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We model the structure of the surface magnetic fields of the hydrogen-rich white dwarfs in the SDSS. We have calculated a grid of state-of-the-art theoretical optical spectra of hydrogen-rich magnetic white dwarfs with magnetic field strengths between 1 MG and 1200 MG for different angles, and for effective temperatures between 7000 K and 50000 K. We used a least-squares minimization scheme with an evolutionary algorithm in order to find the magnetic field geometry best fitting the observed data. We used simple centered dipoles or dipoles which were shifted along the dipole axis to model the coadded SDSS fiber spectrum of each object. We have analysed the spectra of all known magnetic DAs from the SDSS (97 previously published plus 44 newly discovered) and also investigated the statistical properties of magnetic field geometries of this sample. The total number of known magnetic white dwarfs already more than tripled by the SDSS and more objects are expected from a more systematic search. The magnetic fields span a range between ~1 and 900 MG. Our results further support the claim that Ap/Bp population is insufficient in generating the numbers and field strength distributions of the observed MWDs, and either another source of progenitor types or binary evolution is needed. Moreover clear indications for non-centered dipoles exist in about ~50% of the objects which is consistent with the magnetic field distribution observed in Ap/Bp stars.
Among the spectroscopically identified white dwarfs, a fraction smaller than 2% have spectra dominated by carbon lines, mainly molecular C2, but also in a smaller group by CI and CII lines. These are together called DQ white dwarfs. We want to derive
To obtain a 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 estimat
An initial assessment is made of white dwarf and hot subdwarf stars observed in the Sloan Digital Sky Survey. In a small area of sky (190 square degrees), observed much like the full survey will be, 269 white dwarfs and 56 hot subdwarfs are identifie
White dwarfs with helium-dominated atmospheres comprise approximately 20% of all white dwarfs. Among the open questions are the total masses and the origin of the hydrogen traces observed in a large number and the nature of the deficit of DBs in the
In this work we study white dwarfs where $30,000,text{K} {>} mathrm{T}_{rm{eff}} {>} 5,000,text{K}$ to compare the differences in the cooling of DAs and non-DAs and their formation channels. Our final sample is composed by nearly $13,000$ DAs and mor