Pulsation properties of DB white dwarfs: A preliminary analysis

We report preliminary results of a numerical investigation of the nonradial g-mode pulsation properties of evolutionary DB white dwarf models. We have solved the fully nonadiabatic equations for modes corresponding to spherical harmonic index l = 1 through 3. For each of the sequences of models we have examined (M/sub asterisk/ = 0.6 M/sub sun/; and helium layer masses of 10-6 M/sub asterisk/ and 10-4 M/sub asterisk/), we find a nonradial g-mode instability strip about 3000 K wide. For models with standard ML1 convection, this strip lies in the effective temperature range 19,000 K> or approx. =T/sub e/> or approx. =16,000 K. The boundaries of the instability strip are extremely sensitive to the assumed efficiency of convection, however, and for sequences with more efficient (ML3) convection, we find the instability strip to be in the range 29,000 K> or approx. =T/sub e/> or approx. = 26,000 K. Extrapolation of our calculations to 0.4 M/sub sun/ and 0.9 M/sub sun/ indicates that that the instability strip boundaries are insensitive to uncertainties in the total stellar mass. The most unstable modes have e-folding times of the order of days