Carbon enhanced metal poor stars
A star that presents very low iron abundances [Fe/H] < -4 but an anomalous richness in carbon. CEMP stars have been defined as a subset of metal-poor stars that exhibit elevated [C/Fe] ≥ +1.0. It has been recognized that ~15-20% of stars with [Fe/H] < -2.0 are carbon enhanced. This fraction rises to 30% for [Fe/H] < -3.0, to 40% for [Fe/H] < -3.5, and ~75% for [Fe/H] < -4.0. This increasing trend of CEMP-star frequency with declining [Fe/H] is confirmed by the observation of many thousands of CEMP stars.
CEMP stars
Chemically peculiar stars