The effect of He-3 diffusion on the pulsational spectra of DBV models

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