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The dense and asymmetric central star wind of the young PN He 2-138
We present optical European Southern Observatory time series and UVarchival (Far Ultraviolet Spectroscopic Explorer (FUSE), Hubble SpaceTelescope, International Ultraviolet Explorer) spectroscopy of theH-rich central star of He 2-138. Our study targets the central star windin a very young planetary nebula, and explores physical conditions thatmay provide clues to the nature of the preceding post-asymptotic giantbranch superwind phases of the star. We provide evidence for a dense,slowly accelerating outflow that is variable on time-scales of hours.Line-synthesis modelling (Sobolev with exact integration and CMFGEN) oflow- and high-ionization UV and optical lines is interpreted in terms ofan asymmetric, two-component outflow, where high-speed high-ionizationgas forms mostly in the polar region. Slower, low-ionization material isthen confined primarily to a cooler equatorial component of the outflow.A dichotomy is also evident at photospheric levels. We also documenttemporal changes in the weak photospheric lines of He 2-138, withtentative evidence for a 0.36-day modulation in blue-to-red migratingfeatures in the absorption lines. These structures may betray `waveleakage' of prograde non-radial pulsations of the central star. Thesemultiwaveband results on the aspherical outflow of He 2-138 arediscussed in the context of current interest in understanding the originof axi- and point-symmetric planetary nebulae.
| The Origin and Shaping of Planetary Nebulae: Putting the Binary Hypothesis to the Test
Planetary nebulae (PNs) are circumstellar gas ejected during an intensemass-losing phase in the lives of asymptotic giant branch stars. PNshave a stunning variety of shapes, most of which are not sphericallysymmetric. The debate over what makes and shapes the circumstellar gasof these evolved, intermediate mass stars has raged for two decades.Today the community is reaching a consensus that single stars cannottrivially manufacture PNs and impart to them nonspherical shapes andthat a binary companion, possibly even a substellar one, might be neededin a majority of cases. This theoretical conjecture has, however, notbeen tested observationally. In this review we discuss the problem fromboth the theoretical and observational standpoints, explaining theobstacles that stand in the way of a clean observational test and waysto ameliorate the situation. We also discuss indirect tests of thishypothesis and its implications for stellar and galactic astrophysics.
| Recent FUSE Observations of Diffuse O VI Emission from the Interstellar Medium
We present new results from our survey of diffuse O VI-emitting gas inthe interstellar medium with the Far Ultraviolet Spectroscopic Explorer(FUSE). Background observations obtained since 2005 have yielded 11 newO VI detections of 3 σ significance, and archival searches haverevealed two more. An additional 15 sight lines yield interesting upperlimits. Combined with previous results, these observations reveal thelarge-scale structure of the O VI-bearing gas in the quadrant of the skycentered on the Magellanic Clouds. The most prominent feature is a layerof low-velocity O VI emission extending more than 70° from theGalactic plane. At low latitudes (|b|<30deg), the emissioncomes from narrow, high-density interfaces in the local ISM. At highlatitudes, the emission is from extended, low-density regions in theGalactic halo. We also detect O VI emission from the interface regionof the Magellanic system, a structure recently identified from H Iobservations. These are the first detections of emission fromhigh-ionization species in the Magellanic system outside of the Cloudsthemselves.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer. FUSE is operated for NASA by the Johns HopkinsUniversity under NASA contract NAS5-32985.
| Independent Emission and Absorption Abundances for Planetary Nebulae
Emission-line abundances have been uncertain for more than a decade dueto unexplained discrepancies in the relative intensities of theforbidden lines and weak permitted recombination lines in PNe and H IIregions. The observed intensities of forbidden and recombination linesoriginating from the same parent ion differ from their theoreticalvalues by factors of more than an order of magnitude in some of thesenebulae. In this study we observe UV resonance line absorption in thecentral stars of PNe produced by the nebular gas and from the same ionsthat emit optical forbidden lines. We then compare the derivedabsorption column densities with the emission measures determined fromground-based observations of the nebular forbidden lines. We find forour sample of PNe that the collisionally excited forbidden lines yieldcolumn densities that are in basic agreement with the column densitiesderived for the same ions from the UV absorption lines. A similarcomparison involving recombination line column densities produces pooreragreement, although near the limits of the formal uncertainties of theanalyses. An additional sample of objects with larger abundancediscrepancy factors will need to be studied before a stronger statementcan be made that recombination line abundances are not correct.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by AURA,Inc., under NASA contract NAS5-26555.
| Galactic planetary nebulae and their central stars. II. Proper motions
Context: More than 1500 Galactic planetary nebulae (PNe) are known butonly a tiny fraction of them have measured proper motions. To date, thelargest set of proper motion (PM) data for PNe is the one by Cudworth(1974), which includes 62 objects 25 of which have PM with significancebetter than 3σ in at least one component. Aims: With our newcompilation of 234 PNe we enlarge - compared to Cudworth's 25 - byalmost an order of magnitude the number of PNe and central stars (CSs)with reliably measured proper motion (i.e. with significance better than3σ in at least one component) and confirm some previousmeasurements. Methods: We have used all-sky astrometric cataloguesavailable via the Vizier database to collect proper motion informationfor a sample of objects selected from the catalogue of PNe positions ofKerber et al. (2003a, A&A, 408, 1029). Results: We have derivedproper motion information for a total of 234 PNe (274 when including 40doubtful candidates). We include all PNe for which a confidence level ofat least 3σ was achieved in at least one proper motion component.For many objects PM data are available from more than one catalogue andagreement between different catalogues is usually very reasonableproviding independent confirmation of the results. For comparison withCudworth's results we use the proper motion modulus as a metric. Wecross-correlated his 62 objects with our master catalogue and found 12matching objects out of the 18 with >3σ in his list. For thesewe find good agreement for 10 out of the 12 objects, while we findsignificant PM for another five objects with PM σ ≤3 reportedby Cudworth. The number of objects we have in common was limited byseveral factors discussed in the paper. Conclusions: With 234 (274including doubtful candidates) entries our work is the largest availablecompilation of proper motion data for PNe and their CSs. Thiscompilation opens new opportunities for studies of orbital kinematics ofPNe in the Galaxy.Table 3 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/479/155
| Bayesian posterior classification of planetary nebulae according to the Peimbert types
Context: Galactic planetary nebulae are observed with a wide variety ofkinematic properties, spatial distribution, chemical composition andmorphologies, comprising members of the dominant stellar populations ofour Galaxy. Due to their broad astrophysical interest, a propercharacterization of these populations is of major importance. Aims: Inthis paper we present a re-analysis of the criteria used to characterizethe Peimbert classes I, IIa, IIb, III and IV, through a statisticalstudy of a large sample of planetary nebulae previously classifiedaccording to these groups. In the original classification, it is usualto find planetary nebulae that cannot be associated with a single type;these most likely have dubious classifications into two or three types.Statistical methods can greatly contribute in providing a bettercharacterization of planetary nebulae groups. Methods: We use the BayesTheorem to calculate the posterior probabilities for an object to bemember of each of the types I, IIa, IIb, III and IV. This calculation isparticularly important for planetary nebulae that are ambiguouslyclassified in the traditional method. The posterior probabilities aredefined from the probability density function of classificatoryparameters of a well-defined sample, composed only by planetary nebulaeunambiguously fitted into the Peimbert types. Because the probabilitiesdepend on the available observational data, they are conditionalprobabilities, and, as new observational data are added to the sample,the classification of the nebula can be improved, to take into accountthis new information. Results: This method differs from the originalclassificatory scheme, because it provides a quantitative result of therepresentativity of the object within its group. Also, through the useof marginal distributions it is possible to extend the Peimbertclassification even to those objects for which only a few classificatoryparameters are known. Conclusions: We found that ambiguities in theclassification of planetary nebulae into the Peimbert types, should beassociated to difficulties in defining sharp boundaries for theprogenitor star mass for each of these types. Those can be at leastpartially explained by real overlaps of some of the parameters thatcharacterize the different stellar populations. Those results suggestthe need of a larger number of classificatory parameters for a reliablephysical classification of planetary nebulae.Tables [see full textsee full text] and [see full textsee full text] areonly available in electronic form at http://www.aanda.org
| Variability and rapid evolution of the protoplanetary object IRAS 18062+2410=V886 her
We present our long-term photometric and spectroscopic observations of ahigh-latitude B supergiant with an infrared excess—theprotoplanetary nebula IRAS 18062+2410. Our U BV observations in 20002006 have confirmed the rapid irregular photometric variability of thestar with a maximum amplitude as high as 0{./ m }4in V that we found previously. The B— V and U— B colorindices vary with amplitudes as high as 0{./ m }10and 0{./ m }25, respectively, and show no clearcorrelation with the brightness. Our V-band CCD observations on 11nights in 2006 have revealed brightness trends during the night. Thevariability of IRAS18062+2410 is similar in pattern to the lightvariations in other hot post-AGB objects and some of the nuclei of youngplanetary nebulae. We assume that pulsations and a variable stellar windcan be responsible for the variability of these stars. In addition tothe rapid variability, our 12-year-long observations have revealed asystematic decline in the mean brightness of IRAS 18062+2410. This maybe related to a rise in the temperature of the star at constantluminosity as a result of its evolution. Low-resolution spectroscopicobservations have shown a systematic increase in the equivalent widthsof the H α, H β, [NII]λ6584 Å, OI λ8446Å, and [OII] λ7320 7330 Å emission lines. The changesin the star’s emission line spectrum are probably caused by anincrease in the degree of ionization of the gas shell due to a rise inthe temperature of the ionizing star. Our photometric and spectroscopicobservations of IRAS 18062+2410 confirm the previously made assumptionsthat the star evolves very rapidly to the region of planetary nebulae.
| Identification of PN G232.0+05.7 as a new halo planetary nebula and of IRAS 19336-0400 as a new type III planetary nebula
Aims:We determined the nature and Peimbert type of two low-excitationplanetary nebulae, PNG 232.0+05.7 and IRAS 19336-0400. Methods:We used low resolution optical spectroscopy in the range3200-9000Å. Results: We derived line intensities, reddening,physical conditions (electron density and temperature) and ionic andelemental abundances. Based on the abundance analysis and its radialvelocity we conclude that PNG 232.0+05.7 is a halo planetary nebulae.This discovery thus adds this object to the sample of ten known haloplanetary nebulae. IRAS 19336-0400 is probably a type III planetarynebulae, as strongly suggested by its abundances and high radialvelocity, although this conclusion awaits a better estimation of itsdistance.Based on observations collected at the Centro Astronomico Hispano Aleman(CAHA) at Calar Alto, operated jointly by the Max-Planck Institutfür Astronomie and the Instituto de Astrofísica deAndalucía (CSIC).
| An Extended FUSE Survey of Diffuse O VI Emission in the Interstellar Medium
We present a survey of diffuse O VI emission in the interstellar medium(ISM) obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE).Spanning 5.5 yr of FUSE observations, from launch through 2004 December,our data set consists of 2925 exposures along 183 sight lines, includingall of those with previously published O VI detections. The data wereprocessed using an implementation of CalFUSE version 3.1 modified tooptimize the signal-to-noise ratio and velocity scale of spectra from anaperture-filling source. Of our 183 sight lines, 73 show O VIλ1032 emission, 29 at >3 σ significance. Six of the 3σ features have velocities |vLSR|>120 kms-1, while the others have |vLSR|<=50 kms-1. Measured intensities range from 1800 to 9100 LU (lineunit; 1 photon cm-2 s-1 sr-1), with amedian of 3300 LU. Combining our results with published O VI absorptiondata, we find that an O VI-bearing interface in the local ISM yields anelectron density ne=0.2-0.3 cm-3 and a path lengthof 0.1 pc, while O VI-emitting regions associated with high-velocityclouds in the Galactic halo have densities an order of magnitude lowerand path lengths 2 orders of magnitude longer. Although the O VIintensities along these sight lines are similar, the emission isproduced by gas with very different properties.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer. FUSE is operated for NASA by Johns HopkinsUniversity under NASA contract NAS5-32985.
| The structure of planetary nebulae: theory vs. practice
Context.This paper is the first in a short series dedicated to thelong-standing astronomical problem of de-projecting the bi-dimensional,apparent morphology of a three-dimensional mass of gas. Aims.Wefocus on the density distribution in real planetary nebulae (and alltypes of expanding nebulae). Methods. We introduce some basictheoretical notions, discuss the observational methodology, and developan accurate procedure for determining the matter radial profile withinthe sharp portion of nebula in the plane of the sky identified by thezero-velocity-pixel-column (zvpc) of high-resolution spectral images.Results. The general and specific applications of the method (andsome caveats) are discussed. Moreover, we present a series of evolutivesnapshots, combining illustrative examples of both model and trueplanetary nebulae. Conclusions. The zvpc radial-densityreconstruction - added to tomography and 3D recovery developed at theAstronomical Observatory of Padua (Italy) - constitutes a very usefultool for looking more closely at the spatio-kinematics, physicalconditions, ionic structure, and evolution of expanding nebulae.
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| The mean properties of planetary nebulae as a function of Peimbert class
Planetary nebulae are known to possess a broad range of abundances, andthese (with other characteristics) have been used to define five classesof outflow. Peimbert Type I sources, for instance, possess high N and Heabundances, filamentary structures, and low mean scaleheights above theGalactic plane, whilst those of Type III have much lower abundances,high peculiar velocities, and belong to the Galactic thick disc. Apartfrom some rather ill-defined indications, however, very little is knownconcerning their mean physical, spatial, structural, kinematic andthermal characteristics.We have performed a comprehensive study of all of these properties, andfind evidence for strong variations between the various Peimbertclasses. Certain of these differences are consistent with Type I sourceshaving the highest progenitor masses, although it seems that thesenebulae also possess the lowest rms densities and 5-GHz brightnesstemperatures. The latter results are in conflict with a range of recentmodelling.
| Radial-Velocity Survey of Central Stars of Southern Planetary Nebulae .
We have monitored selected southern-hemisphere planetary-nebula nuclei(PNNi) in order to search for radial-velocity (RV) variations. Theobservations have been carried out regularly since early 2003 with theSMARTS Consortium 1.5-m telescope and Cassegrain spectrograph at CerroTololo Inter-American Observatory, Chile. This study is a followup to anearlier survey of northern PNNi made by \citet{demarco04}, whichsuggested that there is a high incidence of RV variability among PNNi.If the variations are due to motion in binary orbits, the fraction ofclose binaries among PNNi must be very high, suggesting that mostplanetary nebulae are ejected through binary-star processes, such ascommon-envelope interactions. We presente here the results of thesouthern portion of our RV survey. Preliminary results indicate that thefraction of variable RVs is also very high among southern PNNi.
| Observations of the Diffuse Far-Ultraviolet Background with the Far Ultraviolet Spectroscopic Explorer
We have used observations taken under the Far Ultraviolet SpectroscopicExplorer (FUSE) S405/505 channel realignment program to explore thediffuse far-ultraviolet (FUV; 1000-1200 Å) radiation field. Of the71 independent locations in that program, we have observed a diffusesignal in 32, ranging in brightness from 1600 to a maximum of2.9×105 photons cm-2 sr-1s-1 Å-1 in Orion. The FUSE data confirm thatthe diffuse FUV sky is patchy with regions of intense emission, usuallynear bright stars, but also with dark regions, even at low Galacticlatitudes. We find a weak correlation between the FUV flux and the 100μm ratio but with wide variations, perhaps due to differences in thelocal radiation field.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer. FUSE is operated for NASA by The Johns HopkinsUniversity under NASA contract NAS5-32985.
| 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}
| 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
| Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
| Comparative Absorption and Emission Abundance Analyses of Nebulae: Ion Emission Densities for IC 418
Recent analyses of nebular spectra have resulted in discrepantabundances from CNO forbidden and recombination lines. We considerindependent methods of determining ion abundances for emission nebulae,comparing ion emission measures with column densities derived fromresonance absorption lines viewed against the central star continuum.Separate analyses of the nebular emission lines and the stellar UVabsorption lines yield independent abundances for ions, and their ratiocan be expressed in terms of a parameterem, the ``emission density'' for eachion. Adequate data for this technique are still scarce, but separateanalyses of spectra of the planetary nebula and central star of IC 418do show discrepant abundances for several ions, especially Fe II. Thediscrepancies are probably due to the presence of absorbing gas thatdoes not emit and/or to uncertain atomic data and excitation processes,and they demonstrate the importance of applying the technique ofcombining emission- and absorption-line data in deriving abundances fornebulae.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained from the STScI, which is operated by AURA, Inc., under NASAcontract NAS 5-26555, and on observations made at CTIO/NOAO, which isoperated by AURA, Inc., under cooperative agreement with the NSF.
| Multi-polar Structures in Young Planetary and Protoplanetary Nebulae (invited review)
Not Available
| Central Stars of Young Planetary Nebulae - A New Class of Variables
Not Available
| Bipolar and Multipolar Jets in Protoplanetary and Planetary Nebulae
One of the most exciting challenges facing theories of post-mainsequence evolution today is to understand how Asymptotic Giant Branch(AGB) stars and their round circumstellar envelopes (CSEs) transformthemselves into planetary nebulae (PNe) with their dazzling variety ofaspherical morphologies. The most succesful model for shaping PNe--the``generalised interacting-stellar-winds'' model, in which a fast (>1000 km s-1) spherical stellar wind interacts with an equatorially-denseAGB CSE to produce an axisymmetric PN--now appears inadequate as aresult of new data from the Hubble Space Telescope (HST). This paperpresents new HST images of proto-planetary and planetary nebulae withcollimated outflows. The outflows appear to be quite often multipolar innature, indicating episodic changes in the axis of a bipolar jet-likeoutflow or the operation of multiple collimated outflows with differentorientations. In particular, our serendipitous discovery of a veryhighly-collimated, extended jet in the planetary nebula Hen 2-90 and itsamazing morphological similarity to low-mass YSOs is the strongestevidence yet for a common physical mechanism for collimated outflows inprotostars and evolved stars. We briefly summarise current theoreticalhypotheses which may lead to a better understanding of the nature andorigin of these outflows.
| A New Look at the Evolution of Wolf-Rayet Central Stars of Planetary Nebulae
On the basis of recent observational evidence and new theoreticalresults, we construct a speculative scenario for the evolution ofWolf-Rayet central stars of planetary nebulae. Although single-starevolutionary calculations have succeeded recently in reproducing thecomposition of these objects, it is clear from the latest infraredobservations that a new perspective has to be adopted; the simultaneouspresence of carbon- and oxygen-rich dust (double-dust chemistry), whilebeing a rare phenomenon for H-rich central stars, is found around thevast majority of cool Wolf-Rayet central stars. This correlation betweenWolf-Rayet characteristics and double-dust chemistry points to a commonmechanism. Within the binary evolution framework established by Soker,two scenarios are proposed, responsible for the majority (80%-85%) andminority (15%-20%) of Wolf-Rayet central stars. In the first scenario,proposed here for the first time, a low-mass main-sequence star, browndwarf, or planet spirals into the asymptotic giant branch star, inducingextra mixing, hence a chemistry change, and terminating the asymptoticgiant branch evolution. In the second scenario, previously proposed, aclose binary companion is responsible for the formation of a disk aroundeither the binary or the companion. This long-lived disk harbors theO-rich dust. Both models are speculative, although they are supported byseveral observations and recent theoretical results.
| 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.
| Shapes and Shaping of Planetary Nebulae
We review the state of observational and theoretical studies of theshaping of planetary nebulae (PNe) and protoplanetary nebulae (pPNe). Inthe past decade, high-resolution studies of PNe have revealed abewildering array of morphologies with elaborate symmetries. Recentimaging studies of pPNe exhibit an even richer array of shapes. Thevariety of shapes, sometimes multiaxial symmetries, carefully arrangedsystems of low-ionization knots and jets, and the often Hubble-flowkinematics of PNe and pPNe indicate that there remains much tounderstand about the last stages of stellar evolution. In many cases,the basic symmetries and shapes of these objects develop on extremelyshort timescales, seemingly at the end of AGB evolution when the mode ofmass loss abruptly and radically changes. No single explanation fits allof the observations. The shaping process may be related to externaltorques of a close or merging binary companion or the emergence ofmagnetic fields embedded in dense outflowing stellar winds. We suspectthat a number of shaping processes may operate with different strengthsand at different stages of the evolution of any individual object.
| Version 2000 of the Catalogue of Galactic Planetary Nebulae
The ``Catalogue of Galactic Planetary Nebulae (Version 2000)'' appearsin Abhandlungen aus der Hamburger Sternwarte, Band XII in the year 2001.It is a continuation of CGPN(1967) and contains 1510 objects classifiedas galactic PNe up to the end of 1999. The lists of possible pre-PNe andpossible post-PNe are also given. The catalogue is restricted only tothe data belonging to the location and identification of the objects. Itgives identification charts of PNe discovered since 1965 (published inthe supplements to CGPN) and those charts of objects discovered earlier,which have wrong or uncertain identification. The question ``what is aplanetary nebula'' is discussed and the typical values of PNe and oftheir central stars are summarized. Short statistics about thediscoveries of PNe are given. The catalogue is also available in theCentre de Données, Strasbourg and at Hamburg Observatory viainternet. The Catalogue is only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/378/843
| Optical Coordinates of Southern Planetary Nebulae
A homogeneous set of new measurements of nearly all (995 out of 1007)objects from the Strasbourg-ESO Catalogue of Galactic Planetary Nebulaeor in the first supplement of this catalogue in the area covered by theDENIS survey (δ < +2 degrees) is given here. A list of 24 newand 27 wrong crossidentifications with sources in the IRAS PSC catalogueand some confusion in the literature is listed as well.
| 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.
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