Carbon-enhanced metal-poor stars, usually referred to as CEMP stars, are a class of chemically peculiar star. CEMP stars have [C/Fe] > +1, which means compared to the Sun these stars have carbon enhanced at least ten times more than iron, and [Fe/H] < -1, meaning that iron is less than a tenth that in the Sun.
These are further categorized by whether r-process or s-process elements are enhanced. CEMP-no stars have no enhancement. Some of these are the earliest formed in the Milky Way. The others are termed CEMP-r, CEMP-s, or CEMP-r/s.[1][2] Metal-poor stars are more likely to be CEMP stars, and once [Fe/H] < -5.0, then all the stars are CEMP stars.[1]