Stability Criteria for Mass Transfer in Binary Stellar Evolution

TL;DR

This paper analyzes the stability of mass transfer in binary star systems, especially red giant-neutron star binaries, providing criteria for stability on thermal and dynamical timescales with new results and illustrative graphs.

Contribution

It introduces new stability criteria for mass transfer in binary systems, extending previous models with updated analysis and graphical representations.

Findings

Mass transfer is generally stable if wind's specific angular momentum is below a threshold.

Unstable systems tend to transfer mass on the thermal timescale.

Graphs show how Roche radius exponent varies with mass ratio.

Abstract

The evolution of a binary star system by various analytic approximations of mass transfer is discussed, with particular attention payed to the stability of these processes against runaway on the thermal and dynamical timescales of the mass donating star. Mass transfer in red giant - neutron star binary systems is used as a specific example of such mass transfer, and is investigated. Hjellming and Webbink's (1987) results on the dynamic timescale response of a convective star with a core to mass loss are applied, with new results. It is found that mass transfer is usually stable, so long as the the wind's specific angular momentum does not exceed the angular momentum per reduced mass of the system. This holds for both dynamical and thermal timescales. Those systems which are not stable will usually transfer mass on the thermal timescale. Included are graphs illustrating the variation of the Roche radius exponent with mass ratio in the binary, for various parameters in the non-conservative mass transfer, as well as evolutionary paths of interacting red giant neutron star binaries.