Evolution of binary stars and the effect of tides on binary populations

TLDR

The authors develop a rapid binary‑evolution algorithm and use it to study the formation and evolution of binary systems, including the impact of tidal friction. The algorithm incorporates detailed single‑star physics, mass transfer, common‑envelope evolution, supernova kicks, angular‑momentum loss, and tidal circularization/synchronization, and is used to generate large binary populations to evaluate formation rates. Comparisons show that tidal friction systematically alters population outcomes, making tidal modeling essential; however, since orbits circularize before Roche lobe overflow, eccentricity has little effect, so population synthesis need not include eccentricity distributions but should use observed semilatera recta separations.

Abstract

We present a rapid binary-evolution algorithm that enables modelling of even the most complex binary systems. In addition to all aspects of single-star evolution, features such as mass transfer, mass accretion, common-envelope evolution, collisions, supernova kicks and angular momentum loss mechanisms are included. In particular, circularization and synchronization of the orbit by tidal interactions are calculated for convective, radiative and degenerate damping mechanisms. We use this algorithm to study the formation and evolution of various binary systems. We also investigate the effect that tidal friction has on the outcome of binary evolution. Using the rapid binary code, we generate a series of large binary populations and evaluate the formation rate of interesting individual species and events. By comparing the results for populations with and without tidal friction, we quantify the hitherto ignored systematic effect of tides and show that modelling of tidal evolution in binary systems is necessary in order to draw accurate conclusions from population synthesis work. Tidal synchronism is important but, because orbits generally circularize before Roche lobe overflow, the outcome of the interactions of systems with the same semilatus rectum is almost independent of eccentricity. It is not necessary to include a distribution of eccentricities in population synthesis of interacting binaries; however, the initial separations should be distributed according to the observed distribution of semilatera recta rather than periods or semimajor axes.