Population synthesis of accreting white dwarfs: rates and evolutionary pathways of H and He novae

Novae are some of the most commonly detected optical transients and have the potential to provide valuable information about binary evolution. Binary population synthesis codes have emerged as the most effective tool for modelling populations of binary systems, but such codes have traditionally employed greatly simplified nova physics, precluding detailed study. In this work, we implement a model treating H and He novae as individual events into the binary population synthesis code binary_c. This treatment of novae represents a significant improvement on the 'averaging' treatment currently employed in modern population synthesis codes. We discuss the evolutionary pathways leading to these phenomena and present nova event rates and distributions of several important physical parameters. Most novae are produced on massive white dwarfs, with approximately 70 and 55 per cent of nova events occurring on O/Ne white dwarfs for H and He novae, respectively. Only 15 per cent of II-nova systems undergo a common-envelope phase, but these systems are responsible for the majority of II nova events. All He-accreting He-nova systems are considered post-common-envelope systems, and almost all will merge with their donor star in a gravitational-wave-driven inspiral. We estimate the current annual rate of novae in M31 (Andromeda) to be approximately 41 +/- 4 for H novae, underpredicting the current observational estimate of 65(-16)(+15), and 0.14 +/- 0.015 for He novae. When varying common-envelope parameters, the II nova rate varies between 20 and 80 events per year.

Automated summary

This study presents valuable insights into novae phenomena and their evolutionary pathways, as well as simulation research on nova events, discussing the current annual rate of novae in M31 and the variation in II nova rates when common-envelope parameters are adjusted.