CH stars are particular type of
carbon stars which are characterized by the presence of exceedingly strong absorption bands due to CH (
methylidyne
Methylidyne, or (unsubstituted) carbyne, is an organic compound whose molecule consists of a single hydrogen atom bonded to a carbon atom. It is the parent compound of the carbynes, which can be seen as obtained from it by substitution of other f ...
) in their
spectra. They belong to the stellar
population II,
[ meaning they are ]metal
A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typi ...
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 by Philip C. Keenan
Philip Childs Keenan (March 31, 1908 – April 20, 2000) was an American astronomer.
Keenan was an American spectroscopist who collaborated with William Wilson Morgan and Edith Kellman (1911–2007) to develop the MKK stellar spectral classi ...
in 1942 as a sub-type of the C classification, which he used for carbon stars. The main molecular feature used in identifying the initial set of five CH stars lies in the Fraunhaufer G band.[
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.][ Many CH stars are known to be members of binary star systems, and it is reasonable to believe this is (or was) the case for all CH stars. Like ]Barium star
Barium stars are spectral class G to K stars whose spectra indicate an overabundance of s-process elements by the presence of singly ionized barium, Ba II, at λ 455.4 nm. Barium stars also show enhanced spectral features of carbon, th ...
s, they are probably the result of a mass transfer
Mass transfer is the net movement of mass from one location (usually meaning stream, phase, fraction or component) to another. Mass transfer occurs in many processes, such as absorption, evaporation, drying, precipitation, membrane filtra ...
from a former classical carbon star companion, now a degenerate white dwarf, to the current CH-classed star.[
]
References
External links
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{{Star, state=collapsed
Carbon stars