Overview
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. Metal-poor stars are more likely to be CEMP stars, and once Fe/H < −5.0, then all the stars are CEMP stars.
Subdivisions
CEMP-r stars have Eu/Fe > +1 and Ba/Eu +1 and Ba/Eu > +0.5 80% of CEMP stars fall into this category. CEMP-r/s stars have Ba/Eu between 0 and +0.5 so they are under the level for CEMP-s stars. CEMP-no stars have Ba/Fe < 0. About 20% of CEMP stars fall into this category.