A&A Supplement series, Vol 122, April I 1997, 193-199
Received February 23; accepted June 15, 1996
H. Markov - T. Valtchev - J. Borissova - V. Golev
Send offprint request: H. Markov
Institute of Astronomy, Bulgarian Academy of Sciences, 72 Tsarigradsko chaussèe, BG-1784 Sofia, Bulgaria
Astron. Obs. of University of Sofia, P.O. box 36, BG-1504 Sofia, Bulgaria
In our effort to study the post-main-sequence evolution of the globular cluster stars we developed some procedures which were designed to perform stellar photometry in moderately crowded fields by using a personal computer. This paper presents a description of an algorithm for cleaning close stellar companions which is included in our data processing. The main goal is to establish how the cleaning procedure biases the accuracy of the derived photometry. As a test for our data reduction, BV photographic photometry for nearly 500 stars, down to 0.6 arcmin from the center of globular cluster has been performed. In addition, we present a comparison of our photometric results with those obtained with the DAOPHOT package for the same cluster region. We also discuss the ability of three kinds of magnitudes - based on Gaussian fits, the use of synthetic apertures and the output of the DAOPHOT package - to reveal morphological features in the color-magnitude diagram.
keywords: globular clusters: individual: M 5 -- technique: image processing