CNO "Breakout" and Nucleosynthesis in Classical Novae

TL;DR

This paper investigates thermonuclear runaways in massive white dwarfs with low initial temperatures, revealing conditions that lead to nuclear breakout and diverse nucleosynthesis in classical novae.

Contribution

It demonstrates that low initial white dwarf temperatures can cause steeper temperature relations and enable nuclear breakout, expanding understanding of nova nucleosynthesis.

Findings

Peak temperatures increase steeply at low Tc

Nuclear breakout from the hot CNO cycle occurs under certain conditions

Heavy element diversity is enhanced during breakout events

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.