The Equilibrium Tide: An Updated Prescription for Population Synthesis Codes

TL;DR

This paper introduces an updated equilibrium tide prescription for population synthesis models, significantly affecting merger rates, supernova occurrences, and binary star properties in simulated stellar populations.

Contribution

The authors develop and implement a metallicity-dependent equilibrium tide prescription into BSE, improving the accuracy of binary evolution predictions in population synthesis.

Findings

16.5% reduction in overall mergers involving main-sequence stars

3.6% decrease in total supernova rate

12.8% reduction in single degenerate Ia supernovae

Abstract

We present an updated prescription for the equilibrium tides suitable for population synthesis codes. A grid of 1D evolutionary models was created and the viscous time-scale was calculated for each detailed model. A metallicity dependent power-law relation was fitted to both the convective cores and convective envelopes of the models. The prescription was implemented into the population synthesis code BSE and predicts an 16.5% reduction in the overall number of merges, with those involving main-sequence stars most affected. The new prescription also reduces the overall supernova rate by 3.6% with individual channels being differently affected. The single degenerate Ia supernova occurrence is reduced by 12.8%. The merging of two Carbon Oxygen white dwarfs to cause a Ia supernova occurs 16% less frequently. The number of sub-synchronously rotating stars in close binaries is substantially increased with our prescription, as is the number of non-circularized systems at the start of common-envelope evolution.