Binary and Grouped Open Clusters: A New Catalogue

Abstract

Understanding the formation and evolution of star clusters in the Milky Way requires precise identification of clusters that form binary or multiple systems. Such systems offer valuable insight into the dynamical processes and interactions that influence cluster evolution. Aims. This study aims to identify and classify star clusters in the Milky Way as part of double or multiple systems. Specifically, we seek to detect clusters that form gravitationally bound pairs or groups of clusters and distinguish between different types of interactions based on their physical properties and spatial distributions. Methods. We used the extensive star cluster database of Hunt & Reffert (2023, 2024), which includes 7167 clusters. By estimating the tidal forces acting on each cluster through the tidal factor (TF), and considering only close neighbours (within 50 pc), we identified a total of 2170 star clusters forming part of double and multiple systems. Pairs were classified as Binaries (B), Capture pairs (C), or Optical pairs (O/Oa) based on proper motion distributions, cluster ages, and color-magnitude diagrams. Results. Our analysis identified 617 paired systems, which were successfully classified using our scheme. Additionally, we found 261 groups of star clusters, each with three or more members, further supporting the presence of multiple systems within the Milky Way that exhibit significant tidal interactions. Conclusions. The method presented provides an improved approach for identifying star clusters that share the same spatial volume and experience notable tidal interactions.