SCATTER: A New Common Envelope Formalism

TL;DR

This paper introduces a novel formalism for modeling the common envelope phase in binary star evolution, using angular momentum to derive a simple expression for the final orbital separation, aiding studies of binary and multiple star systems.

Contribution

It presents a new angular momentum-based formalism for predicting the outcome of common envelope interactions, improving upon existing models especially for higher order multiple systems.

Findings

Derived a simple expression for final orbital separation using angular momentum.

Applicable to binary and higher order multiple star systems.

Facilitates more accurate population synthesis simulations.

Abstract

One of the most mysterious astrophysical states is the common envelope (CE) phase of binary evolution, in which two stars are enshrouded by the envelope shed by one of them. Interactions between the stars and the envelope shrinks the orbit. The CE can lead to mergers or to a subsequent phase of interactions. Mergers may involve any combination of two compact objects and/or stars. Some involving white dwarfs, may produce Type Ia supernovae, while merging neutron stars may yield gamma-ray bursts, and merging compact objects of all kinds produce gravitational radiation. Since CEs can arise from a variety of different initial conditions, and due to the complexity of the processes involved, it is difficult to predict their end states. When many systems are being considered, as in population synthesis calculations, conservation principles are generally employed. Here we use angular momentum in a new way to derive a simple expression for the final orbital separation. This method provides advantages for the study of binaries and is particularly well-suited to higher order multiples, now considered to be important in the genesis of potential mergers. Here we focus on CEs in binaries, and the follow-up paper extends our formalism to multiple star systems within which a CE occurs.