Astrophys. J., 681, 1524-1556 (2008/July-2)
Detailed abundances for 28 metal-poor stars: stellar relics in the Milky Way.
LAI D.K., BOLTE M., JOHNSON J.A., LUCATELLO S., HEGER A. and WOOSLEY S.E.
Abstract (from CDS):
We present the results of an abundance analysis for a sample of stars with -4<[Fe/H]←2. 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]←2.6, including nine with [Fe/H]←3.0 and one with [Fe/H]=-4.0, 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]~-3.5, 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]=-2.85, [Eu/Fe]=1.23, and [Ba/Eu]=-0.51. 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 ((ref???)2008). We find that supernovae with progenitor masses between 10 and 20 M☉ provide the best matches to our abundances.
Nuclear Reactions, Nucleosynthesis, Abundances - Stars: Abundances - Stars: Population II - Stars: Supernovae: General
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