Astronomy and Astrophysics – Astrophysics
Scientific paper
2006-09-26
Astrophys.J.652:L37-L40,2006
Astronomy and Astrophysics
Astrophysics
7 pages, 3 figures. ApJL accepted
Scientific paper
10.1086/509780
We estimate the frequency of Carbon-Enhanced Metal-Poor (CEMP) stars among very metal-poor stars, based on an analysis of 349 stars with available high-resolution spectra observed as part of the Hamburg/ESO R-process Enhanced Star (HERES) survey. We obtain that {\it a lower limit of} 21 $\pm$ 2% of stars with [Fe/H] $\leq -2.0$ exhibit [C/Fe] $\geq +1.0$. These fractions are higher than have been reported by recent examinations of this question, based on substantially smaller samples of stars. We discuss the source of this difference and suggest that in order to take into account effects that result in a decrease of surface carbon abundance with advancing evolution, a definition of CEMP stars based on a [C/Fe] cutoff that varies as a function of luminosity is more appropriate. We discuss the likely occurrence of dilution and mixing for many CEMP stars, which, if properly accounted for, would increase this fraction still further.
Barklem Paul
Beers Timothy
Christlieb Norbert
Lee Young Sun
Lucatello Sara
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