Hydrodynamic Winds From Twin-Star Binaries

TL;DR

This study uses hydrodynamic simulations to analyze nearly-isothermal winds from twin-star binaries, revealing how mass loss and angular momentum depend on wind and orbital velocities, with implications for binary evolution.

Contribution

It introduces a detailed hydrodynamic model of stellar winds in twin binaries, highlighting the impact of Roche lobe filling and wind velocity on mass loss and angular momentum transfer.

Findings

Mass loss rates are enhanced in close twin binaries.

Wind angular momentum varies with wind and orbital velocities.

Results are applicable to the evolution of massive close binaries.

Abstract

Stellar winds shape the evolution of stars through the loss of mass. In binary systems, they also shape the stars' evolution by modifying the orbit. In this paper, we use hydrodynamic simulations to study the emergence of nearly-isothermal winds from identical-twin binaries. We vary the degree to which model stars fill their Roche lobes and the temperature of the wind. Initialized at rest on the stellar surfaces, winds accelerate away from the binary components through a sonic surface to supersonic outward velocities. In cases where the binary fills its Roche lobe, a shared subsonic region surrounds both components. We find that mass loss rates from close twin-star binaries are enhanced relative to the expectation from two single-object winds. This binary enhancement is best modeled as a function of the ratio of wind velocity to orbital velocity. Similarly, we find that the specific angular momentum with which winds emerge can vary between that of the binary components and that of the outer Lagrange points depending on the ratio of wind velocity to orbital velocity. Given that mass and angular momentum loss can be modeled as simple functions of wind velocity, our results may be broadly applicable to the evolution of close, equal-mass binaries. One particularly important potential application is to massive, close binaries which may be progenitors of binary black hole mergers through the chemically-homogeneous evolution channel.