Reanalysis of the OGLE-I Observations with the Image Subtraction Method. I.Galactic Bar Fields MM1-A, MM1-B, MM7-A, and MM7-B

As a result of the reanalysis of the OGLE-I observations by means of the image subtraction method, we present the first part of a catalog, consisting of data for variable stars in four Galactic fields observed by OGLE-I, viz. MM1-A, MM1-B, MM7-A, and MM7-B. In total, 2016 variable stars have been found. This increased the number of known variable stars in these fields more than twofold. We comment on the detectability of the variable stars in previous studies.

Some interesting findings are also discussed. Among others, we found 45 delta Sct stars (38 are new) including several multiperiodic objects. Detailed analysis of the light curves of 47 RR Lyr stars (24 are new detections) allowed us to find five stars which exhibit nonradial pulsations and one RRd star. Three RRab stars are members of the Sagittarius dwarf galaxy (Sgr dSph). We also find four objects which are probably Galactic RV Tau stars and one W Vir star which seems to belong to Sgr dSph. This is the first Population II Cepheid found in this satellite galaxy and dSph other than the Fornax one.

For eclipsing EW-type binaries, which are the most abundant variables in our catalog, we investigate the amplitude and period distributions. A comparison with the previous OGLE-I catalogs indicates that we found more stars with smaller amplitudes. Finally, in addition to the two microlensing events discovered previously in these fields, we find five more.