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The 3-D shaping of NGC 6741: A massive, fast-evolving Planetary Nebula at the recombination-reionization edge
We infer the gas kinematics, diagnostics and ionic radial profiles,distance and central star parameters, nebular photo-ionization model,spatial structure and evolutionary phase of the Planetary Nebula NGC6741 by means of long-slit ESO NTT+EMMI high-resolution spectra at nineposition angles, reduced and analysed according to the tomographic and3-D methodologies developed at the Astronomical Observatory of Padua(Italy). NGC 6741 (distance≃2.0 kpc, age≃ 1400 yr, ionizedmass Mion≃ 0.06 Mȯ) is a dense(electron density up to 12 000 cm-3), high-excitation,almost-prolate ellipsoid (0.036 pc × 0.020 pc × 0.018 pc,major, intermediate and minor semi-axes, respectively), surrounded by asharp low-excitation skin (the ionization front), and embedded in aspherical (radius≃ 0.080 pc), almost-neutral, high-density (n(HI)≃ 7 ×103 atoms cm-3) halo containinga large fraction of the nebular mass (Mhalo≥ 0.20Mȯ). The kinematics, physical conditions and ionicstructure indicate that NGC 6741 is in a deep recombination phase,started about 200 years ago, and caused by the rapid luminosity drop ofthe massive (M*=0.66{-}0.68 Mȯ), hot (logT* ≃ 5.23) and faint (logL*/Lȯ ≃ 2.75) post-AGB star, which hasexhausted the hydrogen-shell nuclear burning and is moving along thewhite dwarf cooling sequence. The general expansion law of the ionizedgas in NGC 6741, Vexp(km s-1)=13 × R arcsec,fails in the innermost, highest-excitation layers, which move slowerthan expected. The observed deceleration is ascribable to the luminositydrop of the central star (the decreasing pressure of the hot-bubble nolonger balances the pressure of the ionized gas), and appears instriking contrast to recent reports inferring that acceleration is acommon property of the Planetary Nebulae innermost layers. A detailedcomparative analysis proves that the "U"-shaped expansion velocity fieldis a spurious, incorrect result due to a combination of: (a) simplisticassumptions (spherical shell hypothesis for the nebula); (b) unfitreduction method (emission profiles integrated along the slit); and (c)inappropriate diagnostic choice (λ4686 Å of He II, i.e. athirteen fine-structure components recombination line). Some generalimplications for the shaping mechanisms of Planetary Nebulae arediscussed.
| The Chemical Composition of Galactic Planetary Nebulae with Regard to Inhomogeneity in the Gas Density in Their Envelopes
The results of a study of the chemical compositions of Galacticplanetary nebulae taking into account two types of inhomogeneity in thenebular gas density in their envelopes are reported. New analyticalexpressions for the ionization correction factors have been derived andare used to determine the chemical compositions of the nebular gas inGalactic planetary nebulae. The abundances of He, N, O, Ne, S, and Arhave been found for 193 objects. The Y Z diagrams for various Heabundances are analyzed for type II planetary nebulae separately andjointly with HII regions. The primordial helium abundance Y p andenrichment ratio dY/dZ are determined, and the resulting values arecompared with the data of other authors. Radial abundance gradients inthe Galactic disk are studied using type II planetary nebulae.
| 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.
| 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.
| Sulfur, Chlorine, and Argon Abundances in Planetary Nebulae. IV. Synthesis and the Sulfur Anomaly
We have compiled a large sample of O, Ne, S, Cl, and Ar abundances thathave been determined for 85 Galactic planetary nebulae in a consistentand homogeneous manner using spectra extending from 3600 to 9600Å. Sulfur abundances have been computed using the near-IR lines of[S III] λλ9069, 9532 along with [S III] temperatures. Wefind average values, expressed logarithmically with a standarddeviation, of log(S/O)=-1.91+/-0.24, log(Cl/O)=-3.52+/-0.16, andlog(Ar/O)=-2.29+/-0.18, numbers consistent with previous studies of bothplanetary nebulae and H II regions. We also find a strong correlationbetween [O III] and [S III] temperatures among planetary nebulae. Inanalyzing abundances of Ne, S, Cl, and Ar with respect to O, we find atight correlation for Ne-O, and loose correlations for Cl-O and Ar-O.All three trends appear to be colinear with observed correlations for HII regions. S and O also show a correlation, but there is a definiteoffset from the behavior exhibited by H II regions and stars. We suggestthat this S anomaly is most easily explained by the existence ofS+3, whose abundance must be inferred indirectly when onlyoptical spectra are available, in amounts in excess of what is predictedby model-derived ionization correction factors in PNe. Finally for thedisk PNe, abundances of O, Ne, S, Cl, and Ar all show gradients whenplotted against Galactocentric distance. The slopes are statisticallyindistinguishable from one another, a result which is consistent withthe notion that the cosmic abundances of these elements evolve inlockstep.
| 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}
| New Emission Line Planetary Nebulae Nuclei in the Direction of the Galactic Center
Not Available
| 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
| Sulfur, Chlorine, and Argon Abundances in Planetary Nebulae. IIB. Abundances in a Southern Sample
We have undertaken a large spectroscopic survey of over 80 planetarynebulae with the goal of providing a homogeneous spectroscopic databasebetween 3600 and 9600 Å, as well as a set of consistentlydetermined abundances, especially for oxygen, sulfur, chlorine, andargon. In the current paper we calculate and report the S/O, Cl/O, andAr/O abundance ratios for 45 southern planetary nebulae (predominantlytype II), using our own recently observed line strengths published in acompanion paper. One of the salient features of our work is the use ofthe near-IR lines of [S III] λλ9069, 9532 coupled with the[S III] temperature, to determine the S+2 ionic abundance. Wefind the following average abundances for these objects:S/O=0.011+/-0.0064, Cl/O=0.00031+/-0.00012, and Ar/O=0.0051+/-0.0020.
| Sulfur, Chlorine, and Argon in Planetary Nebulae. IIA. Observations of a Southern Sample
In this paper we present fully reduced and dereddened emission linestrengths for a sample of 45 southern type II planetary nebulae(PNs).The spectrophotometry for these PNs covers an extendedoptical/near-IR range from 3600 to 9600 Å. This PN study andsubsequent analysis (presented in a companion paper), together with asimilar treatment for a northern PN sample, is aimed at addressing thelack of homogeneous, consistently observed, reduced, and analyzed datasets that include the near-IR [S III] lines at 9069 and 9532 Å.The use of type II objects only is intended to select disk nebulae thatare uncontaminated by nucleosynthetic products of the progenitor star.Extending spectra redward to include the strong [S III] lines enables usto look for consistency between S+2 abundances inferred fromthese lines and from the more accessible, albeit weaker, [S III] line atλ6312.
| V4334 Sgr (Sakurai's Object): The Distance Problem
The central star V4334 Sgr (Sakurai's Object) of the planetary nebula PNG010.4+04.4 underwent in 1995-1996 the rare event of a very late heliumflash. It represents only one out of two such events during the era ofmodern astronomy (the other event was V605 Aql = Nova Aql 1919). All theother prominent objects of that type originate from events occurringseveral thousands of years ago (e.g. A30, A78). Thus it is of specialinterest for stellar evolution theory to model the detailed observationsobtained during the last four years. Those models depend essentially onbasic stellar parameters like effective temperature, surface gravity andstellar radius. Most of them depend strongly on the assumed distance tothe object. Some models may give some constraints on this parameter, butmost of them depend on the assumption as input parameter. Hence todetermine a reliable distance is of considerable significance. Thisshould be obtained through models that give us lower and upperboundaries, or through means which are independent of models. Thedetailed review, by using every kind of determination available up tonow, leads to a Galactic foreground extinction of E_B-V =0^m75 +/-0.05and a distance of D = 2.0_-0.6^+1.0 kpc.
| Sulfur, Chlorine, and Argon in Planetary Nebulae. I. Observations and Abundances in a Northern Sample
This paper is the first of a series specifically studying the abundancesof sulfur, chlorine, and argon in type II planetary nebulae (PNe) in theGalactic disk. Ratios of S/O, Cl/O, and Ar/O constitute important testsof differential nucleosynthesis of these elements and serve as strictconstraints on massive star yield predictions. We present newground-based optical spectra extending from 3600-9600 Å for asample of 19 type II northern PNe. This range includes the strongnear-infrared lines of [S III] λλ9069,9532, which allowsus to test extensively their effectiveness as sulfur abundanceindicators. We also introduce a new, model-tested ionization correctionfactor for sulfur. For the present sample, we find average values ofS/O=1.2×10-2+/-0.71×10-2,Cl/O=3.3×10-4+/-1.6×10-4, andAr/O=5.0×10-3+/-1.9×10-3.
| Helium contamination from the progenitor stars of planetary nebulae: The He/H radial gradient and the ΔY / ΔZ enrichment ratio
In this work, two aspects of the chemical evolution of 4He inthe Galaxy are considered on the basis of a sample of disk planetarynebulae (PN). First, an application of corrections owing to thecontamination of 4He from the evolution of the progenitorstars shows that the He/H abundance by number of atoms is reduced by0.012 to 0.015 in average, leading to an essentially flat He/H radialdistribution. Second, a determination of the helium to heavy elementenrichment ratio using the same corrections leads to values in the range2.8 < ΔY / ΔZ < 3.6 for Y p = 0.23 and 2.0< ΔY / ΔZ < 2.8 for Y p = 0.24, in goodagreement with recent independent determinations and theoretical models.
| 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
| On the abundance gradient of the galactic disk
Estimates of the gas temperature in planetary nebulae obtained from the[O III] emission line ratio and from the Balmer discontinuity indicatedifferences reaching up to 6000 K (Liu & Danziger 1993). The [O III]temperature is commonly used to obtain the ionic fractions of highlyionized ions, particularly the O++ and Ne++ ions when using theempirical method to calculate the elemental abundances of photoionizedgas from the observed emission line intensities. However, if the gastemperature is overestimated the elemental abundances may beunderestimated. In particular this may lead to an incorrect elementalabundance gradient for the Galaxy, usually used as a constraint for thechemical evolution models. Using Monte Carlo simulations, we calculatethe systematic error introduced in the abundance gradient obtained fromplanetary nebulae by an overestimation of the gas temperature. Theresults indicate that the abundance gradient in the Galaxy should besteeper than previously assumed.
| Distances of Galactic Planetary Nebulae Based on a Relationship Between the Central Star Mass and the N/O Abundance
In this paper, we propose a method to determine distances of Galacticplanetary nebulae on the basis of a relationship between the centralstar mass and the nebular N/O abundance ratio. This relationship is usedin combination with some basic parameters of the central stars, such asthe lambda 5480 flux, surface gravity and visual magnitude in order toobtain distances to a sample of a hundred Galactic planetary nebulae.
| 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.
| Abundance gradients in the outer galactic disk from planetary nebulae
Radial abundance gradients of the element ratios O/H, Ne/H, S/H, andAr/H are determined on the basis of a sample of disk planetary nebulae.The behaviour of the gradients at large distances from the galacticcentre, R > R_0 = 7.6 kpc, is emphasized. It is concluded that thederived gradients are consistent with an approximately constant slope inthe inner parts of the Galaxy, and some flattening for distances largerthan R_0. A comparison is made with previous determinations using bothphotoionized nebulae and young stars, and some consequences ontheoretical models for the chemical evolution of the galactic disk arediscussed. Table~1 is available only electronically at the CDS(anonymousftp 130.79.128.5 or http://cdsweb.u-strasbg.fr/Abstract.html)
| 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.
| 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 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.
| 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.
| 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.
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