Pulsational Instabilities in Accreting White Dwarfs

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The detection of g-mode pulsations in accreting white dwarfs (WDs) in cataclysmic variables (CVs) with a large range of effective temperatures ( ) has shown these WDs to be a more diverse class than their isolated Teff counterparts, the ZZ Ceti and DB pulsators. The simplest contrast of CV to isolated pulsators is an envelope of solar-like composition (of various helium enrichments if the donor is evolved) rather than pristine hydrogen or helium. A range of WD masses is expected, from low-mass He core WDs to massive WDs. We investigate the impact of this diversity on the range of for which T g-modes are unstable. Motivated by earlier theoretical eff studies, we compare a fiducial g-mode period to the thermal time at the base of the convection zones created by H and first He (H/He i) ionization or second He (He ii) ionization zones. We find that (for solar composition envelopes), relative to a fiducial WD mass , the blue edge for a He core WD shifts downward 0.6 M, , 0.4 M by ≈1000 K, while that for a massive ≈1.2 M, WD shifts upward by ≈2000 K. Surprisingly, increasing Y by only 10% relative to solar creates an “intermediate” instability strip near . 15,000 K

binaries: close — gravitational waves — novae, cataclysmic variables — white dwarfs
Arras, P., Townsley, D., Bildsten, L. (2006): Pulsational Instabilities in Accreting White Dwarfs. The Astrophysical Journal, 643(2).