Detection of additional Wolf-Rayet stars in the starburst cluster Westerlund 1 with SOAR

¹ Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Rua do Matão 1226, Cidade Universitária, 05508-900 São Paulo, SP, Brazil e-mail: groh@astro.iag.usp.br
² Department of Physics and Astronomy, University of Pittsburgh, 3941 O'Hara Street, Pittsburgh, PA 15260, USA
³ IP&D, Universidade do Vale do Paraíba, Av. Shihima Hifumi 2911, São José dos Campos 12244-000, SP, Brazil

Received: 28 January 2006
Accepted: 27 June 2006

Abstract

Context.The young starburst cluster Westerlund 1 is one of the most massive clusters in the Local Group, harboring a huge population of massive stars.

Aims.We searched for additional Wolf-Rayet stars in Westerlund 1.

Methods.The targets were selected based on 1 μm narrow-band imaging of the cluster carried out at OPD/LNA (Brazil), and then confirmed as Wolf-Rayet stars by K-band spectroscopy performed at the 4.1 m SOAR telescope (Chile).

Results.We report the detection of 3 additional Wolf-Rayet stars in Westerlund 1. Together with previous works, this increases the population of Wolf-Rayet stars detected in the cluster to 22 members. Moreover, a K-band spectrum of the Luminous Blue Variable W243, which apparently implies a higher temperature than that derived from optical spectra taken in 2003, is presented for the first time. The WC9 star WR-F was also observed, showing clear evidence of dust emission in the K-band.