Contents
Images
Upload your image
DSS Images Other Images
Related articles
Density gradients in Galactic planetary nebulae
Certain hydrodynamic models of planetary nebulae (PNe) suggest thattheir shells possess appreciable radial density gradients. However, theobservational evidence for such gradients is far from clear. On the onehand, Taylor et al. claim to find evidence for radio spectral indices0.6 < α < 1.8, a trend which is taken to imply a variationne ~ r-2 in most of their sample of PNe. On theother hand, Siódmiak & Tylenda find no evidence for any suchvariations in density; shell inhomogeneities, where they occur, areprimarily attributable to `blobs or condensations'.It will be suggested that both of these analyses are unreliable, andshould be treated with a considerable degree of caution. A new analysiswithin the log(F(5GHz)/F(1.4GHz))-log(TB(5GHz)) plane will beused to show that at least 10-20 per cent of PNe are associated withstrong density gradients. We shall also show that the ratioF(5GHz)/F(1.4GHz) varies with nebular radius; an evolution that can beinterpreted in terms of varying shell masses, and declining electrondensities.
| 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
| Galactic Planetary Nebulae with Wolf-Rayet Nuclei III. Kinematical Analysis of a Large Sample of Nebulae
Expansion velocities (V_{exp}) of different ions and line widths at thebase of the lines are measured and analyzed for 24 PNe with [WC]-typenuclei (WRPNe), 9 PNe ionized by WELS (WLPNe) and 14 ordinary PNe. Acomparative study of the kinematical behavior of the sample clearlydemonstrates that WRPNe have on average 40-45% larger V_{exp}, andpossibly more turbulence than WLPNe and ordinary PNe. WLPNe havevelocity fields very much like the ones of ordinary PNe, rather than theones of WRPNe. All the samples (WRPNe, WLPNe and ordinary PNe) showexpansion velocities increasing with age indicators, for example is larger for low-density nebulae and also it is largerfor nebulae around high-temperature stars. This age effect is muchstronger for evolved WRPNe, suggesting that the [WC] winds have beenaccelerating the nebulae for a long time, while for non-WRPNe theacceleration seems to stop at some point when the star reaches atemperature of about 90,000 - 100,000. Non-WR nebulae reach a maximumV_{exp} ≤ 30 km s(-1) evolved WRPNe reach maximum V_{exp} about 40km s(-1) . For all kinds of objects (WRPNe and non-WRPNe) it is foundthat on average V_{exp}(N(+) ) is slightly larger than V_{exp}(O(++) ),indicating that the nebulae present acceleration of the external shells.
| The distances of less-evolved planetary nebulae: a further test of statistical distance scales
It has recently been pointed out that a number of the methods used todetermine planetary nebulae (PNe) distances may be appreciably in error.Whilst the scales of Zhang (1995), Bensby & Lundstrom (2001) andothers are appropriate for higher radio brightness temperaturesTB, those of Phillips and Daub are more relevant whereTB is small.We note, in the following, that the absolute bolometric magnitudes ofless-evolved PNe are likely to be similar. The mean value of can therefore be used to constrain PNe distancesD, and confirm the distance scales for higher TB outflows. Wehave used this procedure to evaluate distances to a further 47 PNe, andwe find that the mean values of are consistent with those ofCahn, Kaler & Stanghellini (1992), Zhang (1995), Phillips et al.(2004) and van de Steene & Zijlstra (1995). They are, as expected,inconsistent with the lower TB scale of Phillips (2002a).
| 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.
| The evolution of planetary nebulae. II. Circumstellar environment and expansion properties
We investigate and discuss the expansion properties of planetary nebulaeby means of 1D radiation-hydrodynamics models computed for differentinitial envelope configurations and central star evolutionary tracks. Inparticular, we study how the expansion depends on the initial densitygradient of the circumstellar envelope and show that it is possible toderive information on the very last mass-loss episodes during the star'sfinal evolution along and off the asymptotic giant branch. To facilitatethe comparison of the models with real objects, we have also computedobservable quantities like surface brightness and emission-lineprofiles. With the help of newly acquired high-resolution emission-lineprofiles for a sample of planetary nebulae we show that models withinitial envelopes based on the assumption of a stationary wind outflowfail to explain the observed expansion speeds of virtually all of theobserved planetary nebulae. Instead it must be assumed that during thevery last phase of evolution along the final asymptotic giant branchevolution the mass-loss rate increases in strength, resulting in a muchsteeper slope of the circumstellar radial density distribution. Underthese conditions, the expansion properties of the nebular gas differconsiderably from the self-similar solutions found for isothermalconditions. Furthermore, the mass loss must remain at a rather highlevel until the stellar remnant begins to evolve quickly towards thecentral star regime. Current theoretical computations of dust-drivenmass-loss which are restricted to rather low temperatures cannot beapplied during the star's departure from the asymptotic giant branch.Based on observations obtained at the 3.5 μm NTT and the 1.2 μmCAT telescope of the European Southern Observatory, La Silla, and at the2.6 μm NOT telescope operated on the island of La Palma by NOTSA, inthe Spanish Observatorio del Roque de Los Muchachos of the InstitutodeAstrofísica de Canarias.Dedicated to Prof. V. Weidemann on the occasion of his 80th birthday,October 3, 2004.
| 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.
| The populations of planetary nebulae in the direction of the Galactic bulge. Chemical abundances and Wolf-Rayet central stars
We have observed 44 planetary nebulae (PNe) in the direction of theGalactic bulge, and merged our data with published ones. We havedistinguished, in the merged sample of 164 PNe, those PNe most likely toprtain physically to the Galactic bulge and those most likely to belongto the Galactic disk. We have determined the chemical composition of allthe 164 objects in a coherent way. We looked for stellar emissionfeatures and discovered 14 new [WR] stars and 15 new weak emission linecentral stars. The analyzed data led us to the following conclusions:(1) the spectral type distribution of [WR] stars is very different inthe bulge and in the disk of the Galaxy. However, the observeddistributions are strongly dependent on selection effects. (2) Theproportion of [WR] PNe is significantly larger in the bulge than in thedisk. (3) The oxygen abundances in [WR] stars do no appear to besignificantly affected by nucleosynthesis and mixing in the progenitors.(4) The O/H gradient of the Galactic disk PNe population flattens in themost internal parts of the Galaxy. (5) The median oxygen abundance inthe bulge PN population is larger by 0.2 dex than in the disk populationseen in the direction of the bulge. (6) Bulge PNe with smaller O/H tendto have smaller radial velocities. (7) The oxygen abundance distributionof bulge PNe is similar in shape to that of the metallicity distributionof bulge giants, but significantly narrower. (8) The location ofSB 32 (PN G 349.7-09.1) in the(Vlsr, lII) diagram and its low oxygen abundanceargues that it probably belongs to the halo population.Based on observations made at the South African AstronomicalObservatory.Tables 1-3 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http: / /cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/427/231
| 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.
| Characteristics of Planetary Nebulae with [WC] Central Stars
We have analyzed the plasma diagnostics (electron densities andtemperatures and abundance ratios), and the kinematics of a large sampleof planetary nebulae around [WC] stars by means of high resolutionspectra. The results have been compared with characteristics ofplanetary nebulae around WELS and non-WR central stars. We find that theproportion of nitrogen rich nebulae is larger in WRPNe than innon-WRPNe. None of the 9 nebulae around WELS in our sample showsN-enrichment. WRPNe have larger expansion velocities and/or largerturbulence than non-WRPNe demonstrating that the mechanical energy ofthe massive [WC] stellar wind largely affects the kinematical behaviorof nebulae. A weak relation between stellar temperature and expansionvelocities has been found for all kind of nebulae, indicating that oldernebulae expand faster. The effect is more important for WRPNe. Thiscould be useful in testing the evolutionary sequence [WC]-late ->[WC]-early, proposed for [WC] stars.
| 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}
| Weak Emission-Line Central Stars of Planetary Nebulae
We present new spectroscopic data of 14 candidates for the weakemission-line type of central stars of planetary nebulae ([WELS]). Witha medium resolution of about 2 Å, we confirmed the main spectralcharacteristics of these stars but found that two objects of our sampleare in fact early-type [WC] ([WCE]) stars. The λ4650 and C IVλλ 5801, 5812 features are resolved, and they were used ina tentative classification. Based on the C IV lines the [WELS] stars ofour sample can be divided qualitatively into two main groups: clearemission and very weak or no emission. We compared mean equivalentwidths of carbon and oxygen lines of the [WELS] stars with those of the[WCE] and [WCL] types. The results are not conclusive but point in favorof an increase in temperature from [WCL] to [WCE], followed perhaps by adecrease from [WCE] to [WELS].Based on observations made with the 1.52 m telescope at the EuropeanSouthern Observatory (La Silla, Chile) under agreement with theObservatório Nacional, Brazil.
| 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.
| Abundances of [WC] Central Stars of PN and the Double Dust Chemistry Problem (invited review)
Not Available
| Introductory Review (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
| A Catalogue of IJK Photometry of PNe with DENIS
Near-infrared photometry of planetary nebulae (PNe) allows theclassification of those objects (Whitelock 1985; Peña &Torres-Peimbert 1987). We present the largest homogeneous sample.
| 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.
| 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.
| Gravity distances of planetary nebulae II. Aplication to a sample of galactic objects.
Not Available
| Distances of Galactic Planetary Nebulae Based on a Relationship Between the Central Star Mass and the N/O Abundance
In this paper, we propose a method to determine distances of Galacticplanetary nebulae on the basis of a relationship between the centralstar mass and the nebular N/O abundance ratio. This relationship is usedin combination with some basic parameters of the central stars, such asthe lambda 5480 flux, surface gravity and visual magnitude in order toobtain distances to a sample of a hundred Galactic planetary nebulae.
| The dust content of planetary nebulae: a reappraisal
We have performed a statistical analysis using broad band IRAS data onabout 500 planetary nebulae with the aim of characterizing their dustcontent. Our approach is different from previous studies in that it usesan extensive grid of photoionization models to test the methods forderiving the dust temperature, the dust-to-gas mass ratio and theaverage grain size. In addition, we use only distance independentdiagrams. With our models, we show the effect of contamination by atomiclines in the broad band IRAS fluxes during planetary nebula evolution.We find that planetary nebulae with very different dust-to-gas massratios exist, so that the dust content is a primordial parameter for theinterpretation of far infrared data of planetary nebulae. In contrastwith previous studies, we find no evidence for a decrease in thedust-to-gas mass ratio as the planetary nebulae evolve. We also showthat the decrease in grain size advocated by Natta & Panagia(\cite{NattaPanagia}) and Lenzuni et al. (\cite{Lenzuni}) is an artefactof their method of analysis. Our results suggest that the timescale fordestruction of dust grains in planetary nebulae is larger than theirlifetime. Table~1 is only accessible in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Spectroscopic investigation of old planetaries. IV. Model atmosphere analysis
The results of a NLTE model atmosphere analysis of 27 hydrogen-richcentral stars of old planetary nebulae (PN) are reported. These starswere selected from a previous paper in this series, where we gaveclassifications for a total of 38 central stars. Most of the analyzedcentral stars fill a previously reported gap in the hydrogen-richevolutionary sequence. Our observations imply the existence of twoseparated spectral evolutionary sequences for hydrogen-rich and -poorcentral stars/white dwarfs. This is in line with theoreticalevolutionary calculations, which predict that most post-AGB stars reachthe white dwarf domain with a thick hydrogen envelope of ~ 10(-4) M_sun.We determine stellar masses from the comparison with evolutionary tracksand derive a mass distribution for the hydrogen-rich central stars ofold PNe. The peak mass and the general shape of the distribution is inagreement with recent determinations of the white dwarf massdistribution. The properties of most analyzed stars are well explainedby standard post-AGB evolution. However, for eight stars of the sampleother scenarios have to be invoked. The properties of three of them areprobably best explained by born again post-AGB evolution. Two of theseare hybrid CSPN (hydrogen-rich PG 1159 stars), but surprisingly thethird star doesn't show any signs of chemical enrichment in itsatmosphere. The parameters of five stars are not in accordance withpost-AGB evolution. We discuss alternative scenarios such as thestripping of the hydrogen-rich envelope by a companion during the firstred giant phase or the formation of a common envelope with a possiblemerging of both components. Two stars (HDW 4 andHaWe 5) remain mysterious after all. They resembleordinary hot DA white dwarfs, but due to very large evolutionary agesthe presence of a PN cannot be explained. We speculate that the nebulaemay be shells produced by ancient nova outbursts. A wide spread ofhelium abundances is observed in the photospheres of central stars ofold PNe. It is shown that a good correlation between helium abundancesand luminosity is present. It is inferred that when the stars'luminosities fall below L~ 300 L_sun depletion starts and the heliumabundance steadily decreases with decreasing luminosity. The existenceof this correlation is in qualitative agreement with recent theoreticalcalculations of gravitational settling in the presence of a stellarwind.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
Catalogs and designations:
|
