J/A+A/708/A238 Morphological stability of open clusters (Li+, 2026)
The morphological stability of open clusters: A new 2D perspective.
Li Y., Hu Q., Cai Y., Dai Y., Qin M., Luo Y.
<Astron. Astrophys. 708, A238 (2026)>
=2026A&A...708A.238L 2026A&A...708A.238L (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Clusters, open ; Morphology ; Optical
Keywords: methods: statistical - open clusters and associations: general -
galaxies: star clusters: general
Abstract:
Open clusters (OCs) usually evolve gradually as the number of their
members changes, which can be manifested in their
morphological characteristics. Therefore, the morphological study of
OCs lays the foundation for a better understanding of their formation
and evolutionary processes.
We aim to investigate the morphological stability of 1490 OCs and
further explore the potential change of morphological stability of the
OCs at different spatial positions, using the OC catalog from the
literature.
We delineate the two-dimensional (2D) morphology of OCs quantitatively
in the projection perpendicular to the Galactic disk plane by the rose
diagram and analyze the slope changes between the morphological
stabilities (Score/Souter and Ncore/Nouter) and the number of
members (N) within tidal radii to investigate the influence of the
external environment on the OCs at different spatial positions.
We define for the first time a new morphological stability parameter
Ncore/Nouter, a ratio of member numbers between cluster core and outer
areas within tidal radii, which has a significant positive correlation
against N, with a slope of 1.140±0.039, significantly steeper than
the 0.720±0.026 measured for Score/Souter . This demonstrates that
the stellar density in the core is a more sensitive tracer for
morphological stability than geometry. Spatially, the radial sample
OCs have larger slopes of Ncore/Nouter and Score/Souter against N,
with 1.083±0.116 and 0.733±0.080, respectively, whereas those in
the tangential direction 1.013±0.110 and 0.529±0.075,
respectively, which means that the impact on sample OCs from tidal
forces directed toward the Galactic center is possibly stronger than
that from the shear force caused by the differential rotation of the
Galactic disk. Moreover, the sample OCs within 90° of the Galactic
center, closer to the bar, exhibit slopes below 0.6 of Score /Souter
against N, indicating heightened external perturbations and diminished
stability. But the opposite is true for the side greater than 90°.
Thus, this illustrates that the influence of the external environment
on our sample OCs is asymmetrical. Besides, the sample OCs younger
than 30Myr display a shallow slope of 0.751±0.166, with those older
than 800Myr (1.442±0.128), reflecting that young OCs likely endure
both internal disruptions, such as early dynamical heating weakening
core binding and more severe external disturbances, compared to older
OCs.
The morphological stability of OCs is not only determined by their
gravitational binding, but also strongly modulated by the external
environment in which they are located.
Description:
Complete catalog of parameters for 1490 OCs.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 113 1490 Complete catalog of parameters for 1490 OCs
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- Name Cluster name
16- 21 F6.2 deg RAdeg Right ascension (ICRS)
23- 28 F6.2 deg DEdeg Declination (ICRS)
31- 36 F6.2 pc Rt Mean of the tidal radius
38- 42 F5.2 pc e_Rt Mean of the tidal radius error
44- 47 F4.2 --- Rcore Core radius obtained by rose diagram method
49- 52 F4.2 --- e_Rcore Core radius obtained by rose diagram method
error
54- 60 F7.2 --- N Number of member stars within the tidal
radius of each OC
62- 66 F5.2 --- e_N Number of member stars within the tidal
radius of each OC error
68- 71 F4.2 --- Score Area within the core region of each OC,
πRcore2
73- 76 F4.2 --- e_Score Area within the core region of each OC error
78- 81 F4.2 --- Souter Area within the outer region of each OC,
sum of all areas in the sectors minus
the core area
83- 86 F4.2 --- e_Souter Area within the outer region of each OC error
88- 94 F7.2 --- Ncore Number of member stars in the core region
of each OC
96-100 F5.2 --- e_Ncore Number of member stars in the core region
of each OC error
102-107 F6.2 --- Nouter Number of member stars in the outer region
of each OC
109-113 F5.2 --- e_Nouter Number of member stars in the outer region
of each OC error
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Acknowledgements:
Yuting Li, yutingli1010(at)163.com
(End) Yuting Li [Nanchong, China], Patricia Vannier [CDS] 27-Feb-2026