Planets in Stellar Clusters Extensive Search. V. Search for planets and   identification of 18 new variable stars in the old open cluster NGC 188
  We have undertaken a long-term project, Planets in Stellar Clusters Extensive Search (PISCES), to search for transiting planets in open clusters. In this paper we present the results for NGC 188, an old, rather populous cluster. We have monitored the cluster for more than 87 hours, spread over 45 nights. We have not detected any good transiting planet candidates. We have discovered 18 new variable stars in the cluster, bringing the total number of identified variables to 46, and present for them high precision light curves, spanning 15 months. 
B. J. Mochejska, K. Z. Stanek, D. D. Sasselov, A. H. Szentgyorgyi, R.   L. Cooper, R. C. Hickox, V. Hradecky, D. P. Marrone,...