Numerical simulations of the pulsating DB white dwarf GD 358

Institut für Theoretische Physik und Astrophysik, Universität Kiel, 24098 Kiel, Germany e-mail: weidner@astrophysik.uni-kiel.de

Corresponding author: D. Koester, koester@astrophysik.uni-kiel.de

Received: 7 March 2003
Accepted: 28 April 2003

Abstract

The numerical simulation method for variable white dwarfs of Ising & Koester (2001) is extended to variable DB stars (DBVs or V777 Herculis stars). We find the same general behavior of nonlinear effects, with a sinusoidal light-curve at small amplitudes, strongly non-sinusoidal variations at intermediate amplitudes and a change back to smaller and sinusoidal variations at the largest driving pressure amplitudes. The transition between the various regimes is however shifted to higher amplitudes compared to DAVs because of the smoother reaction of the DB convection zones to perturbations. A peculiar event of the prototype GD358 – with all pulsation power going into one mode only – in August 1996 offers the possibility for a direct comparison of the light-curve with our simulation. We can reproduce the light-curve, but only for higher effective temperature than usually assumed. The wavelength dependent amplitudes (chromatic amplitudes) of this object are not well reproduced by our simulations, and various possible explanations are discussed.