Wind anisotropy and stellar evolution

TL;DR

This paper explores how wind anisotropy caused by stellar rotation influences the evolution and final stages of massive stars, particularly in the context of gamma-ray burst progenitors, highlighting the need to consider magnetic fields for accurate modeling.

Contribution

It introduces the impact of wind anisotropy on stellar evolution at low metallicity and discusses the role of magnetic fields in spinning down stellar cores.

Findings

Polar winds enable significant mass loss while preserving core angular momentum.

Current models predict too fast core rotation rates for gamma-ray burst progenitors.

Magnetic fields are necessary to accurately model core spin-down in massive stars.

Abstract

Mass loss is a determinant factor which strongly affects the evolution and the fate of massive stars. At low metallicity, stars are supposed to rotate faster than at the solar one. This favors the existence of stars near the critical velocity. In this rotation regime, the deformation of the stellar surface becomes important, and wind anisotropy develops. Polar winds are expected to be dominant for fast rotating hot stars. These polar winds allow the star to lose large quantities of mass and still retain a high angular momentum, and they modifie the evolution of the surface velocity and the final angular momentum kept in the star's core. We show here how these winds affect the final stages of massive stars, according to our knowledge about Gamma Ray Bursts. Computation of theoretical Gamma Ray Bursts rate indicates that our models have too fast rotating cores, and that we need to include an additional effect to spin them down. Magnetic fields in stars act in this direction, and we show how they modify the evolution of massive star up to the final stages.