The Most Metal-poor Stars. Iii. the Metallicity Distribution Function and Cemp Fraction1,2,3
نویسنده
چکیده
We examine the metallicity distribution function (MDF) and fraction of carbon-enhanced metal-poor (CEMP) stars in a sample that includes 86 stars with [Fe/H] ≤ −3.0, based on high-resolution, high-S/N spectroscopy, of which some 32 objects lie below [Fe/H] = −3.5. After accounting for the completeness function, the “corrected” MDF does not exhibit the sudden drop at [Fe/H] = −3.6 that was found in recent samples of dwarfs and giants from the Hamburg/ESO survey. Rather, the MDF decreases smoothly down to [Fe/H] = −4.1. Similar results are obtained from the “raw” MDF. We find the fraction of CEMP objects below [Fe/H] = −3.0 is 23 ± 6% and 32 ± 8% when adopting the Beers & Christlieb and Aoki et al. CEMP definitions, respectively. The former value is in fair agreement with some previous measurements, which adopt the Beers & Christlieb criterion. Subject headings: Cosmology: Early Universe, Galaxy: Formation, Galaxy: Halo, Nucleosynthesis, Abundances, Stars: Abundances
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