We present a new catalog of spectroscopically confirmed white dwarf stars from the Sloan Digital Sky Survey (SDSS) Data Release 7 spectroscopic catalog. We find 20,407 white dwarf spectra, representing 19,712 stars, and provide atmospheric model fits to 14,120 DA and 1011 DB white dwarf spectra from 12,843 and 923 stars, respectively. These numbers represent more than a factor of two increase in the total number of white dwarf stars from the previous SDSS white dwarf catalogs based on DR4 data. Our distribution of subtypes varies from previous catalogs due to our more conservative, manual classifications of each star in our catalog, supplementing our automatic fits. In particular, we find a large number of magnetic white dwarf stars whose small Zeeman splittings mimic increased Stark broadening that would otherwise result in an overestimated log g if fit as a non-magnetic white dwarf. We calculate mean DA and DB masses for our clean, non-magnetic sample and find the DB mean mass is statistically larger than that for the DAs.

To obtain better statistics on the occurrence of magnetism among white dwarfs, we searched the spectra of the hydrogen atmosphere white dwarf stars (DAs) in the Data Release 7 of the Sloan Digital Sky Survey (SDSS) for Zeeman splittings and estimated the magnetic fields. We found 521 DAs with detectable Zeeman splittings, with fields in the range from around 1 MG to 733 MG, which amounts to 4% of all DAs observed. As the SDSS spectra has low signal-to-noise ratios, we carefully investigated by simulations with theoretical spectra how reliable our detection of magnetic field was.

We report our observations of the new pulsating hydrogen atmosphere white dwarf SDSS J132350.28+010304.22. We discovered periodic photometric variations in frequency and amplitude that are commensurate with nonradial g-mode pulsations in ZZ Ceti stars. This, along with estimates for the star's temperature and gravity, establishes it as a massive ZZ Ceti star. We used time-series photometric observations with the 4.1 m SOAR Telescope, complemented by contemporary McDonald Observatory 2.1 m data, to discover the photometric variability. The light curve of SDSS J132350.28+010304.22 shows at least nine detectable frequencies. We used these frequencies to make an asteroseismic determination of the total mass and effective temperature of the star: M ? = 0.88 ± 0.02 Mā nd T eff = 12,100 ± 140 K. These values are consistent with those derived from the optical spectra and photometric colors.

Abstract. 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 Külebi 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 ⊙ , while that of our 82 bright DBs with T eff = 16 000 K is M DB = 0.646 ± 0.006M ⊙ . Kleinman et al. [2] is forming a catalog of white dwarf stars with spectra from the Sloan Digital Sky Survey Data Release 7. Using careful human inspections of our more than 23,000 white dwarf spectra, much more than were looked at in past SDSS white dwarf catalogs, we found evidence of magnetic field -Zeeman splittings -in somewhere between 5-10% of our white dwarf sample. The vast majority of these stars are low field. Keywords MAGNETIC WHITE DWARF STARSIndependent of Kleinman et al.[2], Külebi et al.[1] found 44 new magnetic white dwarfs in the SDSS DR7 sample, and used log g=8.0 models to estimate the fields of the 141 known magnetic white dwarfs (1 to 900 MG).Donati & Landstreet [3] discuss extensively that magnetic fields are found in all types of stars and play a role in their formation and evolution, influencing accretion, diffusion, mass loss, turbulence, pulsations, their rotation rates and even their masses and surface chemical composition. The fraction of white dwarf stars that are magnetic is quoted in the literature as anywhere between 2% to 20%. An accurate estimate of this percentage is crucial to understanding the origin of the magnetic field in these stars. We find 5% of the SDSS white dwarf stars show clear evidence of magnetic fields with another 4%