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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 Catalog of Neighboring Galaxies
We present an all-sky catalog of 451 nearby galaxies, each having anindividual distance estimate D<~10 Mpc or a radial velocityVLG<550 km s-1. The catalog contains data onbasic optical and H I properties of the galaxies, in particular, theirdiameters, absolute magnitudes, morphological types, circumnuclearregion types, optical and H I surface brightnesses, rotationalvelocities, and indicative mass-to-luminosity and H I mass-to-luminosityratios, as well as a so-called tidal index, which quantifies the galaxyenvironment. We expect the catalog completeness to be roughly 70%-80%within 8 Mpc. About 85% of the Local Volume population are dwarf (dIr,dIm, and dSph) galaxies with MB>-17.0, which contributeabout 4% to the local luminosity density, and roughly 10%-15% to thelocal H I mass density. The H I mass-to-luminosity and the H Imass-to-total (indicative) mass ratios increase systematically fromgiant galaxies toward dwarfs, reaching maximum values about 5 in solarunits for the most tiny objects. For the Local Volume disklike galaxies,their H I masses and angular momentum follow Zasov's linear relation,expected for rotating gaseous disks being near the threshold ofgravitational instability, favorable for active star formation. We foundthat the mean local luminosity density exceeds 1.7-2.0 times the globaldensity, in spite of the presence of the Tully void and the absence ofrich clusters in the Local Volume. The mean local H I density is 1.4times its ``global'' value derived from the H I Parkes Sky Survey.However, the mean local baryon densityΩb(<8Mpc)=2.3% consists of only a half of the globalbaryon density, Ωb=(4.7+/-0.6)% (Spergel et al.,published in 2003). The mean-square pairwise difference of radialvelocities is about 100 km s-1 for spatial separations within1 Mpc, increasing to ~300 km s-1 on a scale of ~3 Mpc. alsoWe calculated the integral area of the sky occupied by the neighboringgalaxies. Assuming the H I size of spiral and irregular galaxies to be2.5 times their standard optical diameter and ignoring any evolutioneffect, we obtain the expected number of the line-of-sight intersectionswith the H I galaxy images to be dn/dz~0.4, which does not contradictthe observed number of absorptions in QSO spectra.

Bubbles in planetary nebulae and clusters of galaxies: Jet properties
I derive constraints on jet properties for inflating pairs of bubbles inplanetary nebulae and clusters of galaxies. This work is motivated bythe similarity in morphology and some non-dimensional quantities betweenX-ray-deficient bubbles in clusters of galaxies and theoptical-deficient bubbles in planetary nebulae, which were pointed outin an earlier work. In the present Paper I find that for inflating fatbubbles, the opening angle of the jets must be large, i.e., the halfopening angle measured from the symmetry axis of the jets shouldtypically be α  40 o. For such wide-opening anglejets, a collimated fast wind (CFW) is a more appropriate term. Narrowjets will form elongated lobes rather than fat bubbles. I emphasize theneed to include jets with large opening angle, i.e., α ≃30-70o, in simulating bubble inflation in both planetarynebulae and (cooling flow) clusters of galaxies.Research supported by the Israel Science Foundation.

Pairs of Bubbles in Planetary Nebulae and Clusters of Galaxies
I point to an interesting similarity in the morphology and somenondimensional quantities between pairs of X-ray-deficient bubbles inclusters of galaxies and pairs of optical-deficient bubbles in planetarynebulae (PNs). This similarity leads me to postulate a similar formationmechanism. This postulate is used to strengthen models for PN shaping byjets (or collimated fast winds [CFWs]). The presence of dense materialin the equatorial plane observed in the two classes of bubblesconstrains the jets and CFW activity in PNs to occur while theasymptotic giant branch star still blows its dense wind, or very shortlyafter. I argue that only a stellar companion can account for such jetsand CFWs.

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 ( or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/408/1029}

Physical Structure of Planetary Nebulae. I. The Owl Nebula
The Owl Nebula is a triple-shell planetary nebula with the outermostshell being a faint bow-shaped halo. We have obtained deep narrowbandimages and high-dispersion echelle spectra in the Hα, [O III], and[N II] emission lines to determine the physical structure of each shellin the nebula. These spatiokinematic data allow us to rule outhydrodynamic models that can reproduce only the nebular morphology. Ouranalysis shows that the inner shell of the main nebula is slightlyelongated with a bipolar cavity along its major axis, the outer nebulais a filled envelope coexpanding with the inner shell at 40 kms-1, and the halo has been braked by the interstellar mediumas the Owl Nebula moves through it. To explain the morphology andkinematics of the Owl Nebula, we suggest the following scenario for itsformation and evolution. The early mass loss at the TP-AGB phase formsthe halo, and the superwind at the end of the AGB phase forms the mainnebula. The subsequent fast stellar wind compressed the superwind toform the inner shell and excavated an elongated cavity at the center,but this has ceased in the past. At the current old age the inner shellis backfilling the central cavity.Based on observations made with the William Herschel Telescope, operatedon the island of La Palma by the Isaac Newton Group in the SpanishObservatorio del Roque de Los Muchachos of the Instituto deAstrofísica de Canarias, and with the Burrell Schmidt telescopeof the Warner and Swasey Observatory, Case Western Reserve University.

The relation between elemental abundances and morphology in planetary nebulae
An investigation of the variation of elemental abundances with planetarynebula morphology is of considerable interest, since it has a bearingupon how such sources are formed, and from which progenitors they areejected. Recent advances in morphological classification now enable usto assess such trends for a statistically significant number of sources.We find, as a result, that the distribution N[log(X/H)] of sources withrespect to elemental abundance (X/H) varies between the differingmorphologies. Circular sources tend to peak towards low abundancevalues, whilst bipolar nebulae (BPNe) peak towards somewhat highervalues. This applies for most elemental species, although it is perhapsleast apparent for oxygen. In contrast, elliptical sources appear todisplay much broader functions N[log(X/H)], which trespass upon thedomains of both circular and elliptical planetary nebulae (PNe).We take these trends to imply that circular sources derive fromlower-mass progenitors, bipolar sources from higher-mass stars, and thatelliptical nebulae derive from all masses of progenitor, high and low.Whilst such trends are also evident in values of mean abundance, they are much less clear. Only in the cases of He/H, N/H,Ne/H and perhaps Ar/H is there evidence for significant abundancedifferences.Certain BPNe appear to possess low abundance ratios He/H and Ar/H, andthis confirms that a few such outflows may arise from lower-massprogenitors. Similarly, we note that ratios are quite modestin elliptical planetary nebulae, and not much different from those forcircular and bipolar PNe; a result that conflicts with the expectationsof at least one model of shell formation.

Sulfur, Chlorine, and Argon Abundances in Planetary Nebulae. III. Observations and Results for a Final Sample
This paper is the fourth in a series whose purpose is to study theinterstellar abundances of sulfur, chlorine, and argon in the Galaxyusing a sample of 86 planetary nebulae. Here we present new high-qualityspectrophotometric observations of 20 Galactic planetary nebulae withspectral coverage from 3700 to 9600 Å. A major feature of ourobservations throughout the entire study has been the inclusion of thenear-infrared lines of [S III] λλ9069, 9532, which allowsus to calculate accurate S+2 abundances and to either improveupon or convincingly confirm results of earlier sulfur abundancestudies. For each of the 20 objects here, we calculate ratios of S/O,Cl/O, and Ar/O and find average values ofS/O=(1.1+/-1.1)×10-2,Cl/O=(4.2+/-5.3)×10-4, andAr/O=(5.7+/-4.3)×10-3. For six objects, we are able tocompare abundances of S+3 calculated directly from available[S IV] 10.5 μm measurements with those inferred indirectly from thevalues of the ionization correction factors for sulfur. In the finalpaper of the series, we will compile results from all 86 objects, searchfor and evaluate trends, and use chemical evolution models to interpretour results.

Observations of [S IV] 10.5 μm and [Ne II] 12.8 μm in Two Halo Planetary Nebulae: Implications for Chemical Self-Enrichment
We have detected the [S IV] 10.5 μm and [Ne II] 12.8 μmfine-structure lines in the halo population planetary nebula (PN) DdDm 1and set upper limits on their intensities in the halo PN H4-1. We alsopresent new measurements of optical lines from various ions of S, Ne, O,and H for DdDm 1, based on a high-dispersion spectrum covering thespectral range 3800 Å to 1 μm. These nebulae have similar O/Habundances, (O/H)~1×10-4, but S/H and Ne/H are abouthalf an order of magnitude lower in H4-1 than in DdDm 1; thus H4-1appears to belong to a more metal-poor population. This supportsprevious suggestions that PNe arising from metal-poor progenitor starscan have elevated oxygen abundances due to internal nucleosynthesis andconvective dredge-up. It is generally accepted that high abundances ofcarbon in many PNe result from self-enrichment. To the extent thatoxygen can also be affected, the use of nebular O/H values to infer theoverall metallicity of a parent stellar population (for example, inexternal galaxies) may be suspect, particularly for low metallicities.

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.

Is the Galactic Halo Planetary Nebula PN G243-37.1 an ``O VI Sequence'' Variable Object?
Archival IUE spectra of the Galactic halo planetary nebula PN G243-37.1have been reprocessed by the NEWSIPS routine. The new results show amuch richer emission-line spectrum than has previously been reported.Several C iii, C iv, O v, and possibly O vi features were detected. PCygni line profiles could not be identified with certainty. The He iilambda1640 emission, which is the strongest line in the IUE spectrum andis likely a mixture of stellar and nebular origin, increased inintensity as did the stellar continuum level between observationalepochs of 1988 and 1990, which suggests that the object is a variableplanetary nebula. A very recent optical spectrum confirms the UV resultsand suggests that the object underwent a dramatic change, possibly as aresult of an episodic mass-loss event.

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).

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.

A detailed abundance analysis of nine halo planetary nebulae
Using published spectral line data for nine halo planetary nebulae(HPNe), we have calculated photoionization models in an attempt to gaininsight into the physical conditions and chemical abundances of thesenebulae. The nine HPNe reported upon in this paper are K648, DdDm-1, NGC2242, NGC 4361, PN 243.8-37.1, PN 006-41.9, M2-29, BB-1 and H4-1. Thederived abundance ranges for the HPNe are: C 6.60-8.95, N 7.18-8.00, O7.56-8.56, Ne 6.24-7.71, Ar 4.12-7.70, and S 4.90-7.00 [log(x)+12]. Thetemperature range for the central stars of these nebulae is 40 000 to140 000K. Specifically, with a few exceptions, we find that all nineobjects exhibit subsolar O/H; most show enhanced C/O and N/O, and aconstantNe/O ratio. We also note the existence of comparatively largerabundance scatter in the HPNe as opposed to disc PNe, and suggest thatthis is consistent with the accretion model of halo formation formulatedby Searle & Zinn. In addition, we test the effects on derivedabundances and central star temperatures of a variety of modelatmospheres as well as blackbodies for input ionizing spectra. We findthat nebular line strengths are relatively insensitive to atmosphericdetails; thus blackbody spectra are suitable for central star continua.

Large-Scale Structure at Low Galactic Latitude
We have extended the CfA Redshift Survey to low galactic latitudes toinvestigate the relation between the Great Wall in the North GalacticCap and the Perseus-Pisces chain in the South Galactic Cap. We presentredshifts for 2020 galaxies in the Catalogue of Galaxies and of Clustersof Galaxies (Zwicky et al. 1961-68, CGCG) in the following regions: 4^h^<= α <= 8^h^, 17^h^ <= α <= 20^h^, 0^deg^ <=δ <= 45^deg^. In these regions, the redshift catalogue includes1664 galaxies with B(0) <= 15.5 (of which 820 are newly measured) andis 97% complete. We also include redshifts for an additional 356galaxies in these regions with B(O) > 15.5; of these, 148 werepreviously unmeasured. The CGCG samples the galaxy distribution down tob_II_ = 10^deg^. In this paper, we discuss the acquisition and reductionof the spectra, and we examine the qualitative features of the redshiftdistribution. The Great Wall and the Perseus-Pisces chain are not simplyconnected across the Zone of Avoidance. These structures, which at firstappear to be coherent on scales of ~100 h^-1^ Mpc or more, actually formthe boundaries of neighboring voids of considerably smaller scale,approximately 50h^-1^ Mpc. The structures delineated by ouroptically-selected sample are qualitatively similar to those detected bythe far-infrared-selected IRAS 1.2 Jansky Survey (Fisher et al. 1995).Although the IRAS survey probes more deeply into the Zone of Avoidance,our optically-selected survey provides better sampling of structures atb_II_ >= 10^deg^.

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.

Spectrophotometric observations of planetary nebulae high above the Galactic plane.
Spectrophotometric observations at high signal-to-noise ratio for asample of 62 planetary nebulae are presented, together with the plasmaand abundance analyses. The objects were selected homogeneously from the`Strasbourg-ESO Catalogue of Galactic Planetary Nebulae' by their heightabove the disk (over 300pc) and their Hβ surface brightness(between 10^-12^ and 10^-14^mW.m^-2^.arcsec^-2^). The abundances of O,S, Ar, and Cl are tightly correlated. The N/O ratio shows a wide rangeof values, independent of He or O abundance.

A Detailed Abundance Analysis of Nine Halo Planetary Nebulae
Using published spectral line data for nine Halo Planetary Nebulae, wehave calculated photoionization models using the theoretical code CLOUDY(Ferland 1990) in an attempt to gain insight into the physicalconditions and chemical abundances of these nebulae. The nebulae areclassified as halo objects from their galactic plane height, theirkinematical characteristics as compared to disk objects, and/or theirdistinctively low metallicity relative to disk planetary nebulae. Thenine HPNe reported in this paper are K648, DdDm-1, NGC2242, NGC4361,Pn242-37.1, Pn6-41.1, M2-29, BB-1, & H4-1. The derived abundanceranges in this work for the HPNe are: C 7.23-8.95, N 6.63-8.00, O7.56-8.62, Ne 6.24-7.71, Ar 4.12-7.00, and S 4.89-6.90 (In log(x)+12).The temperatures for the central stars were derived by assuming the starto be a blackbody radiator and by using four previously publishedstellar atmospheric models. The temperature range for the central starsof these nebulae spans 40,000K to 185,000K.

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.

The carbon abundance problem in planetary nebulae
We have reexamined the problem of the discrepancy between carbonabundances in planetary nebulae derived from the CII lambda(4267) andCIII) lambda(1909) line intensities. To this end, we have compiled thepublished optical and ultraviolet data allowing to compute C/O inplanetary nebulae, and constructed diagrams providing a synthetic viewof the problem. We have performed Monte-Carlo simulations to study theeffect of observational errors in the measurement of line intensities,and have found that C/O abundance ratios derived from the CIIlambda(4267) lines are strongly biased towards too large values, whichexplains a large part of the trend seen in the observational diagrams.Taking into account the observational errors, we discuss some otherexplanations which have been proposed to resolve the discrepancy, suchas temperature fluctuations. Adopting the C/O values from the CIII)lambda(1909) lines, we find that carbon-rich objects represent less thanone half of the total number of planetary nebulae. This is significantlyless than the proportions quoted in previous studies. The percentage ofcarbon-rich objects among Type I and Non Type I Galactic planetarynebulae are similar, contrary to what is found in the Magellanic Clouds.

Chemical behavior of planetary nebulae and galactic abundance gradients
All modern determinations of chemical abundances of He/H, O/H, C/H, N/Hand Ne/H in 277 galactic Planetary Nebulae have been used to update ourknowledge of the chemical behavior of Planetary Nebulae, as a whole andin Peimbert's groups. The data have been used to set up the problem ofthe chemical gradients in the Galaxy from Planetary Nebulae. TheInterstellar Medium has been found to be more inhomogeneous in the pastepochs of the Galaxy than in the present time.

IUE observations of the halo planetary nebula BB-1 : the C, O and NE abundancse.
Abstract image available at:http://adsabs.harvard.edu/abs/1993RMxAA..27..175P

Ultraviolet and optical spectra of central stars of halo planetary nebulae.
Not Available

Ultraviolet and optical spectra of central stars of halo planetary nebulae
UV and optical spectrophotometric data on central stars of eightPopulation II planetary nebulae are analyzed. Visual magnitudes,spectral classification, color temperatures, and luminosities arederived from these data. All the stars in the sample exhibit anabsorption-type spectrum, and most of them have normal H and Hephotospheric abundances, with the possible exception of M 2-29 andGJJC-1, which appear to be H-deficient.

The extinction constants for galactic planetary nebulae
The extinction constants are determined from Balmer decrementmeasurements for over 900 planetary nebulae. Comparison with publishedextinction constants shows that the results from ESO are fairlyreliable. An analysis of the extinction constants derived from theBalmer decrement and from the radio/Hβ flux ratio indicates thatthe latter tends to be systematically smaller than the former forincreasing extinction. We suggest that the radio measurements ofPottasch's group probably underestimate the radio fluxes, at least forsome (faintest) objects.

Kinematics of disk planetary nebulae
The space distribution and kinematic properties of galactic planetarynebulae are considered, on the basis of a sample containing 150 objects.It is shown that planetary nebulae of Types I, IIa, IIb, III, and IVform an approximately continuous sequence in terms of these properties,confirming similar conclusions based on their chemical composition. Somekinematical consequences regarding the connection between planetarynebulae and H II regions are explored, leading to a determination of thegalactic rotation curve and Oort's constants. It is found that therotation curve presents a flattening near the solar circle and amoderate increase for larger galactocentric distances.

Strasbourg - ESO catalogue of galactic planetary nebulae. Part 1; Part 2
Not Available

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Right ascension:06h34m07.36s
Apparent magnitude:14

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NGC 2000.0NGC 2242

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