Berkeley 29, the most distant old open cluster

Abstract

We present CCD BVI photometry of the old open cluster (OC) Berkeley 29, located in the anticentre direction. Using the synthetic colour-magnitude diagrams (CMDs) technique we estimate at the same time its age, reddening, distance and approximate metallicity using three types of stellar evolutionary tracks. The best solutions give: age = 3.4 or 3.7 Gyr, (m - M) 0 = 15.6 or 15.8 with E(B - V) = 0.13 or 0.10, and metallicity lower than solar (Z = 0.006 or 0.004), depending on the adopted stellar models. Using these derived values, Be 29 turns out to be the most distant OC known, with Galactocentric distance R GC = 21.4 to 22.6 kpc. Hence, Be 29 qualitatively follows both the age-metallicity relation and the metal abundance gradient typical of Galactic disc objects. The cluster position and radial velocity, however, appear to link Be 29 to the family of the Canis Maior debris.