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]


CEMP-r stars have [Eu/Fe] > +1 and [Ba/Eu] < 0.[1]

CEMP-s stars have [Ba/Fe] > +1 and [Ba/Eu] > +0.5[1] 80% of CEMP stars fall into this category.[1]

CEMP-r/s stars have [Ba/Eu] between 0 and +0.5 so they are under the level for CEMP-s stars.[1]

CEMP-no stars have [Ba/Fe] < 0.[1] About 20% of CEMP stars fall into this category.[1]


  1. ^ a b c d e f g h Catherine r. Kennedy (29 May 2014). "Carbon-Enhanced Metal-Poor Stars in the Milky Way" (PDF). Canberra. Archived from the original (PDF) on October 19, 2015. Retrieved 18 December 2016.
  2. ^ Carollo, Daniela; Freeman, Ken; Beers, Timothy; Placco, Vinicius; Tumlinson, Jason; Martell, Sarah (20 June 2014). "Carbon-Enhanced Metal-Poor Stars: CEMP-s and CEMP-no Sub-Classes in the Halo System of the Milky Way". The Astrophysical Journal. 788 (2): 180. arXiv:1401.0574. Bibcode:2014ApJ...788..180C. doi:10.1088/0004-637X/788/2/180. S2CID 59932382.