Helium runaways in white dwarfs

The long-term evolution of a carbon-accreting white dwarf (M = 0.5 solar mass) has been studied from the onset of accretion to the ignition of helium. The variations in the details of the helium-shell flash have been examined with respect to variations in mass accretion rate. For intermediate rates (10 to the -9th to 10 to the -8th solar mass/yr) the helium flash is potentially explosive, whereas for high rates (5 x 10 to the -8th solar mass/yr) the shell flash is relatively weak. The results are discussed in the context of the long-term evolution of novae.