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Density gradients in Galactic planetary nebulae
Certain hydrodynamic models of planetary nebulae (PNe) suggest thattheir shells possess appreciable radial density gradients. However, theobservational evidence for such gradients is far from clear. On the onehand, Taylor et al. claim to find evidence for radio spectral indices0.6 < α < 1.8, a trend which is taken to imply a variationne ~ r-2 in most of their sample of PNe. On theother hand, Siódmiak & Tylenda find no evidence for any suchvariations in density; shell inhomogeneities, where they occur, areprimarily attributable to `blobs or condensations'.It will be suggested that both of these analyses are unreliable, andshould be treated with a considerable degree of caution. A new analysiswithin the log(F(5GHz)/F(1.4GHz))-log(TB(5GHz)) plane will beused to show that at least 10-20 per cent of PNe are associated withstrong density gradients. We shall also show that the ratioF(5GHz)/F(1.4GHz) varies with nebular radius; an evolution that can beinterpreted in terms of varying shell masses, and declining electrondensities.
| Chemical compositions and plasma parameters of planetary nebulae with Wolf-Rayet and wels type central stars
Aims.Chemical compositions and other properties of planetary nebulaearound central stars of spectral types [WC], [WO], and wels are comparedwith those of “normal” central stars, in order to clarifythe evolutionary status of each type and their interrelation. Methods:We use plasma diagnostics to derive from optical spectra the plasmaparameters and chemical compositions of 48 planetary nebulae. We alsoreanalyze the published spectra of a sample of 167 non-WR PN. Theresults as well as the observational data are compared in detail withthose from other studies of the objects in common. Results: We confirmthat [WC], [WO] and wels nebulae are very similar to those“normal” PN: the relation between [N II] and [O III]electron temperatures, abundances of He, N, O, Ne, S and Ar, and thenumber of ionizing photons show no significant differences. However,some differences are observed in their infrared (IRAS) properties. welsnebulae appear bluer than [WR] PN. The central star's spectral type isclearly correlated with electron density, temperature and excitationclass of the nebula, [WC] nebulae tend to be smaller than the othertypes. All this corroborates the view of an evolutionary sequence fromcool [WC 11] central stars inside dense, low excitation nebulae towardshot [WO 1] stars with low density, high excitation nebulae. The wels PN,however, appear to be a separate class of objects, not linked to WRPN byevolution: nebular excitation, electron temperature and density, and thenumber of ionizing photons all cover the whole range found in the othertypes. Their lower mean N/O ratio and slightlylower He/H suggestprogenitor stars less massive than for the other PN types. Furthermore,the differences between results of different works are dominated by thedifferences in observational data rather than differences in theanalysis methods.Based on observations obtained at the European Southern Observatory(ESO), La Silla, Chile. Table 3 and Appendices are only available inelectronic form at http://www.aanda.org Table with fluxes andintensities is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/463/265
| Detailed Far-Ultraviolet to Optical Analysis of Four [WR] Stars
We present far-UV to optical analyses of four hydrogen-deficient centralstars of planetary nebulae: BD +30 3639, NGC 40, NGC 5315, and NGC 6905.Using the radiative transfer code CMFGEN, we determined new physicalparameters and chemical abundances for these stars. The results wereanalyzed in the context of the [WR]-->PG 1159 evolution via thetransformed radius-temperature (RT×T*) andH-R diagrams. NGC 5315 showed itself as an odd object among thepreviously analyzed central stars. Its temperature (~76 kK) isconsiderably lower than other early-type [WR] stars (~120-150 kK). Fromour models for NGC 5315 and NGC 6905, it is unclear if early-type [WR]stars have smaller C/He mass ratios than other spectral classes, asclaimed in the literature. A ratio of ~0.8 is found for NGC 6905. Weanalyzed FUSE spectra of these stars for the first time and identifiedphosphorus in the spectra of BD +30 3639, NGC 40, and NGC 5315 throughthe doublet transition P V λλ1118, 1128 (3p2Po-3s 2S). The Fe, Si, P, S, and Neabundances were analyzed in the context of the nucleosynthesis occurringin previous evolutionary phases. We found evidence for Fe deficiency inBD +30 3639 and NGC 5315, and we determined a solar Si abundance for BD+30 3639 and NGC 40. Regarding P, an oversolar abundance in the NGC 5315model was preferred. Upper limits for the S abundance were estimated. Wefound that Ne is overabundant in BD +30 3639. In the other stars, Ne isweak or undetectable. Our results are in agreement with theoreticalpredictions and show the usefulness of [WR] stars as test beds fornucleosynthesis calculations in the AGB and post-AGB phases.
| Radio-continuum spectrum, brightness temperature, and planetary nebulae properties
Context: .Radio-continuum spectra are frequently used to infer thedensity distribution of ionized gaseous regions, while observedcorrelations between the brightness temperature and otherdistance-independent parameters are used to test evolutionary models ofplanetary nebulae. Aims: .We check empirical correlations amongfeatures derived from the observed radio data and the inferredconclusions available in the literature, using self-consistentphotoionization models. Methods: .Photoionization models arecomputed for the physical conditions of planetary nebulae in order toderive self-consistent radio-continuum spectra, as well as thebrightness temperature. Results: .The temperature and ionizationdistributions throughout the nebulae explain the observed range ofspectral indexes in the thick region of the spectrum, even for a uniformdensity distribution, usually challenged in the literature. The obtainedmodels fit the observed radio spectra for planetary nebulae in a largerange of spectral indexes. Our calculations show a correlation betweenthe spectral index obtained in a given frequency range and the nebulasize, as well as reproduce the observed relations between the brightnesstemperature and other distance-independent parameters. Such diagrams arefrequently used to check evolutionary models of the central star and/orof the nebula. Conclusions: .Since PNe images clearly show thatthe density is not constant inside the nebulae, and models with uniformand non-uniform density distributions can both reproduce the observedradio spectra, we conclude that it is not possible to favour one of themfrom the radio data, or to infer a particular density distribution forplanetary nebulae.
| Circumstellar Atomic Hydrogen in Evolved Stars
We present new results of a spectroscopic survey of circumstellar H I inthe direction of evolved stars made with the NançayRadiotelescope. The H I line at 21 cm has been detected in thecircumstellar shells of a variety of evolved stars: asymptotic giantbranch stars, oxygen-rich and carbon-rich stars, semiregular and Miravariables, and planetary nebulae. The emissions are generally spatiallyresolved, i.e., larger than 4', indicating shell sizes on the order of 1pc, which opens the possibility of tracing the history of mass loss overthe past ~104-105 yr. The line profiles aresometimes composite. The individual components generally have aquasi-Gaussian shape; in particular, they seldom show the double-hornprofile that would be expected from the spatially resolved opticallythin emission of a uniformly expanding shell. This probably implies thatthe expansion velocity decreases outward in the external shells (0.1-1pc) of these evolved stars. The H I line profiles do not necessarilymatch those of the CO rotational lines. Furthermore, the centroidvelocities do not always agree with those measured in the CO linesand/or the stellar radial velocities. The H I emissions may also beshifted in position with respect to the central stars. Without excludingthe possibility of asymmetric mass ejection, we suggest that these twoeffects could also be related to a nonisotropic interaction with thelocal interstellar medium. H I was detected in emission toward severalsources (ρ Per, α Her, δ2 Lyr, U CMi) thatotherwise have not been detected in any radio lines. Conversely, it wasnot detected in the two oxygen-rich stars with substantial mass-lossrate, NML Tau and WX Psc, possibly because these sources are young, withhydrogen in molecular form, and/or because the temperature of thecircumstellar H I gas is very low (<5 K).This paper is dedicated to the memory of Marie-Odile Mennessier(1940-2004).
| Three-Dimensional Photoionization Structure and Distances of Planetary Nebulae. III. NGC 6781
Continuing our series of papers on the three-dimensional (3D) structuresof and accurate distances to planetary nebulae (PNe), we present ourstudy of the planetary nebula NGC 6781. For this object, we construct a3D photoionization model and, using the constraints provided byobservational data from the literature, we determine the detailed 3Dstructure of the nebula, the physical parameters of the ionizing source,and the first precise distance. The procedure consists of simultaneouslyfitting all the observed emission-line morphologies, integratedintensities, and the two-dimensional (2D) density map from the [S II]line ratios to the parameters generated by the model, and in aniterative way obtaining the best fit for the central star parameters andthe distance to NGC 6781, obtaining values of 950+/-143 pc and 385Lsolar for the distance and luminosity of the central star,respectively. Using theoretical evolutionary tracks of intermediate andlow-mass stars, we derive the mass of the central star of NGC 6781 andits progenitor to be 0.60+/-0.03 Msolar and 1.5+/-0.5Msolar, respectively.
| Morpho-kinematic modeling of planetary nebulae
We present a powerful new tool to disentangle the 3-D geometry andkinematic structure of gaseous nebulae. The method consists of combiningcommercially available digital animation software to simulate the 3-Dstructure and expansion pattern of the nebula with a dedicated, purposebuilt rendering software that produces the final images and long slitspectra which are compared to the real data.
| Morpho-Kinematic Modeling of Gaseous Nebulae with SHAPE
We present a powerful new tool to analyse and disentangle the 3-Dgeometry and kinematic structure of gaseous nebulae. The method consistsin combining commercially available digital animation software tosimulate the 3-D structure and expansion pattern of the nebula with adedicated, purpose-built rendering software that produces the finalimages and long slit spectra which are compared to the real data. Weshow results for the complex planetary nebulae NGC 6369 and Abell 30based on long slit spectra obtained at the San Pedro MártirObservatory.
| Galactic Planetary Nebulae with Wolf-Rayet Nuclei III. Kinematical Analysis of a Large Sample of Nebulae
Expansion velocities (V_{exp}) of different ions and line widths at thebase of the lines are measured and analyzed for 24 PNe with [WC]-typenuclei (WRPNe), 9 PNe ionized by WELS (WLPNe) and 14 ordinary PNe. Acomparative study of the kinematical behavior of the sample clearlydemonstrates that WRPNe have on average 40-45% larger V_{exp}, andpossibly more turbulence than WLPNe and ordinary PNe. WLPNe havevelocity fields very much like the ones of ordinary PNe, rather than theones of WRPNe. All the samples (WRPNe, WLPNe and ordinary PNe) showexpansion velocities increasing with age indicators, for example is larger for low-density nebulae and also it is largerfor nebulae around high-temperature stars. This age effect is muchstronger for evolved WRPNe, suggesting that the [WC] winds have beenaccelerating the nebulae for a long time, while for non-WRPNe theacceleration seems to stop at some point when the star reaches atemperature of about 90,000 - 100,000. Non-WR nebulae reach a maximumV_{exp} ≤ 30 km s(-1) evolved WRPNe reach maximum V_{exp} about 40km s(-1) . For all kinds of objects (WRPNe and non-WRPNe) it is foundthat on average V_{exp}(N(+) ) is slightly larger than V_{exp}(O(++) ),indicating that the nebulae present acceleration of the external shells.
| Morpho-kinematic modelling of gaseous nebulae with Shape
We present a powerful new tool to disentangle the 3-D geometry andkinematic structure of gaseous nebulae. The method consists of combiningcommercially available digital animation software to simulate the 3-Dstructure and expansion pattern of the nebula with a dedicated, purposebuilt rendering software that produces the final images and long slitspectra which are compared to the real data. In this contribution weshow results for the complex planetary nebula NGC369 based on long slitspectra obtained at the San Pedro Mártir observatory.
| Polycyclic aromatic hydrocarbon emission bands in selected planetary nebulae: a study of the behaviour with gas phase C/O ratio
Airborne and space-based low-resolution spectroscopy in the 1980sdiscovered tantalizing quantitative relationships between the gas phaseC/O abundance ratio in planetary nebulae (PNe) and the fractions oftotal far-infrared (FIR) luminosity radiated by the 7.7- and 11.3-μmbands (the C = C stretch and C-H bend, respectively), of polycyclicaromatic hydrocarbons (PAHs). Only a very small sample of nebulae wasstudied in this context, limited by airborne observations of the7.7-μm band, or the existence of adequate IRAS Low ResolutionSpectrometer data for the 11.3-μm band. To investigate these trendsfurther, we have expanded the sample of planetaries available for thisstudy using Infrared Space Observatory (ISO) low-resolution spectrasecured with the Short Wavelength Spectrometer and the Long WavelengthSpectrometer. The new sample of 43 PNe, of which 17 are detected in PAHemission, addresses the range from C/O = 0.2-13 with the objective oftrying to delineate the pathways by which carbon dust grains might haveformed in planetaries. For the 7.7-μm and 11.3-μm bands, weconfirm that the ratio of band strength to total infrared (IR)luminosity is correlated with the nebular C/O ratio. Expressed inequivalent width terms, the cut-on C/O ratio for the 7.7-μm band isfound to be 0.6+0.2-0.4, in good accord with thatfound from sensitive ground-based measurements of the 3.3-μ band.
| The Chemical Composition of Galactic Planetary Nebulae with Regard to Inhomogeneity in the Gas Density in Their Envelopes
The results of a study of the chemical compositions of Galacticplanetary nebulae taking into account two types of inhomogeneity in thenebular gas density in their envelopes are reported. New analyticalexpressions for the ionization correction factors have been derived andare used to determine the chemical compositions of the nebular gas inGalactic planetary nebulae. The abundances of He, N, O, Ne, S, and Arhave been found for 193 objects. The Y Z diagrams for various Heabundances are analyzed for type II planetary nebulae separately andjointly with HII regions. The primordial helium abundance Y p andenrichment ratio dY/dZ are determined, and the resulting values arecompared with the data of other authors. Radial abundance gradients inthe Galactic disk are studied using type II planetary nebulae.
| Three-Dimensional Photoionization Structure and Distances of Planetary Nebulae. II. Menzel 1
We present the results of a spatiokinematic study of the planetarynebula Menzel 1 using spectrophotometric mapping and a three-dimensionalphotoionization code. We create several two-dimensional emission-lineimages from our long-slit spectra and use these to derive the linefluxes for 15 lines, the Hα/Hβ extinction map, and the [S II]line ratio density map of the nebula. We use our photoionization codeconstrained by these data to derive the three-dimensional nebularstructure and ionizing star parameters of Menzel 1 by simultaneouslyfitting the integrated line intensities, the density map, and theobserved morphologies in several lines, as well as the velocitystructure. Using theoretical evolutionary tracks of intermediate- andlow-mass stars, we derive a mass for the central star of 0.63+/-0.05Msolar. We also derive a distance of 1050+/-150 pc to Menzel1.
| The populations of planetary nebulae in the direction of the Galactic bulge. Chemical abundances and Wolf-Rayet central stars
We have observed 44 planetary nebulae (PNe) in the direction of theGalactic bulge, and merged our data with published ones. We havedistinguished, in the merged sample of 164 PNe, those PNe most likely toprtain physically to the Galactic bulge and those most likely to belongto the Galactic disk. We have determined the chemical composition of allthe 164 objects in a coherent way. We looked for stellar emissionfeatures and discovered 14 new [WR] stars and 15 new weak emission linecentral stars. The analyzed data led us to the following conclusions:(1) the spectral type distribution of [WR] stars is very different inthe bulge and in the disk of the Galaxy. However, the observeddistributions are strongly dependent on selection effects. (2) Theproportion of [WR] PNe is significantly larger in the bulge than in thedisk. (3) The oxygen abundances in [WR] stars do no appear to besignificantly affected by nucleosynthesis and mixing in the progenitors.(4) The O/H gradient of the Galactic disk PNe population flattens in themost internal parts of the Galaxy. (5) The median oxygen abundance inthe bulge PN population is larger by 0.2 dex than in the disk populationseen in the direction of the bulge. (6) Bulge PNe with smaller O/H tendto have smaller radial velocities. (7) The oxygen abundance distributionof bulge PNe is similar in shape to that of the metallicity distributionof bulge giants, but significantly narrower. (8) The location ofSB 32 (PN G 349.7-09.1) in the(Vlsr, lII) diagram and its low oxygen abundanceargues that it probably belongs to the halo population.Based on observations made at the South African AstronomicalObservatory.Tables 1-3 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http: / /cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/427/231
| Three-Dimensional Photoionization Structure and Distances of Planetary Nebulae. I. NGC 6369
We present the results of mapping the planetary nebula NGC 6369 by usingmultiple long-slit spectra taken with the Cerro Tololo Inter-AmericanObservatory 1.5 m telescope. We create two-dimensional emission-lineimages from our spectra and use these to derive fluxes for 17 lines, theHα/Hβ extinction map, the [S II ] line ratio density map, andthe [N II] temperature map of the nebula. We use our photoionizationcode constrained by these data to determine the distance and theionizing star characteristics and to show that a clumpy hourglass shapeis the most likely three-dimensional structure for NGC 6369. Note thatour knowledge of the nebular structure eliminates all uncertaintiesassociated with classical distance determinations, and our method can beapplied to any spatially resolved emission-line nebula. We use thecentral star, nebular emission line, and optical+IR luminosities to showthat NGC 6369 is matter bound, as about 70% of the Lyman continuum fluxescapes. Using recent evolutionary tracks from Blöcker, we derive acentral star mass of about 0.65 Msolar.
| The distances of Type I planetary nebulae
The distances D of planetary nebulae (PNe) are still extremelyuncertain. Although a variety of methods have been used to evaluate thisparameter, these are often in conflict, and subject to large random andsystematic errors. It is therefore important to evaluate D using as manyindependent procedures as possible. We outline here one further way inwhich this parameter may be assessed. It is noted that where the nebularmass range is narrow, then one might expect observed PNe radii to beroughly similar. This, where it occurs, would also result in acorrelation between their angular diameters Θ, and distances D.We find that just such a trend occurs for Type I nebulae, and we employthis to determine distances to a further 44 such outflows. Our meanvalues of D appear similar to those of Zhang [ApJS 98 (1995) 659],implying a relatively long PNe distance scale.
| A reanalysis of chemical abundances in galactic PNe and comparison with theoretical predictions
New determinations of chemical abundances for He, N, O, Ne, Ar and Sare derived for all galactic planetary nebulae (PNe) so far observedwith a relatively high accuracy, in an effort to overcome differences inthese quantities obtained over the years by different authors usingdifferent procedures. These include: ways to correct for interstellarextinction, the atomic data used to interpret the observed line fluxes,the model nebula adopted to represent real objects and the ionizationcorrections for unseen ions. A unique `good quality' classical-typeprocedure, i.e. making use of collisionally excited forbidden lines toderive ionic abundances of heavy ions, has been applied to allindividual sets of observed line fluxes in each specific position withineach PN. Only observational data obtained with linear detectors, andsatisfying some `quality' criteria, have been considered. Suchobservations go from the mid-1970s up to the end of 2001. Theobservational errors associated with individual line fluxes have beenpropagated through the whole procedure to obtain an estimate of theaccuracy of final abundances independent of an author's `prejudices'.Comparison of the final abundances with those obtained in relevantmulti-object studies on the one hand allowed us to assess the accuracyof the new abundances, and on the other hand proved the usefulness ofthe present work, the basic purpose of which was to take full advantageof the vast amount of observations done so far of galactic PNe, handlingthem in a proper homogeneous way. The number of resulting PNe that havedata of an adequate quality to pass the present selection amounts to131. We believe that the new derived abundances constitute a highlyhomogeneous chemical data set on galactic PNe, with realisticuncertainties, and form a good observational basis for comparison withthe growing number of predictions from stellar evolution theory. Owingto the known discrepancies between the ionic abundances of heavyelements derived from the strong collisonally excited forbidden linesand those derived from the weak, temperature-insensitive recombinationlines, it is recognized that only abundance ratios between heavyelements can be considered as satisfactorily accurate. A comparison withtheoretical predictions allowed us to assess the state of the art inthis topic in any case, providing some findings and suggestions forfurther theoretical and observational work to advance our understandingof the evolution of low- and intermediate-mass stars.
| Characteristics of Planetary Nebulae with [WC] Central Stars
We have analyzed the plasma diagnostics (electron densities andtemperatures and abundance ratios), and the kinematics of a large sampleof planetary nebulae around [WC] stars by means of high resolutionspectra. The results have been compared with characteristics ofplanetary nebulae around WELS and non-WR central stars. We find that theproportion of nitrogen rich nebulae is larger in WRPNe than innon-WRPNe. None of the 9 nebulae around WELS in our sample showsN-enrichment. WRPNe have larger expansion velocities and/or largerturbulence than non-WRPNe demonstrating that the mechanical energy ofthe massive [WC] stellar wind largely affects the kinematical behaviorof nebulae. A weak relation between stellar temperature and expansionvelocities has been found for all kind of nebulae, indicating that oldernebulae expand faster. The effect is more important for WRPNe. Thiscould be useful in testing the evolutionary sequence [WC]-late ->[WC]-early, proposed for [WC] stars.
| The relation between Zanstra temperature and morphology in planetary nebulae
We have created a master list of Zanstra temperatures for 373 galacticplanetary nebulae based upon a compilation of 1575 values taken from thepublished literature. These are used to evaluate mean trends intemperature for differing nebular morphologies. Among the most prominentresults of this analysis is the tendency forη=TZ(HeII)/TZ(HeI) to increase with nebularradius, a trend which is taken to arise from the evolution of shelloptical depths. We find that as many as 87 per cent of nebulae may beoptically thin to H ionizing radiation where radii exceed ~0.16 pc. Wealso note that the distributions of values η and TZ(HeII)are quite different for circular, elliptical and bipolar nebulae. Acomparison of observed temperatures with theoretical H-burning trackssuggests that elliptical and circular sources arise from progenitorswith mean mass ≅ 1 Msolar(although the elliptical progenitors are probably more massive).Higher-temperature elliptical sources are likely to derive fromprogenitors with mass ≅2 Msolar, however, implying thatthese nebulae (at least) are associated with a broad swathe ofprogenitor masses. Such a conclusion is also supported by trends in meangalactic latitude. It is found that higher-temperature ellipticalsources have much lower mean latitudes than those with smallerTZ(HeII), a trend which is explicable where there is anincrease in with increasing TZ(HeII).This latitude-temperature variation also applies for most other sources.Bipolar nebulae appear to have mean progenitor masses ≅2.5Msolar, whilst jets, Brets and other highly collimatedoutflows are associated with progenitors at the other end of the massrange (~ 1 Msolar). Indeed it ispossible, given their large mean latitudes and low peak temperatures,that the latter nebulae are associated with the lowest-mass progenitorsof all.The present results appear fully consistent with earlier analyses basedupon nebular scale heights, shell abundances and the relativeproportions of differing morphologies, and offer further evidence for alink between progenitor mass and morphology.
| Galactic Planetary Nebulae and their central stars. I. An accurate and homogeneous set of coordinates
We have used the 2nd generation of the Guide Star Catalogue (GSC-II) asa reference astrometric catalogue to compile the positions of 1086Galactic Planetary Nebulae (PNe) listed in the Strasbourg ESO Catalogue(SEC), its supplement and the version 2000 of the Catalogue of PlanetaryNebulae. This constitutes about 75% of all known PNe. For these PNe, theones with a known central star (CS) or with a small diameter, we havederived coordinates with an absolute accuracy of ~0\farcs35 in eachcoordinate, which is the intrinsic astrometric precision of the GSC-II.For another 226, mostly extended, objects without a GSC-II counterpartwe give coordinates based on the second epoch Digital Sky Survey(DSS-II). While these coordinates may have systematic offsets relativeto the GSC-II of up to 5 arcsecs, our new coordinates usually representa significant improvement over the previous catalogue values for theselarge objects. This is the first truly homogeneous compilation of PNepositions over the whole sky and the most accurate one available so far.The complete Table \ref{tab2} is only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/408/1029}
| Angular dimensions of planetary nebulae
We have measured angular dimensions of 312 planetary nebulae from theirimages obtained in Hα (or Hα + [NII]). We have appliedthree methods of measurements: direct measurements at the 10% level ofthe peak surface brightness, Gaussian deconvolution and second-momentdeconvolution. The results from the three methods are compared andanalysed. We propose a simple deconvolution of the 10% levelmeasurements which significantly improves the reliability of thesemeasurements for compact and partially resolved nebulae. Gaussiandeconvolution gives consistent but somewhat underestimated diameterscompared to the 10% measurements. Second-moment deconvolution givesresults in poor agreement with those from the other two methods,especially for poorly resolved nebulae. From the results of measurementsand using the conclusions of our analysis we derive the final nebulardiameters which should be free from systematic differences between small(partially resolved) and extended (well resolved) objects in our sample.Table 1 is only available in electronic form athttp://www.edpsciences.org
| Quantitative classification of WR nuclei of planetary nebulae
We analyse 42 emission-line nuclei of Planetary Nebulae (PNe), in theframework of a large spectrophotometric survey of [WC] nuclei of PNeconducted since 1994, using low/medium resolution spectra obtained atESO and at OHP. We construct a grid of selected line-intensities(normalized to C Iv-5806 Å= 100) ordered by decreasing ionisationpotential going from 871 to 24 eV. In this grid, the stars appear tobelong clearly to prominent O (hot [WO1-4] types) or C (cooler [WC4-11]types) line-sequences, in agreement with the classification of massiveWR stars applied to Central Stars of Planetary Nebulae (CSPNe) byCrowther et al. \cite{crowther98} (CMB98). We propose 20 selected lineratios and the FWHM of C Iv and C Iii lines as classificationdiagnostics, which agree well with the 7 line ratios and the FWHMproposed by CMB98. This classification based on ionisation is related tothe evolution of the temperature and of the stellar wind, reflecting themass-loss history. In particular, inside the hot [WO4]-class, wediscover four stars showing very broad lines over the whole spectralrange. These stars possibly mark the transition from the initialmomentum-driven phase to the later energy-driven phase of the CSPNealong their evolution from the post-Asymptotic Giant Branch (post-AGB)phase through [WC] late, [WC4] and [WO]-types. The HR diagram and thediagram linking the terminal velocity and the temperature indicatehighly dispersed values of the stellar mass for our sample, around amean mass higher than for normal CSPNe. The distribution of the 42 starsalong the ionisation sequence shows 24% of [WO1-3], 21% of [WO4], 17% of[WC4] hot stars, and 26% of [WC9-11] cool stars. The [WC5-8] classesremain poorly represented (12%). This distribution is confirmed on thebasis of a large compilation of the 127 known emission-lines CSPNe,which represent about 5% of the known PNe.Based on observations obtained at the European Southern Observatory(ESO), La Silla (Chile), and at the Observatoire de Haute-Provence (OHP,France).Table \ref{liste} is only available in electronic form athttp://www.edpsciences.org
| Ionized haloes in planetary nebulae: new discoveries, literature compilation and basic statistical properties
We present a comprehensive observational study of haloes aroundplanetary nebulae (PNe). Deep Hα+[NII] and/or [OIII] narrow-bandimages have been obtained for 35 PNe, and faint extended haloes havebeen newly discovered in the following 10 objects: Cn 1-5, IC 2165, IC2553, NGC 2792, NGC 2867, NGC 3918, NGC 5979, NGC 6578, PB 4, andpossibly IC 1747. New deep images have also been obtained of other knownor suspected haloes, including the huge extended emission around NGC3242 and Sh 2-200. In addition, the literature was searched, andtogether with the new observations an improved data base containing some50 PN haloes has been compiled.The halo sample is illustrated in an image atlas contained in thispaper, and the original images are made available for use by thescientific community at http://www.ing.iac.es/~rcorradi/HALOES/.The haloes have been classified following the predictions of modernradiation-hydrodynamical simulations that describe the formation andevolution of ionized multiple shells and haloes around PNe. According tothe models, the observed haloes have been divided into the followinggroups: (i) circular or slightly elliptical asymptotic giant branch(AGB) haloes, which contain the signature of the last thermal pulse onthe AGB; (ii) highly asymmetrical AGB haloes; (iii) candidaterecombination haloes, i.e. limb-brightened extended shells that areexpected to be produced by recombination during the late post-AGBevolution, when the luminosity of the central star drops rapidly by asignificant factor; (iv) uncertain cases which deserve further study fora reliable classification; (v) non-detections, i.e. PNe in which no halois found to a level of <~10-3 the peak surface brightnessof the inner nebulae.We discuss the properties of the haloes: detection rate, morphology,location of the central stars in the Hertzsprung-Russell diagram, sizes,surface brightness profiles, and kinematical ages. Among the mostnotable results, we find that, as predicted by models, ionized AGBhaloes are a quite common phenomenon in PNe, having been found in 60 percent of elliptical PNe for which adequately deep images exist. Another10 per cent show possible recombination haloes. In addition, using thekinematical ages of the haloes and inner nebulae, we conclude that mostof the PNe with observed AGB haloes have left the AGB far from a thermalpulse, at a phase when hydrogen burning is the dominant energy source.We find no significant differences between the AGB haloes ofhydrogen-poor and hydrogen-rich central stars.
| Three-Dimensional Photoionization Modeling of the Planetary Nebula NGC 6369
The planetary nebula NGC 6369 has an irregular morphology. We presentpreliminary results of a 3-D modeling effort for this object. We comparethe model with our observed spectrophotometric line images and densitymaps, also presented in this volume. The model results should give amore realistic understanding of the photoionization scenario in thenebula giving important clues to the true gas distribution in thisobject.
| Spectrophotometric Mapping of the Planetary Nebula NGC 6369
In this work we present the results of mapping the planetary nebula NGC6369 with long-slit spectroscopy. The observations were carried out withthe CTIO 1.5 m telescope and Cassegrain spectrograph. Ten slit positionswere observed across the nebula with a total exposure time of 11 hours.All positions were then combined to create ``images'' in emission lineslike [O III] 5007, H alpha , [N II] 6584 and others. These images canthen be used to study the classical diagnostic line ratios such as the[S II] doublet, which is a density indicator. The [S II] ratio maps, aswell as the H alpha /H beta extinction maps for this object and totalline fluxes for the most important lines are presented.
| Percolating Winds through a Clumpy Torus
By way of axisymmetric numerical hydrodynamical simulations we study theinteraction of a fast tenuous stellar wind with a thick toroidaldistribution of high-density clouds embedded in a stationary intercloudmedium with a power-law density fall-off of index -1.9. We find that thesupersonic wind percolates through the cloud ensemble, producingfinger-like structures in the contact discontinuity. We also find thatsuch a toroidal distribution of clouds is sufficient to collimate ajet-like outflow along the symmetry axis. After the start of theinteraction with the stellar wind, cometary tails in the outer regiontemporarily tend to be short and hollow, whereas older tails are longand filled with ablated high-density gas.
| ISO-SWS spectra of [WR] planetary nebulae
Not Available
| Abundances of [WC] Central Stars of PN and the Double Dust Chemistry Problem (invited review)
Not Available
| WR Central Stars (invited review)
Not Available
| The carrier of the ``30'' mu m emission feature in evolved stars. A simple model using magnesium sulfide
We present 2-45 mu m spectra of a large sample of carbon-rich evolvedstars in order to study the ``30'' mu m feature. We find the ``30'' mu mfeature in a wide range of sources: low mass loss carbon stars, extremecarbon-stars, post-AGB objects and planetary nebulae. We extract theprofiles from the sources by using a simple systematic approach to modelthe continuum. We find large variations in the wavelength and width ofthe extracted profiles of the ``30'' mu m feature. We modelled the wholerange of profiles in a simple way by using magnesium sulfide (MgS) dustgrains with a MgS grain temperature different from the continuumtemperature. The systematic change in peak positions can be explained bycooling of MgS grains as the star evolves off the AGB. In severalsources we find that a residual emission excess at ~ 26 mu m can also befitted using MgS grains but with a different grains shape distribution.The profiles of the ``30'' mu m feature in planetary nebulae arenarrower than our simple MgS model predicts. We discuss the possiblereasons for this difference. We find a sample of warm carbon-stars withvery cold MgS grains. We discuss possible causes for this phenomenon. Wefind no evidence for rapid destruction of MgS during the planetarynebula phase and conclude that the MgS may survive to be incorporated inthe ISM. Based on observations obtained with ISO, an ESA project withinstruments funded by ESA Member states (especially the PI countries:France, Germany, The Netherlands and the United Kingdom) with theparticipation of ISAS and NASA. Appendix A (Figs. A.1 and A.2) is onlyavailable in electronic form at http://www.edpsciences.org
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