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

TL;DR

This paper enhances binary population synthesis models by treating H and He novae as individual events, providing detailed predictions of nova rates, pathways, and physical parameters, with implications for understanding binary evolution.

Contribution

It introduces a novel model for simulating H and He novae as discrete events within binary population synthesis, improving upon previous averaged treatments.

Findings

Most novae occur on massive white dwarfs, especially O/Ne types.

Approximately 70% of H novae and 55% of He novae occur on O/Ne white dwarfs.

Estimated nova rate in M31 is about 41 per year for H novae, close to observational estimates.

Abstract

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 \binaryc. 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 H-nova systems undergo a common-envelope phase, but these systems are responsible for the majority of H 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 $41 \pm 4$ for H novae, underpredicting the current observational estimate of $65^{+15}_{-16}$, and $0.14\pm0.015$ for He novae. When varying common-envelope parameters, the H nova rate varies between 20 and 80 events per year.