UBGVRI photometry for the open cluster NGC 2506 is presented. 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)=0-0.07, (m-M)o = 12.6, age = 1.5-2.2 Gyr. The cluster shows a well definite secondary sequence, suggesting that binary systems constitute about 20 % of the cluster members visible in the colour-magnitude diagram.
@article{arxiv.astro-ph/9707076,
title = {Old open clusters: UBGVRI photometry of NGC 2506},
author = {G. Marconi and D. Hamilton and M. Tosi and A. Bragaglia},
journal= {arXiv preprint arXiv:astro-ph/9707076},
year = {2015}
}