Near-infrared time-series photometry in the field of Cygnus OB2 association II. Mapping the variability of candidate members

TL;DR

This study conducted a near-infrared variability survey of the Cygnus OB2 association, revealing significant variability in about half of the candidate members and linking variability characteristics to disk presence and star properties.

Contribution

It provides the first detailed analysis of near-infrared variability in Cygnus OB2, classifies variability types, and demonstrates the potential of variability for identifying disk-bearing stars.

Findings

50% of candidate members show significant variability

Disk-bearing stars are more variable than diskless stars

Identified 18 new disk-bearing stars and 14 eclipsing binary candidates

Abstract

We present the results of a J, H, and K photometric variability survey of the central 0.78 square degrees of the young OB association Cygnus OB2. We used data observed with the Wide-Field CAMera at the United Kingdom Infrared Telescope in 2007 (spanning 217 days) to investigate the light curves of 5083 low mass candidate members in the association and explore the occurrence and main characteristics of their near-infrared variability. We identified 2529 stars ($\sim$50$\%$ of the sample) with significant variability with time-scales ranging from days to months. We classified the variable stars into the following three groups according to their light curve morphology: periodic variability (1697 stars), occultation variability (124 stars), and other types of variability (726 stars). We verified that the disk-bearing stars in our sample are significantly more variable in the near-infrared than diskless stars, with a steep increase in the disk-fraction among stars with higher variability amplitude. We investigated the trajectories described by variable stars in the color-space and measured slopes for 335 stars describing linear trajectories. Based on the trajectories in the color-space, we inferred that the sample analyzed is composed of a mix of young stars presenting variability due to hot and cold spots, extinction by circumstellar material, and changes in the disk emission in the near-infrared. We contemplated using the use of near-infrared variability to identify disk-bearing stars and verified that 53.4$\%$ of the known disk-bearing stars in our sample could have been identified as such based solely on their variability. We present 18 newly identified disk-bearing stars and 14 eclipsing binary candidates among CygOB2 lower-mass members.