Wavelength Dependence of Pulsation Amplitudes in DBV White Dwarfs

Abstract

The wavelength dependence of pulsation amplitudes is a useful method to identify pulsation modes in variable white dwarfs. Robinson et al. (1982) have laid the foundation for all these studies by demonstrating that after proper normalization of the amplitudes they become independent of the inclination of the pulsation axis to the line of sight i and the amplitude of the pulsation a, and depend solely on the spherical degree of the mode l. In general these attempts have not been as successful as expected. Ising & Koester (2001) have therefore developed a different method, following important work by Brickhill (1992). In this method the response of a column through the outer layer of the star on pulsating pressure at the lower boundary is calculated. The resulting temperature distribution at the surface is then integrated numerically with the help of a grid of stellar atmospheres to give the surface flux. While needing its own simplifications these numerical integrations avoid the central assumption of the RKN method: that the spatial distribution of surface temperatures is at all times described by a spherical harmonic function of some degree l.