Mass Transfer in Binary Stars using SPH. II. Eccentric Binaries

TL;DR

This study uses SPH simulations to analyze mass transfer in eccentric binary stars, revealing that transfer episodes peak after periastron and a fraction of transferred mass is ejected, aiding understanding of binary evolution.

Contribution

It introduces a novel SPH simulation method focusing on outer stellar layers to characterize mass transfer in eccentric binaries, extending previous models.

Findings

Mass transfer episodes are Gaussian-shaped with ~0.12 P_orb width.

Peak mass transfer occurs after periastron at phase ~0.58.

About 5% of transferred mass is ejected from the system.

Abstract

Despite numerous efforts to better understand binary star evolution, some aspects of it remain poorly constrained. In particular, the evolution of eccentric binaries has remained elusive mainly because the Roche lobe formalism derived for circular binaries does not apply. Here, we report the results of our Smoothed Particle Hydrodynamics simulations of mass transfer in eccentric binaries using an alternate method in which we model only the outermost layers of the stars with appropriate boundary conditions. Using this technique, along with properly relaxed model stars, we characterize the mass transfer episodes of binaries with various orbital parameters. In particular, we show that these episodes can be described by Gaussians with a FWMH of ~0.12 P_orb and that the peak rates occur after periastron, at an orbital phase of ~0.58, independently of the eccentricity and mass of the stars. The accreted material is observed to form a rather sparse envelope around either or both stars. Although the fate of this envelope is not modeled in our simulations, we show that a constant fraction (~5%) of the material transferred is ejected from the systems. We discuss this result in terms of the non-conservative mass transfer scenario. We suggest our results could be incorporated in analytical and binary population synthesis studies to help better understand the evolution of eccentric binaries and the formation of exotic stellar populations.