AN IMPROVED NUMERICAL-METHOD FOR NONADIABATIC NONRADIAL OSCILLATIONS - AN APPLICATION TO WHITE-DWARF STARS

We present an improved numerical method of calculation for nonadiabati c nonradial oscillations of white dwarf stars. An improved method is d esirable, because the extremely large difference between the thermal a nd dynamical time scales in the degenerate cores of white dwarfs can l ead to numerical artifacts with current fully nonadiabatic calculation s. We use a quasi-adiabatic analysis in the core of our white dwarf mo dels and switch to a fully nonadiabatic calculation in the outer layer s where pulsation driving occurs. Using this hybrid method of calculat ion, we avoid the numerical instability present in the thermal eigenfu nctions of previous methods. We find that the nonadiabatic results obt ained by the hybrid method of calculation agree with the fully nonadia batic results to within 10%.