Numerical simulations of continuum-driven winds of super-Eddington stars

TL;DR

This paper uses numerical simulations to study continuum-driven stellar winds in super-Eddington stars, confirming analytical models and highlighting their role in explaining large mass loss in luminous stars and early universe stars.

Contribution

It provides the first detailed numerical simulations of continuum-driven winds, validating analytical predictions and exploring their implications for massive stellar outflows.

Findings

Simulations closely match analytical scalings.

Mass loss rates are significantly higher than line-driven winds.

Continuum driving explains large outflows in LBV stars and possibly in Population III stars.

Abstract

We present the results of numerical simulations of continuum-driven winds of stars that exceed the Eddington limit and compare these against predictions from earlier analytical solutions. Our models are based on the assumption that the stellar atmosphere consists of clumped matter, where the individual clumps have a much larger optical thickness than the matter between the clumps. This `porosity' of the stellar atmosphere reduces the coupling between radiation and matter, since photons tend to escape through the more tenuous gas between the clumps. This allows a star that formally exceeds the Eddington limit to remain stable, yet produce a steady outflow from the region where the clumps become optically thin. We have made a parameter study of wind models for a variety of input conditions in order to explore the properties of continuum-driven winds. The results show that the numerical simulations reproduce quite closely the analytical scalings. The mass loss rates produced in our models are much larger than can be achieved by line driving. This makes continuum driving a good mechanism to explain the large mass loss and flow speeds of giant outbursts, as observed in eta Carinae and other luminous blue variable (LBV) stars. Continuum driving may also be important in population III stars, since line driving becomes ineffective at low metalicities. We also explore the effect of photon tiring and the limits it places on the wind parameters.