The OGLE project is conducted using the 1-m Swope telescope at Las
Campanas Observatory which is operated by Carnegie Institution of
Washington. A single 
pixels Loral CCD chip, giving the
scale of 0.435 arcsec/pixel is used as the detector. The initial
processing of the raw frames is done automatically in near-real time.
Details of the standard OGLE processing techniques are described by
Udalski et al. (1992).
Table 1: Equatorial coordinates for centers of 5139D-F fields
Table 2: Number of frames reduced for the 
Cen fields
This paper is based mostly on the data obtained during 1995 observing season. The cluster was monitored for a period spanning about 3 months. Detailed logs of observations can be found in Udalski et al. (1995, 1996). We monitored three fields. Fields 5139D and 5139E were centered about 13 arcmin West and about 13 arcmin East of the cluster center, respectively. Field 5139F was centered about 12 arcmin South in respect to field 5139E. The equatorial coordinates of centers of fields 5139D-F are given in Table 1 (click here). Fields 5139E and 5139F were observed only in 1995. Field 5139D was additionally monitored for about 5 hours on the night of 21 June, 1995. A schematic chart with marked location of all monitored fields (Papers I and II) is shown in Fig. 1 (click here). Most of the monitoring was performed through the Johnson V filter. Some exposures in the Kron-Cousins I band were also obtained. Table 2 (click here) gives total numbers of frames reduced for each of surveyed fields. Most of observations in the V-band were collected with an exposure time set to 420 s. For the I-band exposures lasted 300 s. For majority of the analyzed frames seeing was better than 1.6 arcsec. The reduction techniques as well as algorithms used for selecting potential variables are described in Paper I. The profile photometry was extracted with the help of DoPHOT (Schechter et al. 1993). The total number of stars contained in data bases with V photometry was 37771, 49426 and 22115 for fields, 5139D, 5139E and 5139F, respectively. Most of these stars were faint objects with relatively large errors of photometry. Table 3 (click here) gives condensed information about the numbers of stars analyzed for variability and about the quality of derived photometry.
Figure 1:
A schematic chart showing location of fields 5139A-F.
The cluster center is marked with cross.
Each field covers 
armin
Figure 2: Phased V light curves for 10 SX Phe stars identified
in fields 5139D-F. Note the same height of all boxes. Variables
are sorted according to their periods: inserted labels give names of
variables and their periods in days
Table 3:
Basic statistical data about stars from fields 5139D-F examined
for variability. The data are given for bins 0.5 mag wide.
Columns 2, 4 and 6 give median value of rms for
a given bin. Columns 3, 5 and 7 give numbers of stars examined
for variability