White Dwarf Mass Growth in Cataclysmic Variables: Roles of Dwarf Novae

TL;DR

This study investigates how the duty cycle in dwarf novae affects white dwarf mass growth, revealing specific duty cycle ranges that enable significant mass accumulation but not reaching Type Ia supernova thresholds.

Contribution

It systematically analyzes the impact of duty cycles on white dwarf mass growth in dwarf novae using stellar evolution simulations, highlighting conditions for effective mass accumulation.

Findings

White dwarf mass growth depends on specific duty cycle ranges.

Maximum accumulated mass reaches up to 0.21 solar masses.

White dwarfs do not reach the supernova explosion mass in simulations.

Abstract

The disc instability mechanism (DIM) is widely accepted to account for the transient behaviour of dwarf novae (DNe), which experience short outbursts separated by long quiescence. The duty cycle (the ratio between the outburst duration and the recurrence time) determines the amount of accreted mass by the white dwarf (WDs) during outbursts, thus playing an important role in the long-term binary evolution. Employing the code of Modules for Experiments in Stellar Astrophysics, we systemically investigate the influence of the duty cycles on the evolution of DNe and the mass growth of accreting carbon-oxygen (CO) WDs. Our calculations show that, while the DIM can considerably influence the accretion process, efficient WD-mass growth requires a particular range of the duty cycle. For WDs with the initial masses of 0.6, 0.7 and 1.1 $M_\odot$, these duty cycles are 0.006$\,\leq$$d$$\,\leq$0.007, $d$\,=\,0.005 and $d$\,=\,0.003, and the accumulated mass of the WDs can reach 0.1, 0.13 and 0.21 $M_\odot$, respectively. In all of our simulations, no CO WDs can grow their masses to the explosion mass of Type Ia supernovae of about $1.38~M_\odot$. Because of a much short timescale of the outburst state, the final donor-star masses and orbital periods are insensitive to the duty cycles. Therefore, we propose that the DIM in DNe could alleviate the WD mass problem to some extent.