J/ApJ/681/1296ivo://CDS.VizieR/J/ApJ/681/1296doi:10.26093/cds/vizier.16811296CDSZijlstra A.A.van Hoof P.A.M.Perley R.A.2010-12-06T11:26:56Z2010-11-23T07:51:45ZCDS support team

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

cds-question@unistra.frplanetary-nebulaeradio-continuum-emissionWe present the results of a 25yr program to monitor the radio flux evolution of the planetary nebula NGC 7027. We find significant evolution of the spectral flux densities. The flux density at 1465MHz, where the nebula is optically thick, is increasing at a rate of 0.251+/-0.015%/yr, caused by the expansion of the ionized nebula. At frequencies where the emission is optically thin, the spectral flux density is changing at a rate of -0.145+/-0.005%/yr, caused by a decrease in the number of ionizing photons coming from the central star. A distance of 980+/-100pc is derived. By fitting interpolated models of post-AGB evolution to the observed changes, we find that over the 25yr monitoring period, the stellar temperature has increased by 3900+/-900K and the stellar bolometric luminosity has decreased by 1.75+/-0.5%. We derive a distance-independent stellar mass of 0.655+/-0.010M_{sun}_ adopting the Blocker stellar evolution models, or about 0.04M_{sun}_ higher when using models of Vassiliadis & Wood. A Cloudy photoionization model is used to fit all epochs at all frequencies simultaneously. The differences between the radio flux density predictions and the observed values show some time-independent residuals of typically 1%. A possible explanation is inaccuracies in the radio flux scale of Baars and coworkers. We propose an adjustment to the flux density scale of the primary radio flux calibrator 3C 286, based on the Cloudy model of NGC 7027. We also calculate precise flux densities for NGC 7027 for all standard continuum bands used at the VLA, as well as for some new 30 GHz experiments.2008ApJ...681.1296Zhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/681/1296CatalogResearchIsServedByTAP VizieR generic servicerelated-toJ/A+A/442/249 : Integrated spectrum of NGC 7027 (Zhang+, 2005)J/A+A/303/175 : Line spectrum of NGC 7027 (Baluteau+, 1995)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/681/1296https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/681/1296http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/681/1296https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/681/1296https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/681/1296http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/681/1296GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapRadiodefaultJ/ApJ/681/1296/table6Model flux densities for NGC 7027recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintFreqFrequencyGHzem.freqdoubleFluxNGC 7027 model flux density for epoch 2000.0mJyphot.flux.density;em.radiofloatSecVarSecular variation of the flux densitymJy/yrphot.flux.densityfloatJ/ApJ/681/1296/table1*NGC 7027/3C 286 flux density ratios, with uncertaintiesR8435? NGC 7027/3C 286 flux density ratio at 8435MHzphot.flux.density;em.radio.6-12GHzfloatnullablerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintEpochEpoch (in decimal years)time.epochfloatR1275? NGC 7027/3C 286 flux density ratio at 1275MHzphot.flux.density;em.radio.750-1500MHzdoublenullablee_R1275? R1275MHz uncertaintystat.errordoublenullableR1465NGC 7027/3C 286 flux density ratio at 1465MHzphot.flux.density;em.radio.750-1500MHzdoublee_R1465R1465MHz uncertaintystat.errordoubleR4535? NGC 7027/3C 286 flux density ratio at 4535MHzphot.flux.density;em.radio.3-6GHzfloatnullablee_R4535? R4535MHz uncertaintystat.errorfloatnullableR4885NGC 7027/3C 286 flux density ratio at 4885MHzphot.flux.density;em.radio.3-6GHzfloate_R4885R4885MHz uncertaintystat.errorfloate_R8435? R8435MHz uncertaintystat.errorfloatnullableR8735? NGC 7027/3C 286 flux density ratio at 8735MHzphot.flux.density;em.radio.6-12GHzfloatnullablee_R8735? R8735MHz uncertaintystat.errorfloatnullableR14965NGC 7027/3C 286 flux density ratio at 14965MHzphot.flux.density;em.radio.12-30GHzfloate_R14965R14965MHz uncertaintystat.errorfloatR22460NGC 7027/3C 286 flux density ratio at 22460MHzphot.flux.density;em.radio.12-30GHzfloate_R22460R22460MHz uncertaintystat.errorfloatR43340? NGC 7027/3C 286 flux density ratio at 43340MHzphot.flux.density;em.mm.30-50GHzfloatnullablee_R43340? R43340MHz uncertaintystat.errorfloatnullable