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

A surprisingly large fraction (70 per cent) of hot, carbon-dominated atmosphere (DQ) white dwarfs are magnetic and/or photometrically variable on short time-scales 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 per cent on a longer time-scale, with a period of 2.110 ± 0.045 d. We find no evidence of the target fluctuating on short time-scales at an amplitude of ≲±0.5 per cent. 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 rotation of the magnetic hot DQ white dwarf. We suggest that some hot DQ white dwarfs, varying on short time-scales, 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.