Hydrogen-driving and the blue edge of compositionally stratified ZZ Ceti star models

Abstract

We report preliminary results of fully nonadiabatic g-mode pulsation calculations for evolutionary white dwarf models incorporating stratified H/He/C envelopes. For modes corresponding to l = 1 through 3, the theoretical ''blue edge'' of the ZZ Ceti stablity strip occurs at T/sub e///sub blue/approx.11,000 K depending upon model parameters such as H and He content, convective eficiency, and thickness of the transition zones. Comparison with the observed value of T/sub e///sub blue/ suggests 10/sup -12/ 10/sup -10/, we have also found a second narrow instability strip at T/sub e/approx.19,000 K; observations of stars near this temperature may place bounds on the H-layer mass. Perhaps He-driving may also produce variable DB white dwarfs in this T/sub e/ range. We have also carried out a very preliminary exploration of convection/pulsation interactions.