Radio emission from the massive stars in Westerlund 1

Dougherty, S. M.; Clark, J. S.; Negueruela, I.; Johnson, T. W. and Chapman, J. M. (2011). Radio emission from the massive stars in Westerlund 1. Bulletin de la Société Royales des Sciences de Liège, 80 pp. 134–138.

URL: http://www.srsl-ulg.net/

Abstract

The diverse massive stellar population in the young massive clusterWesterlund 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 M_o yr⁻¹. Such a 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 M_o yr⁻¹.

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