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helium star
A helium star or helium strong star is a class O or B star (blue), which has extraordinarily strong helium lines and weaker than normal hydrogen lines, indicating strong stellar winds and a mass loss of the outer envelope. ''Extreme helium stars'' (EHe) entirely lack hydrogen in their spectra.〔(Daviddarling.info: helium star )〕
Previously, a ''helium star'' was a synonym for a B class star, but this usage is considered obsolete.
A ''helium star'' is also a term for a hypothetical star that could occur if two helium white dwarfs with a combined mass of at least 0.5 solar masses merge and subsequently start nuclear fusion of helium, with a lifetime of a few hundred million years. It is believed this is the origin of the extreme helium stars.
==See also==
* R Coronae Borealis variable
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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