[$\alpha$/Fe] Abundances of Four Outer M 31 Halo Stars
Abstract
We present alpha element to iron abundance ratios, [/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 [/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 [/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].
Keywords
Cite
@article{arxiv.1410.3475,
title = {[$\alpha$/Fe] Abundances of Four Outer M 31 Halo Stars},
author = {Luis C. Vargas and Karoline M. Gilbert and Marla C. Geha and Erik J. Tollerud and Evan N. Kirby and Puragra Guhathakurta},
journal= {arXiv preprint arXiv:1410.3475},
year = {2015}
}
Comments
6 pages, 5 figures, resubmitted to ApJ Letters after referee report