Magnetic White Dwarfs in the SDSS and Estimating the Mean Mass of Normal DA and DB WDs

When classifying by eye more than 22 000 spectra selected as possible white dwarf stars from the Sloan Digital Sky Survey Data Release 7, we detected Zeeman splittings in more than 800 stars, increasing by a factor of five the number of known magnetic white dwarfs. Our field estimations range from 90 MG to less than 1 MG, complementing the detections by Kulebi et al. [1] These magnetic white dwarf stars cover the whole range of temperature and spectral classes observed. As the Zeeman splittings broadens the lines, we cannot use the line profiles to estimate surface gravity directly. We therefore excluded the magnetic white dwarfs from our average mass estimate of normal DAs and DBs. Analysis of the remaining 1505 bright and hot DA white dwarfs, i.e., those with S/N >= 20 and T-eff = 12 000 K, results in a mean mass < M >(DA) = 0.604 +/- 0.003M(circle dot), while that of our 82 bright DBs with T-eff = 16 000 K is < M >(DB) = 0.646 +/- 0.006M(circle dot).