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2. Observations and reductions

UBV photoelectric observations of a total of 175 stars in the field of NGC2323 were collected with the University of Toronto's 0.6 m telescope at Las Campanas Observatory (LCO) and with the Cerro Tololo Inter-American Observatory (CTIO) 0.9-m telescope, over a large number of photometric nights from March 1984 to February 1987. Dry-ice cooled RCA1P21 and Ga-As RCA31034 phototubes in single channel photometers with pulse-counting electronics were used for all observations at LCO and CTIO, respectively. Mean extinction coefficients at both observatories were employed and nightly observations of about 13-17 standard stars taken from the lists of Cousins (1973, 1974), Landolt (1973) and Graham (1982) were used to transform instrumental magnitudes into the UBV standard system. External and internal mean errors are nearly similar to those in previous papers (e.g., Clariá et al. 1991). Typically tex2html_wrap_inline1352 mag, tex2html_wrap_inline1354 mag and tex2html_wrap_inline1356 mag for V<12 mag, increasing to 0.018, 0.022 and 0.027 for V>12 mag, respectively. Table 1 lists V magnitudes, U-B and B-V colours, and the number of measurements performed in each filter for all the stars numbered in Fig. 1 (click here), while Table 2 includes the correlation of identifications with other authors.

Figure 1: Identification chart for stars in NGC2323

We compare our photoelectric photometry with the most extensive and recent photographic survey carried out by Mostafa et al. (1983). As can be seen in Fig. 2 (click here), there is no colour dependence between the magnitude scales, an appreciable scatter being the principal feature. The resulting mean differences (in the sense Mostafa et al. minus this study) for a total of 66 stars in common are tex2html_wrap_inline1368, tex2html_wrap_inline1370 and tex2html_wrap_inline1372 for the U, B and V magnitudes, respectively.

Figure 2: Magnitude differences (Mostafa et al. minus this study) versus photoelectric colours

In addition, observations of five stars in the DDO system were carried out with the purpose of obtaining additional information about their reddening, probable membership, luminosity class, and metal content. These measurements were made in April 1985 using the CTIO 0.9-m telescope with an tex2html_wrap_inline1380 photomultiplier. The transformation to the DDO standard system was done by nightly observing between 12 to 16 standards from the list of McClure (1976). All the measurements were performed with a single-channel photometer and pulse counting electronics. The resulting external mean errors in the DDO colours were found to be about or slightly smaller than 0.01 mag. In Table 3 (click here) we list the DDO colours obtained for each star and the number n of individual observations.


Star C(45-48) C(42-45) C(41-42) n
12 1.402 1.140 0.220 2
tex2html_wrap_inline13920.002 tex2html_wrap_inline13920.002 tex2html_wrap_inline13920.016
38 1.254 1.009 0.303 2
0.007 0.004 0.017
42 1.221 0.972 0.217 2
0.011 0.005 0.022
53 1.496 1.394 0.230 2
0.006 0.013 0.016
121 1.486 1.307 0.289 2
0.008 0.020 0.002

Table 3: DDO data

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