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

Bergemann, Maria; Collet, Remo; Amarsi, Anish M.; Kovalev, Mikhail; Ruchti, Greg LU and Magic, Zazralt (2017) In Astrophysical Journal 847(1).
Abstract

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 Teff from 4700 to 6500 K, log g 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... (More)

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 Teff from 4700 to 6500 K, log g 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 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.

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organization
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type
Contribution to journal
publication status
published
subject
keywords
galaxies: abundances, line: formation, radiative transfer, stars: abundances, stars: late-type
in
Astrophysical Journal
volume
847
issue
1
publisher
University of Chicago Press
external identifiers
  • scopus:85030167093
  • wos:000410740100001
ISSN
0004-637X
DOI
10.3847/1538-4357/aa88cb
language
English
LU publication?
yes
id
3e57348a-9852-45da-99c2-4d83f27714e7
date added to LUP
2017-11-28 12:59:36
date last changed
2018-07-08 04:28:32
@article{3e57348a-9852-45da-99c2-4d83f27714e7,
  abstract     = {<p>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</sub> from 4700 to 6500 K, log g 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 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.</p>},
  articleno    = {15},
  author       = {Bergemann, Maria and Collet, Remo and Amarsi, Anish M. and Kovalev, Mikhail and Ruchti, Greg and Magic, Zazralt},
  issn         = {0004-637X},
  keyword      = {galaxies: abundances,line: formation,radiative transfer,stars: abundances,stars: late-type},
  language     = {eng},
  month        = {09},
  number       = {1},
  publisher    = {University of Chicago Press},
  series       = {Astrophysical Journal},
  title        = {Non-local Thermodynamic Equilibrium Stellar Spectroscopy with 1D and 〈3〉 Models. I. Methods and Application to Magnesium Abundances in Standard Stars},
  url          = {http://dx.doi.org/10.3847/1538-4357/aa88cb},
  volume       = {847},
  year         = {2017},
}