Diagnosing small- and large-scale structure in the winds of hot, massive OB-star

TL;DR

This paper explores the multi-scale wind structures in hot OB stars, emphasizing the importance of clumping and magnetic fields, and demonstrates how advanced simulations can replicate observed spectral features.

Contribution

It provides a comprehensive analysis of small- and large-scale wind structures, highlighting the role of magnetic fields and advanced modeling in understanding stellar wind phenomena.

Findings

Clumping near the wind base aligns with observations.

Magneto-hydrodynamical simulations reproduce spectral periodicity.

Proper treatment of wind clumping is crucial for accurate mass-loss estimates.

Abstract

It is observationally as well as theoretically well established that the winds of hot, massive OB-stars are highly structured on a broad range of spatial scales. This paper first discusses consequences of the small-scale structures associated with the strong instability inherent to the line-driving of these winds. We demonstrate the importance of a proper treatment of such wind clumping to obtain reliable estimates of mass-loss rates, and also show that instability simulations that are perturbed at the lower boundary indeed display significant clumping quite close to the wind base, in general agreement with observations. But a growing subset of massive stars has also been found to possess strong surface magnetic fields, which may channel the star's outflow and induce also large-scale wind structures and cyclic behavior of spectral diagnostics. The paper concludes by showing that multi-dimensional, magneto-hydrodynamical wind simulations, together with detailed radiative-transfer modeling, can reproduce remarkably well the periodic Balmer line emission observed in slowly rotating magnetic O stars like HD191612.