[α/Fe] Abundances of Four Outer M31 Halo Stars
Abstract
We present alpha element to iron abundance ratios, [α/Fe], for four stars in the outer stellar halo of the Andromeda Galaxy (M31). The stars were identified as high-likelihood field halo stars by Gilbert et al. and lie at projected distances between 70 and 140 kpc from M31'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 [α/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 [α/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].
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 2014
- DOI:
- 10.1088/2041-8205/797/1/L2
- arXiv:
- arXiv:1410.3475
- Bibcode:
- 2014ApJ...797L...2V
- Keywords:
-
- galaxies: abundances;
- galaxies: evolution;
- galaxies: individual: M31;
- Local Group;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 6 pages, 5 figures, resubmitted to ApJ Letters after referee report