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The distances of less-evolved planetary nebulae: a further test of statistical distance scales
It has recently been pointed out that a number of the methods used todetermine planetary nebulae (PNe) distances may be appreciably in error.Whilst the scales of Zhang (1995), Bensby & Lundstrom (2001) andothers are appropriate for higher radio brightness temperaturesTB, those of Phillips and Daub are more relevant whereTB is small.We note, in the following, that the absolute bolometric magnitudes ofless-evolved PNe are likely to be similar. The mean value of can therefore be used to constrain PNe distancesD, and confirm the distance scales for higher TB outflows. Wehave used this procedure to evaluate distances to a further 47 PNe, andwe find that the mean values of are consistent with those ofCahn, Kaler & Stanghellini (1992), Zhang (1995), Phillips et al.(2004) and van de Steene & Zijlstra (1995). They are, as expected,inconsistent with the lower TB scale of Phillips (2002a).
| Evolution from AGB to planetary nebula in the MSX survey
We investigate the evolution of oxygen- and carbon-rich AGB stars,post-AGB objects, and planetary nebulae using data collected mainly fromthe MSX catalogue. Magnitudes and colour indices are compared with thosecalculated from a grid of synthetic spectra that describe the post-AGBevolution beginning at the onset of the superwind. We find that carbonstars and OH/IR objects form two distinct sequences in the (K-[8.3])×([8.3]-[14.7]) MSX colour diagram. OH/IR objects are distributedin two groups: the bluest ones are crowded near [14.7]-[21.3]≃ 1and [8.3]-[14.7]≃ 2, and a second, redder group is spread over alarge area in the diagram, where post-AGB objects and planetary nebulaeare also found. High mass-loss rate OH/IR objects, post-AGB stars, andplanetary nebulae share the same region in the (K-[8.3])×([8.3]-[14.7]) and [14.7]-[21.3]×([8.3]-[14.7]) colour-colourdiagrams. This region in the diagram is clearly separated from a bluerone where most OH/IR stars are found. We use a grid of models ofpost-AGB evolution, which are compared with the data. The gap in thecolour-colour diagrams is interpreted as the result of the rapidtrajectory in the diagram of the stars that have just left the AGB.Based on results obtained by the MSX survey.Tables 1 to 3 are 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/431/565
| A reexamination of electron density diagnostics for ionized gaseous nebulae
We present a comparison of electron densities derived from opticalforbidden line diagnostic ratios for a sample of over a hundred nebulae.We consider four density indicators, the [O II]λ3729/λ3726, [S II] λ6716/λ6731, [Cl III]λ5517/λ5537 and [Ar IV] λ4711/λ4740 doubletratios. Except for a few H II regions for which data from the literaturewere used, diagnostic line ratios were derived from our own high qualityspectra. For the [O II] λ3729/λ3726 doublet ratio, we findthat our default atomic data set, consisting of transition probabilitiesfrom Zeippen (\cite{zeippen1982}) and collision strengths from Pradhan(\cite{pradhan}), fit the observations well, although at high electrondensities, the [O II] doublet ratio yields densities systematicallylower than those given by the [S II] λ6716/λ6731 doubletratio, suggesting that the ratio of transition probabilities of the [OII] doublet, A(λ3729)/A(λ3726), given by Zeippen(\cite{zeippen1982}) may need to be revised upwards by approximately 6per cent. Our analysis also shows that the more recent calculations of[O II] transition probabilities by Zeippen (\cite{zeippen1987a}) andcollision strengths by McLaughlin & Bell (\cite{mclaughlin}) areinconsistent with the observations at the high and low density limits,respectively, and can therefore be ruled out. We confirm the earlierresult of Copetti & Writzl (\cite{copetti2002}) that the [O II]transition probabilities calculated by Wiese et al. (\cite{wiese}) yieldelectron densities systematically lower than those deduced from the [SII] λ6716/λ6731 doublet ratio and that the discrepancy ismost likely caused by errors in the transition probabilities calculatedby Wiese et al. (\cite{wiese}). Using our default atomic data set for [OII], we find that Ne([O II]) Ne([S II]) ≈Ne([Cl III])< Ne([Ar IV]).
| Radiation-driven winds of hot luminous stars. XV. Constraints on the mass-luminosity relation of central stars of planetary nebulae
We present a new model atmosphere analysis of nine central stars ofplanetary nebulae. This study is based on a new generation of realisticstellar model atmospheres for hot stars; state-of-the-art,hydrodynamically consistent, spherically symmetric model atmospheresthat have been shown to correctly reproduce the observed UV spectra ofmassive Population I O-type stars. The information provided by the windfeatures (terminal velocity, mass loss rate) permits to derive thephysical size of each central star, from which we can derive the stellarluminosity, mass, and distance, without having to assume a relationbetween stellar mass and luminosity taken from the theory of stellarstructure and AGB and post-AGB evolution. The results of our analysisare quite surprising: we find severe departures from the generallyaccepted relation between post-AGB central star mass and luminosity.
| 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}
| GLIMPSE. I. An SIRTF Legacy Project to Map the Inner Galaxy
The Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE),a Space Infrared Telescope Facility (SIRTF) Legacy Science Program, willbe a fully sampled, confusion-limited infrared survey of 2/3 of theinner Galactic disk with a pixel resolution of ~1.2" using the InfraredArray Camera at 3.6, 4.5, 5.8, and 8.0 μm. The survey will coverGalactic latitudes |b|<=1deg and longitudes|l|=10deg-65° (both sides of the Galactic center). Thesurvey area contains the outer ends of the Galactic bar, the Galacticmolecular ring, and the inner spiral arms. The GLIMPSE team will processthese data to produce a point-source catalog, a point-source dataarchive, and a set of mosaicked images. We summarize our observingstrategy, give details of our data products, and summarize some of theprincipal science questions that will be addressed using GLIMPSE data.Up-to-date documentation, survey progress, and information oncomplementary data sets are available on the GLIMPSE Web site.
| 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
| Radiation Driven Atmospheres of O-type stars: Constraints on the Mass-Luminosity Relation of Central Stars of Planetary Nebulae (invited review)
Recent advances in the modelling of stellar winds driven by radiationpressure make it possible to fit many wind-sensitive features in the UVspectra of hot stars, opening the way for a hydrodynamically consistentdetermination of stellar radii, masses, and luminosities from the UVspectrum alone. It is thus no longer necessary to assume a theoreticalmass-luminosity relation. As the method has been shown to work formassive O-stars, we are now able to test predictions from the post-AGBevolutionary calculations quantitatively for the first time. Here wepresent the first rather surprising consequences of using the newgeneration of model atmospheres for the analysis of a sample of centralstars of planetary nebulae.
| Low-Ionization Structures in Planetary Nebulae: Confronting Models with Observations
Around 50 planetary nebulae (PNs) are presently known to possess``small-scale'' low-ionization structures (LISs) located inside oroutside their main nebular bodies. We consider here the different kindsof LISs (jets, jetlike systems, symmetrical and nonsymmetrical knots)and present a detailed comparison of the existing model predictions withthe observational morphological and kinematical properties. We find thatnebulae with LISs appear indistinctly spread among all morphologicalclasses of PNs, indicating that the processes leading to the formationof LISs are not necessarily related to those responsible for theasphericity of the large-scale morphological components of PNs. We showthat both the observed velocities and locations of most nonsymmetricalsystems of LISs can be reasonably well reproduced assuming either fossilcondensations originated in the asymptotic giant branch (AGB) wind or insitu instabilities. The jet models proposed to date (hydrodynamical andmagnetohydrodynamical interacting winds or accretion disk collimatedwinds) appear unable to account simultaneously for several keycharacteristics of the observed high-velocity jets, such as theirkinematical ages and the angle between the jet and the symmetry axes ofthe nebulae. The linear increase in velocity observed in several jetsfavors magnetohydrodynamical confinement compared to pure hydrodynamicalinteracting wind models. On the other hand, we find that the formationof jetlike systems characterized by relatively low expansion velocities(similar to those of the main shells of PNs) cannot be explained by anyof the existing models. Finally, the knots that appear in symmetricaland opposite pairs of low velocity could be understood as the survivalof fossil (symmetrical) condensations formed during the AGB phase or asstructures that have experienced substantial slowing down by the ambientmedium.
| Gravity distances of planetary nebulae II. Aplication to a sample of galactic objects.
Not Available
| Gas Dynamics in Planetary Nebulae: From Macro-structures to FLIERs
Purpose of this paper is to clarify how Planetary Nebulae (PNe) are veryinteresting laboratories to study cosmic gas dynamics. I first recallthe history of PNe which are generated from low and intermediate massstars through successive mass loss processes starting in the Reg Giantphase of evolution and continuing also after the termination of thepulsed AGB phase, where most of the nebular mass is believed to beejected. The correponding stellar winds are the ingredients of thenebula. Their initial properties and subsequent mutual interactions,under the action of the evolving stellar radiation field, areresponsible for the properties of the nebula. The observed structures ofPNe are considered in detail. Larger scale macroscopic structures (MACS)are examined separately from quite smaller scale microscopic structures(MICS). The formation of MACS, at least in cases of round to moderatelyelliptical PNe, is shown to be reasonably well understood in terms ofexisting hydrodynamical models. Considering the kinematical behaviour,MICS can be separated into FLIERs (Fast Low Ionization Emitting Regions)and SLOWERs (slowly moving). Attention is focussed on FLIERs and on theproposed mechanisms to interpret them. Recent observations with theHubble Space Telescope have provided us with a wealth of detailed(subarcsec) information on the nebular structures. The inner structureof FLIERs is here illustrated to consist of substructures of variousshapes with an high degree of individually from object to object, alsowithin the same PN. These new data call for deeper thoretical efforts tosolve the problems of cosmic gas dynamics, posed by their observedproperties. An ample account is given of the most relevant originalworks, in an effort to allow the non specialist reader to quickly becomeacquainted with the status of art in the various aspects of the subject.
| Visual Wide Binaries and the Structure of Planetary Nebulae
In recent work Ciardullo et al. listed 19 planetary nebulae surveyed bythe Hubble Space Telescope for the presence of resolved visual binarycompanions of their central stars. For 10 planetary nebulae they arguefor probable physical association of the resolved stars with the centralstars, while for nine the association is less likely. Such stellarcompanions, at orbital separations of hundreds to thousands ofastronomical units, will cause the structures of these planetary nebulaeto possess a nonaxisymmetric signature. By using images from theliterature of these 19 planetary nebulae, I demonstrate that thestructures of the planetary nebulae are compatible in most cases withthe arguments of Ciardullo et al. for association or nonassociation ofthe resolved stars with the planetary nebulae central stars. This showsthat whether a planetary nebula departs from having purely axisymmetricstructure can be used to strengthen an argument for an association or anonassociation of a putative wide companion with the stellar progenitorof the nebula.
| Spectroscopic investigation of old planetaries. IV. Model atmosphere analysis
The results of a NLTE model atmosphere analysis of 27 hydrogen-richcentral stars of old planetary nebulae (PN) are reported. These starswere selected from a previous paper in this series, where we gaveclassifications for a total of 38 central stars. Most of the analyzedcentral stars fill a previously reported gap in the hydrogen-richevolutionary sequence. Our observations imply the existence of twoseparated spectral evolutionary sequences for hydrogen-rich and -poorcentral stars/white dwarfs. This is in line with theoreticalevolutionary calculations, which predict that most post-AGB stars reachthe white dwarf domain with a thick hydrogen envelope of ~ 10(-4) M_sun.We determine stellar masses from the comparison with evolutionary tracksand derive a mass distribution for the hydrogen-rich central stars ofold PNe. The peak mass and the general shape of the distribution is inagreement with recent determinations of the white dwarf massdistribution. The properties of most analyzed stars are well explainedby standard post-AGB evolution. However, for eight stars of the sampleother scenarios have to be invoked. The properties of three of them areprobably best explained by born again post-AGB evolution. Two of theseare hybrid CSPN (hydrogen-rich PG 1159 stars), but surprisingly thethird star doesn't show any signs of chemical enrichment in itsatmosphere. The parameters of five stars are not in accordance withpost-AGB evolution. We discuss alternative scenarios such as thestripping of the hydrogen-rich envelope by a companion during the firstred giant phase or the formation of a common envelope with a possiblemerging of both components. Two stars (HDW 4 andHaWe 5) remain mysterious after all. They resembleordinary hot DA white dwarfs, but due to very large evolutionary agesthe presence of a PN cannot be explained. We speculate that the nebulaemay be shells produced by ancient nova outbursts. A wide spread ofhelium abundances is observed in the photospheres of central stars ofold PNe. It is shown that a good correlation between helium abundancesand luminosity is present. It is inferred that when the stars'luminosities fall below L~ 300 L_sun depletion starts and the heliumabundance steadily decreases with decreasing luminosity. The existenceof this correlation is in qualitative agreement with recent theoreticalcalculations of gravitational settling in the presence of a stellarwind.
| A HUBBLE SPACE TELESCOPE Survey for Resolved Companions of Planetary Nebula Nuclei
We report the results of a Hubble Space Telescope ``snapshot'' surveyaimed at finding resolved binary companions of the central stars ofGalactic planetary nebulae (PNe). Using the the Wide Field and PlanetaryCamera and Wide Field Planetary Camera 2, we searched the fields of 113PNe for stars whose close proximity to the central star suggests aphysical association. In all, we find 10 binary nuclei that are verylikely to be physically associated and another six that are possiblebinary associations. By correcting for interstellar extinction andplacing the central stars' companions on the main sequence (or, in onecase, on the white dwarf cooling curve), we derive distances to theobjects, and thereby significantly increase the number of PNe withreliable distances. Comparison of our derived distances with thoseobtained from various statistical methods shows that all of the latterhave systematically overestimated the distances, by factors ranging upto a factor of 2 or more. We show that this error is most likely due tothe fact that the properties of our PNe with binary nuclei aresystematically different from those of PNe used heretofore to calibratestatistical methods. Specifically, our PNe tend to have lower surfacebrightnesses at the same physical radius than the traditionalcalibration objects. This difference may arise from a selection effect:the PNe in our survey are typically nearby, old nebulae, whereas most ofthe objects that calibrate statistical techniques are low-latitude, highsurface brightness, and more distant nebulae. As a result, thestatistical methods that seem to work well with samples of distant PNe,for example, those in the Galactic bulge or external galaxies, may notbe applicable to the more diverse population of local PNe. Our distancedeterminations could be improved with better knowledge of themetallicities of the individual nebulae and central stars, measurementsof proper motions and radial velocities for additional candidatecompanions, and deeper HST images of several of our new binary nuclei.
| Electron densities in planetary nebulae, and the unusual characteristics of the [S BT II] emission zone} ] densities in planetary nebulae
We investigate the radial variation of electron densities in planetarynebulae, using values of ne deriving from the [S ii]<~mbda6717/<~mbda6730 line ratio. As a result, we are able to showthat there is a sharp discontinuity in densities of order 1.4 dex closeto nebular radii R=0.1 pc. It is proposed, as a consequence, that mostnebulae contain two primary [S ii] emission zones, with densitiesdiffering by a factor ~ 10(2) . The intensity of emission from thedenser component increases by an order of magnitude where nebulae passfrom radiation to density-bound expansion regimes, resulting in acorresponding discontinuous jump in [S ii]/Hβ line ratios. Theorigins of these changes are not entirely clear, although one mechanismis investigated whereby the superwind outflows shock interact withexterior AGB envelopes. Finally, the derived trends in ne(R)are used to determine distances for a further 262 nebulae. The resultingdistance scale appears to be comparable to that of Daub (1982) and Cahnet al. (1992).
| The kinematics of 867 galactic planetary nebulae
We present a compilation of radial velocities of 867 galactic planetarynebulae. Almost 900 new measurements are included. Previously publishedkinematical data are compared with the new high-resolution data toassess their accuracies. One of the largest samples in the literatureshows evidence for a systematic velocity offset. We calculate weightedaverages between all available data. Of the final values in thecatalogue, 90% have accuracies better than 20 km s(-1) . We use thiscompilation to derive kinematical parameters of the galacticdifferential rotation obtained from least-square fitting and toestablish the Disk rotation curve; we find no significal trend for thepresence of an increasing external rotation curve. We examine also therotation of the bulge; the derived curve is consistent with a linearlyincreasing rotation velocity with l: we find V_b,r=(9.9+/-1.3)l -(6.7+/-8.5) km s(-1) . A possible steeper gradient in the innermostregion is indicated. Table 2 is available in electronic form only, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Properties That Cannot Be Explained by the Progenitors of Planetary Nebulae
I classify a large number of planetary nebulae (458) according to theprocess that caused their progenitors to blow axisymmetrical winds. Theclassification is based primarily on the morphologies of the differentplanetary nebulae, assuming that binary companions, stellar orsubstellar, are necessary in order to have axisymmetrical mass loss onthe asymptotic giant branch. I propose four evolutionary classes,according to the binary-model hypothesis: (1) Progenitors of planetarynebula that did not interact with any companion. These amount to ~10% ofall planetary nebulae. (2) Progenitors that interact with stellarcompanions that avoided a common envelope, 11^{+2}_{-3}% of all nebulae.(3) Progenitors that interact with stellar companions via a commonenvelope phase, 23^{+11}_{-5}% of all nebulae. (4) Progenitors thatinteract with substellar (i.e., planets and brown dwarfs) companions viaa common envelope phase, 56^{+5}_{-8}% of all nebulae. In order todefine and build the different classes, I start with clarifying somerelevant terms and processes related to binary evolution. I then discusskinematical and morphological properties of planetary nebulae thatappear to require the interaction of the planetary nebula progenitorsand/or their winds with companions, stellar or substellar.
| Gravity Distances of Planetary Nebulae
Recent work on the PN classification scheme initially proposed byPeimbert has shown that type I and non-type I objects have markedlydifferent properties. Type I PN have He and N enrichments, lower heightsrelative to the galactic plane, and lower peculiar velocities, whilenon-type I nebulae have normal abundances and increasing heights andpeculiar velocities. This implies some mass and age differences of thedifferent types, which can be used in order to determine distances todisk PN. In this work, the behaviour of PN of different types on the logg× log Teff plane is explored, in view of the fact that centralstars of different masses have different paths on this diagram. As aresult, distances can be derived for some galactic PN, which can becompared with previous determinations. The possibility is discussed ofestablishing a statistical distance scale based on the populationsegregation of PN of different Peimbert types.
| Planetary nebulae morphologies, central star masses and nebular properties.
We have constituted a sample of about 80 PN with defined morphologiesand well observed basic parameters (fluxes, angular radii, expansionvelocities and magnitudes of the central stars). For these PN, we havederived the central star masses by comparing the observed set ofparameters with those predicted by a simple evolutionary model of a PN,expanding at the same velocity as the observed one. We have thenexamined the relations between the PN morphological types and otherproperties, linked to the central star mass. Bipolar PN are shown tohave a wider distribution of central star masses than the rest of PN,and shifted towards higher values. They lie closer to the Galactic planeand tend to have larger N/O ratios. Point symmetric PN, which have notbeen much studied so far, are found to constitute an outstanding class.They show an almost perfect M_*_-v_exp_ correlation. They correspond toa rather short evolutionary stage of PN. They lie, on average, furtherfrom the Galactic plane than bipolar PN and tend to have lower N/O.Globally, PN with higher central star masses are found closer to theGalactic plane, and the observed relation between N/O and M_*_ isroughly consistent with the predictions from evolutionary models for AGBstars.
| Winds in the atmospheres of central stars of Planetary Nebulae (Invited Review)
Not Available
| Unveiling low-ionization microstructures in planetary nebulae.
(Hα+[NII])/[OIII] ratio images have been used to search forlow-ionization small-scale structures in a sample of 258 planetarynebulae. Radially symmetrical knots or jet-like structures, which areenhanced in the ratio images compared to the neighbouring regions of thenebulae, have been identified in 23 objects. Some of these features arebarely detected or invisible in the Hα+[NII] and [OIII] images.Empirical evidence, as well as some simple modelling, demonstrate thatthe selected features are characterized by having a lower ionizationthan the surrounding gas. For the above properties, most of themresemble the low-ionization microstructures discussed recently by Balicket al. (1993, 1994), and named FLIERs (Fast Low-Ionization EmissionRegions). The present work shows that the image-division technique is avery useful tool to look for ionization structures in planetary nebulaeand other HII regions. Its main advantage is that the division removesthe morphological components which are pure density enhancements, sothat the output image remains mostly sensitive to excitation andabundance variations through the nebulae.
| Early Results from the Cycle 5 HST Snapshot Survey of Planetary Nebulae
During Cycle 5 of the HST General Observer program we are carrying out a``snapshot'' survey of the central stars of the nearer planetary nebulae(PNe). These snapshots are taken as short exposures in the V (F555W) andI (F814W) bands during brief scheduling opportunities. The primary aimof the survey is to find close, resolved main-sequence companions of thecentral stars, which through main-sequence fitting will provideexcellent distance estimates for the nebulae. This should in turn allowus to calibrate other, indirect distance methods, and thus materiallyimprove the distance scale for PNe. We will report a number of newdiscoveries of visual binaries in PNe, mostly with separations of lessthan 1'', including the central stars of NGC 650-1 (a resolved triplesystem), NGC 6309, NGC 7008, IC 4637, A 66, A 74, K 1-22, and Sp 3. As abyproduct, the survey produces high-resolution images of the surroundingnebulae, and these have revealed a wealth of new information. Highlightsof our early results include: (1) a resolved circumstellar disk and jetsaround HD 44179, the central star of the ``Red Rectangle''; (2) anextensive network of subarcsecond filamentary dust in IC 4406; (3)``point-symmetric'' or ``spiral'' structure in NGC 5307; (4)subarcsecond dust globules in the Ring Nebula, NGC 6720; and (5) detailsof the diametrically opposed jets emanating from the close-binarycentral star of K 1-2. Supported by STScI Grant GO-6119.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Radiation gasdynamics of planetary nebulae - VI. The evolution of aspherical planetary nebulae
This paper reports the results of the numerical study of the formationof aspherical planetary nebulae through the generalized interactingwinds model, taking into account the effects caused by the evolvingcentral star and fast wind. The results show for the first time thataspherical nebulae do form within the required time-scale. Considerationof the development of the nebula shows that in the early stages it isthe ionization of the aspherical AGB wind that contributes considerablyto the shaping of the nebula. Furthermore, the passing through of theionization front may modify the density distribution in the slow wind,leading to the formation of a surrounding envelope, and sometimes adifferent morphology for the nebula from that to be expected from theinitial conditions. I consider how the different phases of ionizationfronts and wind swept bubbles can be observationally distinguished.
| A statistical distance scale for Galactic planetary nebulae
A statistical distance scale is proposed. It is based on the correlationbetween the ionized mass and the radius and the correlation between theradio continuum surface brightness temperature and the nebular radius.The proposed statistical distance scale is an average of the twodistances obtained while using the correlation. These correlations,calibrated based on the 1`32 planetary nebulae with well-determinedindividual distances by Zhang, can reproduce not only the averagedistance of a sample of Galactic Bulge planetary nebulae exactly at thedistance to the Galactic center, but also the expected Gaussiandistribution of their distances around the Galactic center. This newdistance scale is applied to 647 Galactic planetary nebulae. It isestimated that this distance scale can be accurate on average to35%-50%. Our statistical distance scale is in good agreement with theone recently proposed by Van de Steene and Zijlstra. The correlationsfound in this study can be attributed to the fact that the core mass ofthe central stars has a very sharp distribution, strongly peaked atapprox. 0.6 solar mass. We stress that the scatter seen in thestatistical distance scale is likely to be real. The scatter is causedby the fact that the core mass distribution, although narrow andstrongly peaked, has a finite width.
| A catalogue HeII 4686 line intensities in Galactic planetary nebulae.
We have compiled the intensities of the HeII 4686 lines measured inGalactic planetary nebulae. We present a few observational diagramsrelated to this parameter, and discuss them with the help of theoreticaldiagrams obtained from simple model planetary nebulae surroundingevolving central stars of various masses. We determine the hydrogen andhelium Zanstra temperature for all the objects with accurate enoughdata. We argue that, for Galactic planetary nebulae as a whole, the maincause for the Zanstra discrepancy is leakage of stellar ionizing photonsfrom the nebulae.
| Confrontation of theoretical tracks for post-AGB stars with observations of planetary nebulae
We have constructed a distance-independent diagram to test publishedtheoretical tracks for the evolution of post-AGB stars by comparing themwith the Galactic planetary nebulae data base. We have found noinconsistency between observations and the set of tracks computed bySchoenberner (1981, 1983) and Bloecker & Schoenberner (1990). On theother hand, observations do not seem support the large transition timesbetween the end of the AGB superwind and the beginning of the planetarynebula ionization phase adopted in the models of Vassiliadis & Wood(1994).
| The correlations between planetary nebula morphology and central star evolution
The morphology of 111 Galactic planetary nebulae has been studied inrelation to the evolutionary stage of their central stars. In order tolocate these stars on the log Teff - Log L/solar luminosityplane, we have calculated the Zanstra temperatures with the most up todate fluxes and magnitudes available in the literature. Distances to thenebulae were estimated with statistical methods. The different natureand evolutionary stages of central stars have been related to themorphologies of the surrounding nebulae in a statistical sense. We foundthat multiple shell nebulae contain stars that are at a differentevolutionary stage than those of single shell nebulae; we also foundthat bipolar and elliptical planetary nebulae very likely containcentral stars with a different mass distribution; furthermore, we buildan optical thickness sequence of morphological types.
| On the evolutionary status of WR-type planetary nebula nuclei
The planetary nebula nuclei showing Wolf-Rayet (WR)-type spectraconstitute a unique class of the central stars: they are He-burners.This work presents preliminary results of a study analyzing theobservational characteristics of the WR-type nuclei and their nebulae.The existing He-burning models cannot account for the observations ofthe WR-type nuclei. In the discussion we consider two scenaria: (i)WR-type nuclei are single stars; (ii) WR phenomenon is an evolutionaryphase of binary systems.
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