2. Observations

Five overlapping fields shown in Fig. 1 (click here) were measured during two observational runs, on April 1992 and 1994 respectively, in the UBVRI Cousins system. However, not all frames could be calibrated in the I passband as one night we had no chance of measuring I standards; on the other hand, due to an unfortunate telescope pointing, no overlapping is seen in the cluster finding chart (Fig. 2 (click here)), for 500 < x < 850 and 900 < y < 1000. The observations were carried out with the 60 cm telescope of the University of Toronto Southern Observatory equipped with a PM Metachrome UV coated chip covering an area of on a side (scale is ). Figure 1 (click here) reveals that our observations did not cover the whole of the cluster as defined by Fenkart et al. (1977) but a large portion of it.

  
Figure 1: A reproduction of the Digitized Sky Survey plates, DSS, showing the area of Cr 272 where the circle gives an estimate of the cluster size, ( diameter) calculated from star counts in the DSS plates (see Sect. 4). The location of our five frames is also shown. North is at top

  
Figure 2: The finding chart of Cr 272. The size of the dots is proportional to the star magnitudes, approximately

  
Figure 3: a-e). The color and magnitude errors from DAOPHOT as a function of the V magnitude

  
Figure 4: The two-color diagram of Cr 272. Big dots denote likely cluster members. Small dots are probable members found by comparison among the photometric diagrams. Squares are stars for which no realistic memberships could be determined. The solid line is the Schmidt-Kaler (1982) ZAMS of stars of luminosity class V and the path of the reddening line is indicated with an arrow. Numbers give the star identification

Although the night 8/9 seemed to be veiled, the mean seeing of the observing runs was . To investigate how the field stars contaminate the cluster area, a comparison frame was taken at 30 arcmin from the center of Cr 272 on May 1995 using the same equipment.

PSF fitting using DAOPHOT (Stetson 1987) running within IRAF was employed to get photometry. Previously, the frames were bias subtracted and flat-fielded. Final colors and magnitudes were obtained using two well defined sequences in the clusters NGC 5606 and Hogg 16 (Vázquez & Feinstein 1991a,b) as secondary calibration standards. Most of the calculations were carried out at the Observatory of La Plata but a part of them was preliminary made at the Astronomical Institutes of Bonn University. The rms of the transformation equations have been of the order of 0.01 to 0.02, except in the night 8/9 where the rms reaches up to 0.06. Details of exposure times per filter and night can be found in Table 1 (click here).

   

5/6/7 8/9 9/10 11/12 12/13

Note: The columns give the

  
Figure 5: a)   The V vs. B-V color-magnitude diagram. The Schmidt-Kaler (1982) Zams is superposed according to the distance modulus obtained in Sect. 3.2. Symbols as in Fig. 4.   b)   The V vs. U-B color-magnitude diagram. Symbols as in Fig. 4

  
Figure 6: a)   The V vs. V-I color-magnitude diagram. Symbols as in Fig. 4.  b)   The B-V vs. V-I diagram. Solid lines indicate the intrinsic colors for stars of luminosities V and III according to Cousins (1978). The dotted lines show the path of the reddening with slopes 1.24 (R=3.1) (Dean et al. 1978) and 1.45 (R=3.6) respectively Symbols as in Fig. 4

Table 2 lists 1201 stars with available CCD data containing the identification numbers in Col. 1, x and y coordinates in the second and third columns respectively and magnitudes and colors in the remaining columns. The accuracy of CCD data is given in Figs. 3 (click here)a-e where color and magnitude photometric errors from DAOPHOT are plotted against V.