Radio emission from the massive stars in Westerlund 1

TL;DR

This study uses high-sensitivity radio observations of Westerlund 1 to analyze the diverse radio properties and mass-loss rates of its massive stars, revealing surprisingly uniform rates and evidence of episodic enhanced mass-loss.

Contribution

It provides new radio measurements of mass-loss rates across different types of massive stars in Westerlund 1, highlighting the occurrence of episodic enhanced mass-loss events.

Findings

Mass-loss rates are around 10^-5 solar masses per year across the sample.

W9 shows evidence of two distinct mass-loss episodes with higher rates.

Radio properties vary among different stellar types in the cluster.

Abstract

The diverse massive stellar population in the young massive cluster Westerlund 1 (Wd~1) provides an ideal laboratory to observe and constrain mass-loss processes throughout the transitional phase of massive star evolution. A set of high sensitivity radio observations of Wd~1 leads to the detection of 18 cluster members, a sample dominated by cool hypergiants, but with detections among hotter OB supergiants and WR stars. Here the diverse radio properties of the detected sample are briefly described. The mass-loss rates of the detected objects are surprisingly similar across the whole transitional phase of massive star evolution, at ~10^-5 solar masses per year. Such as rate is insufficient to strip away the H-rich mantle in a massive star lifetime, unless the stars go through a period of enhanced mass-loss. The radio luminous star W9 provides an example of such an object, with evidence for two eras of mass-loss with rates of ~10^-4 solar masses per year.