On the origin of microturbulence in hot stars

TL;DR

This study investigates the origin of microturbulence in hot massive stars, linking it to sub-surface convection zones caused by opacity peaks, and suggests a connection to stellar wind clumping.

Contribution

It provides the first extensive analysis of convection zones near the surface of hot stars and correlates predictions with observational data on microturbulence.

Findings

Convection zones are located close to the stellar surface in hot stars.

Predicted microturbulence levels agree with VLT-Flames observations.

Surface convection may trigger wind clumping in massive stars.

Abstract

We present results from the first extensive study of convection zones in the envelopes of hot massive stars, which are caused by opacity peaks associated with iron and helium ionization. These convective regions can be located very close to the stellar surface. Recent observations of microturbulence in massive stars from the VLT-Flames survey are in good agreement with our predictions concerning the occurrence and the strength of sub-surface convection in hot stars. We argue further that convection close to the surface may trigger clumping at the base of the stellar wind of massive stars.