J/A+A/710/A4 Missing pairs in open cluster catalogs (Hu+, 2026)
Missing pairs in open cluster catalogs.
Hu Q., Cai Y., Soubiran C., Dai Y., Li Y., Luo Y., Qin M.
<Astron. Astrophys. 710, A4 (2026)>
=2026A&A...710A...4H 2026A&A...710A...4H (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Clusters, open ; Optical
Keywords: open clusters and associations: general
Abstract:
Open clusters (OCs) in our Galaxy can be found in pairs, possibly
forming physical binaries, or in groups. These objects offer unique
insights into the process of star formation and testify to the
dynamical interactions at local and galactic scales. Therefore,
building as complete a census as possible is a valuable endeavor.
This work is aimed at identifying and characterizing new OC pair
candidates that had been overlooked in previous studies.
Two recent comprehensive catalogs were cross-matched to identify OCs
in the first catalog that had been missing from the second one. From
this list, counterparts in the second catalog were searched within a
3D distance of 50 pc. Candidate pairs were then selected by applying
constraints on the tangential velocity (TV) difference. An orbital
integration was performed to assess gravitational binding. The
similarity in terms of the radial velocity (RV) and age was evaluated.
We identified seven isolated binary cluster candidates, comprising two
likely bound systems with stable orbits over 100 Myr; two pairs with a
possible common origin but lacking RV confirmation; and three pairs
with significant velocity discrepancies, suggesting they are unbound
or in transitional states. We also identified six cluster group
candidates, while refining the membership of known complexes such as
UBC_672 and NGC_1977, and discovering a new group around FSR_0198.
Notably, the UBC_392 group exhibits coherent proper motions but
inconsistent RVs and large age spreads, indicating that it is not
gravitationally bound. Additionally, we reconciled 15 clusters with
discrepant nomenclature between the two catalogs.
Multi-catalog integration combined with kinematic and dynamical
validation is essential for establishing a complete census of Galactic
cluster pairs. Our findings have effectively expanded the known binary
cluster sample and provided refined targets for future studies.
Description:
This paper presents a systematic search for missing multiple cluster
systems by cross-matching the CG20 (Cantat-Gaudin & Anders, 2020,
J/A+A/633/A99) and H&R24 (Hunt & Reffert 2024, Cat. J/A+A/686/A42)
catalogs. We identify 83 OCs from CG20 that are truly missing in
H&R24 and provide their updated parameters based on Gaia DR3.
Additionally, we discover seven new binary cluster candidates and
four multiple cluster systems through 3D position and kinematic analysis.
Table : Parameters of 83 CG20 OCs missing in H&R24, based on Gaia DR3
Table A: Merged astrometric, kinematic and physical parameters of 32
cluster pair candidates (merged Tables A.1 and A.2 from the paper)
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table.dat 99 83 Parameters of 83 CG20 OCs missing in H&R24
tablea.dat 200 32 Merged parameters of 32 cluster pairs
(tables A1 + A2)
--------------------------------------------------------------------------------
See also:
J/A+A/633/A99 : Gaia DR2 open clusters in the Milky Way. II
(Cantat-Gaudin+, 2020)
J/A+A/686/A42 : Improving the open cluster census. III. (Hunt+, 2024)
Byte-by-byte Description of file: table.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 A13 --- Cluster Cluster name in CG20 (1)
16- 18 I3 --- N Number of member stars from CG20 (1)
21- 28 F8.4 deg RAdeg Median right ascension (J2000)
31- 38 F8.4 deg DEdeg Median declination (J2000)
41- 46 F6.4 mas plx Median parallax
49- 54 F6.4 mas e_plx Uncertainty (MAD) of plx
57- 61 F5.2 mas/yr pmRA Median proper motion in RA
64- 67 F4.2 mas/yr e_pmRA Uncertainty (MAD) of pmRA
70- 74 F5.2 mas/yr pmDE Median proper motion in DEC
77- 80 F4.2 mas/yr e_pmDE Uncertainty (MAD) of pmDE
83- 88 F6.1 km/s RV ? Median radial velocity
91- 95 F5.1 km/s e_RV ? Uncertainty (MAD) of RV
98- 99 I2 --- n_RV Number of members with a RV
--------------------------------------------------------------------------------
Note (1): CG20: Cantat-Gaudin & Anders, Cat. J/A+A/633/A99/
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tablea.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- ClusterCG20 Cluster name in CG20 (1)
15- 27 A13 --- ClusterHR24 Cluster name in H&R24 (2)
30- 34 F5.2 mas/yr pmRACG20 Median proper motion in RA for CG20 (1)
37- 40 F4.2 mas/yr e_pmRACG20 Uncertainty (MAD) of pmRA for CG20 (1)
43- 48 F6.2 mas/yr pmRAHR24 Proper motion in RA from H&R24 (2)
51- 54 F4.2 mas/yr e_pmRAHR24 Error of pmRA from H&R24 (2)
57- 61 F5.2 mas/yr pmDECG20 Median proper motion in Dec for CG20 (1)
64- 67 F4.2 mas/yr e_pmDECG20 Uncertainty (MAD) of pmDE for CG20 (1)
70- 74 F5.2 mas/yr pmDEHR24 Proper motion in Dec from H&R24 (2)
77- 80 F4.2 mas/yr e_pmDEHR24 Error of pmDE from H&R24 (2)
83- 86 F4.2 mas plxCG20 Median parallax for CG20 (1)
89- 92 F4.2 mas e_plxCG20 Uncertainty (MAD) of parallax for CG20 (1)
95- 98 F4.2 mas plxHR24 Parallax from H&R24 (2)
101-105 F5.3 mas e_plxHR24 Error of parallax from H&R24 (2)
108-112 F5.2 pc Delta3D 3D separation between the two clusters
115-120 F6.2 km/s RVCG20 ? Median radial velocity for CG20 (1)
123-127 F5.2 km/s e_RVCG20 ? Uncertainty (MAD) of RV for CG20 (1)
130-131 I2 --- NRVCG20 Number of stars with RV for CG20 (1)
134-139 F6.2 km/s RVHR24 ? Radial velocity from H&R24 (2)
142-146 F5.2 km/s e_RVHR24 ? Error of RV from H&R24 (2)
149-150 I2 --- NRVHR24 Number of stars with RV for H&R24 (2)
153-157 F5.2 km/s TVCG20 Median tangential velocity for CG20 (1)
160-163 F4.2 km/s e_TVCG20 Uncertainty (MAD) of TV for CG20 (1)
166-170 F5.2 km/s TVHR24 Median tangential velocity for H&R24 (2)
173-176 F4.2 km/s e_TVHR24 Uncertainty (MAD) of TV for H&R24 (2)
179-182 F4.2 [yr] logAgeCG20 ? Logarithmic age from CG20 (1)
185-188 F4.2 [yr] logAgeHR24 Logarithmic the 50th age from H&R24 (2)
191-194 F4.2 [yr] b_logAgeHR24 Logarithmic the 16th age from H&R24 (2)
197-200 F4.2 [yr] B_logAgeHR24 Logarithmic the 84th age from H&R24 (2)
--------------------------------------------------------------------------------
Note (1): CG20: Cantat-Gaudin & Anders., Cat. J/A+A/633/A99.
Note (2): H&R24: Hunt & Reffert, Cat. J/A+A/686/A42.
--------------------------------------------------------------------------------
Acknowledgements:
Qingshun Hu, qingshun0801(at)163.com
License: CC-BY-4.0
(End) Qingshun Hu [Bordeaux, France], Patricia Vannier [CDS] 22-Apr-2026