A&A 511, A58 (2010) Astronomy DOI: 10.1051/0004-6361/200913505 & c ESO 2010 Astrophysics Radio emission from the massive stars in the galactic super star cluster Westerlund 1 S. M. Dougherty1,2,J.S.Clark3, I. Negueruela4, T. Johnson1,5, and J. M. Chapman6 1 National Research Council of Canada, Herzberg Institute for Astrophysics, Dominion Radio Astrophysical Observatory, PO Box 248, Penticton, British Columbia V2A 6J9, Canada e-mail:
[email protected] 2 Institute for Space Imaging Science, University of Calgary, 2500 University Dr. NW., Calgary, Alberta, T2N 1N4, Canada 3 Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK 4 Dpto. de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, Apdo. 99, E03080 Alicante, Spain 5 Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Rd, Victoria, B.C., V8P 5C2, Canada 6 Australia National Telescope Facility, PO Box 76, Epping, NSW 2121, Australia Received 20 October 2009 / Accepted 16 November 2009 ABSTRACT Aims. Current mass-loss rate estimates imply that main sequence line-driven winds are not sufficient to strip away the H-rich envelope to yield Wolf-Rayet (WR) stars. The rich transitional population of the young massive cluster Westerlund 1 (Wd 1) provides an ideal laboratory to observe and constrain mass-loss processes throughout the transitional phase of stellar evolution. Methods. We present an analysis of deep radio continuum observations of Wd 1 obtained with the Australia Telescope Compact Array at four frequency bands that permit investigation of the intrinsic characteristics of the radio emission.