J/A+A/704/A180ivo://CDS.VizieR/J/A+A/704/A180CDSCeccarelli E.Massari D.Palla M.Mucciarelli A.Bellazzini M.Helmi A.2026-03-02T06:25:50Z2025-12-15T09:05:00ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frmilky-way-galaxychemical-abundanceseffective-temperatureWe 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.2025A&A...704A.180Chttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/704/A180CatalogResearchIsServedByTAP VizieR generic servicerelated-toI/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/704/A180https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/704/A180http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/704/A180https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/704/A180https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/704/A180http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/704/A180GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapdefaultJ/A+A/704/A180/table2Star ID, orbital parameters and VlosrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintGaiaDR3Source_id from Gaia DR3meta.id;meta.mainEnOrbital energykm**2.s**-2src.orbitalinte_EnUncertainties on the orbital energykm**2.s**-2stat.errorintLzVertical angular momentumkpc.km/sphys.angMomentuminte_LzUncertainties on the vertical angular momentumkpc.km/sstat.errorintLperpPerpendicular angular momentumkpc.km/sphys.angMomentuminte_LperpUncertainties on the perpendicular angular momentumkpc.km/sstat.errorintVlosLine-of-sight velocitykm/sphys.velocfloate_VlosUncertainties on the line-of-sight velocitykm/sstat.errorfloatFlagPotential binary if set to 2meta.code.errorintGaia_DR3Display the Gaia DR3 datameta.ref.urlcharJ/A+A/704/A180/table3Star ID and atmospheric parametersrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintGaiaDR3Source_id from Gaia DR3meta.id;meta.mainTeffEffective temperatureKphys.temperature.effectiveintloggSurface gravitylog(cm.s**-2)phys.gravityfloatvtMicroturbulent velocitykm/sphys.velocfloatJ/A+A/704/A180/table4Star ID and detailed chemical abundancese_[BaII/Fe]Uncertainty on the [BaII/Fe] abundancelog(Sun)stat.error;phys.abundfloat[LaII/Fe]? Abundance [LaII/Fe]log(Sun)phys.abundfloatnullablee_[LaII/Fe]? Uncertainty on the [LaII/Fe] abundancelog(Sun)stat.error;phys.abundfloatnullable[EuII/Fe]? Abundance [EuII/Fe]log(Sun)phys.abundfloatnullablerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintGaiaDR3Source_id from Gaia DR3meta.id;meta.main[Fe/H]Abundance [Fe/H]log(Sun)phys.abund.Fefloate_[Fe/H]Uncertainty on the [Fe/H] abundancelog(Sun)stat.error;phys.abund.Fefloat[Na/Fe]? Abundance [Na/Fe]log(Sun)phys.abundfloatnullablee_[Na/Fe]? Uncertainty on the [Na/Fe] abundancelog(Sun)phys.abundfloatnullable[Mg/Fe]? Abundance [Mg/Fe]log(Sun)phys.abundfloatnullablee_[Mg/Fe]? Uncertainty on the [Mg/Fe] abundancelog(Sun)phys.abundfloatnullable[Al/Fe]? Abundance [Al/Fe]log(Sun)phys.abundfloatnullablee_[Al/Fe]? Uncertainty on the [Al/Fe] abundancelog(Sun)phys.abundfloatnullable[Ca/Fe]Abundance [Ca/Fe]log(Sun)phys.abundfloate_[Ca/Fe]Uncertainty on the [Ca/Fe] abundancelog(Sun)phys.abundfloat[TiI/Fe]Abundance [TiI/Fe]log(Sun)phys.abundfloate_[TiI/Fe]Uncertainty on the [TiI/Fe] abundancelog(Sun)stat.error;phys.abundfloat[Cr/Fe]Abundance [Cr/Fe]log(Sun)phys.abundfloate_[Cr/Fe]Uncertainty on the [Cr/Fe] abundancelog(Sun)phys.abundfloat[Mn/Fe]? Abundance [Mn/Fe]log(Sun)phys.abundfloatnullablee_[Mn/Fe]? Uncertainty on the [Mn/Fe] abundancelog(Sun)phys.abundfloatnullable[Co/Fe]? Abundance [Co/Fe]log(Sun)phys.abundfloatnullablee_[Co/Fe]? Uncertainty on the [Co/Fe] abundancelog(Sun)phys.abundfloatnullable[Ni/Fe]? Abundance [Ni/Fe]log(Sun)phys.abundfloatnullablee_[Ni/Fe]? Uncertainty on the [Ni/Fe] abundancelog(Sun)phys.abundfloatnullable[Cu/Fe]? Abundance [Cu/Fe]log(Sun)phys.abundfloatnullablee_[Cu/Fe]? Uncertainty on the [Cu/Fe] abundancelog(Sun)phys.abundfloatnullable[Zn/Fe]? Abundance [Zn/Fe]log(Sun)phys.abundfloatnullablee_[Zn/Fe]? Uncertainty on the [Zn/Fe] abundancelog(Sun)phys.abundfloatnullable[YII/Fe]? Abundance [YII/Fe]log(Sun)phys.abundfloatnullablee_[YII/Fe]? Uncertainty on the [YII/Fe] abundancelog(Sun)stat.error;phys.abundfloatnullable[BaII/Fe]Abundance [BaII/Fe]log(Sun)phys.abundfloate_[EuII/Fe]? Uncertainty on the [EuII/Fe] abundancelog(Sun)stat.error;phys.abundfloatnullableProgenitor[1/3] Dynamical association: GSE = 1, Thamnos = 3meta.codeint