The effect of the white dwarf temperature on nova outburst characteristics

The evolution of white dwarfs, accreting hydrogen-rich matter prior to a nova outburst, was followed through the development of a thermonuclear runaway and the ensuing decline until the onset of envelope expansion. Diffusion-induced mixing between accreted matter and core material was taken into account. The purpose of this study was to investigate the effect of each of the three basic parameters of nova models - the accretion rate M, the white dwarf's mass M_WD and, in particular, its temperature T_WD - on the outburst characteristics. The values adopted for these parameters were M= 10^-8, 10^-9 and 10^-10 M yr^-1; M_WD = 0.75, 1.00 and 1.25 M; T_WD (in units of 10⁶ K) = 5, 10, 20, 30, 40, 50 and 65. Evolutionary sequences were computed for all combinations of these basic parameter values. We found that the resulting mass and composition of the nova envelope and the peak temperature attained at outburst depend in an intricate manner on all three parameters. The core temperature affects the results in two ways: in cold white dwarfs, heat conduction into the core delays the ignition of hydrogen and results in relatively long accretion times and large accreted masses; in hot white dwarfs the outer core layer is convective and this enhances the mixing process between the accreted hydrogen and the heavy elements of the core. Relations between outburst characteristics and parameters were analysed and compared with other numerical computations. Correlations between these characteristics were investigated in the light of observations.