Volume 628, August 2019
|Number of page(s)||7|
|Published online||13 August 2019|
Carbon-rich (DQ) white dwarfs in the Sloan Digital Sky Survey★
Institut für Theoretische Physik und Astrophysik, Universität Kiel,
24098 Kiel, Germany
2 Instituto de Fisica, Universidade Federal do Rio Grande do Sul, 91501-900 Porto-Alegre, RS, Brazil
Accepted: 26 June 2019
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 C I and C II lines. These are together called DQ white dwarfs.
Aims. We want to derive atmospheric parameters Teff, log g, 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 ~ 10 000 K have masses ~ 0.4 M⊙ larger than the classical DQ, which have masses typical for the majority of white dwarfs (~ 0.6 M⊙). 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 Teff > 14 500 K have atmospheres dominated by carbon.
Key words: stars: atmospheres / white dwarfs / stars: carbon
Full Tables 1 and 2 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (220.127.116.11) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/628/A102
© ESO 2019
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