2012MNRAS.424.1132D

In this paper, we present the investigation of the evolutionary status of three open clusters: Berkeley 27, Berkeley 34 and Berkeley 36, all located in the Galactic anticentre direction. All of them were observed with SUperb Seeing Imager 2 at the New Technology Telescope using the Bessel B, V and I filters. The cluster parameters have been obtained using the synthetic colour–magnitude diagram (CMD) method, i.e. the direct comparison of the observational CMDs with a library of synthetic CMDs generated with different evolutionary sets (Padova, FRANEC and FST). This analysis shows that Berkeley 27 has an age between 1.5 and 1.7 Gyr, a reddening E(B-V) in the range 0.40–0.50 and a distance modulus (m-M)₀ between 13.1 and 13.3; Berkeley 34 is older with an age in the range 2.1–2.5 Gyr, E(B-V) between 0.57 and 0.64 and (m-M)₀ between 14.1 and 14.3; Berkeley 36, with an age between 7.0 and 7.5 Gyr, has a reddening of E(B-V) ∼ 0.50 and a distance modulus (m-M)₀ between 13.1 and 13.2. For all the clusters, our analysis suggests a subsolar metallicity in accord with their position in the outer Galactic disc.

This work is based on data collected at the European Southern Observatory (ESO) telescopes under programme 076.D-0119.