Studies of hot white dwarfs and instrumentation for stellar extreme ultraviolet astronomy

The extreme ultraviolet explorer (EUVE) all-sky survey will enlarge the sample of known hot white dwarfs (T(eff) greater than 20,000K) from approx. 80 to perhaps 2000. The EUV measurements, used in conjunction with observations in other wavelength ranges, will give accurate effective temperatures, helium abundances and interstellar hydrogen columns for significant numbers of hot white dwarfs. Study of multiple stars will result in many more direct mass determinations of white dwarfs. Optimum utilization of the EUV survey data will be achieved by complementing the EUV observations with observations in other wavelength ranges. The efficacy of far ultraviolet (FUV) continuum measurements was evaluated by taking FUV spectra of several hot DA white dwarfs with the international ultraviolet explorer (IUE) satellite. These spectra were analyzed by means of our white dwarf model atmosphere code. In the course of this effort, accurate effective temperatures were obtained for the target stars, the IUE sensitivity was calibrated more accurately, and the visible photometry temperature scale for white dwarfs was revised. A satellite-borne telescope was built which will perform a photometric partial sky survey in a portion of the EUV band, between 80 and 300A. Calibration of this instrument demonstrated that it achieved the sensitivity and resolution necessary for detecting and locating stellar sources of EUV radiation. Further instrumental advances were made in the fabrication of the flight mirrors for the EUVE experiment. The imaging quality of the best of these mirrors exceeds that of the mirror used in the Einstein satellite X-ray telescope. As a result, EUVE will be able to perform a very sensitive all-sky survey which spans the entire EUV band of 70 to 900A.