Non-Radial Pulsations and Large-Scale Structure in Stellar Winds

TL;DR

This paper models large-scale spiral structures in stellar winds caused by non-radial pulsations, explaining observed spectral features in early-type stars through hydrodynamical simulations.

Contribution

It introduces a hydrodynamical model linking non-radial pulsations to co-rotating interaction regions in stellar winds, fitting observed spectral features.

Findings

CIRs are caused by surface spots creating fast streams.

Spots do not rotate with the stellar surface.

CIRs are likely due to interference of non-radial pulsations.

Abstract

Almost all early-type stars show Discrete Absorption Components (DACs) in their ultraviolet spectral lines. These can be attributed to Co-rotating Interaction Regions (CIRs): large-scale spiral-shaped structures that sweep through the stellar wind. We used the Zeus hydrodynamical code to model the CIRs. In the model, the CIRs are caused by "spots" on the stellar surface. Through the radiative acceleration these spots create fast streams in the stellar wind material. Where the fast and slow streams collide, a CIR is formed. By varying the parameters of the spots, we quantitatively fit the observed DACs in HD 64760. An important result from our work is that the spots do not rotate with the same velocity as the stellar surface. The fact that the cause of the CIRs is not fixed on the surface eliminates many potential explanations. The only remaining explanation is that the CIRs are due to the interference pattern of a number of non-radial pulsations.