Radiation pressure and pulsation effects on the Roche lobe

TL;DR

This paper extends the classical Roche model to include effects of radiation pressure and pulsations, analyzing their influence on the Roche lobe's shape and stability during mass transfer in binary systems.

Contribution

It introduces a generalized Roche lobe concept accounting for extra forces, providing analytical expressions for the Roche radius under these conditions.

Findings

Radiation pressure can reduce the Roche radius or make it undefined.

Pulsations influence the Roche lobe through wind velocity profiles.

Impact on RLOF stability is minimal.

Abstract

Several observational pieces of evidence indicate that specific evolutionary channels which involve Roche lobe overflow are not correctly accounted for by the classical Roche model. We generalize the concept of Roche lobe in the presence of extra forces (caused by radiation pressure or pulsations). By computing the distortion of the equipotential surfaces, we are able to evaluate the impact of these perturbing forces on the stability of Roche-lobe overflow (RLOF). Radiative forces are parametrized through the constant reduction factor that they impose on the gravitational force from the radiating star (neglecting any shielding in case of large optical thickness). Forces imparted by pulsations are derived from the velocity profile of the wind that they trigger. We provide analytical expressions to compute the generalized Roche radius. Depending on the extra force, the Roche-lobe radius may either stay unchanged, become smaller, or even become meaningless (in the presence of a radiatively- or pulsation-driven wind). There is little impact on the RLOF stability.