Author name code: fabbian ADS astronomy entries on 2022-09-14 author:"Fabbian, Damian" ------------------------------------------------------------------------ Title: Do MURaM and STAGGER Simulations of Solar Faculae Match Observational Signatures from Magnetic Structures? Authors: Cubas Armas, Melania; Fabbian, Damian Bibcode: 2021ApJ...923..207C Altcode: We compare results of simulations of solar facular-like conditions performed using the numerical codes MURaM and STAGGER. Both simulation sets have a similar setup, including the initial condition of ≍200 G vertical magnetic flux. After interpolating the output physical quantities to constant optical depth, we compare them and test them against inversion results from solar observations. From the snapshots, we compute the monochromatic continuum in the visible and infrared, and the full Stokes vector of the Fe I spectral line pair around 6301-6302 Å. We compare the predicted spectral lines (at the simulation resolution and after smearing to the HINODE SP/SOT resolution) in terms of their main parameters for the Stokes I line profiles, and of their area and amplitude asymmetry for the Stokes V profiles. The codes produce magnetoconvection with similar appearance and distribution in temperature and velocity. The results also closely match the values from recent relevant solar observations. Although the overall distribution of the magnetic field is similar in both radiation-magnetohydrodynamic (RMHD) simulation sets, a detailed analysis reveals substantial disagreement in the field orientation, which we attribute to the differing boundary conditions. The resulting differences in the synthetic spectra disappear after spatial smearing to the resolution of the observations. We conclude that the two sets of simulations provide robust models of solar faculae. Nevertheless, we also find differences that call for caution when using results from RMHD simulations to interpret solar observational data. Title: The CARMENES search for exoplanets around M dwarfs. Not-so-fine hyperfine-split vanadium lines in cool star spectra Authors: Shan, Y.; Reiners, A.; Fabbian, D.; Marfil, E.; Montes, D.; Tabernero, H. M.; Ribas, I.; Caballero, J. A.; Quirrenbach, A.; Amado, P. J.; Aceituno, J.; Béjar, V. J. S.; Cortés-Contreras, M.; Dreizler, S.; Hatzes, A. P.; Henning, Th.; Jeffers, S. V.; Kaminski, A.; Kürster, M.; Lafarga, M.; Morales, J. C.; Nagel, E.; Pallé, E.; Passegger, V. M.; Rodriguez-López, C.; Schweitzer, A.; Zechmeister, M. Bibcode: 2021A&A...654A.118S Altcode: 2021arXiv210812442S Context. M-dwarf spectra are complex and notoriously difficult to model, posing challenges to understanding their photospheric properties and compositions in depth. Vanadium (V) is an iron-group element whose abundance supposedly closely tracks that of iron, but has origins that are not completely understood.
Aims: Our aim is to characterize a series of neutral vanadium atomic absorption lines in the 800-910 nm wavelength region of high signal-to-noise, high-resolution, telluric-corrected M-dwarf spectra from the CARMENES survey. Many of these lines are prominent and exhibit a distinctive broad and flat-bottom shape, which is a result of hyperfine structure (HFS). We investigate the potential and implications of these HFS split lines for abundance analysis of cool stars.
Methods: With standard spectral synthesis routines, as provided by the spectroscopy software iSpec and the latest atomic data (including HFS) available from the VALD3 database, we modeled these striking line profiles. We used them to measure V abundances of cool dwarfs.
Results: We determined V abundances for 135 early M dwarfs (M0.0 V to M3.5 V) in the CARMENES guaranteed time observations sample. They exhibit a [V/Fe]-[Fe/H] trend consistent with that derived from nearby FG dwarfs. The tight (±0.1 dex) correlation between [V/H] and [Fe/H] suggests the potential application of V as an alternative metallicity indicator in M dwarfs. We also show hints that neglecting to model HFS could partially explain the temperature correlation in V abundance measurements observed in previous studies of samples involving dwarf stars with Teff ≲ 5300 K.
Conclusions: Our work suggests that HFS can impact certain absorption lines in cool photospheres more severely than in Sun-like ones. Therefore, we advocate that HFS should be carefully treated in abundance studies in stars cooler than ~5000 K. On the other hand, strong HFS split lines in high-resolution spectra present an opportunity for precision chemical analyses of large samples of cool stars. The V-to-Fe trends exhibited by the local M dwarfs continue to challenge theoretical models of V production in the Galaxy.

Full Table A.1 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/654/A118 Title: VizieR Online Data Catalog: Vanadium measurements for 135 M dwarfs (Shan+, 2021) Authors: Shan, Y.; Reiners, A.; Fabbian, D.; Marfil, E.; Montes, D.; Tabernero, H. M.; Ribas, I.; Caballero, J. A.; Quirrenbach, A.; Amado, P. J.; Aceituno, J.; Bejar, V. J. S.; Cortes-Contreras, M.; Dreizler, S.; Hatzes, A. P.; Henning, T.; Jeffers, S. V.; Kaminski, A.; Kuerster, M.; Lafarga, M.; Morales, J. C.; Nagel, E.; Palle, E.; Passegger, V. M.; Rodriguez-Lopez, C.; Schweitzer, A.; Zechmeister, M. Bibcode: 2021yCat..36540118S Altcode: Table A1 presents the measured V abundances ([V/H]) for 135 nearby early-M dwarfs from the CARMENES GTO sample. Two sets of measurements are given, which are based on two independently measured sets of fundamental stellar parameters for this sample (Schweitzer et al., 2019A&A...625A..68S, Cat. J/A+A/625/A68 and Marfil et al., submitted). Rotational velocities from Reiners et al. (2018A&A...612A..49R, Cat. J/A+A/612/A49) and disk kinematic membership designations (Cortes-Contreras+ in prep) are also included.

(1 data file). Title: The Lines are Not Fine: Measuring Vanadium Abundances in M dwarfs from Hyperfine-Split Lines Authors: Shan, Yutong; Reiners, Ansgar; Fabbian, Damian; Marfil, Emilio; Montes, David; Tabernero, Hugo M.; Ribas, Ignasi; Caballero, Jose A.; Quirrenbach, Andreas; Amado, Pedro J.; Aceituno, J.; Bejar, Victor J. S.; Cortes-Contreras, Miriam; Dreizler, Stefan; Hatzes, Artie P.; Henning, Thomas; Jeffers, Sandra V.; Kaminski, Adrian; Kürster, Martin; Lafarga, Marina; Morales, Juan Carlos; Nagel, Evangelos; Rodriguez-Lopez, Cristina; Passegger, Vera M.; Schweitzer, Andreas; Zechmeister, Mathias Bibcode: 2021csss.confE.160S Altcode: Cool star atmospheres present challenges to chemical abundance studies. To date, only a handful of elements have been quantified for a handful of M dwarfs. In high-resolution spectra from the CARMENES survey, we identify a series of dramatically hyperfine-split vanadium features between 800 and 910 nm, which have strong and clean profiles throughout the early M-dwarf range. These 'bucket-shaped' line regions can be well-modeled with standard model atmospheres combined with the latest atomic data from VALD. From these line regions, we measure vanadium abundances for 140 nearby early M dwarfs in the CARMENES GTO sample and confirm that they follow the same trend with metallicity as the FG-type stars in the solar neighborhood, i.e., significantly above predictions from galactic chemical evolution models. Exhibiting a tight correlation with iron, vanadium abundances show promise as a potential metallicity indicator for M dwarfs. We also present evidence that several well-known chemical studies of K dwarfs have systematically overestimated their vanadium abundances largely as a result of neglecting to model hyperfine structure, a bias that worsens with decreasing temperature. Our work highlights opportunities for robust chemical analysis of cool stars afforded by high-quality spectra redward of visible. Title: Accurate Short-Characteristics Radiative Transfer in A Numerical Tool for Astrophysical RESearch (ANTARES) Authors: Kostogryz, Nadiia M.; Kupka, Friedrich; Piskunov, Nikolai; Fabbian, Damian; Krüger, Daniel; Gizon, Laurent Bibcode: 2021SoPh..296...46K Altcode: We aim to improve the accuracy of radiative energy transport in three-dimensional radiation hydrodynamical simulations in ANTARES (A Numerical Tool for Astrophysical RESearch). We implement in the ANTARES short-characteristics numerical schemes a modification of the Bézier interpolant solver. This method yields a smoother surface structure in simulations of solar convection and reduces the artifacts appearing due to the limited number of rays along which the integration is done. Reducing such artifacts leads to increased stability of the code. We show that our new implementation achieves a better agreement of the temperature structure and its gradient with a semi-empirical model derived from observations, as well as of synthetic spectral-line profiles with the observed solar spectrum. Title: The ANTARES code: recent developments and applications Authors: Kupka, Friedrich; Zaussinger, Florian; Fabbian, Damian; Krüger, Daniel Bibcode: 2020JPhCS1623a2016K Altcode: ANTARES (A Numerical Tool for Astrophysical RESearch) is a multi-purpose numerical tool to solve different variants of the equations of hydrodynamics as they appear in problems of astrophysics, geophysics, and engineering sciences and which require the construction of detailed numerical simulation models. A presentation of the current feature set of the code with a focus on recent add-ons is given here in addition to a summary on several results from recent applications of ANTARES to solar physics, the physics of planets, and basic convection studies including the damping of pressure modes (solar oscillations) in numerical simulations of convection at the solar surface and the coupling of layers in numerical simulations of sheared and non-sheared double-diffusive convection. Title: Comparing Radiative Transfer Codes and Opacity Samplings for Solar Irradiance Reconstructions Authors: Criscuoli, Serena; Rempel, Matthias; Haberreiter, Margit; Pereira, Tiago M. D.; Uitenbroek, Han; Fabbian, Damian Bibcode: 2020SoPh..295...50C Altcode: Some techniques developed to reproduce solar irradiance variations make use of synthetic radiative fluxes of quiet and magnetic features. The synthesis of radiative fluxes of astronomical objects is likely to be affected by uncertainties resulting from approximations and specific input employed for the synthesis. In this work we compare spectra obtained with three radiative transfer codes with the purpose of investigating differences in reproducing solar irradiance variations. Specifically, we compare spectral synthesis produced in non-local thermodynamic equilibrium obtained with COSI and RH using 1-D atmosphere models. We also compare local thermodynamic equilibrium syntheses emerging from 3-D MURaM simulations of the solar atmosphere obtained with two sets of opacity tables generated with the ATLAS9 package and with the RH code, and test the effects of opacity sampling on the emergent spectra. We find that, although the different codes and methodologies employed to synthesize the spectrum reproduce overall the observed solar spectrum with a similar degree of accuracy, subtle differences in quiet Sun spectra may translate into larger differences in the computation of the contrasts of magnetic features, which, in turn, critically affect the estimates of solar variability. Title: On long-duration 3D simulations of stellar convection using ANTARES Authors: Kupka, F.; Fabbian, D.; Krüger, D.; Kostogryz, N.; Gizon, L. Bibcode: 2020IAUGA..30..373K Altcode: We present initial results from three-dimensional (3-D) radiation hydrodynamical simulations for the Sun and targeted Sun-like stars. We plan to extend these simulations up to several stellar days to study p-mode excitation and damping processes. The level of variation of irradiance on the time scales spanned by our 3-D simulations will be studied too. Here we show results from a first analysis of the computational data we produced so far. Title: Shine BRITE: shedding light on stellar variability through advanced models Authors: Fabbian, D.; Kupka, F.; Krüger, D.; Kostogryz, N. M.; Piskunov, N. Bibcode: 2020svos.conf..155F Altcode: 2020arXiv200201560F The correct interpretation of the large amount of complex data from next-generation (in particular, space-based) observational facilities requires a very strong theoretical underpinning. One can predict that, in the near future, the use of atmospheric models obtained with three-dimensional (3-D) radiation magneto-hydrodynamics (RMHD) codes, coupled with advanced radiative transfer treatment including non-local thermodynamic equilibrium (non-LTE) effects and polarisation, will become the norm. In particular, stellar brightness variability in cool stars (i.e., spectral types F-- M) can be caused by several different effects besides pulsation. In this review we have briefly discussed some published results, and mentioned aspects of recent progress. It then attempted to peek into what the future may hold for understanding this important aspect of the lives of stars. Title: On the Challenges of synthetizing solar and stellar spectra for Irradiance reconstructions Authors: Criscuoli, Serena; Rempel, Matthias D.; Haberreiter, Margit; Pereira, Tiago; Uitenbroek, Han; Fabbian, Damian Bibcode: 2019AAS...23421702C Altcode: Syntheses of solar and stellar spectra strongly depend on the adopted approximations and atomic and molecular databases. We compare LTE and NLTE syntheses of solar spectra obtained with widely used radiative transfer codes, utilizing both 3D-MHD simulations and 1D-static atmosphere models. We show that although different codes reproduce reasonably well the observed spectrum, subtle differences may translate into discrepancies of several tens of percents in the estimate of solar and stellar spectral irradiance variability. Title: Comparison of Parameters from Three-Dimensional Magnetoconvection Simulations of the Solar Photosphere Authors: Cubas Armas, M.; Fabbian, D.; Vitas, N. Bibcode: 2019ASPC..526..195C Altcode: We present preliminary results from a comparison of parameters derived from three-dimensional magnetohydrodynamic simulations of a plage obtained with the MURaM and STAGGER codes. We first compared the computed atmospheric physical parameters stored in the output temporal snapshots. Subsequently, we used the same snapshots as input to perform spectral synthesis calculations using the NICOLE code. We compared the synthetic Fe I 630.1 nm and 630.2 nm spectral lines in terms of central intensity, equivalent width, full width at half maximum, as well as area and amplitude asymmetry of the Stokes V profile. Title: Magnetic Flux Density in 3D MHD Simulations and Observations Authors: Beck, C.; Fabbian, D.; Rezaei, R.; Puschmann, K. G. Bibcode: 2019ASPC..526..191B Altcode: We compare the polarization signals induced in three-dimensional (3D) magneto-hydrodynamical (MHD) simulations by the Zeeman effect in the presence of photospheric magnetic fields to those in observations at disc centre. We consider quantities determined from Stokes vector profiles of observations of photospheric spectral lines in the visible and near-infrared, and in corresponding synthetic spectra obtained from numerical 3D MHD simulations with an average magnetic flux density of 20-200 G. We match the spatial resolution of observations by degrading the spectra of the simulations. We find that the total unsigned vertical magnetic flux density in the simulation should be less than 50 G to reproduce the observed polarization signals in the quiet Sun internetwork. A value of ∼30 G best agrees with all observations we employed. Title: The variability of magnetic activity in solar-type stars Authors: Fabbian, D.; Simoniello, R.; Collet, R.; Criscuoli, S.; Korhonen, H.; Krivova, N. A.; Oláh, K.; Jouve, L.; Solanki, S. K.; Alvarado-Gómez, J. D.; Booth, R.; García, R. A.; Lehtinen, J.; See, V. Bibcode: 2017AN....338..753F Altcode: No abstract at ADS Title: The Polarization Signature of Photospheric Magnetic Fields in 3D MHD Simulations and Observations at Disk Center Authors: Beck, C.; Fabbian, D.; Rezaei, R.; Puschmann, K. G. Bibcode: 2017ApJ...842...37B Altcode: 2017arXiv170506812B Before using three-dimensional (3D) magnetohydrodynamical (MHD) simulations of the solar photosphere in the determination of elemental abundances, one has to ensure that the correct amount of magnetic flux is present in the simulations. The presence of magnetic flux modifies the thermal structure of the solar photosphere, which affects abundance determinations and the solar spectral irradiance. The amount of magnetic flux in the solar photosphere also constrains any possible heating in the outer solar atmosphere through magnetic reconnection. We compare the polarization signals in disk-center observations of the solar photosphere in quiet-Sun regions with those in Stokes spectra computed on the basis of 3D MHD simulations having average magnetic flux densities of about 20, 56, 112, and 224 G. This approach allows us to find the simulation run that best matches the observations. The observations were taken with the Hinode SpectroPolarimeter (SP), the Tenerife Infrared Polarimeter (TIP), the Polarimetric Littrow Spectrograph (POLIS), and the GREGOR Fabry-Pèrot Interferometer (GFPI), respectively. We determine characteristic quantities of full Stokes profiles in a few photospheric spectral lines in the visible (630 nm) and near-infrared (1083 and 1565 nm). We find that the appearance of abnormal granulation in intensity maps of degraded simulations can be traced back to an initially regular granulation pattern with numerous bright points in the intergranular lanes before the spatial degradation. The linear polarization signals in the simulations are almost exclusively related to canopies of strong magnetic flux concentrations and not to transient events of magnetic flux emergence. We find that the average vertical magnetic flux density in the simulation should be less than 50 G to reproduce the observed polarization signals in the quiet-Sun internetwork. A value of about 35 G gives the best match across the SP, TIP, POLIS, and GFPI observations. Title: The missing 'M' ingredient in 3D photospheric simulations for solar abundances Authors: Fabbian, Damian Bibcode: 2017psio.confE..28F Altcode: No abstract at ADS Title: Lower solar atmosphere and magnetism at ultra-high spatial resolution Authors: Collet, Remo; Criscuoli, Serena; Ermolli, Ilaria; Fabbian, Damian; Guerreiro, Nuno; Haberreiter, Margit; Peck, Courtney; Pereira, Tiago M. D.; Rempel, Matthias; Solanki, Sami K.; Wedemeyer-Boehm, Sven Bibcode: 2016arXiv161202348C Altcode: We present the scientific case for a future space-based telescope aimed at very high spatial and temporal resolution imaging of the solar photosphere and chromosphere. Previous missions (e.g., HINODE, SUNRISE) have demonstrated the power of observing the solar photosphere and chromosphere at high spatial resolution without contamination from Earth's atmosphere. We argue here that increased spatial resolution (from currently 70 km to 25 km in the future) and high temporal cadence of the observations will vastly improve our understanding of the physical processes controlling solar magnetism and its characteristic scales. This is particularly important as the Sun's magnetic field drives solar activity and can significantly influence the Sun-Earth system. At the same time a better knowledge of solar magnetism can greatly improve our understanding of other astrophysical objects. Title: Spectroscopy at the Solar Limb: II. Are Spicules Heated to Coronal Temperatures? Authors: Beck, C.; Rezaei, R.; Puschmann, K. G.; Fabbian, D. Bibcode: 2016SoPh..291.2281B Altcode: 2016arXiv160606132B; 2016SoPh..tmp..132B Spicules of the so-called type II were suggested to be relevant for coronal heating because of their ubiquity on the solar surface and their eventual extension into the corona. We investigate whether solar spicules are heated to transition-region or coronal temperatures and reach coronal heights (≫6 Mm) using multiwavelength observations of limb spicules in different chromospheric spectral lines (Ca II H, Hε , Hα , Ca II IR at 854.2 nm, He I at 1083 nm) taken with slit spectrographs and imaging spectrometers. We determine the line width of spectrally resolved line profiles in individual spicules and throughout the field of view, and estimate the maximal height that different types of off-limb features reach. We derive estimates of the kinetic temperature and the non-thermal velocity from the line width of spectral lines from different chemical elements. We find that most regular, i.e. thin and elongated, spicules reach a height of at most about 6 Mm above the solar limb. The majority of features found at larger heights are irregularly shaped with a significantly larger lateral extension, of up to a few Mm, than spicules. Both individual and average line profiles in all spectral lines show a decrease in their line width with height above the limb with very few exceptions. The kinetic temperature and the non-thermal velocity decrease with height above the limb. We find no indications that the spicules in our data reach coronal heights or transition-region or coronal temperatures. Title: How different are the Liège and Hamburg atlases of the solar spectrum? Authors: Doerr, H. -P.; Vitas, N.; Fabbian, D. Bibcode: 2016A&A...590A.118D Altcode: 2016arXiv160403748D Context. The high-fidelity solar spectral atlas prepared by http://adsabs.harvard.edu/abs/1973apds.book.....D Delbouille et al. (Liège atlas, 1973) and the atlas by http://adsabs.harvard.edu/abs/1999SoPh..184..421N Neckel (Hamburg atlas, 1999, Sol. Phys., 184, 421) are widely recognised as the most important collection of reference spectra of the Sun at disc centre in the visible wavelength range. The two datasets serve as fundamental resources for many researchers, in particular for chemical abundance analyses. But despite their similar published specifications (spectral resolution and noise level), the shapes of the spectral lines in the two atlases differ significantly and systematically.
Aims: Knowledge of any instrumental degradations is imperative to fully exploit the information content of spectroscopic data. We seek to investigate the magnitude of these differences and explain the possible sources. We provide the wavelength-dependent correction parameters that need to be taken into account when the spectra are to be compared with synthetic data, for instance.
Methods: A parametrically degraded version of the Hamburg spectrum was fitted to the Liège spectrum. The parameters of the model (wavelength shift, broadening, intensity scaling, and intensity offset) represent the different characteristics of the respective instruments, observational strategies, and data processing.
Results: The wavelength scales of the Liège and Hamburg atlases differ on average by 0.5 mÅ with a standard deviation of ± 2 mÅ, except for a peculiar region around 5500 Å. The continuum levels are offset by up to 18% below 5000 Å, but remain stably at a 0.8% difference towards the red. We find no evidence for spectral stray light in the Liège spectrum. Its resolving power is almost independent of wavelength but limited to about 216 000, which is between two to six times lower than specified. When accounting for the degradations determined in this work, the spectra of the two atlases agree to within a few parts in 103.

The fit parameters displayed in Fig. 2 and derived data 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/590/A118 Title: VizieR Online Data Catalog: Differences of atlases of solar spectrum (Doerr+, 2016) Authors: Doerr, H. -P.; Vitas, N.; Fabbian, D. Bibcode: 2016yCat..35900118D Altcode: A parametrically degraded version of the Hamburg spectrum was fitted to the Liege spectrum. The parameters of the model (wavelength shift, broadening, intensity scaling, intensity offset) represent the different characteristics of the respective instruments, observational strategies, and data processing. The fits were carried out for all identified solar lines in the line list provided by Pierce and Breckinridge (1973, The Kitt-Peak Table of Solar Spectrum Wavelengths, Vol. Contribution No. 559 (Kitt Peak National Observatory); hereafter PB73) for an interval of ±15pm around the line cores. From an initial testrun we found that the offset parameter (stray-light) is compatible with zero. The final fits were carried out with only three free parameters. The results from that run are provided in the file 'fitres.dat'.

A second file (liegepar.dat) contains derived parameters (spectral resolving power, position of the continuum) for the Liege spectrum that can be used in studies that compare Liege data to other data (e.g. synthetic spectra).

For instance, synthetic spectra have to be degraded to match the spectral resolving power of the Liege spectrum for a valid comparison. Our analysis showed that a Gaussian convolution kernel with a full-width at half-maximum (FWHM) of lambda/R (lambda: wavelength; R: spectral resolving power) is a very good approximation to the actual instrumental profile of the Liege atlas.

Likewise, the continuum of the Liege atlas at a particular wavelength can be matched to the continuum of the Hamburg atlas by division with the parameter 'C' from liegepar.dat. The correction parameters in liegepar.dat should be interpolated to the desired wavelength range before being applied in any data analysis.

We want to stress that the parameters provided here result from the fitting-procedure as described in the paper, with no further consistency checks or corrections applied. Some fits are affected by nearby telluric blends. We recommend to apply an outlier-rejection (e.g. a median filter) and/or smoothing before using the data. The results need to be carefully checked.

(2 data files). Title: Constraining Solar/Stellar Activity and Magnetically-Driven Variability Authors: Fabbian, Damian; Simoniello, Rosaria Bibcode: 2016IBVS.6161....1F Altcode: No abstract at ADS Title: Continuum Intensity and [O I] Spectral Line Profiles in Solar 3D Photospheric Models: The Effect of Magnetic Fields Authors: Fabbian, D.; Moreno-Insertis, F. Bibcode: 2015ApJ...802...96F Altcode: 2015arXiv150106916F The importance of magnetic fields in three-dimensional (3D) magnetoconvection models of the Sun’s photosphere is investigated in terms of their influence on the continuum intensity at different viewing inclination angles and on the intensity profile of two [O i] spectral lines. We use the RH numerical radiative transfer code to perform a posteriori spectral synthesis on the same time series of magnetoconvection models used in our publications on the effect of magnetic fields on abundance determination. We obtain a good match of the synthetic disk-center continuum intensity to the absolute continuum values from the Fourier Transform Spectrometer (FTS) observational spectrum; the match of the center-to-limb variation synthetic data to observations is also good, thanks, in part, to the 3D radiation transfer capabilities of the RH code. The different levels of magnetic flux in the numerical time series do not modify the quality of the match. Concerning the targeted [O i] spectral lines, we find, instead, that magnetic fields lead to nonnegligible changes in the synthetic spectrum, with larger average magnetic flux causing both of the lines to become noticeably weaker. The photospheric oxygen abundance that one would derive if instead using nonmagnetic numerical models would thus be lower by a few to several centidex. The inclusion of magnetic fields is confirmed to be important for improving the current modeling of the Sun, here in particular in terms of spectral line formation and of deriving consistent chemical abundances. These results may shed further light on the still controversial issue regarding the precise value of the solar oxygen abundance. Title: The Tenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Apache Point Observatory Galactic Evolution Experiment Authors: Ahn, Christopher P.; Alexandroff, Rachael; Allende Prieto, Carlos; Anders, Friedrich; Anderson, Scott F.; Anderton, Timothy; Andrews, Brett H.; Aubourg, Éric; Bailey, Stephen; Bastien, Fabienne A.; Bautista, Julian E.; Beers, Timothy C.; Beifiori, Alessandra; Bender, Chad F.; Berlind, Andreas A.; Beutler, Florian; Bhardwaj, Vaishali; Bird, Jonathan C.; Bizyaev, Dmitry; Blake, Cullen H.; Blanton, Michael R.; Blomqvist, Michael; Bochanski, John J.; Bolton, Adam S.; Borde, Arnaud; Bovy, Jo; Shelden Bradley, Alaina; Brandt, W. N.; Brauer, Dorothée; Brinkmann, J.; Brownstein, Joel R.; Busca, Nicolás G.; Carithers, William; Carlberg, Joleen K.; Carnero, Aurelio R.; Carr, Michael A.; Chiappini, Cristina; Chojnowski, S. Drew; Chuang, Chia-Hsun; Comparat, Johan; Crepp, Justin R.; Cristiani, Stefano; Croft, Rupert A. C.; Cuesta, Antonio J.; Cunha, Katia; da Costa, Luiz N.; Dawson, Kyle S.; De Lee, Nathan; Dean, Janice D. R.; Delubac, Timothée; Deshpande, Rohit; Dhital, Saurav; Ealet, Anne; Ebelke, Garrett L.; Edmondson, Edward M.; Eisenstein, Daniel J.; Epstein, Courtney R.; Escoffier, Stephanie; Esposito, Massimiliano; Evans, Michael L.; Fabbian, D.; Fan, Xiaohui; Favole, Ginevra; Femenía Castellá, Bruno; Fernández Alvar, Emma; Feuillet, Diane; Filiz Ak, Nurten; Finley, Hayley; Fleming, Scott W.; Font-Ribera, Andreu; Frinchaboy, Peter M.; Galbraith-Frew, J. G.; García-Hernández, D. A.; García Pérez, Ana E.; Ge, Jian; Génova-Santos, R.; Gillespie, Bruce A.; Girardi, Léo; González Hernández, Jonay I.; Gott, J. Richard, III; Gunn, James E.; Guo, Hong; Halverson, Samuel; Harding, Paul; Harris, David W.; Hasselquist, Sten; Hawley, Suzanne L.; Hayden, Michael; Hearty, Frederick R.; Herrero Davó, Artemio; Ho, Shirley; Hogg, David W.; Holtzman, Jon A.; Honscheid, Klaus; Huehnerhoff, Joseph; Ivans, Inese I.; Jackson, Kelly M.; Jiang, Peng; Johnson, Jennifer A.; Kinemuchi, K.; Kirkby, David; Klaene, Mark A.; Kneib, Jean-Paul; Koesterke, Lars; Lan, Ting-Wen; Lang, Dustin; Le Goff, Jean-Marc; Leauthaud, Alexie; Lee, Khee-Gan; Lee, Young Sun; Long, Daniel C.; Loomis, Craig P.; Lucatello, Sara; Lupton, Robert H.; Ma, Bo; Mack, Claude E., III; Mahadevan, Suvrath; Maia, Marcio A. G.; Majewski, Steven R.; Malanushenko, Elena; Malanushenko, Viktor; Manchado, A.; Manera, Marc; Maraston, Claudia; Margala, Daniel; Martell, Sarah L.; Masters, Karen L.; McBride, Cameron K.; McGreer, Ian D.; McMahon, Richard G.; Ménard, Brice; Mészáros, Sz.; Miralda-Escudé, Jordi; Miyatake, Hironao; Montero-Dorta, Antonio D.; Montesano, Francesco; More, Surhud; Morrison, Heather L.; Muna, Demitri; Munn, Jeffrey A.; Myers, Adam D.; Nguyen, Duy Cuong; Nichol, Robert C.; Nidever, David L.; Noterdaeme, Pasquier; Nuza, Sebastián E.; O'Connell, Julia E.; O'Connell, Robert W.; O'Connell, Ross; Olmstead, Matthew D.; Oravetz, Daniel J.; Owen, Russell; Padmanabhan, Nikhil; Palanque-Delabrouille, Nathalie; Pan, Kaike; Parejko, John K.; Parihar, Prachi; Pâris, Isabelle; Pepper, Joshua; Percival, Will J.; Pérez-Ràfols, Ignasi; Dotto Perottoni, Hélio; Petitjean, Patrick; Pieri, Matthew M.; Pinsonneault, M. H.; Prada, Francisco; Price-Whelan, Adrian M.; Raddick, M. Jordan; Rahman, Mubdi; Rebolo, Rafael; Reid, Beth A.; Richards, Jonathan C.; Riffel, Rogério; Robin, Annie C.; Rocha-Pinto, H. J.; Rockosi, Constance M.; Roe, Natalie A.; Ross, Ashley J.; Ross, Nicholas P.; Rossi, Graziano; Roy, Arpita; Rubiño-Martin, J. A.; Sabiu, Cristiano G.; Sánchez, Ariel G.; Santiago, Basílio; Sayres, Conor; Schiavon, Ricardo P.; Schlegel, David J.; Schlesinger, Katharine J.; Schmidt, Sarah J.; Schneider, Donald P.; Schultheis, Mathias; Sellgren, Kris; Seo, Hee-Jong; Shen, Yue; Shetrone, Matthew; Shu, Yiping; Simmons, Audrey E.; Skrutskie, M. F.; Slosar, Anže; Smith, Verne V.; Snedden, Stephanie A.; Sobeck, Jennifer S.; Sobreira, Flavia; Stassun, Keivan G.; Steinmetz, Matthias; Strauss, Michael A.; Streblyanska, Alina; Suzuki, Nao; Swanson, Molly E. C.; Terrien, Ryan C.; Thakar, Aniruddha R.; Thomas, Daniel; Thompson, Benjamin A.; Tinker, Jeremy L.; Tojeiro, Rita; Troup, Nicholas W.; Vandenberg, Jan; Vargas Magaña, Mariana; Viel, Matteo; Vogt, Nicole P.; Wake, David A.; Weaver, Benjamin A.; Weinberg, David H.; Weiner, Benjamin J.; White, Martin; White, Simon D. M.; Wilson, John C.; Wisniewski, John P.; Wood-Vasey, W. M.; Yèche, Christophe; York, Donald G.; Zamora, O.; Zasowski, Gail; Zehavi, Idit; Zhao, Gong-Bo; Zheng, Zheng; Zhu, Guangtun Bibcode: 2014ApJS..211...17A Altcode: 2013arXiv1307.7735A The Sloan Digital Sky Survey (SDSS) has been in operation since 2000 April. This paper presents the Tenth Public Data Release (DR10) from its current incarnation, SDSS-III. This data release includes the first spectroscopic data from the Apache Point Observatory Galaxy Evolution Experiment (APOGEE), along with spectroscopic data from the Baryon Oscillation Spectroscopic Survey (BOSS) taken through 2012 July. The APOGEE instrument is a near-infrared R ~ 22,500 300 fiber spectrograph covering 1.514-1.696 μm. The APOGEE survey is studying the chemical abundances and radial velocities of roughly 100,000 red giant star candidates in the bulge, bar, disk, and halo of the Milky Way. DR10 includes 178,397 spectra of 57,454 stars, each typically observed three or more times, from APOGEE. Derived quantities from these spectra (radial velocities, effective temperatures, surface gravities, and metallicities) are also included. DR10 also roughly doubles the number of BOSS spectra over those included in the Ninth Data Release. DR10 includes a total of 1,507,954 BOSS spectra comprising 927,844 galaxy spectra, 182,009 quasar spectra, and 159,327 stellar spectra selected over 6373.2 deg2. Title: APOGEE-2: The Second Phase of the Apache Point Observatory Galactic Evolution Experiment in SDSS-IV Authors: Sobeck, Jennifer; Majewski, S.; Hearty, F.; Schiavon, R. P.; Holtzman, J. A.; Johnson, J.; Frinchaboy, P. M.; Skrutskie, M. F.; Munoz, R.; Pinsonneault, M. H.; Nidever, D. L.; Zasowski, G.; Garcia Perez, A.; Fabbian, D.; Meza Cofre, A.; Cunha, K. M.; Smith, V. V.; Chiappini, C.; Beers, T. C.; Steinmetz, M.; Anders, F.; Bizyaev, D.; Roman, A.; Fleming, S. W.; Crane, J. D.; SDSS-IV/APOGEE-2 Collaboration Bibcode: 2014AAS...22344006S Altcode: The second phase of the Apache Point Observatory Galactic Evolution Experiment (APOGEE-2), a part of the Sloan Digital Sky Survey IV (SDSS-IV), will commence operations in 2014. APOGEE-2 represents a significant expansion over APOGEE-1, not only in the size of the stellar sample, but also in the coverage of the sky through observations in both the Northern and Southern Hemispheres. Observations on the 2.5m Sloan Foundation Telescope of the Apache Point Observatory (APOGEE-2N) will continue immediately after the conclusion of APOGEE-1, to be followed by observations with the 2.5m du Pont Telescope of the Las Campanas Observatory (APOGEE-2S) within three years. Over the six-year lifetime of the project, high resolution (R∼22,500), high signal-to-noise (≥100) spectroscopic data in the H-band wavelength regime (1.51-1.69 μm) will be obtained for several hundred thousand stars, more than tripling the total APOGEE-1 sample. Accurate radial velocities and detailed chemical compositions will be generated for target stars in the main Galactic components (bulge, disk, and halo), open/globular clusters, and satellite dwarf galaxies. The spectroscopic follow-up program of Kepler targets with the APOGEE-2N instrument will be continued and expanded. APOGEE-2 will significantly extend and enhance the APOGEE-1 legacy of scientific contributions to understanding the origin and evolution of the elements, the assembly and formation history of galaxies like the Milky Way, and fundamental stellar astrophysics. Title: DR10 SDSS-III release of APOGEE data Authors: Shetrone, Matthew D.; Allende-Prieto, C.; Beers, T. C.; Cunha, K. M.; Fabbian, D.; Feuillet, D.; Frinchaboy, P. M.; Garcia Perez, A.; Johnson, J.; Majewski, S. R.; Nidever, D. L.; Pinsonneault, M. H.; Smith, V. V.; Zasowski, G.; SDSS-III/APOGEE Collaboration Bibcode: 2014AAS...22344002S Altcode: SDSS-III's newest release is Data Release 10 (DR10). DR10 contains the first spectra of the APO Galactic Evolution Experiment (APOGEE). APOGEE is the first high-resolution (R ~ 22,500), high signal-to-noise ratio (S/N >= 100 per resolution element), H-band (1.51 - 1.70 um) survey of all Galactic stellar populations (bulge, bar, disks, halo) with a uniform set of stellar tracers and spectral diagnostics. This poster will briefly describe the stellar sample included in DR10, review the data made available in DR10, consisting of fully calibrated, 1-d spectra radial velocities and the by-products of the APOGEE Stellar Parameters and Chemical Abundance Pipeline (ASPCAP): effective temperature, surface gravity, metallicity, and alpha, carbon and nitrogen abundances. We will also present the web tools that are available to the public and highlight the most critical warning and bad data flags. Title: Ages of Solar Neighborhood Stars Using APOGEE Authors: Feuillet, Diane; Holtzman, J. A.; Girardi, L.; Allende-Prieto, C.; Beers, T. C.; Cunha, K. M.; Fabbian, D.; Frinchaboy, P. M.; Hayden, M. R.; Majewski, S. Bibcode: 2014AAS...22315209F Altcode: The SDSS-III Apache Point Observatory Galactic Evolution Experiment (APOGEE) is a high resolution (R ~23,000) near-IR (H-band) spectroscopic survey of 100,000 Milky Way stars designed to chemically trace the formation and evolution of Galactic stellar populations. In addition to the primary survey, the APOGEE spectrograph has been fitted with 10 fibers from the robotically controlled NMSU 1 m telescope to maximize the use of this instrument when not on sky with the Sloan 2.5 m telescope. This allows for single object observations with this high resolution NIR spectrograph. Using this new capability provided by the 1 m, we are conducting a survey of bright stars (H < 8) with accurate Hipparcos parallax measurements (μ_err < 10%), which are not accessible to the main APOGEE survey. These data can be reduced and analyzed in the same way as main survey data, resulting in detailed chemical information for hundreds of nearby stars. The atmospheric parameters combined with the Hipparcos distances allow for age estimates of these stars. We present initial age estimates from isochrone matching to Padova isochrones, and an age-metallicity relation for the current sample. Title: Thermodynamic fluctuations in solar photospheric three-dimensional convection simulations and observations (Corrigendum) Authors: Beck, C.; Fabbian, D.; Moreno-Insertis, F.; Puschmann, K. G.; Rezaei, R. Bibcode: 2013A&A...559C...1B Altcode: No abstract at ADS Title: Target Selection for the Apache Point Observatory Galactic Evolution Experiment (APOGEE) Authors: Zasowski, G.; Johnson, Jennifer A.; Frinchaboy, P. M.; Majewski, S. R.; Nidever, D. L.; Rocha Pinto, H. J.; Girardi, L.; Andrews, B.; Chojnowski, S. D.; Cudworth, K. M.; Jackson, K.; Munn, J.; Skrutskie, M. F.; Beaton, R. L.; Blake, C. H.; Covey, K.; Deshpande, R.; Epstein, C.; Fabbian, D.; Fleming, S. W.; Garcia Hernandez, D. A.; Herrero, A.; Mahadevan, S.; Mészáros, Sz.; Schultheis, M.; Sellgren, K.; Terrien, R.; van Saders, J.; Allende Prieto, C.; Bizyaev, D.; Burton, A.; Cunha, K.; da Costa, L. N.; Hasselquist, S.; Hearty, F.; Holtzman, J.; García Pérez, A. E.; Maia, M. A. G.; O'Connell, R. W.; O'Donnell, C.; Pinsonneault, M.; Santiago, B. X.; Schiavon, R. P.; Shetrone, M.; Smith, V.; Wilson, J. C. Bibcode: 2013AJ....146...81Z Altcode: 2013arXiv1308.0351Z The Apache Point Observatory Galactic Evolution Experiment (APOGEE) is a high-resolution infrared spectroscopic survey spanning all Galactic environments (i.e., bulge, disk, and halo), with the principal goal of constraining dynamical and chemical evolution models of the Milky Way. APOGEE takes advantage of the reduced effects of extinction at infrared wavelengths to observe the inner Galaxy and bulge at an unprecedented level of detail. The survey's broad spatial and wavelength coverage enables users of APOGEE data to address numerous Galactic structure and stellar populations issues. In this paper we describe the APOGEE targeting scheme and document its various target classes to provide the necessary background and reference information to analyze samples of APOGEE data with awareness of the imposed selection criteria and resulting sample properties. APOGEE's primary sample consists of ~105 red giant stars, selected to minimize observational biases in age and metallicity. We present the methodology and considerations that drive the selection of this sample and evaluate the accuracy, efficiency, and caveats of the selection and sampling algorithms. We also describe additional target classes that contribute to the APOGEE sample, including numerous ancillary science programs, and we outline the targeting data that will be included in the public data releases. Title: Thermodynamic fluctuations in solar photospheric three-dimensional convection simulations and observations Authors: Beck, C.; Fabbian, D.; Moreno-Insertis, F.; Puschmann, K. G.; Rezaei, R. Bibcode: 2013A&A...557A.109B Altcode: 2013arXiv1306.6093B Context. Numerical three-dimensional (3D) radiative (magneto-)hydrodynamical [(M)HD] simulations of solar convection are nowadays used to understand the physical properties of the solar photosphere and convective envelope, and, in particular, to determine the Sun's photospheric chemical abundances. To validate this approach, it is important to check that no excessive thermodynamic fluctuations arise as a consequence of the partially incomplete treatment of radiative transfer causing radiative damping that is too modest.
Aims: We investigate the realism of the thermodynamics in recent state-of-the-art 3D convection simulations of the solar atmosphere carried out with the Stagger code.
Methods: We compared the characteristic properties of several Fe i lines (557.6 nm, 630 nm, 1565 nm) and one Si i line at 1082.7 nm in solar disc-centre observations of different spatial resolution with spectra synthesized from 3D convection simulations. The observations were taken with ground-based (Echelle spectrograph, Göttingen Fabry-Pérot Interferometer (GFPI), POlarimetric LIttrow Spectrograph, Tenerife Infrared Polarimeter, all at the Vacuum Tower Telescope on Tenerife) and space-based instruments (Hinode/Spectropolarimeter). We degraded the synthetic spectra to the spatial resolution of the observations, based on the distribution of the continuum intensity Ic. We estimated the spectral degradation to be applied to the simulation results by comparing atlas spectra with averaged observed spectra. In addition to deriving a set of line parameters directly from the intensity profiles, we used the SIR (Stokes Inversion based on Response functions) code to invert the spectra.
Results: The spatial degradation kernels yield a similar generic spatial stray-light contamination of about 30% for all instruments. The spectral stray light inside the different spectrometers is found to be between 2% and 20%. Most of the line parameters from the observational data are matched by the degraded HD simulation spectra. The inversions predict a macroturbulent velocity vmac below 10 m s-1 for the HD simulation spectra at full spatial resolution, whereas they yield vmac ≲ 1000 m s-1 at a spatial resolution of 0.″3. The temperature fluctuations in the inversion of the degraded HD simulation spectra do not exceed those from the observational data (of the order of 100-200 K rms for -2 ⪉ log τ500 nm ⪉ -0.5). The comparison of line parameters in spatially averaged profiles with the averaged values of line parameters in spatially resolved profiles indicates a significant change in (average) line properties on a spatial scale between 0.″13 and 0.″3.
Conclusions: Up to a spatial resolution of 0.″3 (GFPI spectra), we find no indications of excessive thermodynamic fluctuations in the 3D HD simulation. To definitely confirm that simulations without spatial degradation contain fully realistic thermodynamic fluctuations requires observations at even higher spatial resolution (i.e. <0.″13).

Appendices A and B are available in electronic form at http://www.aanda.org Title: Solar Fe abundance and magnetic fields. Towards a consistent reference metallicity Authors: Fabbian, D.; Moreno-Insertis, F.; Khomenko, E.; Nordlund, Å. Bibcode: 2012A&A...548A..35F Altcode: 2012arXiv1209.2771F
Aims: We investigate the impact on Fe abundance determination of including magnetic flux in series of 3D radiation-magnetohydrodynamics (MHD) simulations of solar convection, which we used to synthesize spectral intensity profiles corresponding to disc centre.
Methods: A differential approach is used to quantify the changes in theoretical equivalent width of a set of 28 iron spectral lines spanning a wide range in wavelength, excitation potential, oscillator strength, Landé factor, and formation height. The lines were computed in local thermodynamic equilibrium (LTE) using the spectral synthesis code LILIA. We used input magnetoconvection snapshots covering 50 min of solar evolution and belonging to series having an average vertical magnetic flux density of ⟨ Bvert ⟩ = 0,50,100, and 200 G. For the relevant calculations we used the Copenhagen Stagger code.
Results: The presence of magnetic fields causes both a direct (Zeeman-broadening) effect on spectral lines with non-zero Landé factor and an indirect effect on temperature-sensitive lines via a change in the photospheric T - τ stratification. The corresponding correction in the estimated atomic abundance ranges from a few hundredths of a dex up to |Δlog ɛ(Fe)⊙| ~ 0.15 dex, depending on the spectral line and on the amount of average magnetic flux within the range of values we considered. The Zeeman-broadening effect gains relatively more importance in the IR. The largest modification to previous solar abundance determinations based on visible spectral lines is instead due to the indirect effect, i.e., the line-weakening caused by a warmer stratification as seen on an optical depth scale. Our results indicate that the average solar iron abundance obtained when using magnetoconvection models can be ~ 0.03-0.11 dex higher than when using the simpler hydrodynamics (HD) convection approach.
Conclusions: We demonstrate that accounting for magnetic flux is important in state-of-the-art solar photospheric abundance determinations based on 3D convection simulations. Title: Stray-light contamination and spatial deconvolution of slit-spectrograph observations Authors: Beck, C.; Rezaei, R.; Fabbian, D. Bibcode: 2011A&A...535A.129B Altcode: 2011arXiv1109.2421B Context. Stray light caused by scattering on optical surfaces and in the Earth's atmosphere degrades the spatial resolution of observations. Whereas post-facto reconstruction techniques are common for 2D imaging and spectroscopy, similar options for slit-spectrograph data are rarely applied.
Aims: We study the contribution of stray light to the two channels of the POlarimetric LIttrow Spectrograph (POLIS) at 396 nm and 630 nm as an example of a slit-spectrograph instrument. We test the performance of different methods of stray-light correction and spatial deconvolution to improve the spatial resolution post-facto.
Methods: We model the stray light as having two components: a spectrally dispersed component and a "parasitic" component of spectrally undispersed light caused by scattering inside the spectrograph. We used several measurements to estimate the two contributions: a) observations with a (partly) blocked field of view (FOV); b) a convolution of the FTS spectral atlas; c) imaging of the spider mounting in the pupil plane; d) umbral profiles; and e) spurious polarization signal in telluric spectral lines. The measurements with a partly blocked FOV in the focal plane allowed us to estimate the spatial point spread function (PSF) of POLIS and the main spectrograph of the German Vacuum Tower Telescope (VTT). We then used the obtained PSF for a deconvolution of both spectroscopic and spectropolarimetric data and investigated the effect on the spectra.
Results: The parasitic contribution can be directly and accurately determined for POLIS, amounting to about 5% (0.3%) of the (continuum) intensity at 396 nm (630 nm). The spectrally dispersed stray light is less accessible because of its many contributing sources. We estimate a lower limit of about 10% across the full FOV for the dispersed stray light from umbral profiles. In quiet Sun regions, the stray-light level from the close surroundings (d < 2'') of a given spatial point is about 20%. The stray light reduces to below 2% at a distance of 20'' from a lit area for both POLIS and the main spectrograph. The spatial deconvolution using the PSF obtained improves the spatial resolution and increases the contrast, with a minor amplification of noise.
Conclusions: A two-component model of the stray-light contributions seems to be sufficient for a basic correction of observed spectra. The instrumental PSF obtained can be used to model the off-limb stray light, to determine the stray-light contamination accurately for observation targets with large spatial intensity gradients such as sunspots, and also to improve the spatial resolution of observations post-facto. Title: (1) The effect of magnetic fields on solar abundance determinations (2) The solar photosphere in 3D. This time from observations Authors: Fabbian, D.; Socas-Navarro, H. Bibcode: 2010iac..talk..232F Altcode: 2010iac..talk..186F No abstract at ADS Title: Solar Abundance Corrections Derived Through Three-dimensional Magnetoconvection Simulations Authors: Fabbian, D.; Khomenko, E.; Moreno-Insertis, F.; Nordlund, Å. Bibcode: 2010ApJ...724.1536F Altcode: 2010arXiv1006.0231F We explore the effect of the magnetic field when using realistic three-dimensional convection experiments to determine solar element abundances. By carrying out magnetoconvection simulations with a radiation-hydro code (the Copenhagen stagger code) and through a posteriori spectral synthesis of three Fe I lines, we obtain evidence that moderate amounts of mean magnetic flux cause a noticeable change in the derived equivalent widths compared with those for a non-magnetic case. The corresponding Fe abundance correction for a mean flux density of 200 G reaches up to ~0.1 dex in magnitude. These results are based on space- and time-averaged line profiles over a time span of 2.5 solar hours in the statistically stationary regime of the convection. The main factors causing the change in equivalent widths, namely the Zeeman broadening and the modification of the temperature stratification, act in different amounts and, for the iron lines considered here, in opposite directions; yet, the resulting |Δlog epsilonsun(Fe)| coincides within a factor of 2 in all of them, even though the sign of the total abundance correction is different for the visible and infrared lines. We conclude that magnetic effects should be taken into account when discussing precise values of the solar and stellar abundances and that an extended study is warranted. Title: HD 172189: another step in furnishing one of the best laboratories known for asteroseismic studies Authors: Creevey, O. L.; Uytterhoeven, K.; Martín-Ruiz, S.; Amado, P. J.; Niemczura, E.; van Winckel, H.; Suárez, J. C.; Rolland, A.; Rodler, F.; Rodríguez-López, C.; Rodríguez, E.; Raskin, G.; Rainer, M.; Poretti, E.; Pallé, P.; Molina, R.; Moya, A.; Mathias, P.; Le Guillou, L.; Hadrava, P.; Fabbian, D.; Garrido, R.; Decin, L.; Cutispoto, G.; Casanova, V.; Broeders, E.; Arellano Ferro, A.; Aceituno, F. Bibcode: 2009A&A...507..901C Altcode: 2009arXiv0909.3435C HD 172189 is a spectroscopic eclipsing binary system with a rapidly-rotating pulsating δ Scuti component. It is also a member of the open cluster IC 4756. These combined characteristics make it an excellent laboratory for asteroseismic studies. To date, HD 172189 has been analysed in detail photometrically but not spectroscopically. For this reason we have compiled a set of spectroscopic data to determine the absolute and atmospheric parameters of the components. We determined the radial velocities (RV) of both components using four different techniques. We disentangled the binary spectra using KOREL, and performed the first abundance analysis on both disentangled spectra. By combining the spectroscopic results and the photometric data, we obtained the component masses, 1.8 and 1.7 M⊙, and radii, 4.0 and 2.4 R⊙, for inclination i = 73.2°, eccentricity e = 0.28, and orbital period Π = 5.70198 days. Effective temperatures of 7600 K and 8100 K were also determined. The measured v sin i are 78 and 74 km s-1, respectively, giving rotational periods of 2.50 and 1.55 days for the components. The abundance analysis shows [Fe/H] = -0.28 for the primary (pulsating) star, consistent with observations of IC 4756. We also present an assessment of the different analysis techniques used to obtain the RVs and the global parameters. Title: The C/O ratio at low metallicity: constraints on early chemical evolution from observations of Galactic halo stars Authors: Fabbian, D.; Nissen, P. E.; Asplund, M.; Pettini, M.; Akerman, C. Bibcode: 2009A&A...500.1143F Altcode: 2008arXiv0810.0281F Aims: We present new measurements of the abundances of carbon and oxygen derived from high-excitation C i and O i absorption lines in metal-poor halo stars, with the aim of clarifying the main sources of these two elements in the early stages of the chemical enrichment of the Galaxy.
Methods: We target 15 new stars compared to our previous study, with an emphasis on additional C/O determinations in the crucial metallicity range -3 ⪉ [Fe/H]⪉ -2. The stellar effective temperatures were estimated from the profile of the Hβ line. Departures from local thermodynamic equilibrium were accounted for in the line formation for both carbon and oxygen. The non-LTE effects are very strong at the lowest metallicities but, contrary to what has sometimes been assumed in the past due to a simplified assessment, of different degrees for the two elements. In addition, for the 28 stars with [Fe/H] < -1 previously analysed, stellar parameters were re-derived and non-LTE corrections applied in the same fashion as for the rest of our sample, giving consistent abundances for 43 halo stars in total.
Results: The new observations and non-LTE calculations strengthen previous suggestions of an upturn in C/O towards lower metallicity (particularly for [O/H] ⪉ -2). The C/O values derived for these very metal-poor stars are, however, sensitive to excitation via the still poorly quantified inelastic H collisions. While these do not significantly affect the non-LTE results for C i, they greatly modify the O i outcome. Adopting the H collisional cross-sections estimated from the classical Drawin formula leads to [C/O] ≈ 0 at [O/H] ≈ -3. To remove the upturn in C/O, near-LTE formation for O i lines would be required, which could only happen if the H collisional efficiency with the Drawin recipe is underestimated by factors of up to several tens of times, a possibility which we consider unlikely.
Conclusions: The high C/O values derived at the lowest metallicities may be revealing the fingerprints of Population III stars or may signal rotationally-aided nucleosynthesis in more normal Population II stars.

Based on data collected with the European Southern Observatory's Very Large Telescope (VLT) at the Paranal, Chile (programmes No. 67.D-0106 and 73.D-0024) and with the Magellan Telescope at Las Campanas Observatory, Chile. Title: Neutral oxygen spectral line formation revisited with new collisional data: large departures from LTE at low metallicity Authors: Fabbian, D.; Asplund, M.; Barklem, P. S.; Carlsson, M.; Kiselman, D. Bibcode: 2009A&A...500.1221F Altcode: 2009arXiv0902.4472F Aims: A detailed study is presented, including estimates of the impact on elemental abundance analysis, of the non-local thermodynamic equilibrium (non-LTE) formation of the high-excitation neutral oxygen 777 nm triplet in model atmospheres representative of stars with spectral types F to K.
Methods: We have applied the statistical equilibrium code MULTI to a number of plane-parallel MARCS atmospheric models covering late-type stars (4500 ≤ T_eff ≤ 6500 K, 2 ≤ log g ≤ 5 [cgs], and -3.5 ≤ [Fe/H] ≤ 0). The atomic model employed includes, in particular, recent quantum-mechanical electron collision data.
Results: We confirm that the O i triplet lines form under non-LTE conditions in late-type stars, suffering negative abundance corrections with respect to LTE. At solar metallicity, the non-LTE effect, mainly attributed in previous studies to photon losses in the triplet itself, is also driven by an additional significant contribution from line opacity. At low metallicity, the very pronounced departures from LTE are due to overpopulation of the lower level (3s ^5S^o) of the transition. Large line opacity stems from triplet-quintet intersystem electron collisions, a form of coupling previously not considered or seriously underestimated. The non-LTE effects generally become severe for models (both giants and dwarfs) with higher T_eff. Interestingly, in metal-poor turn-off stars, the negative non-LTE abundance corrections tend to rapidly become more severe towards lower metallicity. When neglecting H collisions, they amount to as much as |Δlog ɛ_O| ~ 0.9 dex and ~1.2 dex, respectively at [Fe/H] = -3 and [Fe/H] = -3.5. Even when such collisions are included, the LTE abundance remains a serious overestimate, correspondingly by |Δlog ɛ_O| ~ 0.5 dex and ~0.9 dex at such low metallicities. Although the poorly known inelastic hydrogen collisions thus remain an important uncertainty, the large metallicity-dependent non-LTE effects seem to point to a resulting “low” (compared to LTE) [O/Fe] in metal-poor halo stars.
Conclusions: Our results may be important in solving the long-standing [O/Fe] debate. When applying the derived non-LTE corrections, the LTE oxygen abundance inferred from the 777 nm permitted triplet will be decreased substantially at low metallicity. If the classical Drawin formula is employed for O+H collisions, the derived [O/Fe] trend becomes almost flat below [Fe/H] ~ -1, in better agreement with recent literature estimates generally obtained from other oxygen abundance indicators. A value of [O/Fe] ⪉ +0.5 may therefore be appropriate, as suggested by standard theoretical models of type II supernovae nucleosynthetic yields. If neglecting impacts with H atoms instead, [O/Fe] decreases towards lower [Fe/H], which would open new questions. Our tests using ATLAS model atmospheres show that, though non-LTE corrections for metal-poor dwarfs are smaller (by ~0.2 dex when adopting efficient H collisions) than in the MARCS case, our main conclusions are preserved, and that the LTE approach tends to seriously overestimate the O abundance at low metallicity. However, in order to finally reach consistency between oxygen abundances from the different available spectral features, it is of high priority to reduce the large uncertainty regarding H collisions, to undertake a full investigation of the interplay of non-LTE and 3D effects, and to clarify the issue of the temperature scale at low metallicity. Title: Chemical compositions of stars in the light of non-LTE spectral line formation: The evolution of carbon and oxygen in the Galaxy Authors: Fabbian, Damian Bibcode: 2008PhDT.......131F Altcode: No abstract at ADS Title: [C/O] Observations in Low-[Fe/H] Halo Stars Authors: Fabbian, D.; Nissen, P. E.; Asplund, M.; Akerman, C. J.; Pettini, M. Bibcode: 2008psa..conf...45F Altcode: We have observed 15 halo stars to determine the [C/O] behaviour at low [Fe/H]. Making use of our recent non-LTE calculations, which show that the high excitation C and O lines used in previous studies in the literature are affected by very significant departures from LTE, we aim to obtain accurate [C/O] ratios down to [Fe/H]∼ —3.2, which will enable us to shed light on the possible presence of an upturn of [C/O] at low metallicities. Title: Sulphur Abundances in Metal-poor Stars Authors: Nissen, P. E.; Akerman, C.; Asplund, M.; Fabbian, D.; Pettini, M. Bibcode: 2008psa..conf...51N Altcode: We report on sulphur abundances in halo stars as derived from near-IR UVES spectra. The importance of removing telluric lines and residual CCD fringing patterns by using early B-type stars as calibrators is emphasized. Comparison of data from the weak λ8694.6 and the stronger λ9212.9, 9237.5 pair of S I lines provides important constraints on non-LTE effects. We do not confirm the high sulphur abundances reported by others for some metal-poor stars; our results instead indicate that sulphur behaves like other typical α-capture elements with a plateau at [S/Fe] ∼ +0.3 dex in the Galactic halo. Title: Chemical compositions of stars in the light of non-LTE spectral line formation: the evolution of carbon and oxygen in the Galaxy Authors: Fabbian, D. Bibcode: 2008PhDT........12F Altcode: Non-LTE effects affect the formation of many spectral features in the spectra of late-type stars. This thesis investigates the effect on carbon and oxygen abundances. The non-LTE calculations have been performed with the code MULTI, using MARCS atmospheric models with 4500<Teff<6500 K, 2<log g<5 [cgs], and -3.5<[Fe/H]<0. The large negative non-LTE abundance corrections found for high-excitation IR lines of both C I and O I previously used in the literature, are due to dilution of the line source function (due to photon losses in the lines) at solar metallicity, and to increased line opacity in non-LTE for metal-poor stars. The tendency of the non-LTE abundance corrections to become more important when moving to very low metallicity has important implications in terms of galactic chemical evolution. The results are applied to high-quality observation for a sample of 43 turnoff halo stars with -3.24<[Fe/H]<-1.10. At low-metallicity, in particular due to decreasing Si background opacity, the non-LTE corrections affecting the 777 nm oxygen triplet are found to be more significant than those affecting the C I lines. The presence of a [C/O] upturn at low [Fe/H], here for the first time based on a solid non-LTE analysis, is confirmed, pointing to significant C yields from early generations of stars. This could be tracing the products of so-far elusive earlier Population III stars, or may signal rotationally-aided nucleosynthesis in more normal Population II stars. Title: Sulphur and zinc abundances in Galactic halo stars revisited Authors: Nissen, P. E.; Akerman, C.; Asplund, M.; Fabbian, D.; Kerber, F.; Kaufl, H. U.; Pettini, M. Bibcode: 2007A&A...469..319N Altcode: 2007astro.ph..2689N Aims:Based on a new set of sulphur abundances in very metal-poor stars and an improved analysis of previous data, we aim at resolving current discrepancies on the trend of S/Fe vs. Fe/H and thereby gain better insight into the nucleosynthesis of sulphur. The trends of Zn/Fe and S/Zn will also be studied.
Methods: High resolution VLT/UVES spectra of 40 main-sequence stars with -3.3 < [Fe/H] < -1.0 are used to derive S abundances from the weak λ 8694.6 S I line and the stronger λ λ 9212.9,9237.5 pair of S I lines. For one star, the S abundance is also derived from the S I triplet at 1.046 μm recently observed with the VLT infrared echelle spectrograph CRIRES. Fe and Zn abundances are derived from lines in the blue part of the UVES spectra, and effective temperatures are obtained from the profile of the Hβ line.
Results: Comparison of sulphur abundances from the weak and strong S I lines provides important constraints on non-LTE effects. The high sulphur abundances reported by others for some metal-poor stars are not confirmed; instead, when taking non-LTE corrections into account, the Galactic halo stars distribute around a plateau at [S/Fe] ~ +0.2 dex with a scatter of 0.07 dex only. [Zn/Fe] is close to zero for metallicities in the range -2.0 < [Fe/H] < -1.0 but increases to a level of [Zn/Fe] ~ +0.1 to +0.2 dex in the range -2.7 < [Fe/H] < -2.0. At still lower metallicities [Zn/Fe] rises steeply to a value of [Zn/Fe] ~ +0.5 dex at [Fe/H] = -3.2.
Conclusions: The trend of S/Fe vs. Fe/H corresponds to the trends of Mg/Fe, Si/Fe, and Ca/Fe and indicates that sulphur in Galactic halo stars has been made by α-capture processes in massive SNe. The observed scatter in S/Fe is much smaller than predicted from current stochastic models of the chemical evolution of the early Galaxy, suggesting that either the models or the calculated yields of massive SNe should be revised. We also examine the behaviour of S/Zn and find that departures from the solar ratio are significantly reduced at all metallicities if non-LTE corrections to the abundances of these two elements are adopted. This effect, if confirmed, would reduce the usefulness of the S/Zn ratio as a diagnostic of past star-formation activity, but would bring closer together the values measured in damped Lyman-alpha systems and in Galactic stars.

Based on observations collected at the European Southern Observatory at Paranal, Chile (programmes No. 67.D-0106, 73.D-0024 and CRIRES science verification program 60.A-9072). Table 1 and Appendices are only available in electronic form at http://www.aanda.org Title: Sulphur Abundances in Metal-Poor Stars First Result from CRIRES Science Verification Authors: Nissen, Poul Erik; Asplund, Martin; Fabbian, Damian; Kerber, Florian; Käufl, Hans Ulrich; Pettini, Max Bibcode: 2007Msngr.128...38N Altcode: Sulphur is the tenth most abundant element in the Universe and plays an im-portant role in studies of the chemical enrichment and star formation history of distant galaxies. Due to the lack of suitable sulphur lines in the visible part of stellar spectra there is, however, still no agreement on the abundance of sulphur in Galactic metal poor stars, and we are therefore uncertain about the nucleosynthetic origin of sulphur. New observations of infrared sulphur lines with the cryogenic high resolution infrared echelle spectrograph (CRIRES) at ESO's VLT are helping to solve this problem. Title: The non-LTE line formation of neutral carbon in late-type stars Authors: Fabbian, D.; Asplund, M.; Carlsson, M.; Kiselman, D. Bibcode: 2006A&A...458..899F Altcode: 2006astro.ph..8284F Aims.We investigate the non-Local Thermodynamic Equilibrium (non-LTE) line formation of neutral carbon in late-type stars in order to remove some of the potential systematic errors in stellar abundance analyses employing C i features.
Methods: .The statistical equilibrium code MULTI was used on a grid of plane-parallel 1D MARCS atmospheric models.
Results: .Within the parameter space explored, the high-excitation C i lines studied are stronger in non-LTE due to the combined effect of line source function drop and increased line opacity due to overpopulation of the lower level for the transitions considered; the relative importance of the two effects depends on the particular combination of T{eff}, log g, [Fe/H] and [C/Fe] and on the analysed C i line. As a consequence, the non-LTE abundance corrections are negative and can be substantially so, for example ∼ -0.4 dex in halo turn-off stars at [Fe/H]∼ -3. The magnitude of the non-LTE corrections is rather insensitive to whether inelastic H collisions are included or not.
Conclusions: .Our results have implications on studies of nucleosynthetic processes and on Galactic chemical evolution models. When applying our calculated corrections to recent observational data, the upturn in [C/O] at low metallicity might still be present (thus apparently still necessitating contributions from massive Pop. III stars for the carbon production), but at a lower level and possibly with a rather shallow trend of ∼ -0.2 dex/dex below [O/H]∼ -1. Title: Ci Non-LTE Spectral Line Formation in Late-Type Stars Authors: Fabbian, D.; Asplund, M.; Carlsson, M. Bibcode: 2006cams.book...52F Altcode: We present the results from our non-LTE investigation for neutral carbon, which was carried out to remove potential systematic errors in stellar abundance analyses. The calculations were performed for late-type stars and give substantial negative non-LTE abundance corrections. When applied to observations of extremely metal-poor stars, which within the LTE framework seem to suggest a possible [C/O] uprise at low metallicities (Akerman et al. 2004), these improvements will have important implications, enabling us to understand if the standard chemical evolution model is adequate, with no need to invoke signatures by Pop. III stars for the carbon nucleosynthesis. Title: Abundance Anomalies in Hot Horizontal Branch Stars of the Galactic Globular Cluster NGC 1904 Authors: Recio-Blanco, A.; Fabbian, D.; Gratton, R. G. Bibcode: 2006cams.book..151R Altcode: We present abundance measurements, based on high resolution optical spectroscopic data obtained with the UVES at VLT, for 10 stars in the blue horizontal branch (BHB) of the Galactic globular cluster NGC 1904 (M79). In agreement with previous findings for other clusters, we obtain normal abundances for stars cooler than Te. ~ 11000 K, and largely anomalous abundances for hotter stars: large He depletions and overabundances of Fe, Ti, Cr, P and Mn. The abundances of Mg, Si and Ca are roughly normal, in the hot stars as well as in the cooler ones. This abundance pattern can be attributed to the onset of diffusion and to radiation pressure in the stable atmospheres of hot HB stars. A possibly related discontinuity in the stellar rotation rate seems also to occur at Te. ~ 11000 K. Title: Abundance anomalies in hot horizontal branch stars of the galactic globular cluster NGC1904 Authors: Fabbian, D.; Recio-Blanco, A.; Gratton, R. G.; Piotto, G. Bibcode: 2005A&A...434..235F Altcode: 2005astro.ph..1321F We present abundance measurements, based on high-resolution optical spectroscopic data obtained with the Ultraviolet and Visual Echelle Spectrograph mounted on Kueyen (Very Large Telescope UT2), for ten stars in the extended blue horizontal branch of the Galactic globular cluster NGC 1904 (M79). In agreement with previous findings for other clusters, we obtain normal abundances for stars cooler than T_eff∼ 11 000 K, and largely anomalous abundances for hotter stars: large He depletions, and overabundances of Fe, Ti, Cr, P and Mn. The abundances of Mg, Si and Ca are roughly normal, in the hot stars as well as in the cooler ones. This abundance pattern can be attributed to the onset of diffusion and to radiation pressure in the stable atmospheres of hot horizontal branch stars. Title: Effective temperatures and lithium abundances of halo turnoff stars Authors: Nissen, P. E.; Akerman, C.; Asplund, M.; Fabbian, D.; Pettini, M. Bibcode: 2005IAUS..228..101N Altcode: Effective temperatures of 30 turnoff stars with -3.2 {[Fe/H]{ have been derived from the profiles of Balmer lines in high S/N, VLT/UVES spectra. While the systematic error of Teff may be of the order of 100K, the differential values of Teff are determined with a one-sigma precision of ∼25K. These precise Teff values are used in a study of the slope and dispersion of the Li abundance as a function of [Fe/H]. A small, but significant cosmic dispersion in A(Li) appears to be present exemplified by the two very metal-poor stars G64-12 and G64-37. Title: CI non LTE spectral line formation in late-type stars Authors: Fabbian, D.; Asplund, M.; Carlsson, M.; Kiselman, D. Bibcode: 2005IAUS..228..255F Altcode: 2005astro.ph..8063F We present non-Local Thermodynamic Equilibrium (non-LTE) calculations for neutral carbon spectral line formation, carried out for a grid of model atmospheres covering the range of late-type stars. The results of our detailed calculations suggest that the carbon non-LTE corrections in these stars are higher than usually adopted, remaining substantial even at low metallicity. For the most metal-poor stars in the sample of Akerman et al (2004), the effects are of the order of ΔlogɛC ≃ -0.35ldots-0.45 (when neglecting H collisions). Applying our results to those observations, the apparent [C/O] upturn seen in their LTE analysis is no longer present, thus revealing no need to invoke contributions from Pop. III stars to the carbon nucleosynthesis. Title: VizieR Online Data Catalog: Abundances of BHB stars in NGC 1904 (Fabbian+, 2005) Authors: Fabbian, D.; Recio-Blanco, A.; Gratton, R. G.; Piotto, G. Bibcode: 2005yCat..34340235F Altcode: The abundance measurements are based on high-resolution optical spectroscopical data, obtained during 2 observing runs with the Ultraviolet and Visual Echelle Spectrograph mounted on Kueyen (Very Large Telescope UT2). Ten target stars in the extended blue horizontal branch of the Galactic globular cluster NGC 1904 (M79) have been analysed.

(2 data files). Title: Chemical and Rotational Properties of Cluster Hot HB Stars. Authors: Recio-Blanco, Alejandra; Piotto, Giampaolo; Gratton, Raffaele; Fabbian, Damian; Aparicio, Antonio Bibcode: 2003IAUJD...4E..11R Altcode: In this contribution we analize the chemical and rotational properties of a sample of hot HB stars in the globular clusters M15 M79 M80 and NGC 2808 with effective temperatures Teff between 7000 K and 25000 K. To this purpose we have used high resolution spectroscopy with UVES+VLT. Our study reveals the existence of a discontinuity in the rotational rate distribution with temperature detected also by Behr et al. 1999 and 2000 in M13 and M15. Stars with Teff< 11000 K show a range of vsini values up to 30 km/s. All the stars with Teff > 11000 K however are slow rotators with vsini < 12 km/s. This discontinuity seems to coincide with the onset of diffusive processes in the stellar atmosphere which cause abundance anomalies in the hotter stars: overabundances of metals and helium depletion. This is confirmed also by the chemical analysis performed in 10 of the M79 targets in which we have found evidences of radiative levitation of metals and gravitational settling of helium for stars with temperatures hotter than 11000 K.