Carbon enhanced metal poor stars, usually referred to as CEMP stars, are a class of

chemically peculiar star In astrophysics, chemically peculiar stars (CP stars) are stars with distinctly unusual metal abundances, at least in their surface layers. Classification Chemically peculiar stars are common among hot main-sequence (hydrogen-burning) stars. Thes ...

. CEMP stars have /Fe> +1, which means compared to the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared rad ...

these stars have

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes ...

enhanced at least ten times more than

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...

, and e/H< -1, meaning that iron is less than a tenth that in the Sun. These are further categorized by whether

r-process In nuclear astrophysics, the rapid neutron-capture process, also known as the ''r''-process, is a set of nuclear reactions that is responsible for the creation of approximately half of the atomic nuclei heavier than iron, the "heavy elements", ...

s-process The slow neutron-capture process, or ''s''-process, is a series of reactions in nuclear astrophysics that occur in stars, particularly asymptotic giant branch stars. The ''s''-process is responsible for the creation ( nucleosynthesis) of approxim ...

elements are enhanced. CEMP-no stars have no enhancement. Some of these are the earliest formed in the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked ey ...

. The others are termed CEMP-r, CEMP-s, or CEMP-r/s. Metal poor stars are more likely to be CEMP stars, and once e/H< -5.0, then all the stars are CEMP stars.

Subdivisions

CEMP-r stars have Eu/Fe">Europium.html" ;"title="nowiki/>Europium">Eu/Fe> +1 and [Barium">Ba/Eu">Europium">Eu/Fe">Europium.html" ;"title="nowiki/>Europium">Eu/Fe> +1 and [Barium">Ba/Eu< 0. CEMP-s stars have a/Fe> +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 a/Fe< 0. About 20% of CEMP stars fall into this category.

References

{{Star Star types