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Published online by Cambridge University Press: 12 April 2016
Simple theories of hydrogen shell flashes on accreting white dwarfs are used to find the requisite conditions for classical novae. It is shown that enhancement of CNO abundances, relative to the Sun, is necessary for fast novae yet slow novae, such as DQ Her, can still occur with large CNO abundances. An analysis of observational data indicates that the white dwarfs in nova binaries have masses typically 1.1 Mʘ. For some old novae, the accretion rate, deduced from the accretion disk luminosity, is too high to permit a strong enough hydrogen flash to give the observed nova strength. Some possible resolutions to this paradox are suggested.
Recurrent novae are probably not thermonuclear runaways on accreting white dwarfs.