AAS 207th Meeting, 8-12 January 2006
Session 71 (WIYN) Open Clusters and Associations
Poster, Tuesday, 9:20am-6:30pm, January 10, 2006, Exhibit Hall

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[71.11] Chandra and NTT Observations of Massive Young Stars in the Heavily Reddened Galactic Cluster Westerlund 1

S.L. Skinner (Univ. of Colorado), A. Damineli (IAG / Univ. of Sao Paulo), F. Palla (INAF / Osserv. Astrof. di Arcetri), S.A. Zhekov (JILA - Univ. of Colorado and Space Research Inst. Sofia), A.E. Simmons (Univ. of Colorado), M. Teodoro (IAG/Univ. of Sao Paulo)

The southern galactic starburst cluster Westerlund 1 (Wd1) contains a rich population of massive young stars that is spectacularly revealed in infrared images. Recent studies give a mean extinction in the range Av = 9.5 - 13.6 mag and age estimates of ~3 - 5 Myr (Brandner et al. 2005, Clark et al. 2005). The cluster contains numerous supergiants, hypergiants, a LBV candidate, and at least 19 Wolf-Rayet (WR) stars. We present new results from Chandra X-ray and NTT near-IR observations of Wd1. Our immediate objectives are to obtain an X-ray census, identify optical or near-IR counterparts to the X-ray sources, and quantify the X-ray properties of the cluster members. Chandra detections include a newly-discovered 10.61 sec pulsar, the unusual B[e] supergiant W9, and half of the currently known WR stars in the cluster. The Chandra ACIS-S CCD spectrum of the Wd1 pulsar (CXO J164710.2-455217) can be acceptably reproduced by an absorbed soft blackbody emission model, but the model is not uniquely constrained by the existing data. A high-temperature component is clearly present in the X-ray spectrum of W9, suggesting that it is a close binary or unresolved multiple. Most of the Chandra WR detections are nitrogen-rich WN stars, but a few carbon-rich WC stars are surprisingly detected. At an assumed distance of 4 kpc, the X-ray luminosity of W87-239 (WC9) is two orders of magnitude greater than upper limits previously obtained for closer less-obscured single WC stars such as WR 135 (WC8, log Lx < 29.82 ergs/s; Skinner et al. 2005). The luminous X-ray emission and hot plasma in W87-239 point toward binarity.

This study was supported by NASA/SAO grants GO5-6009X (PI: S.S.) and GO4-5003X (PI: S.Z.).

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