The massive star-forming region Cygnus OB2. I : Chandra catalog of association members

Abstract

We present a catalog of 1696 X-ray sources detected in the massive star-forming region (SFR) Cygnus OB2 and extracted from two archival Chandra observations of the center of the region. A deep source extraction routine, exploiting the low background rates of Chandra observations, was employed to maximize the number of sources extracted. Observations at other wavelengths were used to identify low count-rate sources and remove likely spurious sources. Monte Carlo simulations were also used to assess the authenticity of these sources. X-ray spectra were fitted with thermal plasma models to characterize the objects and X-ray light curves were analyzed to determine their variability. We used a Bayesian technique to identify optical or near-IR counterparts for 1501 (89%) of our sources, using deep observations from the INT Photometric Hαsurvey, the Two Micron All Sky Survey, and the UKIRT Infrared Deep Sky Survey-Galactic Plane Survey. Seven hundred and fifty seven (45%) of these objects have six-band r′, Hα, i′, J, H, and K optical and near-IR photometry. From an analysis of the Poisson false-source probabilities for each source we estimate that our X-ray catalog includes