J/A+A/336/339ivo://CDS.VizieR/J/A+A/336/339doi:10.26093/cds/vizier.33360339CDSMolinari S.Brand J.Cesaroni R.Palla F.Palumbo G.G.C.2013-02-27T06:34:57Z1998-08-25T12:05:30ZCDS support team

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

cds-question@unistra.fryoung-stellar-objectsradio-sourcesinfrared-sourcesWe have used the Very Large Array (VLA) to search for radio continuum emission towards a sample of 67 IRAS sources selected from a previous study. All observed sources are associated with high density molecular gas, exhibit an infrared spectral energy distribution characteristic of very cold young stellar objects and many of them are associated with H_2_O masers. The observed sample is divided into two groups of sources: High, with IRAS spectral energy distributions resembling those of ultracompact HII regions, and Low, for which previously collected evidence suggests that they may contain a higher fraction of protostellar objects than the High group; such objects might not have started hydrogen burning yet. Radio continuum emission was detected towards 37 sources (55%), although only in 22 cases an association with the IRAS source is established. Of the latter, 9 (24%) objects belong to the Low type and 13 (43%) to the High type. Thus, we find that 76% of Low and 57% of High sources are not associated with a radio counterpart. Because the majority of the sources have luminosities above ~10^4^L_{sun}_, corresponding to central stars of spectral type between B2 and O7, the lack of radio emission is interpreted as being due to the action of accreting matter that chokes off the expansion of the ionised gas. We show that this require s only moderate mass accretion rates, below ~10^-4^M_{sun}_/yr. Alternatively, dust absorption can also effectively absorb UV photons and the gas column density implied by our observations indicates values in excess of 10^22^cm^-2^. The physical properties of IRAS sources with associated radio counterpa rt derived from the present observations do not distinguish between High and Low sources. These sources are likely to be ZAMS stars with variable amounts of dust within the ionised region which acts as UV field absorber. The large majority of detected sources (75%) have spherical or unresolved morphology, while 15% are irregular or multiply peaked and only 10% have a core-halo structure. These results agree with the known properties of ultracompact HII regions, even though the average luminosity of the present sample is an order of magnitude lower than that in previous studies.1998A&A...336..339Mhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/336/339CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/A+A/308/573 : Ammonia on YSOs IRAS sources, Paper I. (Molinari+ 1996)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/336/339https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/336/339http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/336/339https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/336/339https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/336/339http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/336/339GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/336/339/table1a (High sources at 6-cm (obs. data))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/336/339/table1a?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/336/339/table1a?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/336/339/table1a?GETtext/xml+votable180.050000trueCone search capability for table J/A+A/336/339/table1b (Low sources at 2 and 6-cm (obs. data))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/336/339/table1b?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/336/339/table1b?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/336/339/table1b?GETtext/xml+votable180.050000true5/7579 6/1307 13050 14314 14317 14355 14622 14642 14647 14693 15394 15430 15458 24499 28831 28891 29112 29118 29556 30245 30259 30341 30416-30417 30421 30602 30604 30616 30618 30694 30715https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/336/339?format=asciiInfraredRadiodefaultJ/A+A/336/339/table1aHigh sources at 6-cm (obs. data)Note1Note (3)meta.notecharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMolMolinari number from Paper I (Cat. <J/A+A/308/573>)meta.id;meta.mainintprimaryAssAn * indicates association of radio emission with the IRAS sourcemeta.notecharComIdentification of multiple components within a source, or multiple sources within a fieldmeta.notecharLamWavelength of observationcmem.wl;obsintRunCode for observing run (1)meta.id;obscharRA1950? Right ascension (1950) (2)pos.eq.ra;meta.mainnullableDE1950? Declination (1950)pos.eq.dec;meta.mainnullableSep? Angular distance radio- and IRAS sourcesarcsecpos.angDistanceintnullableMaj? Observed major axis of radio peakarcsecphys.angSize;instr.beamfloatnullableMin? Observed minor axis of radio peakarcsecphys.angSize;instr.beamfloatnullablePA[-90/90]? Position angle radio peak (E of N)degpos.posAng;stat.maxfloatnullableMajd? Major axis radio peak, deconvolved by beamarcsecphys.angSize;em.radio;stat.maxfloatnullableMind? Minor axis radio peak, deconvolved by beamarcsecphys.angSize;em.radio;stat.maxfloatnullablePAd[0/180]? Position angle deconvolved radio peak (E of N)degpos.posAng;stat.maxfloatnullableHa1? Size of halo in one direction (4)arcsecphys.angSizeintnullableHa2? Size of halo in other directionarcsecphys.angSizeintnullableMcMorphological class (5)src.morph.typecharl_F[<] To indicate next number is upper limitmeta.code.errorcharF? Observed peak flux density (mJy/beam)mJyphot.flux.density;em.radiofloatnullableS? Observed integrated fluxmJyphot.flux.density;em.radio.3-6GHzfloatnullablerms? Observed rms (mJy/beam) (6)mJystat.stdevfloatnullableNoteIndividual notes in note1a.dat or note1b.datmeta.notechar_RA.icrsRight ascension (ICRS) (computed by VizieR, not part of the original data)pos.eq.ranullableindexed_DE.icrsDeclination (ICRS) (computed by VizieR, not part of the original data)pos.eq.decnullableindexedJ/A+A/336/339/table2aHigh sources at 6-cm derived physical parametersrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMolMolinari number from Paper I (Cat. <J/A+A/308/573>)meta.id;meta.mainintprimaryAssAn * indicates association of radio emission with the IRAS sourcemeta.notecharComIdentification of multiple components within a source, or multiple sources within a fieldmeta.notecharLamWavelength of observationcmem.wl;obsintNote1Note (1)meta.notecharl_DiamP[<] To indicate DiamP is upper limitmeta.code.errorcharDiamPPeak diameterpcpos.distancefloatDiamH? Mean halo diameterpcpos.distancefloatnullableTb? Brightness temperatureKphys.temperaturefloatnullabletau? Optical depth * 1000.phys.absorption.opticalDepthfloatnullablel_Ne[>] To indicate ne is lower limitmeta.code.errorcharNeElectron density10000cm**-3phys.density;phys.electronfloatl_EM[>] To indicate EM is lower limitmeta.code.errorcharEMEmission measure1e+06pc.cm**-6phys.emissMeasurefloatl_M(Hii)[<] To indicate M(Hii) is upper limitmeta.code.errorcharM(Hii)Mass of ionized hydrogen0.001solMassphys.massfloatlog(Nly)Log10 of Lyman continuum fluxlog(s**-1)phot.flux.density;spect.continuumfloatRat? Ratio of integrated and peak fluxesphot.flux;arith.ratiofloatnullableSpI? Spectral indexspect.indexfloatnullableNoteCommentsmeta.notecharJ/A+A/336/339/table2bLow sources at 2 and 6-cm derived phys. parametersrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMolMolinari number from Paper I (Cat. <J/A+A/308/573>)meta.id;meta.mainintprimaryAssAn * indicates association of radio emission with the IRAS sourcemeta.notecharComIdentification of multiple components within a source, or multiple sources within a fieldmeta.notecharLamWavelength of observationcmem.wl;obsintNote1Note (1)meta.notecharl_DiamP[<] To indicate DiamP is upper limitmeta.code.errorcharDiamPPeak diameterpcpos.distancefloatDiamH? Mean halo diameterpcpos.distancefloatnullableTb? Brightness temperatureKphys.temperaturefloatnullabletau? Optical depth * 1000.phys.absorption.opticalDepthfloatnullablel_Ne[>] To indicate ne is lower limitmeta.code.errorcharNeElectron density10000cm**-3phys.density;phys.electronfloatl_EM[>] To indicate EM is lower limitmeta.code.errorcharEMEmission measure1e+06pc.cm**-6phys.emissMeasurefloatl_M(Hii)[<] To indicate M(Hii) is upper limitmeta.code.errorcharM(Hii)Mass of ionized hydrogen0.001solMassphys.massfloatlog(Nly)Log10 of Lyman continuum fluxlog(s**-1)phot.flux.density;spect.continuumfloatRat? Ratio of integrated and peak fluxesphot.flux;arith.ratiofloatnullableSpI? Spectral indexspect.indexfloatnullableNoteCommentsmeta.notecharJ/A+A/336/339/note1aIndividual notes to table1a.datrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMolMol numbermeta.id;meta.mainintprimaryComIdentification of multiple componentsmeta.notecharNtotTotal number of lines for the commentmeta.numberintNlineRunning line number in range [1,Ntot]meta.idintCommCommentmeta.notecharJ/A+A/336/339/note1bIndividual notes to table1b.datrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMolMol numbermeta.id;meta.mainintprimaryComIdentification of multiple componentsmeta.notecharNtotTotal number of lines for the commentmeta.numberintNlineRunning line number in range [1,Ntot]meta.idintCommCommentmeta.notecharJ/A+A/336/339/table1bLow sources at 2 and 6-cm (obs. data)S? Observed integrated fluxmJyphot.flux.density;em.radio.3-6GHzfloatnullablerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMolMolinari number from Paper I (Cat. <J/A+A/308/573>)meta.id;meta.mainintprimaryAssAn * indicates association of radio emission with the IRAS sourcemeta.notecharComIdentification of multiple components within a source, or multiple sources within a fieldmeta.notecharLamWavelength of observationcmem.wl;obsintRunCode for observing run (1)meta.id;obscharRA1950? Right ascension (1950) (2)pos.eq.ra;meta.mainnullableDE1950? Declination (1950)pos.eq.dec;meta.mainnullableSep? Angular distance radio- and IRAS sourcesarcsecpos.angDistanceintnullableNote1Note (3)meta.notecharMaj? Observed major axis of radio peakarcsecphys.angSize;instr.beamfloatnullableMin? Observed minor axis of radio peakarcsecphys.angSize;instr.beamfloatnullablePA[-90/90]? Position angle radio peak (E of N)degpos.posAng;stat.maxfloatnullableMajd? Major axis radio peak, deconvolved by beamarcsecphys.angSize;em.radio;stat.maxfloatnullableMind? Minor axis radio peak, deconvolved by beamarcsecphys.angSize;em.radio;stat.maxfloatnullablePAd[0/180]? Position angle deconvolved radio peak (E of N)degpos.posAng;stat.maxfloatnullableHa1? Size of halo in one direction (4)arcsecphys.angSizeintnullableHa2? Size of halo in other directionarcsecphys.angSizeintnullableMcMorphological class (5)src.morph.typecharl_F[<] To indicate next number is upper limitmeta.code.errorcharF? Observed peak flux density (mJy/beam)mJyphot.flux.density;em.radiofloatnullablerms? Observed rms (mJy/beam) (6)mJystat.stdevfloatnullableNoteIndividual notes in note1a.dat or note1b.datmeta.notechar_RA.icrsRight ascension (ICRS) (computed by VizieR, not part of the original data)pos.eq.ranullableindexed_DE.icrsDeclination (ICRS) (computed by VizieR, not part of the original data)pos.eq.decnullableindexedJ/A+A/336/339/figmap/* titlesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMolMol numbermeta.id;meta.mainintprimaryFileNamemap name, stored in subdirectory mapmeta.id;obs.fieldcharTitleTitle of the mapmeta.bibchar