J/A+A/712/A6 Chemo-dynamical complexity of omega Centauri (Pagnini+, 2026)
The chemo-dynamical complexity of omega Centauri:
Different kinematics for different populations.
Pagnini G., Bianchini P., Di Matteo P., Mastrobuono-Battisti A.
<Astron. Astrophys. 712, A6 (2026)>
=2026A&A...712A...6P 2026A&A...712A...6P (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Stars, giant ; Abundances ;
Populations, stellar
Keywords: stars: abundances - stars: kinematics and dynamics -
globular clusters: individual: NGC 5139
Abstract:
The origin of omega Centauri remains one of the key open problems in
stellar dynamics and chemical evolution. Its large abundance spreads
and multiple populations suggest a formation history more complex than
that of a typical globular cluster. Aims. We investigate whether the
chemical sub-populations identified in APOGEE DR17 also exhibit
distinct spatial and kinematic signatures, and what constraints these
provide on the formation pathways of omega Cen.
We analyse a sample of APOGEE DR17 red-giant stars using a Gaussian
Mixture Model in an eight-dimensional chemical-abundance space. The
resulting chemical components are combined with Gaia proper motions
and APOGEE line-of-sight velocities to derive intrinsic mean
velocities and velocity dispersions in all three observable
directions. We measure both global kinematic quantities and radial
profiles for each chemically defined group, extending from the inner
regions to ∼4 half-light radii.
The Gaussian Mixture Model identifies five chemical components, which,
when examined through their radial cumulative distributions, naturally
group into two broader families characterised by lower and higher
aluminium enrichment. The two families differ significantly in their
spatial and kinematic properties: the Al-rich stars are more centrally
concentrated and exhibit stronger radial anisotropy than the Al-poor
stars, which remain closer to isotropy over the radial range probed.
Despite these significant differences (>2σ), the two populations
share a common rotation pattern, with comparable intrinsic rotation
amplitudes and rotation-axis inclinations within the uncertainties
(∼0.5km/s). Both families span a wide range in metallicity,
indicating that they do not simply correspond to a first- and
second-generation dichotomy, but rather trace chemically and
dynamically complex substructures within omega Cen.
This work represents the first chemo-dynamical study of omega Cen
linking detailed chemical tagging to internal kinematics from the
inner regions to the cluster outskirts, and provides a key benchmark
for models of its formation. A formation path involving both
hierarchical assembly within a dwarf-galaxy potential and centrally
concentrated, chemically enriched star formation offers a natural
explanation for the observed chemo-dynamical complexity. Extending
this approach to larger fields of view and to more numerous, fainter
stars will be essential to robustly uncover the origin of this
uniquely complex system.
Description:
We investigate the chemo-dynamical complexity of omega Centauri using
APOGEE DR17 chemical abundances and Gaia astrometry. A Gaussian
Mixture Model applied to the eight-dimensional chemical-abundance
space identifies five chemically distinct stellar populations whose
kinematic properties are analysed and compared.
This catalogue corresponds to Table A.1 of the paper. It contains the
APOGEE DR17 identifiers and the Gaussian Mixture Model (GMM) component
assigned to each of the 588 stars analysed in this work.
Objects:
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RA (2000) DE Designation(s)
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13 26 47.28 -47 28 46.1 NGC 5139 = NAME ome Cen Cluster
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 20 588 APOGEE IDs and GMM labels
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See also:
III/286 : APOGEE-2 DR17 final allStar catalog (Abdurro'uf+, 2022)
Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- APOGEE APOGEE DR17 identifier
20 I1 --- Comp [0/4] Assigned GMM component label
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Acknowledgements:
Giulia Pagnini, pagnini(at)astro.unistra.fr
License: CC-BY-4.0
(End) Patricia Vannier [CDS] 06-Jul-2026