An R- and I-Band Photometric Variability Survey of the Cygnus OB2 Association

TL;DR

This study presents the first deep optical variability survey of the Cygnus OB2 region, identifying 121 variable stars, including eclipsing binaries, Herbig Ae/Be candidates, and pulsating stars, enhancing understanding of its stellar population.

Contribution

It provides the first comprehensive variability catalog of Cyg OB2 with extensive spatial coverage and depth, discovering new variable stars and associating them with multi-wavelength data.

Findings

121 variable stars identified, 116 newly discovered

27 eclipsing binaries and candidates found

20 potential Herbig Ae/Be stars identified

Abstract

We present a catalog of photometrically variable stars discovered within two 21'.3 X 21'.3 fields centered on the Cygnus OB2 association. There have hitherto been no deep optical variability studies of Cyg OB2 despite it being replete with early-type massive stars, perhaps due to the high and variable extinction (up to A_V ~ 20) that permeates much of the region. Here we provide results of the first variability study with this combination of spatial coverage (~ 0.5 deg) and photometric depth (R ~ 21 mag). We find 121 stars to be variable in both R- and I-band, 116 of them newly discovered. Of the 121 variables, we identify 27 eclipsing binaries (EBs) and eclipsing binary candidates, 20 potential Herbig Ae/Be stars, and 52 pulsating variables. 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, 2MASS near-IR (NIR) data, and Chandra X-ray observations to find counterparts to new variables in other wavelengths.