J/A+A/604/A78ivo://CDS.VizieR/J/A+A/604/A78doi:10.26093/cds/vizier.36040078CDSRamirez-Tannus M.C.Kaper L.de Koter A.Tramper F.Bik A.,Ellerbroek L.E.Ochsendorf B.B.Ramirez-Agudelo O.H.Sana H.2017-10-02T08:05:02Z2017-08-18T10:39:11ZCDS support team

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

cds-question@unistra.frh-ii-regionspre-main-sequence-starsyoung-stellar-objectsob-starsspectroscopyThe formation process of massive stars is still poorly understood. Massive young stellar objects (mYSOs) are deeply embedded in their parental clouds; these objects are rare, and thus typically distant, and their reddened spectra usually preclude the determination of their photospheric parameters. M17 is one of the best-studied HII regions in the sky, is relatively nearby, and hosts a young stellar population. We have obtained optical to near-infrared spectra of previously identified candidate mYSOs and a few OB stars in this region with X-shooter on the ESO Very Large Telescope. The large wavelength coverage enables a detailed spectroscopic analysis of the photospheres and circumstellar disks of these candidate mYSOs. We confirm the pre-main-sequence (PMS) nature of six of the stars and characterise the O stars. The PMS stars have radii that are consistent with being contracting towards the main sequence and are surrounded by a remnant accretion disk. The observed infrared excess and the double-peaked emission lines provide an opportunity to measure structured velocity profiles in the disks. We compare the observed properties of this unique sample of young massive stars with evolutionary tracks of massive protostars and propose that these mYSOs near the western edge of the HII region are on their way to become main-sequence stars (~6-20M_{sun}_) after having undergone high mass accretion rates (dMacc/dt~10^-4^-10^-3^M_{sun}_/yr) Their spin distribution upon arrival at the zero age main-sequence (ZAMS) is consistent with that observed for young B stars, assuming conservation of angular momentum and homologous contraction.2017A&A...604A..78Rhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/604/A78CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toII/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)II/336 : AAVSO Photometric All Sky Survey (APASS) DR9 (Henden+, 2016)J/ApJS/169/353 : Chandra sources in M17 (Broos+, 2007)J/ApJ/714/L285 : YSO candidates in M17 SWex (Povich+, 2010)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/604/A78https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/604/A78http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/604/A78https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/604/A78https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/604/A78http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/604/A78GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/604/A78/table1 (Journal of X-shooter observations)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/604/A78/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/604/A78/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/604/A78/table1?GETtext/xml+votable180.050000true275.1444583-16.16958330.0055555555555555566/29116 29118https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/604/A78?format=asciiOpticaldefaultJ/A+A/604/A78/table1Journal of X-shooter observationsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNameObject name (BNNN) as in Master's thesis of Bumgardner (1992, thesis, Ohio State Univ., Columbus), Cl* NGC 6618 B NNN in Simbadmeta.id;meta.maincharn_Name[*] Note on Name (1)meta.notecharONameOther namemeta.idcharCEN? Chini et al. (1980A&A....91..186C) identification number, Cl* NGC 6618 CEN NNN in Simbadmeta.idintnullableOI? Ogura & Ishida (1976PASJ...28...35O) identification number, NGC 6618 NNN in Simbadmeta.idintnullableRAJ2000Right ascension (J2000)pos.eq.ra;meta.mainDEJ2000Declination (J2000)pos.eq.dec;meta.mainVmag? V magnitudemagphot.mag;em.opt.Vfloatnullabler_Vmag[abc] Reference for Vmag (2)meta.ref;pos.framecharKmag2MASS K magnitude (Cutri et al., 2003, Cat. II/246)magphot.mag;em.IR.KfloatObs.DateObservation datetime.epoch;obsnullablespShow the spectrummeta.ref.urlcharFileNameName of the file with spectrum, in subdirectory spmeta.id;meta.filecharExpTUVBUVB arm exposure times (s)time.expocharExpTVISVIS arm exposure times (s)time.expocharExpTNIRNIR arm exposure times (s)time.expocharSimbadSimbad column added by the CDSmeta.ref.urlchar