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arXiv · 1410.2223

Carbon-Enhanced Metal-Poor Star Frequencies in the Galaxy: Corrections for the Effect of Evolutionary Status on Carbon Abundances

Vinicius M. Placco·Anna Frebel·Timothy C. Beers·Richard J. Stancliffe
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Abstract

We revisit the observed frequencies of Carbon-Enhanced Metal-Poor (CEMP) stars as a function of the metallicity in the Galaxy, using data from the literature with available high-resolution spectroscopy. Our analysis excludes stars exhibiting clear over-abundances of neutron-capture elements, and takes into account the expected depletion of surface carbon abundance that occurs due to CN processing on the upper red-giant branch. This allows for the recovery of the initial carbon abundance of these stars, and thus for an accurate assessment of the frequencies of carbon-enhanced stars. The correction procedure we develope is based on stellar-evolution models, and depends on the surface gravity, log g, of a given star. Our analysis indicates that, for stars with [Fe/H]<=-2.0, 20% exhibit [C/Fe]>=+0.7. This fraction increases to 43% for [Fe/H]<=-3.0 and 81% for [Fe/H]<=-4.0, which is higher than have been previously inferred without taking the carbon-abundance correction into account. These CEMP-star frequencies provide important inputs for Galactic and stellar chemical-evolution models, as they constrain the evolution of carbon at early times and the possible formation channels for the CEMP-no stars. We also have developed a public online tool with which carbon corrections using our procedure can be easily obtained.

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Vinicius M. Placco, Anna Frebel, Timothy C. Beers, Richard J. Stancliffe. 2014-10-08. Carbon-Enhanced Metal-Poor Star Frequencies in the Galaxy: Corrections for the Effect of Evolutionary Status on Carbon Abundances. https://doi.org/10.1088/0004-637x/797/1/21

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