%0 Journal Article
%T Carbon-rich (DQ) white dwarfs in the Sloan Digital Sky Survey
%A D. Koester
%A S. O. Kepler
%J -
%D 2019
%R 10.1051/0004-6361/201935946
%X <i>Context.<i/> Among the spectroscopically identified white dwarfs, a fraction smaller than 2% have spectra dominated by carbon lines, mainly molecular C<sub>2<sub/>, but also a smaller group dominated by C£¿I and C£¿II lines. These are together called DQ white dwarfs.<i>Aims.<i/> We want to derive atmospheric parameters <i>T<i/><sub>eff<sub/>, log <i>g<i/>, and carbon abundances for a large sample of these stars and discuss implications for their spectral evolution.<i>Methods.<i/> Sloan Digital Sky Survey spectra and <i>ugriz<i/> photometry were used, together with <i>Gaia<i/> Data Release 2 parallaxes and <i>G<i/> band photometry. These were fitted to synthetic spectra and theoretical photometry derived from model atmospheres.<i>Results.<i/> We found that the DQ hotter than <i>T<i/><sub>eff<sub/> ~ 10 000 K have masses ~ 0.4 <i>M<i/><sub>¡Ñ<sub/> larger than the classical DQ, which have masses typical for the majority of white dwarfs (~ 0.6 <i>M<i/><sub>¡Ñ<sub/>). We found some evidence that the peculiar DQ below 10 000 K also have significantly larger masses and may thus be the descendants of the hot and warm DQ above 10 000 K. A significant fraction of the hotter objects with <i>T<i/><sub>eff<sub/> > 14 500 K have atmospheres dominated by carbon
%U https://www.aanda.org/articles/aa/full_html/2019/08/aa35946-19/aa35946-19.html