Peculiarities of the Internal Photometrical Calibration Method Using Density Stellar Profiles

Extract

On photographic plates taken for the purposes of classical stellar photometry (using a standard stellar sequence) there usually is no external photometrical calibration scale, neither a wedge nor spots; and hence the transition to relative intensity is a problem. The construction of a characteristic curve D(I) (hereafter CHC) by combining density profiles of several standard stars is a perfect solution of this task (Agnelli et al. 1979; de Vaucouleurs 1984). We have developed this method in order to obtain internal photometric calibrations for a large number of plates taken at the RC focus of the 2m telescope (F/8, scale 12.86) at the National Astronomical Observatory (NAO); these do not have any photometrical calibration. Our long term project provides UBV stellar photometry in the central regions of some globular clusters — M5, M10, M12, M56, M71, for which we have good collections of short exposure plates. The task also requires a background determination which can be done precisely only in relative intensities. We apply the method using Arp's UBV standard sequence in M5 globular cluster. In our investigation we demonstrate some peculiarities of the method: