A study of wide binary open clusters in the Milky Way from Gaia DR3

Institute of Astronomy and Information, Dali University, Dali 671003, China

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Received: 27 November 2025
Accepted: 1 January 2026

Abstract

Context. Some Galactic open clusters may form in binary or multiple systems. Binary clusters provide direct constraints on the clustered star-formation process, the gravitational potential of the Galactic disk, and the internal dynamical evolution of star clusters. However, only dozens of gravitationally bound binary clusters have been firmly recognized so far.

Aims. As a part of the Dali Binary Cluster Project (DL-BCP), we searched for the wide binary open clusters (WBOCs) in the Milky Way using the data from Gaia Data Release 3 (Gaia DR3), and derived their fundamental astrophysical parameters and possible orbital evolution.

Methods. We started from a Gaia-based open cluster catalog of 7167 clusters, and selected cluster pairs with separations of less than 100 pc and larger than the sum of the radii of sub-clusters at first. Then we checked whether the sub-clusters of every pair are gravitationally bound. Gravitationally bound pairs with two gravitationally bound sub-clusters are regarded as WBOCs. The ages, reddenings, and metallicities of their sub-clusters were re-derived by isochrone fitting in the (G_BP–G_RP) versus G color–magnitude diagram. Three-dimensional orbits were integrated in a three-component axisymmetric Galactic potential for the following 500 Myr and for the period before now.

Results. We finally identified four new WBOCs and two known WBOCs. Two certain primordial binary open clusters (PBOCs) were found and studied. The cluster masses of these WBOCs range from 131.13 M_⊙ to 1155.86 M_⊙. Age differences between the two components are ≤40 Myr for all of these WBOCs, and their separations vary from 20 to near 100 pc. The result enlarges the currently known BOC sample and provides a uniform set of fundamental parameters and orbital analysis for six WBOCs.