Estimating the outcomes of common envelope evolution in triple stellar systems

TL;DR

This paper introduces a new model for the evolution of triple star systems undergoing common envelope phases, highlighting how dynamical interactions lead to star ejection and envelope dispersal, with implications for post-envelope system properties.

Contribution

It develops a combined analytic and numerical model to describe the complex evolution of triple stars during common envelope phases, focusing on dynamical interactions and ejection outcomes.

Findings

Outer orbit shrinks faster than the inner binary due to dynamical friction.

Most systems experience chaotic interactions leading to star ejection.

Envelope disperses after stars escape, affecting system survivability.

Abstract

We present a new model describing the evolution of triple stars which undergo common envelope evolution, using a combination of analytic and numerical techniques. The early stages of evolution are driven by dynamical friction with the envelope, which causes the outer triple orbit to shrink faster than the inner binary. In most cases, this leads to a chaotic dynamical interaction between the three stars, culminating in the ejection of one of the stars from the triple. This ejection and resulting recoil on the remnant binary are sufficient to eject all three stars from the envelope, which expands and dissipates after the stars have escaped. These results have implications for the properties of post-common envelope triples: they may only exist in cases where the envelope was ejected before the onset of dynamical instability, the likelihood of which depends on the initial binary separation and the envelope structure. In cases where the triple becomes dynamically unstable, the triple does not survive and the envelope dissipates without forming a planetary nebula.