J/A+A/291/261ivo://CDS.VizieR/J/A+A/291/261doi:10.26093/cds/vizier.32910261CDSCodella C.Felli M.Natale V.Palagi F.Palla F.2025-06-13T20:00:08Z2010-01-20T14:07:28ZCDS support team

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

cds-question@unistra.frastrophysical-masersradio-astronomyh-ii-regionsThe results of a survey of 22.2GHz H2O maser emission towards a large sample of HII regions (427) detected in hydrogen recombination lines (Lockman) are presented. The sample favours classical HII regions with large excitation parameter. We found 68 water maser sources, 17 of which are new detections. Adding the detections found in the literature, the total number of masers associated with the sample is 80. The overall maser percentage is low (19%), much less than what found in samples of ultracompact (UC) HII regions. The percentage changes if we divide our sample into two sub-classes: HII regions known to have ultracompact components (i.e. where a younger generation of star formation is also present) and the rest. In the first sub-class the maser percentage is 28%, in the second 15%. The total number of masers in HII regions where no UC component has been (so far) reported is 43. This value is greater than that expected from the ratio between the lifetime of the HII region (10^6^yr) and that of the maser phase, even assuming a maser lifetime as long as 10^5^yr. This implies that maser excitation (and star formation) occurs several times in the lifetime of the same star forming complex. From 410 positions observed, 230 can be associated with a high degree of confidence to an IRAS Point Source. We expect that most of the HII regions not associated with IRAS PS are diffuse regions in the last phases of their evolution. The percentage of water masers in this sub-class is very low: 8%. The number of masers with no counterpart in the Lockman sample (and above Dec=-30{deg}) is very large: 334. This number most probably reflects the extreme high density conditions known to exist in the earliest phases of an HII region, which strongly reduce its radio continuum and line emission. The analysis of a homogeneous sample of classical HII regions allows to confirm in a quantitative fashion the well known result that the maser phenomenon occurs during the earliest phase of the evolution of a massive star and that it fades away as the HII region evolves into the diffuse stage.1994A&A...291..261Chttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/291/261CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/291/261https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/291/261http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/291/261https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/291/261https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/291/261http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/291/261GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/291/261/table1 (Summary of the observed sources)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/291/261/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/291/261/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/291/261/table1?GETtext/xml+votable180.050000true13.08681756.5745530.005555555555555556Cone search capability for table J/A+A/291/261/table2 (Derived parameters of the detected maser sources)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/291/261/table2?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/291/261/table2?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/291/261/table2?GETtext/xml+votable180.050000true13.08681756.5745530.0055555555555555565/3672-3673 7275 7278 7377 7383 7564 7604 7654 6/1287 1297 1330 1781 1839 1848 1952 3011 3290 3302 3606 3649 3755 12975 14029 14255 14263 14293 14299 14306-14307 14311 14314 14317 14344 14353 14355 14358-14359 14402 14406 14409 14430 14453 14621-14622 14624 14633 14641 14644 14665-14668 14670-14671 14682-14683 14687 14696-14698 14704 14706 14716 14719 15362 15368 15458 21439 21458 21504 21550 21641 22080 22243 22855 23764 23969 23982 24554 28875 28890-28892 28896-28897 28900-28901 28912-28913 28915 28918-28919 29090-29091 29093-29097 29116 29118-29119 29162 29463 29505-29506 29512 29515 29522-29523 29528-29529 30218-30219 30222 30241 30244-30245 30262-30263 30268-30269 30312-30313 30315 30317-30319 30328-30330 30341 30405 30420 30423 30592 30595 30601 30604-30605 30622 30624 30644-30645 30691-30692 30694-30695 30701 30707 30712 30715-30716 30718-30719 39804https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/291/261?format=asciiRadiodefaultJ/A+A/291/261/table1Summary of the observed sourcesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRA1950Right ascension 1950pos.eq.ra;meta.mainDE1950Declination 1950pos.eq.dec;meta.mainGLONGalactic longitudedegpos.galactic.lonGLATGalactic latitudedegpos.galactic.latfloatd? Distancekpcpos.distance;pos.heliocentricfloatnullableIRASIRAS namemeta.id;meta.maincharDl? Detection limit (3 r.m.s.)Jyinstr.sensitivityfloatnullableMas[M] A 'M' indicates that maser is detectedmeta.notecharRemRemarks (1)meta.notechar_RA.icrsRight ascension (ICRS) (computed by VizieR, not part of the original data. The format may include more digits than the original data because of internal accuracy requirements in VizieR and across other CDS services)pos.eq.raindexed_DE.icrsDeclination (ICRS) (computed by VizieR, not part of the original data. The format may include more digits than the original data because of internal accuracy requirements in VizieR and across other CDS services)pos.eq.decindexedJ/A+A/291/261/table2Derived parameters of the detected maser sourcesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRA1950Right ascension 1950pos.eq.ra;meta.mainDE1950Declination 1950pos.eq.dec;meta.mainObsID of source observed in table1meta.id.parentintnullableDateObservation date'Y:M:D'time.epochnullablel_Fpeaklimit flag on Fpeakmeta.code.errorcharFpeakFlux of the strongest componentJyphot.flux.density;em.radio.12-30GHzinte_Fpeak? Noise of the spectrum (r.m.s.)Jystat.errorintnullable_RA.icrsRight ascension (ICRS) (computed by VizieR, not part of the original data. The format may include more digits than the original data because of internal accuracy requirements in VizieR and across other CDS services)pos.eq.raindexed_DE.icrsDeclination (ICRS) (computed by VizieR, not part of the original data. The format may include more digits than the original data because of internal accuracy requirements in VizieR and across other CDS services)pos.eq.decindexedFWHM? FWHM of the strongest componentkm/sspect.line.widthfloatnullableVpeak? Velocity of the strongest componentkm/sspect.dopplerVelocfloatnullableVmin? Lower extreme of the emission intervalkm/sspect.dopplerVelocfloatnullableVmax? Upper extreme of the emission intervalkm/sspect.dopplerVelocfloatnullableVresSpectral resolutionkm/sspect.resolutionfloatFH2O? Integrated fluxJy.km/sphot.fluxintnullableLH2O? Water maser luminositysolLumphys.luminosityfloatnullable