UBVRI CCD photometry of the old open cluster NGC 6253

Abstract

We present UBVRI photometry for the old open cluster NGC 6253. From comparison of the observed colour-magnitude diagrams with simulations based on stellar evolutionary models we derive in a self consistent way reddening, distance, and age of the cluster: E(B-V) = 0.23-0.32, (m-M)$_0$ = 10.9$\pm$0.1, metallicity roughly double than solar, and age $\simeq$ 3 Gyr. The cluster has a binary sequence, discernible even through the field contamination, suggesting that about 1/3 of the cluster members belong to binary, or multiple, systems.

13 pages, plain LaTeX, uses mn.sty, 12 .ps figures, also available at http://www.bo.astro.it/bap/BAPhome.html or from ftp://boas3.bo.astro.it/bap/files/ (files bap96-31-fig*.ps) -- to be published by MNRAS (revised addresses for figures)