J/A+A/686/A251ivo://CDS.VizieR/J/A+A/686/A251doi:10.26093/cds/vizier.36860251CDSWinnberg A.Brand J.Engels D.2024-11-29T20:03:13Z2024-06-19T08:13:52ZCDS support team

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

cds-question@unistra.frvariable-starsastrophysical-masersradio-astronomyradio-spectroscopyWater maser emission is often found in the circumstellar envelopes of evolved stars, that is, asymptotic-giant-branch stars and red supergiants with oxygen-rich chemistry. The H_2_O emission shows strong variability in evolved stars of both of these types. We wish to understand the reasons for the strong variability of water masers emitted at 22GHz. In this paper we study U Her and RR Aql as representatives of Mira variable stars. We monitored U Her and RR Aql in the 22-GHz maser line of water vapour with single-dish telescopes. The monitoring period covered about two decades between 1990 and 2011, with a gap between 1997 and 2000 in the case of RR Aql. Observations were also made in 1987 and 2015 before and after the period of contiguous monitoring. In addition, maps of U Her were obtained in the period 1990-1992 with the Very Large Array. We find that the strongest emission in U Her is located in a shell with boundaries 11-25AU. The gas-crossing time is 8.5 years. We derive lifetimes for individual maser clouds of <=4 years, based on the absence of detectable line-of-sight velocity drifts of the maser emission. The shell is not evenly filled, and its structure is maintained over much longer timescales than those of individual maser clouds. Both stars show brightness variability on several timescales. The prevalent variation is periodic, following the optical variability of the stars with a lag of 2-3 months. Superposed are irregular fluctuations, of a few months in duration, with increased or decreased excitation at particular locations, and long-term systematic variations on timescales of a decade or more. The properties of the maser emission are governed by those of the stellar wind while traversing the H_2_O maser shell. Inhomogeneities in the wind affecting the excitation conditions and prevalent beaming directions likely cause the variations seen on timescales longer than the stellar pulsation period. We propose the existence of long-living regions in the shells, which maintain favourable excitation conditions on timescales of the wind-crossing times through the shells or orbital periods of (sub)stellar companions. The H_2_O maser properties in these two Mira variables are remarkably similar to those in the semiregular variables studied in our previous papers, regarding shell location, outflow velocity, and lifetime. The only difference is the regular brightness variations of the Mira variables caused by the periodic pulsation of the stars.2024A&A...686A.251Whttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/686/A251CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/A+A/644/A45 : R Crt and RT Vir Medicina spectra (Brand+, 2020)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/686/A251https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/686/A251http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/686/A251https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/686/A251https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/686/A251http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/686/A251GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/686/A251/list (List of datacubes and spectra)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/686/A251/list?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/686/A251/list?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/686/A251/list?GETtext/xml+votable180.050000true245.896319.004890.005555555555555556Associated datahttps://cdsarc.cds.unistra.fr/assocdata/?obs_collection=J/A+A/686/A2516/8532 30086https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/686/A251?format=asciiRadiodefaultJ/A+A/686/A251/tablea1Maser spectral components B-E of U HerrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintDateObservation datetime.epoch;obsnullableTJDTruncated Julian date (JD-2440000.5)dtime.epochintrmsrmsJystat.errorfloatS(tot)Total flux densityJy.km/sphot.flux.density;em.radio.12-30GHzintphisOptical brigthnessphot.mag;em.optfloatVlosB? Vlos for B componentkm/sphys.velocfloatnullablel_SpBLimit flag on SpBmeta.code.errorcharSpB? Peak flux for B componentJyphot.flux.density;em.radio.12-30GHzfloatnullableVlosC? Vlos for C componentkm/sphys.velocfloatnullablel_VlosCLimit flag on spCmeta.code.errorcharSpC? Peak flux for C componentJyphot.flux.density;em.radio.12-30GHzfloatnullableVlosD'? Vlos for D' componentkm/sphys.velocfloatnullableSpD'? Peak flux for D' componentJyphot.flux.density;em.radio.12-30GHzfloatnullableVlosD''? Vlos for D'' componentkm/sphys.velocfloatnullableSpD''? Peak flux for D'' componentJyphot.flux.density;em.radio.12-30GHzfloatnullableu_SpD''Uncertainty flag on SpD"meta.code.errorcharVlosE? Vlos for E componentkm/sphys.velocfloatnullableu_VlosEUncertainty flag on VlosEmeta.code.errorcharl_SpELimit flag on SpEmeta.code.errorcharSpE? Peak flux for E componentJyphot.flux.density;em.radio.12-30GHzfloatnullableu_SpEUncertainty flag on SpEmeta.code.errorcharl_SpD''Limit flag on SpD''meta.code.errorcharJ/A+A/686/A251/tablea2Maser spectral components G-M of U Herl_SpELimit flag on SpEmeta.code.errorcharSpE? Peak flux for E componentJyphot.flux.density;em.radio.12-30GHzfloatnullableu_SpEUncertainty flag on SpEmeta.code.errorcharVlosM? Vlos for M componentkm/sphys.velocfloatnullablel_SpMLimit flag on SpMmeta.code.errorcharSpM? Peak flux for M componentJyphot.flux.density;em.radio.12-30GHzfloatnullableu_SpMUncertainty flag on SpMmeta.code.errorcharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintDateObservation datetime.epoch;obsnullableTJDTruncated Julian date (JD-2440000.5)dtime.epochintrmsrmsJystat.errorfloatS(tot)Total flux densityJy.km/sphot.flux.density;em.radio.12-30GHzintphisOptical brigthnessphot.mag;em.optfloatVlosG'? Vlos for G' componentkm/sphys.velocfloatnullablel_SpG'Limit flag on SpG'meta.code.errorcharSpG'? Peak flux for G' componentJyphot.flux.density;em.radio.12-30GHzfloatnullableVlosG''? Vlos for G'' componentkm/sphys.velocfloatnullablel_VlosG''Limit flag on spG''meta.code.errorcharSpG''? Peak flux for G'' componentJyphot.flux.density;em.radio.12-30GHzfloatnullableVlosI? Vlos for I componentkm/sphys.velocfloatnullableu_VlosIUncertainty flag on VlosImeta.code.errorcharl_SpILimit flag on SpImeta.code.errorcharSpI? Peak flux for I componentJyphot.flux.density;em.radio.12-30GHzfloatnullableVlosK? Vlos for K componentkm/sphys.velocfloatnullableu_VlosKUncertainty flag on VlosKmeta.code.errorcharl_SpKLimit flag on SpKmeta.code.errorcharSpK? Peak flux for K componentJyphot.flux.density;em.radio.12-30GHzfloatnullableu_SpKUncertainty flag on SpKmeta.code.errorcharVlosE? Vlos for E componentkm/sphys.velocfloatnullableu_VlosEUncertainty flag on VlosEmeta.code.errorcharJ/A+A/686/A251/tableb1Maser spectral components of RR AqlrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintDateObservation datetime.epoch;obsnullableTJDTruncated Julian date (JD-2440000.5)dtime.epochintrmsrmsJystat.errorfloatl_SpCLimit flag on SpCmeta.code.errorcharSpC? Peak flux for C componentJyphot.flux.density;em.radio.12-30GHzfloatnullableVlosD? Vlos for D componentkm/sphys.velocfloatnullablel_SpDLimit flag on SpDmeta.code.errorcharSpD? Peak flux for D componentJyphot.flux.density;em.radio.12-30GHzfloatnullableVlosE? Vlos for E componentkm/sphys.velocfloatnullablel_SpELimit flag on SpEmeta.code.errorcharSpE? Peak flux for E componentJyphot.flux.density;em.radio.12-30GHzfloatnullableS(tot)Total flux densityJy.km/sphot.flux.density;em.radio.12-30GHzintphisOptical brigthnessphot.mag;em.optfloatVlosA? Vlos for A componentkm/sphys.velocfloatnullablel_SpALimit flag on SpAmeta.code.errorcharSpA? Peak flux for A componentJyphot.flux.density;em.radio.12-30GHzfloatnullableVlosB? Vlos for B componentkm/sphys.velocfloatnullablel_VlosBLimit flag on spBmeta.code.errorcharSpB? Peak flux for B componentJyphot.flux.density;em.radio.12-30GHzfloatnullableVlosC? Vlos for C componentkm/sphys.velocfloatnullableJ/A+A/686/A251/listList of datacubes and spectrarecnoRecord 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-axis for the datacubesmeta.numberintnullableNz? Number of pixels along Z-axis for the datacubesmeta.numberintnullableObs.dateObservation datestime.epoch;obsnullablebVELO-LSR? Lower value of VELO-LSR interval for the datacubesm/sphys.velocdoublenullableBVELO-LSR? Upper value of VELO-LSR interval for the datacubesm/sphys.velocdoublenullabledVELO-LSR? VELO-LSR resolution for the datacubesm/sspect.resolutiondoublenullablebFREQ? Lower value of frequency interval for the spectraHzem.freqdoublenullableBFREQ? Upper value of frequency interval for the spectraHzem.freqdoublenullabledFREQ? Frequency resolution for the spectraHzspect.resolutiondoublenullablesizeSize of FITS fileKibytephys.size;meta.fitsintFileNameName of FITS file, in subdirectory fitsmeta.id;meta.fitscharTitleTitle of the FITS filemeta.title;meta.fitscharAssocDataAssociated Data web pagemeta.ref.urlchar