J/A+A/695/A22 Fractal dimension of open clusters (Qin+, 2025)
The 3D morphology of open clusters in the solar neighborhood.
III. Fractal dimension of open clusters.
Qin C., Pang X., Pasquato M., Kouwenhoven M.B.N., Vallenari A.
<Astron. Astrophys. 695, A22 (2025)>
=2025A&A...695A..22Q 2025A&A...695A..22Q (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Clusters, open ; Stars, ages ; Morphology
Keywords: stars: formation - stars: general -
open clusters and associations: general
Abstract:
We analyzed the fractal dimension of open clusters using 3D spatial
data from Gaia DR3 for 93 open clusters from Pang et al.
(2024ApJ...966..169P 2024ApJ...966..169P) and 127 open clusters from Hunt & Reffert
(2024A&A...686A..42H 2024A&A...686A..42H, Cat. J/A+A/686/A42) mainly within 500pc. The
box-counting method was adopted to calculate the fractal dimension of
each cluster in three regions: the all- member region, r≤rt (inside
the tidal radius), and r>rt (outside the tidal radius). In both the
Pang and Hunt catalogs, the fractal dimensions are smaller for the
regions r>rt than those for r≤rt, indicating that the stellar
distribution is more clumpy in the cluster outskirts. We classified
cluster morphology based on the fractal dimension via the Gaussian
mixture model. Our study shows that the fractal dimension can
efficiently classify clusters in the Pang catalog into two groups. The
fractal dimension of the clusters in the Pang catalog declines with
age, which is attributed to the development of tidal tails. This is
consistent with the expectations from the dynamical evolution of open
clusters. We found strong evidence that the fractal dimension
increases with cluster mass, which implies that higher-mass clusters
are formed hierarchically from the mergers of lower-mass filamentary-
type stellar groups. The transition of the fractal dimension for the
spatial distribution of open clusters provides a useful tool to trace
the Galactic star-forming structures, from the location of the Local
Bubble within the solar neighborhood to the spiral arms across the
Galaxy.
Description:
We determine the fractal dimension for open clusters in
the solar neighborhood using 3D position from Gaia DR3.
Our cluster sample includes 93 clusters from the catalog of Pang et
al. (2024ApJ...966..169P 2024ApJ...966..169P) in table A1, and 127 clusters from the
catalog of Hunt & Reffert (2024A&A...686A..42H 2024A&A...686A..42H, Cat. J/A+A/686/A42) in
table A2, mainly within 500pc from the Sun.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 86 93 Fractal dimension for the Pang catalog clusters
tablea2.dat 83 127 Fractal dimension for the Hunt catalog clusters
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See also:
I/350 : Gaia EDR3 (Gaia Collaboration, 2020)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/ApJ/877/12 : Coma Ber & Neighbor Stellar Group tidal tails (Tang+, 2019)
J/ApJ/923/20 : Hierarchical clustering in Vela OB2 complex (Pang+, 2021)
J/A+A/646/A104 : Improving the open cluster census. I. (Hunt+, 2021)
J/ApJ/937/L7 : Collinder132-Gulliver21 stream members from Gaia DR3
(Pang+, 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)
J/ApJ/912/162 : Open clusters in solar neighborhood (Pang+, 2021)
J/ApJ/931/156 : 3D morphology of open clusters with Gaia EDR3. II
(Pang+, 2022)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 17 A17 --- Cluster Cluster Name
19- 24 F6.1 Myr Age Cluster Age
26- 27 A2 --- Type Morphological type (1)
29- 46 F18.16 --- fdim-all Fractal dimension for the all-member region
48- 66 F19.16 --- fdim-inrt ? Fractal dimension for the region inside
the tidal radius (r≤rt)
68- 86 F19.16 --- fdim-outrt ? Fractal dimension for the region outside
the tidal radius (r>rt)
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Note (1): The morphological type of the cluster substructures outside rt
as follows:
f1 = filamentary (19 occurrences)
f2 = fractal (21 occurrences)
h = halo (3 occurrences)
t = tidal tail (10 occurrences)
d = Group X; for its total disruption state
(Tang et al., 2019ApJ...877...12T 2019ApJ...877...12T, Cat. J/ApJ/877/12).
See Pang et al. (2022ApJ...931..156P 2022ApJ...931..156P) for a further description.
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Byte-by-byte Description of file: tablea2.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- Cluster Cluster Name
15- 24 F10.8 [yr] logAge Logarithm of cluster age (1)
26- 43 F18.16 --- fdim-all Fractal dimension for the all-member region
45- 63 F19.16 --- fdim-inrt ? Fractal dimension for the region inside
the tidal radius (r≤rt)
65- 83 F19.16 --- fdim-outrt ? Fractal dimension for the region outside
the tidal radius (r>rt)
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Note (1): Adapted from the column logAge50 in Hunt et al.
(2024A&A...686A..42H 2024A&A...686A..42H, Cat. J/A+A/686/A42).
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Acknowledgements:
Chang Qin, changqin(at)mails.ccnu.edu.cn
Xiaoying Pang, Xiaoying.Pang(at)xjtlu.edu.cn
References:
Pang et al., Paper I 2021ApJ...912..162P 2021ApJ...912..162P, cat. J/ApJ/912/162
Pang et al., Paper II 2022ApJ...931..156P 2022ApJ...931..156P, cat. J/ApJ/931/156
(End) Patricia Vannier [CDS] 06-Feb-2025