The Temperature Scale and Mass Distribution of Hot DA White Dwarfs

摘要

Results are presented for individual stars, including a number of subdwarf identifications and reports of detections of cool companions. Properties of some of the more interesting binaries are discussed. We also report on some stars in the sample that evidently have varying He abundances. WD 0612+177 (G104-27) had been observed, at one point, to have photospheric He I; we confirm that He has remained absent since then. WD 0718-316 (RE 0720-314) is in a postcommon-envelope binary and has photospheric He II, the abundance of which appears to vary by more than an order of magnitude over timescales of months.