Astronomy and Astrophysics – Astrophysics – Solar and Stellar Astrophysics
Scientific paper
2010-02-15
Astronomy and Astrophysics, 513, A34 (2010)
Astronomy and Astrophysics
Astrophysics
Solar and Stellar Astrophysics
15 pages, 16 figures. Replaced to match the published version; very minor corrections.
Scientific paper
10.1051/0004-6361/200913759
The NIR Ca II triplet absorption lines have proven to be an important tool for quantitative spectroscopy of individual red giant branch stars in the Local Group, providing a better understanding of metallicities of stars in the Milky Way and dwarf galaxies and thereby an opportunity to constrain their chemical evolution processes. An interesting puzzle in this field is the significant lack of extremely metal-poor stars, below [Fe/H]=-3, found in classical dwarf galaxies around the Milky Way using this technique. The question arises whether these stars are really absent, or if the empirical Ca II triplet method used to study these systems is biased in the low-metallicity regime. Here we present results of synthetic spectral analysis of the Ca II triplet, that is focused on a better understanding of spectroscopic measurements of low-metallicity giant stars. Our results start to deviate strongly from the widely-used and linear empirical calibrations at [Fe/H]<-2. We provide a new calibration for Ca II triplet studies which is valid for -0.5<[Fe/H]<-4. We subsequently apply this new calibration to current data sets and suggest that the classical dwarf galaxies are not so devoid of extremely low-metallicity stars as was previously thought.
Battaglia Giuseppina
de Boer Thomas
Gonzalez Hernandez Jonay I.
Helmi Amina
Hill Vanessa
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