CH stars are particular type ofcarbon stars which are characterized by the presence of exceedingly strong absorption bands due to CH (methylidyne) in theirspectra. They belong to the stellarpopulation II,^[1] meaning they aremetal poor and generally pretty middle-aged stars, and are under-luminous compared to the classical C–N carbon stars. The term 'CH star' was coined byPhilip C. Keenan in 1942 as a sub-type of the C classification, which he used forcarbon stars. The main molecular feature used in identifying the initial set of five CH stars lies in theFraunhaufer G band.^[2]

In 1975, Yasuho Yamashita noted that some higher temperature carbon stars displayed the typical spectral characteristics of a CH star, but did not have the same kinematic properties. That is, they did not have the higher space velocities characteristic of the older stellar population. These were dubbed CH-like stars.^[3] Many CH stars are known to be members ofbinary star systems, and it is reasonable to believe this is (or was) the case for all CH stars. LikeBarium stars, they are probably the result of amass transfer from a formerclassical carbon star companion, now a degeneratewhite dwarf, to the current CH-classed star.^[4]

• David Darling."CH star". Retrieved2 January 2009.

• Carbon stars

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