J/A+A/701/A48 Binary clusters in the Galactic disk (Liu+, 2025)
Binary clusters in the Galactic disk.
I: Systematic identification and classification using Gaia DR3.
Liu G., Zhang Y., Zhong J., Qin S., Jiang Y., Chen L.
<Astron. Astrophys. 701, A48 (2025)>
=2025A&A...701A..48L 2025A&A...701A..48L (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Clusters, open ; Optical
Keywords: open clusters and associations: general
Abstract:
Binary clusters (BCs) provide valuable observational constraints on
the formation, early evolution, and dynamical interactions of star
clusters. Their spatial and kinematic associations offer unique
insights into the hierarchical star formation process and tidal
interactions within the Galactic disk.
We aim to identify and classify BCs using high-precision astrometric
and kinematic data, and to investigate their physical properties,
mutual gravitational interactions, and formation rates.
We used a comprehensive star cluster catalog that contains 4084
high-quality clusters. Based on spatial and kinematic proximity, we
identified 400 cluster pairs involving 686 unique clusters. These
pairs were classified into three types: primordial BCs, systems formed
through tidal capture or resonant trapping, and hyperbolic encounter
pairs. For each system, we calculated the tidal factor to quantify the
strength of mutual tidal interaction. Additionally, we constructed
multi-cluster systems by identifying transitive connections among
cluster pairs.
Among the 400 identified cluster pairs, nearly 60.8% (243 pairs) are
probably primordial BCs, exhibiting both similar ages and motions.
This supports a scenario where they formed together in the same giant
molecular cloud. We find that 82.5% of the cluster pairs have strong
mutual tidal forces. In addition, 278 star clusters are identified as
members of 82 multi-cluster systems, including 27 newly reported
groups. Cross-matching with the literature confirms the recovery of
previously reported systems and leads to the discovery of 268 new
cluster pairs. In our sample, about 16.8% of star clusters are
involved in some type of interaction with another cluster, and 9.94%
of star clusters are likely born in primordial BCs.
Our results provide a comprehensive, homogeneously identified sample
of Galactic BCs. The high fraction of primordial BCs and their mutual
tidal interaction suggest that cluster formation in pairs is a main
outcome of star formation. This work offers new observational
constraints on the formation and dynamical evolution of multiple star
cluster systems.
Description:
We present a catalog of binary and multiple open clusters (OCs) in the
Milky Way, identified from a homogeneous, high-quality sample of 4084
OCs in Hunt & Reffert (2024A&A...686A..42H 2024A&A...686A..42H, Cat. J/A+A/686/A42) with
Gaia DR3 kinematics. We identify 400 candidate binary cluster (BC)
pairs, classified as primordial binaries (PBC), tidal capture/resonant
pairs (TBC), or hyperbolic encounters (HEP), along with 82
multi-cluster systems (including 27 newly discovered groups). About
16.8% of OCs are interacting, with 9.94% likely formed as PBCs. This
work adds 268 new BC pairs and provides a homogeneous dataset for
studies of cluster formation and dynamical evolution.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 99 800 Binary cluster candidates
table3.dat 93 278 Multiple system candidates
--------------------------------------------------------------------------------
See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/A+A/673/A114 : Improving the open cluster census. II. (Hunt+, 2023)
J/A+A/686/A42 : Improving the open cluster census. III. (Hunt+, 2024)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Pair [1/400] Pair identification number
5- 8 I4 --- IDHR24 [1/7166] Cluster ID from Hunt et al.
(2024, Cat. J/A+A/686/A42)
10- 29 A20 --- Cluster Star cluster name
31- 36 F6.3 pc sep3D The 3D separation between clusters,
38- 41 F4.2 km/s Dvt Tangential velocity difference
43- 48 F6.2 km/s Dv3d ? 3D velocity differences between clusters
50- 55 F6.2 Myr Dage Age difference of the pair clusters
57- 60 F4.2 [yr] logt Cluster age from isochrone fitting
62- 67 F6.3 mag DM Distance modulus from isochrone fitting
69- 73 F5.3 mag E(B-V) Reddening from isochrone fitting
75- 77 A3 --- Type Pair classification
79- 99 A21 --- overlap Previous references (1)
--------------------------------------------------------------------------------
Note (1): References as follows:
Palma_2025 = Palma et al., 2025A&A...693A.218P 2025A&A...693A.218P
Li_2024 = Li et al., 2024arXiv240502530L 2024arXiv240502530L
Qin_2023 = Qin et al., 2023ApJS..265...12Q 2023ApJS..265...12Q
Song_2022 = Song et al., 2022A&A...666A..75S 2022A&A...666A..75S
Angelo_2022 = Angelo et al., 2022MNRAS.510.5695A 2022MNRAS.510.5695A
Piecka_2021 = Piecka & Paunzen, 2021A&A...649A..54P 2021A&A...649A..54P
Casado_2021a = Casado, 2021RAA....21..117C 2021RAA....21..117C
Casado_2021b = Casado, 2021ARep...65..755C 2021ARep...65..755C
LP_2019 = Liu & Pang, 2019ApJS..245...32L 2019ApJS..245...32L, Cat. J/ApJS/245/32
Soubiran_2019 = Soubiran et al., 2019A&A...623C...2S 2019A&A...623C...2S, Cat. J/A+A/619/A155
Conrad_2017 = Conrad et al., 2017A&A...600A.106C 2017A&A...600A.106C, Cat. J/A+A/600/A106
deLaFuenteMarcos = de la Fuente Marcos & de la Fuente Marcos,
2009A&A...500L..13D 2009A&A...500L..13D
Subramaniam_1995 = Subramaniam et al., 1995A&A...302...86S 1995A&A...302...86S
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Group [1/82] Group identification number
4- 6 I3 --- Pair [1/400] Pair identification number
8- 11 I4 --- IDHR24 [1/7163] Cluster ID (1)
13- 32 A20 --- Cluster Cluster name
34- 39 F6.2 deg RAdeg Right Ascension (ICRS) at Ep=2016.0 (1)
41- 46 F6.2 deg DEdeg Declination (ICRS) at Ep=2016.0 (1)
48- 53 F6.3 mas Plx Parallax (1)
55- 60 F6.2 mas/yr pmRA Proper motion in RA*cos(Dec) (1)
62- 67 F6.2 mas/yr pmDE Proper motion in Dec (1)
69- 75 F7.2 km/s RV ? Radial velocity (1)
77- 80 F4.2 --- logt Cluster age from isochrone fitting
82- 87 F6.3 mag DM Distance modulus from isochrone fitting
89- 93 F5.3 mag E(B-V) Reddening from isochrone fitting
--------------------------------------------------------------------------------
Note (1): from Hunt et al. (2024, Cat. J/A+A/686/A42).
--------------------------------------------------------------------------------
Acknowledgements:
Guimei Liu, liuguimei20(at)mails.ucas.ac.cn
Yu Zhang, zhangyu(at)xao.ac.cn
Jing Zhong, jzhong(at)shao.ac.cn
(End) Guimei Liu [XAO], Patricia Vannier [CDS] 11-Aug-2025