Hot DQ White Dwarf Stars as Failed Type Ia Supernovae

Of the two hundred or so white dwarf stars showing spectroscopic signatures of carbon (the DQs), the hottest dozen are unique in having atmospheres dominated by carbon and oxygen. At least a third of these hot DQs are photometrically variable, and roughly 70% are magnetic. We provide evidence that the hot DQs are the result of CO-core white dwarf mergers that were not tuned to explode as type Ia supernovae (SNe). In this scenario, the variable hot DQs are magnetic rotators whose magnetic fields, fast rotation rates, and atmospheric composition are all explained by the merger. Consequently, their masses and formation rates will constrain type Ia SNe progenitors, and their field strengths and spin periods will provide observational constraints for models of double-degenerate mergers and magnetic field generation.