The Temperature Scale and Mass Distribution of Hot DA White Dwarfs

Results are presented from a comprehensive spectroscopic survey of DA white dwarfs hotter than ~25,000 K. The observations consisted of CCD spectra with signal-to-noise ratios of ~100 in the blue, with ~5 Å resolution. The majority of the spectra covered the wavelength range of 3500-7500 Å, allowing the detection of a number of cool companions. To date, spectra have been obtained and analyzed for 174 DA stars. The spectra were analyzed using our model atmospheres, which are described in detail here, resulting in temperatures and gravities with average internal errors of 1% and 0.04 dex, respectively. Comparisons with previously published results showed that temperature determinations for Teff < 30,000 K were generally consistent at the 1% or better level, while spectroscopic gravity determinations based on the latest models were consistent at the 0.02 dex level. Wood's evolutionary sequences were used to derive masses for the observed stars with average internal errors of 0.02 M☉. The mass distribution for this hot sample peaked at 0.570 M☉, consistent with previous spectroscopic results for cooler samples.