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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.

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.

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 ( 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 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.

Temperature of the Central Stars of Planetary Nebulae and the Effect of the Nebular Optical Depth
The effect of the nebula optical depth on the determination of thetemperature (T*) of the central stars in planetary nebulae isdiscussed. Based on photoionization models for planetary nebulae withdifferent optical depths, we show, quantitatively, that the details ofthe distribution of the H and He II Zanstra temperatures are mainlyexplained by an optical depth effect; in particular, that thediscrepancy is larger for low stellar temperatures. The results alsoshow that for high stellar temperatures the He II Zanstra temperatureunderestimates the stellar temperature, even for high optical depths.The stellar temperature, as well as the optical depth, can be obtainedfrom a Zanstra temperature ratio (ZR) plotZR=TZ(HeII)/TZ(H)versus TZ(He II). The effects of departures from a blackbodyspectrum, as well as of the He abundance in the nebulae, are alsodiscussed. For nebulae of very low optical depth and/or high stellartemperature the distribution ZR versus TZ(He II) onlyprovides lower limits for T*. In order to obtain bettervalues for the optical depth and T*, we propose the use ofthe line intensity ratio HeII/HeI versusTZ(He II) diagram.

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 ( 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.

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.

The Chemical Abundances of the Hydrogen-poor Planetary Nebulae A30 and A58
Abstract image available at:http://adsabs.harvard.edu/abs/1996ApJ...472..711G

A statistical distance scale for Galactic planetary nebulae
A statistical distance scale is proposed. It is based on the correlationbetween the ionized mass and the radius and the correlation between theradio continuum surface brightness temperature and the nebular radius.The proposed statistical distance scale is an average of the twodistances obtained while using the correlation. These correlations,calibrated based on the 1`32 planetary nebulae with well-determinedindividual distances by Zhang, can reproduce not only the averagedistance of a sample of Galactic Bulge planetary nebulae exactly at thedistance to the Galactic center, but also the expected Gaussiandistribution of their distances around the Galactic center. This newdistance scale is applied to 647 Galactic planetary nebulae. It isestimated that this distance scale can be accurate on average to35%-50%. Our statistical distance scale is in good agreement with theone recently proposed by Van de Steene and Zijlstra. The correlationsfound in this study can be attributed to the fact that the core mass ofthe central stars has a very sharp distribution, strongly peaked atapprox. 0.6 solar mass. We stress that the scatter seen in thestatistical distance scale is likely to be real. The scatter is causedby the fact that the core mass distribution, although narrow andstrongly peaked, has a finite width.

Distribution of supernovae relative to spiral arms and H II regions
We have studied the association of supernovae in spiral galaxies withsites of recent stars formation -- sprial arms and H II regions. It isshown that supernovae (SNe) of Types Ia, Ib, and II exhibitconcentration to spiral arms and their distributions over the distanceto the nearest spiral arm do not differ significantly. This result isconfirmed by a Kolmogorov-Smirnov test comparison with the distancedistributions, expected if SNe are distributed randomly inside the modelgalaxy. SNe of types Ib and II show a strong concentration towards H IIregions, while distribution of SNe Ia can be explained by chancesuperposition. All studied distributions of SNe Ib and II show strikingsimilarity, which suggests that their progenitors are massive stars withsimilar ages and initial masses. The association of SNe Ia with spiralarms suggests that their progenitors in spiral galaxies are likely to beintermediate mass stars.

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 features of chemical abundances in Galactic planetary nebulae
The chemical composition of 217 Galactic planetary nebulae isinvestigated; 203 of them are subdivided into four classes according tothe masses of nebulae and progenitor stars. The values of localabundances, Galactic abundance gradients and Galactic electrontemperature gradients are found for each class of nebula. Thecorrelations between the abundances of pairs of elements are alsocalculated for each class of nebula. The results are compared withtheoretical predictions. In particular, it is concluded that CN cyclingcan play a role in progenitor stars for all classes of planetary nebula.

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.

A catalogue of absolute fluxes and distances of planetary nebulae
The paper presents a complete list of averaged recalibrated absoluteH-beta fluxes, global (where possible) relative He II lambda 4686fluxes, 5 GHz radio flux densities, and H-alpha/H-beta interstellarextinction constants for 778 Galactic planetary nebulae. The catalogprovides much of the fundamental data required to generate Zanstratemperatures. When data with the lowest errors are selected, the opticaland radio/optical extinctions show a peculiar correlation, with theradio values slightly high at low extinction and notably low at highextinction. The data are used, along with the best estimates of angulardiameters, to calculate Shklovsky distances according to the Daub schemeon the scale used earlier by Cahn and Kaler (1971). Use of this distancescale shows approximate equality of the death rates of optically thickand optically thin planetary nebulae. The method gives the correctdistances to the Magellanic Clouds.

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

The absolute H-beta fluxes for galactic planetary nebulae
The absolute H-beta flux measurements from spectrophotometricobservations of about 880 galactic planetary nebulae are presented. Thegalactic coordinates of PNe and the adopted diameters for the nebulae inarcsec are given. The final values of the H-beta flux, corrected for thenebular extension, are presented and compared to the results of othermeasurements.

Excitation class of nebulae - an evolution criterion?
A principally new quantitative system of the classification of thespectra of planetary nebulae is proposed. Spectral class of excitationclass of the nebula p is determined according to the relativeintensities of forbidden mission lines (N1 + N2) O III/4686 He II and(N1 + N2) O III/H-beta. The excitation classes are obtained for 142planetary nebulae of all classes - low (p = 1-3), middle (p = 4-8), andhigh (p = 9-12/+/). An empirical relationship between excitation classp, as an independent parameter, admit an evolutionary interpretation. Itis shown that after reaching the highest class of excitation p = 12(+)the nebulae decrease their class of excitation with the furtherincreases of sizes.

Chemical abundances in planetary nebulae - Basic data and correlations between elements
To form a critical compilation of the abundances of He, C, N, O and Ne,all the individual determinations of chemical abundances in PN obtainedwith linear detectors have been considered. The data cover allobservations of the Galactic PN made in the 20 years up to the end of1989. Average chemicql abundances have been evaluated separately fornebulae of type I and of types II-III of Peimbert. For the first, theyare He/H = 0.137, C/H = 8.72, N/H = 8.60, O/H = 8.66, and Ne/H = 8.05.For the second they are He/H = 0.103, C/H= 8.82, N/H = 8.07, O/H = 8.66,and Ne/H = 7.99, in the usual units. The data analysis suggests that theenrichment of nitrogen in type I PNs is due mostly to the ON cycle,while that in PNs of type II-III is due mostly to the CN cycle.

Large planetary nebulae and their significance to the late stages of stellar evolution
Spectrophotometry of 75 large PNe with Shklovsky radii greater than 0.15pc is presented and used to calculate nebular parameters andcompositions, stellar Zanstra temperatures and luminosities, and coremasses. Nine new Peimbert type I nebulae are identified. About 40percent of the stars that are on cooling tracks are above 0.7 solarmass, and over 15 percent are above 0.8 solar mass. The largeplanetaries demonstrate a clear positive correlation between nitrogenenrichment and core mass. N/O is anticorrelated with O/H. The radii ofthe nebulae whose stars lie along specific cooling tracks increasemonotonically with decreasing central star temperature. For a givencentral temperature, the nebular radii also increase with increasingcore mass, showing that in this part of the log L-log T plane the highermass cores evolve more slowly in agreement with theoretical prediction.However, theoretical evolutionary rates for the large nebulae starsappear to be much too slow.

Central star temperatures of optically thick planetary nebulae and a distance-independent test of dredge-up theory
The effective temperatures are calculated and the V magnitudes arepredicted for the central stars of 62 optically thick planetary nebulasby forcing agreement between the hydrogen and ionized helium Zanstratemperatures. Comparison to the measured V for 34 of the stars showsgood agreement and validates the method for the other 28, for which noZanstra analysis is available. In many cases the predicted V magnitudesare actually likely to be better than the currently measured values. Thecomparison suggests that optical depth and not an ultraviolet excess isthe dominant cause of the Zanstra discrepancy. Nebular N/O correlatespositively with effective temperature, demonstrating that the N/O-coremass relation rises more steeply than predicted by dredge-up theory.

A catalogue of VLA radio continuum observations of planetary nebulae with the Very Large Array
An extended VLA survey of about 300 planetary nebulae, ranging in sizefrom 4 arcsec to 8 arcmin, has been completed. The maps and the measuredparameters, such as radio flux density, diameter, and position, arepresented. The brightness temperatures, total far-infrared flux, andinfrared excess are derived. Newly measured optical positions are givenfor a few sources. A compilation of all published VLA data of planetarynebulae is also included. High-resolution radio synthesis observationsare now available for approximately 400 nebulae.

Vertical abundance gradients of planetary nebulae.
Abstract image available at:http://adsabs.harvard.edu/abs/1988RMxAA..16..105F

The temperatures of the nuclei of high-excitation planetary nebulae
An empirical relationship between the ratio of the intensities of theemission lines 4686 He II/H-beta and N1 + N2 forbidden O III/4868 He IIin the spectra of planetary nebulae is proposed. Upper and lower limitsfor the nucleus temperature have been obtained for 97 planetary nebulae.A new quantitative system for the determination of the excitationclasses of nebulae has been derived.

IRAS pointed observations of planetary nebulae
The pointed observations made by IRAS satellite have been analyzed inorder to find extended planetary nebulas. Of the 67 nebulas observedonly 10 were larger than the IRAS beams. IR data of these nebulas havebeen compared with optical data. Also a comparison with other IRAS dataproducts has been made. The major part of the IR emission originates inthe ionized region. No evidence for weak extended IR haloes could befound. The IR emission has a single temperature and its brightness dropssuddenly at the IR edge. In BD + 30 3639 and NGC 6543 there is evidencefor IF emission which envelopes the ionized region. This dust could be aremnant of the progenitor shell. IR sizes have been determined by modelfits. The calculations indicate a mass loss rate in dust between 10 tothe -7th and 10 to the -6th solar masses/yr, which is caused by theonset of some 'superwind'. The models support the existence of atemperature gradient in NGC 6543 and BD + 30 3639.

Statistical evolutionary properties of planetary nebulae Thicknesses of the nebulae and temperatures of the stars
A comparative study of Zanstra temperatures of the central stars ofplanetary nebulae indicates that when present the discrepancies betweenTZ H I and TZ He II can be mainly ascribed to the variation of theoptical thickness of a nebulae of hydrogen and helium ionized by a starwhich emits as a black-body. Different evolutionary trends of TZ H I andTZ He II are obtained for planetary nebulae of the subclasses B and C ofGreig (1971, 1972): B nebulae spend most of their life in a thickstatus, whereas C nebulae start as thick objects but they quickly becomeoptically thin. These results give further support to the suggestion bySabbadin (1984) that planetary nebulae of the subclass B have stellarmasses and/or nebular masses which are statistically larger than thoseof planetary nebulae belonging to the subclass C.

A catalogue of distances of planetary nebulae
This catalog contains distances of 468 galactic planetary nebulae pluslower limits to 61 objects and upper limits for 134 nebulae. Thedistances were calculated assuming a relationship between the nebularionized mass and radius.

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Right ascension:18h59m20.03s
Apparent magnitude:15

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NGC 2000.0NGC 6742

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