J/A+A/665/A46ivo://CDS.VizieR/J/A+A/665/A46doi:10.26093/cds/vizier.36650046CDSMatsuno T.Dodd E.Koppelman H.H.Helmi A.Ishigaki M.N.Aoki W.,Zhao J.-K.Yuan Z.Hattori K.2022-11-13T17:27:05Z2022-09-07T08:49:03ZCDS support team

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

cds-question@unistra.frhalo-starschemical-abundancesspectroscopyline-intensitiesvisible-astronomyThe Helmi streams are a kinematic substructure whose progenitor is likely a dwarf galaxy. Although 20 years have passed since their discovery, it is still unclear whether their members are chemically distinguishable from other halo stars in the Milky Way. We aim to precisely characterize the chemical properties of the Helmi streams. We analyzed high-resolution, high signal-to-noise ratio spectra for 11 Helmi stream stars through a line-by-line abundance analysis. We compared the derived abundances to homogenized literature abundances of the other halo stars, including those belonging to other kinematic substructures, such as Gaia-Enceladus and Sequoia. Compared to typical halo stars, the Helmi stream members clearly show low values of [X/Fe] in elements produced by massive stars, such as Na and alpha-elements. This tendency is seen down to metallicities of at least [Fe/H]~-2.2, suggesting type Ia supernovae already started to contribute to the chemical evolution at this metallicity. We find that the [alpha/Fe] ratio does not evolve significantly with metallicity, making the Helmi stream stars less distinguishable from Gaia-Enceladus stars at [Fe/H]>-1.5. The almost constant but low value of [alpha/Fe] might be indicative of quiescent star formation with low efficiency at the beginning and bursty star formation at later times. We also find extremely low values of [Y/Fe] at low metallicity, providing further support for the claim that light neutron-capture elements are deficient in Helmi streams. While Zn is deficient at low metallicity, it shows a large spread at high metallicity. The origin of the extremely low Y abundances and Zn variations remains unclear. The Helmi stream stars are distinguishable from the majority of the halo stars if homogeneously derived abundances are compared.2022A&A...665A..46Mhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/665/A46CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/A+A/661/A103 : High-precision chemical abundances of Sequoia (Matsuno+, 2022)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/665/A46https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/665/A46http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/665/A46https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/665/A46https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/665/A46http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/665/A46GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/665/A46/table1 (Summary of the data)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/665/A46/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/665/A46/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/665/A46/table1?GETtext/xml+votable180.050000true0.8685361-3.26397970.0055555555555555566/8357 9781 10061 10853 17393 20542 32429 35518 43846 47007 49129https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/665/A46?format=asciiOpticaldefaultJ/A+A/665/A46/table1Summary of the dataS/N6370Signal-to-noise ratio at 6370{AA}stat.snrintNNumber of measurements in linelist.dat filemeta.numberintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintObjectObject name used in this studymeta.id;meta.maincharGaiaDR2Gaia DR2 identification numbermeta.idS/N4500Signal-to-noise ratio at 4500{AA}stat.snrintS/N5533Signal-to-noise ratio at 5533{AA}stat.snrintSimbadSimbad column added by the CDSmeta.ref.urlchar_RARight Ascension (J2000) from SIMBAD (not part of the original data)degpos.eq.ra;meta.main_DEDeclination (J2000) from SIMBAD (not part of the original data)degpos.eq.dec;meta.mainJ/A+A/665/A46/table5Linelist and line-by-line abundancerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintObjectObject name used in this studymeta.id;meta.maincharSpeciesName of the speciesphys.atmol.elementcharlambdaWavelength0.1nmem.wldoublechiExcitation potentialeVphys.atmol.excitationfloatloggflog gf valuephys.absorption.coefffloatEWEquivalent width (in m{AA})0.1pmspect.line.eqWidthfloate_EWUncertainty in equivalent width (in m{AA})0.1pmstat.error;spect.line.eqWidthfloatAAbundance from this linephys.abundfloateATeffUncertainty in abundance due to effective temperaturestat.errorfloateAloggUncertainty in abundance due to surface gravitystat.errorfloateAvtUncertainty in abundance due to microturbulent velocitystat.errorfloateA[Fe/H]Uncertainty in abundance due to metallicitystat.errorfloateAEWUncertainty in abundance due to equivalent widths of this star and the reference starstat.errorfloatsXUncertainty floorstat.errorfloatWeightWeight used to obtain the best estimate for the abundance of the speciesphys.atmol.weight;meta.modelleddouble