Global survey of star clusters in the Milky Way: The open cluster distance scale

Abstract

AbstractWe present the Milky Way Star Clusters (MWSC) survey based on 470 million stars extracted from the all-sky catalogues PPMXL and 2mass. The target list comprises 3784 entries and includes all open and globular clusters, as well as all cluster candidates, known at present. By means of a combined photometric/astrometric pipeline process, we determine individual membership probabilities for cluster stars and provide fundamental cluster parameters such as cluster centre coordinates, mean proper motions, radial velocity, distance, reddening, age and tidal radius. This sample includes ~ 700 clusters with fundamental parameters based on optical data and offers a good opportunity for a comparison of the near-infrared (NIR) and optical cluster distance scales. We find that distances and reddening values obtained from the colour–magnitude diagrams (CMDs) in the NIR agree well with earlier distance estimates based on optical CMDs. These newly obtained homogeneous distances, together with the other cluster parameters, allow us to study the properties of the open cluster population in the Galactic disk.