A CCD Photometric Survey of Variable Stars in the Field of NGC 188

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Abstract
The results of a recent CCD photometry survey of variables in a 1° field covering the old open cluster NGC 188 are presented. A total of 16 short-period variables were identified during five nights, among which eight are new variables in the program field. By adopting the method of phase-dispersion minimization, the periods for seven of the eight new variables are determined. The main properties, the classifications, as well as the memberships are discussed for all of these variable stars, based on the behavior of light curves, the locations in the color-magnitude diagram, and the results of proper motions. Among the eight new objects, six are W UMa binaries, in which one definitely is and two probably are members of the cluster. A detached or semidetached eclipsing binary with an orbital period longer than 1 day is found, which is a likely cluster star. In addition, a field star with a peculiar light curve is detected, which can be classified as a RRd–type variable. Moreover, revised basic data for the eight old variables are given according to our observations. V8 can be classified as an RS CVn–type star with light variations larger than 0.2 mag.