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

TL;DR

This study characterizes three old open clusters in the Galactic anti-centre, determining their ages, reddening, distances, and metallicities using synthetic CMD analysis, thereby expanding the BOCCE project's database.

Contribution

It provides new detailed parameters for Berkeley 27, 34, and 36, adding valuable data on old open clusters in the outer Galaxy.

Findings

Berkeley 27 is 1.5-1.7 Gyr old with E(B-V)=0.40-0.50.

Berkeley 34 is 2.1-2.5 Gyr old with E(B-V)=0.57-0.64.

Berkeley 36 is 7.0-7.5 Gyr old with E(B-V)~0.50.

Abstract

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 anti-centre direction. All of them were observed with SUSI2@NTT 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 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) 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 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 sub-solar metallicity in accord with their position in the outer Galactic disc.