Hot DQ White Dwarfs: Something Different
P. Dufour, G. Fontaine, J. Liebert, G. D. Schmidt, N. Behara

TL;DR
This paper provides a comprehensive analysis of Hot DQ white dwarfs with carbon-dominated atmospheres, revealing their temperature range, surface composition, magnetic fields, and pulsation properties, suggesting they are a distinct evolutionary phase.
Contribution
It offers the first detailed spectroscopic and photometric characterization of all known Hot DQ white dwarfs, proposing their connection to a new class of hydrogen and helium deficient stellar remnants.
Findings
All Hot DQ stars have temperatures between 18,000 and 24,000 K.
Most have normal surface gravity around log g = 8.0.
One star shows a weak magnetic field and pulsations.
Abstract
We present a detailed analysis of all the known Hot DQ white dwarfs in the Fourth Data Release of the Sloan Digital Sky Survey (SDSS) recently found to have carbon dominated atmospheres. Our spectroscopic and photometric analysis reveals that these objects all have effective temperatures between ~18,000 and 24,000 K. The surface composition is found to be completely dominated by carbon, as revealed by the absence of Hbeta and HeI 4471 lines (or determination of trace amount in a few cases). We find that the surface gravity of all objects but one seems to be ''normal'' and around log g = 8.0 while one is likely near log g = 9.0. The presence of a weak magnetic field is directly detected by spectropolarimetry in one object and is suspected in two others. We propose that these strange stars could be cooled down versions of the weird PG1159 star H1504+65 and form a new family of hydrogen…
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