We present ugriz photometry and optical spectroscopy for 28 DB and DO white dwarfs with temperatures between 28,000 and 45,000 K. 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 30,000 K. 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 30,000 than at 20,000 K, 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 30,000 to 20,000 K.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science