Planets in stellar clusters extensive search. II. Discovery of 57 variables in the cluster NGC 2158 with millimagnitude image subtraction photometry

We have undertaken a long-term project, Planets in Stellar Clusters Extensive Search (PISCES), to search for transiting planets in open clusters. NGC 2158 is one of the targets we have chosen - an intermediate age, populous, rather metal-poor cluster. In this paper we present the results of a search for variable stars in the data from the first season of monitoring at the FLWO 1.2 m telescope. This is the first variability search ever conducted in this cluster. We present a catalog of 57 variable stars, most with low-amplitude variability. Among the variables is a cataclysmic variable (CV) that underwent a 2.5 mag outburst. If it is a member of NGC 2158, this would be the fourth CV known in an open cluster. We have also found five delta Scuti stars, three of which have two or more detectable modes of pulsation. Of the 57 variables discovered, 28 have R-band amplitudes of 5% or below. Six of those vary at or below the 2% level, including one with 0.08% variability.