Carbon-rich (DQ) white dwarfs in SDSS

These are together called DQ white dwarfs. We derive atmospheric parameters Teff, logg, and carbon abundances for a large sample of these stars and discuss implications for their spectral evolution.

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. We found that the DQs hotter than Teff ~10000K have masses ~0.4M_{sun}_ larger than the classical DQ, which have masses typical for the majority of white dwarfs (~0.6M_{sun}_).