paper

Detailed Abundances for 28 Metal-poor Stars: Stellar Relics in the Milky Way

arXiv:0804.1370 · doi:10.1086/588811 10.1088/0004-637X/722/2/1984

Abstract

We present the results of an abundance analysis for a sample of stars with [Fe/H]. The data were obtained with the HIRES spectrograph at Keck Observatory. The set includes 28 stars, with effective temperature ranging from 4800 to 6600 K. For 13 stars with [Fe/H], including nine with [Fe/H] and one with [Fe/H], these are the first reported detailed abundances. For the most metal-poor star in our sample, CS 30336-049, we measure an abundance pattern that is very similar to stars in the range [Fe/H], including a normal C+N abundance. We also find that it has very low but measurable Sr and Ba, indicating some neutron-capture activity even at this low of a metallicity. We explore this issue further by examining other very neutron-capture-deficient stars, and find that at the lowest levels, [Ba/Sr] exhibits the ratio of the main r-process. We also report on a new r-process-enhanced star, CS 31078-018. This star has [Fe/H], [Eu/Fe], and [Ba/Eu]. CS 31078-018 exhibits an ``actinide boost'', i.e. much higher [Th/Eu] than expected and at a similar level to CS 31082-001. Our spectra allow us to further constrain the abundance scatter at low metallicities, which we then use to fit to the zero-metallicity Type II supernova yields of Heger & Woosley (2008). We find that supernovae with progenitor masses between 10 and 20 M provide the best matches to our abundances.

48 pages, 30 figures, 17 tables. Updated to ApJ version. Multiple typos and errors fixed

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