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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.
| White dwarf masses derived from planetary nebula modelling
Aims.We compare the mass distribution of central stars of planetarynebulae (CSPNe) with those of their progeny, white dwarfs (WD). Methods: We use a dynamical method to measure masses with an uncertaintyof 0.02 M_ȯ. Results: The CSPN mass distribution is sharplypeaked at 0.61~M_ȯ. The WD distribution peaks at lower masses(0.58~M_ȯ) and shows a much broader range of masses. Some of thedifference can be explained if the early post-AGB evolution is fasterthan predicted by the Blöcker tracks. Between 30 and 50 per cent ofWD may avoid the PN phase because they have too low a mass. However, thediscrepancy cannot be fully resolved and WD mass distributions may havebeen broadened by observational or model uncertainties.Data is only available in electronic form at http://www.aanda.org
| Planetary nebula distances re-examined: an improved statistical scale
The distances of planetary nebulae (PNe) are still quite uncertain.Although observational estimates are available for a small proportion ofPNe, based on statistical parallax and the like, such distances are verypoorly determined for the majority of galactic PNe. In particular,estimates of so-called `statistical' distance appear to differ byfactors of ~2.7.We point out that there is a well-defined correlation between the 5-GHzluminosity of the sources, L5, and their brightnesstemperatures, TB. This represents a different trend to thoseinvestigated in previous statistical analyses, and permits us todetermine independent distances to a further 449 outflows. Thesedistances are shown to be closely comparable to those determined using aTB-R correlation, providing that the latter trend is taken tobe non-linear.This non-linearity in the TB-R plane has not been noted inprevious analyses, and is likely responsible for the broad (andconflicting) ranges of distance that have previously been published.Finally, we point out that there is a close accord between observedtrends within the L5-TB and TB-Rplanes, and the variation predicted through nebular evolutionarymodelling. This is used to suggest that observational biases areprobably modest, and that our revised distance scale is reasonablytrustworthy.
| 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.
| 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
| Gas temperature and excitation classes in planetary nebulae
Empirical methods to estimate the elemental abundances in planetarynebulae usually use the temperatures derived from the [O III] and [N II]emission-line ratios, respectively, for the high- and low-ionizationzones. However, for a large number of objects these values may not beavailable. In order to overcome this difficulty and allow a betterdetermination of abundances, we discuss the relationship between thesetwo temperatures. Although a correlation is not easily seen when asample of different PNe types is used, the situation is improved whenthey are gathered into excitation classes. From [OII]/[OIII] andHeII/HeI line ratios, we define four excitation classes. Then, usingstandard photoionization models which fit most of the data, a linearrelation between the two temperatures is obtained for each of the fourexcitation classes. The method is applied to several objects for whichonly one temperature can be obtained from the observed emission linesand is tested by recalculation of the radial abundance gradient of theGalaxy using a larger number of PNe. We verified that our previousgradient results, obtained with a smaller sample of planetary nebulae,are not changed, indicating that the temperature relation obtained fromthe photoionization models are a good approximation, and thecorresponding statistical error decreases as expected. Tables 3-5, 7 and9 are only available in electronic form at http://www.edpsciences.org
| An analysis of the observed radio emission from planetary nebulae
We have analysed the radio fluxes for 264 planetary nebulae for whichreliable measurements of fluxes at 1.4 and 5 GHz, and of nebulardiameters are available. For many of the investigated nebulae, theoptical thickness is important, especially at 1.4 GHz. Simple modelslike the one specified only by a single optical thickness or spherical,constant density shells do not account satisfactorily for theobservations. Also an r-2 density distribution is ruled out.A reasonable representation of the observations can be obtained by atwo-component model having regions of two different values of opticalthickness. We show that the nebular diameters smaller than 10arcsec areuncertain, particularly if they come from photographic plates orGaussian fitting to the radio profile. While determining theinterstellar extinction from an optical to radio flux ratio, cautionshould be paid regarding optical thickness effects in the radio. We havedeveloped a method for estimating the value of self absorption. At 1.4GHz self absorption of the flux is usually important and can exceed afactor of 10. At 5 GHz self absorption is negligible for most of theobjects, although in some cases it can reach a factor of 2. The Galacticbulge planetary nebulae when used to calibrate the Shklovsky method givea mean nebular mass of 0.14 Msun. The statistical uncertaintyof the Shklovsky distances is smaller than a factor of 1.5. Table 1 isonly available in electronic form at http://www.edpsciences.org.
| Gravity distances of planetary nebulae II. Aplication to a sample of galactic objects.
Not Available
| Expansion velocities and dynamical ages of planetary nebulae
The [O Iii] expansion velocities are presented for planetary nebulae inthe Galactic Bulge and Halo, and in the Sagittarius Dwarf spheroidalgalaxy. The velocities are shown to increase with the distance from thestar, in agreement with hydrodynamical models. Dynamical ages arederived from these velocities and are corrected for the effects ofpost-AGB acceleration and non-uniform velocities. Masses for the centralstars are obtained from relations between dynamical ages and stellartemperatures. The stellar core mass distribution is narrow, peaking at0.61 M_sun. This is higher than predicted for the Bulge by initial-finalmass relations, but consistent with the local white dwarf massdistribution. Based on observations obtained at ESO
| The dust content of planetary nebulae: a reappraisal
We have performed a statistical analysis using broad band IRAS data onabout 500 planetary nebulae with the aim of characterizing their dustcontent. Our approach is different from previous studies in that it usesan extensive grid of photoionization models to test the methods forderiving the dust temperature, the dust-to-gas mass ratio and theaverage grain size. In addition, we use only distance independentdiagrams. With our models, we show the effect of contamination by atomiclines in the broad band IRAS fluxes during planetary nebula evolution.We find that planetary nebulae with very different dust-to-gas massratios exist, so that the dust content is a primordial parameter for theinterpretation of far infrared data of planetary nebulae. In contrastwith previous studies, we find no evidence for a decrease in thedust-to-gas mass ratio as the planetary nebulae evolve. We also showthat the decrease in grain size advocated by Natta & Panagia(\cite{NattaPanagia}) and Lenzuni et al. (\cite{Lenzuni}) is an artefactof their method of analysis. Our results suggest that the timescale fordestruction of dust grains in planetary nebulae is larger than theirlifetime. Table~1 is only accessible in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Infrared Planetary Nebulae in the NRAO VLA Sky Survey
In order to construct a sample of planetary nebulae (PNe) unbiased bydust extinction, we first selected the 1358 sources in the IRAS PointSource Catalog north of J2000 declination delta=-40^deg having measuredS(25 μm)>=1 Jy and colors characteristic of PNe: detections orupper limits consistent with both S(12 μm)<=0.35S(25 μm) andS(25 μm)>=0.35S(60 μm). The majority are radio-quietcontaminating sources such as asymptotic giant branch stars. Free-freeemission from genuine PNe should make them radio sources. The 1.4 GHzNRAO VLA Sky Survey (NVSS) images and source catalog were used to rejectradio-quiet mid-infrared sources. We identified 454 IRAS sources withradio sources brighter than S~2.5 mJy beam^-1 (equivalent to T~0.8 K inthe 45" FHWM NVSS beam) by positional coincidence. They comprise 332known PNe in the Strasbourg-ESO Catalogue of Galactic Planetary Nebulaeand 122 candidate PNe, most of which lie at very low Galactic latitudes.Exploratory optical spectroscopic observations suggest that most ofthese candidates are indeed PNe optically dimmed by dust extinction,although some contamination remains from H II regions, Seyfert galaxies,etc. Furthermore, the NVSS failed to detect only 4% of the known PNe inour infrared sample. Thus it appears that radio selection can greatlyimprove the reliability of PN candidate samples withoutsacrificingcompleteness.
| A Survey of Planetary Nebulae in the Southern Galactic Bulge
We present the results of a deep and uniform narrowband Hα imagingsurvey for planetary nebulae (PNs) in the southern Galactic bulge. Inour survey, we have found 56 new PNs and have rediscovered 45 known PNs.We have measured the radial velocities of this uniformly selected sampleand have also remeasured radial velocities for a subset of 317 PNs fromthe Acker catalog. Using the COBE/DIRBE 1.25, 2.2, and 3.5 μm images,we show that there is a similar longitude distribution of the PNs andthe COBE light in the zone of our deep survey. Also, we find that theextinction in our surveyed fields is not severe and that itsdistribution is fairly uniform. Finally, we present Hα fluxes for47 of our 56 newly discovered PNs and estimate the survey detectionlimit.
| 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
| The planetary nebulae populations in five galaxies: abundance patterns and evolution
We have collected photometric and spectroscopic data on planetarynebulae (PNe) in 5 galaxies: the Milky Way (bulge), M 31 (bulge), M 32,the LMC and the SMC. We have computed the abundances of O, Ne and N andcompared them from one galaxy to another. In each Galaxy, thedistribution of oxygen abundances has a large dispersion. The averageO/H ratio is larger in the M 31 and the Galactic bulge PNe than in thosein the Magellanic Clouds. In a given galaxy, it is also larger for PNewith [O III] luminosities greater than 100 L_ȯ, which are likely toprobe more recent epochs in the galaxy history. We find that the M 31and the Galactic bulge PNe extend the very tight Ne/H-O/H correlationobserved in the Galactic disk and Magellanic Clouds PNe towards highermetallicities. We note that the anticorrelation between N/O and O/H thatwas known to occur in the Magellanic Clouds and in the disk PNe is alsomarginally found in the PNe of the Galactic bulge. Furthermore, we findthat high N/O ratios are higher for less luminous PNe. In M 32, all PNehave a large N/O ratio, indicating that the stellar nitrogen abundanceis enhanced in this galaxy. We have also compared the PN evolution inthe different galactic systems by constructing diagrams that areindependent of abundances, and have found strikingly differentbehaviours of the various samples. In order to help in theinterpretation of these data, we have constructed a grid of expanding,PN photoionization models in which the central stars evolve according tothe evolutionary tracks of Bl{öcker (1995). These models show thatthe apparent spectroscopic properties of PNe are extremely dependent,not only on the central stars, but also on the masses and expansionvelocities of the nebular envelopes. The main conclusion of theconfrontation of the observed samples with the model grids is that thePN populations are indeed not the same in the various parent galaxies.Both stars and nebulae are different. In particular, the central starsof the Magellanic Clouds PNe are shown to evolve differently from thehydrogen burning stellar evolutionary models of Bl{öcker (1995). Inthe Galactic bulge, on the other hand, the behaviour of the observed PNeis roughly compatible with the theoretical stellar evolutionary tracks.The case of M 31 is not quite clear, and additional observations arenecessary. It seems that the central star mass distribution is narrowerfor the M 31 PNe than for the Galactic bulge PNe. We show thatspectroscopy of complete samples of PNe down to a factor 100 below themaximum luminosity would help to better characterize the PN central starmass distribution. Tables 1 and 2 are only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http: //cdsweb.u-strasbg.fr/Abstract.html
| Planetary Nebulae in the NRAO VLA Sky Survey
The 1.4 GHz NRAO VLA Sky Survey (NVSS) images and source catalog wereused to detect radio emission from the 885 planetary nebulae north ofJ2000 declination delta = -40 deg in the Strasbourg-ESO Catalogue ofGalactic Planetary Nebulae. We identified 680 radio sources brighterthan about S = 2.5 mJy beam-1 (equivalent to T ~ 0.8 K in the 45" FWHMNVSS beam) with planetary nebulae by coincidence with accurate opticalpositions measured from Digitized Sky Survey (DSS) images. Totalextinction coefficients c at lambda = 4861 Angstroms were calculated forthe 429 planetary nebulae with available H beta fluxes and low free-freeoptical depths at 1.4 GHz. The variation of c with Galactic latitude andlongitude is consistent with the extinction being primarily interstellarand not intrinsic.
| A self-consistent determination of distances, physical parameters, and chemical composition for a large sample of galactic planetary nebulae: chemical composition
The relative abundances of He, C, N, O, Ne, Mg, Si, S, and Ar arepresented for, respectively, 185, 65, 212, 221, 180, 13, 41, 197, and205 Galactic planetary nebulae. The observed stages of ionization weretaken into account using the relations between the relative abundancesof different ions derived from a grid of photoionization models for thenebular emission. The chemical compositions of all the planetary nebulaewere determined using the same method and the same atomic data, so thatthe results have a high degree of uniformity; this is the first timethis has been done for such a large sample of Galactic planetary nebulae(221 objects).
| Abundances in planetary nebulae near the galactic centre. I. Abundance determinations
Abundance determinations of about 110 planetary nebulae, which arelikely to be in the Galactic Bulge are presented. Plasma diagnosticshave been performed by making use of the available forbidden line ratioscombined with radio continuum measurements. Chemical abundances of He,O, N, Ne, S, Ar, and Cl are then derived by employing theoreticalnebular models as interpolation devices in establishing the ionizationcorrection factors (ICFs) used to estimate the distribution of atomsamong unobserved ionization stages. The overall agreement between theresults derived by using the model-ICFs and those obtained from thetheoretical models is reasonably good. The uncertainties related to thetotal abundances show a clear dependence on the level of excitation. Inmost cases, the abundances of chlorine can be derived only in objectswith a relatively high Cl-abundance. Contrary to the conclusionpreviously drawn by \cite[Webster (1988)]{we88}, we found the excitationclasses are not uniformly distributed. A clear peak at about classes 5and 6 is noticed. The distribution is shifted toward a lower excitationrange with respect to that of the nearby nebulae, reflecting thedifference in the central star temperature distribution between the twosamples.
| Radial velocities of planetary nebulae towards the Galactic bulge
Accurate radial velocities for a sample of 71 planetary nebulae, mostlylocated in the direction of the Galactic Centre, are presented. Most ofthe nebulae discussed in this paper are likely members of the Galacticbulge, based on their radial velocity, longitude and derived distance.The data give a large improvement over existing catalogues, doubling thesample of bulge planetary nebulae with well-determined velocities andsuggesting that kinematics of the Galactic Bulge can usefully be studiedby planetary nebulae. Based on observations obtained at the EuropeanSouthern Observatory. Table 1 is also available in electronic form atthe CDS vis anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Classification of planetary nebulae by cluster analysis and artificial neural networks.
According to the chemical composition, a sample of 192 Planetary Nebulaeof different types has been re-classified, and 41 others have beenclassified for the first time, by means of two methods not employed sofar in this field: hierarchical cluster analysis and supervisedartificial neural network. The cluster analysis reveals itself as a goodfirst guess for grouping Planetary Nebulae, while an artificial neuralnetwork provides reliable automated classification of this kind ofobjects.
| 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.
| 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.
| On an alternative statistical distance scale for planetary nebulae. Catalog with statistical distances to planetary nebulae.
We have proposed a statistical method to determine distances toplanetary nebulae. The method is based on an empirical correlationbetween the radio-continuum brightness temperature and radius. Here wepresent a catalog of distance determinations calculated using thismethod.
| Abundances and radial gradients from disk planetary nebulae: He, N, C, and CL
Chemical abundances of the elements He, N, C, and Cl are presented fordisk planetary nebulae, comprising Peimbert types I, II, and III.Average abundances for these classes are determined and compared withthe remaining abundances available. The presence of abundance gradientsrelative to hydrogen for disk nebulae is investigated in a region ofabout 8 kpc centered in the solar system. It can be concluded that thegradients of the ratios N/H, Cl/H, and probably C/H are similar to theO/H gradient, especially for type II objects.
| 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.
| Element abundances in planetary nebulae from recombination line spectra.
Not Available
| Trace of planetary nebula evolution by distance-independent parameters
Using existing infrared and radio data on a sample of 432 planetarynebulae, we derived a number of distance-independent parameters forcomparison with evolutionary models of planetary nebulae. We find thatmany of the observed properties of planetary nebulae can be explained bycurrent central star evolutionary models, even if the time scales aresubject to significant change by a factor of up to an order ofmagnitude. Specifically, we find that the evolutionary tracks are wellseparated in the radio surface brightness-central star temperatureplane, therefore allowing us to determine the core mass of individualplanetary nebulae. We also obtain the luminosity and gravity of thecentral stars of individual nebulae, from their temperature and coremass, without relying on the distance assumptions. We find that ourresults of the core mass are in good agreement with those of Mendez etal. (1992) and Tylenda et al. (1991). A systematic, large discrepancy isfound between the luminosity found in this work and that found byGathier and Pottasch (1986).
| The features of chemical abundances in Galactic planetary nebulae
The chemical composition of 217 Galactic planetary nebulae isinvestigated; 203 of them are subdivided into four classes according tothe masses of nebulae and progenitor stars. The values of localabundances, Galactic abundance gradients and Galactic electrontemperature gradients are found for each class of nebula. Thecorrelations between the abundances of pairs of elements are alsocalculated for each class of nebula. The results are compared withtheoretical predictions. In particular, it is concluded that CN cyclingcan play a role in progenitor stars for all classes of planetary nebula.
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