CNO "Breakout" and Nucleosynthesis in Classical Novae

Abstract

For very slow white dwarf accretors in CV's Townsley and Bildsten (2004) found a relation between the accretion rate and the central temperature of the white dwarf Tc. According to this relation for accretion rates less than 10^-10 solar masses per year Tc is much lower than 10^7 K. Motivated by this study we follow the thermonuclear runaway on massive white dwarfs (M_WD=1.25 - 1.40 solar masses) with Tc lower than 10^7 K, accreting matter of solar composition. We demonstrate that in that range of the relevant parameter space (Tc,M_WD and accretion rate) the slope of the relation between the peak temperatures achieved during the runaway and Tc becomes much steeper than its value for Tc above 10^7 K. The peak temperatures we derive can lead to nuclear breakout from the conventional "hot carbon-nitrogen-oxygen" cycle. When breakout conditions are achieved the heavy element abundances can show a much wider variety than what is possible with the common enrichment mechanisms.