Old open clusters: UBGVRI photometry of NGC 2506

Abstract
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 the reddening, distance and age of the cluster. E (BV) = 0−0.07, (mM)0 = 12.6 ± 0.1, τ = 1.5–2.2 Gyr. The cluster shows a well-defined secondary sequence, suggesting that binary systems constitute ≳ 20 per cent of the cluster members visible in the colour-magnitude diagram.
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