AN R- AND I-BAND PHOTOMETRIC VARIABILITY SURVEY OF THE CYGNUS OB2 ASSOCIATION

We present a catalog of photometrically variable stars discovered within two 21.'3 x 21.'3 fields centered on the Cygnus OB2 association (Cyg OB2). There have hitherto been no deep optical variability studies of Cyg OB2, despite it being replete with early-type massive stars, likely due to the high and variable extinction (up to A(V) approximate to 20) that permeates much of the region. Here, we provide results of the first variability study with this combination of spatial coverage (similar to 0.5 deg) and photometric depth (R similar to 21 mag). We find 121 stars to be variable in both R and I bands, 115 of them newly discovered. Of the 121 variables, we identify 27 eclipsing binaries and eclipsing-binary candidates, 52 pulsating variables, and 20 potential Herbig Ae/Be stars. Confirming both the status and the cluster membership of the Herbig Ae/Be stars would address the uncertainty regarding the age and star formation history of Cyg OB2. We match our catalog to known variables and binaries in the region, Two Micron All Sky Survey near-IR data, and Chandra X-ray observations to find counterparts to new variables in other wavelengths.