SDSS hot DB white dwarfs

About 10 of these are particularly well observed; the remainder are candidates. These are the hottest DB stars yet found, and they populate the DB gap between the hotter DO stars and the familiar DB stars cooler than 30000K.

Nevertheless, after carefully matching the survey volumes we find that the ratio of DA stars to DB stars is a factor of 2.5 larger at 30000 than at 20000K, suggesting that the DB gap is indeed deficient and that some kind of atmospheric transformation takes place in roughly 10% of DA stars as they cool from 30000 to 20000K.