Follow-up Observations of the Second and Third Known Pulsating Hot DQ White Dwarfs

TL;DR

This study confirms and extends the discovery of pulsations in two Hot DQ white dwarfs, revealing multiple oscillation modes and suggesting magnetic properties in one of them, thereby advancing understanding of this new pulsating white dwarf class.

Contribution

First detailed follow-up observations of the second and third known pulsating Hot DQ white dwarfs, identifying multiple pulsation modes and potential magnetic characteristics.

Findings

SDSS J220029.08-074121.5 shows a dominant 654.4 s pulsation with harmonic components.

SDSS J234843.30-094245.3 exhibits a main pulsation at 1044.2 s and a possible additional mode at 417 s.

Evidence suggests SDSS J220029.08-074121.5 is likely magnetic, while SDSS J234843.30-094245.3 is probably not.

Abstract

We present follow-up time-series photometric observations that confirm and extend the results of the significant discovery made by Barlow et al.(2008) that the Hot DQ white dwarfs SDSS J220029.08-074121.5 and SDSS J234843.30-094245.3 are luminosity variable. These are the second and third known members of a new class of pulsating white dwarfs, after the prototype SDSS J142625.71+575218.3 (Montgomery et al. 2008). We find that the light curve of SDSS J220029.08-074121.5 is dominated by an oscillation at 654.397+-0.056 s, and that the light pulse folded on that period is highly nonlinear due to the presence of the first and second harmonic of the main pulsation. We also present evidence for the possible detection of two additional pulsation modes with low amplitudes and periods of 577.576+-0.226 s and 254.732+-0.048 s in that star. Likewise, we find that the light curve of SDSS J234843.30-094245.3 is dominated by a pulsation with a period of 1044.168+-0.012 s, but with no sign of harmonic components. A new oscillation, with a low amplitude and a period of 416.919+-0.004 s, is also probably detected in that second star. We argue, on the basis of the very different folded pulse shapes, that SDSS J220029.08-074121.5 is likely magnetic, while SDSS J234843.30-094245.3 is probably not.