5 Description of the sample

The astrometric positions were used to assign individual identifiers to the stars in our sample. First of all, the different fields were numbered from 1 to 11 following the order of the increasing mean right ascension. Inside each field, stars were numbered following the order of the increasing right ascension.

Figure 17: Identification chart of field #10 around Landolt stars SA 100 267 (labelled "A"), SA 100 269 (labelled "B") and SA 100 162 (labelled "C")

Figure 18: Identification chart of field #11 around Landolt stars SA 114 750 (labelled "A") and SA 114 654 (labelled "B")

Table 4 contains both data sets #1 and #2. This table (available also in electronic form) contains: field number and star number inside that field, J2000.0 equatorial coordinates, photometry (V, B-V, U-B, V-R, V-I, each quantity followed by its internal error), number of observational runs in which useful data were obtained, number of useful measurements in V, cross-identification with USNO-A V2.0 catalogue, and notes. Notes give further cross-identifications with AC 2000, Tycho and Hipparcos (ESA 1997) catalogues (matches with Tycho and Hipparcos are directly drawn from AC 2000) and the Selected Areas. Stars belonging to set #2 are marked with an asterisk in the notes. Stars from set #1 are not marked.

The colour index and apparent visual magnitude distributions of the stars included in sets #1 and #2 are shown in Figs. 1 to 5. The photometric errors as a function of apparent visual magnitude are given in Fig. 6 for set #1 and in Fig. 7 for set #2.

Table 5 includes our photometric values for several Landolt standard stars. Individual differences with Landolt's photometry are given in Table 6. The rms of the residuals with the values given by Landolt (1983, 1992) are $\sigma_V= 0.009$ mag, $\sigma_{B-V}=0.014$ mag, $\sigma_{U-B}=0.032$ mag, $\sigma_{V-R}=0.005$ mag and $\sigma_{V-I}=0.013$ mag, which are of the same order as the residuals quoted in Table 3.

Figures 8 to 18 display identification charts for our 11 fields. Figure captions identify each field by its number, and the stars in our sample are labelled with the same numbering system used in Table 4. Landolt stars are marked with capital letters, and their identifiers are given in figure captions.