Accurate Metallicities for Very Metal-poor Stars from the Ca ii Infrared Triplet
Authors
Publication Date
2022-04-01Journal Title
The Astrophysical Journal
ISSN
0004-637X
Publisher
American Astronomical Society
Volume
928
Issue
2
Language
en
Type
Article
This Version
VoR
Metadata
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Osorio, Y., Aguado, D. S., Prieto, C. A., Hubeny, I., & González Hernández, J. I. (2022). Accurate Metallicities for Very Metal-poor Stars from the Ca ii Infrared Triplet. The Astrophysical Journal, 928 (2) https://doi.org/10.3847/1538-4357/ac5a53
Abstract
<jats:title>Abstract</jats:title>
<jats:p>The Ca <jats:sc>ii</jats:sc> H and K lines are among the few features available to infer the metallicity of extremely metal-poor stars from medium-resolution spectroscopy. Unfortunately, these lines can overlap with absorption produced in the intervening interstellar medium, introducing systematic errors in the derived metallicities. The strength of the Ca <jats:sc>ii</jats:sc> infrared triplet lines can also be measured at extremely low metallicities, and it is not affected by interstellar absorption, but it suffers significant departures from local thermodynamic equilibrium (LTE). We investigate the feasibility of adopting the Ca <jats:sc>ii</jats:sc> infrared triplet as a metallicity indicator in extremely metal-poor stars using state-of-the art non-LTE models including the most recent atomic data. We find that the triplet lines exhibit non-LTE abundance corrections that can exceed 0.5 dex. When interstellar absorption affecting the Ca <jats:sc>ii</jats:sc> resonance lines is accounted for using high-resolution observations, the agreement between non-LTE abundances for the triplet and those for the resonance lines, with only minor departures from LTE, is excellent. Non-LTE effects strengthen the Ca <jats:sc>ii</jats:sc> IR triplet lines, facilitating measurements at very low metallicities, compared with LTE estimates, down to [Fe/H] = −6.0. This result has important implications for the discovery of primitive stars in our Galaxy and others, since instruments are most sensitive at red/near-infrared wavelengths, and tens of millions of spectra covering the Ca <jats:sc>ii</jats:sc> IR triplet will soon become available from the Gaia, DESI, WEAVE, and PFS missions.</jats:p>
Keywords
340, Stars and Stellar Physics
Identifiers
apjac5a53, ac5a53, aas36760
External DOI: https://doi.org/10.3847/1538-4357/ac5a53
This record's URL: https://www.repository.cam.ac.uk/handle/1810/335910
Rights
Licence:
http://creativecommons.org/licenses/by/4.0/
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