EUVE Observations of Hot DA White Dwarfs

We present analyses of EUV photometric observations of hot DA white dwarfs from the sky survey now being completed by the Extreme Ultraviolet Explorer (EUVE) satellite. The EUVE data are from one to four bandpasses, centered at 100, 200, 450, and 600 Angstroms. We also include data from the ROSAT Wide Field Camera (WFC) and EXOSAT where applicable. We determine limits on the temperatures and gravities by fitting Koester's model fluxes to the Balmer line profiles from our high S/N optical spectra. The solid angle is set using published V magnitudes. The EUV data are then used to determine limits to the photospheric composition and the interstellar columns for the targets. The composition is evaluated using both stratified models, and models with uniformly distributed trace elements such as C, N, O, Si, and Fe. We present our results and discuss the implications for the theoretical understanding of trace element distributions in hot DA white dwarfs. This work has been supported by NASA contracts NAS5-30180 and NAS5-29298.