J/A+A/534/A53ivo://CDS.VizieR/J/A+A/534/A53doi:10.26093/cds/vizier.35340053CDSPancino E.Mucciarelli A.Bonifacio P.Monaco L.Sbordone L.2011-11-30T15:25:45Z2011-09-30T08:56:54ZCDS support team

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

cds-question@unistra.frglobular-star-clustersgiant-starspopulation-ii-starsline-intensitiesWe analyze spectra of 18 stars belonging to the faintest subgiant branch in omega Centauri (the SGB-a), obtained with GIRAFFE@VLT at a resolution of R~=17000 and a S/N ratio between 25 and 50. We measure abundances of Al, Ba, Ca, Fe, Ni, Si, and Ti and we find that these stars have <[Fe/H]>=-0.73+/-0.14dex, similarly to the corresponding red giant branch population (the RGB-a). We also measure <[alpha/Fe]>=+0.40+/-0.16dex, and <[Ba/Fe]>=+0.87+/-0.23dex, in general agreement with past studies. It is very interesting to note that we found a uniform Al abundance, <[Al/Fe]>=+0.32+/-0.14dex, for all the 18 SGB-a stars analysed here, thus supporting past evidence that the usual (anti-)correlations are not present in this population, and suggesting a non globular cluster-like origin of this particular population. In the dwarf galaxy hypothesis for the formation of omega Cen, this population might be the best candidate for the field population of its putative parent galaxy, although some of its properties appear contradictory. It has also been suggested that the most metal-rich population in omega Cen is significantly enriched in helium. If this is true, the traditional abundance analysis techniques, based on model atmospheres with normal helium content, might lead to errors. We have computed helium enhanced atmospheres for three stars in our sample and verified that the abundance errors due to the use of non-enhanced atmospheres are negligible. Additional, indirect support to the enhanced helium content of the SGB-a population comes from our Li upper limits.2011A&A...534A..53Phttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/534/A53CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/MNRAS/357/265 : BVI photometry of omega Cen red giants (Sollima+, 2005)J/ApJ/661/L155 : Radial velocities Rgb stars in omega Cen (Pancino+, 2007)J/A+A/527/A18 : EW of 6 subgiants of {omega} Cen (Pancino+, 2011)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/534/A53https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/534/A53http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/534/A53https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/534/A53https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/534/A53http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/534/A53GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/534/A53/table1 (Observing Logs and atmospheric parameters)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/534/A53/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/534/A53/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/534/A53/table1?GETtext/xml+votable180.050000true201.76627583-47.548827780.0055555555555555566/43227https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/534/A53?format=asciiOpticaldefaultJ/A+A/534/A53/table1Observing Logs and atmospheric parametersrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintWFIWFI identification number, \dicS{Cl* NGC 5139 WFI NNNNNN} in Simbad \linkRole{equivalent widths of this star }meta.id;meta.mainintprimaryFORSFORS identification number (Sollima et al. 2005, Cat. J/MNRAS/357/265), \dicS{Cl* NGC 5139 SGP NNNNNN} in Simbad (1)meta.idintRAJ2000Right ascension in decimal degrees (J2000)degpos.eq.ra;meta.mainDEJ2000Declination in decimal degrees (J2000)degpos.eq.dec;meta.mainVmagV magnitude (1)magphot.mag;em.opt.Vfloat(B-V)0Deredenned B-V colour index (1)magphot.color;em.opt.B;em.opt.Vfloat(V-I)0Deredenned V-I_J_ colour index (1)magphot.color;em.opt.V;em.opt.IfloatNobsNumber of observationsmeta.numberintS/NSignal-to-noise ratiostat.snrintTeffH{alpha} effective temperatureKspect.line.intensity;em.line.Halpha;spect.lineintloggSurface gravitylog(cm.s**-2)phys.gravityfloatvtMicroturbulent velocitykm/sphys.velocfloatJ/A+A/534/A53/table2Equivalent widths for 18 subgiants in {omega} CentaurirecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintWFIWFI identification number of subgiantmeta.id;meta.mainintlambdaWavelength in Angstroms0.1nmem.wlfloatIonElement name and ionization stagemeta.id;phys.atmol.ionStage;phys.atmol.ionizationcharEPExcitation potentialeVphys.atmol.excitationfloatloggfLogarithm of the oscillator strengthphys.atmol.oscStrengthfloatEWEquivalent width in m{AA}0.1pmspect.line.eqWidthfloate_EWFormal DAOSPEC error on EW (in m{AA})0.1pmstat.error;spect.line.eqWidthfloatq_EWDAOSPEC Q parameter on EWmeta.code.qual;spect.line.eqWidthfloat