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 ] \leq - 2.0 , 20 % exhibit [ C/Fe ] \geq + 0.7 .
This fraction increases to 43 % for [ Fe/H ] \leq - 3.0 and 81 % for [ Fe/H ] \leq - 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 .