For 10 points identify this type of star with a varying luminosity that is held together by electron degenerate pressure.
Richer and Ulrych identified one of these stars in Leo Minor that is considered to be the most stable celestial clock. In May of 2012, Hermes et. al claimed to have found one with extremely low mass; its hydrogen atmosphere means that star is classified in the ZZ Ceti type of these objects. Another class of these objects, predicted by D.E. Winget, is designated DBV. The first star of this type to be observed was seen by Haro and Luyten in 1961; seven years later, Arlo Landolt determined that star, HL Tau 76, was one of these stars. Still another variety of these stars uses carbon and oxygen to carry out the kappa mechanism, which manages to occur despite the presence of helium in its atmosphere. That variety, the GW Vir star, is suggested to eventually become the result of the collapse of a star below the Chandrasekhar Limit. For 10 points identify this type of star with a varying luminosity that is held together by electron degenerate pressure.
Richer and Ulrych identified one of these stars in Leo Minor that is considered to be the most stable celestial clock.
Pulsating White Dwarf [Prompt on Variable White Dwarf]