SDSS J000555.90-100213.5: a hot, magnetic carbon-atmosphere WD rotating with a 2.1 day period

TL;DR

This paper reports the discovery of a hot, magnetic carbon-atmosphere white dwarf with a 2.1-day rotation period, emphasizing the importance of monitoring hot DQ white dwarfs for rotation-induced variability rather than pulsation.

Contribution

It presents the first long-period photometric variability detection in a hot DQ white dwarf, attributing it to rotation rather than pulsation, and highlights the need for further long-term monitoring.

Findings

SDSS J000555.90-100213.5 varies with a 2.1-day period.

No short-term variability detected at <+/-0.5%.

Long-period variability likely due to rotation, not pulsation.

Abstract

A surprisingly large fraction (70%) of hot, carbon dominated atmosphere (DQ) white dwarfs are magnetic and/or photometrically variable on short timescales up to ~1000 s. However, here we show that the hot DQ magnetic white dwarf SDSS J000555.90-100213.5 is photometrically variable by 11% on a longer timescale, with a period of 2.110 +/- 0.045 days. We find no evidence of the target fluctuating on short timescales at an amplitude of <+/-0.5%. Short period hot DQ white dwarfs have been interpreted as non-radial pulsators, but in the case of SDSS J0005-1002, it is more likely that the variability is due to the magnetic hot DQ white dwarf rotating. We suggest that some hot DQ white dwarfs, varying on short timescales, should be more carefully examined to ascertain whether the variability is due to rotation rather than pulsation. All hot DQs should be monitored for long period modulations as an indicator of rotation and magnetism.