Are there stars primarily composed of helium?
There are many stars whose CORES are composed of helium -- and even stars with cores of heavier elements.
There is a class designated "Extreme Helium Stars", but this comes from the spectra of the surface only where Hydrogen is low or lacking. Most would be the "remnant" (white dwarf) of an evolved star, leaving behind the outer helium burning shell as a "surface", even though the interior would still be composed mostly of carbon and oxygen.
But, there is one model where colliding white dwarfs could cause the combination of helium total to exceed the other elements. So, I guess the answer is probably yes, in rare occassion.
A star that was smaller
than solar mass by a factor of two or three might never get past the Hydrogen to Helium stage but that would take a long time, it would be older than the universe is now before the Hydrogen was all used up.
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