J/A+A/707/A242 Gaia-Enceladus/Sausage population 1 and 2 stars (Berni+, 2026)
Evidence for multiple crossings and stripping of Gaia-Enceladus/Sausage across
the Milky Way.
Berni L., Palla M., Magrini L., Spina L.
<Astron. Astrophys. 707, A242 (2026)>
=2026A&A...707A.242B 2026A&A...707A.242B (SIMBAD/NED BibCode)
ADC_Keywords: Infrared sources ; Abundances ; Radial velocities
Keywords: stars: abundances - Galaxy: abundances - Galaxy: evolution -
Galaxy: formation - Galaxy: halo - Galaxy: kinematics and dynamics
Abstract:
The accretion of Gaia-Enceladus/Sausage (GES) onto the Milky Way is
one of the most prominent features of the Galactic halo revealed by
the combination of the Gaia satellite and large spectroscopic surveys.
This massive accretion is responsible for a notable amount of the
Milky Way stellar mass and was significant enough to alter the
formation history and the morphology of the MW.
In this work, we aim to analyse the selection of stars identified in
Berni et al. (2025A&A...700A.160B 2025A&A...700A.160B) in GES with different kinematics
and chemical properties to test the hypothesis of a two-phase
accretion event.
We apply several statistical tests to assess the significance of the
separation between the two populations in GES. We then employ Galactic
chemical evolution models to investigate the origin of the chemical
differences encountered in the analysis.
We confirm the presence of two distinct populations, with consistently
different dynamical and chemical properties. The low-energy population
seems to show higher overall abundances, whereas the high-energy one
may be more metal-poor. We attribute this difference to the presence
of at least two separate populations of stars within Gaia-Enceladus,
likely associated with the innermost (low-energy) and outermost
(high-energy) regions of the progenitor. The models successfully
reproduce the patterns in metallicity and [alpha/M] distributions in
an inside-out scenario.
Our analysis supports the presence of a former metallicity gradient in
Gaia-Enceladus, and reinforces the interpretation of its accretion as
a multi-passage event through the Milky Way disc.
Description:
Combining the use of chemistry and dynamics, we are able to identify
two populations within Gaia Enceladus. The table Pop1.dat and Pop2.dat
contain data for the two populations. Abundance data are from the
APOGEE DR17 survey.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 452 293 Population 1
table2.dat 452 389 Population 2
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See also:
III/286 : APOGEE-2 DR17 final allStar catalog (Abdurro'uf+, 2022)
J/A+A/691/A333 : Gaia-Sausage-Enceladus abundances (Ernandes+, 2024)
Byte-by-byte Description of file: table1.dat table2.dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- APOGEE APOGEE name (2MHHMMSSss+DDMMSSs)
20- 39 F20.16 deg RAdeg Right ascension (J2000)
41- 52 F12.10 deg e_RAdeg Error on right ascension
54- 73 F20.16 deg DEdeg Declination (J2000)
75- 86 F12.10 deg e_DEdeg Error on declination
88-101 F14.9 km/s RV ? Radial velocity
103-114 F12.8 km/s e_RV ? Error on radial velocity
116-122 I7 kpc/cm2/s2 E Orbital energy
124-128 I5 kpc/cm2/s2 e_E Error on orbital energy
130-136 F7.1 kpc.km/s Lz Angular momentum
138-143 F6.1 kpc.km/s e_Lz Error on angular momentum
145-151 F7.4 --- [M/H] Metallicity [M/H]
153-164 F12.10 --- e_[M/H] Error on metallicity
166-177 F12.9 --- [alpha] Alpha element abundance
179-190 F12.10 --- e_[alpha] Error on alpha element abundance
192-204 F13.10 --- [C/Fe] ? Abundance [C/Fe]
206-217 F12.9 --- e_[C/Fe] ? Error on [C/Fe]
219-232 F14.11 --- [N/Fe] ? Abundance [N/Fe]
234-245 F12.9 --- e_[N/Fe] ? Error on [N/Fe]
247-258 F12.9 --- [O/Fe] Abundance [O/Fe]
260-270 F11.9 --- e_[O/Fe] Error on [O/Fe]
272-284 F13.10 --- [Na/Fe] ? Abundance [Na/Fe]
286-297 F12.9 --- e_[Na/Fe] ? Error on [Na/Fe]
299-311 F13.10 --- [Mg/Fe] Abundance [Mg/Fe]
313-323 F11.9 --- e_[Mg/Fe] Error on [Mg/Fe]
325-336 F12.9 --- [Al/Fe] ? Abundance [Al/Fe]
338-349 F12.9 --- e_[Al/Fe] ? Error on [Al/Fe]
351-362 F12.9 --- [Si/Fe] Abundance [Si/Fe]
364-374 F11.9 --- e_[Si/Fe] Error on [Si/Fe]
376-388 F13.10 --- [Ca/Fe] ? Abundance [Ca/Fe]
390-401 F12.9 --- e_[Ca/Fe] ? Error on [Ca/Fe]
403-410 F8.5 --- [Fe/H] Abundance [Fe/H]
412-423 F12.10 --- e_[Fe/H] Error on [Fe/H]
425-439 F15.12 --- [Ce/Fe] ? Abundance [Ce/Fe]
441-452 F12.9 --- e_[Ce/Fe] ? Error on [Ce/Fe]
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Acknowledgements:
Leda Berni, leda.berni(at)inaf.it
(End) Patricia Vannier [CDS] 28-Jan-2026