Magnetism, rotation and large-scale wind variability of O-type stars

TL;DR

This paper reviews the evidence for large-scale wind structures in O-type stars, exploring their connection to stellar rotation, magnetic fields, and observed variability patterns to better understand massive star wind behavior.

Contribution

It synthesizes observational evidence and theoretical insights on wind variability, magnetic fields, and rotation in O-type stars, highlighting their interrelations and implications.

Findings

Large-scale wind structures are common in O-type stars.

Recurrence timescales of variability often match stellar rotation periods.

Magnetic fields are linked to certain wind variability phenomena.

Abstract

The common - arguably ubiquitous - large-scale variability of optical and UV lines profiles of hot, massive stars is widely interpreted as the direct consequence of structured, variable winds. Many of the variability phenomena are observed to recur on timescales compatible with stellar rotation, suggesting a picture in which perturbations at the base of the wind - carried into view by stellar rotation - produce large-scale outward-propagating density structures. Magnetic fields have been repeatedly proposed to be at the root of these phenomena, although evidence supporting this view remains tenuous. In this review I discuss the evidence for large-scale structures in the winds of O-type stars, the relationship between the observed recurrence timescales and the expected stellar rotational periods, the magnetic and variability properties of known magnetic O-type stars, and their implications for understanding wind variability of the broader population.