Continuum driven winds from super-Eddington stars. A tale of two limits

TL;DR

This paper investigates continuum-driven stellar winds from super-Eddington stars, analyzing how they behave relative to the Eddington and photon-tiring limits, with implications for low-metallicity star evolution.

Contribution

It introduces a numerical simulation framework for continuum-driven winds, exploring their dynamics across the photon-tiring limit, which was not thoroughly studied before.

Findings

Steady, large mass loss rates are possible below the photon-tiring limit.

Wind velocities are approximately the escape velocity below the photon-tiring limit.

Above the photon-tiring limit, steady solutions are not possible, and winds have reduced velocities.

Abstract

Continuum driving is an effective method to drive a strong stellar wind. It is governed by two limits: the Eddington limit and the photon-tiring limit. A star must exceed the effective Eddington limit for continuum driving to overcome the stellar gravity. The photon-tiring limit places an upper limit on the mass loss rate that can be driven to infinity, given the energy available in the radiation field of the star. Since continuum driving does not require the presence of metals in the stellar atmosphere it is particularly suited to removing mass from low- and zero-metallicity stars and can play a crucial part in their evolution. Using a porosity length formalism we compute numerical simulations of super-Eddington, continuum driven winds to explore their behaviour for stars both below and above the photon-tiring limit. We find that below the photon tiring limit, continuum driving can produce a large, steady mass loss rate at velocities on the order of the escape velocity. If the star exceeds the photon-tiring limit, a steady solution is no longer possible. While the effective mass loss rate is still very large, the wind velocity is much smaller