CCD photometry of the old open cluster Collinder 261

Abstract

We present UBVI photometry for the old open cluster Collinder 261. 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)=0.25$-$0.34, (m-M)$_0$=11.7-12.0, and age=7$-$8 Gyr or 9$-$11 Gyr, depending on the adopted stellar tracks. The models in better agreement with the data turn out to have metallicity at most solar.