer for the Masses
Authors: Tomkin, J.; Lambert, D. L.
Bibcode: 1994ASPC...56..397T
Altcode: 1994ibs..conf..397T
No abstract at ADS
Title: Chemical abundances in the Orion association.
Authors: Cunha, K.; Lambert, D. L.
Bibcode: 1994BAAS...26R.795C
Altcode:
No abstract at ADS
Title: The McDonald 2.7-in Echelle Spectrometer
Authors: Tull, Robert G.; MacQueen, Phillip; Sneden, Chris; Lambert,
David L.
Bibcode: 1994ASPC...55..148T
Altcode: 1994oaem.conf..148T
No abstract at ADS
Title: Interstellar Carbon Monoxide toward zeta Ophiuchi
Authors: Lambert, David L.; Sheffer, Yaron; Gilliland, Ronald L.;
Federman, S. R.
Bibcode: 1994ApJ...420..756L
Altcode:
Interstellar CO A-X bands in the spectrum of zeta Oph were recorded
at high Sound-to-Noise (S/N) with grating G160M of the Goddard High
Resolution Spectrograph on the Hubble Space Telescope. Isotopic
fractionation of CO is severe: CO-12/CO-13 = 167, C(16)O/C(18)O
approximately equal to 1550 and C(16)O/C(17)O is greater than 5900 are
found where C-12/C-13 = 70, O-16/O-18 = 500, and O-16.O-17 = 2600 are
observed or expected. Standard models of the zeta Oph cloud predict
CO-12/CO-13 is less than or approximately 70. The higher observed
ratio suggests that photodissociation of CO, not the isotopic charge
exchange reaction ((13)C(+) + CO reversible reaction (12)C(+) +
(13)(CO), is the dominant influence on the CO-12/CO-13 ratio.
Title: Report of IAU Commission 29: Stellar spectra (Spectres
stellaires).
Authors: Lambert, D. L.
Bibcode: 1994IAUTA..22..305L
Altcode:
No abstract at ADS
Title: Stellar Photospheres and Molecules - a View from the Bridge
Authors: Lambert, David L.
Bibcode: 1994LNP...428....1L
Altcode: 1994mse..conf....1L; 1994IAUCo.146....1L
No abstract at ADS
Title: The Nature of Interstellar Cloud Envelopes -- Physical
Conditions and Structure
Authors: Lambert, David
Bibcode: 1994hst..prop.5389L
Altcode: 1994hst..prop.1835L
GHRS/G160M spectra of interstellar CO bands and atomic lines toward
two stars will be analyzed to give the column density ratio 12C16O/
13C16O and excitation temperatures for CO and C I. The ratio of column
densities will not, in general, equal the 'true' 12C/13C ratio provided
by optical spectroscopy of the CH+ molecular ion. The fractionation
of CO is driven in opposite directions by isotopic charge exchange
and selective photodissociation. The ratio 12C16O/ 13C16O for a known
12C/13C provides novel information on the physical conditions in a
diffuse cloud. These conditions are also obtained from analysis of
excitation. Since different probes sample different regions of a cloud,
the structure of the cloud is discernible. The proposed experiment
has been applied successfully by us to Zeta Oph's diffuse clouds. Now,
we propose to use fractionation and excitation as new tools to probe
other portions of the Rho Oph Molecular Cloud.
Title: Stars and planets
Authors: Lambert, David; Donohoe, Bill; Townsend, Tony
Bibcode: 1994stpl.book.....L
Altcode:
No abstract at ADS
Title: Physical Conditions in Cloud Envelopes from Measurements of
Optical Absorption Lines
Authors: Federman, S. R.; Strom, C. J.; Lambert, D. L.; Smith, V. V.;
Cardelli, Jason A.; Joseph, C. L.
Bibcode: 1994ASPC...58...60F
Altcode: 1994icdi.conf...60F
No abstract at ADS
Title: The chemical compositions of Algol systems - V. Confirmation
of carbon deficiencies in the primaries of eight systems.
Authors: Tomkin, J.; Lambert, D. L.; Lemke, M.
Bibcode: 1993MNRAS.265..581T
Altcode:
We use low-noise CCD spectra of 4267-Å C II line in the spectra of
eight Algol-type eclipsing binaries to measure the C abundances of
their primaries. A differential LTE analysis of the Algol binaries
with respect to single standard stars of the same spectral type
shows marginal to moderate deficiencies of C in the primaries of the
binaries. We find [C/H] abundances of -0.62 for U CrB, -0.34 for u Her,
≤+0.24 for δ Lib, -0.22 for β Per, -0.18 for U Sge, -0.48 for λ
Tau, -0.35 for TX UMa and -0.16 for RS Vul with respect to the average
C abundance of single B-type standard stars. These results confirm
those of Cugier and Hardorp, who have used IUE observations of the
1300-Å C II lines to determine C abundances in the same stars. The C
deficiencies are a consequence of a previous episode of mass transfer
in which the secondary, which was initially the more massive star,
has transferred C-deficient, CNO-cycle processed material to the
primary. A comparison of observed and theoretical abundances suggests
that the mass transfer cannot have been extremely non-conservative,
although it may have been mildly so.
Title: The hot R Coronae Borealis star DY Centauri : nebular and
photospheric lines.
Authors: Rao, N. Kameswara; Giridhar, S.; Lambert, D. L.
Bibcode: 1993A&A...280..201R
Altcode:
High resolution spectra in the red region of the hot R CrB star DY Cen
show the following characteristics: a strong absorption line spectrum
dominated by lines of C II, N II, and Ne I inverse P-Cygni type profiles
of some C II and He I lines, and emission lines of (N II), (S II)
and (O I). The star also seems to posses an expanding chromosphere or
stellar wind region. The forbidden lines indicate the presence of a low
excitation nebula with an electron temperature of less than or equal
to 10 000 K and an electron density of 450/cu cm. The presence of low
excitation nebulae may be a common property of the hotter R CrB stars.
Title: Lithium Abundances and Other Clues to Envelope Burning in
Small Magellanic Cloud Asymptotic Giant Branch Stars
Authors: Plez, Bertrand; Smith, Verne V.; Lambert, David L.
Bibcode: 1993ApJ...418..812P
Altcode:
We present a chemical analysis of seven luminous asymptotic giant
branch stars and one M supergiant of the Small Magellanic Cloud. The
abundances are derived from high-resolution spectra by spectrum
synthesis using new, spherically symmetric, opacity sampling model
atmospheres. The average metallicity is [Fe/H] = -0.5, in accordance
with other determinations of the SMC's metallicity. The AGB stars
show signs of envelope burning, being Li rich, C poor, and with a
low 12C/13C ratio. The s-process elements (Rb,
Zr, Nd) abundance pattern is different from that in the solar system,
and is characteristic of a high exposure at low neutron density. This
is not peculiar to the SMC, however, but seems to be an effect of
metallicity: Galactic Ba, CH, and S-type stars at the same metallicity
display similar s-process element abundance patterns. Apparently, the
13C neutron source is operating in these intermediate-mass
thermally pulsing AGB stars.
Title: The chemical evolution of the galactic disk II. Observational
data.
Authors: Edvardsson, B.; Andersen, J.; Gustafsson, B.; Lambert, D. L.;
Nissen, P. E.; Tomkin, J.
Bibcode: 1993A&AS..102..603E
Altcode:
We recently discussed the chemical evolution of the galactic disk based
on the detailed analysis of 189 F and early G disk dwarfs (Edvardsson
et al. 1993). Here we describe the related solar observations, compare
equivalent widths of programme stars observed both from ESO and McDonald
observatories and tabulate equivalent widths.
Title: Abundances in CH Subgiants: Evidence of Mass Transfer onto
Main-Sequence Companions
Authors: Smith, Verne V.; Coleman, Howard; Lambert, David L.
Bibcode: 1993ApJ...417..287S
Altcode:
Carbon, oxygen, and s-process abundances, as well as abundances of other
metals, such as iron, calcium, or nickel, are presented for a sample
of nine CH subgiants. The abundances are derived from high-resolution,
high-S/N spectra. The CH subgiants in this sample are found to have
mild metal-deficiencies ([Fe/H] ≍ 0.0 to -0.4), a range of s-process
overabundances ([s-process/Fe] ≍ +0.2 to +1.0),
and C/O ratios from 0.4 to 2.0. When compared to the barium giant stars,
the CH subgiants tend to have larger C/O ratios, however, the barium
giants have deep convective envelopes that are presumably absent from
the CH subgiants, which lie on, or near, the main sequence. As the CH
subgiants evolve up the red giant branch and develop deep convective
envelopes, their carbon-rich atmospheres will be mixed with material
less abundant in C and their C/O ratios will decrease. It is thus quite
probable that the majority of the barium giant stars have evolved from
CH subgiant progenitors. The heavy-element abundance distributions of
the CH subgiants studied here, as well as published analyses of other
barium and CH giant stars, indicate that the s-process abundance
enhancements are created by neutrons from the 13C(α,
n)16O neutron source.
Title: Ultraviolet Transitions of Low Condensation Temperature Heavy
Elements and New Data for Interstellar Arsenic, Selenium, Tellurium,
and Lead
Authors: Cardelli, Jason A.; Federman, S. R.; Lambert, David L.;
Theodosiou, C. E.
Bibcode: 1993ApJ...416L..41C
Altcode:
No abstract at ADS
Title: Detection of Boron, Cobalt, and Other Weak Interstellar Lines
toward zeta Ophiuchi
Authors: Federman, S. R.; Sheffer, Y.; Lambert, D. L.; Gilliland, R. L.
Bibcode: 1993ApJ...413L..51F
Altcode:
Numerous weak lines from interstellar atomic species toward Zeta
Ophiuchi were observed with the Goddard High-Resolution Spectrograph. Of
particular note are the first interstellar detection of cobalt and
the detection of boron in this sight line. These measurements provide
estimates for the amount of depletion for the two elements. Boron,
a volatile, and cobalt, a refractory element, display the depletion
pattern found by Savage et al. (1992). The abundance of phosphorus
in the H II region associated with the star was obtained from a
detection of P III. Additional weak lines from S I, C I, Ni II, and
Cu II were detected for the first time; these lines provide the basis
for refinements in oscillator strength and column density. Analysis of
the neutral sulfur data indicates that the atomic gas is more widely
distributed than the molecular material in the main component.
Title: The Chemical Evolution of the Galactic Disk - Part One -
Analysis and Results
Authors: Edvardsson, B.; Andersen, J.; Gustafsson, B.; Lambert, D. L.;
Nissen, P. E.; Tomkin, J.
Bibcode: 1993A&A...275..101E
Altcode: 2009A&A...500..391E
No abstract at ADS
Title: Optical emission bands in the spectrum of the R CrB star V854
CEN at minimum.
Authors: Rao, N. K.; Lambert, D. L.
Bibcode: 1993MNRAS.263L..27K
Altcode: 1993MNRAS.263L..27R
Several unidentified broad emission features, previously seen only
in the spectrum of the nebulosity in the Red Rectangle, have been
observed in a spectrum of the R CrB star V854 Cen taken in a deep
minimum. Similarities and differences between the bands from the
two sources are noted. The presence of the bands associated with an
R CrB star may suggest that their carrier does not contain hydrogen
atoms. Extended red emission seen from the Red Rectangle and probably
associated with hydrogenated carbon grains is not present in the
spectrum of V854 Cen.
Title: Lithium in the Barium Stars
Authors: Lambert, David L.; Smith, Verne V.; Heath, James
Bibcode: 1993PASP..105..568L
Altcode:
Analysis of high resolution (lambda/Delta-lambda - 150,000) spectra
of classical barium giants reveals that an unidentiifed line is
a major contribtor to the stellar absorption feature at 6707.8 A
attributed previously to a blend of CN lines and the Li I resonance
doublet. The strength of the unidentified line is well correlated
with the strength of a Ce II line. In contrast to published reports
of positive identifications of absorption due to the Li I doublet,
an acceptable fit of a synthetic spectrum to the observed spectrum of
a barium giant is obtainable without a significant contribution from
the Li I doublet. Upper limits to the Li abundance of classical barium
giants are now consistent with those expected of CH subgiants evolve
into barium giants. (SECTION: Stars)
Title: On the Absolute Magnitude of V482 Cygni, an R Coronae
Borealis Star
Authors: Rao, N. K.; Lambert, David L.
Bibcode: 1993PASP..105..574R
Altcode:
An identification of V482 Cyg, an R CrB star, with a quadruple system
containing a K5III star is rejected. High-resolution spectra show that
the radial velocity of V482 Cyg and the K5III star differ by 35 km
s^-1, and the interstellar NaD lines are much stronger in the spectrum
of V482 Cyg. These observations suggest that V482 Cyg is much more
distant than the K5III star and has an absolute magnitude of M_V ~-5,
similar to that of R CrB stars in the LMC. (SECTION: Stars)
Title: The 6Li/ 7Li Ratio in the Metal-poor Halo Dwarfs HD 19445
and HD 84937
Authors: Smith, Verne V.; Lambert, David L.; Nissen, Poul E.
Bibcode: 1993ApJ...408..262S
Altcode:
High-resolution high SNR spectra of the Li I 6707 A line in the
subdwarfs HD 19445 and HD 84937 have been analyzed for the presence
of Li-6. By measurement of the Li I line's wavelength and analysis
of its profile, the atmosphere of HD 84937 is shown to have a small
amount of Li-6: R = Li-6/Li = 0.05 +/- 0.02. For HD 19445, an upper
limit is set of R less than 0.02. The presence of Li-6 in HD 84937
is consistent with the mild depletion of Li-6 predicted by standard
(nonrotating) models and the initial presence of Li-6 in the halo
produced by (principally) alpha-on-alpha fusion reactions involving
the cosmic rays that are required to account for the Be and B observed
in subdwarfs. Depletion of Li-6 in the lower mass star HD 19445 is
expected to remove the initial Li-6 content and, hence, the absence of
Li-6 is expected. If Yale models of rotating subdwarfs are adopted,
the predicted severe depletion of Li-6 and the observed survival of
Li-6 in HD 84937 have to be reconciled. Four suggestions are made:
the rotating models are inapplicable to halo dwarfs, production of Li-6
by cosmic rays has been underestimated, the required high initial Li-6
abundance of the halo was produced prior to the formation of the Galaxy,
or the Li-6 was produced in stellar flares.
Title: VizieR Online Data Catalog: Chemical evolution of the galactic
disk II. (Edvardsson+ 1993)
Authors: Edvardsson, B.; Andersen, J.; Gustafsson, B.; Lambert, D. L.;
Nissen, P. E.; Tomkin, J.
Bibcode: 1993yCat..41020603E
Altcode:
(1993A&A...275..101E, see catalog <J/A+A/275/101>) from
observations at ESO and McDonald observatories are compared. (4
data files).
Title: VizieR Online Data Catalog: Chemical evolution of the galactic
disk I. (Edvardsson+ 1993)
Authors: Edvardsson, B.; Andersen, J.; Gustafsson, B.; Lambert, D. L.;
Nissen, P. E.; Tomkin, J.
Bibcode: 1993yCat..32750101E
Altcode:
From high resolution, high S/N spectroscopic observations of carefully
selected northern and southern stars, abundances of O, Na, Mg, Al,
Si, Ca, Ti, Fe, Ni, Y, Zr, Ba and Nd, as well as photometric ages,
are derived for 189 nearby field F and G stars. (2 data files).
Title: High Resolution Spectroscopy of the R Coronae Borealis Star,
V854 Centauri, During A Deep Minimum
Authors: Kameswara Rao, N.; Lambert, David L.
Bibcode: 1993AJ....105.1915K
Altcode: 1993AJ....105.1915R
The R Coronae Borealis star V854 Cen was observed at minimum light (V
about 15) at high spectral resolution from 5480 to 7070 A. The spectrum
consists of three components: a continuum devoid of photospheric lines,
a collection of sharp emission lines of Sc II, Ti II, Y II, and Ba II,
and broad emission lines of forbidden O I, forbidden N II, forbidden S
II, H-alpha, Na D, and C2 Swan bands. A low resolution spectrum reveals
additional lines of Ca II, forbidden C I, and other species. The sharp
emission lines are considered to be chromospheric lines. The broad
lines with a full width of 400-500 km/s come from an extended region
with a temperature of about 7000 K, but an electron density of 50/cu
cm or less. It is suggested that V854 Cen may be a bipolar nebula.
Title: The Boron Abundance of Procyon
Authors: Lemke, Michael; Lambert, David L.; Edvardsson, Bengt
Bibcode: 1993PASP..105..468L
Altcode:
The B I 2496.8 A resonance line and HST/GHRS echelle spectra are used
with model atmospheres and synthetic spectra to derive the B abundance
of the F dwarfs Procyon (alpha CMi), Theta UMa, and Iota Peg. The B
abundance (log epsilon(B)~/=2.3) of Theta UMa and Iota Peg is similar
to that derived by Boesgaard and Heacox from the B II resonance line in
spectra of A and B-type stars. These two dwarfs show normal abundances
of Li, Be, and B. Procyon, which is highly depleted in Li and Be, is
depleted in B by a factor of at least 3. Comparison of the spectra
of Procyon and the halo dwarf HD 140283 shows that the B abundance
assigned by Duncan, Lambert, and Lemke (1992) to three halo dwarfs is
not greatly overestimated as a result of contamination of the B I line
by an unidentified line. (SECTION: Stars)
Title: Books-Received - Frontiers of Stellar Evolution
Authors: Lambert, D. L.
Bibcode: 1993JBAA..103...42L
Altcode:
No abstract at ADS
Title: The observed chemical evolution of the Galactic disk.
Authors: Edvardsson, B.; Gustafsson, B.; Andersen, J.; Nissen, P. E.;
Lambert, D. L.; Tomkin, J.
Bibcode: 1993AGAb....8..105E
Altcode: 1993AGAb....8..105.
No abstract at ADS
Title: Optical emission bands in the spectrum of the R CrB star V854
Cen at minimum.
Authors: Rao, N. K.; Lambert, D. L.
Bibcode: 1993oebs.book.....R
Altcode:
Several unidentified broad emission features previously seen only
in the spectrum of the nebulosity in the Red Rectangle have been
observed in a spectrum of the R CrB star V854 Cen taken in a deep
minimum. Similarities and differences between the bands from the
two sources are noted. The presence of the bands associated with a
R CrB star may suggest that their carrier does not contain hydrogen
atoms. Extended red emission seen from the Red Rectangle and probably
associated with hydrogenated carbon grains is not present in the
spectrum of V854 Cen.
Title: Quantitative stellar spectroscopy with large optical
telescopes.
Authors: Lambert, D. L.
Bibcode: 1993PhST...47..186L
Altcode:
After noting that a generation of large optical telescopes is under
construction and commenting briefly on the problems in stellar
spectroscopy that these telescopes will address, the review focuses
on the need for more complete information on the interactions between
H atoms and the atoms whose spectral lines are to be investigated in
stellar spectra. The H-atom collisions may determine the atomic lines'
widths and may influence the excitation and ionization of the atom.
Title: CNO abundances in the Orion OB association.
Authors: Cunha, K.; Lambert, D. L.
Bibcode: 1993oee..conf..274C
Altcode:
No abstract at ADS
Title: Observational signatures of stellar nucleosynthesis -
a sampler.
Authors: Lambert, D. L.
Bibcode: 1993oee..conf..257L
Altcode:
No abstract at ADS
Title: Nucleosynthesis and mixing in C and Ba stars
Authors: Busso, M.; Beglio, L.; Gallino, R.; Lambert, D. L.; Raiteri,
C. M.; Smith, V. V.
Bibcode: 1993nuco.conf..515B
Altcode:
No abstract at ADS
Title: MS and S stars with and without Tc.
Authors: Busso, M.; Gallino, R.; Lambert, D. L.; Raiteri, C. M.;
Smith, V. V.
Bibcode: 1993oee..conf..416B
Altcode:
No abstract at ADS
Title: Detection of boron, cobalt, and other weak interstellar lines
toward Zeta Ophiuchi.
Authors: Federman, S. R.; Sheffer, Y.; Lambert, D. L.; Gilliland, R. L.
Bibcode: 1993dbco.book.....F
Altcode:
Numerous weak lines from interstellar atomic species toward ζ Ophiuchi
were observed with the Goddard High Resolution Spectrograph. Of
particular note are the first interstellar detection of cobalt and
the detection of boron in this sight line. These measurements provide
estimates for the amount of depletion for the two elements. Boron,
a volatile, and cobalt, a refractory element, display the depletion
pattern found by Savage et al. (1992). The abundance of phosphorus
in the H II region associated with the star was obtained from a
detection of P III. Additional weak lines from S I, C I, Ni II, and
Cu II were detected for the first time, these lines provide the basis
for refinements in oscillator strength and column density. Analysis of
the neutral sulfur data indicates that the atomic gas is more widely
distributed than the molecular material in the main component.
Title: The Abundance of Boron in Three Halo Stars
Authors: Duncan, Douglas K.; Lambert, David L.; Lemke, Michael
Bibcode: 1992ApJ...401..584D
Altcode:
B abundances for three halo stars: HD 140283, HD 19445, and HD 201891
are presented. Using recent determinations of the Be abundance in HD
140283, B/Be of 10 +5/-4 is found for this star, and similar ratios
are inferred for HD 19445 and HD 201891. This ratio is equal to the
minimum value of 10 expected from a synthesis of B and Be by high-energy
cosmic-ray spallation reactions in the interstellar medium. It is
shown that the accompanying synthesis of Li by alpha on alpha fusion
reactions is probably a minor contributor to the observed 'primordial'
Li of halo stars. The observed constant ratios of B/O and Be/O are
expected if the principal channel of synthesis involves cosmic-ray
CNO nuclei from the supernovae colliding with interstellar protons.
Title: High Resolution Spectroscopy of the Semi-Regular Variable
Lr-Scorpii
Authors: Giridhar, Sunetra; Rao, N. K.; Lambert, David L.
Bibcode: 1992JApA...13..307G
Altcode:
A detailed spectroscopic investigation of LR Sco which was earlier
misclassified as R CrB star is made. Atmospheric parameters and
elemental abundances are determined using detailed depth-dependent model
atmospheres and line synthesis technique. Most of the elements show
near solar abundances. The strength of circumstellar components seen in
Na D lines are used to derive the mass loss rate. Another independent
estimate of mass loss rate is made using the observed infrared flux
from 1-100Μm. These two approaches lead to nearly the same value of
mass loss rate when M vis assumed to be - 4.5 for this star.
Title: Nucleosynthesis and Mixing on the Asymptotic Giant
Branch. I. MS and S Stars with and without TC
Authors: Busso, M.; Gallino, R.; Lambert, D. L.; Raiteri, C. M.;
Smith, V. V.
Bibcode: 1992ApJ...399..218B
Altcode:
The study fits the elemental abundances observed in MS and S giants
using self-consistent models of nucleosynthesis and dredge-up for the
TP-AGB evolutionary phases of low-mass stars. The initial envelope
abundances of C-12, C-13, and N-14 are taken from observations of red
giants that experienced the first dredge-up and are not yet on the
AGB. It is found that the observed abundances of MS and S stars are
readily explained by TP-AGB models of low-mass stars in which neutrons
are released by the C-13(alpha, n)O-16 neutron source and in which
the effects of mass loss and mixing due to envelope penetration are
taken into account. The observed distributions of s-elements alone do
not suffice to derive the neutron exposure in the He-shell, because
the observed distributions are strongly affected also by how and
when the third dredge-up occurs. The relative roles of mixing and of
nucleosynthesis may be estimated by requiring the models to reproduce
the abundances of C as well as of the s-elements. It is shown that
single Tc-poor S star may exist, if the dredge-up phenomenon occurs
rarely enough to allow Tc to decay between successive mixing episodes.
Title: Behavioral Study of Yellow Supergiants: III. [N II] Emission
of HR 8752 from 1961-1991
Authors: Sheffer, Yaron; Lambert, David L.
Bibcode: 1992PASP..104.1054S
Altcode:
McDonald spectra of HR 8752 from the last 16 years reveal a constant
radial velocity and a variable equivalent width of the [N II]
emission at 6583A. The 1976-91 interval confirms and expands the
increasing equivalent width trend first reported in Sheffer and Lambert
(1987). The current equivalent wideth of 230 mA is the strongest [N
II] emission ever observed from HR 8752. By analyzing published Band
V photometry we establish that the cuase of [N II] equivalent width
variability is the variable continuum of HR 8752. Extension of the
analyzed interval back to the 1961 discovery epoch is accomplished by
a survey of both the spectroscopic and photometric literature. This
uncovers a remarkable minimum in [N II] strength around 1973 and
possibly demonstrates a cyclical behavior of the continuum with a
30-year period, or longer. (SECTION: Stars)
Title: Chemical Evolution of the Orion Association. I. The Oxygen
Abundance of Main-Sequence B Stars
Authors: Cunha, Katia; Lambert, David L.
Bibcode: 1992ApJ...399..586C
Altcode:
Oxygen abundances are presented from LTE and non-LTE analyses of O
II lines in spectra of 18 B mainsequence stars of the four subgroups
comprising the Orion association. The lowest abundances are found in the
oldest subgroups (Ia and Ib). The youngest subgroup Id, the Trapezium
cluster, and some stars of the slightly older Ic subgroup seem to have
an abundance that is up to about 40 percent higher. It is suggested
that this enrichment resulted from the mixing of supernovae ejecta from
the Ic subgroup with those adjacent portions of the dense molecular
cloud that subsequently collapsed to form the Trapezium cluster. These
stellar analyses confirm published abundance analyses of the H II
region's emission lines that show Orion to have an oxygen abundance
that is less than that of the Sun: the mean LTE/NLTE abundances are
log epsilon(O) = 8.67/8.65 +/- 0.12 for the 18 stars whereas the solar
abundance is log epsilon(O) = 8.93.
Title: Book-Review - Frontiers of Stellar Evolution
Authors: Lambert, D. L.
Bibcode: 1992Sci...258.1015L
Altcode:
No abstract at ADS
Title: Fractionation of CO in the Diffuse Clouds toward zeta Ophiuchi
Authors: Sheffer, Yaron; Federman, S. R.; Lambert, David L.; Cardelli,
Jason A.
Bibcode: 1992ApJ...397..482S
Altcode:
An analysis of CO A-X bands in diffuse clouds toward Zeta Ophiuchi
is presented. The results provide isotopic ratios that constitute
the strongest observational evidence for highly localized isotopic
fractionation of CO in diffuse portions of an interstellar cloud. The
value of the fractionation implies that selective photodissociation
is the controlling influence of the fractionation. The molecule's
excitation temperature is discussed and a lower limit to the O-16/O-18
ratio is provided. The absence of CO lines from the gas that provides
broad CH+ and CH lines commonly attributed to warm gas behind a shock
front is addressed.
Title: The Carbon-to-Oxygen Ratio in Halo Dwarfs
Authors: Tomkin, Jocelyn; Lemke, Michael; Lambert, David L.; Sneden,
Christopher
Bibcode: 1992AJ....104.1568T
Altcode:
C I and O I lines have been observed in 34 metal-poor dwarfs and
subgiants, and both LTE and non-LTE analyses of these lines have
been performed. Analysis of the lines is vitiated by a systematic
temperature-dependent error, showing that present methods of analysis
may not give the correct elemental abundances. The (C/O) ratios are,
however, almost independent of effective temperature and are therefore
reliable. These ratios are found to be essentially constant over the
metallicity range (Fe/H) = -2.7 - -1.0 in the survey. The mean value
is (C/O) = -0.57 +/- 0.12. Analysis of CH lines gives (C/Fe) = -0.14
+/- 0.20. It is considered that the O abundance in halo stars is more
reliably indicated by the forbidden O I line, and it is suggested that
(O/Fe) = +0.45 +/- 0.1 is representative for (Fe/H) less than -1. It is
suggested that (C/Fe) = -0.1 and (O/Fe) about +0.5 are representative
of the halo.
Title: A fine analysis of calcium and iron lines in the spectrum of
the subdwarf Groombridge 1830.
Authors: Smith, G.; Lambert, D. L.; Ruck, M. J.
Bibcode: 1992A&A...263..249S
Altcode:
A detailed model atmosphere analysis of calcium and iron lines is
used to derive a set of self-consistent atmospheric parameter for
the subdwarf Gmb 1830. T(eff) is found to be 5170 +/- 70 K, slightly
hotter than previous estimates based on photometric indices. The
surface gravity is slightly greater than that of the sun. There is a
clear difference in logarithmic abundance, relative to the sun, between
calcium and iron such that (Ca/H) exceeds (Fe/H) by about 0.3 dex. The
logarithmic abundance of magnesium, relative to the sun, is close to
that of calcium. Test calculations indicate that it is the relative
abundance of alpha-particle elements, presumably mainly Mg and Si,
which largely controls the electron pressure of the atmosphere. The
microturbulence in Gmb 1830 is similar to that found in other G and
early K type dwarf stars.
Title: Lithium-Rich Red Giants in the Magellanic Clouds
Authors: Lubowich, D. A.; Smith, V. V.; Lambert, D. L.
Bibcode: 1992AAS...181.2306L
Altcode: 1992BAAS...24.1158L
No abstract at ADS
Title: High- Velocity Interstellar Gas Toward HD 169454
Authors: Federman, S. R.; Lambert, D. L.
Bibcode: 1992AJ....104..691F
Altcode:
The interstellar spectrum of HD 169454 reveals Na D and Ca K absorption
at about + 100 km/s. Measurements made at high resolution resolve
4 narrow (about 2-3 km/s) features whose N(Ca II)/N(Na I) ratios
are small. This high-velocity gas is, therefore, unique in that it
resembles local quiescent gas, not shocked gas. Redshifted gas is also
seen in moderate-resolution spectra of faint stars lying in the same
portion of the sky as HD 169454. The resulting picture is one in which
a supernova explosion or stellar winds within the Sct OB3 association
at a distance of about 1.5 kpc is pushing quiescent gas away from the
sun. The gas is seen only in stars estimated to be at most 3 kpc, but
greater than 2 kpc, away. If HD 169454 is at this greater distance,
its absolute magnitude would be about -9, making it the second most
luminous B star in the Galaxy.
Title: Fluorine in red giant stars : evidence for nucleosynthesis.
Authors: Jorissen, A.; Smith, V. V.; Lambert, D. L.
Bibcode: 1992A&A...261..164J
Altcode:
Flourine abundances were determined in several K giants and asymptotic
giant branch (AGB) stars, using the infrared vibration-rotation lines of
HF. The data presented constitute the only available information on the
fluorine abundance outside the solar system and provide invaluable clues
to the question of the nucleosynthetic origin of F. The observations
confirm that F production occurs at a He-burning site and constrain
the current models of AGB stars.
Title: Scientific Requirements for High-Resolution Spectroscopy with
the VLT
Authors: Lambert, D. L.
Bibcode: 1992ESOC...40...11L
Altcode: 1992hrsw.conf...11L
No abstract at ADS
Title: Stellar Evolution Nucleosynthesis and High-Resolution
Spectroscopy
Authors: Lambert, D. L.
Bibcode: 1992ESOC...40...23L
Altcode: 1992hrsw.conf...23L
No abstract at ADS
Title: Boron in Main Sequence STARS-CYC3HIGH
Authors: Lambert, David
Bibcode: 1992hst..prop.4840L
Altcode:
Boron abundances have been obtained for a sample of Pop. I and Pop. II
stars from GHRS grating/echelle spectra of the BI resonance lines
at 2497 A. Stars to be observed in Cycle 3 include Procyon and high
galactic latitude early type stars. Boron will A B I line at 2089A will
be observed in Procyon in order to measure the 11B/10B ratio. In the
high latitude B stars, Boron will be sought from the B II doublet at
1362A. A second region at 1305A will provide profiles of SiIII lines; a
SiIII line is blended with the B II line. Boron will provide a new clue
to origins of these young solar-metallicity massive stars in the halo.
Title: Boron and Chemical Evolution of the Galactic Disk CYC3-MEDIUM
Authors: Lambert, David
Bibcode: 1992hst..prop.4418L
Altcode:
Exploratory observations will be made of the B I resonance 2090A in
Theta UMa from which the 11B/10B may be measureable.
Title: The Transitions Involving the Chemistry of C2
and CN in Interstellar Cloud Envelopes
Authors: Strom, C. J.; Federman, S. R.; Lambert, D. L.; Smith, V. V.;
Cardelli, J. A.; Joseph, C. L.
Bibcode: 1992AAS...180.4304S
Altcode: 1992BAAS...24..797S
No abstract at ADS
Title: Li Abundances in Luminous Magellanic Cloud AGB stars
Authors: Plez, B.; Smith, V. V.; Lambert, D. L.
Bibcode: 1992AAS...180.2607P
Altcode: 1992BAAS...24..768P
Improved model atmospheres including spherical geometry and better
opacities treated in Opacity Sampling (Plez, Brett, Nordlund, 1992,
Astron. Astrophys., in press) have been used to extract Li abundances in
Magellanic Cloud AGB and Supergiant stars. The effect of sphericity on
the derivation of stellar parameters and chemical composition has been
investigated. The C/O ratio has been found to be a critical parameter
that has to be carefully estimated in S type stars, before any reliable
abundance may be determined. This is due to the rapid variation of TiO
partial pressure with the C/O ratio when it nears one. This results in
changes in the atmospheric structure and in the veiling of the spectrum
by the numerous TiO lines. Preliminary results will be discussed that
suggest Li enhancement in the most luminous AGB stars. This confirms the
discovery by Smith and Lambert (1989, Ap.J. letters, 345, L75 and 1990,
Ap.J. Letters, 361, L69) of Li enrichment in luminous S stars of the
Magellanic Clouds and supports their conclusion that the excess Li was
produced as a result of envelope burning. This research is supported
in part by the NSF (AST 91-15090) and the Robert A. Welch Foundation
of Houston, Texas.
Title: The Chemical Composition of Magellanic Cloud Cepheids and
Nonvariable Supergiants
Authors: Luck, R. E.; Lambert, David L.
Bibcode: 1992ApJS...79..303L
Altcode:
Abundance analyses of 14 Cepheids and nonvariable supergiants in the
Magellanic Clouds (seven stars in each Cloud) are presented along with
comparison data on four Galactic objects. Elemental abundances derived
include Li, C, N, O, the α-elements, the Fe peak, and limited data on
the heavy elements. Only HV 5497 in the LMC shows any detectable Li
[log ɛ(Li) = 2.5] among the Cloud objects. It is also unique (among
LMC objects analyzed) in that it is metal-rich ([Fe/HI~+0.2) which may
explain its Li-rich nature. Our CNO data when combined with previous
results suggest a disparity between the LMC and the SMC supergiants in
that the SMC stars have an essentially constant [0/Fe] ratio, while
the LMC stars do not. The [0/Fe] ratios within both Clouds are lower
than the ratio found in Galactic stars of similar metallicity, but are
comparable to the [0/Fe] ratios found in Galactic supergiants. Both
Clouds show a range of CNO abundances larger than that of Galactic
supergiants, but this could be a result of analysis deficiencies and
small sample sizes. The [Fe/H] ratios are consistent with the analysis
errors dominating the abundance dispersion in the SMC, while within the
LMC a real dispersion in [Fe/H] is possible. For the heavier elements,
we confirm previous results which indicate the light s-and r-process
elements (Sr, Y, Zr) show Galactic ratios with respect to Fe, but that
the heavy s- and r-process elements (Ba-Sm) are enhanced in the Clouds.
Title: The p-nuclei: abundances and origins
Authors: Lambert, David L.
Bibcode: 1992A&ARv...3..201L
Altcode:
The review discusses the solar system (meteoritic) abundances
and the possible modes of nucleosynthesis of the 30-odd
p-nuclei from74Se to196Hg. In addition
to a discussion of the abundances for bulk meteorites, isotopic
anomalies related to the p-nuclei are discussed; e.g., the Xe-HL
associated with the ‘interstellar’ diamonds and the extinct
radionuclides146Sm and92Nb. Various proposed
schemes of synthesizing p-nuclei are reviewed. It is noted that the
7-process (i.e., photoerosion) operating in SN Ia (exploding C-O white
dwarfs) appears capable of accounting for the relative and absolute
abundances of all but one or two of the rarest of p-nuclei. Synthesis
of these latter nuclei is also discussed.
Title: Carbon, Nitrogen, and Oxygen Abundances in Early B-Type Stars
Authors: Gies, Douglas R.; Lambert, David L.
Bibcode: 1992ApJ...387..673G
Altcode:
A survey of the C, N, and O abundances in a sample of early B-type
stars which was undertaken to test the hypothesis of Liubimkov (1984)
that CN-cycled material is mixed to the surfaces of these stars during
their core hydrogen-burning phase. Equivalent widths of generally weak
lines are obtained using high-signal-to-noise Reticon spectra of 39
stars in four spectral regions. Effective temperatures and gravities
for these stars are derived. Projected rotational velocities are
measured using a cross-correlation technique. Abundances are derived
using LTE methods and non-LTE equivalent width calculations. He, C, N,
and O abundances of the nonsupergiant stars in the sample are found
to be very close to the values found for the Orion Nebula, with the
notable exception of a few stars which show enhanced N, a signature of
CN-cycled material. No compelling evidence for a systematic increase in
N abundance with evolutonary age was found; thus Liubimkov's claim that
mixing occurs generally in main-sequence B stars cannot be confirmed.
Title: The Chemical Composition of Blue Horizontal Branch Stars in
M4 and NGC 6397
Authors: Lambert, David L.; McWilliam, Andrew; Smith, Verne V.
Bibcode: 1992ApJ...386..685L
Altcode:
High-resolution (lambda/Delta lambda is approximately equal to 18,000)
spectra of two horizontal branch stars in M4 and one in NGC 6397
provide a metallicity in good agreement with the values obtained
previously by others from analyses of cluster red giants. For one HB
star in M4, the C, N, O abundances derived from near-infrared C I,
N I, O I lines are consistent with those obtained for red giants by
Brown et al. (1990). The result suggests that the He-core flash cannot
always result in products of He-burning being mixed into the envelope.
Title: Detection of boron in halo dwarf stars : implications for
early galactic cosmic rays and primordial nucleosynthesis.
Authors: Lemke, M.; Lambert, D. L.; Duncan, D. K.
Bibcode: 1992BAAS...24..681L
Altcode:
No abstract at ADS
Title: Detection of Boron in Halo Dwarf Stars: Implications for
Early Galactic Cosmic Rays and Primordial Nucleosynthesis
Authors: Lemke, M.; Lambert, D. L.; Duncan, D. K.
Bibcode: 1992AAS...179.1309L
Altcode: 1992BAAS...24Q.681L
No abstract at ADS
Title: The Chemical and Dynamical Evolution of the Galactic Disk
Authors: Gustafsson, B.; Edvardsson, B.; Nissen, P.; Lambert, D. L.;
Tomkin, J.; Andersen, J.
Bibcode: 1992IAUS..149...75G
Altcode:
No abstract at ADS
Title: Observational Effects of Nucleosynthesis in Evolved Stars
Authors: Lambert, D. L.
Bibcode: 1992eatc.conf...92L
Altcode:
No abstract at ADS
Title: The Abundance of Boron in Three Halo Stars
Authors: Lambert, D. L.; Lemke, M.
Bibcode: 1992ESOC...44..319L
Altcode: 1992swhs.conf..319L
No abstract at ADS
Title: Lithium-rich red giants in the Magellanic Clouds.
Authors: Lubowich, D. A.; Smith, V. V.; Lambert, D. L.
Bibcode: 1992BAAS...24R1158L
Altcode:
No abstract at ADS
Title: Observation of Bariam star HD 46407
Authors: Lambert, David
Bibcode: 1992iue..prop.4418L
Altcode:
No abstract at ADS
Title: Atomic data, stellar atmospheres, and the Hubble Space
Telescope
Authors: Lambert, D. L.
Bibcode: 1992HiA.....9..557L
Altcode:
No abstract at ADS
Title: The chemical evolution of luminous stars; problems or
opportunities?
Authors: Lambert, D. L.
Bibcode: 1992iesh.conf..156L
Altcode:
No abstract at ADS
Title: Chemical evolution of the Orion association. I. The oxygen
abundance of main sequence B stars.
Authors: Cunha, K.; Lambert, D. L.
Bibcode: 1992ceoa.book.....C
Altcode:
Oxygen abundances are presented from LTE and non-LTE analyses of O
II lines in spectra of 18 B main sequence stars of the four subgroups
comprising the Orion association. The lowest abundances are found in the
oldest subgroups (Ia and Ib). The youngest subgroup Id, the Trapezium
cluster, and some stars of the slightly older Ic subgroup seem to have
an abundance that is up to about 40 percent higher. It is suggested that
this enrichment resulted from the mixing of supernovae ejecta from the
Ic subgroup with those adjacent portions of the dense molecular cloud
that subsequently collapsed to form the Trapezium cluster. These stellar
analyses confirm published abundance analyses of the H II region's
emission lines that show Orion to have an oxygen abundance that is
less than that of the Sun: the mean LTE/NLTE abundances are logɛ(O) =
8.67/8.65±0.12 for the 18 stars whereas the solar abundance is logɛ(O)
= 8.93.
Title: Diffuse interstellar clouds
Authors: Lambert, D. L.; Federman, S. R.
Bibcode: 1992HiA.....9...65L
Altcode:
No abstract at ADS
Title: Lithium abundances for 81 F dwarfs.
Authors: Lambert, David L.; Heath, James E.; Edvardsson, Bengt
Bibcode: 1991MNRAS.253..610L
Altcode:
Lithium abundances are presented for 81 main-sequence stars with
effective temperatures of about 5800-6700 K. A novel result of the
survey is that, in old disk dwarfs too low in mass to belong to
the Li-gap, Li is generally not depleted beyond the moderate level
attributed to the convection zone of the premain- and main-sequence
phase but, when depletion occurs, it is very effective. Li-poor old
disk stars at luminosities too low to be identified with the Li-gap
exist, but are rare.
Title: Interstellar 12C/ 13C Ratio Revisited
Authors: Crane, Philippe; Hegyi, Dennis J.; Lambert, David L.
Bibcode: 1991ApJ...378..181C
Altcode:
Recent 107-in telescope observations of the molecular ion CH(+) at 4232
A in the direction of Zeta Oph are reported. One-dimensional spectra
were extracted from the frames using procedures in IRAF. A Gaussian
line profile was fitted to the data at random points well separated
from the CH(+) features. The resulting distribution of equivalent
widths is presented. Results for the individual spectra are summarized
as well as the errors assigned to the individual results. Histograms
of the equivalent widths for the CH-12(+) and CH-13(+) lines are shown
and compared to the data from Stahl at al. (1989), and good agreement
is found. It is concluded that the C-12/C-13 ratio toward Zeta Oph is
closer to 70 than to 45, as argued by Hawkins et al. (1985).
Title: Lithium Abundances in Carbon Stars
Authors: Denn, Grant R.; Luck, R. E.; Lambert, David L.
Bibcode: 1991ApJ...377..657D
Altcode:
High-dispersion, high SNR ratio spectra near 6707 A have provided
Li abundances for 29 cool carbon stars. For the carbon stars, with
the exception of the J star WZ Cas, the Li abundance ranges from log
epsilon(Li) = -0.6 to -1.7 and is uncorrelated with the C-12/C-13,
C/O and other abundance ratios, and the effective temperature. The
Li abundances are on average lower than found for M giants. This
difference may be due to a systematic underestimate of the carbon stars'
effective temperatures by 200-400 K. It is possible that Li may be
destroyed at the base of an asymptotic giant branch star's convective
envelope. When the base temperature increases substantially, Li may
be produced by the B-7 transport mechanism, as in the super Li-rich SC
(J-type) star WZ Cas with log epsilon(Li) = 6.5.
Title: First Results from the Goddard High-Resolution Spectrograph:
C i, S i, and CO toward XI Persei and the Physical Conditions in
Diffuse Clouds
Authors: Smith, Andrew M.; Bruhweiler, Frederick C.; Lambert, David
L.; Savage, Blair D.; Cardelli, Jason A.; Ebbets, Dennis C.; Lyu,
Cheng-Hsuan; Sheffer, Yaron
Bibcode: 1991ApJ...377L..61S
Altcode:
Observations made by the Goddard High Resolution Spectrograph of
the cool, neutral interstellar gas in the line of sight to Xi Per
are reported. Heliocentric velocities and equivalent widths were
measured for absorption lines of C I and S I. Synthetic spectra were
computed and fitted to the observed CO(2-0) and (3-0) bands in the A
IPi - X 1Sigma(+) system. Derived populations of the C I ground-state
fine-structure levels and the CO ground-state rotational levels were
used to derive densities of two of the three, and possibly four,
detected cloud components. The velocity component displaying the
strongest C I absorption reveals extraordinarily high pressure.
Title: Oxygen abundances in Orion-association B-stars
Authors: Cunha, K.; Lambert, D. L.
Bibcode: 1991BAAS...23.1264C
Altcode:
No abstract at ADS
Title: Vibration-rotation bands of CH in the solar infrared spectrum
and the solar carbon abundance
Authors: Grevesse, N.; Lambert, D. L.; Sauval, A. J.; van Dishoeck,
E. F.; Farmer, C. B.; Norton, R. H.
Bibcode: 1991A&A...242..488G
Altcode:
High resolution solar spectra obtained from the ATMOS Fourier Transform
Spectrometer (Spacelab 3 flight on April 29-May 6, 1985) have made
it possible to identify and measure a large number of lines of the
vibration-rotation fundamental bands of the X2 Pi state of CH. From
about 100 lines of the 1-0, 2-1, and 3-2 bands and adopting theoretical
transition probabilities, a solar carbon abundance of 8.60 + or -
0.05 is derived. This value is compared with new results inferred
from other carbon abundance indicators. The final recommended solar
abundance of carbon is 8.60 + or - 0.05.
Title: The Chemical Composition of Asymptotic Giant Branch Stars -
the S-Process
Authors: Lambert, D. L.
Bibcode: 1991IAUS..145..299L
Altcode:
No abstract at ADS
Title: Frontiers of stellar evolution
Authors: Lambert, David L.
Bibcode: 1991ASPC...20.....L
Altcode: 1991fse..conf.....L
Bibliographic codes for individual papers begin with "1992fse..book".
Title: An abundance analysis of three Lambda Bootis stars.
Authors: Venn, K.; Lambert, D. L.
Bibcode: 1991ASPC...20..624V
Altcode:
No abstract at ADS
Title: The Abundance Connection - the View from the Trenches
Authors: Lambert, D. L.
Bibcode: 1991IAUS..145..451L
Altcode:
No abstract at ADS
Title: The chemical composition of luminous stars: problems or
opportunities?
Authors: Lambert, D. L.
Bibcode: 1991ccls.book.....L
Altcode:
The surface chemical composition of a luminous star changes as the
star evolves. Spectroscopic definition of the changes may be used to
test stellar evolutionary models. This essay discusses some of the
observed and predicted changes in three different groups of luminous
stars: hot massive stars, yellow supergiants, and luminous asymptotic
giant branch stars.
Title: Surface Chemical Composition, Nuclear Processing, and Deep
Mixing: Main Sequence to First Dredge-Up
Authors: Lambert, David L.
Bibcode: 1991LNP...388..325L
Altcode: 1991ctsm.conf..325L
The standard theory of the structure of moderate mass stars predicts
that, except for a few light nuclides, the composition of a main
sequence star is identical to that of its parental interstellar
cloud. Aspects of the depletion of Li in main sequence stars are
discussed. Standard theory predicts that the composition of a red giant
and its main sequence progenitor must differ because the giant's deep
convective envelope brings to the surface material previously exposed
to warm protons. Observations of Li, 12C/13C and 16O/17O/18O in giants
are related to the predictions for standard models.
Title: Isotopic Abundances of Carbon and Oxygen and Fractionation
in Interstellar Carbon Monoxide
Authors: Lambert, David
Bibcode: 1990hst..prop.1065L
Altcode:
HRS observations of the CO A-X system between 1250 and 1550 A will
be acquired and analyzed to obtain abundances of 12C16O, 13C16O,
12C17O, and 12C18O, and to study the rotational excitation of the
CO molecule. Additional observations of the weak inter-combination
line of C II at 2324 A have provided the C+ abundance which plays an
important role in chemical fractionation. Diffuse interstellar gas
towards local stars (e.g. Zeta Oph) will be observed lines of the less
abundant isotopic species of CO. A check on the Galactic gradient in
the 12C/13C ratio will be attempted by observing stars about 1 kpc
towards and away from the Galactic center.
Title: Carbon Chemistry in Interstellar Diffuse Clouds - the c2
Molecule :CYCLE 1 Observations
Authors: Lambert, David
Bibcode: 1990hst..prop.1066L
Altcode:
Observations of the C2 molecule in interstellar diffuse clouds are
based on the Phillips near-infrared system. The ultraviolet D-X (lambda
~2310 A) and F-X (lambda ~1341 A) transitions should provide detectable
C2 lines on HRS echelle spectra for lines-of-sight for which Phillips
system lines are essentially undetectable. Observations of C2 will be
attempted for line of sight containing rather little H2 (log N(H2) <~
20.6). The D-X and F-X bands transitions will be calibrated against the
Phillips system through observations of zeta Oph. The relation between
C2, H2, and other abundant molecules will be interpreted using cloud
models and thorough chemical reaction networks. Rotational excitation
will also be measured and interpreted.
Title: High resolution spectroscopy of R Coronae Borealis during
the 1988-1989 minimum.
Authors: Lambert, David L.; Rao, N. Kameswara; Giridhar, Sunetra
Bibcode: 1990JApA...11..475L
Altcode:
Moderate-resolution spectra of the C2 Swan 0-1 bandhead, the Na I D
lines and the K I resonance lines near 7660 A obtained at minimum light
during the 1988-1989 decline of R CrB are discussed and interpreted in
terms of a popular model for R CrB declines. High-resolution spectra
obtained at maximum light show blue-shifted, chromospheric emission
in the cores of the Na I D and the Sc II 4246.8 A lines.
Title: The Chemical Composition of Three Lambda Bootis Stars
Authors: Venn, Kim A.; Lambert, David L.
Bibcode: 1990ApJ...363..234V
Altcode:
Abundance analyses are reported for three certain members (Lambda
Boo, 29 Cyg, Pi1 Ori) of the class of rapidly rotating, metal-poor
A-type stars known as Lambda Bootis stars. Model atmosphere analysis
of high-resolution, high signal-to-noise spectra shows that the metal
deficiencies are more severe than previously reported: Fe/H = -2.0,
-1.8, -1.3 for Lambda Boo, 29 Cyg, and Pi1 Ori, respectively. Other
metals (Mg, Ca, Ti, and Sr) are similarly underabundant, with Na
often having a smaller underabundance. C, N, O, and S have near-solar
abundances. Vega is shown to be a mild Lambda Boo star. The abundance
anomalies of the Lambda Boo stars resemble those found for the
interstellar gas in which the metals are depleted through formation
of interstellar grains. It is suggested that the Lambda Boo stars are
created when circumstellar (or interstellar) gas is separated from
the grains and accreted by the star. The bulk of the interstellar
grains comprises a circumstellar cloud or disk that is detectable by
its infrared radiation.
Title: The Interstellar 12C/ 13C Ratio toward MU Normae
Authors: Crane, Philippe; Lambert, David L.; Palazzi, Eliana
Bibcode: 1990ApJ...363..192C
Altcode:
In this paper, the (C-12)/(C-13) ratio in the interstellar cloud
toward the star Mu Normae (HD 149038) is determined by estimating the
abundance of (C-13)H(+) relative to (C-12)H(+). The equivalent widths
of the lines for these ions were determined at 4232 and 3957 A. For
the (C-12)H(+) lines, these values were 26.988 + or - 0.108 mA at
4232 A and 15.561 + or - 0.250 mA, respectively, and for (C-13)H(+)
the corresponding values were 0.556 + or - 0.0 mA and 0.202 + or -
0.171 mA. The (C-12)/(C-13) ratio obtained from the 4232 A line was
56.9 + or - 6.4, while that from the 3957 A line was 85 + or - 72.
Title: On the Occurrence of Enhanced Lithium in Magellanic Cloud
Red Giants
Authors: Smith, Verne V.; Lambert, David L.
Bibcode: 1990ApJ...361L..69S
Altcode:
High-resolution spectra have been obtained for 27 red giants in the
Magellanic Clouds spanning a range in bolometric absolute magnitudes
(M_bol_ ~ -5 to -9). In a previous study, we found that five out of five
luminous asymptotic giant branch (AGB) stars in the Small Magellanic
Cloud (SMC) showed enhanced Li I resonance doublets (6707 A); the
extension here of our previous work reveals that the "Li- strong"
red giants in both Magellanic Clouds are luminous (M_bol_ ~ -6 to -7)
stars on the AGB. Lower luminosity (M_bol_ ~ -5.0 to -5.5) AGB stars
show no Li I features, while the very luminous (M_bol_ ~ -7 to -9)
red giants that are identified as massive, core-burning supergiants
also show no Li I features. We suggest that the enhanced Li abundances
in these luminous AGB stars are a byproduct of envelope burning in the
more massive (M ~ 4-8 M_sun_) AGB stars. We also demonstrate that these
Li-strong AGB stars may be a significant source of ^7^Li in a galaxy.
Title: High Dispersion Spectral Observations with the GHRS/HST of
Interstellar Lines Toward Xi Persei
Authors: Smith, A. M.; Savage, B.; Jura, M.; Ebbets, D.; Bruhweiler,
F.; Cardelli, J.; Lambert, D.
Bibcode: 1990BAAS...22.1277S
Altcode:
No abstract at ADS
Title: Is LR SCO and RCB star?
Authors: Giridhar, S.; Kameswara-Rao, N.; Lambert, D. L.
Bibcode: 1990Obs...110..120G
Altcode:
No abstract at ADS
Title: CN, CH, and CH + toward zeta Ophiuchi
Authors: Lambert, David L.; Sheffer, Yaron; Crane, Philippe
Bibcode: 1990ApJ...359L..19L
Altcode:
Observations with a resolution of 600,000 of interstellar absorption
from the CN 3874.6 A, CH 4300.3 A, and CH(+) 4232.5 A lines reveal
several new features of the clouds along the line of sight toward
Zeta Oph. The CN line consists of two overlapping components which
are similar to those seen in the CO pure rotational lines. The CH(+)
line is well described by a single Gaussian line profile with FWHM
of 3.5 km/s. The CH profile is a composite of a CN-like profile and
a CH(+)-like profile, indicating for the first time that CH exists in
two regions of very different character.
Title: Chemical Compositions of Four High-Latitude A--F Supergiants
Authors: Luck, R. Earle; Bond, Howard E.; Lambert, David L.
Bibcode: 1990ApJ...357..188L
Altcode:
The atmospheric parameters and chemical composition of HR 6144,
HD 161796, 89 Her, and HR 7671, four representative members of the
class of A- and F-type supergiants lying at high Galactic latitudes,
are determined. The abundance results for HR 6144, HD 161796, and 89
Her are strongly atypical of Population I supergiants in that they are
slightly metal-poor and have an overabundance of both C and N. Their
locations in the H-R diagram and the difficulty of assigning them to
Population I suggest that high-latitude supergiants are low-mass stars
in a post-AGB evolutionary stage. However, they do not reveal the heavy
s-process element enhancements seen in highly evolved B stars. HR 7671
differs from the other three stars in that it is very metal-poor,
slightly deficient in C and O, has s-process abundances enhanced by
a factor of four above solar, and has a surprising amount of Li. It
may be a post-AGB star descended from a Li-rich S-type star.
Title: S Stars without Technetium: The Binary Star Connection
Authors: Brown, Jeffery A.; Smith, Verne V.; Lambert, David L.;
Dutchover, Edward, Jr.; Hinkle, Kenneth H.; Johnson, Hollis R.
Bibcode: 1990AJ.....99.1930B
Altcode:
An exploratory survey of non-Mira MS and S star radial velocities
and the He I 10830 A triplet are used to test the assertion that S
stars without Tc are spectroscopic binaries, probably with white-dwarf
companions. It is found that the He I 10830 A triplet is a prominent
feature of the spectra of S stars without Tc, but the He I line is
undetectable in the spectra of most S stars without Tc. Also, when
radial-velocity variations attributable to orbital motion are detected
for S stars without Tc, the variations have a higher frequency that
that of S stars with Tc. The results suggest that the S stars without
Tc are spectroscopic binaries and are probably related to the G and
K giant Barium stars.
Title: Identification of solar vibration-rotation lines of NH and
the solar nitrogen abundance
Authors: Grevesse, N.; Lambert, D. L.; Sauval, A. J.; van Dishoeck,
E. F.; Farmer, C. B.; Norton, R. H.
Bibcode: 1990A&A...232..225G
Altcode:
High resolution solar spectra obtained from the ATMOS Fourier Transform
Spectrometer (Spacelab 3 flight on April 29 - May 6, 1985) made it
possible to detect for the first time vibration-rotation lines of NH
from the X3 Sigma(-) state near 3 microns. Using recent theoretical
results for the transition probabilities of 23 selected measured lines
of the 1-0 and 2-1 bands, a solar abundance of nitrogen of 8.06 + or -
0.07 is derived. This value is compared with the result derived from
N I lines and agrees with the abundance obtained from the 3s-3p, 3p-3d
and 3s-prime - 3p-prime transitions, A(N) = 8.00 + or - 0.09. The final
recommended solar abundance of nitrogen is A(N) = 8.00 + or - 0.05.
Title: Infrared Spectroscopy of Four Carbon Stars with 9.8-Micron
Emission from Silicate Grains
Authors: Lambert, David L.; Hinkle, Kenneth H.; Smith, Verne V.
Bibcode: 1990AJ.....99.1612L
Altcode:
High-resolution K band and low resolution 4 micron spectra were obtained
for four carbon stars showing IR emission by silicate grains. The
results of the analysis of the K band spectra show that they are J-type
stars. These results, together with published spectral classifications,
show that all known carbon stars with a silicate emission feature are
J-type stars. The 4 micron spectra are very similar to the spectra
of classical J-type carbon stars, and do not show SiO bands that
might come from a M giant companion. A binary model with a luminous
M giant companion as a source of the silicate grain is rejected. It
is proposed that the silicate grains formed from gas ejecta at or
before the He-core flash, and that the flash initiates severe mixing,
leading to the star's conversion to a J-type carbon star. The ejecta are
stored in an accretion disk around a low mass unevolved companion. If
it can be shown that the hypothesized accretion disk is stable and may
be heated adequately, this binary model appears to account for these
peculiar carbon stars.
Title: Carbon, Nitrogen, and Oxygen Abundances in the Chemically
Peculiar Stars of the Upper Main Sequence
Authors: Roby, Scott W.; Lambert, David L.
Bibcode: 1990ApJS...73...67R
Altcode:
Low-noise, high-resolution Reticon spectra are used to obtain C, N,
and O abundances for chemically peculiar stars with surface temperatures
between 7,000 and 15,000 K. The analysis includes C I, C II, N I, and O
I lines for 13 Am and related stars, nine Hg-Mn stars, 15 magnetic Ap
stars, and five standard stars. The C and O abundances show a roughly
monotonic increase with surface temperature. The C and O results are in
general agreement with radiative diffusion theory. The N abundances,
however, show that N is slightly deficient in cool nonmagnetic stars
and very deficient above 10,000 K in nonmagnetic stars. The results
for N disagree with simple diffusion predictions, suggesting that
a more detailed model is needed for partially ionized N near the
stellar surface.
Title: High-Resolution Spectroscopy of the C 2 Swan 0--0 Band from
Comet P/Halley
Authors: Lambert, D. L.; Sheffer, Y.; Danks, A. C.; Arpigny, C.;
Magain, P.
Bibcode: 1990ApJ...353..640L
Altcode:
High-resolution spectra of the C2 Swan system's 0-0 band from Comet
P/Halley in March 1986 show that the populations of the upper state's
rotational levels may be described by two rotational temperatures. The
low rotational levels provide a low temperature, Trot = about 600 -
700 K. The higher levels correspond to about 3200 K. If a contribution
from the 3200-K molecules is subtracted from the populations of the
low-J-prime levels, the latter are characterized by Trot = about 190
K. A comparison with recent predictions for C2 molecules fluorescing
in sunlight shows that the observed and predicted level populations
are in good agreement for J-prime greater than about 15, but there is
a sharp disagreement for the low rotational levels.
Title: The Chemical Composition of Red Giants. III. Further CNO
Isotopic and s-Process Abundances in Thermally Pulsing Asymptotic
Giant Branch Stars
Authors: Smith, Verne V.; Lambert, David L.
Bibcode: 1990ApJS...72..387S
Altcode:
Near-IR and IR spectra are analyzed to obtain elemental and isotopic C,
N, and O abundance, iron peak abundances, and heavy element s-process
abundances for a sample of M, MS, and S giants. The compositions of
the M giants are similar to those of G and K giants and consistent
with predictions for giants that have deep convective envelopes and
so have experienced the first dredge-up. The MS and S giants have
compositions that show the signatures of the third dredge-up that
occurs in thermally pulsing AGB stars. The sample shows that C-12,
a principal product of the He-burning shell, has been added to the
envelopes of MS and S stars. The C-12 enrichment is correlated with
a more marked enrichment of the s-process elements that are predicted
to be synthesized when a neutron source is ignited in the He-burning
shell. The MS and S giants show a higher N abundance than the M giants,
attributed to the expected deep mixing that occurs with the onset of
the episodic third dredge-up.
Title: On a Search for O-17 in Super-Metal-Rich Red Giants
Authors: Campbell, Bruce; Lambert, David L.; Maillard, Jean-Pierre
Bibcode: 1990PASP..102...79C
Altcode:
High-resolution infrared (4100-4500/cm) spectra of the SMR giants
Alpha Ser and Tau Dra and eight other giants are analyzed to obtain
the C-12/C-13 and O-16/O-17/O-18 ratios from the CO vibration-rotation
first-overtone bands. It is shown that the lower limits to the O-16/0-17
ratios together with published estimates for Alpha Ser and Mu Leo are
consistent with predictions for giants after the first dredge-up.
Title: The Chemical Composition of Stars
Authors: Lambert, David L.
Bibcode: 1990arpf.symp...75L
Altcode: 1990arpf.conf...75L
A review is presented of how advances in astronomical spectrometers are
providing opportunities for stellar spectroscopists to address a wide
variety of problems of stellar nucleosynthesis and evolution. Three
major topics are addressed in detail: (1) important astrophysical
problems whose solutions are dependent on accurate data on stellar
chemical compositions; (2) the stellar spectra that are basic
ingredients with which an abundance analysis commences; and (3) the
methods and associated tools of the abundance analysis that are applied
to the stellar spectra and other observations, such as photometry,
to obtain the abundances. These tools include a library of atomic and
molecular data and model stellar atmospheres.
Title: The chemical evolution of the galactic disk.
Authors: Edvardsson, B.; Gustafsson, B.; Andersen, J.; Nissen, P. E.;
Lambert, D. L.; Tomkin, J.
Bibcode: 1990apsu.conf...21E
Altcode:
No abstract at ADS
Title: Abundances in solar type disk stars.
Authors: Edvardsson, B.; Gustafsson, B.; Andersen, J.; Nissen, P. E.;
Lambert, D. L.; Tomkin, J.
Bibcode: 1990nba..meet...93E
Altcode: 1990taco.conf...93E
Abundances of O, Na, Mg, Al, Si, Ca, Ti, Fe, Ni, Y, Zr, Ba and Nd
have been derived for up to 189 solar type stars with known ages and
space velocities.
Title: The chemical composition of Algol systems - IV. The primary
of R CMa.
Authors: Tomkin, Jocelyn; Lambert, David L.
Bibcode: 1989MNRAS.241..777T
Altcode:
Low-noise Reticon observations of visible and near-infrared C, N,
O, S, and Fe lines were used to determine the abundances of these
elements in the F1 V primary of the eclipsing binary R CMa. It was
found that C/H = 0.0 + or - 0.2, N/H = 0.4 + or - 0.2, O/H = 0.3 +
or - 0.3, S/H = 0.1 + or - 0.2, and Fe/H = 0.1 + or - 0.1. Except
for a possible reduction of the C/N ratio (C/N = -0.4 + or - 0.2)
resulting from a small C depletion and N enhancement, this composition
is the same as the solar one enriched by approximately 0.1 dex. The
very low-mass secondary of this semi-detached system must have lost
a large fraction of its original mass. Some of this material would
have been extensively processed during the secondary's main-sequence
lifetime and would therefore have had a highly non-solar CNO-abundance
distribution. A discussion of the primary's observed CNO abundances
suggests that they are consistent with most, but not all, plausible
mass-transfer scenarios.
Title: Synthesis of Lithium and s-Process Elements in Small Magellanic
Cloud Asymptotic Giant Branch Stars
Authors: Smith, Verne V.; Lambert, David L.
Bibcode: 1989ApJ...345L..75S
Altcode:
High-resolution spectroscopy is presented for five luminous (M_bol_ ~
-6 to -7) asymptotic giant branch (AGB) stars in the Small Magellanic
Cloud (SMC). These stars are found to be metal-poor ([Fe/H] ~ -0.5)
but s-process-enriched, relative to Fe-peak elements, by up to a factor
of 10: these are s-process enhancements that are comparable to those
observed in Galactic S stars; thus, these SMC AGB stars have experienced
a third dredge-up. Of more interest is the fact that all five red
giants have rather strong Li I resonance lines (6707 A); an abundance
analysis reveals these stars to have Li abundances that are 100-1000
times that expected in red giants. We argue that these very luminous
(and probably massive) AGB stars have synthesized Li as predicted by
certain stellar models of hot-bottom convective-envelope burning. We
discuss the observations and models as a basis for understanding certain
phases of red giant evolution and as a potentially significant source
of Li in the universe.
Title: Analysis of coordinated observations of a giant stellar flare
Authors: Lambert, David L.
Bibcode: 1989uta..rept.....L
Altcode:
Multi-wavelength observations of a giant flare on the star AD Leo were
obtained with the 2.1 m and 0.9 m telescopes at McDonald Observatory
and the International Ultraviolet Explorer satellite. The quality,
spectral coverage, and time resolution of the data represented a major
improvement over any published stellar flare data. Two theoretical,
quantitative flare models were developed. Combining the models,
the chromospheric emission model predictions in the hydrogen Balmer
lines, Da II K, Mg II h + k and the optical continuum were compared
to the observations, with the result that much of the gradual phase
flare emission could be produced by the x ray and conductive heated
atmospheres. The models lend insight into the impulsive phase flare
emission, but do not reproduce it. Soft x ray and conductive heating of
the chromosphere is a natural consequence of the coronal temperatures
that have been observed during the gradual phase of flares on the sun
and on M dwarf stars. The improved flare observations and quantitative
flare models presented here show that these heating mechanisms can
produce atmospheres whose emission matches many of the observed stellar
flare features.
Title: A Search for Lithium-rich Giant Stars
Authors: Brown, Jeffery A.; Sneden, Christopher; Lambert, David L.;
Dutchover, Edward, Jr.
Bibcode: 1989ApJS...71..293B
Altcode:
Lithium abundances or upper limits have been determined for 644 bright
G-K giant stars selected from the DDO photometric catalog. Two of these
giants possess surface lithium abundances approaching the 'cosmic' value
of the interstellar medium and young main-sequence stars, and eight more
giants have Li contents far in excess of standard predictions. At least
some of these Li-rich giants are shown to be evolved to the stage of
having convectively mixed envelopes, either from the direct evidence
of low surface carbon isotope ratios, or from the indirect evidence
of their H-R diagram positions. Suggestions are given for the unique
conditions that might have allowed these stars to produce or accrete new
lithium for their surface layers, or simply to preserve from destruction
their initial lithium contents. The lithium abundance of the remaining
stars demonstrates that giants only very rarely meet the expectations
of standard first dredge-up theories; the average extra Li destruction
required is about 1.5 dex. The evolutionary states of these giants and
their average masses are discussed briefly, and the Li distribution
of the giants is compared to predictions of Galactic chemical evolution.
Title: HR 107 - an F-type mild barium dwarf star.
Authors: Tomkin, J.; Lambert, D. L.; Edvardsson, B.; Gustafsson, B.;
Nissen, P. E.
Bibcode: 1989A&A...219L..15T
Altcode:
The bright star HR 107 (HD 2454) with a spectral type F5V is shown
to have a composition similar to that of a mild Barium giant. This
discovery, which extends detection of bariumlike abundance anomalies
to the early F dwarfs, is consistent with the idea that barium stars
are created when the secondary star (the present barium star) of a
binary accretes mass from the primary (now, the white dwarf companion)
when the latter is an asymptotic giant branch star self-enriched in
carbon and the s-process elements.
Title: Zirconium sulphide in S stars.
Authors: Hinkle, Kenneth H.; Lambert, David L.; Wing, Robert F.
Bibcode: 1989MNRAS.238.1365H
Altcode:
Observations of J-band spectra from 7400-9700/cm were obtained for
three type-M and type-S Mira variables near minimum light. Two sets
of triple-headed bands been been discovered in the J-band spectrum of
the S-type Mira R And: at 7877, 7957, and 8030/cm and at 8379, 8459,
and 8530/cm. Additional heads are noted in R And at 7477/cm, near the
short-wavelength edge of the atmospheric window, and at 8968, 9031,
and 9063/cm. Conspicuous features in the spectra of Chi Cyg and R Cas
have been identified with the VO, TiO, and H2O bands.
Title: Classical Yang-Mills fields with conformal invariance: from
exact solutions to qualitative analysis
Authors: Antoine, J. -P.; Lambert, D.; Sepulchre, J. -A.
Bibcode: 1989CQGra...6..295A
Altcode:
No abstract at ADS
Title: Molecular Bands in the 1.1.-1.4μm Spectra of M-S Stars
Authors: Hinkle, K. H.; Lambert, D. L.; Wing, R. F.
Bibcode: 1989eprg.proc...61H
Altcode: 1989IAUCo.106...61H
No abstract at ADS
Title: The chemical composition of main sequence stars
Authors: Lambert, David L.
Bibcode: 1989AIPC..183..168L
Altcode: 1989cam..conf..168L
This review examines some recent observational enquires into the
chemical evolution of the Galaxy. After brief discussions of the
galactic abundance gradient and the age-metallicity relationship, the
major part of the review is devoted to a compilation and discussion of
the variation of the abundances of the chemical elements in disk and
halo stars; i.e., the run of [el/Fe] vs [Fe/H] for all the key elements
(el) from C to Eu.
Title: The Chemical Composition of Asymptotic Giant Branch
Stars(invited Paper)
Authors: Lambert, David L.
Bibcode: 1989eprg.proc..101L
Altcode: 1989IAUCo.106..101L
Low resolution spectroscopic and photometric studies of Magellanic
Cloud AGB stars are reviewed. Consideration is given to the spectral
classification and chemical composition of AGB stars, the role of
technetium in the atmospheres of S stars, and the chemical composition
of Galactic M, S, and C stars. The role of the third dredge-up of C-12
and s-process elements in the M-S-C sequence is examined. Data on the
chemical compositions of normal Galactic M-S-C- stars are reviewed,
showing that the data are consistent with the expectations for the
third dredge-up on AGB stars.
Title: Neutron source, neutron density and the origin of barium stars.
Authors: Malaney, Robert A.; Lambert, David L.
Bibcode: 1988MNRAS.235..695M
Altcode:
The authors present new high resolution spectra of the MgH profiles
in nine barium stars, and determine, by spectral synthesis techniques,
the magnesium isotopic ratios in each star. When compared with recent
AGB nucleosynthesis calculations, they can emphatically rule out the
operation of the 22Ne(α, n)25Mg reaction as the
neutron source responsible for the s-process enhancements observed in
these barium stars. The authors identify the properties required of
future AGB stellar models if the much favoured origin for the barium
stars, namely an AGB mass transfer scenario, is to be made consistent
with the observations reported here. Alternative evolutionary origins
of the barium stars are discussed.
Title: The Peculiar Supergiant HR 4049
Authors: Lambert, David L.; Hinkle, Kenneth H.; Luck, R. Earle
Bibcode: 1988ApJ...333..917L
Altcode:
New high-resolution spectra of the HR 4049, a warm supergiant with
an infrared excess in the visible and near-infrared as well as the
K band, are discussed. The K band spectrum shows weak absorption
lines attributable to circumstellar CO. The CO lines provide an
excitation temperature of 300 K and a column density of 10 to the
20th/sq cm. The chemical composition of the photosphere is derived
from visible and near-infrared spectra and an LTE model atmosphere
analysis. Spectroscopic indicators indicate that T(eff) is roughly 7500
K and log g is roughly 1.0. The star is very metal-poor but rich in C,
N, and O. The star resembles the previously analyzed halo stars BD +39
deg 4926 and HD 46703, which appear to be evolving between the tip of
the AGB and the top of the white dwarf cooling track.
Title: S-Process--Enriched Cool Stars with and without Technetium:
Clues to Asymptotic Giant Branch and Binary Star Evolution
Authors: Smith, Verne V.; Lambert, David L.
Bibcode: 1988ApJ...333..219S
Altcode:
High-resolution spectra at λ4260 have been obtained for 40 stars
of type MS or S to search for the presence of Tc I. In addition,
previously published Tc surveys provide an additional 18 stars for
a total sample of 58 MS or S stars. Most of these stars have also
been observed in Zr I, Y II, La II, and Nd II lines. These stars
show general s-process abundance enhancements. Of the total sample,
38% of these s-process-enriched stars do not show Tc. The authors
suggest that the MS and S stars are composed of two major groups: (1)
Tc-containing stars which are currently thermally pulsing AGB stars
undergoing third dredge-up and (2) Tc-poor stars which represent the
coolest members of the barium star class, where s-process enrichment
is probably the result of binary mass transfer in the past.
Title: Lithium in Lower--Main-Sequence Stars of the alpha Persei
Cluster
Authors: Balachandran, Suchitra; Lambert, David L.; Stauffer, John R.
Bibcode: 1988ApJ...333..267B
Altcode:
Lithium abundances are presented for main-sequence stars of spectral
types F, G, and K in the young open cluster Alpha Per. For 46
cluster members, a correlation between Li abundance and projected
rotational velocity v sin i is found: all of the Li-poor stars are slow
rotators. Two explanations are proposed to account for the correlation:
(1) that the Li depletion is introduced following a rapid spin-down
phase experienced by young low-mass stars, and that this episode of
Li depletion may be the dominant one determining the spread of Li
abundances among young low-mass main-sequence stars, and (2) that
star formation has occurred over a finite period such that the older
stars have undergone a spin-down and depletion of Li by a means that
may or may not depend on rotation. The Li abundance in the warm and
rapidly rotating stars appears to be undepleted, as is predicted by
recent models of pre-main-sequence stars. The depletion observed in
the cool stars exceeds the level predicted by these models.
Title: On the Identification of Molecules in the Cool Carbon Stars
Authors: Lambert, David L.
Bibcode: 1988PASP..100.1202L
Altcode:
Various problems encountered in identifying molecular lines in the
rich spectra of cool carbon and related stars are considered. Special
attention is given to the FeH, ZrS, and CN molecules. Following a review
of the principles of identifying stellar lines, recent successful
identifications are discussed that illustrate the wide range in the
incompleteness of the laboratory spectroscopy.
Title: Erratum - the Rapidly Rotating Spotted Red Dwarf Flare Star
GLIESE:890
Authors: Pettersen, B. R.; Lambert, D. L.; Tomkin, J.; Sandmann,
W. H.; Huang, L.
Bibcode: 1988A&A...203..210P
Altcode:
No abstract at ADS
Title: Frontiers in Stellar Evolution
Authors: Barnes, T. G., III; Lambert, D. L.
Bibcode: 1988BAAS...20R.966B
Altcode:
No abstract at ADS
Title: Possible identifications of the 3.4 μm feature.
Authors: Danks, Anthony C.; Lambert, D. L.
Bibcode: 1988ioch.rept...86D
Altcode:
A feature at 3.4 micrometer was first detected in Comet Halley by
the IKS spectrometer on board the Vega 1 probe; and subsequently from
the ground. The feature has since been reported in Comet Wilson. The
presence of the feature is of considerable interest for a number of
reasons. First, it may represent the detection of a new parent molecule,
and when combined with data from Giotto and Vega yield new information
on cometary chemistry and the early solar system composition. Secondly,
it may represent a link to the interstellar medium, the feature
corresponds in wavelength and shape with an interstellar feature
seen in absorption in a luminous star, towards the Galactic center
known as GC-IRS7. The feature in turn is thought to be related with
a growing family of unidentified infrared emission features seen in
stellar objects, planetary nebulae, reflection nebulae, HII regions
and extra galactic sources. These features occur at wavelengths 3.3,
3.4, 3.5, 6.2, 7.7, 8.6, and 11.25 micrometers. Further identification
theory is given.
Title: The Carbon Chemistry in Interstellar Clouds toward Moderately
Reddened Stars
Authors: Federman, S. R.; Lambert, D. L.
Bibcode: 1988ApJ...328..777F
Altcode:
New data for C2 toward X Per, HD 206267, HD 207198, and Gamma Cep,
for CH and CN toward X Per, and for CO toward HD 207198 have been
obtained. The column densities of CH, C2, CN, and CO toward the stars
in the Cepheus OB2 association are similar to reddened directions in
Perseus and in Ophiuchus, indicating a similarity in physical conditions
for the foreground clouds. The available data for other directions have
been analyzed and the resulting data applied to study the transition
from a photochemical regime to a chemical regime. The data for N(CN),
N(C2), and N(CO) have been plotted against N(CH) to elucidate the
chemistry of carbon-bearing molecules more clearly. The observed trends
for CN and C2 suggest a change in slope at N(CH) of roughly 5 x 10
to the 13th/sq cm. Below this value, photodestruction is predicted
to dominate and the slope is determined by the photochemistry. For
directions with more N(CH), a linear correlation consistent with
destruction by chemical reactions is expected.
Title: Oxygen Isotopic Abundances in Evolved Stars. IV. Five K Giants
Authors: Harris, Michael J.; Lambert, David L.; Smith, Verne V.
Bibcode: 1988ApJ...325..768H
Altcode:
Oxygen isotopic ratios have been measured in the atmospheres of
Alpha UMa, Beta Gem, Beta UMi, Alpha Ari, and Alpha Ser. It is shown
that some of the stars in this and previous samples have probably
experienced the helium core flash, and that the O-16/O-17 ratios tend
to confirm that 'extramixing' of CNO-cycled material into the stars'
envelopes has occurred as a result of the flash. The oxygen isotopic
ratios are much smaller than the anomalously high ratios seen in stars
in the later thermal-pulsing state of evolution. Hence, the anomalous
ratios cannot be explained by the helium core flash. It is proposed
that they are due to the addition by the third dredge-up mechanism
of helium-burned material which is devoid of both O-17 and O-18 and
therefore dilutes the O-17 and O-18 abundances acquired during earlier
evolutionary stages. This process may also explain the oxygen isotope
ratios seen in barium stars, if these are formed by mass transfer from
a thermally pulsing binary companion.
Title: Isotopic magnesium abundances in stars.
Authors: McWilliam, Andrew; Lambert, David L.
Bibcode: 1988MNRAS.230..573M
Altcode:
High-resolution spectra of the MgH A-X system near 5130 Å provide
the isotopic abundance ratios 25Mg/24Mg and
26Mg/24Mg for a sample of stars including several
old disc dwarfs and giants, a classical and a mild barium star, and a
weak G-band giant. The 25Mg and 26Mg isotopes
are underabundant in metal-poor stars. This result is qualitatively
consistent with predictions of stellar nucleosynthesis. The isotopic
ratios are normal for the barium stars and the weak G-band star.
Title: Solutions of Minkowskian sigma models on hyperbolic complex
Grassmann manifolds
Authors: Lambert, D.; Piette, B.
Bibcode: 1988CQGra...5..307L
Altcode:
No abstract at ADS
Title: The 12C/13C Ratio in Unevolved Cool Stars
Authors: Chmielewski, Y.; Lambert, D. L.
Bibcode: 1988IAUS..132..589C
Altcode:
The authors show that the carbon isotope ratio
12C/13C in the atmosphere of dwarf stars
can be determined with reasonable accuracy from high resolution,
high signal-to-noise ratio observations of the CH G-band in their
spectra. A preliminary analysis of these features in the spectra of
μ Her, δ Eri and τ Cet yields 12C/13C values
of 84, 80 and 150, respectively.
Title: Chemical Composition as a Signature of Stellar Evolution :
the Barium Stars
Authors: Lambert, D. L.
Bibcode: 1988IAUS..132..563L
Altcode:
The hypothesis that barium stars are the product of mass transfer
across a binary system is reviewed with special attention given to the
chemical composition of AGB stars (the mass-losing star in the binary)
and the Ba stars (the mass-gaining star).
Title: A New Absorption - Line Orbit for the Symbiotic Nova AG Pegasi
Authors: Slovak, M. H.; Lambert, D. L.
Bibcode: 1988ASSL..145..265S
Altcode: 1988IAUCo.103..265S; 1988syph.book..265S
Precise cross-correlation absorption-line velocities have been derived
using high resolution near infrared coudé spectra for the symbiotic
nova AG Pegasi. A revised weighted orbital solution is presented based
on both extant photographic and the new absorption-line velocities.
Title: Observations of s-Process Indicators in Barium Stars
Authors: Malaney, R. A.; Lambert, D. L.
Bibcode: 1988ode..conf..522M
Altcode:
The relative abundances of the magnesium isotopes and the abundance
of atomic rubidium observed in a stellar atmosphere are known to
be indicators of the s-process neutron source and neutron density,
respectively. This paper reports observations of these key s-process
indicators in the cool Ba II star, HD 178717, using molecular MgH
lines at 5101 Å and 5107 Å, and the Rb I line at 7800 Å. It is
determined that the 22Ne(α, n)25Mg source,
believed to operate in intermediate-mass AGB stars, is unlikely to be
responsible for the s-process in this star.
Title: Spectroscopic observations of yellow supergiants :
II. Multiperiodic variability of HR 8752.
Authors: Sheffer, Yaron; Lambert, David L.
Bibcode: 1987PASP...99.1277S
Altcode:
The authors discuss optical spectra obtained over the decade 1977 to
1986 and find complex variations in radial velocity and in Fe I emission
intensity. Power spectra of core velocities of high-excitation N I lines
reveal two significant peaks, at 421 days and at 315 days. A bimodal
radial pulsation for HR 8752 is inferred. Possible longer periods may
involve other modes and/or an orbital period due to the hot companion
of the supergiant. Short-term quasi-periodic variability in V and in
(B-V) supports the pulsation scenario with its dominant time scale
of 420 days. Various observables set the behavior of HR 8752 apart
from that of ρ Cas. This may be due to evolutionary or environmental
effects, or both.
Title: Further Observations of the He i 10830 Angstrom Chromospheric
Line in Stars
Authors: Lambert, David L.
Bibcode: 1987ApJS...65..255L
Altcode:
Observations obtained from July 1983 to January 1987 of the
chromospheric He I triplet at 10830 A are presented for 19 late-type
stars. The results confirm the suggestion by O'Brien and Lambert (1986)
that the 10830 A feature in K giants to the left of the coronal dividing
line (CDL) is broad, shallow, and constant. Arcturus and Gamma Dra to
the right of the CDL are found to show a variable 10830 A feature. The
variations appear to be periodic for Alpha Boo, with a basic interval
of about 78 days. It is suggested that the rotational period is about
233 days. For Gamma Dra the He I triplet was in emission with a variable
equivalent width from 1983 to 1987.
Title: The Strange Case of Beta Lyrae
Authors: Tomkin, Jocelyn; Lambert, David L.
Bibcode: 1987S&T....74..354T
Altcode:
The interior structure and composition of Beta Lyrae are examined. Beta
Lyrae is composed of a primary (B8 giant) and a secondary component; the
primary component is less massive (2 solar masses) than the secondary
component (12 solar masses) and is shedding its outer layer and
transferring it to the secondary component. The development of binaries
from main-sequence dwafs to red giants is described. The chemical
composition of Beta Lyrae and the CNO cycle are analyzed. The binary
displays He poorness, He richness, C,N,O abundances characteristic
of hydrogen burning, and a cosmic dose of other elements. The three
episodes of mass transfer for Beta Lyrae, which will result in the
Beta Lyrae system forming a single compact object, are discussed.
Title: On the Absence of Young White Dwarf Companions to Five
Technetium Stars
Authors: Smith, Verne V.; Lambert, David L.
Bibcode: 1987AJ.....94..977S
Altcode:
A search for hot companions to five stars of type MS and S has
been carried out using the International Ultraviolet Explorer
(IUE) satellite. No hot companions were detected for the MS stars
HR 85, 4647, 6702, and 8062, and the S star HR 8714. Limits on
the luminosities of possible white dwarf companions provide lower
limits of 2 - 5×108yr to the ages of any degenerate
companions. All five stars exhibit strong Tc I lines, and the presence
of technetium, with a half-life of 2.1×105yr, signifies
recent nucleosynthesis. The limits on the ages of possible white dwarf
companions that are ≥1000 half-lives of Tc exclude the possibility
that the s-process elemental enhancements seen in these MS and S stars
resulted from mass transfer from a more highly evolved companion (as
is probably the mechanism by which barium stars are created). These
MS and S stars represent a sample of true thermally pulsing asymptotic
giant-branch stars.
Title: On the evolutionary status of MU Leonis.
Authors: Harris, Michael J.; Lambert, David L.; Smith, Verne V.
Bibcode: 1987PASP...99.1003H
Altcode:
The paper presents the abundances of carbon, nitrogen, and oxygen and
the carbon and oxygen isotopic ratios measured in the CN-strong giant
star Mu Leo from CO and CN lines derived from a new 2-2.5 spectrum
and published equivalent widths of C2 and forbidden O I lines. The
relative abundances of C-12, N-14, and O-16 and the C-12/C-13 ratio
suggest that Mu Leonis has undergone the first red-giant dredge-up. The
CNO abundances suggest that Mu Leo is probably a metal-rich red giant
that has experienced the first dredge-up.
Title: A Revised Orbit for the Symbiotic Nova AG Pegasi
Authors: Slovak, M. H.; Lambert, D. L.
Bibcode: 1987BAAS...19.1087S
Altcode:
No abstract at ADS
Title: Neutron-Exposure Variations in MS and S Stars, and the
Implications for s-Process Nucleosynthesis
Authors: Smith, Verne V.; Lambert, David L.; McWilliam, Andrew
Bibcode: 1987ApJ...320..862S
Altcode:
High-resolution, near-infrared spectra have been obtained for 34
stars of types MS and S along with 14 M giants used as comparison
stars. Equivalent width measurements of spectral lines arising from
the heavy s-process species La II and Nd II, relative to the lighter
s-process species Y II, indicate a large range of neutron exposures in
the MS and S stars. The indicated range of mean neutron exposures is
approximately τ0 ≈ 0.1 - 0.6 mb-1. The solar
system s-process distribution is characterized by τ0 =
0.26 mb-1.The overall enhancement of s-process elements
observed in the MS and S stars indicates that they are substantial
contributors to the Galactic production of s-process nuclei.
Title: Stellar Spectroscopy, Evolution, and Nucleosynthesis on the
Asymptotic Giant Branch
Authors: Lambert, D. L.
Bibcode: 1987BAAS...19.1113L
Altcode:
No abstract at ADS
Title: High Resolution Spectroscopy and Analysis of the
C2(0,0) Band in Comet P/Halley
Authors: Danks, A. C.; Lambert, D. L.; Sheffer, Y.; Arpigny, C.;
Dossin, F.; Magain, P.
Bibcode: 1987BAAS...19.1124D
Altcode:
No abstract at ADS
Title: The rapidly rotating spotted red dwarf flare star Gliese 890.
Authors: Pettersen, B. R.; Lambert, D. L.; Tomkin, J.; Sandmann,
W. H.; Lin, H.
Bibcode: 1987A&A...183...66P
Altcode:
The authors present the results of spectroscopic, photometric, and
polarimetric observations of the spotted rapidly rotating M-dwarf
Gliese 890. Broad spectral lines and starspot modulation of the star's
luminosity with a period of 0.4312 days imply a rotational velocity
of 70 km s-1 with the rotation axis inclined 60°-90° to
the line of sight. Flare activity is reported for the first time on
this dM1.5e red dwarf. The authors discuss briefly some scenarios to
explain why this spotted flare star rotates so unusually rapidly.
Title: A Search for 14C 16O in the Atmospheres of Evolved Stars
Authors: Harris, Michael J.; Lambert, David L.
Bibcode: 1987ApJ...318..868H
Altcode:
The detection of (C-14)(O-16) in the spectra of MS, S, and C stars
would provide evidence of the operation of the (C-13)(alpha, n)(O-16)
process in the helium-burning shell during the double shell-burning
phase corresponding to a star's sojourn on the AGB. In this paper, MS,
S, and C star spectra of the first-overtone vibration-rotation bands
of the CO molecule at 2.4 microns are analyzed, and no evidence for
the presence of (C-14)(O-16) is found. Lower limits on the C-12/C-14
ratio ranging from 5000 to 28,500 are determined.
Title: Are the red supergiants epsilon Peg and 12 PUP victims of
mild s-processing ?
Authors: Smith, Verne V.; Lambert, David L.
Bibcode: 1987MNRAS.226..563S
Altcode:
An abundance analysis of eight G and K supergiants has been performed
with particular emphasis on two stars, Epsilon Peg and 12 Pup. It has
been reported (Kovacs, 1983) that these two stars exhibit selective
enhancement of Ba and, in the case of 12 Pup, Sr. Such a pattern
of abundance enhancement would occur for very mild s-processing
followed by extensive pollution of the star's outer envelope with this
processed material. This type of mixing is not predicted by current
models of stellar evolution. The previous Ba and Sr abundances were
based on very strong lines of Ba II and Sr II and such lines are
sensitive to microturbulence and conditions in the higher layers
of the stellar atmosphere. This analysis compares the Ba II and
Sr II line-strengths in Epsilon Peg and 12 Pup with six other cool
supergiants and also utilizes weak Ba I and Sr I lines seen in the
spectra of these stars. No enhancements of Ba or Sr, relative to the
other supergiants, are found for Epsilon Peg or 12 Pup. In addition,
calculations of the abundances produced by mild s-processing followed
by extensive mixing with the outer envelope show that Co and Sc should
also be enhanced substantially. Such enhancements are not observed in
any of the supergiants.
Title: Chemical evolution of the galaxy: abundances of the light
elements (sodium to calcium).
Authors: Lambert, David L.
Bibcode: 1987JApA....8..103L
Altcode:
The abundances of the light (Na to Ca) elements in disk and halo
stars are reviewed. New analyses are emphasized. Elements considered
are the alpha nuclei (Mg, Si, and Ca), and the odd-even nuclei (Na
and Al, also Mg-25 and Mg-26). The alpha nuclei are overabundant
(relative to Fe) in the old disk and halo stars. Halo stars have
alpha/Fe = about 0.3 with extreme halo stars showing possibly higher
overabundances. The scatter in alpha/Fe at a given Fe/H is small. To
within the observational errors, the abundance patterns for Mg, Si,
and Ca are identical. For disk stars, the Na and Al abundances relative
to Mg are almost independent of Fe/H. Halo stars show Na/Mg less than 0
and Al/Mg less than 0, but the form of the mean relation and the scatter
about the relation between odd-even/Mg and Fe/H remains uncertain.
Title: Isotopic Abundances of Silicon in Four Red Giants
Authors: Lambert, David L.; McWilliam, Andrew; Smith, Verne V.
Bibcode: 1987Ap&SS.133..369L
Altcode:
High-resolution spectra near 4 μm of the four red giants—β
Peg,o 1 Ori, 10 Dra, and HR 1105—have been
analysed to obtain estimates of the28Si/29Si
and28Si/30Si abundance ratios. For βPeg and the
S star HR 1105, the28Si/29Si ratio is close to
the solar ratio (28Si/29Si=20).29Si
appears to be underabundant in the MS staro 1 Ori
(28Si/29Si=40) and the M star 10 Dra
(28Si/29Si∼53). The30Si isotope
appears to be underabundant by, perhaps, about a factor of 2 in all
four stars.
Title: Oxygen Isotopic Abundances in Evolved Stars. III. 26 Carbon
Stars
Authors: Harris, Michael J.; Lambert, David L.; Hinkle, Kenneth H.;
Gustafsson, Bengt; Eriksson, Kjell
Bibcode: 1987ApJ...316..294H
Altcode:
Oxygen isotope ratios have been measured in 21 ordinary N-type carbon
stars and in five 13C-rich J-type stars. The ratios in
the ordinary N-type stars are 550 ≤ 16O/17O
≤ 4100 and 700 ≤ 16O/18O ≤ 2400. These
ratios are much higher than expected and are extremely difficult to
explain in terms of present theories of stellar evolution. The J-type
stars exhibit ratios 350 ≤ 16O/17O ≤ 850,
16O/18O ratios being very uncertain. Together with
nitrogen abundances measured by Lambert et al., these ratios preclude
the envelope burning (hot-bottom convection) hypothesis which has been
proposed for these stars.
Title: Lithium in the Alpha Per Cluster
Authors: Balachandran, S.; Lambert, D. L.; Stauffer, J. R.
Bibcode: 1987BAAS...19..702B
Altcode:
No abstract at ADS
Title: Velocity Structure of Stellar Atmospheres: R Scuti
Authors: Mozurkewich, David; Gehrz, R. D.; Hinkle, K. H.; Lambert,
D. L.
Bibcode: 1987ApJ...314..242M
Altcode:
Ten 2 micron spectra of R Scuti, the brightest RV Tauri variable, are
analyzed. The period, determined from the atomic absorption lines, is
142 days, not 70 days as proposed to explain the visible spectrum. The
infrared atomic absorption lines trace out a continuous, repeatable
velocity curve which is interpreted as the radial pulsation of the
star. The mean velocity is 37 km/s and the net displacement during
a cycle is 5 x 10 to the 12th cm. The CO lines form in the cooler
upper atmosphere. The dominant feature is material falling toward the
star at about 20 km/s. The region is supported by a shock wave which
passes through it once each pulsation; material heated by the shock
is responsible for the formation of the CO emission lines. An extended
envelope where the atomic emission lines form surrounds the star.
Title: Alpha Cygni as a radial-velocity variable.
Authors: Parthasarathy, M.; Lambert, David L.
Bibcode: 1987JApA....8...51P
Altcode:
One hundred and twentythree radial velocities for α Cyg are derived
between December 1977 and October 1982. These photospheric velocities
are derived from N I lines near 8700 Å. Semiregular variations in
radial velocities are present with periods of 7 to 20 days. The range
of variation of 14.3 km s-1 observed in present radial
velocities of α Cyg is close to the sum of the amplitudes (10.44 km
s-1) of all the pulsation periods from 7 to 101 days and
is also approximately equal to micro- and macro-turbulent velocities.
Title: Combined satellite and ground-based observations of the
quiescent, high latitude symbiotic variable AG Draconis=BD+67°922
Authors: Slovak, M. H.; Cassinelli, J. P.; Anderson, C. M.; Lambert,
D. L.
Bibcode: 1987Ap&SS.131..765S
Altcode: 1987IAUCo..93..765S
Satellite observations, from Einstein, IUE, and IRAS, have been
combined with ground-based observations to derive the quiescent energy
distribution of the symbiotic star AG Draconis. A detailed comparison
is made between the combined observations and various steady-state
composite models, including blackbody accretion disks.
Title: The C-12/C-13 and O-16/O-18 ratios in the solar photosphere
Authors: Harris, Michael J.; Lambert, David L.; Goldman, Aaron
Bibcode: 1987MNRAS.224..237H
Altcode:
The abundances of C-12, C-13 and O-18 in the solar photosphere have been
measured from more than 900 lines of the fundamental vibration-rotation
bands of isotopically substituted CO species. It is found that log
N(C-12) = 8.71 + or - 0.10, C-12/C-13 = 84 + or - 5, and O-16/O-18
= 440 + or - 50, i.e., the solar and terrestrial isotopic ratios
are essentially identical. These results, together with the known
abundances of lighter isotopes, constrain unorthodox models of the sun's
evolution which require the surface layers to have been subjected to
high temperatures. A requirement that the derived molecular abundance
be independent of the excitation potential and wavelength is not met by
all empirical model solar atmospheres. The Holweger and Muller (1974)
model meets the requirement and the Vernazza, Avrett and Loeser (1976)
model does not.
Title: The chemical composition of peculiar field stars in the
galactic halo.
Authors: Lambert, David L.
Bibcode: 1987ESOC...27...47L
Altcode: 1987sedo.work...47L
Data on the chemical composition of selected peculiar field halo stars
are reviewed. The selection of unevolved stars includes those early-type
stars with a Pop. I composition despite their residency and, perhaps,
their birth in the halo. The rare N-rich subdwarfs and dwarf stars
with anomalous elemental abundance ratios are discussed. Selection of
evolved peculiar stars is restricted to the post He-core flash stars on
and beyond the horizontal branch. The chemical composition of A-type
horizontal branch, RR Lyrae, Pop. II variable (BL Her, W Vir, RV Tau)
and A-F supergiant stars is reviewed.
Title: Observations of molecules in stellar atmospheres - Chemistry
near thermal equilibrium.
Authors: Lambert, David L.
Bibcode: 1987IAUS..120..583L
Altcode:
A general review is given of the astrophysical information obtainable
from observations of molecules in stellar photospheres. Through selected
examples, the use of molecules as thermometers (e.g., the OH 3 μm
V-R lines in the Sun and α Ori) and as probes of the isotopic (e.g.,
iMg in metal-poor dwarfs, 12C/13C
in cool carbon stars) and elemental abundances (e.g., CNO in red
giants) is sketched. All of the selected analyses assume that local
thermodynamic equilibrium (LTE) prevails.
Title: Spectroscopic Observations of Nova Cygni 1975: The Coronal
Line Region Revisited: Erratum
Authors: Ferland, G. J.; Lambert, D. L.; Woodman, J. H.
Bibcode: 1986ApJS...62..939F
Altcode:
No abstract at ADS
Title: The 10830 Angstrom Chromospheric Line of Helium in Bright Stars
Authors: Obrien, George T., Jr.; Lambert, David L.
Bibcode: 1986ApJS...62..899O
Altcode:
Results of a survey of the chromospheric line He I 10830 A in sixty F,
G, and K giants are presented. A weak He line appears in middle and
late F supergiants, increases greatly in strength by spectral type G0,
appears in all observed K stars, and disappears around type M1. Many of
the less luminous K stars show a constant 10830 A line which appears
similar in shape to that seen in the sun. Stars showing this profile
lie to the left of a well-defined boundary in the H-R diagram. Most
of the luminous and cooler K stars to the right of this boundary line
show highly variable He I profiles; variations on a time scale of a
month are common. Observations suggest episodic ejection of matter and
a subsequent return of some fraction of this matter to the photosphere
in these stars. The non-LTE radiative transfer problem for helium in
a stellar chromosphere is modelled.
Title: Heavy-Element Abundances in the Mild Barium Stars Omicron
Virginis and 16 Serpentis
Authors: Tomkin, Jocelyn; Lambert, David L.
Bibcode: 1986ApJ...311..819T
Altcode:
High-resolution Digicon and Reticon observations are used to determine
detailed heavy-element abundances for the mild barium stars O Vir and 16
Ser and a standard star (Ep Vir). A comparison of their heavy-element
abundances with those of the classical Ba II stars does not reveal
any significant difference in the element-to-element ratios, but the
overall enhancements (relative to iron) are smaller in the mild barium
stars. This suggests that the mild barium stars originated from the
same binary mechanism as the classical Ba II stars. The initial masses
of the Ba II stars' former AGB components may have been significantly
less than those of normal field red giants. Low masses for the Ba
II star progenitors imply that the Ba II stars, while they belong to
Population I, are older than the average Population I object, and so
account for their observed tendency to be metal deficient.
Title: Resolution of the (OI)+NH2 Blend in Comet P/halley
Authors: Arpigny, C.; Magain, P.; Manfroid, J.; Dossin, F.; Danks,
A. C.; Lambert, D. L.
Bibcode: 1986ESASP.250c..81A
Altcode:
Spectra of P/Halley were taken at very high resolution (0.15A)
to evaluate contamination of the forbidden oxygen doublet by NH2
features at low resolution. Comparison is made with other bright
comets. Appreciable variations are found in the NH2/(OI) ratio and
in the relative intensities of the NH2 emissions themselves. The
accuracy obtained on the oxygen abundance derived from the (OI) lines
is discussed. Mapping of these emissions over the coma is required to
correctly remove any important NH2 contribution at low resolution. This
should also provide information on the origin of the oxygen atoms in
the 1D level.
Title: The Chemical Composition of Red Giants. II. Helium Burning
and the s-Process in the MS and S Stars
Authors: Smith, Verne V.; Lambert, David L.
Bibcode: 1986ApJ...311..843S
Altcode:
Carbon, nitrogen, oxygen, Fe-peak, and heavy s-process elemental
abundances have been determined for an additional 12 stars of type M,
MS, or S. When combined with results obtained previously for nine stars
of type M or MS and the K5 giant α Tau, abundances are available for
22 cool red giants. Mg-isotopic ratios and technetium abundances are
estimated for selected stars. Of the 22 stars studied, eight are of
type MS and three of type S. Four of the MS stars show no measurable
enhancements of the s-process elements. The seven stars which exhibit
s-process enhancements also show increasing 12C abundances
and the 12C abundances correlate with both absolute s-process
enhancement and integrated neutron exposure. The results for the
s-process and 12C-rich stars are compared to theoretical
models of low-mass (1 - 2 M_sun;), thermally pulsing AGB stars.
Title: The Chemical Composition of Carbon Stars. I. Carbon, Nitrogen,
and Oxygen in 30 Cool Carbon Stars in the Galactic Disk
Authors: Lambert, David L.; Gustafsson, Bengt; Eriksson, Kjell;
Hinkle, Kenneth H.
Bibcode: 1986ApJS...62..373L
Altcode:
Chemical compositions of 30 Galactic carbon stars are determined from
high-resolution infrared spectra and new model atmospheres. Elemental C,
N, and O abundances are quite similar to those seen in planetary nebulae
and are consistent with those reported for G to M giants. Carbon stars
show only modest carbon enrichments: C/O is less than 1.6, and half the
sample have C/O less than 1.1. The 12C/13C ratio
is between 20 and 90 except for a few 13C-rich stars. When
line blanketing by HCN and C2H2 is included,
models predict the observed intensity of the H2 quadrupole
lines. This and other evidence shows that the carbon stars are not
hydrogen-deficient.
Title: Carbon abundances and meridional mixing in rapidly rotating
early-A stars.
Authors: Lambert, David L.; McKinley, Lindsay K.; Roby, Scott W.
Bibcode: 1986PASP...98..927L
Altcode:
Carbon abundances are obtained from lines of C I at 9100 A for 22
early-A main-sequence stars with projected rotational velocities of up
to 180 km/s. The abundance shows no significant trend with increasing
rotation. A preliminary conclusion is that meridional mixing currents
do not bring CN-processed material into the atmospheres of these
rotating A stars. Several carbon deficient stars are tentatively
identified as chemically peculiar A stars. Future surveys should cover
a sufficient wavelength interval to permit a spectral classification
and a determination of the microturbulence.
Title: Spectroscopic observations of yellow supergiants: I. Radial
pulsations of Rho Cassiopeiae.
Authors: Sheffer, Yaron; Lambert, David L.
Bibcode: 1986PASP...98..914S
Altcode:
High-resolution Reticon spectra of the F8 Ia-0 supergiant ρ Cas
providing lines of differing excitation potential are employed to
construct radial-velocity curves which reveal a semiregular pulsation
of the atmosphere. Analysis of line-doubling episodes supports the
presence of a dominant radial pulsation mode with a period around 500
days, significantly longer than the radial fundamental mode predicted
on the basis of Cepheid-like PLC relations for a star evolving to
the red supergiant region. Predicted periods for fundamental radial
pulsations in stars returning toward the blue supergiant region are
comparable to the observed quasi-period.
Title: The Carbon Chemistry in Interstellar Clouds Toward Moderately
Reddened Stars
Authors: Federman, S. R.; Lambert, D. L.
Bibcode: 1986BAAS...18.1025F
Altcode:
No abstract at ADS
Title: Spectroscopy, Photometry and Direct Filter Imagery of Comet
P/Halley
Authors: Arpigny, C.; Dossin, F.; Manfroid, J.; Magain, P.; Danks,
A. C.; Lambert, D. L.; Sterken, C.
Bibcode: 1986Msngr..45....8A
Altcode: 1986Msngr..45....8S
Observational techniques and instrumentation applied in ground-based
studies of the cometary coma during the post-perihelion phase of
the recent passage of Comet Halley are summarized. Applications of
a 1.5 m telescope equipped with a coude spectrograph for long slit
investigations of spectral intensity distributions, a 1.4 m CAT,
coude echelle spectrometer and reticon to evaluate the C-12/C-13
isotopic abundance ratio, and a 50 cm photometric telescope for
narrow bandwidth spectroscopy are described. Finally, the 1.5 m Danish
telescope, equipped with a CCD camera, collected high spatial resolution
photographs of the various coma components when the comet was 0.42 AU
from the sun.
Title: Spectroscopic Observations of Nova Cygni 1975: The Coronal
Line Region Revisited
Authors: Ferland, G. J.; Lambert, D. L.; Woodman, J. H.
Bibcode: 1986ApJS...60..375F
Altcode:
A synopsis of the McDonald Observatory spectrophotometric observations
of Nova Cyg 1975 (V1500 Cyg) is presented. These data are presented
in a form in which they can be readily accessed in the future, and
also a study is conducted of the continuous spectrum during the early
nebular phase. It is shown that: (1) the remnant probably maintained a
luminosity at or above the Eddington limit for at least a year after
outburst, (2) free-free emission from the coronal line region made a
significant contribution to the optical continuum, and (3) the coronal
line region was probably a significant source of ionizing radiation. The
energetics of this nova appear to be dominated by the lift-off energy
from the white dwarf and radiation from the coronal line region. Thus
the light curve of Nova Cyg may tell more about the cooling of the
coronal line region than about the decline of the central object. In
appendices the argon abundance of Nova Cyg (less than 8 times solar)
is discussed and it is described how to obtain copies of the McDonald
nova data.
Title: Isotopic Abundances of Magnesium in the Metal-poor Subgiant
nu INDI
Authors: Lambert, D. L.; McWilliam, A.
Bibcode: 1986ApJ...304..436L
Altcode:
An isotopic abundance analysis for Mg in the metal-poor subgiant v Indi
is reported. A high-resolution, high signal-to-noise spectrum centered
near 5131 Å in combination with synthetic spectra gives the ratios
25Mg/24Mg and 26Mg/24Mg
< 3%. The 25Mg and 26Mg isotopes are
obviously underabundant relative to solar system material, where
25Mg/24Mg = 13% and 26Mg/24Mg =
14%. These results confirm an earlier finding for Gmb 1830, a slightly
cooler and more metal-rich dwarf. An elemental abundance analysis
is presented for an interesting set of elements: Li, C, O, Mg, Si,
Ca, V, Mn, Ti, Fe, Co, Ni, Y, Ba, La, Ce, and Eu. The results show
that v Ind is a typical metal-poor subgiant with [Fe/H] = -1.52, and,
relative to Fe, a significant overabundance of oxygen ([O/Fe] = +0.52),
Mg, Si, and Ca.
Title: Lithium in Late-Type Giants. IV. The Subgiant CH Stars
Authors: Smith, V. V.; Lambert, D. L.
Bibcode: 1986ApJ...303..226S
Altcode:
Lithium abundances in 10 subgiant CH stars and one giant CH star are
reported. In no star was the Li I resonance doublet detected, and
upper limits to the lithium abundance in the range log epsilon-(Li)
of no more than 0.7 to log epsilon(Li) = 1.5 /log epsilon(H) = 12.0/
were determined for this sample of stars. The subgiant CH stars are on,
or near, the main sequence, and as they evolve up the red giant branch,
the deepening convective envelopes will dilute lithium by a factor
of about 30-50. This dilution factor, along with the upper limits
to the current lithium abundances, would give the subgiant CH stars
when they become red giants distinctly lower Li abundances than are
observed in the classical barium stars. This suggests that subgiant
CH stars are not progenitors of the classical barium stars. As the
subgiant CH stars do show C-12 and s-process enhancements and are
all binaries with low-luminosity companions, they may represent mass
transfer from a former asymptotic giant branch star (now a white dwarf)
onto a main-sequence companion (now a subgiant CH star).
Title: The chemical compositions of algol systems - III. Beta
Lyrae-nucleosynthesis revealed.
Authors: Balachandran, S.; Lambert, D. L.; Tomkin, J.; Parthasarathy,
M.
Bibcode: 1986MNRAS.219..479B
Altcode:
The B8 primary of the eclipsing binary star Beta Lyr is subjected to
high S/N ratio Reticon observations of the visible and near-IR lines
of He, C, N, O, Ne, and Fe, in order to determine their abundances. N
is noted to be extremely overabundant (20 times more so than in the
sun); C and O are very overabundant relative to N. The resulting C/N
and O/N ratios of respectively 5 and 8 are sufficiently close to the
equilibrium ratios of the CNO cycle as to leave little doubt that the
material has been fully processed by the CNO cycle. The spectroscopic
evidence found for He enrichment and extreme CNO cycling confirms the
major compositional changes demanded by the theory of nuclear burning,
thereby supporting current understanding of Beta Lyr.
Title: On the CH + Ion in Diffuse Interstellar Clouds
Authors: Lambert, D. L.; Danks, A. C.
Bibcode: 1986ApJ...303..401L
Altcode:
A survey of 65 lines of sight in the southern Milky Way for the
interstellar line of CH(+) at 4232 A yielded 30 detections. The
CH(+) column density N(CH+) is shown to be well correlated with
the rotationally excited H2 detected by surveys with the Copernicus
satellite: log N(CH+)/N(H2)ex inversely proportional to 2500/T(ex),
where T(ex) is the excitation temperature of H2 provided by the observed
populations in rotational levels J of about 3-5. This correlation is
strong evidence that CH(+) is formed in warm gas where the reaction
C(+) + H2 yields CH(+) + H is effective. Shocks probably provide the
necessary heating.
Title: Epsilon Aurigae in eclipse. II. Optical absorption lines from
the secondary.
Authors: Lambert, D. L.; Sawyer, S. R.
Bibcode: 1986PASP...98..389L
Altcode:
Optical high-resolution 2.7-m McDonald Observatory observations of
Epsilon Aur obtained during the 1982-1985 eclipse are discussed, with
focus on the K I resonance lines, some Fe II and Ti II lines in the
blue, and the near-infrared N I excitation lines. The N I lines are
immune to contamination by the secondary, and their radial velocity
decline over the three-year interval fits the predicted velocity
curve. The 7664 A and 7699 A K I lines strengthen greatly during the
eclipse due to gas in orbit around the secondary passing in front of
the primary, and the velocity pattern analysis indicates a mass of the
secondary to solar mass ratio of between about 3 and 6 and a primary
mass of 3 solar masses. The data are consistent with the picture of
a low-mass post-AGB primary having lost mass through a wind and by
Roche-lobe transfer to the secondary, and which will evolve to a white
dwarf in less than 10,000 years.
Title: Infrared flux excesses of the warm carbon stars.
Authors: Dominy, J. F.; Lambert, D. L.; Gehrz, R. D.; Mozurkewich, D.
Bibcode: 1986AJ.....91..951D
Altcode:
Infrared photometry of 31 stars having enhanced atmospheric carbon
abundances (types R, CH, Ba II) has been obtained to test for the
presence of circumstellar dust emission reported by others. Supplemented
by published ground-based and IRAS photometry, energy distributions
spanning the range 0.33-100 microns have been examined. No new excesses
large enough to be ascribed to the presence of dust having T = 1000-1500
K have been found in this survey of warm carbon stars. Some marginal
evidence exists for the presence of warm (T = 300 K) dust associated
with two stars. One star, BD + 17 deg 3325, earlier reported to have
excess emission at 3.5 microns, has been shown to have no substantail
flux excess at wavelengths as long as 4.6 microns, and perhaps 10.2
microns. The distinctive colors of carbon-rich stars are found to be
caused by increased line blanketing relative to the ordinary giants,
and not due to circumstellar dust emission.
Title: Carbon Abundances in Halo Dwarfs
Authors: Tomkin, J.; Sneden, C.; Lambert, D. L.
Bibcode: 1986ApJ...302..415T
Altcode:
A spectrum synthesis analysis has been made of Digicon observations
of CH in 32 halo F and G dwarfs with iron abundances as low as (Fe/H)
approximately equal to -2.5. The results, combined with earlier results,
also based on spectrum synthesis of Digicon CH spectra, show that
carbon follows iron down to (Fe/H) about -1.8; at lower metallicities
there is evidence of a positive trend in (C/Fe). It is suggested that
the change in slope of the (C/Fe) vs (Fe/H) relationship at (Fe/H)
about -1.8 is due to the appearance of Type I supernovae. The sense
of the change of slope is consistent with the prediction that Type I
supernovae are inefficient producers of carbon. More carbon abundances,
determined from analysis of CH in even more metal-deficient stars and,
also, determined from C I lines, are needed in order to establish
the relationship between carbon and iron abundances in extremely
metal-deficient (Fe/H less than about -2.0) dwarfs more firmly. One of
the program stars (BD -0 degrees 4470) is found to be a double-lined
spectroscopic binary composed of two nearly identical halo dwarfs.
Title: A spectrocopic view of Epsilon Aurigae.
Authors: Lambert, D. L.
Bibcode: 1986HiA.....7..151L
Altcode:
Spectroscopic observations from the ultraviolet, visible, and infrared
obtained at the recent eclipse are discussed. The rotation curve for
the disk around the secondary suggests that secondary is a low mass star
(or binary). This result with the known mass function suggests that the
primary may be a low mass (m1 ≤ the Chandrasekhar limit,
1.4 M_sun;) star leaving the AGB and evolving to the white dwarf region.
Title: The Chemical Composition of Cool Stars: II-The Hydrogen
Deficient Stars (review)
Authors: Lambert, David L.
Bibcode: 1986ASSL..128..127L
Altcode: 1986hdsr.proc..127L; 1986IAUCo..87..127L
The chemical composition of the R Coronae Borealis and cool hydrogen
deficient carbon stars is reviewed. Similarities and differences
between these stars and the hot He stars are noted. Proposed origins
for the hydrogen deficient stars are sketched. Recent claims that
normal (spectral type N) cool carbon stars are hydrogen deficient
are shown to be unfounded. Attention is drawn to the curious case of
population II variables (RV Tauri, W Virginis, and RR Lyrae stars)
whose atmospheres show striking deficiencies of heavy elements and
may be hydrogen deficient.
Title: Oxygen isotopic abundances in evolved stars. II. Eight MS
and S stars.
Authors: Harris, M. J.; Lambert, D. L.; Smith, V. V.
Bibcode: 1985ApJ...299..375H
Altcode:
Oxygen isotope ratios have been measured in five MS stars, two S
stars, and the slightly s-process-rich M giant 30 Her. Both the
16O/17O and 16O/18O
ratios are found to be much larger than expected from stellar
evolution theories. Both 16O/17O and
16O/18O are found to correlate well with
the abundance of 12C and with the degree of neutron
exposure necessary to explain the s-process element abundances. These
correlations cannot be explained by current theoretical models of
AGB stars, nor by simple modifications of these models. Explosive
nucleosynthesis in the envelope at extremely high temperatures during
the helium core flash is tentatively proposed to explain them.
Title: Carbon, nitrogen and oxygen in intermediate-mass supergiants :
is oxygen underabundant ?
Authors: Luck, R. E.; Lambert, D. L.
Bibcode: 1985ApJ...298..782L
Altcode:
New CNO analyses of two southern Cepheids and four early F-type
nonvariable supergiants are presented. Results for the new and
previous CNO analyses of intermediate-mass supergiants of spectral
type F, G, and K including the Cepheid variables are scrutinized for
possible causes of the systematically low oxygen abundances found in
these stars. A mild oxygen deficiency (0.3 dex relative to the solar
abundance) is confirmed. After a comprehensive discussion of potential
sources of error, it is concluded that the uncertainties arising from
the abundance analysis, as well as the uncertainty surrounding the
stars' initial composition, do not yet demand that the O deficiency
be attributed exclusively to the dredge-up of ON-cycled material.
Title: Isotopic Abundances of Magnesium in Metal Poor Stars
Authors: McWilliam, A.; Lambert, D. L.
Bibcode: 1985BAAS...17..841M
Altcode:
No abstract at ADS
Title: Erratum - Oxygen Isotopic Abundances in the Atmospheres of
Seven Red Giant Stars
Authors: Harris, M. J.; Lambert, D. L.
Bibcode: 1985ApJ...295..285H
Altcode:
No abstract at ADS
Title: The chemical composition of red giants. I. Dredge-up in the
M and MS stars.
Authors: Smith, V. V.; Lambert, D. L.
Bibcode: 1985ApJ...294..326S
Altcode:
Carbon, nitrogen, oxygen, Fe-peak, and heavy, s-process elemental
abundances have been determined for nine red giants of type M and
MS. The source material are high-resolution, high signal-to-noise
digital spectra in the infrared and near-infrared. The abundances of
the Fe-peak and heavier elements are based on atomic lines and are
referenced to a comparison red giant, alpha Tau, to minimize non-LTE
effects. The CNO abundances are based on molecular lines from CO, OH,
and CN. The CNO abundances clearly show the effects of CN-processed
material being dredged to the surface, while one MS giant shows an
excess of C-12, probably the result of He-burning products being dredged
up during thermal pulses on the asymptotic giant branch (AGB). The three
MS giants studied all show enhancements of the s-process elements Sr,
Y, Zr, Ba, and Nd. A range of integrated neutron exposures is evident
with one star showing a large enhancement of Ba and Nd relative to Sr,
Y, and Zr, while the other two show much lower enhancements of Ba and
Nd. It is suggested that the MS stars are AGB stars and that their
compositions reflect the addition of C-12 and s-process material from
He-burning thermal pulses.
Title: The chromospheric He I D3 line in main-sequence stars.
Authors: Danks, A. C.; Lambert, D. L.
Bibcode: 1985A&A...148..293D
Altcode:
High-resolution low-noise spectra of 21 unevolved stars of spectral
types, F, G, and K and luminosity classes V or IV were examined for the
chromospheric He I 5876 Å (D3) line. The equivalent width
of the D3 absorption line is correlated with the coronal
soft X-ray flux, and with the flux in the Ca II H and K chromospheric
emission cores. Rotational modulation of the D3 line is
detected in χ1Ori, and suggested for κ Cet and ɛ Eri.
Title: Oxygen isotopic abundances in evolved stars. I. Six barium
stars.
Authors: Harris, M. J.; Lambert, D. L.; Smith, V. V.
Bibcode: 1985ApJ...292..620H
Altcode:
Harris and Lambert (1984) have reported observations of the O-16/O-17
and O-16/O-18 ratios in several red giant stars. The obtained data
may be used as a basis for interpretation of the oxygen isotope ratios
in stars which are believed to be further evolved, namely the barium,
carbon, and S stars. The present investigation is concerned with the
results for a group of classical and mild barium stars. Abundance
determinations were made by analysis of high-resolution 2.3 micron
spectra. In this spectral region the first overtone vibration-rotation
bands of the CO molecule's ground electronic state give rise to a large
number of absorption lines, including lines due to the isotopically
substituted species (C-13)(O-16), (C-12)(O-17), and (C-12)(O-18). The
stars studied include the Ba II stars HD 178717, HD 121447, HD 101013,
and HR 774, and the mild barium stars 0 Vir and 16 Ser.
Title: Oxygen in Intermediate-Mass Supergiants
Authors: Luck, R. E.; Lambert, D. L.
Bibcode: 1985BAAS...17Q.560L
Altcode:
No abstract at ADS
Title: Light-element abundances in 20 F and G dwarfs.
Authors: Tomkin, J.; Lambert, D. L.; Balachandran, S.
Bibcode: 1985ApJ...290..289T
Altcode:
Red and near-IR spectral lines of the Galaxy are analyzed to extract
Na, Mg, Al, Si and Ca abundances. The data were obtained using a 2.7
m telescope fitted with a coudespectrograph and a Reticon photodiode
array tuned to the 6160, 6350, 6570, 6696, 7860 and 8740 wavelengths
of 20 F and G dwarfs in the disk and halo. The abundances were then
compared to recorded Fe abundances, particularly the forbidden Fe/H
ratio. Even numbered atomic number elemental abundances followed the
ratio down to values of -0.4, then increased relative to Fe in the
transition from disk to halo. The abundances of odd-numbered elements
more closely tracked the abundance of Mg in the disk, and experienced
a fairly abrupt decrease in the disk-halo transition.
Title: CNO abundances and 12C/13C ratios in
30 galactic N stars.
Authors: Gustafsson, B.; Lambert, D. L.; Hinkle, K. H.; Eriksson, K.
Bibcode: 1985ESOC...21..151G
Altcode: 1985pdce.work..151G; 1985pdcn.conf..151G
CNO abundances and C-12/C-13 ratios have been determined for 30 bright
galactic N stars by means of high-resolution FTS spectra, obtained with
the Kitt Peak 4 m Mayall reflector and covering the spectral region
from 4000/cm to 6600/cm. The spectra were analyzed with a new grid of
model atmospheres. Weak second-overtone vibration-rotation lines of CO
were used for determining the oxygen abundances, while C2 lines of the
Phillips system were used in the carbon determinations. Lines of the
Ballik-Ramsay system give similar results. The nitrogen abundances
were obtained from weak CN lines of the red system, and such lines
were also used for the determination of C-12/C-13 ratios. Consistent
isotopic ratios were obtained from the C-13O lines.
Title: The chemical composition of cool stars: I - The barium
stars. (Review paper)
Authors: Lambert, D. L.
Bibcode: 1985ASSL..114..191L
Altcode: 1985cseh.proc..191L
The chemical composition of barium stars and their putative relatives
is reviewed. Main sequence stars showing heavy element excesses,
subgiant CH stars, classical and mild barium giants, Sr-Ba supergiants,
and early R stars are reviewed. A cursory interpretation of the
abundance anomalies in terms of the key processes of nucleosynthesis
is presented. Mass transfer across a binary system is identified as
a plausible explanation for composition of barium stars.
Title: A Search for White Dwarf Companions of Asymptotic Giant
Branch Stars
Authors: Lambert, David L.
Bibcode: 1985iue..prop.2178L
Altcode:
A search will be carried out for hot, degenerate companions of red
giant stars whose atmospheres show evidence of recent contamination
by the products of Heburning nucleosynthesis. Observational data will
consist-of IUE short wavelength spectra of Peculiar M giants whose
chemical compositions have already been determined by Smith and Lambert
(1984). Many of these stars appear to be true asymptotic giant branch
(AGB) stars undergoing thermal pulses and the resultant dredge-up of
12C and s-process material. However, as is the case with the G and K
giant Barium stars, mass transfer across a binary system may turn a
normal star into one whose composition mimics that of an AGB star. In
understanding stellar evolution, the question of whether a peculiar
red giant is the result of its own internal processes or the result
of mass transfer from a more highly evolved companion is of crucial
importance. Many of the stars in Smith and Lambert's study show the
presence of the unstable element technetium (half-life = 2 x 10^5
yr), thus if they are the result of mass transfer from a former AGB
companion, the remnant stellar core must be hot and luminous; an ideal
target for IUE. Lack of a hot companion will provide hard evidence that
Smith and Lambert have indeed analyzed true AGB stars whose peculiar
compositions are the result of internal processes and, hence, key
objects in our understanding of the late stages of stellar evolution.
Title: The CN radical in diffuse interstellar clouds.
Authors: Federman, S. R.; Danks, A. C.; Lambert, D. L.
Bibcode: 1984ApJ...287..219F
Altcode:
A survey of 15 lines of sight for the CN B2Sigma(+) X2Sigma(+)
interstellar absorption lines shows that the CN column density
in diffuse interstellar clouds follows the relation log N(CN) is
proportional to m log N(H2), where m is approximately equal to 3. This
result is reproduced by a reaction network in which CN is produced
primarily from C2 by the neutral-neutral reaction C2 + N yields CN + C,
and photodissociation is the main destruction pathway for the neutral
molecules CH, C2, and CN. The CN radical is the first molecular species
observed in diffuse clouds that requires a neutral-neutral reaction
for its formation in the gas phase. The network also reproduces the
observed ratio N(CN)/N(H2).
Title: Carbon monoxide band intensities in M giant.
Authors: McWilliam, A.; Lambert, D. L.
Bibcode: 1984PASP...96..882M
Altcode:
The strength of the CO 2.3 μm bands was measured photometrically in
an attempt to identify extremely carbon poor M giants. Magnitudes
of about 200 bright M stars were obtained through a J filter, and
narrow filters centered on 2.17 μm, and 2.40 μm. No M giants with CO
indices indicative of extremely low carbon abundances were positively
identified. The tight correlation of CO index to effective temperature
does not extend to the extremely late and variable M giants. The CO
index in M giants defined by the 2.17 μm and 2.40 μm magnitudes
was calibrated by a spectrum synthesis technique. The dependence of
CO index upon carbon abundance, the 12C/13C
ratio, surface gravity, effective temperature, and microturbulent
velocity was investigated. Predicted and observed CO indices are in
excellent agreement for stars with a spectroscopically determined
carbon abundance.
Title: Oxygen isotopic abundances in the atmospheres of seven red
giant stars.
Authors: Harris, M. J.; Lambert, D. L.
Bibcode: 1984ApJ...285..674H
Altcode:
Theoretical arguments and observations indicate that on joining the red
giant branch all stars undergo a dredge-up process which brings to the
surface material which underwent CN-cycle reaction during the preceding
main-sequence evolution. The stars' atmospheres are thus enriched in,
for example, C-13 and N-14, Harris and Lambert (1984) have shown that
measurements of O-17 and O-18 abundances in the red supergiants Alpha
Ori and Alpha Sco may constrain explanations of the low C-12/C-13
ratios observed in these stars. The present investigation is concerned
with an extension of this analysis to seven other red giants of lower
mass. The considered stars cover a range of spectral types from K1 to
M5, and include the metal-poor low-mass object Alpha Boo. The results
obtained for the seven red giants and the data of Harris and Lambert for
the two red supergiants, show that the O-16/O-18 ratios in these stars
are consistent with the solar system and local interstellar values.
Title: Light element abundances in disk and halo dwarfs.
Authors: Tomkin, J.; Lambert, D. L.; Balachandran, S.
Bibcode: 1984PASP...96R.796T
Altcode:
No abstract at ADS
Title: Carbon, nitrogen and oxygem abundances in Betelgeuse.
Authors: Lambert, D. L.; Brown, J. A.; Hinkle, K. H.; Johnson, H. R.
Bibcode: 1984ApJ...284..223L
Altcode:
Elemental abundances of C, N, and O in the red M supergiant Belegeuse
are discussed to characterize their source. The discussion is based
on previous data on weak CO second-overtone V-R lines near 1.6 micron,
the NH fundamental V-R 1-0 and 2-1 bands between 3 and 4 microns, the OH
fundamental V-R bands near 3 microns, and the CN red system lines near
2 microns. Attention is also given to the forbidden O I lines and the
8000 A CN red system lines, and to comparisons between models for the
stellar atmosphere and the data. A model for an effective temperature
of 3800 K, a surface gravity of 0.0, and a microturbulence of 4 km/sec
is adopted which, if Betelgeuse is metal rich, would require forbidden
lines of Fe/H to be near 0.1. The forbidden CNO would be -0.04 relative
to the sun. The C/N ratio is nonsolar, which suggests contamination
of the Betelgeuse atmosphere with CN processed material.
Title: The Two Micron Spectrum of R Souti
Authors: Mozurkewich, D.; Gehrz, R. D.; Hinkle, K. H.; Lambert, D. L.
Bibcode: 1984BAAS...16.1013M
Altcode:
No abstract at ADS
Title: Lithium in late-type giants. III. The weak G band giants.
Authors: Lambert, D. L.; Sawyer, S. R.
Bibcode: 1984ApJ...283..192L
Altcode:
Li abundances are presented for nine different stars to demonstrate that
the abundances are consistent with the cosmic value. The observations
were made with the coude telescope and echelle spectrometer on
La Silla, covering the Li I 6707 A resonance doublet and the 800
A 2-0 band. The survey included the HD stars 18636, 31274, 36552,
40402, 78146 and 82595 and the HR stars 1299 and 4154, all Southern
Hemisphere weak Fraunhofer G band objects. Both Li-6 and Li-7 were
detected in HR 1299. It is suggested that the Li detected in all the
stars convected outward quickly and survived, while C diffused inward
and was converted to C-13 and N-14. The Li abundances can be observed
in both main sequence and red giant stars.
Title: The lithium isotope ratio in F and G stars.
Authors: Andersen, J.; Gustafsson, B.; Lambert, D. L.
Bibcode: 1984A&A...136...65A
Altcode:
The lithium doublet at 6707 Å has been observed at high spectral
resolution in the spectra of 8 solar-type dwarfs, known to have strong
Li lines, and in the Population II star ν Ind. The wavelength shifts of
the lines and the line profiles were analyzed in attempts to determine
the 6Li/7Li ratios. An upper limit of about 0.10
was found, in conflict with earlier claims that some of these stars
are rich in 6Li. However, it is suggested that some of them
have a 6Li/7Li ratio significantly different from
zero and that the isotopic ratio possibly is correlated with v sin i.
Title: IUE observations of DQ Herculis and its nebula, and the nature
of thecold nova shells.
Authors: Ferland, G. J.; Williams, R. E.; Lambert, D. L.; Shields,
G. A.; Slovak, M.; Gondhalekar, P. M.; Truran, J. W.
Bibcode: 1984ApJ...281..194F
Altcode:
The nebula ejected in the 1934 outburst of the classical nova DQ Her
is remarkable for its unprecedentedly low temperature of Te 500 K as
measured by Williams et al. (1978). In this paper, IUE observations
are combined with Steward optical spectra. It is confirmed that the
gas is quite cold. It is further shown that the gas is ionized by the
radiation field of the central object. X-ray, ultraviolet, optical and
infrared observations of the underlying binary are combined with the
extreme-ultraviolet continuum deduced from the level of ionization of
the nebula to obtain a composite energy distribution for the central
object. This energy distribution bears no resemblance to that predicted
by theoretical models of accretion disks. Photoionization models of the
nebula using the deduced continuum, as well as theoretical accretion
disk continua, are presented to show that the low electron temperature
is the result of the very high metal abundances which characterize
nova shells. Infrared fine-structure lines are efficient coolants,
and low temperatures are achieved for a wide variety of radiation
fields. The implications of these results for nebulae surrounding
other old novae are discussed.
Title: Oxygen isotopes in the atmospheres of Betelgeuse and Antares.
Authors: Harris, M. J.; Lambert, D. L.
Bibcode: 1984ApJ...281..739H
Altcode:
Betelgeuse (Alpha Ori) and Antares (Alpha Sco) are red supergiants with
an extensive convective outer envelope. The present investigation is
concerned with an analysis of high-resolution 5 micron spectra of the
two stars. The considered spectra had been acquired with the Fourier
transform spectrometer at the coude focus of the Mayall 4 m reflector. A
red supergiant's extensive atmosphere ensures that the less abundant
species involving O-17 and O-18 contribute a significant number of
lines. The obtained isotopic abundance ratios are presented in a table,
taking into account C-12/C-13, O-16/O-17, O-16/O-18, and O-17/O-18. The
nucleosynthesis of oxygen isotopes is discussed. An analysis of the
oxygen isotopes in the atmosphere of the two stars shows that O-17 is
enriched because of the CNO cycles and convective mixing.
Title: Nitrogen abundances in disk and halo dwarfs.
Authors: Tomkin, J.; Lambert, D. L.
Bibcode: 1984ApJ...279..220T
Altcode:
Atmospheric parameters and abundances are calculated for 14 F and
G dwarfs of the disk and halo populations with metal deficiencies
between -2.3 and -0.3 on the basis of high-resolution spectra of the
3360-A NH and 4310-A CH bands obtained using a coudespectrograph and
a 936-diode Digicon on the 2.7-m telescope at McDonald Observatory,
with resolutions 26 pm (NH) and 12 pm (CH). The results are presented
in tables and graphs and discussed in the light of theoretical models
of N nucleosynthesis through CNO cycles. The identification of N as
a primary element in these objects is explained by the tendency of O
to be less deficient than C, N, or Fe.
Title: The CN Radical in Diffuse Interstellar Clouds
Authors: Federman, S. R.; Danks, A. C.; Lambert, D. L.
Bibcode: 1984BAAS...16..484F
Altcode:
No abstract at ADS
Title: A high-resolution infrared spectrum of the Wolf-Rayet star
HD 193793.
Authors: Lambert, D. L.; Hinkle, K. H.
Bibcode: 1984PASP...96..222L
Altcode:
A high-resolution infrared (2.0 - 2.4 μm) spectrum of
the WC7 Wolf-Rayet star HD 193793 is presented. A weak He I
2p1P0 - 2s1S absorption line is
identified at a velocity of -2650 km s-1. Emission lines
are identified with transitions in He I, He II (weak), and C IV. The
strongest emission line at about 2.06 μm has previously been assigned
to He I 2p1P0 - 2s1S with C IV 3d
→ 3p as a minor contributor but the authors' spectrum shows that
C IV not He I is the dominant contributor. A preliminary analysis of
the recombination lines gives an abundance ratio C/He > 0.08.
Title: A Search for Lithium-Rich Giant Stars
Authors: Sneden, C.; Brown, J. A.; Dutchover, E., Jr.; Lambert, D. L.
Bibcode: 1984BAAS...16R.490S
Altcode:
No abstract at ADS
Title: Niobium and rubidium in the barium star zeta Capricorni.
Authors: Smith, V. V.; Lambert, D. L.
Bibcode: 1984PASP...96..226S
Altcode:
An abundance analysis of the elements Rb to Nb (relative to the
G-giant standard ɛ Vir) has been carried out for the barium
star ζ Cap using low-noise, high-resolution Digicon and Reticon
spectra. Tech's (1971) low abundance of Nb in ζ Cap suggests that the
s-process ceased less than about a million years ago. The authors'
improved analysis finds a higher Nb abundance consistent with the
complete decay of 93Zr to 93Nb; i.e., more than
3×106 years have elapsed since the principal phase of
s-processing. The abundance of Rb suggests a neutron density of N(n)
≡ 107cm-3 for the s-process site at the close
of s-processing.
Title: High Latitude F-Type Supergiants
Authors: Luck, R. E.; Bond, H. E.; Lambert, D. L.
Bibcode: 1984BAAS...16R.490L
Altcode:
No abstract at ADS
Title: La Terre, notre planète
Authors: Lambert, D.
Bibcode: 1984C&T...100Q.112L
Altcode:
No abstract at ADS
Title: The CH radical in diffuse interstellar clouds.
Authors: Danks, A. C.; Federman, S. R.; Lambert, D. L.
Bibcode: 1984A&A...130...62D
Altcode:
Observations of the interstellar CH A-X R2(1) line at 4300.3
Å are presented for 29 lines of sight extending form 140 to 2800
pc in the Galactic plane. A comparison of the CH and H2
column density shows that N(CH) ∝ N(H2) as expected
for production of CH by a gas phase reaction network running in
molecular hydrogen. The network also reproduces the observed ratio
N(CH)/N(H2) for these diffuse interstellar clouds.
Title: The solar system
Authors: Lambert, David
Bibcode: 1984sosy.book.....L
Altcode: 1984QB501.3.L354...
Text and photographs demonstrate that of the various planets, only
Earth can support life.
Title: Nitrogen Abundances in Disk and Halo Dwarfs
Authors: Tomkin, Jocelyn; Lambert, David L.
Bibcode: 1984LNP...193..220T
Altcode: 1984csss....3..220T
High-resolution Digicon spectra of the NH band at 3360 Å have been
analyzed by spectrum synthesis to determine nitrogen abundances in
14 disk and halo F and G dwarfs with metal deficiencies covering the
range -2.3 ≤ [Fe/H] ≤ -0.3. We have determined carbon abundances
from parallel observations and analysis of CH. In all stars nitrogen
closely follows carbon and iron; i.e. [N/C] = 0.0. We conclude that
nitrogen is a primary element.
Title: High resolution stellar spectrometry - Application to the Li
isotope problem
Authors: Andersen, J.; Gustafsson, B.; Lambert, D. L.
Bibcode: 1983Msngr..34...26A
Altcode:
The ESO's CoudeEchelle Spectrometer is presently used in investigtions
of the mechanisms by which Li is produced in stars and the connection
between atmospheric Li abundance and the degree of mixing in the stellar
envelope. Determinations are made by measurements of the Li-6/Li-7
isotopic abundance ratio, and of the Li abundance in such evolved
stars as those with weak G-bands, whose chemical composition suggests
that their atmospheres are mixed with large amounts of CNO-processed
interior materials. The present observations have nearly doubled the
number of weak G-band stars with Li, enlarging the observational
bases for attempts to understand the conditions under which these
stars preserve or produce Li.
Title: The D3 5876 Å line in main sequence stars:
a search for rotational modulation in ɛ Eri and κ Cet.
Authors: Lambert, D. L.; Obrien, G. T.
Bibcode: 1983A&A...128..110L
Altcode:
High-resolution, low-noise spectra of the He I 5876 Å (D3)
absorption line in 6 main sequence stars are discussed. A marked
variation of D3 in κ Cet over a 17 d period is attributed
to rotational modulation: the equivalent width Wλ varied
between 17.4 and 25.8 mÅ. No modulation is seen in ɛ Eri. The
D3 line was also seen in spectra of χ1 Ori,
χ Eri, and ζ Dor, but not seen in ο2 Eri.
Title: Epsilon Aurigae in eclipse. I. Ultraviolet spectroscopy during
INGRESS and totality.
Authors: Parthasarathy, M.; Lambert, D. L.
Bibcode: 1983PASP...95.1012P
Altcode:
Epsilon Aurigae is a long-period eclipsing system containing a F0 Ia
supergiant and an unseen slightly less-massive secondary. A primary
eclipse began in mid-1982 with the unseen companion passing in front
of the supergiant. Low-resolution ultraviolet (IUE) spectra of Epsilon
Aur in 1982 and early 1983 provide eclipse light curves extending
into the total phase of the current eclipse. The depth of eclipse
from 3000 A to 1700 A is slightly deeper than at visual wavelengths
(0.8 m). The depth declines for wavelengths less than 1700 A and
is just 0.2 m at wavelengths less than 1300 A. The disappearance of
the eclipse at wavelengths less than 1300 A may be attributed to a
hot star or spot within the disk-shaped secondary. A main-sequence
star of spectral type B0 accounts for the observations. However, an
alternative site of the ultraviolet excess may be the primary's upper
photosphere or chromosphere.
Title: Heavy-element abundances in the classical barium star HR 774.
Authors: Tomkin, J.; Lambert, D. L.
Bibcode: 1983ApJ...273..722T
Altcode:
Low-noise high-resolution Digicon and Reticon spectra of HR 774 are
analyzed to determine abundances for all accessible heavy elements in
the visual and near-infrared. The authors find evidence of departures
from LTE as large as 0.5 dex affecting the low-excitation neutral
lines of heavy elements in HR 774 and the standard star (β Gem). These
severe effects cancel in a comparison of HR 774 with β Gem. Abundances
of 19 heavy elements (Z ≥ 37) are determined and used to derive
s-process overabundances. The predicted s-process abundances fit the
derived s-process abundances remarkably well. The pattern of s-process
abundances is consistent with the 13C(α, n)16O
reaction as the neutron source and excludes the 22Ne(α,
n)25Mg reaction.
Title: The Chemical Composition of M and MS Giants
Authors: Smith, V. V.; Lambert, D. L.
Bibcode: 1983BAAS...15R.981S
Altcode:
No abstract at ADS
Title: Epsilon Aurigae
Authors: Parthasarathy, M.; Lambert, D. L.
Bibcode: 1983IAUC.3857....1P
Altcode: 1983IAUC.3857....0P
M. Parthasarathy and D. L. Lambert, McDonald Observatory, communicate
the following correction to their note on IAUC 3848: "Observations of
epsilon Aur during totality phase show variation in the strength of the
K 770-nm resonance line. W-lambda was 0.055 nm during 1982 Dec.-1983
Mar. and 0.043 nm during 1983 Apr.-July. The H-alpha line is broad,
and the emission in the wings has disappeared."
Title: Interstellar C2 in the Ophiucus clouds.
Authors: Danks, A. C.; Lambert, D. L.
Bibcode: 1983A&A...124..188D
Altcode:
Interstellar lines of the C2 molecule are reported from high
resolution high signal to noise spectra of ζ Oph, χ Oph and ρ Oph
A. Rotational level populations for the C2 toward ζ Oph are
not described by a single rotational temperature. The populations are
quite consistent with a competition between collisional and radiative
excitation under conditions expected for the ζ Oph cloud. The
excitation of the C2 molecules toward χ Oph and ρ Oph A
is similar to the results found for ζ Oph. The C2 column
density is N(C2) = 2.2×1013, 3.5×1013
and 2.6×1013 cm-2 toward ζ Oph, χ Oph and ρ
Oph A respectively.
Title: Epsilon Aurigae
Authors: Parthasarathy, M.; Lambert, D. L.
Bibcode: 1983IAUC.3848....2P
Altcode: 1983IAUC.3848....0P
M. Parthasarathy and D. L. Lambert, McDonald Observatory, report:
" Observations of epsilon Aur during totality near zero phase show a
significant decrease in the strength of the K 770-nm resonance line:
W-lambda was 0.055 nm during 1982 Dec.-1983 Mar., 0.040 nm during
Apr.-May and 0.024 nm during July. The Na D lines also decreased
in strength, their strength now being similar to that before the
eclipse. The H-alpha line is broad, and the emission in the wings has
disappeared. These observations suggest that the neutral gas is mostly
confined to the outer regions of the eclipsing object."
Title: Do all barium stars have a white dwarf companion ?
Authors: Dominy, J. F.; Lambert, D. L.
Bibcode: 1983ApJ...270..180D
Altcode:
International Ultraviolet Explorer short-wavelength, low-dispersion
spectra were analyzed for four barium, two mild barium, and one R-type
carbon star in order to test the hypothesis that the barium and related
giants are produced by mass transfer from a companion now present as
a white dwarf. An earlier tentative identification of a white dwarf
companion to the mild barium star Zeta Cyg is confirmed. For the
other stars, no ultraviolet excess attributable to a white dwarf is
seen. Limits are set on the bolometric magnitude and age of a possible
white dwarf companion. Since the barium stars do not have obvious
progenitors among main-sequence and subgiant stars, mass transfer must
be presumed to occur when the mass-gaining star is already on the
giant branch. This restriction, and the white dwarf's minimum age,
which is greater than 8 x 10 to the 8th yr, determined for several
stars, effectively eliminates the hypothesis that mass transfer from
an asymptotic giant branch star creates a barium star. Speculations
are presented on alternative methods of producing a barium star in a
binary system.
Title: HR 4912 : a variable of the old-disk population.
Authors: Luck, R. E.; Lambert, D. L.; Bond, H. E.
Bibcode: 1983PASP...95..413L
Altcode:
Spectrographic observations of the F3 Ia low-amplitude variable (period
44-68 days) star HR 4912 are reported. Spectra obtained with an echelle
spectrograph on the 4-m telescope at Cerro Tololo in April, 1981, at
5200-6900 A and nominal resolution 0.1 A were digitized using the KPNO
microdensitometer, reconstructed, and smoothed; digital spectra obtained
with a Reticon-equipped coudespectrometer on the 2.7-m reflector at
McDonald Observatory in June, 1982, in 100-A exposures at 5380, 6300,
6385, 6470, 6560, and 8710 A were FFT smoothed; the continuum was set
by hand from both data sets, and usable equivalent widths were obtained
for about 300 lines. The analytical model and its basic assumptions
are discussed. Tables of calculated metallic and CNO abundances are
presented. From the relatively low Fe/H ratio (-1.2) it is inferred
that HR 4912 is a representative of the old-disk population and not
a classical cepheid. The absolute magnitude estimation (about -4)
places the star to the left of the asymptotic giant branch on the
HR-diagram evolutionary track for a 0.6-solar-mass-function CO-core
model, consistent with an SRd-variable classification.
Title: The chemical composition of Algol systems- II. The carbon
and nitrogen abundances of the secondaries of U CEP and U Sge.
Authors: Parthasarathy, M.; Lambert, D. L.; Tomkin, J.
Bibcode: 1983MNRAS.203.1063P
Altcode:
A spectrum synthesis analysis of Digicon spectra of CH and CN in the
secondaries of U Cep and U Sge shows that they are carbon deficient,
[C/Fe] ∼ -0.5, and nitrogen rich, [N/Fe] ∼ +0.5. The metal
abundance of both secondaries is normal, [Fe/H] = 0.0 ± 0.3. The
C deficiency and N overabundance of the secondaries are the result of
conversion of C to N by the CN cycle, while the secondaries were on the
main sequence, followed by mixing to the surface. These abundances are
therefore observational evidence in favour of the generally accepted
idea that the secondaries of semi- detached systems are post- main-
sequence objects. The C deficiency and N overabundance of the
secondaries are more marked than in the typical single G or K giant. We
interpret this as a result of mass loss of the unprocessed surface
material prior to the onset of mixing. At the time of mixing in the
secondaries there was less unprocessed material and therefore less
dilution of the CN cycle processed material than in a single G or K
giant. Mass loss subsequent to mixing does not alter the surface
composition of the secondaries. This explains why secondaries that
have suffered much more extensive mass loss than those of U Cep or
U Sge do not show the extremes of composition that one would expect
in the absence of mixing. An example is the secondary of S Cnc (K2),
which has a mass of only 0.2Msun and for which - from a
preliminary analysis of CH - we find [C/Fe] ∼ -0.5.
Title: High-resolution spectra of C2 Swan bands from comet West
1976 VI
Authors: Lambert, D. L.; Danks, A. C.
Bibcode: 1983ApJ...268..428L
Altcode:
The present study of the comet West 1976 VI was intended to probe the
C2 band structure by using sufficient spectral resolution to resolve
the rotational structure of the bands. The study demonstrates that
high-resolution spectra of the 0-0 Swan band provide an accurate
determination of the C-12/C-13 ratio. The spectral resolution should,
if possible, slightly exceed that employed on comet West. The conducted
analysis of the C2 Swan Delta v = -1 sequence provides an excitation
temperature of 3500 K for comet West at a heliocentric distance of
0.78 AU, which is considerably cooler than the vibrational temperature
predicted by two recent calculations describing cometary C2 molecules
bathed in sunlight.
Title: The pure rotation spectrum of the hydroxyl radical and the
solar oxygen abundance
Authors: Goldman, A.; Murcray, D. G.; Lambert, D. L.; Dominy, J. F.
Bibcode: 1983MNRAS.203..767G
Altcode:
Observations of pure rotation 2pi (0-0) lines of the hydroxyl radical
in the solar photospheric spectrum provide a new and independent
determination of the solar oxygen abundance. These OH lines with
the Holweger-Mueller (1974) model atmosphere give log epsilon (O)
= 8.84, which is within 0.08 dex of the abundance provided by the
O I forbidden lines and the same model. It is pointed out that a
detection of the CH pure rotation lines would permit a determination
of the O/C abundance ratio with a much reduced sensitivity to the
model atmosphere uncertainties. Selected combinations of atomic and
molecular (not including the OH pure rotation lines) lines give log
epsilon (O)/epsilon (C) = 0.23 + or - 0.03 dex.
Title: Combined X-ray, Ultraviolet and Ground-based Observations of
the Symbiotic Star AG Draconis at Quiescence
Authors: Slovak, M. H.; Anderson, C. M.; Cassinelli, J. P.; Lambert,
D. L.
Bibcode: 1983BAAS...15Q.665S
Altcode: 1983BAAS...15Z.665S
No abstract at ADS
Title: Evidence of non-LTE in photospheric lines of G and K giants.
Authors: Brown, J. A.; Tomkin, J.; Lambert, D. L.
Bibcode: 1983ApJ...265L..93B
Altcode:
A local thermodynamic equilibrium (LTE) model atmosphere analysis of
weak Zr I and Ti I lines in 33 field G and K giants suggests that,
on the average, Zr is 0.4 dex less abundant relative to Ti than it is
in the sun. The fact that Zr and Ti abundances based on Zr II and Ti
II lines do not show any relative overabundance of Zr shows that this
Zr underabundance is not real; rather it is strong evidence that some
lines of neutral metal atoms are subject to significant departures from
LTE. The departures from LTE are more pronounced for the Zr I lines
than for the Ti I lines. The nearly identical ionization potentials
of Zr and Ti and the similarity of the excitation potentials of the
Zr and Ti lines rule out alternative explanations of the spurious Zr
underabundance, such as poor choice of the stellar temperatures and
gravities or errors in the model atmospheres.
Title: Non-resonance lines of neutral calcium in the spectra of
Arcturus and beta Virginis.
Authors: Smith, G.; Lambert, D. L.
Bibcode: 1983A&A...117..177S
Altcode:
Selected regions containing calcium lines of moderately high excitation
(2.5-3.0 eV) in the spectra of Arcturus (K2III, m/v/ =0.0) and Beta
Virginis (F8V, m/v/ =3.6) have been recorded at a dispersion of 1
A/mm and with signal/noise of approximately 100 using a silicon diode
array. A conventional analysis, based on an LTE model atmosphere and
using all relatively unblended lines for which precise oscillator
strengths are now available, leads to extremely consistent values for
calcium abundance and microturbulence. The microturbulence is shown
to have a value of about 1.5 km/s in both stars. There is marginal
evidence for a departure from LTE in one multiplet in the Arcturus
spectrum. The dependence of the derived abundance on model atmosphere,
effective temperature, and surface gravity is investigated.
Title: Epsilon Aurigae in Eclipse
Authors: Lambert, David L.
Bibcode: 1983iue..prop.1484L
Altcode:
A continuation of our IUE program of ultraviolet spectroscopy and
spectrophotometry of the unique long-period binary Epsilon Aur is
proposed during the current total eclipse, the first since 1956. The
ultraviolet eclipse curves are being used to define the characteristics
of the secondary and the geometry of the system. High-dispersion
spectra of the supergiant primary, which is eclipsed by the secondary,
provides absorption/emission lines produced by circumstellar gas and,
perhaps, the large disk around the secondary. A complementary program
of ground-based spectroscopy begun in November 1981 will be continued
beyond the predicted date of fourth contact (1984 May).
Title: Planet earth
Authors: Lambert, David; Bailey, Jacqui
Bibcode: 1983plea.book.....L
Altcode: 1983QB631.L24......
Presents various aspects of the earth, including its origin, weather,
oceans and seas, atmosphere, living inhabitants, and possible future
appearance.
Title: Epsilon Aurigae
Authors: Parthasarathy, M.; Lambert, D. L.
Bibcode: 1983IAUC.3766....2P
Altcode: 1983IAUC.3766....0P
M. Parthasarathy and D. L. Lambert, McDonald Observatory, report:
"Observations of epsilon Aur made since 1981 show a systematic
increase in the strength of the K I 770-nm resonance line: W-lambda
= 12 pm in early March 1982 (before the eclipse) but W-lambda = 54
pm now. The Na D lines behave similarly. The strengths of the high-
excitation lines Mg II 448 nm, Si II 635 nm and N 869 nm have not varied
significantly. Our IUE observations show that the eclipse depth is ~
1 mag from 310 to 155 nm. However, the eclipse depth at 125 to 143
nm is ~ 0.3 mag. First contact occurred before July 29. The O 130-nm
emission and the P-Cyg-type emission of Mg II 280-nm lines do not seem
to show significant variation associated with the eclipse. Fe II lines
of ultraviolet multiplets 1, 62 and 63 show variation in the strength
of their emission components."
Title: On C3 molecules in diffuse interstellar clouds.
Authors: Clegg, R. E. S.; Lambert, D. L.
Bibcode: 1982MNRAS.201..723C
Altcode: 1982MNRAS.201..722C
New observations at 4050 A of reddened stars are presented, the
excitation of C3 levels is analyzed and the limits on C3 abundance are
discussed. The details of the observed stars and obtained spectra are
shown. Upper limits to the column density of C3 were calculated from
the weak-line approximation for the absorption band equivalent width,
and the radiative life-time of several vibrational levels in the upper
1-pi-u state was measured through a laser fluorescence technique. It
is shown that the population of C3 molecules in excited vibrational
states is neglible. The radiative deexcitation rate from v(2) = 1 is
estimated from the harmonic oscillator relation, and the relative
populations having v(2) = O and 1 are calculated. The C3 molecules
are expected to be in the (0,0,0) ground vibrational state for which
the rotational levels are thermalized. The interstellar C3 chemistry
is examined, showing rates for reactions relevant to C3 formation and
destruction. Predicted concentrations of C0, C2, and C3 are plotted
as a function of visual extinction.
Title: The chemical composition of R CrB and XX Cam.
Authors: Cottrell, P. L.; Lambert, D. L.
Bibcode: 1982ApJ...261..595C
Altcode:
The R Coronae Borealis stars R CrB and XX Cam are examined using
extensive high-resolution Reticon data. Effective temperatures, values
of log g, microturbulent velocities, and C/He values are determined,
along with elemental abundances and abundance ratios for a wide range of
species, including the light and heavy s-process elements. Helium- and
carbon-rich models are employed, as is an appropriate model atmosphere
code. The evolutionary history of R CrB stars is discussed in detail. It
is concluded that both CNO cycle and 3-alpha processed material must
have been mixed into the observable layers. The He core and He shell
flashes are suggested as possible triggers for the mixing and for the
extensive mass loss required to expose the heavily processed layers.
Title: High-resolution 3 μm spectroscopy of IRC +10216.
Authors: Clegg, R. E. S.; Hinkle, K. H.; Lambert, D. L.
Bibcode: 1982MNRAS.201...95C
Altcode:
The fundamental vibration-rotation lines of HCl near 3 microns were
sought in high-resolution spectra of IRC+10216, obtained with a
Fourier transform spectrometer, and an analysis of the CH4 nu3 band
was made. The predicted value of the HCl column density, based on the
expectation that Cl is fully associated into HCl in the circumstellar
shell, is 10 to 20 times greater than the upper limit on the observed
column density of HCl-35, which is 2.3 x 10 to the fifteenth/cm2. This
discrepancy suggests that Cl is not fully associated into HCl, but
rather may reside in another molecule, such as CH3Cl, or a condensate,
such as FeCl2 or MgCl2. Although the CH3Cl nu1 band is not present,
the limit on its column density does not exclude it as a sink of Cl
atoms. CH4 nu3 lines yield a rotational temperature of 160 K plus or
minus 25 K, and a column density of 1.8 x 10 to the sixteenth/cm2.
Title: Physical conditions in the accretion disk of V603 Aql.
Authors: Ferland, G. J.; Lambert, D. L.; McCall, M. L.; Shields,
G. A.; Slovak, M. H.
Bibcode: 1982ApJ...260..794F
Altcode:
Ultraviolet and optical spectra of the old nova V603 Aql are
discussed. The UV-optical continuum is dominated by emission from the
accretion disk. Emission lines from ions of H, He, C, N, and O are
identified. These lines are probably formed in a circumstellar shell
with radius comparable to the binary separation, density ten billion
per cu cm, and a roughly solar chemical composition. This corona
is probably heated by radiation emitted by the underlying accretion
disk. Photoionization calculations of the structure and emission-line
spectrum of the corona are presented, and the effects of this gas on
the X-ray continuum are discussed.
Title: The peculiar spectroscopic behaviour of the R Coronae Borealis
star RY SGR
Authors: Cottrell, P. L.; Lambert, D. L.
Bibcode: 1982Obs...102..149C
Altcode:
No abstract at ADS
Title: The CN red system in the solar spectrum
Authors: Sneden, C.; Lambert, D. L.
Bibcode: 1982ApJ...259..381S
Altcode:
Solar CN lines from leading bands of the Delta-v = -2, -1, 0, +1, +2,
and +3 sequences of the A 2Pi-X 2 Sigma(+) red system are analyzed to
provide band absorption oscillator strengths, radiative lifetimes of
the A 2Pi state and the electronic transition moment. The results
are compared with recent experimental results and an ab initio
calculation. In general, the solar analysis is consistent with both
the experiments and the ab initio predictions. Additional experiments
are called for in order to resolve one outstanding discrepancy and to
provide accurate oscillator strengths for the infrared (Delta-v is
less than or equal to -1) sequences which are potentially key bands
in the analysis of spectra of cool stars.
Title: Lithium in late-type giants. II. 31 M giants and supergiants.
Authors: Luck, R. E.; Lambert, D. L.
Bibcode: 1982ApJ...256..189L
Altcode:
A spectrum-synthesis technique accounting for TiO line blanketing and
extracting Li abundances was developed to compensate for the unresolved
TiO line depression of the Li I 6707 A doublet in high-resolution,
high-SNR spectra of 31 M giants and supergiants. Li abundances in
a 25-star sample show a large scatter about a mean log epsilon(Li)
value of about -0.2. A renewed discussion of Li abundances for G and K
giants offers new evidence for Li abundance control by stellar mass,
consistent with M giant data. Two stars, Alpha Ori and 119 Tau, show
no detectable Li line, and it is suggested that this Li deficiency may
result from mass loss at the pre-main sequence phase, or from internal
mixing and nuclear processing leading to Li destruction.
Title: Carbon, nitrogen and oxygen abundances in Sirius and Vega.
Authors: Lambert, D. L.; Roby, S. W.; Bell, R. A.
Bibcode: 1982ApJ...254..663L
Altcode:
Carbon, nitrogen, and oxygen abundances are obtained from C I,
N I, and O I high excitation permitted lines in the spectra of the
standard A star Vega and the 'hot' Am star Sirius. Vega has normal
abundances. Relative to Vega, Sirius is C deficient by 0.60 dex,
N enhanced by 0.22 dex, and O deficient by 0.27 dex.
Title: Time-resolved spectroscopy of the C2 Phillips
system and revised interstellar C2 abundances.
Authors: Erman, P.; Lambert, D. L.; Larsson, M.; Mannfors, B.
Bibcode: 1982ApJ...253..983E
Altcode:
The high frequency deflection technique is used to measure radiative
lifetimes of vibrational levels of the C2 A 1Pi u state. The mean
lifetime for levels v-prime = 3, 4, 6, and 7 is found to be 11
microseconds, and results are used to derive absorption oscillation
strengths of the Phillips (A 1Pi u-X1Sigma g +) system. The f-values
for the infrared band which correspond to those for the near infrared
bands are subject to larger uncertainty, due to the lack of information
on the R e 2 variation at large internuclear separations, and the R
e 2 model can be better defined by extending the lifetime results to
both the lower (v-prime not greater than 2) and higher (v-prime not
less than 8) levels.
Title: Binary stars: mass transfer and chemical composition.
Authors: Lambert, D. L.
Bibcode: 1982NASCP2238..114L
Altcode: 1982IUE82......114L; 1982NASCP2338..114L; 1982auva.nasa..114L
It is noted that mass exchange (and mass loss) within a binary system
should produce observable changes in the surface chemical composition
of both the mass losing and mass gaining stars as a stellar interior
exposed to nucleosyntheses is uncovered. Three topics relating
mass exchange and/or mass loss to nucleosynthesis are sketched:
the chemical composition of Algol systems; the accretion disk of a
cataclysmic variable fed by mass from a dwarf secondary star; and the
hypothesis that classical Ba II giants result from mass transfer from
a more evolved companion now present as a white dwarf.
Title: The Primary Component of Algol Systems of Low Mass Ratio
Authors: Lambert, David L.
Bibcode: 1982iue..prop.1130L
Altcode:
High dispersion spectra between 1300 and 1800 A are to be obtained for
the primary component of low mass-ratio Algol systems. The spectra
will yield the chemical abundance of carbon, nitrogen, boron, and
other elements. It is predicted that nuclear processed material from
inside the secondary and transferred to the primary will have produced
abundance anomalies on the primary. In conjunction with ground-based
spectroscopy, definition of these anomalies and a comparison with
theoretical predictions is the primary goal of the program.
Title: Ultraviolet properties of the symbiotic stars.
Authors: Slovak, M. H.; Lambert, D. L.
Bibcode: 1982ASSL...95..103S
Altcode: 1982nss..coll..103S; 1982IAUCo..70..103S
A general discussion of the UV spectra of symbiotic stars, including
both the emission lines and the continua, is presented, with AG
Pegasi considered as an illustrative example. It is noted that the
IUE observations of the symbiotics have revealed UV properties which
rival the diversity of the optical features. Nevertheless, the UV
data have for the first time permitted the hot component to be studied
relatively uncontaminated by the giant companion, which dominates the
optical regime. The UV observations provide convincing evidence that
many of the symbiotics have hot stellar companions embedded in the
enshrouding nebula or accretion shell formed from the wind from one
or possibly both of the components.
Title: Epsilon Aurigae in Eclipse
Authors: Lambert, David L.
Bibcode: 1982iue..prop.1139L
Altcode:
Ultraviolet spectroscopy and spectrophotometry of the unique
long-period binary Epsilon Aur is proposed during the first total
eclipse since 1956. The ultraviolet eclipse curves will be used to
define the characteristics of the secondary and the geometry of the
system. High-dispersion spectra of the supergiant primary, which is
eclipsed by the secondary, will provide absorption/emission lines
produced by circumstellar gas and, perhaps, the large disk around the
secondary. A complementary program of ground-based spectroscopy will
be conducted.
Title: A detailed analysis of three R CrB stars.
Authors: Cottrell, P. L.; Lambert, D. L.; Schönberner, D.
Bibcode: 1982BAAS...14..576C
Altcode:
No abstract at ADS
Title: Carbon, nitrogen and oxygen abundances in main-sequence
stars. II. 20F and G stars.
Authors: Clegg, R. E. S.; Lambert, D. L.; Tomkin, J.
Bibcode: 1981ApJ...250..262C
Altcode:
High-resolution Reticon spectra of red and near-infrared C I, N I,
and O I lines have been analyzed to determine C, N, and O abundances
in a sample of 20 F and G main-sequence stars. Their iron abundances,
which have been determined from analysis of additional Reticon spectra
of red Fe I lines, cover the Fe/H range from -0.9 to 0.4. Sulfur
abundances have also been obtained. It is found that the variations
of the carbon and sulfur abundances closely follow those of iron. The
oxygen abundance varies much more slowly than iron (O/Fe = 0.48 (+ or -
0.07) Fe/H). This result confirms an earlier conclusion that oxygen is
overabundant in more metal-deficient stars. The behavior of the nitrogen
abundance appears to be similar to that of iron (N/Fe = 0.0 + or -
0.2). However, the unavailability of nitrogen abundances for the most
metal-deficient stars in the sample makes this result less certain than
the results for the other elements. These results are discussed in the
light of current theories of stellar nucleosynthesis of the elements.
Title: A high resolution IUE spectrum of the GO-GSIA supergiant
HR 8752.
Authors: Stickland, D. J.; Lambert, D. L.
Bibcode: 1981A&A...102..296S
Altcode:
A high-resolution long-wavelength IUE spectrum of the G0-G5Ia supergiant
HR 8752 and its B main sequence companion is discussed. The supergiant,
which dominates for wavelengths greater than approximately 2700 A,
appears to have a normal spectrum. The spectrum of the B star contains
several deep asymmetric absorption lines. It is argued that these
lines are interstellar and not circumstellar in origin.
Title: Circumstellar shells of luminous supergiants. I. Carbon
monoxide in rho CAS and HR 8752.
Authors: Lambert, D. L.; Hinkle, K. H.; Hall, D. N. B.
Bibcode: 1981ApJ...248..638L
Altcode:
High resolution spectra are presented for the 2.3 micron, CO Delta-v =
2 region in the two F Ia supergiants HR 8752 and Rho Cas, which have
extensive circumstellar shells without infrared excesses that indicate
circumstellar gas with little dust. The new spectra show strong CO
Delta-v = 2 lines of circumstellar origin at kinetic temperatures
near 2000 K. The CO line profile in Rho Cas resembles that of the
circumstellar component of atomic lines at shorter wavelengths,
and a standard model with spherical symmetry and acceleration to the
escape velocity gives a lower limit to the rate of mass loss of 0.01
solar masses/year. Infrared CO and visual circumstellar lines in HR
8752 show a progression of line profiles with time over the five-year
interval 1975-1979, with the C-12/C-13 ratio being 15 and a photosphere
pulsation period of nearly three years.
Title: Carbon, nitrogen, and oxygen abundances in G and K giants.
Authors: Lambert, D. L.; Ries, L. M.
Bibcode: 1981ApJ...248..228L
Altcode:
C, N and O abundances are presented for 32 G and K giants and
subgiants, where the primary indicators of abundances are: (1) the
C(2) lines at 5086 and 5135 A; (2) the O I forbidden lines at 6300
and 6363 A, and (3) CN red system lines. The CNO abundances show that
CN-processed material has been dredged to the surface of the giants,
with the C abundance reduced, that of N increased, and O remaining
unchanged. Lower mass giants are found to be C-13-rich, relative
to standard predictions. Relative to the C-13-normal clump giants,
a larger mass of processed material is dredged to the surface of
the rich giants. This material is, however, less processed than that
of the normal stars. This result is consistent with the view of the
occurrence of mixing in the radiative zone between the core and the
outer convection zone of a main sequence star.
Title: A study of CNO elements in barium stars.
Authors: Sneden, C.; Lambert, D. L.; Pilachowski, C. A.
Bibcode: 1981ApJ...247.1052S
Altcode:
Carbon, nitrogen, and oxygen abundances are presented for seven mild
barium stars and two classical barium stars. The mild barium stars
do not show the carbon enhancement typical of the classical Ba II
stars. The CNO abundances of the mild barium and normal G and K giants
are identical. An s-process enhancement is confirmed for some of the
mild barium stars. The marked division in the abundance patterns and
the recent discovery of low-mass comparisons to the classical Ba II
stars but not the mild barium stars suggest that the two types of barium
stars are unrelated. A possible explanation for the mild barium stars
is that the abundance of rare s-process elements in the interstellar
clouds is not uniform. The mild barium stars were formed in clouds
containing an above average abundance of the s-process elements but
approximately normal abundances of other elements.
Title: The ultraviolet spectrum of the twin-degenerate interacting
binary G 61-29.
Authors: Lambert, D. L.; Slovak, M. H.
Bibcode: 1981PASP...93..477L
Altcode:
A low-resolution IUE spectrum (1200 A-1900 A) of the twin-degenerate
white-dwarf binary star G61-29 is presented. A comparison is made to
similar IUE spectra of the old novae DQ Her and V603 Aql. G61-29 shows
N V 1240 A and He II 1640 A in emission. Unlike the old novae, the C
IV 1550 A doublet is not present. It is proposed that the mass-losing
He white dwarf (with a mass of 0.02 solar mass) is the H-exhausted,
He-rich core of an old star in which the original CNO nuclei have been
converted to N-14 by the CNO-cycles.
Title: The abundances of carbon, nitrogen and oxygen in the
atmospheres of cepheid variables : evidence for helium enrichment.
Authors: Luck, R. E.; Lambert, D. L.
Bibcode: 1981ApJ...245.1018L
Altcode:
An analysis is presented of the abundances of carbon, nitrogen,
oxygen and 14 heavier elements in the atmospheres of 14 Cepheid
variables and five nonvariable supergiants. Model atmospheres and a
spectrum synthesis code were used to derive CNO and metal abundances
as well as effective temperatures, surface gravities, microturbulences
and macroturbulences for the program stars on the basis of Reticon
spectra obtained in 100-A spectral regions centered at 5380, 6300,
6385, 6560 and 8710 A. The CNO abundances obtained indicate a level
of atmospheric mixing with CN-cycle and ON-cycle processed material
beyond that predicted by standard calculations for both the Cepheids
and nonvariable supergiants, particularly evident in a reduction of O
abundances. A possible explanation for the mixing level is suggested
in which core convection or meridional mixing induced by rapid rotation
caused extensive mixing into the H-burning shell and ON processing zone
when the Cepheids were main-sequence OB stars. The O depletion is noted
to imply a significant He enrichment, corresponding to an envelope He
mass fraction of up to 0.8 in the double-mode Cepheid TU Cas.
Title: Rho Cassiopeiae
Authors: Hinkle, K. H.; Lambert, D. L.; Tomkin, J.; Luck, R. E.
Bibcode: 1981IAUC.3580....3H
Altcode:
K. H. Hinkle, Kitt Peak National Observatory; D. L. Lambert and
J. Tomkin, University of Texas at Austin; and R. E. Luck, Louisiana
State University, write that they observed rho Cas = HR 9045 during
Feb. 23-26. The circumstellar line profiles now contain a striking
emission component. The circumstellar CO vibration-rotation band heads
near 2.3 um, which were previously seen in absorption, are now in
emission. Low J CO lines show the emission superposed on an absorption
line. Similar profiles are seen in many neutral atomic lines in the red
and near infrared. While the profiles of the circumstellar lines have
developed strong emission since they were last observed in June 1980,
the current phase may have begun in Sept. 1979 when the photospheric
lines were observed to double. Photometric and spectroscopic monitoring
of this peculiar supergiant would be of interest.
Title: UV Spectroscopy of Symbiotic Stars, Recurrent & Old Novae
Authors: Lambert, David L.
Bibcode: 1981iue..prop..788L
Altcode:
This proposal describes a combination of a program of ultraviolet
spectroscopy of the symbiotic variables, and the old and recurrent
novae. Low resolution IUE spectra have been obtained which provide both
the emission line spectra of the nebula as well as the continuum of
the hot, underlying star. A completion of the low resolution survey
is proposed. A program of IUE observations of the symbiotic variable
AG Pegasus was initiated in June 1979, and has continued through
1980. Line profile and radial velocity variations provide important
clues to the distribution of hot gas within the binary. These data
are being complemented by optical observations at the McDonald
Observatory. Nearinfrared data yield the orbit of the cool M giant;
the line profiles of [O III], H-alpha, He II, He I, and Fe II
provide information on the ionized gas within the system. The IUE
low resolution spectra for other symbiotics are being combined with
groundbased observations to determine the physical structure of these
peculiar variables. Old novae are being studied, using the IUE low
resolution spectra to derive the structure of the accretion disk and
the hot gaseous region (a corona above the disk?) responsible for
the emission lines. A series of complementary groundbased and IUE
observations are proposed in the event of a recurrent nova eruption.
Title: Peculiar Red Giants: A Search For White Dwarf Companions
Authors: Lambert, David L.
Bibcode: 1981iue..prop..784L
Altcode:
The carbon and s-process element abundances in the atmosphere of a
red giant are not predicted to be enhanced until the star is in a
thermally pulsing double shell burning phase, that is, the red giant
has become cool and highly luminous. The classical Barium (and other
peculiar giants) which are warm and not highly luminous do not fit
this prediction. Special conditions (e.g. anomalous mixing events
at the time of the He-core flash) in a small fraction of red giants
have been invoked to explain these low luminosity peculiar giants. The
recent discovery by McClure and collaborators that some, possibly all,
classical Ba II giants are binaries with low mass companions provides
a new explanation for the composition anomalies. it is possible that
mass from a thermally pulsing primary was transferred to the secondary
which we now detect as the red giant. The primary may remain as a
white dwarf (or neutron star). Indeed, IUE spectra of the Ba II star
Zeta Cap indicates a white dwarf companion (Bohm-Vitense 1980). We
propose to search for the ultraviolet continuum of a WD companion to
the classical R (hot carbon) stars, additional Ba II stars, and the
CH or Population II Ba II stars in order to test the hypothesis that
the low-luminosity peculiar red giants of types equivalent to G and
K result from mass transfer.
Title: Ultraviolet spectroscopy of old novae and symbiotic stars.
Authors: Lambert, D. L.; Slovak, M. H.; Shields, G. A.; Ferland, G. J.
Bibcode: 1981NASCP2171..461L
Altcode: 1981uviu.nasa..461L; 1980IUE80......461L; 1981NASCP3171..461L
The IUE spectra are presented for two old novae and for two of the
symbiotic variables. Prominent emission line spectra are revealed as a
continuum whose appearance is effected by the system inclination. These
data provide evidence for hot companions in the symbiotic stars, making
plausible the binary model for these peculiar stars. Recent IUE spectra
of dwarf novae provide additional support for the existence of optically
thick accretion disks in active binary systems. The ultraviolet data
of the eclipsing dwarf novae EX Hya and BV Cen appear flatter than
for the noneclipsing systems, an effect which could be ascribed to
the system inclination.
Title: The chemical composition of red giants - The first dredge-up
phase
Authors: Lambert, D. L.
Bibcode: 1981ASSL...88..115L
Altcode: 1981pprg.work..115L
The first dredge-up changes the red giant atmosphere abundances of Li,
Be and B and the participants in the CNO-cycle. Theoretical predictions
are reviewed and compared with the observed abundance changes. For the
G and K giants of mass less than about 3 solar masses, the observed
and predicted abundance changes are in fair agreement. The (C-13) rich
giants appear during the main sequence phase to have experienced a slow
mixing within the radiative zone outside the core. The supergiants
including Cepheids show an O deficiency that is not predicted by
standard theory. The speculation is offered that the ON-cycle processed
material is transported out by rotationally induced meridional currents
or by convection cells to layers that during the red giant phase fall
within the deep convective envelope. Several classes of peculiar low
luminosity red giants are briefly discussed.
Title: The iron abundance in the Hyades cluster.
Authors: Branch, D.; Lambert, D. L.; Tomkin, J.
Bibcode: 1980ApJ...241L..83B
Altcode:
Low-noise Reticon spectra of the moon and two Hyades G dwarfs are
used to derive the metallicity of the Hyades Cluster. The relative
temperatures of the sun and the Hyades stars are determined from the
wings of their H-alpha profiles, and iron abundances are based on weak
Fe I lines. The spectroscopic result is an Fe/H ratio of 0.20 + or -
0.1, in good agreement with photometric determinations of the Hyades
metallicity. The B-V color of the sun is inferred to be 0.64 + or 0.02.
Title: The size and surface brightness of the circumstellar gas
shell surrounding Betelgeuse
Authors: Honeycutt, R. K.; Kephart, J. E.; Bernat, A. P.; Gow, C. E.;
Sandford, M. T., II; Lambert, D. L.
Bibcode: 1980ApJ...239..565H
Altcode:
We have obtained direct images of the K i gas shell surrounding the
M supergiant Betelgeuse using a two-dimensional television system and
a 2 Å bandpass filter. The emission extends to at least 50".
Title: The Keenan and Wing bands in S stars.
Authors: Lambert, D. L.; Clegg, R. E. S.
Bibcode: 1980MNRAS.191..367L
Altcode:
The paper presents new observations of the near infrared spectra of S
stars as part of a survey of the unidentified Keenan and Wing bands. A
new band is found at 9014 A, and the bands were not present in normal
M giants and dwarfs. Several new identifications are proposed including
two new bands in the near infrared at 8219 and 8235 A provided by CeO;
a new band with heads at 7503 and 7509 A in a spectrum of R And is
tentatively attributed to YS. It is suggested that the heavy element
sulfides and possibly chlorides are leading candidates as the potential
carriers of Keenan and Wing bands.
Title: Isotopic abundances of magnesium in five G and K dwarfs.
Authors: Tomkin, J.; Lambert, D. L.
Bibcode: 1980ApJ...235..925T
Altcode:
The paper reports on an analysis of high-resolution low-noise Reticon
observations of MgH lines in the spectra of Mu Cas, Epsilon Eri, 61
Cyg A and B, and Gmb 1830 by spectrum synthesis. It is shown that the
mixtures of the isotopes in Mu Cas, Epsilon Eri, and 61 Cyg A and B
are not significantly different from the terrestrial mixture. Attention
is also given to a nonterrestrial mixture which is found in Gmb 1830.
Title: The study of small molecules in stellar atmospheres
Authors: Lambert, D. L.
Bibcode: 1980LIACo..21..173L
Altcode: 1980smsl.conf..173L
The review discusses several important or unique contributions of small
molecules to the study of the chemical composition and atmospheric
structure of main sequence and evolved stars. Highlighted topics
include: the line identification problem and the astrophysical needs
for extensions of available laboratory spectra; the determination of
stellar C, N and O abundances and the f values for relevant transitions
of diatomic molecules; the isotopic abundance ratios C-12/C-13 in G
and K giants and carbon stars and Mg-24/Mg-25/Mg-26 in late-type stars;
the role of small molecules in defining the chromospheres of late-type
stars and the complex atmospheres of long-period variables.
Title: Lithium in late-type giants. I. G and K giants.
Authors: Lambert, D. L.; Dominy, J. F.; Sivertsen, S.
Bibcode: 1980ApJ...235..114L
Altcode:
Lithium abundances for about 50 G and K giants have been derived from
new high-resolution, low-noise spectra by spectrum synthesis. Ca
abundances obtained from the 6798 A Ca I line are well correlated
with the Fe/H forbidden line abundance given by published narrow-band
photometry. This correlation is strong evidence that the Ca and,
therefore, the Li abundances are free from large systematic errors. The
Li abundance and the C-12/C-13 ratio are correlated. Red giants with
mass not less than 1.3 solar mass show the predicted Li abundance
and C-12/C-13 ratio. Giants with a high C-13 abundance show lower Li
abundances. It is suggested that Li is a rough measure of a star's mass
and that the high C-13 stars are low-mass giants with mass not greater
than 1.3 solar mass. The CN cycle is probably the source of the excess
C-13. Spallation reactions cannot account for these abundances.
Title: UV Spectroscopy of Symbiotic Stars, Recurrent and Old Novae
Authors: Lambert, David L.
Bibcode: 1980iue..prop..470L
Altcode:
I propose to obtain low resolution ultraviolet spectra of two magnetic
white dwarfs. For one of these stars, the main point is to search
for evidence of elements other than hydrogen in the spectrum, and to
improve the data on which magnetic modelling is based. The other star
is the remarkable high-field (B >= 10^8 gauss) white dwarf GD229,
which has a unique spectrum of strong, broad lines. It is hoped that an
ultraviolet spectrum will make it possible to understand the spectrum
of this star.
Title: The oxygen abundance in metal-poor stars.
Authors: Sneden, C.; Lambert, D. L.; Whitaker, R. W.
Bibcode: 1979ApJ...234..964S
Altcode:
Oxygen abundances in the atmospheres of a dozen unevolved stars
of various metallicities (Fe/H in the closed interval -2.3 -0.3)
have been derived. In nearly all cases, the metal-poor stars exhibit
an enhanced oxygen triplet at 7700 A. Substantial overabundances of
oxygen are indicated for the program stars. This result is discussed
in the light of current galactic nucleosynthesis theories.
Title: Isotopes of titanium in cool stars.
Authors: Clegg, R. E. S.; Lambert, D. L.; Bell, R. A.
Bibcode: 1979ApJ...234..188C
Altcode:
A program of stellar Ti isotopic-abundance determinations is described
and related to changes that may have occurred in the Ti isotopic
abundance ratios during the chemical evolution of the Galaxy, and to
whether the abundance ratios are perturbed in the S and MS stars having
atmospheres with enhanced abundances of s-process nuclei resulting from
convective mixing after internal exposure to neutrons. High-resolution
(0.07 A) Reticon spectra of portions of the TiO gamma (0,0), gamma
(0,1), and delta (0,0) bands were the source material, and particular
emphasis was placed on the definition of the continuum level. The
isotopic abundance ratios are terrestrial in all of the sample, and
errors in the (Ti-i)/(Ti-48) ratio are typically plus or minus 25%
for the dwarfs and plus or minus 50% for the giants. The observations
show that the magic nucleus Ti-50 is not enhanced in S and MS stars.
Title: Observations of emission lines in M supergiants
Authors: Lambert, D. L.
Bibcode: 1979uta..rept.....L
Altcode:
Copernicus observations of Mg 2 h and k emission lines from M
giants and supergiants are described. Supergiants with extensive
circumstellar gas shells show an asymmetric k line. The asymmetry is
ascribed to superimposed lines of Fe 1 and Mn 1. The Mg 2 line width
fit the Wilson-Bappu relation derived from observations of G and K
Stars. Results of correlated ground-based observations include (1) the
discovery of K 1 fluorescent emission from the Betelgeuse shell; (2)
extimates of the mass-loss rates; and (3) the proposal that silicate
dust grains must account for the major fraction of the Si atoms in
the Betelgeuse shell.
Title: He I 10830 Å emission from alpha Bootis and alpha
1Herculis.
Authors: Obrien, G.; Lambert, D. L.
Bibcode: 1979ApJ...229L..33O
Altcode:
The He I 10830 A line has been detected in emission in the spectra
of Alpha Boo and Alpha-1 Her, two stars for which evidence of a
high-temperature chromosphere has heretofore been lacking. The 10830
A emission from Alpha Boo is variable on a time scale of 1 week. He I
10830 A emission from Alpha-1 Her, a star surrounded by an extensive
circumstellar gas and dust shell, is surprising. It is proposed that
the emission may result from a shock front created when high-velocity
infalling gas meets the photosphere.
Title: He I 10830 Å Studies of Chromospheres and Mass Loss in Late
Type Stars
Authors: O'Brien, G.; Lambert, D.
Bibcode: 1979BAAS...11..448O
Altcode:
No abstract at ADS
Title: The chemical composition of Algol systems - I. The secondary
in U Cep.
Authors: Parthasarathy, M.; Lambert, D. L.; Tomkin, J.
Bibcode: 1979MNRAS.186..391P
Altcode:
An abundance analysis of the G8 III secondary of the U Cep system is
performed on the basis of the Reticon spectra 430 A wide, centered at
wavelengths of 6200, 6320, and 8620 A, and obtained with a resolution
of 1.9 A. A rotational velocity of 90 + or - 8 km/s applied to the
spectrum of the standard star Kappa Gem is found to provide an excellent
fit to the secondary's spectrum, indicating that the star is rotating
synchronously. A spectrum-synthesis analysis of the secondary's chemical
composition reveals normal abundances of metals (Fe/H = 0.0 + or - 0.3)
and s-process elements, which are consistent with the values expected
from theories of close-binary evolution. It is noted that the Ca II IR
triplet lines are weak in the secondary of U Cep relative to standard
stars and that a weakening of the IR absorption lines is likely to
be accompanied by enhanced chromospheric emission in the Ca II H and
K lines.
Title: A search for coronal emission lines in HD 153919 (3U 1700-37).
Authors: Lambert, D. L.; Tomkin, J.
Bibcode: 1979ApJ...228L..37L
Altcode:
Low-noise Reticon spectra of HD 153919, which is identified with
the X-ray source 3U 1700-37, do not show the 5303-A forbidden Fe XIV
emission line previously reported by Dupree et al. (1977). The new
spectra provides an upper limit to the central intensity of a forbidden
Fe XIV line which is at least a factor of 6 below the intensity reported
by Dupree et al. A variation in the forbidden Fe XIV emission-line flux
could occur if the X-ray flux were variable on a time scale of years.
Title: Carbon monoxide emission and the eta Carinae stage of nova
NQ Vulpculae.
Authors: Ferland, G. J.; Lambert, D. L.; Netzer, H.; Hall, D. N. B.;
Ridgway, S. T.
Bibcode: 1979ApJ...227..489F
Altcode:
The detection of first-overtone vibration-rotation emission bands
of CO at 2.3 microns from Nova NQ Vul is reported. These bands were
detected in a 1.6-2.4-micron spectrum obtained shortly after the first
sharp drop in visual magnitude. It is suggested that the previously
discovered 5-micron excess can be identified with emission in the
stronger fundamental bands of CO and that the CO emission originates
within or near the nova ejecta. A temperature of 3500 + or - 750 K
is derived, a lower limit of 3 is placed on the C-12/C-13 isotopic
abundance ratio, and the fundamental-band CO emission at 4.8 microns is
predicted to be approximately 40 times stronger than the first-overtone
emission at 2.3 microns. Other emission lines in the spectrum are
identified as recombination lines of H, C, and Na. A model of the
ionization structure of the ejecta is presented which can explain in
a semiquantitative way several important features of the spectrum.
Title: Magnesium isotopes and s-process elements in the barium star
HR 774.
Authors: Tomkin, J.; Lambert, D. L.
Bibcode: 1979ApJ...227..209T
Altcode:
We have analyzed low-noise high-resolution Reticon spectra of MgH and
selected unblended s-process element lines in the Ba star HR 774. We
find that the isotopic abundances of Mg are terrestrial (24Mg: 25Mg:
26Mg = 79:10:11). Large overabundances of the s-process elements (Y,
+0.9dex; Zr, +0.8dex; Mo, +1.0dex; La, +1.1 dex; Nd, +1.Sdex) with
respect to the normal K giant p Gem are determined. These results
imply that the neutrons responsible for the s-process enhancements
are provided by the `3C(a, n)'6O reaction and not the 22Ne(a, n)25Mg
reaction. If the latter reaction were the primary neutron source,
substantial overabundances of 25Mg and 26Mg would be predicted for HR
774, e.g., 24Mg 25Mg 26Mg. This is incompatible with our analysis of
the MgH lines. Our conclusion accords with the theoretical expectations
of Truran and Iben who suggest that in low-mass Ba stars, such as
HR 774, `3C(a, n)'6O rather than 22Ne(a, n)25Mg is the major source
of neutrons. Iron is found to be 0.2 dex deficient with respect
to Gem. Carbon, nitrogen, and oxygen abundances are determined by
analysis of Reticon spectra of Swan system C2 lines, red system CN
lines, and the 6300 A forbidden 0 1 line. Nitrogen and oxygen have the
same abundances as in a 0.2 dex metal-deficient, and otherwise normal,
mixed K giant, while carbon is 0.4 dex overabundant. The 12C/13C ratio
is 23 + 2. In addition, `2C/'3C ratios of 23 + 3 13 + 1, and 24 + 2
have been determined for the Ba stars HR 2392, HR 4474, and HR 5058,
respectively. These results are used to interpret the evolutionary
state of the Ba stars. Subject headings: nucleosynthesis - stars:
abundances - stars: Ba ii - stars: individual - stars: late type
Title: Ultraviolet Spectroscopy of Symbiotic Stars
Authors: Lambert, David L.
Bibcode: 1979iue..prop..215L
Altcode:
This proposal describes a program of ultraviolet spectroscopy of
the symbiotic stars, recurrent and old novae. Low resolution spectra
should provide both the emission line spectrum of the hot gas in these
systems and the continuous spectrum of the hot (T ~ 10^5 K) star in the
binary system. Selected stars will also be observed at high resolution
in order to obtain useful line- profile information. Some stars will
also be observed from the McDonald Observatory to obtain complementary
spectrophotometry. The ultraviolet spectrum and - when available -
the groundbased observations will be combined to obtain information
on the physical structure of these binary systems and the chemical
composition of the surrounding nebula.
Title: On the identification of FeH and CeO in S stars.
Authors: Clegg, R. E. S.; Lambert, D. L.
Bibcode: 1978ApJ...226..931C
Altcode:
Observations of stellar spectra at a resolution of 0.2 A support the
identification of FeH and CeO in S stars by resolving the rotational
structure of the bands. FeH lines are also identified in 61 Cyg B (K5
V), Alpha Tau (K5 III), and in two M giants. CeO is present in the
pure S star R Gem and in R And, an S star with TiO. The possibility
of measuring Fe and Ce isotope ratios is discussed.
Title: Electron scattering in the expanding atmosphere of P Cygni.
Authors: Bernat, A. P.; Lambert, D. L.
Bibcode: 1978PASP...90..520B
Altcode:
High signal4onoise observations of hydrogen- and helium-line profiles
in the spectrum of P Cyg show a new feature-broad weak emission
wings extending to :1: 1500 km 1 from the line center. The wings are
attributed to electron scattering in the extended atmosphere above
the line formation region. A simple model calculation shows that an
optical depth Te 0.2 for the electron scattering layer will fit the Ha
observations. The broad wings are stronger for the He I lines and Te
0.4 is suggested. Key words: broad emission lines-stellar atmospheres-P
Cygni stars-electron scattering
Title: Emission lines in the spectrum of Vega?
Authors: Barker, E. S.; Lambert, D. L.; Tomkin, J.; Africano, J.
Bibcode: 1978PASP...90..514B
Altcode:
High-resolution low-noise spectra of the OI and Ca II near-infrared
lines in Vega were obtained in 1977 and 1978. The violet-shifted
emission components discovered by Johnson and Wisniewski are not
detected. The absence of the emission lines suggests that either Vega
is a subtle variable or the emission lines were of instrumental origin.
Title: Titanium Isotope Ratios in Cool Stars
Authors: Clegg, R. E. S.; Lambert, D. L.; Bell, R. A.
Bibcode: 1978BAAS...10..636C
Altcode:
No abstract at ADS
Title: HeI 10830 Å Observations of Late Type Stars
Authors: O'Brien, G.; Lambert, D.
Bibcode: 1978BAAS...10..647O
Altcode:
No abstract at ADS
Title: The 12C/13C ratio in stellar
atmospheres. IX. The cool carbon star V460 Cygni.
Authors: Dominy, J. F.; Hinkle, K. H.; Lambert, D. L.; Hall, D. N. B.;
Ridgway, S. T.
Bibcode: 1978ApJ...223..949D
Altcode:
The isotopic abundance ratio 12C/13C is derived for the cool carbon star
V460 Cygni (= DS Pegasi). A new 0.2 A resolution, low-noise (S/N >
200) spectrum of the 7650-8460 A region was obtained with a silicon
diode Reticon array. A curve-of-growth analysis of the CN red system
lines gives 12C/13C = 30 + 13. An independent analysis was made of CO
vibrationrotation lines identified on a 0.08 cm -1 resolution spectrum
obtained with a Fourier transform spectrometer. This gave 12C/13C =
35 + 12. A mean value 12C/13C - 32 + 9 is proposed. It is suggested
that the 3a process was the primary source of the additional carbon
which converted the oxygen-rich progenitor into its present carbon-rich
state. Subject headings: stars: abundances - stars: carbon - stars:
individual
Title: Spectrum variations of the superluminous star HR 8752.
Authors: Lambert, D. L.; Luck, R. E.
Bibcode: 1978MNRAS.184..405L
Altcode:
The spectral evolution of the Ia-O supergiant HR 8752 from 1950 to 1977
is discussed on the basis of near-IR spectroscopy performed in 1977
and plate material for the years 1965, 1969, 1973, 1974, and 1976. It
is demonstrated observationally that HR 8752 has developed into a
spectroscopic twin of the F8 Ia supergiant Rho Cas and returned close
to the spectral type of G0 Ia assumed in 1950, that HR 8752 migrated
slowly to the right across the H-R diagram in the intervening 30 yr to
reach a spectral type of K2-K5 Ia in 1973, that a faster return to an
earlier spectral type commenced after 1973, and that the star may now
be in its 'equilibrium' position. The data suggest that a shell of gas
was ejected and that HR 8752 underwent a 'flare' in the period between
1973 and 1976. Possible models for the spectrum changes are examined,
and a tentative explanation is considered for the ionized gas shell
around the star.
Title: Carbon, nitrogen, and oxygen abundances in main-sequence
stars. I. Procyon and the Hyades cluster stars 45 Tauri and HD 27561.
Authors: Tomkin, J.; Lambert, D. L.
Bibcode: 1978ApJ...223..937T
Altcode:
High signal-to-noise observations of C I, N I, and 0 1 lines in the
near-infrared spectra of Procyon and the Hyades cluster main-sequence
stars 45 Tau and HD 27561 have been analyzed to determine their carbon,
nitrogen, and oxygen abundances. The carbon, nitrogen, and oxygen
abundances of all three stars are solar. The estimated uncertainty of
the abundances is +0.2 dex. Analysis of observations of the forbidden
carbon and oxygen lines, CH blue system (0, 0) and (1, 1) band lines,
and CN violet system (0, 0) band lines in Procyon provides a check
of the results obtained from the permitted atomic lines. The solar
C/N ratio of the Hyades cluster dwarfs allows the less-than-solar C/N
ratio of the Hyades giants recently determined by Lambert and Ries to be
unambiguously interpreted as the effect of CNO cycle processing during
the giants' main-sequence lifetime. The iron abundances of Procyon,
45 Tau, and HD 27561 derived from the equivalent widths of Fe I and Fe
ii lines are found to be solar. This result is consistent with previous
spectroscopic determinations of the iron abundance of Hyades cluster
stars. The discrepancy between the spectroscopic determinations of a
solar metal content of the Hyades and the metal richness inferred from
photometry is discussed. Subject headings: clusters: open - stars:
abundances - stars: individual
Title: Detection of the secondary of Algol.
Authors: Tomkin, J.; Lambert, D. L.
Bibcode: 1978ApJ...222L.119T
Altcode:
The first spectroscopic detection of Algol B is reported. The
Na D lines of the secondary of Algol are identified on low-noise
spectra, and measurements of these lines are used to determine the
primary/secondary mass ratio as well as the individual masses of Algol
A, B, and C. Solutions for the orbital elements yield values of 201
(+ or 6) km/s for the semiamplitude of the Algol B velocity curve
and -9 (+ or - 11) km/s for the systemic velocity, in addition to a
primary/secondary mass ratio of 4.6 + or - 0.1. The masses of Algol A,
B, and C are estimated to be approximately 3.7, 0.81, and 1.7 solar
masses, respectively. It is concluded that Algol B fills its Roche
lobe and that mass transfer from Algol B to Algol A could explain the
radio and X-ray emission from this eclipsing binary system.
Title: Light-element abundances in the weak G-band star HR 6766.
Authors: Sneden, C.; Lambert, D. L.; Tomkin, J.; Peterson, R. C.
Bibcode: 1978ApJ...222..585S
Altcode:
Results are presented for a model-atmosphere analysis of iron-peak
elements, the CNO group, and lithium in the weak G-band star HR
6766. Synthetic spectra are generated to derive the carbon, nitrogen,
oxygen, and lithium abundances; the C-12/C-13 ratio is determined from
a curve-of-growth analysis. An effective temperature of 4750 + or 100
K is estimated along with log g of 2.0 + or - 0.4 and a microturbulent
velocity of 2.0 + or - 0.5 km/s. The overall metal abundance derived
from these parameters is shown to indicate a marginally significant
metal deficiency, and it is suggested that HR 6766 appears to be in
most respects a normal late G or early K giant. An analysis of the
carbon abundance based purely on the G band of CH reveals a very large
underabundance of carbon. A C-12/C-13 ratio of about 4.1 is obtained,
the results are compared with those for Epsilon Virginis, and the mass
and luminosity of HR 6766 are discussed.
Title: Constraints on the properties of circumstellar shells from
observations of thermal CO and SiO millimeter line emission.
Authors: Lambert, D. L.; Vanden Bout, P. A.
Bibcode: 1978ApJ...221..854L
Altcode:
An attempt to detect CO and SiO microwave emission from Betelgeuse and
long-period variables (LPVs) is described. The absence of SiO 86 GHz
emission from the Betelgeuse circumstellar shell is shown to require
that either all Si is associated into silicate dust grains or SiO
molecule formation is inhibited. The former explanation is consistent
with published estimates of the column density of silicate grains. The
latter explanation is supported by the absence of emission in the CO 115
GHz line. Circumstellar absorption lines are not present in the TiO y(0,
0) band near 7100 A. TiO, like SiO and CO, appears to be underabundant
in the shell. The new detections of circumstellar microwave emission
include an observation of the CO 115 GHz line from R Cas (the first LPV
for which both SiO 86 GHz emission and CO 115 GHz emission are seen)
and of the SiO 86 GHz line from the S star Cyg. The absence of the
isotopic line 30SiO at 84 GHz shows that the shells around R Cas,
R Leo, and Cyg have an optical depth in the 86 GHz line of r <
10. This suggests that the SiO molecules contain a minor fraction
of the total Si and that a substantial fraction of the Si is in the
silicate grains. The shell around R Leo has been detected through
the K I fluorescent emission. This confirms that the shells are
large. Subject headings: radio sources: lines - stars: abundances -
stars: circumstellar shells - stars: long-period variables
Title: Mg II h and k emission from luminous M stars.
Authors: Bernat, A. P.; Lambert, D. L.
Bibcode: 1978MNRAS.183P..17B
Altcode:
Mg II h and k emission lines of the M2 giant beta Peg and the M5
supergiant alpha Her were detected in Copernicus observations. In the
alpha Her profiles, similar to alpha Ori and alpha Sco profiles, the k
line is asymmetric and the h line is symmetric. The possibility that the
k line asymmetry is produced by overlying absorption is discussed. In
beta Peg, both h and k lines are asymmetric, and line formation in an
expanding chromosphere is indicated. The observations are in accord
with one formulation of the Wilson-Bappu relation but deviate from
another form of the Wilson-Bappu relation.
Title: The abundances of the elements in the solar in the solar
photosphere - IX: Na top Ca.
Authors: Lambert, D. L.; Luck, R. E.
Bibcode: 1978MNRAS.183...79L
Altcode:
A critical rediscussion of photospheric abundances is given for elements
in the periodic table between sodium and calcium. The photospheric
evidence for each element except chlorine and argon is briefly reviewed,
and a critical assessment is presented concerning theoretical and
experimental information on the f-values for each spectrum. Results of
an abundance analysis are examined for a reference model atmosphere
obtained by combining the model of Holweger and Mueller (1974) with
a constant isotropic microturbulent velocity of 1.0 km/s. Effects of
model-atmosphere uncertainties are evaluated by comparing the results
with sample abundances yielded by five other recent model atmospheres. A
comparison of the solar abundances with those determined for type C-1
carbonaceous chondrites shows that the accuracy of the solar abundances
within the Na-Ca range is now at the + or - 0.1 dex level.
Title: The remarkable extent of the circumstellar gas shell
surrounding Betelgeuse.
Authors: Bernat, A. P.; Honeycutt, R. K.; Kephart, J. E.; Gow, C. E.;
Sandford, M. T., II; Lambert, D. L.
Bibcode: 1978ApJ...219..532B
Altcode:
A two-dimensional television system has been used to study the spatial
extent of the K I 7699-A resonance-line emission from the gas shell
surrounding the M supergiant Betelgeuse. This emission has been traced
out to a minimum radius of 29 arcsec (about 600 stellar radii).
Title: The abundances of the elements in the solar photosphere -
VIII. Revised abundances of carbon, nitrogen and oxygen.
Authors: Lambert, D. L.
Bibcode: 1978MNRAS.182..249L
Altcode:
All available atomic and molecular signatures of carbon, nitrogen
and oxygen are integrated to provide solar photospheric abundances
of the three elements. The CI 8727 wavelength line, the CH A-X and
C2 Swan systems, the NI lines and the OI 6300 and 6363 wavelength
lines are the principal sources for the abundances; the effects of
such phenomena as solar granulation and infrared limb darkening on
the assessments are mentioned. Abundance ratios (by number of atoms)
are calculated as 0.56 for carbon/oxygen and 0.12 for nitrogen/oxygen.
Title: Carbon, nitrogen, and oxygen abundances in 11 G and K giants.
Authors: Lambert, D. L.; Ries, L. M.
Bibcode: 1977ApJ...217..508L
Altcode:
Carbon, nitrogen, and oxygen abundances have been determined for
11 G and K giants. High resolution photoelectric scans of C2, CH,
CN, forbidden OI, and forbidden CI lines have been combined with
recent model atmospheres. Relative to the solar atmosphere, the
C abundances are depressed, the N abundances enhanced, and the O
abundances unchanged. The observed CNO abundances and the previously
obtained C-12/C-13 ratios are in good agreement with the predictions
for a giant after the convective envelope has mixed material to the
surface from the zone which was partially processed during the star's
main-sequence lifetime.
Title: Direct Observations of the Circumstellar Gas Shell of
Betelgeuse.
Authors: Bernat, A. P.; Honecutt, R. K.; Kephart, J. E.; Lambert,
D. L.; Gow, C. E.; Sandford, M. T.
Bibcode: 1977BAAS....9..650B
Altcode:
No abstract at ADS
Title: Determination and Interpretation of Stellar Chemical and
Isotopic Abundances
Authors: Lambert, D.
Bibcode: 1977BAAS....9..573L
Altcode:
No abstract at ADS
Title: Spectrum Variations in the Superluminous star HR 8752
Authors: Luck, R. E.; Lambert, D. L.
Bibcode: 1977BAAS....9..643L
Altcode:
No abstract at ADS
Title: The 12C13C Ratio of V460 Cygni.
Authors: Dominy, J. F.; Lambert, D. L.; Kinkle, K. H.; Hall, D. N. B.;
Ridgway, S. T.
Bibcode: 1977BAAS....9Q.604D
Altcode:
No abstract at ADS
Title: The 12C/13C ratio in stellar
atmospheres. VIII. The very metal-deficient giant HD 122563.
Authors: Lambert, D. L.; Sneden, C.
Bibcode: 1977ApJ...215..597L
Altcode:
High-resolution Digicon spectra of the CH 4300-A band in the
metal-deficient giant HD 122563 are analyzed for the atmospheric
C-12/C-13 ratio. Nine (C-13)H lines are identified. A C-12/C-13 ratio of
5 + or - 2 is deduced. This low value shows that the present atmosphere
has been seriously affected by internal mixing and processing. This
extreme mixing is not predicted by stellar evolutionary calculations. It
is suggested that the anomalous abundances of CNO may be explained on
the assumption that modified products of He burning in the core or in
a shell have been mixed to the surface.
Title: A high-resolution infrared spectrum of IRC +10216.
Authors: Barnes, T. G.; Beer, R.; Hinkle, K. H.; Lambert, D. L.
Bibcode: 1977ApJ...213...71B
Altcode:
The IR-emitting core and shell of IRC +10216 are investigated using
a high-resolution spectrum covering the wavelength interval between 3
and 5 microns. Line identifications made or confirmed include those due
to (C-12)(O-16), (C-13)(O-16), (C-12)(O-17), and (C-12)(O-18). A mean
heliocentric velocity of about -32 km/s is obtained from the 42 least
blended (C-12)O and (C-13)O lines, and the following isotopic abundance
ratios are derived by comparing equivalent widths of the observed lines:
C-12/C-13, C-12/C-14, O-16/O-17, and O-17/O-18. The structure of the
expanding gas shell is examined, an explanation is offered for the
lack of P Cygni profiles in the spectrum, and an unsuccessful search
for other molecules is briefly discussed. It is concluded that a low
C-12/C-13 ratio is not necessarily a signature of a carbon star.
Title: Spectroscopic observations of Nova Cygni 1975: the coronal
line phase.
Authors: Ferland, G.; Lambert, D. L.; Woodman, J. H.
Bibcode: 1977ApJ...213..132F
Altcode:
Identifications of the coronal lines [Fe x] 6374 A, [Fe xi] 7892 A, and
[S VIII] 9911 A in Nova Cygni 1975 are discussed. These lines appear on
moderate ( 8 A) resolution photoelectric scans from late 1975 September
through 1976 January. As the coronal lines weakened, the [Fe vii]
6087 A line strengthened. Coronal line profiles differ from those
of the other forbidden lines. Identification of these coronal lines
confirms the infrared discovery of coronal lines. Subject headings:
line identifications - stars: individual - stars: novae
Title: Isotopes of titanium in Aldebaran.
Authors: Lambert, D. L.; Luck, R. E.
Bibcode: 1977ApJ...211..443L
Altcode:
The titanium isotopic abundance ratios in the K5 giant Aldebaran
(Alpha Tau) are estimated from photoelectric high-resolution (40 mA)
scans of portions of the TiO gamma-system (0, 0) band between 7070
and 7082 A. An application of spectrum synthesis techniques shows that
the overall Ti isotopic abundance ratio is terrestrial to within 50%,
with individual ratios terrestrial to within 25%. The (1, 0) and (0,
1) gamma-system band heads are reviewed as potential isotopic abundance
indicators in late M stars.
Title: The 12C/13C ratio in stellar
atmospheres. VI. Five luminous cool stars.
Authors: Hinkle, K. H.; Lambert, D. L.; Snell, R. L.
Bibcode: 1976ApJ...210..684H
Altcode:
A simple curve-of-growth technique is described for extracting the
C-12/C-13 ratio for M stars from high-resolution spectra of CO infrared
vibration-rotation lines. The technique is applied to the CO lines at
1.6 and 2.3 microns in spectra of two M supergiants (Alpha Ori and
Alpha Sco), two M giants (Alpha Her and Beta Peg), and a Mira-type
variable (Chi Cyg). As a check on the CO analysis, the C-12/C-13 ratio
is derived from the red CN system at 8000 A for Alpha Sco, Alpha Ori,
and Beta Peg. The CO analysis is also applied to the K giant Alpha
Boo as a check. The CN and CO results are found to be in general
agreement, and the C-12/C-13 ratio in all the examined stars is shown
to be considerably lower than the solar-system value. It is suggested
that these stars were formed from clouds with a C-12/C-13 ratio of 40
to 89 and that their atmospheres now exhibit an enhancement of C-13
abundance due to internal production and mixing to the surface.
Title: K I 7699 Å emission from the Betelgeuse shell.
Authors: Bernat, A. P.; Lambert, D. L.
Bibcode: 1976ApJ...210..395B
Altcode:
A map of the circumstellar gas shell around Betelgeuse is presented
from observations of the fluorescent emission in the K I 7699 A
resonance line. The observations obtained at 3 sec and 5 sec from
the star indicate approximate spherical symmetry in the 10 km/s
expanding shell responsible for the blueshifted sharp cores seen in
strong resonance and low excitation lines. Calculations show that the
density of neutral K atoms is approximately constant between 3 sec and
5 sec from the star. The emission profiles in the west show a second,
higher velocity, component at 5 sec from the star.
Title: Silicon monoxide in the 4 micron infrared spectrum of
long-period variables.
Authors: Hinkle, K. H.; Barnes, T. G.; Lambert, D. L.; Beer, R.
Bibcode: 1976ApJ...210L.141H
Altcode:
The first-overtone sequence of vibration-rotation transitions of the
free radical silicon monoxide are shown to have extreme phase-dependent
variations in the spectra of two M-type long-period variables,
Omicron Ceti and R Leonis, and the mild S-type long-period variable,
Chi Cygni. At maximum light, the SiO band heads are not detectable. Near
minimum light, the band heads of (Si-25)O are detected in the 4-micron
spectra of all three stars. The band heads of the terrestrially less
abundant isotopic species, (Si-29)O and (Si-30)O, are detected in
Chi Cygni. Possible explanations of the phase-dependent behavior are
discussed, and the role of the stellar chromosphere is considered.
Title: The 12C/13C ratio in stellar
atmospheres. VII. 38 giants and supergiants.
Authors: Tomkin, J.; Luck, R. E.; Lambert, D. L.
Bibcode: 1976ApJ...210..694T
Altcode:
The `2C/'8C ratios of 38 G, K, and M giants and supergiants have
been determined. Included are the four Hyades cluster giants y Tau,
Tau, E Tau, and 0' Tau (ratios 19, 23, 22, and 20, respectively); the
primary of a Aur (ratio 27); the Ba star 16 Ser (ratio 33); and the KO
Il-Ill star 37 Com which has the low ratio of 3.4. We point out that,
at all giant and supergiant luminosities, there are stars with `2C/13C
ratios too low to be explained by models of the evolution of static
single stars. We discuss the effects of mass loss, meridional mixing,
mixing at the helium flash, and the presence of a low-mass companion;
we suggest that these four effects offer adequate scope to account for
the observed low `2C/13C ratios. Subject headings: stars: abundances -
stars: late-type - stars: supergiants
Title: Isotopic Abundances of Magnesium in Arcturus
Authors: Tomkin, J.; Lambert, D. L.
Bibcode: 1976ApJ...208..436T
Altcode:
High-resolution photoelectric scans of selected lines oftheA2H-X2 +
(0,0) band of MgH in the spectrum of Arcturus are compared with
synthetic spectra to show that the 24Mg/26Mg isotope ratio in the
atmosphere of Arcturus is 7.2( +3, - 1.5), the same as the terrestrial
ratio. There is evidence that the 25Mg isotope is deficient. We
tentatively conclude that the 24Mg/25Mg ratio is about twice the
terrestrial ratio of 7.9. Subject headings: molecular processes -
stars: abundances - stars: individual - stars: late-type
Title: V1500 Cygni
Authors: Young, P. J.; Lambert, D. L.; Kemp, J. C.; Rudy, R. J.;
Sykes, M. V.
Bibcode: 1976IAUC.2981....1Y
Altcode:
P. J. Young, Department of Astronomy, University of Texas at Austin,
writes: "This nova was examined visually with the 208-cm Struve
reflector at McDonald Observatory on July 6 (coude periscope 500 x)
and July 8 (Cassegrain focus 1200 x) with excellent seeing conditions
on both occasions. No associated nebulosity as large as 0".1 was
observed with either scotopic or photopic vision when the Airy disks,
of size ~ 0".05, of the two twelfth-magnitude stars < 1' north
of the nova could be seen. Spectroscopic scans by D. L. Lambert at
the coude focus of the 270-cm reflector indicate that 10 percent
of the luminosity in the scotopic visual band is due to the [O III]
emission at 4959 A and 5007 A; this also accounts for 30 percent of
the luminosity seen in the photopic band with minor contributions
from H-alpha blended with [N II]. The scotopic visual magnitude was
11.20, and photoelectric measurement yielded mean values V 12.00, B-V =
+0.51, U-B = -0.25 (on July 8.353 UT; with cooled 8575 photomultiplier
tube). The absence of an observed nebulosity is in conflict with
the prediction that the gas shell should be ~ 0".4 in diameter,
assuming an expansion velocity of 1300 km/s, a distance of 1.4 kpc
and a roughly spherically-symmetric ejection." J. C. Kemp, R. J. Rudy
and M. V. Sykes, Department of Physics, University of Oregon, report:
"Based on 12 cycles observed from 1 July to 25 July 1976 the current
light curve has a peak-to-peak amplitude of 0m.20 in unfiltered light
(3500-5500 A). The period of variations is currently 0d.1384 with an
epoch of the even minimum on 1976 July 16.333 UT. The true orbital
period might be twice the period of light variations. The even minima
are rounded and symmetrical, while the odd minima tend to show a
slow drop and a rapid rise. The difference, if real, is obscured by
random variability and by progressive changes. A careful search for
the even/odd effect is urged. Power spectra of the rapid flickering
(IAUC 2973) show peaks at 122s and 196s, but it has not been established
that either of these is a real or persistent period."
Title: Profiles of the RB I resonance lines in the Arcturus spectrum
Authors: Lambert, D. L.; Luck, R. E.
Bibcode: 1976Obs....96..100L
Altcode:
No abstract at ADS
Title: Spectroscopic observations of nova Cygni 1975.
Authors: Tomkin, J.; Woodman, J.; Lambert, D. L.
Bibcode: 1976A&A....48..319T
Altcode:
Summary. High resolution photoelectric scans of the CaiiH, Cai, CH+,
NaiD2, Lii and Ki 7699A interstellar lines in the spectrum of Nova
Cygni 1975 provide a distance estimate that yields an absolute visual
magnitude of the nova at maximum of -9.5 to -10.5. Low resolution scans
of the spectrum from 3100 to 11000 A and medium resolution scans of
Hcc are discussed. These observations cover the period August 30 to
September 18. Key words: novae - interstellar lines
Title: Copernicus observations of Betelgeuze and Antares.
Authors: Bernat, A. P.; Lambert, D. L.
Bibcode: 1976ApJ...204..830B
Altcode:
The Mg II h and k lines were observed strongly in emission by
Copernicus scans of the M supergiants alpha Ori and alpha Sco. The
striking symmetry in the k line as contrasted with the symmetric h
line, as observed previously was confirmed. Estimates of absolute
chromospheric fluxes were obtained. Measured values for the widths
of the h and k lines do not follow a Wilson-Bappu relationship. Upper
limits determined for other chromospheric lines of alpha Ori tend to
exclude the existence of extensive and/or hot regions surrounding this
supergiant. Observed weakening by fluorescence of the Fe L 4307 A line
is good evidence that the Mn I and Fe I resonance transitions overlying
the Mg II k-line profile are responsible for the strong asymmetry of
this line in the two stars. However, quantitative study shows that the
absorption provided by the cool circumstellar shells is insufficient to
provide the observed asymmetry. Additional absorption may be provided
by a cool turbulent region at the top of the chromosphere.
Title: Line profiles of diffuse interstellar lines at 5780 Å,
5797 Å.
Authors: Danks, A. C.; Lambert, D. L.
Bibcode: 1976MNRAS.174..571D
Altcode:
Photoelectric coude scanner observations of the interstellar diffuse
lines at 5780 and 5797 A are reported. With a resolution of about 0.2 A,
line-profile differences are seen in the sample of eight stars. In part,
these are attributed to the overlapping contributions from several
clouds in the line of sight. Intrinsic profile differences are also
suggested. The hypothesis that some of the diffuse lines represent
electronic transitions in large molecules is examined. Synthetic
spectra are shown which approximate the observed profiles. Excitation
of these hypothetical molecules is examined. Their stability against
photodissociation by the interstellar ultraviolet-radiation field is
noted as a key problem for future study.
Title: The 12C/13C ratio in the classical
cepheid T Monocerotis.
Authors: Loumos, G. L.; Lambert, D. L.; Tomkin, J.
Bibcode: 1975PASP...87..859L
Altcode:
Observations of the CN lines at 8000 A in the classical cepheid T Mon
near minimum light are discussed. Weak ` CN features are identified and
an abundance ratio `2C/' C = 9 3 is derived. Similar observations for
two other cepheids show no detectable ` CN lines; the corresponding
limits are `2C/' C > 17 ( Gem) and > 12 (7)Aql). Key words:
cepheids - abundances - stellar evolution - spectroscopy
Title: Observations of circumstellar gas shells around Betelgeuse
and Antares.
Authors: Bernat, A. P.; Lambert, D. L.
Bibcode: 1975ApJ...201L.153B
Altcode:
Results are presented on the direct observations of the circumstellar
shell around alpha-Ori, along with new observations of the Ca II
infrared triplet lines which provide lower limits for the Ca(+)
shell radii for alpha-Ori and alpha-Sco (Antares). The 8542-A line
in alpha-Ori does not show a circumstellar absorption core, and
the shell radius limit is estimated to be at least 31 times stellar
radius. A 108-mA circumstellar core is observed in the 8542-A line in
Antares for which a shell radius equal to 4.0 times stellar radius is
suggested. The discovery of circumstellar emission through resonance
line scattering will provide valuable additional information on the
physical conditions in the shell.
Title: The 12C/13C ratio in stellar
atmospheres. V. Twelve K giants and subgiants.
Authors: Dearborn, D. S. P.; Lambert, D. L.; Tomkin, J.
Bibcode: 1975ApJ...200..675D
Altcode:
High-resolution photoelectric scans of portions of the CN red system
in the spectra of 12 K giants and subgiants have been analyzed for the
12C/13C abundance ratio with the following results: >50 (5 Eri),
>30 ( Cep), 51 I 5 (v2 CMa), 24 I 3 (y Cep), 34 I 4 (53 Eri), 16 +
2 (L Cep), 12 I 2(0 Cet), 22 I 2 (A Sgr), 20 I 2 ( Dra), 15 I 2 (p
Boo), 18 I 2(5 Sgr), and 25 + 2 (5 And). This sample of stars have
relatively low absolute luminosities (log L/L0 < 2.1). Stellar
evolution calculations predict that their atmospheres will contain
an overabundance of 13C as a result of a convective envelope which
has brought to the surface 13C produced in the interior during
main-sequence burning. The 13C is observed in all except the two
faintest stars. Interpretations of the observed range of results, 5
< 12C/'3C < 55, for giants and subgiants are discussed. Subject
headings: abundances, stellar - late-type stars molecules
Title: The infrared excess of cool giant stars: a chromospheric
contribution.
Authors: Lambert, D. L.; Snell, R. L.
Bibcode: 1975MNRAS.172..277L
Altcode:
The idea that the infrared excesses of evolved M stars may contain a
contribution from a chromosphere is explored using alpha Ori and W Hya
as test cases. The spectrum of alpha Ori between 8 and 30 millimicrons
can be interpreted satisfactorily in terms of three components: a
photosphere, a silicate dust cloud, and a cool chromosphere (temperature
about 5000 K), which is optically thick at 14 millimicrons. A similar
modelling for W Hya suggests a hotter chromosphere (temperature about
8000 K), with unit optical depth at 30 millimicrons. Some consequences
of these chromospheres are briefly discussed.
Title: Absence of the 4400 Å diffuse emission feature.
Authors: Danks, A. C.; Lambert, D. L.
Bibcode: 1975A&A....41..455D
Altcode:
Summary. New spectroscopic observations of 7 stars which exhibit the
4430 A diffuse interstellar line are presented. A previously reported
emission wing at 4400 A is not confirmed. An alternative mechanism to
grains for the production of the 4430 feature is proposed. Key words:
interstellar medium molecules
Title: The 12C/13C ratio in stellar
atmospheres. IV. Eleven G and K type giants.
Authors: Tomkin, J.; Lambert, D. L.; Luck, R. E.
Bibcode: 1975ApJ...199..436T
Altcode:
High-resolution photoelectric scans of portions of the 44), 5-1,
2-0, 3-1, and 42 bands of the CN red system in the spectra of 11
late-type giants have been obtained. Analysis of the 12CN and `3CN
line intensities gives the following 12C!13C abundance ratios: 20 +
3 (E Vir), 22 + 3 ( Cyg), 19 + 2 (p Cet), 11.5 + 1.5 (E Cyg), 22 + 4
(46 LMi), 17 + 4 ( Cep), 19 I 3 (a Ari), 6.5 + 1 (y Leo A), 18 I 3 (a
Hya), 13 I 2 ( Dra), and 13 I 3 ( Sge). Revised 12C!13C ratios of 14
and 9 are derived for a Ser and a Tau, respectively. The low 12C/13C
ratios of E Cyg and a Ser are interpreted as evidence that they have
been extensively mixed during the core helium flash. Subject headings:
abundances, stellar - late-type stars - molecules
Title: Copernicus observations of Betelgeuse and Antares
Authors: Bernat, A. P.; Lambert, D. L.
Bibcode: 1975STIN...7524598B
Altcode:
Copernicus observations of the M-supergiants, alpha Ori and alpha Sco,
are presented. The MgII h and k resonance lines are strongly in emission
in both stars. The k line is highly asymmetric in both stars but the
h line is symmetric. Upper limits for several other resonance lines
are given for alpha Ori. The possibility is explored that the k line
asymmetry is caused by overlying resonance lines of MnI and FeI formed
in the cool circumstellar gas shells around these stars. Observations
of the MnI 4030-4033 A lines are used to show that circumstellar shell
absorption is too weak to explain the asymmetry. It is suggested that
the absorption occurs in a cool turbulent region between the base of
the circumstellar shell and the top of the chromosphere.
Title: Ultraviolet Observations of the Chromosphere of Two
M-Supergiants
Authors: Bernat, A. P.; Lambert, D. L.
Bibcode: 1975BAAS....7..359B
Altcode:
No abstract at ADS
Title: Formation of molecular lines in stellar atmospheres.
Authors: Hinkle, K. H.; Lambert, D. L.
Bibcode: 1975MNRAS.170..447H
Altcode:
Statistical equilibrium of electronic states of diatomic molecules
in stellar atmospheres is examined. Atmospheres discussed are
representative of the sun, Arcturus (K-giant) and Betelgeuse
(M-supergiant). A comparison of the relative collisional and radiative
contributions to the equilibrium of the ground electronic state shows
that this state is collisionally controlled and that the line source
function for vibration-rotation transitions within this state is
equivalent to the Planck function. Examination of the equilibrium for
excited electronic states demonstrates that the exchange between these
states and the ground electronic state is most probably determined by
radiative excitation. This result implies that scattering rather than
pure absorption is the appropriate mechanism for the formation of lines
belonging to these electronic transitions. The scattering hypothesis
is given a preliminary check against solar observations. Areas for
future investigations are outlined.
Title: Isotopic abundance ratios for carbon and nitrogen in nova
Herculis 1934.
Authors: Sneden, C.; Lambert, D. L.
Bibcode: 1975MNRAS.170..533S
Altcode:
Spectra of Nova Herculis 1934 taken during an episode of intense CN
absorption are analyzed to determine the isotopic abundance ratios
of C12/C13 and N14/N15. Synthetic spectrum analysis, based on the
wavelengths, excitation potentials, and oscillator strengths for the
CN lines, and radial velocity measurements indicate that C(12)N(14) was
the dominant species in the Nova, and that the minimum abundance limit
for C12/C13 is about 1.5, while the minimum for N14/N15 is about 2. The
results are compared with predictions based on models of thermonuclear
runaways in hydrogen-rich envelopes of white dwarfs. It is noted that
the nova material may have been contaminated with C13-rich material
prior to or during the eruption. Possible causes of this isotope
enrichment are presented.
Title: The 12C/13C ratio in comet Kohoutek
(1973f).
Authors: Danks, A. C.; Lambert, D. L.; Arpigny, C.
Bibcode: 1975NASSP.355..137D
Altcode: 1975coko.conf..137D
No abstract at ADS
Title: The 12C/13C ratio in late-type stellar
atmospheres.
Authors: Lambert, D. L.
Bibcode: 1975MSRSL...9..405L
Altcode: 1975assp.conf..405L; 1975apes.conf..405L
No abstract at ADS
Title: The 12C/13C Ratio in the Atmosphere of
the k2 Supergiant Epsilon Pegasi
Authors: Lambert, D. L.; Tomkin, J.
Bibcode: 1974ApJ...194L..89L
Altcode:
The 12C/13C abundance ratio in the atmosphere of the K2 Th supergiant
E Peg is derived from high-resolution photoelectric spectral scans
of lines from the CN red system. The high 13C abundance, 12C/13C =
5.1 + 0 5 and Greene's demonstration that the atmosphere is rich in
N and deficient in C and 0, are consistent with the hypothesis that
the star has undergone extensive internal mixing. Subject headings:
abundances, stellar - late-type stars - stars, individual
Title: The 12C/13C ratio in comet Kohoutek
(1973f).
Authors: Danks, A. C.; Lambert, D. L.; Arpigny, C.
Bibcode: 1974ApJ...194..745D
Altcode:
Results are presented for photoelectric scans of the C2
1 to 0 band head at 4737 A at resolutions of 0.14 to 0.50 A in the
comet Kohoutek. On the basis of medium-resolution scans and of one
high-resolution scan two values are obtained for the C-12/C-13 ratio
which are consistent within the experimental errors with the terrestrial
values of C-12/C-13 equal to 89. The study also demonstrates the
limitations imposed by NH2 blends.
Title: The 12C/13C ratio in stellar
atmospheres. III. Alpha Tauri, Beta Geminorum, and Mu Leonis.
Authors: Tomkin, J.; Lambert, D. L.
Bibcode: 1974ApJ...193..631T
Altcode:
High-resolution photoelectric scans of portions of the 2-0 and 4-0
bands of the CN red system in the spectra of three K giants alpha Tau,
beta Gem, and mu Leo have been obtained. Analysis of the C-12N and
C-13N line intensities provides the C-12/C-13 abundance ratios for
these atmospheres. The results are C-12/C-13 equals 12 plus or minus 2
(alpha Tau), equals 16 plus or minus (2 beta Gem), equals 18 plus or
minus 2 (mu Leo).
Title: The 12C/13C ratio in stellar
atmospheres. II. CN and CO in Alpha Orionis.
Authors: Lambert, D. L.; Dearborn, D. S.; Sneden, C.
Bibcode: 1974ApJ...193..621L
Altcode:
The isotopic abundance ratio C-12/C-13 for the M supergiant alpha
Orionis is derived from photoelectric high-resolution scans of the
CN 2-0 red system and high-resolution interferometric spectra of the
CO second-overtone bands. The two molecules yield consistent results
and the final value for the C-12/C-13 ratio is 7.0 plus or minus
1.5. Rationale is offered for the causes contributing to an earlier
suggestion that C-12/C-13 ratios from CO and CN were in disagreement.
Title: The Silicon Monoxide Radical and the Atmosphere of α Orionis
Authors: Beer, R.; Lambert, D. L.; Sneden, C.
Bibcode: 1974PASP...86..806B
Altcode:
We present new molecular constants, line positions, and transition
probabilities for the first-overtone vibration-rotation bands in the X 1
Sigma+ electronic ground state of SiO, together with an estimate of the
SiO abundance and silicon isotope ratios in the atmosphere of alpha Ori.
Title: Atmospheric Motions in Red Supergiants
Authors: Brooke, A. L.; Lambert, D. L.; Barnes, T. G., III
Bibcode: 1974PASP...86..419B
Altcode:
Radial velocities obtained from interferometric spectra of a a Ori,
a Her, and a Sco have been analyzed to investigate expansion and other
large-scale motions in their atmospheres. In a Ori evidence of such
motions is found. They appear to be sporadic in time or position on the
surface of the star. If these motions are an observational indication
of mass loss, they lead to extremely high instantaneous loss rates. It
has not been possible to infer an average rate of mass loss. Key words:
supergiant - radial velocity - mass loss - infrared - interferometer
Title: Aluminum Oxide in Stellar Spectra: an Infrared Electronic
Transition
Authors: Luck, R. Earle; Lambert, David L.
Bibcode: 1974PASP...86..276L
Altcode:
The possibility of detecting the infrared electronic transition A2llj -
X2 + of AlO in spectra of cool stars is reviewed. It is shown that the
transition may be of importance in Mira-type variables. Additional
laboratory investigation of the transition is needed. Key words:
molecular spectra - infrared - Mira variables
Title: The oxygen abundance in the metal-deficient star HD 122563.
Authors: Lambert, D. L.; Sneden, C.; Ries, L. M.
Bibcode: 1974ApJ...188...97L
Altcode:
The forbidden neutral oxygen line at 6300.3 A has been detected in the
spectrum of the metaldeficient star HD 122563. The [0 1] equivalent
width, WA = 6.0 i 1.0 mA, and a modelatmosphere analysis provide an
oxygen abundance log [N(O)/N(H)] = - 5.38 i 0.15 or a logarithmic
overabundance of oxygen relative to the metals of [0/Fe] = +0.6. This
relative overabundance of oxygen may be common to other metal-deficient
stars. The probable role of convective mixing in altering the surface
composition of evolved metal-deficient stars is pointed out. Subject
headings: abundances, stellar - convection - stars, individual -
weak-lined stars
Title: High resolution interferometry of cool stars
Authors: Lambert, D. L.
Bibcode: 1974HiA.....3..237L
Altcode:
A description is given of results obtained in a program of infrared high
resolution spectroscopy of cool stars. The nature of infrared stellar
spectra is considered along with questions regarding astrophysics
and stellar infrared spectroscopy. An abundance analysis for alpha Ori
(Betelgeuse) is conducted. The C-12/C-13 abundance ratio is examined and
attention is given to the O-16/O-18 and O-16/O-17 abundance ratios. M
stars and SiO vibration-rotation bands are discussed and questions
regarding the characteristics of the molecular hydrogen quadrupole
vibration-rotation lines are explored.
Title: Identification of the C2 Phillips System in the
Solar Spectrum
Authors: Lambert, D. L.; Mallia, E. A.
Bibcode: 1974BAICz..25..216L
Altcode:
No abstract at ADS
Title: Infrared spectra of gamma 2 Velorum and zeta Puppis.
Authors: Barnes, T. G.; Lambert, D. L.; Potter, A. E.
Bibcode: 1974ApJ...187...73B
Altcode:
Observations of y2 Vel and Pup are presented for the spectral region
580() l 1,000 cm-1 (1.7- 0.9 M) at resolutions of 2 and 4 cm-1,
respectively. This constitutes the first reported spectroscopy of a
Wolf. Rayet star beyond 1.1 . The new spectral region contained numerous
emission features for the WC8 component of y2 Vel, but only the Pfl
line in absorption for the O4f star Pup. Line identifications are given
for y2 Vel and are shown to be consistent with visual spectroscopy. The
species identified are H, He i-li, and C ii-iv. in the spectral region
0.8-il our identifications are in excellent accord with previous
spectroscopy. However, after correcting the emission-line intensities
for dilution by the O9 I component of y2 Vel, we find the lines to be
2-5 times stronger than the same lines in the WC7 star HD 192103, as
given by Kuhi. This is attributed in part to a 1-M excess in HD 192103
and in part to a lower excitation in y2 Vel. From the absence of He I Al
0830 in Pup we are able to exclude the presence of an oft-conjectured
WN companion. The blueshifted absorption component to He I Al 0830
in y2 Vel and the line profile of the He ii A10,124 emission feature
in Pup are also discussed. Subject headings: line identifications -
spectra, infrared - stars, individual - Wolf-Rayet stars
Title: High resolution interferometry of cool stars.
Authors: Lambert, D. L.
Bibcode: 1974sis..conf..237L
Altcode:
No abstract at ADS
Title: H2 quadrupole rotation-vibration lines in infrared
spectra of cool stars.
Authors: Lambert, D. L.; Brooke, A. L.; Barnes, T. G.
Bibcode: 1973ApJ...186..573L
Altcode:
The H2 quadrupole rotation-vibration fundamental band has been searched
for in highresolution spectra of M giants and supergiants. H2 has been
identified in the spectrum of a Her (MS II). Upper limits to the H2
intensities are set for a Ori (M2 lab), a Sco (Ml-2 lab), R Leo (M8
III), W Hya (M8e), and o Cet (M4 III-M7 III). These results are shown
to be consistent with recent model-atmosphere predictions. Earlier
identifications of 2-0 lines near 1 micron are reviewed, and alternative
identifications for these stellar lines are presented. Subject headings:
late-type stars - line identifications - molecules - spectra, infrared
Title: The 12C/13C ratio in stellar
atmospheres. I. Alpha Serpentis and Alpha Bootis.
Authors: Day, R. W.; Lambert, D. L.; Sneden, C.
Bibcode: 1973ApJ...185..213D
Altcode:
High-resolution photoelectric scans of portions of the (2-0) band of
the CN red system have been analyzed to obtain the isotopic abundance
ratio for two K giants. The results are 12C/11C = 12 i 2 for a Serpentis
and 7.2 t 1.5 for a Bootis. An attempted independent determination
of the 12C/13C ratio for a Ser from the CH A4200 band is discussed
briefly. The marked enhancement of the isotope 13C relative to the
solar-system abundance (12C/13C = 89) is in qualitative agreement with
recent theoretical ideas on mixing in red giants. Subject headings:
abundances, stellar - late-type stars - molecules - stars, individual
Title: The Possible Presence of C2 Lines in Sunspot Spectra
Authors: Lambert, D. L.; Mallia, E. A.
Bibcode: 1973SoPh...31..123L
Altcode:
Indirect evidence against the presence of C2 lines
in umbral spectra is discussed. The dominant role of CO in the
molecular equilibrium of C at umbral temperatures ensures that
CN, CH and C2 lines are formed in the same atmospheric
regions. Observations of CN and CH umbral lines are in good accord
with predictions based on accepted umbral model atmospheres. This
implies that C2 must follow the predictions and that it is
too weak to contribute to the umbral spectrum. C2 lines in
the photosphere and penumbrae are in excellent quantitative agreement
with predictions. Additional tests are proposed.
Title: Improved Parameters for the 28Si16O
and 16O1H Molecule
Authors: Beer, R.; Barnes, T. G.; Lambert, D. L.
Bibcode: 1973rgs..conf...84B
Altcode:
No abstract at ADS
Title: Molecular Spectra in Cool Stars: Lessons from Solar
Spectroscopy?
Authors: Hinkle, K. H.; Lambert, D. L.; Mallia, E. A.
Bibcode: 1973rgs..conf...63H
Altcode:
No abstract at ADS
Title: The 12C/13C Abundance Ratio in the
Atmospheres of Arcturus and Alpha Serpentis
Authors: Day, R. W.; Lambert, D. L.; Sneden, C.
Bibcode: 1973rgs..conf...79D
Altcode:
No abstract at ADS
Title: Infrared Spectra of γ2 Velorum and ζ Puppis.
Authors: Barnes, T. G.; Lambert, D. L.; Potter, A. E.
Bibcode: 1973BAAS....5...10B
Altcode:
No abstract at ADS
Title: Model Atmosphere Calculations of Molecular Line Intensities
for α Orionis
Authors: Lambert, D. L.
Bibcode: 1973rgs..conf..350L
Altcode:
No abstract at ADS
Title: Vibration-Rotation Bands of NH in the Spectrum of Alpha Orionis
Authors: Lambert, D. L.; Beer, R.
Bibcode: 1972ApJ...177..541L
Altcode:
Several lines of the 1-0 and 2-1 fundamental vibration-rotation bands
of the NH radical are identified on a high-resolution spectrum of the
supergiant a Orionis.
Title: Thallium in the Solar Atmosphere
Authors: Lambert, D. L.; Mallia, E. A.; Smith, G.
Bibcode: 1972SoPh...26..250L
Altcode:
Umbral spectra are shown to contain an absorption
feature attributable to the Tl I transition
6p2P°3/2−7s2S1/2 at
5350 Å. Analysis of the umbral spectrum suggests a solar abundance
in the 0.72< log N(Tl)T<1.10 on the standard scale log N(H)
= 12.00. Unidentified blends limit the accuracy of the abundance
determination.
Title: Transition Probabilities for the Vibration-Rotation Bands of
Silicon Monoxide
Authors: Hedelund, J.; Lambert, D. L.
Bibcode: 1972ApL....11...71H
Altcode:
No abstract at ADS
Title: Astronomical Infrared Spectroscopy with a Connes-Type
Interferometer. III. Alpha Orionis, 2600-3450 CM^{-1}.
Authors: Beer, Reinhard; Hutchison, Robert B.; Norton, Robert H.;
Lambert, David L.
Bibcode: 1972ApJ...172...89B
Altcode:
Recent spectra of a Ori in the 3-4- region at a resolving power
of about t0,000 show clear evidence of the v = 1 sequence of the
rotation-vibration bands of OH. A detailed investigation of the
rotational and vibrational populations suggests that the OH is close to
being in LTE at an apparent temperature of 4100 + 2002 K. We deduce an
OH abundance of 1.2 X 1020 molecules and upper limits for H2O and H Cl
of 8 X 1018 and 8 X 1012 molecules , respectively. We further deduce
that the rms turbulence velocity in the region of OH line formation
is 11.5 + 2 km s '. The implications of these data on abundances in
M supergiant atmospheres are discussed.
Title: The 12C/13C ratio in the atmosphere
of Arcturus.
Authors: Lambert, D. L.; Dearborn, D. S.
Bibcode: 1972saim.conf..147L
Altcode:
No abstract at ADS
Title: The (0,0) band of the gamma -system of TiO in the umbral
spectrum: The isotopic abundances of Ti.
Authors: Lambert, D. L.; Mallia, E. A.
Bibcode: 1972MNRAS.156..337L
Altcode:
Photoelectric spectra of the y-system of TiO in sunspot umbrae are
examined for the presence of the less abundant stable isotopes of
Ti. From comparisons of computed spectra with observations in the
wavelength region of minimum line density (7065-7085 A), the solar and
terrestrial abundances of 46.47,49, 50Ti relative to 45Ti are shown to
be equal to within +30 per cent. Analysis of 45TiO lines yields a value
for the band oscillator strength: fo,o = with an adopted dissociation
energy of TiO of eV and the model umbral atmosphere proposed by
Stellmacher and Wiehr. A significant dependence of the f-value on
dissociation energy and model atmosphere is found. Line profiles in
the cc- and y-systems require a microturbulent velocity of = 1.2 0.1 km
Title: Observations of the OH radical in Betelgeuse.
Authors: Beer, R.; Norton, R. H.; Hutchison, R. B.; Lambert, D. L.;
Martonchik, J. V.
Bibcode: 1972saim.conf..145B
Altcode:
No abstract at ADS
Title: On the Abundance of Chlorine in the Sun
Authors: Lambert, D. L.; Mallia, E. A.; Brault, J.
Bibcode: 1971SoPh...19..289L
Altcode:
A low-noise photoelectric scan which
includes the predicted position of the ClI transition
4s4P5/2-4p4D07/2
provides inconclusive evidence for the presence of the line in the solar
photospheric spectrum. An upper limit logN(Cl) ⩽ 5.5 is derived. It
is pointed out that the fundamental vibration rotation band of HC1 at
3.3 μ should be detectable in the sunspot spectrum unless logN(Cl)
< 4.6. Sunspot spectra may also provide the isotopic abundance
ratio N(Cl35)/N(Cl37).
Title: A Review of Models of the Solar Photosphere and Low
Chromosphere: The Temperature-Height Profile
Authors: Lambert, D. L.
Bibcode: 1971RSPTA.270....3L
Altcode:
Empirical and theoretical models of the photosphere and low chromosphere
are reviewed with especial reference to the Bilderberg continuum
atmosphere. The observations and analysis of the continuous spectrum
are emphasized. A minimum electron temperature of 4300 K at lg τ
0≈ -4 is suggested by new observations in the ultraviolet
and far infrared.
Title: λ 4097.3 N iii emission in the chromospheric spectrum?
Authors: Lambert, D. L.
Bibcode: 1971SoPh...16..336L
Altcode:
The recent tentative identification of a chromospheric emission
line at λ⊙ = 4097.342 Å with the NIII transition
3s2S1/2 $#x2212; 3p2P∘3/2
is discussed. It is shown that the observed intensity is inconsistent
with the observed flux in the XUV resonance lines and considerably
greater than the predicted intensity from the chromosphere-corona
transition zone. Microphotometry of a plate shows that the `line'
is a short interval of continuum between absorption lines.
Title: Magnesium hydride in theSun
Authors: Lambert, D. L.; Mallia, E. A.; Petford, A. D.
Bibcode: 1971MNRAS.154..265L
Altcode:
Low noise photoelectric scans of the MgH A2ll-X2 (o, o) band in the
spectrum of the solar disk are examined and accurate equivalent widths
obtained. Analysis of these widths with a recent photospheric model
atmosphere provides an estimate for the band oscillator strength:
Jo,o = . A discussion of these weak MgH and strong Mg I lines in the
disk spectrum and weak lines of MgH in the penumbral spectrum shows
that limits can be set on the isotopic abundance ratios 25Mg/24Mg
and 26Mg/24Mg. These limits are consistent with the terrestrial
abundance ratios. Recent analyses of sunspot spectra which claim a
marked overabundance of 25Mg and 25Mg relative to 24Mg are critically
examined. It is proposed that these results are in error owing to the
neglect of a contribution to the spectrum from bright umbral dots. A
new method of analysis is outlined.
Title: Identification of NiH in the sunspot spectrum
Authors: Lambert, D. L.; Mallia, E. A.
Bibcode: 1971MNRAS.151..437L
Altcode:
Photoelectric scans of the umbral spectrum in the wavelength interval
6200-6700 A are examined and positive identifications established for
NiH lines. The band oscillator strengths for the A2A - X2A and B2A -
X2A systems are derived, foo = 5 X I0- and 6 x I0- respectively, for
an adopted dissociation energy of eV. It is also shown that the solar
isotopic and terrestrial isotopic abundance ratios for Ni55 and Ni60
are probably equal.
Title: The Excitation of the Forbidden Coronal Lines. II: [Caxv]
λλ 5694 and 5446
Authors: Chevalier, R. A.; Lambert, D. L.
Bibcode: 1970SoPh...11..243C
Altcode:
The excitation of the 2s22p2 ground configuration
of CaXV is calculated for coronal densities and temperatures. The
calculations include electron and proton excitation of the
forbidden transitions and electron excitation via the first excited
(2s2p3) configuration. It is shown that measurements of the
line intensity ratio I(λ 5694)/I(λ 5446) are in good agreement with
the predictions. The line to continuum observations for limb flares and
coronal condensations are discussed. It is suggested that the calcium
abundance in condensations is enhanced owing to diffusion processes.
Title: The SiH A2A-,X211 (o, o) band in theFraunhofer spectrum
Authors: Lambert, D. L.; Mallia, E. A.
Bibcode: 1970MNRAS.148..313L
Altcode:
Low noise photoelectric scans of the solar disc and sunspot spectra are
examined for lines attributable to the (o, o) band of the SiH system A2
-X2H. Satisfactory identifications are established. A model atmosphere
calculation provides a result for the band oscillator strength: foo =
. Isotope shifts are calculated for the less abundant species, Si29H
and Si30H. It is shown that the isotopic abundances are probably normal.
Title: The forbidden line [Ca ii] λ7323 in the fraunhofer spectrum
Authors: Lambert, D. L.; Mallia, E. A.
Bibcode: 1969SoPh...10..311L
Altcode:
New observations of the [CaII] λ7323 Fraunhofer line are
reported. The blending H2O line was weak at the time of
observation. Accurate estimates of the centre-limb variation of the
equivalent width of the [CaII] transition are obtained and shown to
be consistent with the calcium abundance log N(Ca) = 6.33.
Title: Forbidden Lines of NiIV in the Spectrum of RR Telescopii
Authors: Lambert, D. L.; Thackeray, A. D.
Bibcode: 1969Ap&SS...5..283L
Altcode:
The rich spectrum of the slow nova RR Telescopii contains several strong
unidentified lines. The possibility is re-examined that some of these
lines are due to forbidden transitions of [Ni iv]. Success is partial
but the new identifications include four strong lines (λλ5363, 5288,
5060, 5042) from the multiplet a4F-a2G.
Title: The Excitation of the Forbidden Coronal Lines. I: Fe XIII
λλ 10747, 10798 and 3388
Authors: Chevalier, R. A.; Lambert, D. L.
Bibcode: 1969SoPh...10..115C
Altcode:
The excitation of the lowest (3s23p2)
configuration of FeXIII is discussed for the range of density and
temperatures experienced in the solar corona. The principal features
are the introduction of proton collisions as an important mechanism
for exciting the 3p23P levels, the use of
improved electron collision strengths and a detailed discussion of
the influence of the excited configurations. The predicted intensity
ratios are shown to be consistent with available observations with
the single exception of an eclipse measurement of the ratio of the
intensities of the infrared lines.
Title: Intrinsic Reddening of Eta Carinae
Authors: Lambert, D. L.
Bibcode: 1969Natur.223..726L
Altcode:
PAGEL1 has proposed a new method for the determination of
the intrinsic and interstellar reddening for peculiar objects which is
based on the intensities of the forbidden lines of ionized iron, and
has applied the method to the interesting southern object Eta Carinae.
Title: The Excitation of the Coronal Lines of Fe XIII and Ca XV
Authors: Chevalier, R. A.; Lambert, D. L.
Bibcode: 1969BAAS....1R.274C
Altcode:
No abstract at ADS
Title: Forbidden Lines of Ca II in the Photospheric Spectrum
Authors: Lambert, D. L.; Mallia, E. A.; Warner, B.
Bibcode: 1969SoPh....7...11L
Altcode:
On scans obtained with the Oxford photoelectric spectrometer,
the [Ca II] transition 4s 2S1/2-3d
2D3/2; is identified with a weak Fraunhofer
line. It is argued that the strength of the line is consistent with
the abundance of calcium which is derived from the permitted lines of
Ca I and Ca II.
Title: Forbidden Sulphur I Lines in the Solar Spectrum
Authors: Swings, J. P.; Lambert, D. L.; Grevesse, N.
Bibcode: 1969SoPh....6....3S
Altcode:
The [SI] lines are due to transitions within the
3s23p4 ground configuration of neutral
sulphur. The results are presented from a search for the
[SI] lines in the Fraunhofer spectrum. Two identifications
are proposed with faint features in the Fraunhofer spectrum:
1D2-1S0 at λ⊙
= 7725.02 Å and 3P2-1D2
at λ⊙ = 10821.23 Å. Their measured equivalent widths
are shown to confirm the value for the solar abundance of sulphur,
logNS = 7.21 (in the scale logNH = 12.00),
which is derived from the permitted high-excitation lines. These
lines give the first convincing identification of [SI] lines in an
astrophysical source.
Title: The abundances of the elements in the solar
photosphere-VII. Zn, Ga, Ge, Cd, In, Sn, Hg, Tl and Pb
Authors: Lambert, D. L.; Mallia, E. A.; Warner, B.
Bibcode: 1969MNRAS.142...71L
Altcode:
A detailed account is presented of the limited number of Fraunhofer
lines which are attributable to the heavier elements with ground state
configurations of S2, s2p or s2p2. The Oxford photoelectric spectrometer
was used to obtain new measurements of the equivalent width for selected
lines of Zn I, Ge I, Cd I, In I and TI I. A thorough discussion is given
of the available expe1imental and theoretical oscillator strengths. The
following abundances are obtained on the standard scale where log N(H)
= : logN(Zn) = logN(Ga) = logN(Ge) = 3'32 logN(Cd) = logN(In) = 1.71
logN(Sn) = 1.71 logN(Hg) < logN(Tl) 0.2 logN(Pb) =
Title: 20. Forbidden Sulphur I Lines in the Solar Spectrum
Authors: Swings, J. P.; Lambert, D. L.; Grevesse, N.
Bibcode: 1969LIACo..15..209S
Altcode: 1969MSRSL..17..209S
No abstract at ADS
Title: Forbidden sulphur I lines in the solar spectrum.
Authors: Swings, J. P.; Lambert, D. L.; Grevesse, N.
Bibcode: 1969MSRSL..25..209S
Altcode: 1969tisa.conf..209S
No abstract at ADS
Title: The Abundance of Chlorine in the Sun
Authors: Lambert, D. L.; Mallia, E. A.
Bibcode: 1968SoPh....5..181L
Altcode:
The CLI line λ 8375.943 (4s 4P5/2 − 4p
4D∘7/2) is identified in the solar spectrum. This is
the first identification of a chlorine line in solar spectrum. The
measured equivalent width (Wλ = 0.8 mÅ) corresponds to
an abundance log N(Cl) = 5.65 on the scale log N(H) = 12.00.
Title: Absolute Wavelengths of Fraunhofer Lines: Convective Motions
in the Solar Photosphere and the Gravitational Red Shift
Authors: Lambert, D. L.; Mallia, E. A.
Bibcode: 1968SoPh....3..499L
Altcode:
Absolute wavelengths for Fraunhofer lines are compared with laboratory
measurements for several atomic and molecular spectra. The wavelength
differences are shown to be consistent with the proposal that the deeper
layers of the photosphere are in convective motion: νe
∼ -3 km/sec for log τ0> -1.0. Convective motions in
the outer layers (logτ0< - 1.0) are shown to be very
small. Wavelength shifts of Fraunhofer lines formed in these outer
layers are in good quantitative agreement with the predictions of the
General Theory of Relativity.
Title: The dissociation equilibrium of H^- in stellar atmospheres
Authors: Lambert, D. L.; Pagel, B. E. J.
Bibcode: 1968MNRAS.141..299L
Altcode:
The assumption that the source function for continuous thermal
radiation arising from H- in solar-type stellar atmospheres is
adequately represented by the Planck function has previously been
justified on the grounds that the dissociation equilibrium of the H-
ion is governed by the associative detachment reaction H- + H H2 +
e. This argument is re-examined in the light of recent theoretical
and laboratory data on the rates of the relevant processes, taking
into account (schematically) the presence of separate vibrational
and rotational levels of the H2 molecule. The earlier conclusions are
confirmed for the photospheres of main-sequence stars and of normal
giants, at any rate for those giants in the range of spectral type
G III to K III, and they are shown to be consistent with observed
infra-red colour indices. A rise of temperature caused by departures
from LTE in the solar chromosphere is found to be rather unlikely,
though not altogether impossible, in view of plausible estimates of
the relevant atomic parameters.
Title: The abundances of the elements in the solar photosphere-I,
Carbon, nitrogen and oxygen
Authors: Lambert, D. L.
Bibcode: 1968MNRAS.138..143L
Altcode:
This paper discusses the determination of the abundances of carbon,
nitrogen and oxygen in the solar atmosphere from an analysis of atomic
and molecular spectra. A detailed discussion of the neutral atomic
spectra is presented. Five molecular bands are considered: C2 Swan
Band, CN red and violet systems, CO first overtone bands, and the CH
(A2A-X211) band. With the exception of the CH band, the analysis of
the molecular bands yields abundances which are in good accord with
the results from the neutral atomic spectra. The following abundances
are derived: log Ac = 8 , log AN = 7.93 and log A0 = on the standard
scale log N11 = .
Title: The abundances of the elements in the solar
photosphere-III. Silicon
Authors: Lambert, D. L.; Warner, B.
Bibcode: 1968MNRAS.138..213L
Altcode:
The solar photospheric abundance of silicon is derived from application
of theoretical oscillator strengths for transition arrays of the type
3Pns- ' in Si I and 4s-4p in Si ii. The two stages of ionization are
in agreement and lead to log N(Si) = 7.55 on the scale where log N(H)
= . We discuss the interpretation of the proffles of strong Si I lines
and suggest a modification of the solar model atmosphere. The [Si i]
line at 1099141 A is found to be only a minor contributor to a blend
with a telluric line.
Title: The C12/C13 Ratio in the Solar
Photosphere
Authors: Lambert, D. L.; Mallia, E. A.
Bibcode: 1968ApL.....1...85L
Altcode:
No abstract at ADS
Title: The abundance of the elements in the solar
photosphere-VI. Rubidium
Authors: Lambert, D. L.; Mallia, E. A.
Bibcode: 1968MNRAS.140...13L
Altcode:
Low noise photoelectric scans of the Rb I resonance lines (AA 7800
and 7947) have been obtained with the Oxford spectrometer. An analysis
results in an improved abundance determination. logN(Rb) = 263 on the
standard scale where log N(H) = .
Title: A Model Solar Photosphere.
Authors: Lambert, David L.
Bibcode: 1968AJS....73Q..67L
Altcode:
The results are presented of a comprehensive analysis of all available
observations of the solar continuous spectrum between 5000 A and 25
microns. The observations include absolute intensity measurements
at the center of the solar disk and limb darkening observations at
disk positions cos 6 ~ 0.2. A model photosphere is presented. The
absolute intensities predicted by the model are in good agreement
with the observed intensities; the differences do not exceed 4%. The
predicted and observed limb darkening ratios differ by less than
1%. The limitations on the model imposed by the present observations
are discussed.
Title: Radiation Pressure and the Composition of the Solar Corona
Authors: Lambert, D. L.
Bibcode: 1968ApL.....2...37L
Altcode:
No abstract at ADS
Title: Absorption lines of neutral silicon in the solar spectrum
Authors: Lambert, D. L.; Warner, B.
Bibcode: 1968MNRAS.139...35L
Altcode:
We present a comprehensive description of the occurrence of Si I lines
in the solar spectrum in the wavelength range 2935-25 578 A. Theoretical
equivalent widths are calculated using a detailed curve of growth method
and the f-values given in the preceding paper. Si I is found to account
for, or is an important contributor in, about 550 solar lines. Some
200 of these are new identifications. Many more Si I lines of moderate
strength will appear in the solar spectrum but are masked by telluric
absorption. It has been found possible to locate 32 new energy levels
in Si I, mostly in the 7f, 8f and 9f confignrations. Transitions to
these levels account for some previously unidentified, but moderately
strong, solar lines.
Title: The abundances of the elements in the solar photosphere-V. The
alkaline earths Mg, Ca, Sr, Ba
Authors: Lambert, D. L.; Warner, B.
Bibcode: 1968MNRAS.140..197L
Altcode:
A detailed account is given of available solar absorption lines arising
from the neutral and ionized alkaline earth elements. Careful use of
theoretical and experimental oscillator strengths leads to the following
revized abundances, on the scale where log N(H) = : log N(Mg) = logN(Ca)
= 633 log N(Sr) = log N(Ba) =
Title: The abundances of the elements in the solar
photosphere-II. Sodium, aluminium, phosphorous, sulphur and potassium
Authors: Lambert, D. L.; Warner, B.
Bibcode: 1968MNRAS.138..181L
Altcode:
A comprehensive account is given of the available solar absorption
lines arising from the elements sodium, aluminium, phosphorus, sulphur
and potassium. The use of improved oscillator strengths for selected
lines leads to a revision of the abundances of these elements. The
final values, on the scale log N(H) = , are logN(Na) = log N(Al) =
logN(P) = log N(S) = 721 logN(K) = 505.
Title: A Simplified Model Solar Atmosphere
Authors: Lambert, D. L.
Bibcode: 1968SoPh....3..118L
Altcode:
A simplified representation of the temperature distribution in the
solar photosphere is proposed: θ (τ0) = θ0
- θ1 logτ0. An expression is derived for the
emergent continuous spectrum from the simple model. The limitations
and applications of the simple model are discussed.
Title: The abundance of neon in the Sun
Authors: Lambert, D. L.
Bibcode: 1967Obs....87..228L
Altcode:
No abstract at ADS
Title: Abundance of Helium in the Sun
Authors: Lambert, D. L.
Bibcode: 1967Natur.215...43L
Altcode:
THE observed abundances of elements are largely understood in terms
of stellar nucleosynthesis. The origin of helium, however, remains
a major problem. Indeed, Hoyle and Tayler1 concluded that
the chief fraction of the helium in the Galaxy was synthesized not in
stellar interiors but either in the primordial fireball or in a massive
object which preceded the formation of the stars. This communication
presents a re-determination of the abundance of helium in the Sun and
also reviews determinations of the abundance of helium in other objects.
Title: Forbidden Carbon I Lines in the Solar Spectrum
Authors: Lambert, D. L.; Swings, J. P.
Bibcode: 1967SoPh....2...34L
Altcode:
No abstract at ADS
Title: Forbidden nitrogen I lines in the infra-red solar spectrum
Authors: Lambert, D. L.; Swings, J. P.
Bibcode: 1967Obs....87..113L
Altcode:
No abstract at ADS
Title: Abundance of Boron in the Sun
Authors: Lambert, D. L.; Mallia, E. A.; Warner, B.
Bibcode: 1966Natur.211...56L
Altcode:
IN a recent paper, Waddell and Slaughter1 suggested
that the composite feature at 8668.43 Å in the solar spectrum
includes a high excitation line of B I. This line is one of a number
first reported in the laboratory spectrum of B I by Gunnvald and
Minnhagen2 (Table 1). From the observed central depth
of 0.015, a boron: hydrogen ratio of 4.0 × 10-7 was
deduced. The terrestrial ratio3 is 7.6 × 10-10,
while Russell's4 photospheric upper limit is 1.1 ×
10-7. This figure was later reduced by Babcock5
to 2.8 × 10-8.
Title: The energy distribution in the solar continuous spectrum
Authors: Lambert, D. L.; Willstrop, R. V.
Bibcode: 1965Obs....85..124L
Altcode:
No abstract at ADS
Title: Abstract of solar limb-darkening in the infra-red region
Authors: Lambert, David L.
Bibcode: 1965PhDT........76L
Altcode:
No abstract at ADS
Title: The spectroscopic binary H.D. 27149
Authors: Lambert, D. L.; Norman, A. R. D.; Jones, D. H. P.
Bibcode: 1961Obs....81..145L
Altcode:
No abstract at ADS
Title: Observations de Neptune
Authors: Lambert
Bibcode: 1929JO.....12...88L
Altcode:
No abstract at ADS