RED SUPERGIANT STARS AS COSMIC ABUNDANCE PROBES. II. NLTE EFFECTS IN J -BAND SILICON LINES

Medium-resolution J-band spectroscopy of individual red supergiant stars is a promising tool to investigate the chemical composition of the young stellar population in star-forming galaxies. As a continuation of recent work on iron and titanium, detailed non-LTE (NLTE) calculations are presented to...

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Bibliographic Details
Published in:Astrophysical journal. Letters 2013-02, Vol.764 (2), p.1-11
Main Authors: Bergemann, Maria, KUDRITZKI, ROLF-PETER, Wurl, Matthias, Plez, Bertrand, Davies, Ben, Gazak, Zach
Format: Article
Language:English
Subjects:
ABSORPTION SPECTRA
ABSORPTION SPECTROSCOPY
Abundance
ASTRONOMY
ASTROPHYSICS
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
CHEMICAL COMPOSITION
CORRECTIONS
ELEMENT ABUNDANCE
EMISSION SPECTRA
EMISSION SPECTROSCOPY
GALAXIES
IRON
Local thermodynamic equilibrium
LTE
Physics
RADIANT HEAT TRANSFER
Red giant stars
RESOLUTION
Sciences of the Universe
SILICON
Solar and Stellar Astrophysics
SUPERGIANT STARS
TITANIUM
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Summary:Medium-resolution J-band spectroscopy of individual red supergiant stars is a promising tool to investigate the chemical composition of the young stellar population in star-forming galaxies. As a continuation of recent work on iron and titanium, detailed non-LTE (NLTE) calculations are presented to investigate the influence of NLTE on the formation of silicon lines in the J-band spectra of red supergiants. Substantial effects are found resulting in significantly stronger absorption lines of neutral silicon in NLTE. As a consequence, silicon abundances determined in NLTE are significantly smaller than in local thermodynamic equilibrium (LTE) with the NLTE abundance corrections varying smoothly between -0.4 dex and -0.1 dex for effective temperatures between 3400 K and 4400 K. The effects are largest at low metallicity. The physical reasons behind the NLTE effects and the consequences for extragalactic J-band abundance studies are discussed.
ISSN:0004-637X
2041-8205
1538-4357
2041-8213
DOI:10.1088/0004-637X/764/2/115