Fundamental parameters of six neglected old open clusters

Abstract

In this paper, we present the first BV I CCD photometry of six overlooked old open clusters (Berkeley 44, NGC 6827, Berkeley 52, Berkeley 56, Skiff 1 and Berkeley 5) and derive estimates of their fundamental parameters by using isochrones from the Padova library. We found that all the clusters are older than the Hyades, with ages ranging from 0.8 Gyr (NGC 6827 and Berkeley 5) to 4.0 Gyr (Berkeley 56). The latter is one of the old open clusters with the largest heliocentric distance. In the field of Skiff 1, we recognize a faint blue main sequence identical to the one found in the background of open clusters in the second and third Galactic quadrant, and routinely attributed to the Canis Major accretion event. We use the synthetic colour-magnitude diagram method and a Galactic model to show that this population can be easily interpreted as a thick disc and halo population towards Skiff 1. We finally revise the age distribution of the old open clusters, showing that the previously suggested peak at 5 Gyr looses importance as additional old clusters are discovered.