Carbon-Oxygen Classical Novae are Galactic $^7$Li Producers as well as Potential Supernova Ia Progenitors

TL;DR

This study models classical nova explosions on carbon-oxygen white dwarfs, showing they produce significant lithium and could evolve into Type Ia supernova progenitors, with implications for galactic chemical enrichment.

Contribution

The paper introduces detailed hydrodynamic simulations of CO white dwarf novae, demonstrating their role in lithium production and potential as supernova progenitors.

Findings

CO novae produce large $^7$Be enrichments, contributing to galactic $^7$Li.

White dwarfs in these systems tend to grow in mass, supporting their evolution into SNe Ia.

Simulations show less material is ejected than accreted, indicating mass growth of the WD.

Abstract

We report on studies of Classical Nova (CN) explosions where we follow the evolution of thermonuclear runaways (TNRs) on Carbon Oxygen (CO) white dwarfs (WDs). We vary both the mass of the WD (from 0.6 M$_\odot$ to 1.35 M$_\odot$) and the composition of the accreted material. Our simulations are guided by the results of multi-dimensional studies of TNRs in WDs that find sufficient mixing with WD core material occurs after the TNR is well underway, reaching levels of enrichment that agree with observations of CN ejecta abundances. We use NOVA (our 1-dimensional hydrodynamic code) to accrete solar matter until the TNR is ongoing and then switch to a mixed composition (either 25% WD material and 75% solar or 50% WD material and 50% solar). Because the amount of accreted material is inversely proportional to the initial $^{12}$C abundance, by first accreting solar matter the amount of material taking part in the outburst is larger than in those simulations where we assume a mixed composition from the beginning. Our results show large enrichments of $^7$Be in the ejected gases implying that CO CNe may be responsible for a significant fraction ($\sim$ 100 M$_\odot$) of the $^7$Li in the galaxy ($\sim$1000 M$_\odot$). In addition, although the ejected gases are enriched in WD material, the WDs in these simulations eject less material than they accrete. We predict that the WD is growing in mass as a consequence of the accretion-outburst-accretion cycle and CO CNe may be an important channel of Supernova Ia progenitors.