Breaking the curtain: the old open cluster VdB-Hagen 67 in the background of the Vela Molecular Ridge

Abstract

We present optical and infrared photometry for VdB-Hagen 67, an overlooked old open cluster located at ⁠, J2000.0) in the fourth Galactic quadrant, in the direction of the Vela Molecular Ridge. VdB-Hagen 67 is immersed in a dense stellar field which is characterized by highly patchy extinction, and AV in the line of sight to the cluster is larger than 3 mag. The cluster looks symmetric and it clearly stands out from the general Galactic field. By means of a star count analysis, both in the optical and IR, we have estimated that its radius is of about 2 arcmin. Before this study, only very general information was available for this cluster, but here we have determined its fundamental parameters. The age of VdB-Hagen 67 has been estimated, both empirically and with theoretical isochrones, and turns out to be about 1.3 Gyr. The difficulty to separate cluster members from interlopers prevented us from estimating its metallicity. No traces of subgiant or red-giant branch stars are visible in its field-star-decontaminated colour–magnitude diagrams; VdB-Hagen 67 is an old, poorly populated, star cluster on the verge of dissolving into the general Galactic field. We derive a heliocentric distance of ∼7.5 kpc and a galactocentric distance of ∼11.5 kpc. With the exception of FSR 1415 at 8.6 kpc, and with an age of ∼2.5 Gyr, no other old clusters are known so far from the Sun in this Galactic sector. We argue that in this region of the Galactic plane several other distant clusters of this age have to exist, but have not been unravelled mainly because of the significant extinction produced by the dense Vela Molecular Ridge.