2 Observations and data reduction

Observations of Tr 5 were collected during three observing runs at the Kitt Peak National Observatory. Table 1 gives the essential information about these runs.

  

Table 1: Summary of observations of Tr 5

Preliminary processing of the data was done with the standard routines in the IRAF-CCDPROC package. The instrumental photometry was extracted using DAOPHOT/ALLSTAR package (Stetson 1987, 1991). The constant point spread function (PSF) was adopted while reducing data from run #1. For runs #2 and #3 PSF varying linearly with coordinates was applied to extract instrumental photometry. A sufficient number of Landolt standards (Landolt 1983, 1992) was observed during each of the runs to establish reliable transformations from the instrumental to the standard $BVI_{\rm C}$ system.

Two overlapping sub-fields covering the central part of the cluster were observed during run #1. We obtained four exposures for each sub-field: 70 s and 300 s exposures in the V-band plus 70 s and 300 s exposures in the I-band.

Two overlapping sub-fields covering the central part of the cluster were observed during run #2. We obtained four exposures for each sub-field: 60 s and 300 s exposures in the V-band, 100 s and 700 s exposures in the B-band.

Two overlapping sub-fields were observed during run #3. Sub-field a was centered on the cluster center. Sub-field b was centered about 6 arcmin north of the center of sub-field a. The following set of exposures was obtained for sub-field a: B-3 $\times$ 900 s, B-200 s, B-180 s, V-3 $\times$ 600, V-150 s, V-120 s. For sub-field b we obtained only long exposures: B-900 s and V-600 s.

The three data sets described above were calibrated independently of one another. The zero points of the V photometry derived during runs #1, #2 and #3 are in a good agreement with each other. The observed systematic differences do not exceed 0.02 mag. Also the zero point of the B-V photometry based on the data from run #2 agrees to 0.02 mag with the zero point of photometry based on run #3. The V/V-I and V/B-V color-magnitude diagrams (CMD) based on the observations collected during runs 1-3 are shown in Fig. 1.

  

Figure 1: Color magnitude diagrams for stars from the region of Tr 5 based on photometry obtained during runs #1 (left), #2 (center) and #3 (right)