On continuum driven winds from rotating stars

TL;DR

This paper models continuum-driven winds from rotating stars, revealing how near-critical rotation influences mass ejection patterns, shapes nebulae like the Homunculus, and impacts stellar angular momentum evolution, with applications to ta-Carinae.

Contribution

It introduces an analytical model for continuum-driven winds from rotating stars and applies it to explain nebula shapes and stellar evolution phenomena.

Findings

Winds are concentrated towards the poles near the Eddington limit.

Critical rotation leads to a twin-lobe nebula structure.

The model's predictions match observed features of ta-Carinae's nebula.

Abstract

We study the dynamics of continuum driven winds from rotating stars, and develop an approximate analytical model. We then discuss the evolution of stellar angular momentum, and show that just above the Eddington limit, the winds are sufficiently concentrated towards the poles to spin up the star. A twin-lobe structure of the ejected nebula is seen to be a generic consequence of critical rotation. We find that if the pressure in such stars is sufficiently dominated by radiation, an equatorial ejection of mass will occur during eruptions. These results are then applied to {\eta}-Carinae. We show that if it began its life with a high enough angular momentum, the present day wind could have driven the star towards critical rotation, if it is the dominant mode of mass loss. We find that the shape and size of the Homunculus nebula, as given by our model, agree with recent observations. Moreover, the contraction expected due to the sudden increase in luminosity at the onset of the Great Eruption explains the equatorial "skirt" as well.