Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: [$\alpha$/Fe] Abundances of Four Outer M 31 Halo Stars   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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The categories of this paper are: cond-mat
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The categories of this paper are: hep-th
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The categories of this paper are: q-bio
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The categories of this paper are: quant-ph
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The categories of this paper are: adap-org
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The categories of this paper are: comp-gas
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The categories of this paper are: patt-sol
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The categories of this paper are: math-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: ao-sci
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The categories of this paper are: solv-int
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The categories of this paper are: mtrl-th
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The categories of this paper are: funct-an
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The categories of this paper are: q-alg
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The categories of this paper are: supr-con
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The categories of this paper are: econ