Recurrent Novae

Abstract

AbstractThermonuclear models of recurrent novae demand white dwarf accretors near the Chandrasekhar mass. In this case, the known recurrent novae should possess classical counterparts bearing the same structural parameters and space distribution, save for having only marginally less massive white dwarfs. Furthermore, recurrent novae should occur exclusively on ONeMg white dwarfs, and display in their ejecta either neon-group overabundances (if the white dwarfs are eroded through an outburst cycle) or no heavy element enhancements whatever (if the white dwarfs increase in mass).The known recurrent novae are reviewed in the light of these and other characteristics of thermonuclear runaway models, and also in terms of accretion-powered events, with special attention to the difficulties encountered by both models. Pivotal tests to distinguish between between thermonuclear and accretion models rely on the fact that the latter require far more mass transferred than the former to produce the same outburst energetics. Thus, photospheric opacities in thermonuclear recurrent novae are dominated by scattering; those in recurrent accretion events by true absorption. Orbital period changes through outburst are 103 times greater in accretion models than in thermonuclear models.