A two-stage formalism for common-envelope phases of massive stars

TL;DR

This paper introduces a two-stage formalism for predicting post-common-envelope orbital separations in massive star binaries, emphasizing the role of the radiative layer and donor evolution stage, with implications for astrophysical phenomena.

Contribution

A new physically-motivated two-stage formalism for common-envelope evolution in massive stars, improving predictions of orbital separations over classical methods.

Findings

Predicts wider post-CE separations than classical models.

Shows final separations depend on donor stage and companion mass.

Provides an alternative for population synthesis studies.

Abstract

We propose a new simple formalism to predict the orbital separations after common-envelope phases with massive star donors. We focus on the fact that massive red supergiants tend to have a sizeable radiative layer between the dense helium core and the convective envelope. Our formalism treats the common-envelope phase in two stages: dynamical in-spiral through the outer convective envelope and thermal timescale mass transfer from the radiative intershell. With fiducial choices of parameters, the new formalism typically predicts much wider separations compared to the classical energy formalism. Moreover, our formalism predicts that final separations strongly depend on the donor evolutionary stage and companion mass. Our formalism provides a physically-motivated alternative option for population synthesis studies to treat common-envelope evolution. This treatment will impact on predictions for massive-star binaries, including gravitational-wave sources, X-ray binaries and stripped-envelope supernovae.