The final decline of novae and the hibernation hypothesis

Analyses of long series of visual and photoelectric observations of nine old novae yield a mean rate of decline of $10 \pm 3$ millimag per year, half a century after outburst. Individual objects may deviate markedly from the mean, showing more rapid decline or even brightening. This is compatible with predictions of the hibernation hypothesis. The slopes appear to depend on orbital period, indicating that irradiation-induced mass transfer powers at least part of the accretion luminosity of post-novae. Objects with orbital periods below 5 hr show a stronger tendency to enter hibernation in the centuries following outburst than those with longer periods.