Variable stars in the 50BiN open cluster survey. III. NGC 884

Open clusters are the basic building blocks that serve as an the laboratory for the study of young stellar populations in the Milky Way. Variable stars in open clusters provide a unique way to accurately probe the internal structure, temporal and dynamical evolutionary stages of individual stars and the host cluster. The most powerful tool for such studies is time-domain photometric observations. This paper follows the route of our previous work, concentrating on a photometric search for variable stars in NGC 884. The target cluster is the companion of NGC 869, forming the well-known double cluster system that is gravitationally bound. From the observation run in November 2016, a total of 9247 B-band CCD images and 8218 V-band CCD images were obtained. We detected a total of 15 stars with variability in visual brightness, including 5 Be stars, 3 eclipsing binaries, and 7 of unknown type. Two new variable stars were discovered in this work. We also compared the variable star content of NGC 884 with its companion NGC 869.