Pulsational instabilities in accreting white dwarfs

The detection of g-mode pulsations in accreting white dwarfs (WDs) in cataclysmic variables (CVs) with a large range of effective temperatures (T-eff) has shown these WDs to be a more diverse class than their isolated 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 T-eff for which g-modes are unstable. Motivated by earlier theoretical 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 0.6 M-., the blue edge for a 0.04 M-. He core WD shifts downward by approximate to 1000 K, while that for a massive approximate to 1.2 M-. WD shifts upward by approximate to 2000 K. Surprisingly, increasing Y by only 10% relative to solar creates an "intermediate" instability strip near 15,000 K.