On mixing at the core-envelope interface during classical nova outbursts

Classical novae are powered by thermonuclear runaways that occur on the white dwarf component of close binary systems. During these violent stellar events, whose energy release is only exceeded by gamma-ray bursts and supernova explosions, about 10^-4-10^-5 $M-{\odot}$ of material is ejected into the interstellar medium. Because of the high peak temperatures attained during the explosion, T_peak ∼ (1-4) × 10⁸ K, the ejecta are enriched in nuclear-processed material relative to solar abundances, containing significant amounts of ¹³C, ¹⁵N, and ¹⁷O and traces of other isotopes. The origin of these metal enhancements observed in the ejecta is not well-known and has puzzled theoreticians for about 40 years. In this paper, we present new 2-D simulations of mixing at the core-envelope interface. We show that Kelvin-Helmholtz instabilities can naturally lead to self-enrichment of the solar-like accreted envelopes with material from the outermost layers of the underlying white dwarf core, at levels that agree with observations.