Next generation population synthesis of accreting white dwarfs - I. Hybrid calculations using BSE+MESA

Accreting, nuclear-burning white dwarfs (WDs) have been deemed to be candidate progenitors of Type Ia supernovae (SNe Ia), and to account for supersoft X-ray sources, novae, etc. depending on their accretion rates. We have carried out a binary population synthesis study of their populations using two algorithms. In the first, we use the binary population synthesis code BSE as a baseline for the `rapid' approach commonly used in such studies. In the second, we employ a `hybrid' approach, in which we use BSE to generate a population of WDs with non-degenerate companions on the verge of filling their Roche lobes. We then follow their mass transfer phase using the detailed stellar evolution code MESA. We investigate the evolution of the number of rapidly accreting white dwarfs (RAWDs) and stably nuclear-burning white dwarfs (SNBWDs), and estimate the SNe Ia rate produced by `single degenerate' (SD) systems. We find significant differences between the two algorithms in the predicted numbers of SNBWDs at early times, and also in the delay time distribution (DTD) of SD SNe Ia. Such differences in the treatment of mass transfer may partially account for differences in the SNe Ia rate and DTD found by different groups. Adopting 100 per cent efficiency for helium burning, the rate of SNe Ia produced by the SD channel in a Milky Way-like galaxy in our calculations is 2.0 × 10^-4 yr^-1, more than an order of magnitude below the observationally inferred value. In agreement with previous studies, our calculated SD DTD is inconsistent with observations.