These stars are hot, with surface temperatures between 75,000 K and 200,000 K,[2] and are characterized by atmospheres with little hydrogen and absorption lines for helium, carbon and oxygen.
It is thought that the atmospheric composition of PG 1159 stars is odd because, after they have left the asymptotic giant branch, they have reignited helium fusion.
They are believed to eventually lose mass, cool, and become DO white dwarfs.
These stars vary slightly (5–10%) in brightness due to non-radial gravity wave pulsations within themselves.
They vibrate in a number of modes simultaneously, with typical periods between 300 and 3,000 seconds.