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arXiv · 1410.3475

[$\alpha$/Fe] Abundances of Four Outer M 31 Halo Stars

Luis C. Vargas·Karoline M. Gilbert·Marla C. Geha·Erik J. Tollerud·Evan N. Kirby·Puragra Guhathakurta
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Abstract

We present alpha element to iron abundance ratios, [$\alpha$/Fe], for four stars in the outer stellar halo of the Andromeda Galaxy (M 31). The stars were identified as high-likelihood field halo stars by Gilbert et al. (2012) and lie at projected distances between 70 and 140 kpc from M 31's center. These are the first alpha abundances measured for a halo star in a galaxy beyond the Milky Way. The stars range in metallicity between [Fe/H]= -2.2 and [Fe/H]= -1.4. The sample's average [$\alpha$/Fe] ratio is +0.20+/-0.20. The best-fit average value is elevated above solar which is consistent with rapid chemical enrichment from Type II supernovae. The mean [$\alpha$/Fe] ratio of our M31 outer halo sample agrees (within the uncertainties) with that of Milky Way inner/outer halo stars that have a comparable range of [Fe/H].

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Luis C. Vargas, Karoline M. Gilbert, Marla C. Geha, Erik J. Tollerud, Evan N. Kirby, Puragra Guhathakurta. 2014-10-13. [$\alpha$/Fe] Abundances of Four Outer M 31 Halo Stars. https://doi.org/10.1088/2041-8205/797/1/l2

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