Time-Series Ensemble Photometry and the Search for Variable Stars in the Open Cluster M11

Abstract

This work presents the first large-scale photometric variability survey of the intermediate-age (∼200 Myr) open cluster M11. Thirteen nights of data over two observing seasons were analyzed (using crowded field and ensemble photometry techniques) to obtain high relative precision photometry. In this study we focus on the detection of candidate member variable stars for follow-up studies. A total of 39 variable stars were detected and can be categorized as follows: one irregular (probably pulsating) variable, six δ Scuti variables, 14 detached eclipsing binary systems, 17 W UMa variables, and one unidentified/candidate variable. While previous proper-motion studies allow for cluster membership determination for the brightest stars, we find that membership determination is significantly hampered below V = 15, R = 15.5 by the large population of field stars overlapping the cluster main sequence. Of the brightest detected variables that have a high likelihood of cluster membership, we find five systems in which further work could help constrain theoretical stellar models, including one potential W UMa member of this young cluster.