J/A+A/704/A180 A Walk on the Retrograde Side (WRS) project II (Ceccarelli+ 2025)
A Walk on the Retrograde Side (WRS) project.
II. Chemistry to disentangle in situ and accreted components in Thamnos.
Ceccarelli E., Massari D., Palla M., Mucciarelli A., Bellazzini M., Helmi A.
<Astron. Astrophys. 704, A180 (2025)>
=2025A&A...704A.180C 2025A&A...704A.180C (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, normal ; Abundances ; Effective temperatures
Keywords: stars: abundances - Galaxy: abundances - Galaxy: formation -
Galaxy: halo - Galaxy: kinematics and dynamics
Abstract:
We present the results of the first systematic and dedicated
high-resolution chemical analysis of the Thamnos substructure, a
candidate relic of the process of hierarchical merging of the Milky
Way. The analysis is performed in comparison with the
Gaia-Sausage-Enceladus (GSE) remnant, within the fully self-consistent
and homogeneous framework established by the WRS project. We analyse
high-resolution and high signal-to-noise ratio spectra obtained with
UVES at VLT for 212 Red Giant Branch stars classified as candidate
members of Thamnos and GSE, based on selections in the space of the
integrals of motion. We derive precise abundances for 16 atomic
species. Compared to GSE, stars attributed to the Thamnos substructure
are, on average, more metal-poor, yet most of them show relatively
higher [X/Fe] abundance ratios in several elements, like Na, Mg, Al,
Ca, Cu, Zn, as well as lower [Eu/Fe]. The majority of candidate
Thamnos stars show chemical signatures more consistent with the in
situ Milky Way halo rather than a typical low-mass accreted dwarf
galaxy. Our findings are further supported by comparisons with
tailored galactic chemical evolution models, which fall short in
reproducing the observed enhancement in the alpha-elements, but are
able to fit the more metal-poor component present in the Thamnos
substructure. These results confirm a high level of contamination in
the Thamnos substructure from the in situ population and to a lesser
degree from GSE, while still leaving room for a genuine accreted
population from a small disrupted dwarf galaxy.
Description:
Source ID from Gaia DR3, stellar parameters, orbital parameters,
line-of-sight velocity, and abundances of Fe, Na, Mg, Al, Ca, TiI, Cr,
Mn, Co, Ni, Cu, Zn, YII, BaI, LaII, and EuII. Stars were observed with
UVES at VLT using the Blue Arm 390 and Red Arm 580 CD3 gratings.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 63 212 Star ID, orbital parameters and Vlos
table3.dat 33 212 Star ID and atmospheric parameters
table4.dat 239 212 Star ID and detailed chemical abundances
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See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- GaiaDR3 Source_id from Gaia DR3
21- 27 I7 km2/s2 En Orbital energy
29- 32 I4 km2/s2 e_En Uncertainties on the orbital energy
34- 38 I5 kpc.km/s Lz Vertical angular momentum
40- 42 I3 kpc.km/s e_Lz Uncertainties on the
vertical angular momentum
44- 46 I3 kpc.km/s Lperp Perpendicular angular momentum
48- 50 I3 kpc.km/s e_Lperp Uncertainties on the
perpendicular angular momentum
52- 57 F6.1 km/s Vlos Line-of-sight velocity
59- 61 F3.1 km/s e_Vlos Uncertainties on the line-of-sight velocity
63 I1 --- Flag Potential binary if set to 2
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- GaiaDR3 Source_id from Gaia DR3
21- 24 I4 K Teff Effective temperature
26- 29 F4.2 [cm/s2] logg Surface gravity
31- 33 F3.1 km/s vt Microturbulent velocity
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- GaiaDR3 Source_id from Gaia DR3
21- 25 F5.2 [Sun] [Fe/H] Abundance [Fe/H]
27- 30 F4.2 [Sun] e_[Fe/H] Uncertainty on the [Fe/H] abundance
32- 38 F7.2 [Sun] [Na/Fe] ?=999 Abundance [Na/Fe]
40- 45 F6.2 [Sun] e_[Na/Fe] ?=999 Uncertainty on the [Na/Fe] abundance
47- 52 F6.2 [Sun] [Mg/Fe] ?=999 Abundance [Mg/Fe]
54- 59 F6.2 [Sun] e_[Mg/Fe] ?=999 Uncertainty on the [Mg/Fe] abundance
61- 67 F7.2 [Sun] [Al/Fe] ?=999 Abundance [Al/Fe]
69- 74 F6.2 [Sun] e_[Al/Fe] ?=999 Uncertainty on the [Al/Fe] abundance
76- 79 F4.2 [Sun] [Ca/Fe] Abundance [Ca/Fe]
81- 84 F4.2 [Sun] e_[Ca/Fe] Uncertainty on the [Ca/Fe] abundance
86- 90 F5.2 [Sun] [TiI/Fe] Abundance [TiI/Fe]
92- 95 F4.2 [Sun] e_[TiI/Fe] Uncertainty on the [TiI/Fe] abundance
97-101 F5.2 [Sun] [Cr/Fe] Abundance [Cr/Fe]
103-106 F4.2 [Sun] e_[Cr/Fe] Uncertainty on the [Cr/Fe] abundance
108-114 F7.2 [Sun] [Mn/Fe] ?=999 Abundance [Mn/Fe]
116-121 F6.2 [Sun] e_[Mn/Fe] ?=999 Uncertainty on the [Mn/Fe] abundance
123-129 F7.2 [Sun] [Co/Fe] ?=999 Abundance [Co/Fe]
131-136 F6.2 [Sun] e_[Co/Fe] ?=999 Uncertainty on the [Co/Fe] abundance
138-144 F7.2 [Sun] [Ni/Fe] ?=999 Abundance [Ni/Fe]
146-151 F6.2 [Sun] e_[Ni/Fe] ?=999 Uncertainty on the [Ni/Fe] abundance
153-159 F7.2 [Sun] [Cu/Fe] ?=999 Abundance [Cu/Fe]
161-166 F6.2 [Sun] e_[Cu/Fe] ?=999 Uncertainty on the [Cu/Fe] abundance
168-174 F7.2 [Sun] [Zn/Fe] ?=999 Abundance [Zn/Fe]
176-181 F6.2 [Sun] e_[Zn/Fe] ?=999 Uncertainty on the [Zn/Fe] abundance
183-189 F7.2 [Sun] [YII/Fe] ?=999 Abundance [YII/Fe]
191-196 F6.2 [Sun] e_[YII/Fe] ?=999 Uncertainty on the [YII/Fe] abundance
198-202 F5.2 [Sun] [BaII/Fe] Abundance [BaII/Fe]
204-207 F4.2 [Sun] e_[BaII/Fe] Uncertainty on the [BaII/Fe] abundance
209-215 F7.2 [Sun] [LaII/Fe] ?=999 Abundance [LaII/Fe]
217-222 F6.2 [Sun] e_[LaII/Fe] ?=999 Uncertainty on the [LaII/Fe] abundance
224-230 F7.2 [Sun] [EuII/Fe] ?=999 Abundance [EuII/Fe]
232-237 F6.2 [Sun] e_[EuII/Fe] ?=999 Uncertainty on the [EuII/Fe] abundance
239 I1 --- Progenitor [1/3] Dynamical association:
GSE = 1, Thamnos = 3
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Acknowledgements:
Edoardo Ceccarelli, edoardo.ceccarelli3(at)unibo.it
(End) Patricia Vannier [CDS] 18-Nov-2025