Mass loss from binary stars approaching merger

TL;DR

This paper explores the prolonged mass loss in binary stars before merger events, revealing observational evidence and theoretical interpretation of how this mass loss influences the dynamics and observable phenomena of stellar mergers.

Contribution

It provides the first detailed theoretical interpretation of prolonged pre-merger mass loss in binary stars, supported by observations of specific transient events.

Findings

Binary stars undergo significant mass loss before merger.

Mass loss is concentrated in the orbital plane, forming outflows or disks.

Collision of outflows with dynamical ejecta causes bright transients.

Abstract

Some binary stars experience common envelope evolution, which is accompanied by drastic loss of angular momentum, mass, and orbital energy and which leaves behind close binaries often involving at least one white dwarf, neutron star, or black hole. The best studied phase of common envelope is the dynamical inspiral lasting few original orbital periods. We show theoretical interpretation of observations of V1309 Sco and AT2018bwo revealing that binaries undergo substantial prolonged mass loss before the dynamical event amounting up to few solar masses. This mass loss is concentrated in the orbital plane in the form of an outflow or a circumbinary disk. Collision between this slower mass loss and the subsequent faster dynamical ejection powers a bright red transient. The resulting radiative shock helps to shape the explosion remnant and provides a site of dust and molecule formation.