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Description
This table contains the list of X-ray sources detected in 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. The authors obtained a ~ 40 ks X-ray image of a ~ 17' x 17' field using the Chandra X-Ray Observatory and deep NIR images using the Infrared Survey Facility in a concentric ~ 8.3' x 8.3' region. They detected 468 X-ray sources with a photometric significance >=1.0 and a 1% or less chance of being a background fluctuation, and identified optical, near-infrared (NIR), and Spitzer mid-infrared (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) The authors 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. The X-ray observation of RCW 49 was carried out using the Advanced CCD Imaging Spectrometer (ACIS) on board the Chandra X-Ray Observatory from 2003 August 23 UT 18:20 to August 24 UT 4:54. Four imaging array (ACIS-I) chips covered a 17 by 17 arcminutes field centered at (R.A., Dec.) = (10h24m00.5s, -57d 45' 18") in the equinox J2000.0 for a 36.7 ks exposure. ACIS-I covers the 0.5 - 8.0 keV energy band with a spectral resolution of ~ 150 eV at 6 keV and a point-spread function (PSF) radius of ~ 0.5" within ~ 2' of the on-axis position, degrading to ~ 6" at a 10' off-axis angle. The data were taken with the very faint telemetry mode and the timed exposure CCD operation with a frame time of 3.2 s. Sources with photometric significance of larger than 2 were fitted with an absorbed thin thermal plasma model. The abundance was fixed to be 0.3 times the solar value. Fits lacking uncertainties, fits with large uncertainties, and fits with frozen parameters should be viewed merely as splines to the data to obtain rough estimates of the X-ray luminosities: the listed parameter values are considered unreliable in such cases. The authors also conducted NIR observations on 2004 December 25 and 28 using the Simultaneous three-color Infrared Imager for Unbiased Surveys (SIRIUS) mounted on the Cassegrain focus of the IRSF 1.4 m telescope at the South African Astronomical Observatory. SIRIUS is a NIR imager capable of obtaining simultaneous images in the J, H, and K<sub>s</sub> bands. The instrument is equipped with three HAWAII arrays of 1024 by 1024 pixels. The pixel scale of 0.45" is an excellent match with the on-axis spatial resolution of Chandra. The authors covered 8.3 by 8.3 arcminute fields at two positions, one aimed at RCW 49 (10h24m01.9s, -57d 45' 31") and the other at a control region. This table was created by the HEASARC in October 2007 based on the versions of Tables 1, 2, and 3 from the paper which were obtained from the electronic ApJ website. This is a service provided by NASA HEASARC .
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