2001A&A...372...71D

We present multicolour CCD photometry for two poorly studied open clusters (King 5 and Be 20). Photometry for a field near King 5 was also carried out to estimate the contamination by field stars. The colour magnitude diagrams (CMD) of the clusters show a well defined main sequence extending to the limit of the photometry, V≃20mag. The reddening for King 5, estimated from the colour-colour diagram, is ∼0.82, whereas that for Be 20 as estimated by comparing theoretical main-sequence (MS) with the observed MS is 0.10. The morphology of the CMDs indicates that these clusters are old. The CMD of Be 20 shows a globular cluster-like horizontal branch. In case of King 5 the comparison of observational CMDs with the standard isochrones of VandenBerg (1985ApJS...58..711V) indicates an apparent discrepancy between the shape of the turnoff and isochrones. The CMDs of King 5 seem to be better understood in terms of stellar models with convective overshoot. The comparison of the CMDs with the stellar models by Bertelli et al. (1985A&A...150...33B) with convective overshoot produces a good fit for a metallicity Z=0.008 and an age of 1Gyr for King 5 and 5Gyr for Be 20. An apparent distance modulus (m-M)=14.0 and 15.1 has been estimated for King 5 and Be 20 respectively. They correspond to a distance of 1900±100pc and 9026±480pc, respectively. The radial density distribution in King 5 indicates that there is an excess of low mass stars in the outer region of the cluster, whereas the density distribution in Be 20 shows a good fit with the empirical King (1962AJ.....67..471K) model. For both clusters, observations have also been carried out to search for variable stars.