A Differential Abundance Analysis of Very Metal-poor Stars

Journal Article · Sat Apr 01 04:00:00 EDT 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/AA62A2· OSTI ID:22872841

O’Malley, Erin M.; Chaboyer, Brian ^[1]; McWilliam, Andrew; Thompson, Ian ^[2]

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1. Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03784 (United States)
2. Observatories of the Carnegie Institution for Science, Pasadena, CA 91101 (United States)

We have performed a differential line-by-line chemical abundance analysis, ultimately relative to the Sun, of nine very metal-poor main-sequence (MS) halo stars, near [Fe/H] = −2 dex. Our abundances range from −2.66⩽[Fe/H]⩽−1.40 dex with conservative uncertainties of 0.07 dex. We find an average [α/Fe] = 0.34 ± 0.09 dex, typical of the Milky Way. While our spectroscopic atmosphere parameters provide good agreement with Hubble Space Telescope parallaxes, there is significant disagreement with temperature and gravity parameters indicated by observed colors and theoretical isochrones. Although a systematic underestimate of the stellar temperature by a few hundred degrees could explain this difference, it is not supported by current effective temperature studies and would create large uncertainties in the abundance determinations. Both 1D and 〈3D〉 hydrodynamical models combined with separate 1D non-LTE effects do not yet account for the atmospheres of real metal-poor MS stars, but a fully 3D non-LTE treatment may be able to explain the ionization imbalance found in this work.

• OSTI ID: 22872841
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 838; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ELEMENT ABUNDANCE
GRAVITATION
IONIZATION
LTE
MILKY WAY
SPACE
STELLAR ATMOSPHERES
TELESCOPES