White dwarf mass distribution in the SDSS

We determined masses for the 7167 DA and 507 DB white dwarf stars classified as single and non-magnetic in Data Release 4 of the Sloan Digital Sky Survey (SDSS). We obtained revised T-eff and log g determinations for the most massive stars by fitting the SDSS optical spectra with a synthetic spectra grid derived from model atmospheres extending to log g = 10.0. We also calculate radii from evolutionary models and create volume-corrected mass distributions for our DA and DB samples. The mean mass for the DA stars brighter than g = 19 and hotter than T-eff = 12 000 K is [M](DA) similar or equal to 0.593 +/- 0.016 M-.. For the 150 DBs brighter than g = 19 and hotter than T-eff = 16 000 K, we find [M](DB) = 0.711 +/- 0.009 M-.. It appears the mean mass for DB white dwarf stars may be significantly larger than that for DAs. We also report the highest mass white dwarf stars ever found, up to 1.33 M-..