The anticentre old open clusters Berkeley 27, Berkeley 34, and Berkeley 36: new additions to the BOCCE project

摘要

In this paper we present the investigation of the evolutionary status ofthree open clusters: Berkeley 27, Berkeley 34, and Berkeley 36, all located inthe Galactic anti-centre direction. All of them were observed with SUSI2@NTTusing the Bessel B, V, and I filters. The cluster parameters have been obtainedusing the synthetic colour-magnitude diagram (CMD) method i.e. the directcomparison of the observational CMDs with a library of synthetic CMDs generatedwith different evolutionary sets (Padova, FRANEC, and FST). This analysis showsthat Berkeley 27 has an age between 1.5 and 1.7 Gyr, a reddening E(B-V) in therange 0.40 and 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 and 2.5 Gyr, E(B-V) between0.57 and 0.64, and (m-M)_0 between 14.1 and 14.3; Berkeley 36, with an agebetween 7.0 and 7.5 Gyr, has a reddening 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 asub-solar metallicity in accord with their position in the outer Galactic disc.