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 thermonucl ear runaway and the ensuing decline until the onset of envelope expans ion. Diffusion-induced mixing between accreted matter and core materia l 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, it s temperature T(WD) - on the outburst characteristics. The values adop ted 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 10(6) K) = 5, 10, 2 0, 30, 40, 50 and 65. Evolutionary sequences were computed for all com binations of these basic parameter values. We found that the resulting mass and composition of the nova envelope and the peak temperature at tained at outburst depend in an intricate manner on all three paramete rs. The core temperature affects the results in two ways: in cold whit e dwarfs, heat conduction into the core delays the ignition of hydroge n and results in relatively long accretion times and large accreted ma sses; in hot white dwarfs the outer core layer is convective and this enhances the mixing process between the accreted hydrogen and the heav y elements of the core. Relations between outburst characteristics and parameters were analysed and compared with other numerical computatio ns. Correlations between these characteristics were investigated in th e light of observations.