Two new accreting, pulsating white dwarfs: SDSS J1457+51 and BW Sculptoris

Abstract

We report the discovery of rapid periodic signals in the light curves of two cataclysmic variables with prominent white dwarf components in their spectra, SDSS J1457+51 and BW Sculptoris. These stars therefore appear to be new members of the GW Librae class of variable stars, in which the fast periodic (and non-commensurate with the orbital period) signals are believed to arise from non-radial pulsations in the underlying white dwarf. The power spectra of both stars show complex signals with primary periods near 10 and 20min, respectively. These signals change in frequency by a few per cent on a time-scale of weeks or less, and probably contain an internal fine structure unresolved by our observations. We also detect double-humped waves signifying the underlying orbital periods, near 78min for both stars. In addition, BW Sculptoris shows a transient but powerful signal with a period near 87min, a quiescent superhump. The ∼11 per cent excess over the orbital period is difficult to understand, and may arise from an eccentric instability near the 2:1 resonance in the accretion disc. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.