Three new bricks in the wall: Berkeley 23, Berkeley 31 and King 8

A comprehensive census of Galactic open cluster properties places unique constraints on the Galactic disc structure and evolution. In this framework, we investigate the evolutionary status of three poorly studied open clusters, Berkeley 31, Berkeley 23 and King 8, all located in the Galactic anticentre direction. To this aim, we make use of deep Large Binocular Telescope observations, reaching more than 6 mag below the main-sequence turn-off. To determine the cluster parameters, namely age, metallicity, distance, reddening and binary fraction, we compare the observational colour–magnitude diagrams (CMDs) with a library of synthetic CMDs generated with different evolutionary sets (Padova, FRANEC and FST) and metallicities. We find that Berkeley 31 is relatively old, with an age between 2.3 and 2.9 Gyr, and rather high above the Galactic plane, at about 700 pc. Berkeley 23 and King 8 are younger, with best-fitting ages in the range 1.1–1.3 and 0.8–1.3 Gyr, respectively. The position above the Galactic plane is about 500–600 pc for the former and 200 pc for the latter. Although a spectroscopic confirmation is needed, our analysis suggests a subsolar metallicity for all three clusters.

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