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Planetary Nebula Abundances and Morphology: Probing the Chemical Evolution of the Milky Way
This paper presents a homogeneous study of abundances in a sample of 79northern Galactic planetary nebulae (PNe) whose morphological classeshave been uniformly determined. Ionic abundances and plasma diagnosticswere derived from selected optical line strengths in the literature, andelemental abundances were estimated with the ionization correctionfactor developed by Kingsbourgh & Barlow in 1994. We compare theelemental abundances to the final yields obtained from stellar evolutionmodels of low- and intermediate-mass stars, and we confirm that mostbipolar PNe have high nitrogen and helium abundance and are the likelyprogeny of stars with main-sequence mass greater than 3Msolar. We derive =0.27 and discuss the implication of such ahigh ratio in connection with the solar neon abundance. We determine theGalactic gradients of oxygen and neon and foundΔlog(O/H)/ΔR=-0.01 dex kpc-1 andΔlog(Ne/H)/ΔR=-0.01 dex kpc-1. These flat PNgradients are irreconcilable with Galactic metallicity gradientsflattening with time.
| 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]).
| 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.
| Electron temperatures and densities of planetary nebulae determined from the nebular hydrogen recombination spectrum and temperature and density variations
A method is presented to derive electron temperatures and densities ofplanetary nebulae (PNe) simultaneously, using the observed hydrogenrecombination spectrum, which includes continuum and line emission. Bymatching theoretical spectra to observed spectra around the Balmer jumpat about 3646 Å, we determine electron temperatures and densitiesfor 48 Galactic PNe. The electron temperatures based on this method -hereafter Te(Bal) - are found to be systematically lower thanthose derived from [OIII] λ4959/λ4363 and [OIII] (88 μm+ 52 μm)/λ4959 ratios - hereafterTe([OIII]na) andTe([OIII]fn). The electron densities based on thismethod are found to be systematically higher than those derived from[OII] λ3729/λ3726, [SII] λ6731/λ6716,[ClIII] λ5537/λ5517, [ArIV] λ4740/λ4711 and[OIII] 88 μm/52 μm ratios. These results suggest that temperatureand density fluctuations are generally present within nebulae. Thecomparison of Te([OIII]na) and Te(Bal)suggests that the fractional mean-square temperature variation(t2) has a representative value of 0.031. A majority oftemperatures derived from the Te([OIII]fn) ratioare found to be higher than those of Te([OIII]na),which is attributed to the existence of dense clumps in nebulae - those[OIII] infrared fine-structure lines are suppressed by collisionalde-excitation in the clumps. By comparingTe([OIII]fn), Te([OIII]na)and Te(Bal) and assuming a simple two-density-componentmodel, we find that the filling factor of dense clumps has arepresentative value of 7 × 10-5. The discrepanciesbetween Te([OIII]na) and Te(Bal) arefound to be anticorrelated with electron densities derived from variousdensity indicators; high-density nebulae have the smallest temperaturediscrepancies. This suggests that temperature discrepancy is related tonebular evolution. In addition, He/H abundances of PNe are found to bepositively correlated with the difference betweenTe([OIII]na) and Te(Bal), suggestingthat He/H abundances might have been overestimated generally because ofthe possible existence of H-deficient knots. Electron temperatures anddensities deduced from spectra around the Paschen jump regions at 8250Åare also obtained for four PNe: NGC 7027, NGC 6153, M 1-42 andNGC 7009. Electron densities derived from spectra around the Paschenjump regions are in good agreement with the corresponding values derivedfrom spectra around the Balmer jump, whereas temperatures deduced fromthe spectra around the Paschen jump are found to be lower than thecorresponding values derived from spectra around the Balmer jump for allthe four cases. The reason remains unclear.
| 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.
| 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
| The Correlations between Planetary Nebula Morphology and Central Star Evolution: Analysis of the Northern Galactic Sample
Northern Galactic planetary nebulae (PNs) are studied to disclosepossible correlations between the morphology of the nebulae and theevolution of the central stars (CSs). To this end, we have built thebest database available to date, accounting for homogeneity andcompleteness. We use updated statistical distances and an updatedmorphological classification scheme, and we calculate Zanstratemperatures for a large sample of PNs. With our study we confirm thatround, elliptical, and bipolar PNs have different spatial distributionswithin the Galaxy, with average absolute distances to the Galactic planeof 0.73, 0.38, and 0.21 kpc, respectively. We also find evidence thatthe distributions of the CS masses are different across thesemorphological groups, although we do not find that CSs hosted by bipolarPNs are hotter, on average, than CSs within round and elliptical PNs.Our results are in broad agreement with previous analyses, indicatingthat round, elliptical, and bipolar PNs evolve from progenitors indifferent mass ranges and might belong to different stellar populations,as also indicated by the helium and nitrogen abundances of PNs ofdifferent morphology.
| 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
| A Catalogue of IJK Photometry of PNe with DENIS
Near-infrared photometry of planetary nebulae (PNe) allows theclassification of those objects (Whitelock 1985; Peña &Torres-Peimbert 1987). We present the largest homogeneous sample.
| Study of electron density in planetary nebulae. A comparison of different density indicators
We present a comparison of electron density estimates for planetarynebulae based on different emission-line ratios. We have considered thedensity indicators [O Ii]lambda 3729/lambda 3726, [S Ii]lambda6716/lambda 6731, [Cl Iii]lambda 5517/lambda 5537, [Ar Iv]lambda4711/lambda 4740, C Iii]lambda 1906/lambda 1909 and [N I]lambda5202/lambda 5199. The observational data were extracted from theliterature. We have found systematic deviations from the densityhomogeneous models, in the sense that: Ne(ion {N}i) <~Ne(ion {O}{ii}) < Ne(ion {S}{ii}, ion {C}{iii},ion {Cl}{iii} or ion {Ar}{iv}) and Ne(ion {S}{ii}) ~Ne(ion {C}{iii}) ~ Ne(ion {Cl}{iii}) ~Ne(ion {Ar}{iv}). We argue that the lower [O Ii] densityestimates are likely due to errors in the atomic parameters used.
| Gravity distances of planetary nebulae II. Aplication to a sample of galactic objects.
Not Available
| 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
| 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
| 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 Morphological Study of Planetary Nebulae
We have produced simulated images of 110 planetary nebulae using theellipsoidal shell model. This process has allowed us to remove theprojection effects from the morphological classification of planetarynebulae and has provided quantitative measures of the intrinsicasymmetries of the nebulae. It is shown that the morphology of mostplanetary nebulae can be reproduced with pole-to-equator density ratiosof 0.1-1. Many planetary nebulae also show a modest departure from axialsymmetry. Contrary to previous findings by Khromov & Kohoutek, thesky orientation of planetary nebulae in this sample is consistent with apurely random distribution. Extremely bipolar nebulae (e.g., those ofbutterfly shape) point to a steep density profile in the AGB envelopeand are more likely to be type I (high helium and/or nitrogen abundance)nebulae. We found evidence that these nebulae are likely to have moremassive progenitors and are at a more advanced stage of dynamicalevolution.
| Orientation of planetary nebulae within the Galaxy
Narrow-band CCD images of 209 axially symmetrical planetary nebulae(PNe) have been examined in order to determine the orientation of theiraxes within the disc of the Galaxy. The nebulae have been divided intothe bipolar (B) and elliptical (E) PNe morphological types, according tothe scheme of Corradi & Schwarz. In both classes, contrary to theresults of Melnick & Harwit and Phillips we do not find any strongevidence for non-random orientations of the nebulae in the Galaxy.Compared with previous work in this field, the present study takesadvantage of the use of larger and morphologically more homogeneoussamples and offers a more rigorous statistical analysis.
| 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).
| Inhomogeneous planetary nebulae: carbon and oxygen abundances
We reconsider the problem of the difference between the abundances ofcarbon and oxygen in galactic planetary nebulae (PN) derived from theintensities of the recombination and collisionally excited lines. Thisdiscrepancy can be explained by an inhomogeneity of the PNe and anoverestimation of the weak line intensities. The formulae forcalculation of the nebular line intensities in presence of bothtemperature and density fluctuations are given. The intensities of theforbidden [OIII] lines, the CII, CIII and CIV recombination lines andthe CIII]lambda 1909 UV intercombination doublet for different values ofthe mean electron temperature T_0 in PNe and the rms temperaturevariation t^2, are calculated. Results of these calculations are used tofind the values of T_0 and t^2 which allow to provide the best fit ofthe observed and calculated line intensities (taking into account theobservational errors). In most cases, the obtained values of T_0 appearto be significantly smaller than ordinarily used for the abundancedeterminations T_e([OIII]), while t^2<0.16. The carbon and oxygenabundances for more than 70 PNe are calculated. For these PNe averagechemical abundances are evaluated separately for nebulae of type I, IIand III. For the first, we found C/H=6.67*10(-4) cm(-3) andO/H=5.74*10(-4) 4cm(-3) . For the second they are C/H=8.94*10(-4) cm(-3)and O/H=6.36*10(-4) cm(-3) . For the third we obtained C/H=3.94*10(-4)cm(-3) and O/H=4.79*10(-4) cm(-3) . Results of the fitting of the lineintensities for the NIII lambda 4640 and NIV] lambda 1486 lines are alsogiven.
| A self-consistent determination of the distances, physical parameters, and chemical composition for a large sample of galactic planetary nebulae: The distances and parameters of central stars and the optical depths of envelopes
The distances and parameters of the central stars and the optical depthsof the envelopes in the Lyman limits of neutral hydrogen and neutralhelium were determined in a self-consistent way for 170 Galacticplanetary nebulae (PNe). The distance to each PN was so chosen that thetheoretically calculated evolutionary age of its nucleus was equal tothe dynamical age of its expanding envelope. The effective temperatureof the central star and its related parameters were determined either bythe generalized energy-balance method or, where appropriate, byZanstra's method. The derived distance estimates lend support to a`long' distance scale for PNe and are generally in agreement withcurrent individual and statistical estimates of the distances to PNeavailable in the literature. The mean distance to the bulge PNe is 7.9+/- 0.3 kpc, in agreement with the distance to the Galactic center. Themasses of the central stars of PNe corresponding to the deriveddistances are closely correlated with the nebular nitrogen-to-oxygenabundance ratio.
| 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.
| 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.
| The molecular envelopes of planetary nebulae.
We report the results of a survey of millimeter CO emission in 91planetary nebulae using the IRAM 30 m and SEST 15 m telescopes. Theobservations provide new detections or improved data for 23 nebulae inthe CO(2-1) and/or CO(1-0) line, and sensitive limits for those not seenin CO. Analysis of the results together with previous observationsconfirms the existence of an important class of planetary nebulae withmassive (10^-2^-a few M_sun__) envelopes of molecular gas.These nebulae typically have abundance ratios of N/O>0.3 and bipolarmorphologies indicative of a young disk population. The column densitythrough the envelopes and their mass relative to the mass of ionized gasshow dramatic decreases with increasing nebular size, documenting theexpansion of the envelopes and the growth of the optical nebulae at theexpense of the molecular gas. The molecular envelopes remain a majormass component in these objects until the nebulae reach a radius ofR=~0.1pc. The nebulae not detected in CO have little or no molecular gas(<~10^-2^-10^-3^Msun_), and their envelopes must berapidly photo-dissociated before or during the compact phase. The largedifferences in the molecular gas content of the nebulae highlight thedifferent evolutionary paths for planetary nebula formation which resultfrom the range in mass of the progenitors and the structure of theircircumstellar envelopes.
| [N II] and [O III] Mean Electron Temperatures in Planetary Nebulae
Mean electron tempertures for 106 planetary nebulae are presented, whichhave been derived using calculations of the values of electrontemperature-sensitive line ratios involving forbidden transitions amongthe 2s^2 2p^2 3P, 1D, and 1S levels of N+ and O++, based on new electronimpact rates and transition probabilities. Comparison of these resultswith values of T_e[N II] and T_e[O III] determined previously by Kalerreveal that the present electron temperatures are systematically lowerfor both ions, and that this discrepancy is correlated with the electrondensity in the nebula. It is also shown that the average differencetween T_e[N II] and T_e[O III] in a planetary nebula is somewhat smallerthan that derived by Kaler, with the present results implying that the NII and O III temperatures disagree on average by 2070 K as opposed tothe 2210 K average found by Kaler. (SECTION: Interstellar Medium andNebulae)
| H2 Emission from Planetary Nebulae: Signpost of Bipolar Structure
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...462..777K&db_key=AST
| 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.
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