An X-ray imaging study of the stellar population in RCW 49

M. Tsujimoto, E. D. Feigelson, L. K. Townsley, P. S. Broos, K. V. Getman, J. Wang, G. P. Garmire, D. Baba, T. Nagayama, M. Tamura, E. B. Churchwell

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30 Scopus citations


We present the results of a high-resolution X-ray imaging study of the stellar population in the Galactic massive star-forming region RCW 49 and its central OB association Westerlund 2. We obtained a ∼40 ks X-ray image of a ∼ 17′ × 17′ field using the Chandra X-Ray Observatory and deep NIR images using the Infrared Survey Facility in a concentric ∼ 8.3′ × 8.3′ region. We detected 468 X-ray sources and identified optical, NIR, and Spitzer MIR counterparts for 379 of them. The unprecedented spatial resolution and sensitivity of the X-ray image, enhanced by optical and infrared imaging data, yielded the following results: (1) The central OB association Westerlund 2 is resolved for the first time in the X-ray band. X-ray emission is detected from all spectroscopically identified early-type stars in this region. (2) Most (∼86%) X-ray sources with optical or infrared identifications are cluster members in comparison with a control field in the Galactic plane. (3) A loose constraint (2-5 kpc) for the distance to RCW 49 is derived from the mean X-ray luminosity of T Tauri stars. (4) The cluster X-ray population consists of low-mass pre-main-sequence and early-type stars as obtained from X-ray and NIR photometry. About 30 new OB star candidates are identified. (5) We estimate a cluster radius of 6′-7′ based on the X-ray surface number density profiles. (6) A large fraction (∼90%) of cluster members are identified individually using complimentary X-ray and MIR excess emission. (7) The brightest five X-ray sources, two Wolf-Rayet stars and three O stars, have hard thermal spectra.

Original languageEnglish (US)
Pages (from-to)719-735
Number of pages17
JournalAstrophysical Journal
Issue number1 PART 1
StatePublished - Aug 10 2007

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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