J/A+A/606/A52ivo://CDS.VizieR/J/A+A/606/A52doi:10.26093/cds/vizier.36060052CDSHerpin F.Baudry A.Richards A.M.S.Gray M.D.Schneider N.,Menten K.M.Wyrowski F.Bontemps S.Simon R.Wiesemeyer H.2017-10-16T08:12:05Z2017-10-09T10:26:41ZCDS support team

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

cds-question@unistra.frinfrared-sourcesastrophysical-masersradio-astronomyThe formation of massive stars (M>10M_{sun}_, L>10^3^L_{sun}_) is still not well understood. Accumulating a large amount of mass infalling within a single entity in spite of radiation pressure is possible if, among several other conditions, enough thermal energy is released. Despite numerous water line observations, over a broad range of energies, with the Herschel Space Observatory, in most of the sources observations were not able to trace the emission from the hot core around the newly forming protostellar object. We want to probe the physical conditions and water abundance in the inner layers of the host protostellar object NGC7538-IRS1 using a highly excited H_2_O line. Water maser models predict that several THz water masers should be detectable in these objects. We therefore aim to detect for the first time the o-H_2_O 8_2,7_-7_3,4_ line in a star forming region, which model calculations predict to show maser action. We present SOFIA observations of the o-H_2_O 8_2,7_-7_3,4_ line at 1296.41106GHz and a 6_16_-5_23_ 22GHz e-MERLIN map of the region (first-ever 22GHz images made after the e-MERLIN upgrade). In order to be able to constrain the nature of the emission - thermal or maser - we use near-simultaneous observations of the 22GHz water maser performed with the Elsberg radiotelescope and e-MERLIN. A thermal water model using the RATRAN radiative transfer code is presented based on HIFI pointed observations. Molecular water abundances are derived for the hot core. The of the o-H_2_O 8_2,7_-7_3,4_ line is detected toward NGC7538-IRS1 with one feature at the source velocity (-57.7km/s) and another one at -48.4km/s. We propose that the emission at the source velocity is consistent with thermal excitation and is excited in the innermost part of the IRS1a massive protostellar object's closest circumstellar environment. The other emission is very likely the first detection of a water THz maser line, pumped by shocks due to IRS1b outflow, in a star-forming region. Assuming thermal excitation of the THz line, the water abundance in NGC7538-IRS1's hot core is estimated to be 5.2x10^-5^ with respect to H_2_.2017A&A...606A..52Hhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/606/A52CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/ApJ/696/471 : MIR spectroscopy of NGC 7538 IRS 1 (Knez+, 2009)J/A+A/543/A88 : NGC7538IRS1 and NGC7538S 1.36mm maps (Beuther+, 2012)J/A+A/558/A81 : NGC 7538 IRS1 maps in CH3OH, HCN and HCO+ (Beuther+, 2013)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/606/A52https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/606/A52http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/606/A52https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/606/A52https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/606/A52http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/606/A52GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/606/A52/list (List of fits files)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/606/A52/list?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/606/A52/list?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/606/A52/list?GETtext/xml+votable180.050000true348.4387461.469440.0055555555555555566/14317https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/606/A52?format=asciiInfraredRadiodefaultJ/A+A/606/A52/listList of fits filesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000Right Ascension of center (J2000)degpos.eq.ra;meta.mainDEJ2000Declination of center (J2000)degpos.eq.dec;meta.mainNxNumber of pixels along X-axismeta.numberintNy? Number of pixels along Y-axismeta.numberintnullableNz? Number of slicesmeta.numberintnullableObs.DateObservation date (YYYY-MM-DDThh:mm:ss.sss)time.epoch;obscharsizeSize of FITS fileKibytephys.size;meta.fitsintFileNameName of FITS file, in subdirectory fitsmeta.id;meta.fitscharTitleTitle of the FITS filemeta.title;meta.fitscharbFreq? Lower value of relative frequency interval (for the spectrum files)Hzem.freq;stat.mindoublenullableBFreq? Upper value of relative frequency interval (for the spectrum files)Hzem.freq;stat.maxdoublenullabledFreq? Frequency resolution (for the spectrum files)Hzspect.resolutiondoublenullablebVlsr? Lower value of LSR velocity (for the datacube)m/sphys.veloc;pos.lsrdoublenullableBVlsr? Upper value of LSR velocity (for the datacube)m/sphys.veloc;pos.lsrdoublenullabledVlsr? LSR velocity resolution (for the datacube)m/sspect.resolutiondoublenullable