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Mapping the Instability Domains of GW Vir Stars in the Effective Temperature-Surface Gravity Diagram
We present the results of a detailed stability study of models of GW Virpulsators. These are extremely hot, evolved, and compact stars that areon their way to the white dwarf cooling phase and that showmultiperiodic luminosity variations due to gravity-mode pulsationalinstabilities. Our nonadiabatic survey confirms that cyclic ionizationof carbon and oxygen is at the origin of the GW Vir phenomenon. We findthat the extent of the instability domain in the logg-Teffplane is a strong function of the C and O content in the envelopes ofthese stars. Given that GW Vir stars show important variations inatmospheric composition from one object to another, this implies thatthe notion of a blue edge for the GW Vir instability domain isnecessarily a ``fuzzy'' concept. We investigate the effects of varyingthe total mass, of adding hydrogen, and of changing the metallicity. Wesummarize our results in the form of extensive stability maps in thelogg-Teff diagram and produce tables and graphs showing theexpected ranges of excited periods under various conditions.
| White dwarf masses derived from planetary nebula modelling
Aims.We compare the mass distribution of central stars of planetarynebulae (CSPNe) with those of their progeny, white dwarfs (WD). Methods: We use a dynamical method to measure masses with an uncertaintyof 0.02 M_ȯ. Results: The CSPN mass distribution is sharplypeaked at 0.61~M_ȯ. The WD distribution peaks at lower masses(0.58~M_ȯ) and shows a much broader range of masses. Some of thedifference can be explained if the early post-AGB evolution is fasterthan predicted by the Blöcker tracks. Between 30 and 50 per cent ofWD may avoid the PN phase because they have too low a mass. However, thediscrepancy cannot be fully resolved and WD mass distributions may havebeen broadened by observational or model uncertainties.Data is only available in electronic form at http://www.aanda.org
| Chemical compositions and plasma parameters of planetary nebulae with Wolf-Rayet and wels type central stars
Aims.Chemical compositions and other properties of planetary nebulaearound central stars of spectral types [WC], [WO], and wels are comparedwith those of “normal” central stars, in order to clarifythe evolutionary status of each type and their interrelation. Methods:We use plasma diagnostics to derive from optical spectra the plasmaparameters and chemical compositions of 48 planetary nebulae. We alsoreanalyze the published spectra of a sample of 167 non-WR PN. Theresults as well as the observational data are compared in detail withthose from other studies of the objects in common. Results: We confirmthat [WC], [WO] and wels nebulae are very similar to those“normal” PN: the relation between [N II] and [O III]electron temperatures, abundances of He, N, O, Ne, S and Ar, and thenumber of ionizing photons show no significant differences. However,some differences are observed in their infrared (IRAS) properties. welsnebulae appear bluer than [WR] PN. The central star's spectral type isclearly correlated with electron density, temperature and excitationclass of the nebula, [WC] nebulae tend to be smaller than the othertypes. All this corroborates the view of an evolutionary sequence fromcool [WC 11] central stars inside dense, low excitation nebulae towardshot [WO 1] stars with low density, high excitation nebulae. The wels PN,however, appear to be a separate class of objects, not linked to WRPN byevolution: nebular excitation, electron temperature and density, and thenumber of ionizing photons all cover the whole range found in the othertypes. Their lower mean N/O ratio and slightlylower He/H suggestprogenitor stars less massive than for the other PN types. Furthermore,the differences between results of different works are dominated by thedifferences in observational data rather than differences in theanalysis methods.Based on observations obtained at the European Southern Observatory(ESO), La Silla, Chile. Table 3 and Appendices are only available inelectronic form at http://www.aanda.org Table with fluxes andintensities is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/463/265
| A search for photometric variability of hydrogen-deficient planetary-nebula nuclei
Aims.We searched for photometric variability in a sample of hot,hydrogen-deficient planetary nebula nuclei (PNNi) with "PG 1159" or "OVI" spectral type, most of them embedded in a bipolar or ellipticalplanetary nebula envelope (PNe). These characteristics may indicate thepresence of a hidden close companion and an evolution affected byepisodes of interaction between them. Methods: .We obtainedtime-series photometry from a sample of 11 candidates using the NordicOptical Telescope (NOT) with the Andalucía Faint ObjectSpectrograph and Camera (ALFOSC), modified with our own control softwareto be able to observe in a high-speed multi-windowing mode. The datawere reduced on-line with the real time photometry (RTP) code, whichallowed us to detect periodic variable stars with small amplitudes fromCCD data in real time. We studied the properties of the observedmodulation frequencies to investigate their nature. Results: .Wereport the first detection of low-amplitude pulsations in the PNNiVV 47, NGC 6852, and Jn1. In addition, we investigated the photometric variability ofNGC 246. Time-series analysis shows that the powerspectra of VV 47, NGC 6852, andNGC 246 are variable on time scales of hours. Powerspectra from consecutive nights of VV 47 andNGC 6852 show significant peaks in differentfrequency regions. The same type of variability is present in NGC 246 in2 observing runs separated by 3 days. Changes are also found in thepower spectra of VV 47 and NGC 246during the same night. The VV 47 power spectra arepeculiar since they present modulation frequencies in a wide range from175 to 7600 μHz. This is different from the previously knownpulsating PNNi where no frequencies are found above ~3000 μHz. Thehigh-frequency modulation observed in VV 47 may bedue to g-modes triggered by the ɛ-mechanism, observed for thefirst time.
| The Dynamical Evolution of Planetary Nebulae after the Fast Wind
We explore the dynamics of ionization-bounded planetary nebulae afterthe termination of the fast stellar wind. When the stellar wind becomesnegligible, the hot, shocked bubble depressurizes, and the thermalpressure of the photoionized region, at the inner edge of the swept-upshell, becomes dominant. At this stage the shell tends to fragment,creating clumps with comet-like tails and long, photoionized trails inbetween, while the photoionized material expands back toward the centralstars as a rarefaction wave. Once the photoionized gas fills the innercavity, it develops a kinematical pattern of increasing velocity fromthe center outward, with a typical range of velocities starting from thesystemic velocity to ~50 km s-1 at the edges. The HelixNebula is a clear example of a planetary nebula at this lateevolutionary stage.
| The Chemical Composition of Galactic Planetary Nebulae with Regard to Inhomogeneity in the Gas Density in Their Envelopes
The results of a study of the chemical compositions of Galacticplanetary nebulae taking into account two types of inhomogeneity in thenebular gas density in their envelopes are reported. New analyticalexpressions for the ionization correction factors have been derived andare used to determine the chemical compositions of the nebular gas inGalactic planetary nebulae. The abundances of He, N, O, Ne, S, and Arhave been found for 193 objects. The Y Z diagrams for various Heabundances are analyzed for type II planetary nebulae separately andjointly with HII regions. The primordial helium abundance Y p andenrichment ratio dY/dZ are determined, and the resulting values arecompared with the data of other authors. Radial abundance gradients inthe Galactic disk are studied using type II planetary nebulae.
| Some implications of the introduction of scattered starlight in the spectrum of reddened stars
This paper presents new investigations on coherent scattering in theforward direction (orders of magnitude; conservation of energy;dependence of scattered light on geometry and wavelength), and on howscattered light contamination in the spectrum of reddened stars ispossibly related to as yet unexplained observations (the diminution ofthe 2200 Å bump when the obscuring material is close to the star,the difference between Hipparcos and photometric distances). This paperthen goes on to discuss the fit of the extinction curve, a possible roleof extinction by the gas in the far-UV, and the reasons of theinadequacy of the Fitzpatrick and Massa [ApJSS, 72 (1990) 163] fit.
| Detection of non-radial g-mode pulsations in the newly discovered PG 1159 star HE 1429-1209
We performed time-series photometry of the PG 1159-type star HE1429-1209, which was recently discovered in the ESO SPYsurvey. We show that the star is a low-amplitude (≈0.05 mag)non-radial g-mode pulsator with a period of 919 s. HE1429-1209 is among the hottest known post-AGB stars(Teff = 160 000 K) and, together with the known pulsatorRX J2117.1+3412, it defines empirically the blue edgeof the GW Vir instability strip in the HRD at high luminosities.
| Chemical abundances of Planetary Nebulae in M 33
Using spectroscopic data presented in Magrini et al. (\cite{m03}), wehave analyzed with the photoionization code CLOUDY 94.00 (Ferland et al.\cite{ferland}) 11 Planetary Nebulae belonging to the spiral galaxy M33. Central star temperatures and nebular parameters have beendetermined. In particular the chemical abundances of He/H, O/H, N/H,Ar/H, and S/H have been measured and compared with values obtained viathe Ionization Correction Factors (ICF) method, when available. Chemicalabundance relationships have been investigated; in particular, acorrelation between N/H and N/O similar to the Galactic one (Henry\cite{henry}), and a feeble anti-correlation between O/H and N/O havebeen found. A gradient in O/H across the disc of M 33 is consistent withthe one found from H Ii regions in this galaxy (Vílchez et al.\cite{vilchez88}). Further studies in the outer parts of M 33 arehowever needed to ascertain this point. The present result shows thatoxygen and helium abundances (with lower accuracy also nitrogen, argonand sulphur) can be actually estimated from the brightest PNe of agalaxy, even if the electron temperature cannot be measured. We alsofound that the oxygen abundance is quite independent of the absolutemagnitude of the PN and consequently the brightest PNe arerepresentative of the whole PN population. This represents an importanttool for measuring the metallicity of galaxies at the time of theformation of PNe progenitors.Based on observations obtained at the 4.2 m WHT telescope operated onthe island of La Palma by the Isaac Newton Group in the SpanishObservatorio del Roque de Los Muchachos of the Instituto de Astrofisicade Canarias.
| Planetary nebula distances re-examined: an improved statistical scale
The distances of planetary nebulae (PNe) are still quite uncertain.Although observational estimates are available for a small proportion ofPNe, based on statistical parallax and the like, such distances are verypoorly determined for the majority of galactic PNe. In particular,estimates of so-called `statistical' distance appear to differ byfactors of ~2.7.We point out that there is a well-defined correlation between the 5-GHzluminosity of the sources, L5, and their brightnesstemperatures, TB. This represents a different trend to thoseinvestigated in previous statistical analyses, and permits us todetermine independent distances to a further 449 outflows. Thesedistances are shown to be closely comparable to those determined using aTB-R correlation, providing that the latter trend is taken tobe non-linear.This non-linearity in the TB-R plane has not been noted inprevious analyses, and is likely responsible for the broad (andconflicting) ranges of distance that have previously been published.Finally, we point out that there is a close accord between observedtrends within the L5-TB and TB-Rplanes, and the variation predicted through nebular evolutionarymodelling. This is used to suggest that observational biases areprobably modest, and that our revised distance scale is reasonablytrustworthy.
| A reanalysis of chemical abundances in galactic PNe and comparison with theoretical predictions
New determinations of chemical abundances for He, N, O, Ne, Ar and Sare derived for all galactic planetary nebulae (PNe) so far observedwith a relatively high accuracy, in an effort to overcome differences inthese quantities obtained over the years by different authors usingdifferent procedures. These include: ways to correct for interstellarextinction, the atomic data used to interpret the observed line fluxes,the model nebula adopted to represent real objects and the ionizationcorrections for unseen ions. A unique `good quality' classical-typeprocedure, i.e. making use of collisionally excited forbidden lines toderive ionic abundances of heavy ions, has been applied to allindividual sets of observed line fluxes in each specific position withineach PN. Only observational data obtained with linear detectors, andsatisfying some `quality' criteria, have been considered. Suchobservations go from the mid-1970s up to the end of 2001. Theobservational errors associated with individual line fluxes have beenpropagated through the whole procedure to obtain an estimate of theaccuracy of final abundances independent of an author's `prejudices'.Comparison of the final abundances with those obtained in relevantmulti-object studies on the one hand allowed us to assess the accuracyof the new abundances, and on the other hand proved the usefulness ofthe present work, the basic purpose of which was to take full advantageof the vast amount of observations done so far of galactic PNe, handlingthem in a proper homogeneous way. The number of resulting PNe that havedata of an adequate quality to pass the present selection amounts to131. We believe that the new derived abundances constitute a highlyhomogeneous chemical data set on galactic PNe, with realisticuncertainties, and form a good observational basis for comparison withthe growing number of predictions from stellar evolution theory. Owingto the known discrepancies between the ionic abundances of heavyelements derived from the strong collisonally excited forbidden linesand those derived from the weak, temperature-insensitive recombinationlines, it is recognized that only abundance ratios between heavyelements can be considered as satisfactorily accurate. A comparison withtheoretical predictions allowed us to assess the state of the art inthis topic in any case, providing some findings and suggestions forfurther theoretical and observational work to advance our understandingof the evolution of low- and intermediate-mass stars.
| 12C/13C Ratio in Planetary Nebulae from the IUE Archives
We investigated the abundance ratio of 12C/13C inplanetary nebulae by examining emission lines arising from C III2s2p3Po2,1,0-->2s21S0.Spectra were retrieved from the International Ultraviolet Explorerarchives, and multiple spectra of the same object were co-added toachieve improved signal-to-noise ratio. The 13C hyperfinestructure line at 1909.6 Å was detected in NGC 2440. The12C/13C ratio was found to be ~4.4+/-1.2. In allother objects, we provide an upper limit for the flux of the 1910Å line. For 23 of these sources, a lower limit for the12C/13C ratio was established. The impact on ourcurrent understanding of stellar evolution is discussed. The resultinghigh-signal-to-noise ratio C III spectrum helps constrain the atomicphysics of the line formation process. Some objects have the measured1907/1909 Å flux ratio outside the low-electron densitytheoretical limit for 12C. A mixture of 13C with12C helps to close the gap somewhat. Nevertheless, someobserved 1907/1909 Å flux ratios still appear too high to conformto the currently predicted limits. It is shown that this limit, as wellas the 1910/1909 Å flux ratio, are predominantly influenced byusing the standard partitioning among the collision strengths for themultiplet1S0-3PoJaccording to the statistical weights. A detailed calculation for thefine-structure collision strengths between these individual levels wouldbe valuable.
| 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.
| Stellar paleontology using planetary nebulae
Photoionization and winds interactions cause a complete redistributionof the circumstellar density in the brightest, innermost regions ofplanetary nebulae, cancelling all the information about the mass losshistory of the AGB progenitors. On the contrary, the faint extendedhaloes that are observed around planetary nebulae can still be used totrace back the AGB mass loss history. In particular, the edges of thesehaloes are the imprint of the last AGB thermal pulse, and can be used toderive timescales and mass loss rates for the latest AGB evolution. Idescribe below the recent advances on this topic.
| 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
| Quantitative classification of WR nuclei of planetary nebulae
We analyse 42 emission-line nuclei of Planetary Nebulae (PNe), in theframework of a large spectrophotometric survey of [WC] nuclei of PNeconducted since 1994, using low/medium resolution spectra obtained atESO and at OHP. We construct a grid of selected line-intensities(normalized to C Iv-5806 Å= 100) ordered by decreasing ionisationpotential going from 871 to 24 eV. In this grid, the stars appear tobelong clearly to prominent O (hot [WO1-4] types) or C (cooler [WC4-11]types) line-sequences, in agreement with the classification of massiveWR stars applied to Central Stars of Planetary Nebulae (CSPNe) byCrowther et al. \cite{crowther98} (CMB98). We propose 20 selected lineratios and the FWHM of C Iv and C Iii lines as classificationdiagnostics, which agree well with the 7 line ratios and the FWHMproposed by CMB98. This classification based on ionisation is related tothe evolution of the temperature and of the stellar wind, reflecting themass-loss history. In particular, inside the hot [WO4]-class, wediscover four stars showing very broad lines over the whole spectralrange. These stars possibly mark the transition from the initialmomentum-driven phase to the later energy-driven phase of the CSPNealong their evolution from the post-Asymptotic Giant Branch (post-AGB)phase through [WC] late, [WC4] and [WO]-types. The HR diagram and thediagram linking the terminal velocity and the temperature indicatehighly dispersed values of the stellar mass for our sample, around amean mass higher than for normal CSPNe. The distribution of the 42 starsalong the ionisation sequence shows 24% of [WO1-3], 21% of [WO4], 17% of[WC4] hot stars, and 26% of [WC9-11] cool stars. The [WC5-8] classesremain poorly represented (12%). This distribution is confirmed on thebasis of a large compilation of the 127 known emission-lines CSPNe,which represent about 5% of the known PNe.Based on observations obtained at the European Southern Observatory(ESO), La Silla (Chile), and at the Observatoire de Haute-Provence (OHP,France).Table \ref{liste} is only available in electronic form athttp://www.edpsciences.org
| Ionized haloes in planetary nebulae: new discoveries, literature compilation and basic statistical properties
We present a comprehensive observational study of haloes aroundplanetary nebulae (PNe). Deep Hα+[NII] and/or [OIII] narrow-bandimages have been obtained for 35 PNe, and faint extended haloes havebeen newly discovered in the following 10 objects: Cn 1-5, IC 2165, IC2553, NGC 2792, NGC 2867, NGC 3918, NGC 5979, NGC 6578, PB 4, andpossibly IC 1747. New deep images have also been obtained of other knownor suspected haloes, including the huge extended emission around NGC3242 and Sh 2-200. In addition, the literature was searched, andtogether with the new observations an improved data base containing some50 PN haloes has been compiled.The halo sample is illustrated in an image atlas contained in thispaper, and the original images are made available for use by thescientific community at http://www.ing.iac.es/~rcorradi/HALOES/.The haloes have been classified following the predictions of modernradiation-hydrodynamical simulations that describe the formation andevolution of ionized multiple shells and haloes around PNe. According tothe models, the observed haloes have been divided into the followinggroups: (i) circular or slightly elliptical asymptotic giant branch(AGB) haloes, which contain the signature of the last thermal pulse onthe AGB; (ii) highly asymmetrical AGB haloes; (iii) candidaterecombination haloes, i.e. limb-brightened extended shells that areexpected to be produced by recombination during the late post-AGBevolution, when the luminosity of the central star drops rapidly by asignificant factor; (iv) uncertain cases which deserve further study fora reliable classification; (v) non-detections, i.e. PNe in which no halois found to a level of <~10-3 the peak surface brightnessof the inner nebulae.We discuss the properties of the haloes: detection rate, morphology,location of the central stars in the Hertzsprung-Russell diagram, sizes,surface brightness profiles, and kinematical ages. Among the mostnotable results, we find that, as predicted by models, ionized AGBhaloes are a quite common phenomenon in PNe, having been found in 60 percent of elliptical PNe for which adequately deep images exist. Another10 per cent show possible recombination haloes. In addition, using thekinematical ages of the haloes and inner nebulae, we conclude that mostof the PNe with observed AGB haloes have left the AGB far from a thermalpulse, at a phase when hydrogen burning is the dominant energy source.We find no significant differences between the AGB haloes ofhydrogen-poor and hydrogen-rich central stars.
| Kinematics, turbulence and evolution of planetary nebulae
This paper discusses the location of a sample of planetary nebulae onthe HR diagram. We determine the internal velocity fields of 14planetary nebulae from high-resolution echelle spectroscopy, with thehelp of photoionization models. The mass averaged velocity is shown tobe a robust, simple parameter describing the outflow. The expansionvelocity and radius are used to define the dynamical age; together withthe stellar temperature, this gives a measurement of the luminosity andcore mass of the central star. The same technique is applied to otherplanetary nebulae with previously measured expansion velocities, givinga total sample of 73 objects. The objects cluster closely around theSchönberner track of 0.61 Msun, with a very narrowdistribution of core masses. The masses are higher than found for localwhite dwarfs. The luminosities determined in this way tend to be higherby a factor of a few than those derived from the nebular luminosities.The discrepancy is highest for the hottest (most evolved) stars. Wesuggest photon leakage as the likely cause. The innermost regions of thenon-[WC] nebulae tend to show strong acceleration. Together with theacceleration at the ionization front, the velocity field becomes``U''-shaped. The presence of strong turbulent motions in [WC] nebulaeis confirmed. Except for this, we find that the [WC] stars evolve on thesame tracks as non-[WC] stars.Based on observations taken at the ESO.Appendix A is only available in electronic form athttp://www.edpsciences.org
| Abundances of [WC] Central Stars of PN and the Double Dust Chemistry Problem (invited review)
Not Available
| WR Central Stars (invited review)
Not Available
| The Dynamical Evolution of the Circumstellar Gas around Low- and Intermediate-Mass Stars. II. The Planetary Nebula Formation
We have studied the effect of the mass of the central star (CS) on thegas evolution during the planetary nebula (PN) phase. We have performednumerical simulations of PN formation using CS tracks for six stellarcore masses corresponding to initial masses from 1 to 5Msolar. The gas structure resulting from the previousasymptotic giant branch (AGB) evolution is used as the startingconfiguration. The formation of multiple shells is discussed in thelight of our models, and the density, velocity, and Hα emissionbrightness profiles are shown for each stellar mass considered. We havecomputed the evolution of the different shells in terms of radius,expansion velocity, and Hα peak emissivity. We find that theevolution of the main shell is controlled by the ionization front ratherthan by the thermal pressure provided by the hot bubble during the earlyPN stages. This effect explains why the kinematical ages overestimatethe age in young CSs. At later stages in the evolution and for low-massprogenitors the kinematical ages severely underestimate the CS age.Large (up to 2.3 pc), low surface brightness shells (less than 2000times the brightness of the main shell) are formed in all of our models(with the exception of the 5 Msolar model). These PN haloscontain most of the ionized mass in PNe, which we find is greatlyunderestimated by the observations because of the low surface brightnessof the halos.
| Gas temperature and excitation classes in planetary nebulae
Empirical methods to estimate the elemental abundances in planetarynebulae usually use the temperatures derived from the [O III] and [N II]emission-line ratios, respectively, for the high- and low-ionizationzones. However, for a large number of objects these values may not beavailable. In order to overcome this difficulty and allow a betterdetermination of abundances, we discuss the relationship between thesetwo temperatures. Although a correlation is not easily seen when asample of different PNe types is used, the situation is improved whenthey are gathered into excitation classes. From [OII]/[OIII] andHeII/HeI line ratios, we define four excitation classes. Then, usingstandard photoionization models which fit most of the data, a linearrelation between the two temperatures is obtained for each of the fourexcitation classes. The method is applied to several objects for whichonly one temperature can be obtained from the observed emission linesand is tested by recalculation of the radial abundance gradient of theGalaxy using a larger number of PNe. We verified that our previousgradient results, obtained with a smaller sample of planetary nebulae,are not changed, indicating that the temperature relation obtained fromthe photoionization models are a good approximation, and thecorresponding statistical error decreases as expected. Tables 3-5, 7 and9 are only available in electronic form at http://www.edpsciences.org
| Sulfur, Chlorine, and Argon Abundances in Planetary Nebulae. IIB. Abundances in a Southern Sample
We have undertaken a large spectroscopic survey of over 80 planetarynebulae with the goal of providing a homogeneous spectroscopic databasebetween 3600 and 9600 Å, as well as a set of consistentlydetermined abundances, especially for oxygen, sulfur, chlorine, andargon. In the current paper we calculate and report the S/O, Cl/O, andAr/O abundance ratios for 45 southern planetary nebulae (predominantlytype II), using our own recently observed line strengths published in acompanion paper. One of the salient features of our work is the use ofthe near-IR lines of [S III] λλ9069, 9532 coupled with the[S III] temperature, to determine the S+2 ionic abundance. Wefind the following average abundances for these objects:S/O=0.011+/-0.0064, Cl/O=0.00031+/-0.00012, and Ar/O=0.0051+/-0.0020.
| Sulfur, Chlorine, and Argon in Planetary Nebulae. IIA. Observations of a Southern Sample
In this paper we present fully reduced and dereddened emission linestrengths for a sample of 45 southern type II planetary nebulae(PNs).The spectrophotometry for these PNs covers an extendedoptical/near-IR range from 3600 to 9600 Å. This PN study andsubsequent analysis (presented in a companion paper), together with asimilar treatment for a northern PN sample, is aimed at addressing thelack of homogeneous, consistently observed, reduced, and analyzed datasets that include the near-IR [S III] lines at 9069 and 9532 Å.The use of type II objects only is intended to select disk nebulae thatare uncontaminated by nucleosynthetic products of the progenitor star.Extending spectra redward to include the strong [S III] lines enables usto look for consistency between S+2 abundances inferred fromthese lines and from the more accessible, albeit weaker, [S III] line atλ6312.
| Study of electron density in planetary nebulae. A comparison of different density indicators
We present a comparison of electron density estimates for planetarynebulae based on different emission-line ratios. We have considered thedensity indicators [O Ii]lambda 3729/lambda 3726, [S Ii]lambda6716/lambda 6731, [Cl Iii]lambda 5517/lambda 5537, [Ar Iv]lambda4711/lambda 4740, C Iii]lambda 1906/lambda 1909 and [N I]lambda5202/lambda 5199. The observational data were extracted from theliterature. We have found systematic deviations from the densityhomogeneous models, in the sense that: Ne(ion {N}i) <~Ne(ion {O}{ii}) < Ne(ion {S}{ii}, ion {C}{iii},ion {Cl}{iii} or ion {Ar}{iv}) and Ne(ion {S}{ii}) ~Ne(ion {C}{iii}) ~ Ne(ion {Cl}{iii}) ~Ne(ion {Ar}{iv}). We argue that the lower [O Ii] densityestimates are likely due to errors in the atomic parameters used.
| Infrared properties of planetary nebulae with [WR] central stars
We have gathered from the literature near and mid infrared (photometricand spectroscopic) data for Galactic planetary nebulae, with specialattention to planetary nebulae surrounding Wolf-Rayet type central stars([WR] PN). These data have been analyzed to obtain insight into thedust-properties of [WR] PN and their evolutionary status. We have foundthat a sizeable fraction of [WR] PN seems to contain hot dust (1000-2000K), probably located in the winds of the central stars. The mean dusttemperature is shown to decrease with decreasing [WC] spectral type.This is in line with suggestions that the [WC] sequence is anevolutionary sequence from late to early types. [WR] PN in differentdiagrams, when compared to those of non-[WR] PN, suggest that [WR] PNform a homogeneous class of planetary nebulae. There is an unusuallylarge proportion of [WR] PN showing PAH features in their spectra.
| Helium contamination from the progenitor stars of planetary nebulae: The He/H radial gradient and the ΔY / ΔZ enrichment ratio
In this work, two aspects of the chemical evolution of 4He inthe Galaxy are considered on the basis of a sample of disk planetarynebulae (PN). First, an application of corrections owing to thecontamination of 4He from the evolution of the progenitorstars shows that the He/H abundance by number of atoms is reduced by0.012 to 0.015 in average, leading to an essentially flat He/H radialdistribution. Second, a determination of the helium to heavy elementenrichment ratio using the same corrections leads to values in the range2.8 < ΔY / ΔZ < 3.6 for Y p = 0.23 and 2.0< ΔY / ΔZ < 2.8 for Y p = 0.24, in goodagreement with recent independent determinations and theoretical models.
| 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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