Three-dimensional simulations of classical novae

We present first results of three-dimensional (3D-) calculations of turbulent and degenerate hydrogen-burning on top of a C+O white dwarf of 1.0 M. The simulations are car- ried out by means of a code which solves Euler's equation for an arbitrary equation of state together with a nuclear reaction network and the energy input from nuclear reactions on a Carte- sian grid covering a fraction of the white dwarf's surface and accreted envelope. The flow patterns we obtain are very differ- ent from those of earlier 2D simulations using the same initial conditions and the same numerical resolution. The possibility of self-enrichment of the accreted hydrogen-rich envelope with carbon and oxygen from the surface layers of the white dwarf during the violent phase of the burning is investigated, and it is demonstrated that self-enrichment proceeds too slowly if the accreted gas has near-solar CNO-abundances at the onset of the thermonuclear runaway. As a result, we do not find a fast nova outburst. This conclusion remains valid if the initial metallicity of the accreted gas is raised by a factor of five. Therefore we con- clude that fast nova outbursts indeed require huge enrichments of C and O, as postulated from spherically symmetric models, and that the mechanism which leads to such enhancements must operate prior to the outburst.