The Effect of [TSUP]3[/TSUP]H[CLC]e[/CLC] Diffusion on the Pulsational Spectra of DBV Models

We consider envelopes of DB white dwarfs that are not composed of pure 4 He but rather a mixture of 3 He and 4 He. Given this assumption, the same diffusive processes that produce a relatively pure H layer overlying an He layer in the DA's should work to produce an 3 He layer overlying an 4 He layer in the DB's. We examine the relevant timescales for diffusion in these objects and compare them with the relevant evolutionary timescales in the context of the DBV white dwarfs. We then explore the consequences that 3 He separation has on the pulsational spectra of DBV models. Since GD 358 is the best-studied member of this class of variables, we examine fits to its observed pulsation spectrum. We find that the inclusion of an 3 He layer results in a modest improvement in a direct fit to the periods, while a fit to the period spacings is significantly improved.