Non-local Thermodynamic Equilibrium Stellar Spectroscopy with 1D and 〈3D〉 Models. I. Methods and Application to Magnesium Abundances in Standard Stars

Journal Article · Wed Sep 20 04:00:00 EDT 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/AA88CB· OSTI ID:22875791

Bergemann, Maria; Amarsi, Anish M.; Kovalev, Mikhail ^[1]; Collet, Remo ^[2]; Ruchti, Greg ^[3]; Magic, Zazralt ^[4]

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1. Max-Planck Institute for Astronomy, D-69117, Heidelberg (Germany)
2. Stellar Astrophysics Centre, Ny Munkegade 120, Aarhus University, DK-8000 Aarhus (Denmark)
3. Lund Observatory, Box 43, SE-221 00 Lund (Sweden)
4. Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen (Denmark)

We determine Mg abundances in six Gaia benchmark stars using theoretical one-dimensional (1D) hydrostatic model atmospheres, as well as temporally and spatially averaged three-dimensional (〈3D〉) model atmospheres. The stars cover a range of T{sub eff} from 4700 to 6500 K, logg from 1.6 to 4.4 dex, and [Fe/H] from −3.0 dex to solar. Spectrum synthesis calculations are performed in local thermodynamic equilibrium (LTE) and in non-LTE (NLTE) using the oscillator strengths recently published by Pehlivan Rhodin et al. We find that: (a) Mg abundances determined from the infrared spectra are as accurate as the optical diagnostics, (b) the NLTE effects on Mg i line strengths and abundances in this sample of stars are minor (although for a few Mg i lines the NLTE effects on abundance exceed 0.6 dex in 〈3D〉 and 0.1 dex in 1D, (c) the solar Mg abundance is 7.56±0.05 dex (total error), in excellent agreement with the Mg abundance measured in CI chondritic meteorites, (d) the 1D NLTE and 〈3D〉 NLTE approaches can be used with confidence to analyze optical Mg i lines in spectra of dwarfs and sub-giants, but for red giants the Mg i 5711 Å line should be preferred, (e) low-excitation Mg i lines are sensitive to the atmospheric structure; for these lines, LTE calculations with 〈3D〉 models lead to significant systematic abundance errors. The methods developed in this work will be used to study Mg abundances of a large sample of stars in the next paper in the series.

• OSTI ID: 22875791
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 847; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
BENCHMARKS
ELEMENT ABUNDANCE
EXCITATION
GALAXIES
HYDROSTATICS
INFRARED SPECTRA
LTE
MAGNESIUM
METEORITES
ONE-DIMENSIONAL CALCULATIONS
RADIANT HEAT TRANSFER
SIMULATION
SPECTROSCOPY
STARS
STELLAR ATMOSPHERES
THERMODYNAMICS
THREE-DIMENSIONAL CALCULATIONS