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Abstract Four years after the discovery of a unique DAQ white dwarf with a hydrogen-dominated and carbon-rich atmosphere, we report the discovery of four new DAQ white dwarfs, including two that were not recognized properly in the literature. We find all five DAQs in a relatively narrow mass and temperature range ofM= 1.14–1.19M⊙andTeff= 13,000–17,000 K. In addition, at least two show photometric variations due to rapid rotation with ≈10 minute periods. All five are also kinematically old, but appear photometrically young, with estimated cooling ages of about 1 Gyr based on standard cooling tracks, and their masses are roughly twice the mass of the most common white dwarfs in the solar neighborhood. These characteristics are smoking gun signatures of white dwarf merger remnants. Comparing the DAQ sample with warm DQ white dwarfs, we demonstrate that there is a range of hydrogen abundances among the warm DQ population and that the distinction between DAQ and warm DQ white dwarfs is superficial. We discuss the potential evolutionary channels for the emergence of the DAQ subclass, suggesting that DAQ white dwarfs are trapped on the crystallization sequence and may remain there for a significant fraction of the Hubble time.
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The ubiquity of carbon dredge-up in hydrogen-deficient white dwarfs as revealed by GALEX
ABSTRACT The convective dredge-up of carbon from the interiors of hydrogen-deficient white dwarfs has long been invoked to explain the presence of carbon absorption features in the spectra of cool DQ stars ($$T_{\rm eff} \lt 10\,000\,$$K). It has been hypothesized that this transport process is not limited to DQ white dwarfs and also operates, albeit less efficiently, in non-DQ hydrogen-deficient white dwarfs within the same temperature range. This non-DQ population is predominantly composed of DC white dwarfs, which exhibit featureless optical spectra. However, no direct observational evidence of ubiquitous carbon pollution in DC stars has thus far been uncovered. In this Letter, we analyse data from the Galaxy Evolution Explorer to reveal the photometric signature of ultraviolet carbon lines in most DC white dwarfs in the $$8500\, {\rm K} \le T_{\rm eff} \le 10\,500\,$$K temperature range. Our results show that the vast majority of hydrogen-deficient white dwarfs experience carbon dredge-up at some point in their evolution.
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- PAR ID:
- 10438780
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society: Letters
- Volume:
- 525
- Issue:
- 1
- ISSN:
- 1745-3925
- Format(s):
- Medium: X Size: p. L112-L116
- Size(s):
- p. L112-L116
- Sponsoring Org:
- National Science Foundation
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