Interacting Binaries with Eccentric Orbits II. Secular Orbital Evolution Due To Non-Conservative Mass Transfer

TL;DR

This paper studies how mass transfer affects the long-term orbital evolution of eccentric binary star systems, considering both mass and angular momentum loss, and challenges the assumption of rapid circularization.

Contribution

It extends previous models by including non-conservative mass transfer effects and provides insights into how mass and angular momentum loss influence orbital changes.

Findings

Orbital semi-major axis and eccentricity can increase or decrease depending on initial conditions.

Mass and angular momentum loss broaden or narrow the range of orbital evolution outcomes.

Rapid circularization assumptions are not justified regardless of systemic mass and angular momentum loss.

Abstract

We investigate the secular evolution of the orbital semi-major axis and eccentricity due to mass transfer in eccentric binaries, allowing for both mass and angular momentum loss from the system. Adopting a delta function mass transfer rate at the periastron of the binary orbit, we find that, depending on the initial binary properties at the onset of mass transfer, the orbital semi-major axis and eccentricity can either increase or decrease at a rate linearly proportional to the magnitude of the mass transfer rate at periastron. The range of initial binary mass ratios and eccentricities that leads to increasing orbital semi-major axes and eccentricities broadens with increasing degrees of mass loss from the system and narrows with increasing orbital angular momentum loss from the binary. Comparison with tidal evolution timescales shows that the usual assumption of rapid circularization at the onset of mass transfer in eccentric binaries is not justified, irrespective of the degree of systemic mass and angular momentum loss. This work extends our previous results for conservative mass transfer in eccentric binaries and can be incorporated into binary evolution and population synthesis codes to model non-conservative mass transfer in eccentric binaries.