J/A+A/601/A31ivo://CDS.VizieR/J/A+A/601/A31doi:10.26093/cds/vizier.36010031CDSLiu C.Ruchti G.Feltzing S.Primas F.2020-01-31T15:51:15Z2017-04-25T07:43:45ZCDS support team

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

cds-question@unistra.frglobular-star-clustersspectroscopyHere we explore robust ways of determining the iron content of metal-rich giant stars. We aim to understand what biases and shortcomings the widely applied methods suffer from. In this study we were mainly concerned with standard methods of analysing stellar spectra. These include the analysis of individual lines to determine stellar parameters, and analysis of the broad wings of certain lines (e.g. Halpha and calcium lines) to determine effective temperature and surface gravity for the stars. For NGC 6528 we find that [Fe/H]=+0.04dex with a scatter of 0.07dex, which gives an error in the derived mean abundance of 0.02dex. Our work has two important conclusions for analysis of metal-rich red giant branch stars. Firstly, for spectra with S/N of below about 35 per reduced pixel, [Fe/H] becomes too high. Secondly, determination of Teff using the wings of the H{alpha} line results in [Fe/H] values about 0.1dex higher than if excitational equilibrium is used. The last conclusion is perhaps unsurprising, as we expect the NLTE effect to become more prominent in cooler stars and we can not use the the wings of the H{alpha} line to determine Teff for the cool stars in our sample. We therefore recommend that in studies of metal-rich red giant stars care should be taken to obtain sufficient calibration data to enable use of the cooler stars.2017A&A...601A..31Lhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/601/A31CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/AJ/84/1305 : UBV photometry in NGC 6528 (van den Bergh+, 1979)J/A+AS/127/167 : V,I CCD photometry of NGC 6528 (Richtler+ 1998)J/A+A/385/67 : NGC 6528 HST VI photometry & proper motions (Feltzing+, 2002)J/A+A/565/A8 : Stroemgren photometry near NGC 6528 (Calamida+, 2014)J/A+A/573/A13 : Metal abundances in 6 globular cluster (Dias+, 2015)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/601/A31https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/601/A31http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/601/A31https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/601/A31https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/601/A31http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/601/A31GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/601/A31/table2 (Basic information for all stars analysed in this study)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/601/A31/table2?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/601/A31/table2?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/601/A31/table2?GETtext/xml+votable180.050000true271.200083-30.0416670.0055555555555555566/28778https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/601/A31?format=asciidefaultJ/A+A/601/A31/table2Basic information for all stars analysed in this studySimbadNameSimbad column added by the CDSmeta.idcharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSeq[1/34] Sequential number of the sourcemeta.recordintIDIdentification number of the sourcemeta.numbercharNameSource name (2MASS or VVV)meta.id;meta.maincharRAJ2000Right ascension (J2000)pos.eq.ra;meta.mainDEJ2000Declination (J2000)pos.eq.dec;meta.mainJmag0? De-reddened J magnitude (1)magphot.mag;em.IR.JfloatnullableHmag0? De-reddened H magnitude (1)magphot.mag;em.IR.HfloatnullableKmag0? De-reddened K magnitude (1)magphot.mag;em.IR.KfloatnullableRVRadial velocitykm/sphys.veloc;pos.heliocentricfloate_RVrms uncertainty on RVkm/sstat.errorfloatn_RV[c] Note on RV (2)meta.notecharObs.DateObservation datetime.epoch;obsnullableExpTimeExposure timestime.duration;obs.exposurecharInstInstrumentmeta.id;instrcharS/NSignal-to-noise ratio measured from the spectrum (3)stat.snrintJ/A+A/601/A31/listList of gfits spectrarecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSeq[1/34] Sequentail number of the sourcemeta.numberintNxNumber of pixels along X-axismeta.numberintObs.DateObservation date (YYYY-MM-DDThh:mm:ss.sss)time.epoch;obscharblambdaLower value of wavelength interval0.1nmem.wlfloatBlambdaUpper value of wavelength interval0.1nmem.wlfloatdlambdaResolution0.1nmpos.angResolutiondoublesizeSize of FITS fileKibytephys.size;meta.fitsintspShow the spectrummeta.ref.urlcharFileNameName of FITS file, in subdirectory fitsmeta.id;meta.fitscharTitleTitle of the FITS filemeta.title;meta.fitschar