Two-dimensional simulations of mixing in classical novae: the effect of the white dwarf composition and mass

Context. Classical novae are explosive phenomena that take place in stellar binary systems. They are powered by mass transfer from a low-mass main sequence star onto a white dwarf (either CO or ONe). The material accumulates for 10+4 - 10+5 yr until ignition under degenerate conditions, resulting in a thermonuclear runaway. The nuclear energy released produces peak temperatures of about 0.1 - 0.4 GK. During these events, 10-7 - 10-3 Msun enriched in intermediate-mass elements (with respect to solar abundances) are ejected into the interstellar medium. However, the origin of the large metallicity enhancements and the inhomogeneous distribution of chemical species observed in high-resolution spectra of ejected nova shells is not fully understood. Aims. Recent multidimensional simulations have demonstrated that Kelvin-Helmholtz instabilities that operate at the core-envelope interface can naturally produce self-enrichment of the accreted envelope with material from the underlying white dwarf at levels that agree with observations. However, such multidimensional simulations have been performed for a small number of cases, and much of the parameter space remains unexplored. Methods. Here we investigate the dredge-up, driven by Kelvin-Helmholtz instabilities, for white dwarf masses in the range 0.8-1.25 Msun and different core compositions (CO-rich and ONe-rich substrates). We present a set of five numerical simulations performed in two dimensions aimed at analyzing the possible impact of the white dwarf mass (and composition) on the metallicity enhancement and on the explosion characteristics. Results. We observe greater mixing (about 30 per cent higher when measured in the same conditions), at the time we stop the simulations, and more energetic outbursts for ONe-rich substrates than for CO-rich substrates and for more massive white dwarfs.
Comment: Accepted for Publication in Astronomy and Astrophysics