Automatic Variability Analysis of Bulge Stars in OGLE-II Image Subtraction Database

We present results of star variability analysis in the OGLE-II bulge field BUL_SC1. Photometric database was derived by means of image subtraction method and contains 4597 objects preclassified as variables. We analyzed all the light curves in order to find periodic variables, non periodic but all-time variables and stars showing episodic changes in their brightness, e.g., gravitational lenses. Variability of 3969 stars was confirmed, among them we detected 12 lensing event candidates whose light curves are shown. We found 762 periodic variables. Algorithmic methods allowed us to identify 71 RR Lyr and 110 W UMa stars. Almost all luminous red giants are found to be variable. Most of red clump giants are not variable. Classification of all 4597 objects is presented online.