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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 (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/408/1029}
| Angular dimensions of planetary nebulae
We have measured angular dimensions of 312 planetary nebulae from theirimages obtained in Hα (or Hα + [NII]). We have appliedthree methods of measurements: direct measurements at the 10% level ofthe peak surface brightness, Gaussian deconvolution and second-momentdeconvolution. The results from the three methods are compared andanalysed. We propose a simple deconvolution of the 10% levelmeasurements which significantly improves the reliability of thesemeasurements for compact and partially resolved nebulae. Gaussiandeconvolution gives consistent but somewhat underestimated diameterscompared to the 10% measurements. Second-moment deconvolution givesresults in poor agreement with those from the other two methods,especially for poorly resolved nebulae. From the results of measurementsand using the conclusions of our analysis we derive the final nebulardiameters which should be free from systematic differences between small(partially resolved) and extended (well resolved) objects in our sample.Table 1 is only available in electronic form athttp://www.edpsciences.org
| The 3-D ionization structure of NGC 6818: A Planetary Nebula threatened by recombination
Long-slit NTT+EMMI echellograms of NGC 6818 (the Little Gem) at nineequally spaced position angles, reduced according to the 3-D methodologyintroduced by Sabbadin et al. (\cite{Sabbadin00}a,b), allowed us toderive: the expansion law, the diagnostics and ionic radial profiles,the distance and the central star parameters, the nebularphoto-ionization model, the 3-D reconstruction in He II, [O III] and [NII], the multicolor projection and a series of movies. The Little Gemresults to be a young (3500 years), optically thin (quasi-thin in somedirections) double shell (Mion =~ 0.13 Msun) ata distance of 1.7 kpc, seen almost equatorial on: a tenuous and patchyspherical envelope (r =~ 0.090 pc) encircles a dense and inhomogeneoustri-axial ellipsoid (a/2 =~ 0.077 pc, a/b =~ 1.25, b/c =~ 1.15)characterized by a hole along the major axis and a pair of equatorial,thick moustaches. NGC 6818 is at the start of the recombination phasefollowing the luminosity decline of the 0.625 Msun centralstar, which has recently exhausted the hydrogen shell nuclear burningand is rapidly moving toward the white dwarf domain (log T*=~ 5.22 K; log L*/Lsun =~ 3.1). The nebula isdestined to become thicker and thicker, with an increasing fraction ofneutral, dusty gas in the outermost layers. Only over some hundreds ofyears the plasma rarefaction due to the expansion will prevail againstthe slower and slower stellar decline, leading to a gradual re-growingof the ionization front. The exciting star of NGC 6818 (mV =~17.06) is a visual binary: a faint, red companion (mV =~17.73) appears at 0.09 arcsec in PA =190degr , corresponding to aseparation ge 150 AU and to an orbital period ge 1500 years.Based on observations made with ESO Telescopes at the La SillaObservatories, under programme ID 65.I-0524, and on observations madewith the NASA/ESA Hubble Space Telescope, obtained from the data archiveat the Space Telescope Institute (observing programs GO 7501 and GO8773; P.I. Arsen Hajian). STScI is operated by the association ofUniversities for Research in Astronomy, Inc. under the NASA contract NAS5-26555. We have applied the photo-ionization code CLOUDY, developed atthe Institute of Astronomy of the Cambridge University.
| The distance scale of planetary nebulae
By collecting distances from the literature, a set of 73 planetarynebulae with mean distances of high accuracy is derived. This sample isused for recalibration of the mass-radius relationship, used by manystatistical distance methods. An attempt to correct for a statisticalpeculiarity, where errors in the distances influences the mass-radiusrelationship by increasing its slope, has been made for the first time.Distances to PNe in the Galactic Bulge, derived by this new method aswell as other statistical methods from the last decade, are then usedfor the evaluation of these methods as distance indicators. In order ofachieving a Bulge sample that is free from outliers we derive newcriteria for Bulge membership. These criteria are much more stringentthan those used hitherto, in the sense that they also discriminateagainst background objects. By splitting our Bulge sample in two, onewith optically thick (small) PNe and one with optically thin (large)PNe, we find that our calibration is of higher accuracy than most othercalibrations. Differences between the two subsamples, we believe, aredue to the incompleteness of the Bulge sample, as well as the dominanceof optical diameters in the ``thin'' sample and radio diameters in the``thick'' sample. Our final conclusion is that statistical methods givedistances that are at least as accurate as the ones obtained from manyindividual methods. Also, the ``long'' distance scale of Galactic PNe isconfirmed.
| 3-D ionization structure (in stereoscopic view) of planetary nebulae: the case of NGC 1501.
Long-slit echellograms of the high excitation planetary nebula NGC 1501,reduced according to the methodology developed by Sabbadin et al.(2000a,b), allowed us to obtain the "true" distribution of the ionizedgas in the eight nebular slices covered by the spectroscopic slit. A 3-Drendering procedure is described and applied, which assembles thetomographic maps and rebuilds the spatial structure. The images of NGC1501, as seen in 12 directions separated by 15o, form a series ofstereoscopic pairs giving surprising 3-D views in as many directions.The main nebula consists of an almost oblate ellipsoid of moderateellipticity (a ~= 44 arcsec, a/b ~= 1.02, a/c ~= 1.11), brighter in theequatorial belt, deformed by several bumps, and embedded in a quitehomogeneous, inwards extended cocoon. Some reliability tests are appliedto the rebuilt nebula; the radial matter profile, the small scaledensity fluctuations and the 2-D (morphology) -3-D (structure)correlation are presented and analysed. The wide applications of the 3-Dreconstruction to the morphology, physical conditions, ionizationparameters and evolutionary status of expanding nebulae in general(planetary nebulae, nova and supernova remnants, shells aroundPopulation I Wolf-Rayet stars, nebulae ejected by symbiotic stars,bubbles surrounding early spectral type main sequence stars etc.) areintroduced.
| An atlas of images of Planetary Nebulae
A catalogue of narrowband CCD images of 100 southern and 1 northernPlanetary Nebulae is presented. The data are images taken in the lightof the Hα , Hβ , [OIII]500.7 nm, and [NII]658.4 nm lines. Foreach image we give the exposure time, the maximum extent of the nebula,and the seeing measured from the frames themselves. For ease ofreference, we have added an alphabetical list of the objects. Our listwill be useful for morphological studies of Planetary Nebulae, and iscomplementary to previously published lists, especially the one of\cite[Schwarz et al. (1992)]{sch92}. Based on observations obtained atthe European Southern Observatory, La Silla, Chile.
| 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
| A Morphological Study of Planetary Nebulae
We have produced simulated images of 110 planetary nebulae using theellipsoidal shell model. This process has allowed us to remove theprojection effects from the morphological classification of planetarynebulae and has provided quantitative measures of the intrinsicasymmetries of the nebulae. It is shown that the morphology of mostplanetary nebulae can be reproduced with pole-to-equator density ratiosof 0.1-1. Many planetary nebulae also show a modest departure from axialsymmetry. Contrary to previous findings by Khromov & Kohoutek, thesky orientation of planetary nebulae in this sample is consistent with apurely random distribution. Extremely bipolar nebulae (e.g., those ofbutterfly shape) point to a steep density profile in the AGB envelopeand are more likely to be type I (high helium and/or nitrogen abundance)nebulae. We found evidence that these nebulae are likely to have moremassive progenitors and are at a more advanced stage of dynamicalevolution.
| Orientation of planetary nebulae within the Galaxy
Narrow-band CCD images of 209 axially symmetrical planetary nebulae(PNe) have been examined in order to determine the orientation of theiraxes within the disc of the Galaxy. The nebulae have been divided intothe bipolar (B) and elliptical (E) PNe morphological types, according tothe scheme of Corradi & Schwarz. In both classes, contrary to theresults of Melnick & Harwit and Phillips we do not find any strongevidence for non-random orientations of the nebulae in the Galaxy.Compared with previous work in this field, the present study takesadvantage of the use of larger and morphologically more homogeneoussamples and offers a more rigorous statistical analysis.
| Planetary nebulae morphologies, central star masses and nebular properties.
We have constituted a sample of about 80 PN with defined morphologiesand well observed basic parameters (fluxes, angular radii, expansionvelocities and magnitudes of the central stars). For these PN, we havederived the central star masses by comparing the observed set ofparameters with those predicted by a simple evolutionary model of a PN,expanding at the same velocity as the observed one. We have thenexamined the relations between the PN morphological types and otherproperties, linked to the central star mass. Bipolar PN are shown tohave a wider distribution of central star masses than the rest of PN,and shifted towards higher values. They lie closer to the Galactic planeand tend to have larger N/O ratios. Point symmetric PN, which have notbeen much studied so far, are found to constitute an outstanding class.They show an almost perfect M_*_-v_exp_ correlation. They correspond toa rather short evolutionary stage of PN. They lie, on average, furtherfrom the Galactic plane than bipolar PN and tend to have lower N/O.Globally, PN with higher central star masses are found closer to theGalactic plane, and the observed relation between N/O and M_*_ isroughly consistent with the predictions from evolutionary models for AGBstars.
| The molecular envelopes of planetary nebulae.
We report the results of a survey of millimeter CO emission in 91planetary nebulae using the IRAM 30 m and SEST 15 m telescopes. Theobservations provide new detections or improved data for 23 nebulae inthe CO(2-1) and/or CO(1-0) line, and sensitive limits for those not seenin CO. Analysis of the results together with previous observationsconfirms the existence of an important class of planetary nebulae withmassive (10^-2^-a few M_sun__) envelopes of molecular gas.These nebulae typically have abundance ratios of N/O>0.3 and bipolarmorphologies indicative of a young disk population. The column densitythrough the envelopes and their mass relative to the mass of ionized gasshow dramatic decreases with increasing nebular size, documenting theexpansion of the envelopes and the growth of the optical nebulae at theexpense of the molecular gas. The molecular envelopes remain a majormass component in these objects until the nebulae reach a radius ofR=~0.1pc. The nebulae not detected in CO have little or no molecular gas(<~10^-2^-10^-3^Msun_), and their envelopes must berapidly photo-dissociated before or during the compact phase. The largedifferences in the molecular gas content of the nebulae highlight thedifferent evolutionary paths for planetary nebula formation which resultfrom the range in mass of the progenitors and the structure of theircircumstellar envelopes.
| H2 Emission from Planetary Nebulae: Signpost of Bipolar Structure
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...462..777K&db_key=AST
| A statistical distance scale for Galactic planetary nebulae
A statistical distance scale is proposed. It is based on the correlationbetween the ionized mass and the radius and the correlation between theradio continuum surface brightness temperature and the nebular radius.The proposed statistical distance scale is an average of the twodistances obtained while using the correlation. These correlations,calibrated based on the 1`32 planetary nebulae with well-determinedindividual distances by Zhang, can reproduce not only the averagedistance of a sample of Galactic Bulge planetary nebulae exactly at thedistance to the Galactic center, but also the expected Gaussiandistribution of their distances around the Galactic center. This newdistance scale is applied to 647 Galactic planetary nebulae. It isestimated that this distance scale can be accurate on average to35%-50%. Our statistical distance scale is in good agreement with theone recently proposed by Van de Steene and Zijlstra. The correlationsfound in this study can be attributed to the fact that the core mass ofthe central stars has a very sharp distribution, strongly peaked atapprox. 0.6 solar mass. We stress that the scatter seen in thestatistical distance scale is likely to be real. The scatter is causedby the fact that the core mass distribution, although narrow andstrongly peaked, has a finite width.
| On an alternative statistical distance scale for planetary nebulae. Catalog with statistical distances to planetary nebulae.
We have proposed a statistical method to determine distances toplanetary nebulae. The method is based on an empirical correlationbetween the radio-continuum brightness temperature and radius. Here wepresent a catalog of distance determinations calculated using thismethod.
| 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.
| Confrontation of theoretical tracks for post-AGB stars with observations of planetary nebulae
We have constructed a distance-independent diagram to test publishedtheoretical tracks for the evolution of post-AGB stars by comparing themwith the Galactic planetary nebulae data base. We have found noinconsistency between observations and the set of tracks computed bySchoenberner (1981, 1983) and Bloecker & Schoenberner (1990). On theother hand, observations do not seem support the large transition timesbetween the end of the AGB superwind and the beginning of the planetarynebula ionization phase adopted in the models of Vassiliadis & Wood(1994).
| Trace of planetary nebula evolution by distance-independent parameters
Using existing infrared and radio data on a sample of 432 planetarynebulae, we derived a number of distance-independent parameters forcomparison with evolutionary models of planetary nebulae. We find thatmany of the observed properties of planetary nebulae can be explained bycurrent central star evolutionary models, even if the time scales aresubject to significant change by a factor of up to an order ofmagnitude. Specifically, we find that the evolutionary tracks are wellseparated in the radio surface brightness-central star temperatureplane, therefore allowing us to determine the core mass of individualplanetary nebulae. We also obtain the luminosity and gravity of thecentral stars of individual nebulae, from their temperature and coremass, without relying on the distance assumptions. We find that ourresults of the core mass are in good agreement with those of Mendez etal. (1992) and Tylenda et al. (1991). A systematic, large discrepancy isfound between the luminosity found in this work and that found byGathier and Pottasch (1986).
| On the distance to Galactic planetary nebulae
The distances are determined for 145 Galactic PNe using two methods. Thedistances for a sample of 131 PNe are determined using method A, basedon the stellar mass and surface gravity. Method B, making use of thestellar luminosity, is applied to another sample of 61 PNe, of which 47are in common with those in the sample for method A. The properties ofthe central star, such as the core mass, luminosity, and surfacegravity, are inferred from the modeling of the distance-independentparameters. The results from the two methods used in this paper areconsistent with each other. A distance of 11.3 kpc is found for K648using method A of this work. This is in good agreement with the distanceof 10 kpc of its hosting globular cluster M15.
| The Neutral Envelopes of Planetary Nebulae: Molecules and H I
Not Available
| 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.
| 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.
| 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.
| Morphology of bipolar planetary nebulae. II - The three-dimensional structures
Isophotal maps of bipolar planetary nebulae (BPN) are used here to studythe BPN morphology and to produce maps of their normalized densitydistribution. Shell models are calculated, and the theoretical isophotesare compared with CCD contours. It is shown that a simple large-scalesmooth structure can be derived and that a unique prolate model with twoor three adjustable parameters seems suitable for most BPN. The BPNNGC6720, NGC7293, and He2-66 are shown to be morphologically identical.
| Morphology of bipolar planetary nebulae. I - Two-dimensional spectrophotometry
Two-dimensional spectrophotometric observations of bipolar planetarynebulas were performed by using a CCD detector mounted at the Cassegrainfocus of either 1.54 m Danish Telescope or 2.2 m German Telescope at LaSilla (ESO) in Chile. Emission lines have been selected with the help ofnarrow band-pass interference filters. Isophotal maps in various linesH-alpha NII 6584, OIII 5007, and SII 6717-6731 are presented. Particularattention has been given to scrutinizing the symmetries inside a fewbipolar planetary nebulas, in order to subsequently investigate theirspace structure.
| The Energy-Balance temperature of central stars of galactic planetary nebulae
The color temperature of the central star of planetary nebulae iscalculated assuming that thermal equilibrium holds in the photoionizednebula. The ratio of H-beta of the dereddened intensities of observedcollisionally excited lines, with two additional terms is used toestimate the total emissivity of unobserved lines: (1) the contributionof unseen lines of ions visible in the survey's spectral range and (2)the contribution of lines of undetected or unobserved ions of O, Ne, andS. The energy-balance temperature is determined for 388 central stars.The present study shows that the energy-balance method represents auseful way to estimate the temperature of large samples of planetarynebulae.
| A catalogue of expansion velocities of Galactic planetary nebulae
Published observational data on 288 Galactic PN are compiled in tables,graphs, and sketches based on spatiokinematical models and brieflycharacterized. The criteria used in selecting the data are discussed,and particular attention is given to the accuracies of the distanceestimates and their implications for theoretical models of PN or stellarevolution.
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