A Rich Population of X-ray Emitting Wolf-Rayet Stars in the Galactic Starburst Cluster Westerlund 1

S.L. Skinner $^1$
A.E. Simmons $^1$
S.A. Zhekov $^2$
M. Teodoro $^3$
A. Damineli $^3$
F. Palla $^4$

1 - CASA, Univ. of Colorado, Boulder, CO 80309-0389
2 - Space Research Institute, Moskovska str. 6, Sofia-1000, Bulgaria
3 - Instituto de Astronomia, Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, Rua do Matao 1226, Cidade Universitaria, 05508-900 Sao Paulo, SP, Brazil
4 - INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy

Recent optical and infrared studies have revealed that the heavily-reddened starburst cluster Westerlund 1 (Wd 1) contains at least 22 Wolf-Rayet (WR) stars, comprising the richest WR population of any galactic cluster. We present results of a sensitive Chandra X-ray observation of Wd 1 which detected 12 of the 22 known WR stars and the mysterious emission-line star W9. The fraction of detected WN stars is nearly identical to that of WC stars. The WN stars WR-A and WR-B as well as W9 are exceptionally luminous in X-rays and have similar hard heavily-absorbed X-ray spectra with strong Si XIII and S XV emission lines. The luminous high-temperature X-ray emission of these three stars is characteristic of colliding wind binary systems but their binary status remains to be determined.

Reference: ApJL, in press
Status: Manuscript has been accepted

Weblink: astro-ph/0601550


Email: skinners@casa.colorado.edu