VI photometry of NGC 6397

The data taken in service mode in 1999 (field2, RA=17 41 03.5, DE=-53 45 36) and in 2000 (field1, RA=17 41 14.3, DE=-53 44 27.6) were retrieved electronically from the ESO-STECF archive (proposals: 63.H-0721(A) and 65.H-0531(B)). The resulting V, V-I photometry reachs a limiting magnitude of V~27.

As our fields were affected by a large number of saturated stars and, as the photometric procedures can include those peaks in the final photometric catalogue, we decided to eliminate from the catalogue the spurious identifications before performing the data analysis. In this way, a total of 15081 and 11161 objects were detected, respectively, in the fields f1 and f2. We used the 7059 objects in common between these two fields to optimize our photometry by computing a weighted average between the values of the magnitudes of a given star in each catalogue and to transform the frame coordinates to a common coordinate system referred to the field f2.