An improved numerical method for nonadiabatic nonradial oscillations: An application to white dwarf stars

We present an improved numerical method of calculation for nonadiabatic nonradial oscillations of white dwarf stars. An improved method is desirable, because the extremely large difference between the thermal and dynamical time scales in the degenerate cores of white dwarfs can lead to numerical artifacts with current fully nonadiabatic calculations. We use a quasi-adiabatic analysis in the core of our white dwarf models and switch to a fully nonadiabatic calculation in the outer layers where pulsation driving occurs. Using this hybrid method of calculation, we avoid the numerical instability present in the thermal eigenfunctions of previous methods. We find that the nonadiabatic results obtained by the hybrid method of calculation agree with the fully nonadiabatic results to within 10%.