J/A+A/624/A63ivo://CDS.VizieR/J/A+A/624/A63doi:10.26093/cds/vizier.36240063CDSBik A.Henning T.Wu S.-W.Zhang M.Brandner W.Pasquali A.Stolte A.2019-05-27T08:40:01Z2019-04-11T09:00:24ZCDS support team

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

cds-question@unistra.fropen-star-clustersob-starsccd-photometryinfrared-photometryinfrared-astronomyspectroscopyThe interplay between the formation of stars, stellar feedback and cloud properties strongly influences the star formation history of giant molecular clouds. The formation of massive stars leads to a variety of stellar clusters, ranging from low stellar density OB associations to dense, gravitationally bound starburst clusters. We aimed at identifying the massive stellar content and reconstructing the star formation history of the W51 giant molecular cloud. We performed near-infrared imaging and K-band spectroscopy of the massive stars in W51. We analysed the stellar populations using colour-magnitude and colour-colour diagrams and compared the properties of the spectroscopically identified stars with stellar evolution models. We derive the ages of the different sub-clusters in W51 and, based on our spectroscopy derive an age for W51 of 3Myrs or less. The age of the P Cygni star LS1 and the presence of two still forming proto- clusters suggests that the star formation history of W51 is more complex than a single burst. We did not find evidence for triggered star formation and we concluded that the star formation in W51 is multi seeded. We finally concluded that W51 is a OB association where different sub-clusters form over a time span of at least 3-5Myrs.2019A&A...624A..63Bhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/624/A63CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/ApJ/706/83 : Embedded YSO candidates in W51 (Kang+, 2009)J/ApJ/839/108 : YSOs in the star-forming regions W51 + W43 (Saral+, 2017)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/624/A63https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/624/A63http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/624/A63https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/624/A63https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/624/A63http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/624/A63GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/624/A63/list (Spectroscopically classified OB stars in W51 (table 3) with spectra)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/624/A63/list?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/624/A63/list?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/624/A63/list?GETtext/xml+votable180.050000true290.559958314.05250.005555555555555556Cone search capability for table J/A+A/624/A63/w51-phot (Near-infrared photometry of the stars in W51)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/624/A63/w51-phot?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/624/A63/w51-phot?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/624/A63/w51-phot?GETtext/xml+votable180.050000true290.94812514.56733330.005555555555555556Associated datahttps://cdsarc.cds.unistra.fr/assocdata/?obs_collection=J/A+A/624/A636/30692 30694-306958.603629998553875e-20 1.7782101297878868e-19https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/624/A63?format=asciiInfrareddefaultJ/A+A/624/A63/listSpectroscopically classified OB stars in W51 (table 3) with spectraNxNumber of pixels along X-axismeta.numberintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNo[1/16] Seauential numbermeta.idintn_No[ac] Note on No (1)meta.notecharObsIDObservation IDmeta.id;obscharFieldField designationmeta.id;meta.maincharRAJ2000Right ascension (J2000)pos.eq.ra;meta.mainDEJ2000Declination (J2000)pos.eq.dec;meta.mainJmagSOFI/NTT J magnitudemagphot.mag;em.IR.Jfloate_Jmagrms uncertainty on Jmagmagstat.error;phot.mag;em.IR.JfloatHmagSOFI/NTT H magnitudemagphot.mag;em.IR.Hfloate_Hmagrms uncertainty on Hmagmagstat.error;phot.mag;em.IR.HfloatKsmagSOFI/NTT Ks magnitudemagphot.mag;em.IR.Kfloate_Ksmagrms uncertainty on Ksmagmagstat.error;phot.mag;em.IR.KfloatSpTypeSpectral type (2)src.spTypecharspShow the spectrummeta.ref.urlcharObs.dateObservation datestime.epoch;obsnullableblambdaLower value of wavelength interval0.1nmem.wlfloatBlambdaUpper value of wavelength interval0.1nmem.wlfloatdlambdaWavelength resolution0.1nmspect.resolutiondoublesizeSize of FITS fileKibytephys.size;meta.fitsintFileNameName of the fits spectrum in subdirectory fitsmeta.id;meta.fitscharAssocDataAssociated Data web pagemeta.ref.urlcharJ/A+A/624/A63/w51-photNear-infrared photometry of the stars in W51RAJ2000Right ascension (J2000.0)pos.eq.ra;meta.mainindexedHmagSOFI/NTT H magnitudemagphot.mag;em.IR.HfloatrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintObject[1/15145] object numbermeta.idintFieldObserved Field (I, II III or IV)meta.id;obs.fieldcharDEJ2000Declination (J2000.0)pos.eq.dec;meta.mainJmagSOFI/NTT J magnitudemagphot.mag;em.IR.Jfloate_Jmagrms uncertainty on Jmagmagstat.error;phot.mag;em.IR.Jfloate_Hmagrms uncertainty on Hmagmagstat.error;phot.mag;em.IR.HfloatKsmagSOFI/NTT Ks magnitudemagphot.mag;em.IR.Kfloate_Ksmagrms uncertainty on Ksmagmagstat.error;phot.mag;em.IR.Kfloat