J/A+A/708/A161 APOGEE DR17 Nephele candidate stars (Pagnini+, 2026)
The Nephele ecosystem: Stars, globular clusters, and stellar streams associated
with the progenitor galaxy of omega Centauri.
Pagnini G., Di Matteo P., Haywood M., Bianchini P., Ferrone S.,
Mastrobuono-Battisti A., Agertz O., Khoperskov S., Renaud F., Ryde N.
<Astron. Astrophys. 708, A161 (2026)>
=2026A&A...708A.161P 2026A&A...708A.161P (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Stars, giant ; Abundances ; Infrared
Keywords: Galaxy: abundances; Galaxy: formation - globular clusters: general -
globular clusters: individual: omega Centauri (NGC 5139)
Abstract:
Globular clusters (GCs) and their associated stellar streams are key
tracers of the hierarchical assembly history of the Milky Way. omega
Centauri, the most massive and chemically complex GC in the Galaxy, is
widely believed to be the remnant nucleus of an accreted dwarf galaxy.
Identifying its associated debris and that of chemically similar
clusters can provide important constraints on the nature of this
progenitor system.
We aim to identify stars in the Galactic field that are chemically and
kinematically associated with omega Cen and with a group of GCs
hypothesised to share a common origin. This group, recently proposed
to form a coherent system named Nephele, may represent the remnants of
a single, massive accretion event.
We analysed APOGEE DR17 data to select field stars with high-quality
chemical abundances. We applied a Gaussian mixture model (GMM) in an
8D chemical abundance space to identify stars compatible with omega
Cen chemistry. We then computed the orbital energy and angular
momentum of these stars and applied a second GMM, calibrated on
simulations from the e-TidalGCs project, to determine the kinematic
compatibility with the predicted streams of omega Cen and the
associated Nephele GCs.
We identify 470 stars chemically compatible with omega Cen, of which
58 are also Al-rich, consistent with second-generation stars found in
GCs. Of these, six stars show kinematics consistent with the predicted
omega Cen stream, and additional stars are linked to the tidal streams
of NGC 6205, NGC 6254, NGC 6273, NGC 6656, and NGC 6809. These
findings suggest the presence of extended stellar streams that have
not been previously detected. We also find overlap in chemical and
kinematic properties between Nephele stars and the Gaia
Sausage-Enceladus population.
Our results suggest the presence of stellar debris associated with
omega Cen and its candidate family of GCs. The combined chemical and
kinematic analysis supports the scenario in which these systems
originated in a common progenitor, which has now been disrupted. While
uncertainties remain-particularly due to disc contamination and
limited sky coverage - this work illustrates the potential of chemical
and dynamical methods to trace the remnants of past accretion events
in the inner Galaxy.
Description:
This table lists APOGEE DR17 field stars with non-zero probability of
being chemically compatible with omega Centauri according to the
GMMChem model described in Sect. 3.1 of the paper.
Each row provides the APOGEE identifier, the probability of chemical
compatibility with omega Centauri, a boolean flag indicating aluminum
enhancement, and a boolean flag indicating whether the star is
classified as a Nephele candidate.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 39 1411 *APOGEE DR17 Nephele candidate stars
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Note on table1.dat: Only stars with SNREV>70, 3500K<Teff<5500K, logg<3.6,
and abundance flags equal to zero for the adopted chemical elements are
included in the parent sample (see Sect. 2 of the paper).
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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- 18 A18 --- APOGEE APOGEE DR17 identifier based on the
2MASS designation
21- 24 F4.2 --- Pcomp Probability of compatibility with omega
Centauri (1)
27- 31 A5 --- AlRich Aluminum-enhancement flag (True/False) (2)
35- 39 A5 --- Nephele Nephele candidate flag (True/False) (3)
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Note (1): Probability of chemical compatibility with omega Centauri.
Defined as the fraction of bootstrap realizations (Nboot=100)
in which the star satisfies the GMMChem selection criterion.
Note (2): Boolean flag indicating aluminum enhancement.
True if [Al/Fe]>0.73*[Fe/H]+1.09 (Eq. 1 of the paper), False otherwise.
Note (3): Boolean flag indicating Nephele candidate classification.
True for stars with Pcomp ≥ 0.7 and False otherwise.
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Acknowledgements:
Giulia Pagnini, pagnini(at)astro.unistra.fr
License: CC-BY-4.0 [see https://spdx.org/licenses/]
(End) Patricia Vannier [CDS] 25-Mar-2026