The optical gravitational lensing experiment. Variable stars in globular clusters

Three fields located close to the center of the globular cluster ω Cen were surveyed in a search for variable stars. We present V-band light curves for 32 periodic variables. This sample includes 10 SX Phe stars, 19 eclipsing binaries, and three likely spotted variables (FK Com or RS CVn type stars). Only 5 of these variables were previously known (including two objects reported in Paper I). All SX Phe stars and 8 eclipsing binaries from our sample belong to blue stragglers. Five binaries occupy positions on the upper main-sequence of the cluster and another four are located at the base of the subgiant branch. Of particular interest is detection of a detached binary system with a period $P=4.64$ day. Further study of this star can provide direct information about properties of turnoff stars in ω Cen. All SX Phe stars and most of eclipsing binaries discovered in our survey are likely cluster members. We present V vs. $V-I$ color-magnitude diagrams for the monitored fields. A populous group of likely hot subdwarfs as well as numerous candidates for blue stragglers can be noted in these diagrams. Our data indicate that ω Cen possesses the largest number of blue stragglers among all galactic globulars