Astronomy and Astrophysics, volume 628A, 102-102 (2019/8-1)
Carbon-rich (DQ) white dwarfs in the Sloan Digital Sky Survey.
KOESTER D. and KEPLER S.O.
Abstract (from CDS):
Context. Among the spectroscopically identified white dwarfs, a fraction smaller than 2% have spectra dominated by carbon lines, mainly molecular C2, but also a smaller group dominated by CI and CII lines. These are together called DQ white dwarfs. Aims. We want to derive atmospheric parameters Teff, logg, and carbon abundances for a large sample of these stars and discuss implications for their spectral evolution. Methods. Sloan Digital Sky Survey spectra and ugriz photometry were used, together with Gaia Data Release 2 parallaxes and G band photometry. These were fitted to synthetic spectra and theoretical photometry derived from model atmospheres. Results. We found that the DQ hotter than Teff∼10000K have masses ∼0.4M☉ larger than the classical DQ, which have masses typical for the majority of white dwarfs (∼0.6M☉). We found some evidence that the peculiar DQ below 10000K also have significantly larger masses and may thus be the descendants of the hot and warm DQ above 10000K. A significant fraction of the hotter objects with Teff>14500K have atmospheres dominated by carbon.