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M 27 (Dumbbell Nebula)



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The shaping of planetary nebula Sh2-188 through interactionwith the interstellar medium
Sh2-188 is an example of strong interaction between a planetary nebula(PN) and the interstellar medium (ISM). It shows a single arc-likestructure, consisting of several filaments, which is postulated to bethe result of motion through the ISM. We present new Hα imagesfrom the Isaac Newton Telescope Photometric Hα Survey of theNorthern Galactic Plane which reveal structure behind the filamentarylimb. A faint, thin arc is seen opposite the bright limb, in combinationforming a closed ring. Behind the faint arc a long wide tail isdetected, doubling the size of the nebula. The nebula extends 15 arcminon the sky in total. We have developed a `triple-wind' hydrodynamicalmodel, comprising of the initial `slow' asymptotic giant branch (AGB)wind and the later `fast' stellar wind (the interacting stellar windsmodel), plus a third wind reflecting the motion through the ISM.Simulations at various velocities of the central star relative to theISM indicate that a high velocity of 125 kms-1 is required toreproduce the observed structure. We find that the bright limb and thetail already formed during the AGB phase, prior to the formation of thePN. The closure of the ring arises from the slow-fast wind interaction.Most of the mass lost on the AGB has been swept downstream, providing apotential explanation of the missing-mass problem in PNe. We report aproper motion for the central star of 30 +/- 10masyr -1 inthe direction of the bright limb. Assuming the central star is moving at125 +/- 25kms-1, the distance to the nebula is estimated tobe 850+500-420 pc, consistent with a spectroscopicdistance to the star. Expansion velocities measured from spectroscopicdata of the bright filaments are consistent with velocities measuredfrom the simulation. Sh2-188 is one of the largest PNe known, with anextent of 2.8 pc. The model shows that this size was already set duringthe AGB phase.

VAR Vul 05 - Entdeckung eines neuen kataklysmischen Veraenderlichen bei M 27.
Not Available

Aus der Sektion Kataklysmische Sterne: Aktivitaeten zwischen Aug. und Dez. 2005.
Not Available

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.

Observed Planetary Nebulae as Descendants of Interacting Binary Systems
We examine recent studies on the formation rate of planetary nebulae andfind this rate to be about one-third of the formation rate of whitedwarfs. This implies that only about one-third of all planetary nebulaethat evolve to form white dwarfs are actually bright enough to beobserved. This finding corresponds with the claim that it is necessaryfor a binary companion to interact with the asymptotic giant branchstellar progenitor for the descendant planetary nebulae to be brightenough to be detected. The finding about the formation rate alsostrengthens O. De Marco's conjecture that the majority of observedplanetary nebulae harbor binary systems. In other words, single starsalmost never form observed planetary nebulae.

Discovery of Lyα-pumped Molecular Hydrogen Emission in the Planetary Nebulae NGC 6853 and NGC 3132
We report the first observation of Lyα pumped molecular hydrogenemission lines in planetary nebulae. The H2 emission observedin the ultraviolet spectra of NGC 6853 and NGC 3132 can be explained byexcitation of vibrationally hot H2 by Lyα photons.Constraints are placed on the nebular Lyα emission profile, aswell as the molecular hydrogen temperature, column density, andturbulent motion. These parameters are similar for the two nebulae,pointing to similar physical conditions in these objects. Therovibrational cascade following Lyα pumping is predicted to havelow surface brightness signatures in the visible and near-infrared.

Hybrid characteristics: 3D radiative transfer for parallel adaptive mesh refinement hydrodynamics
We have developed a three-dimensional radiative transfer method designedspecifically for use with parallel adaptive mesh refinementhydrodynamics codes. This new algorithm, which we call hybridcharacteristics, introduces a novel form of ray tracing that can neitherbe classified as long, nor as short characteristics, but which appliesthe underlying principles, i.e. efficient execution throughinterpolation and parallelizability, of both.
Primary applicationsof the hybrid characteristics method are radiation hydrodynamicsproblems that take into account the effects of photoionization andheating due to point sources of radiation. The method is implemented inthe hydrodynamics package FLASH. The ionization, heating, and coolingprocesses are modelled using the DORIC ionization package. Uponcomparison with the long characteristics method, we find that our methodcalculates the column density with a similarly high accuracy andproduces sharp and well defined shadows. We show the quality of the newalgorithm in an application to the photoevaporation of multipleover-dense clumps.
We present several test problems demonstratingthe feasibility of our method for performing high resolutionthree-dimensional radiation hydrodynamics calculations that span a largerange of scales. Initial performance tests show that the ray tracingpart of our method takes less time to execute than other parts of thecalculation (e.g. hydrodynamics and adaptive mesh refinement), and thata high degree of efficiency is obtained in parallel execution. Althoughthe hybrid characteristics method is developed for problems involvingphotoionization due to point sources, and in its current implementationignores the effects of diffuse radiation and scattering, the algorithmcan be easily adapted to the case of more general radiation fields.

The Global Kinematics of the Dumbbell Planetary Nebula (NGC 6853, M27, PN G060.8-03.6)
Spatially resolved profiles of the He II 560 Å, H α - [N II]6548 and 6584 Å emission lines have been obtained in twoorthogonal long cuts over the Dumbbell planetary nebula. The central HeII 6560 Å volume of the bright dumbbell structure is shown to beparticularly inert with an expansion velocity of s-1. This is envelopedby an inner [O III] 5007 Å shell expanding at 13km s-1, an outer[O III] 5007 Å expanding at 31 km s-1 is on the inside of theouter [N II] 6584 Å shell expanding at 35 km s-1. A new H α[N II] 6548 and 6584 Å continuum-subtracted image of the15'diameter halo has also been compared with recent proper motionmeasurements of the central star and the present line profiles from thehalo's inner edge. Interaction with the ambient interstellar medium issuggested. The bright [N II] 6584 Å shell must be running intothis relatively inert halo with a differential velocity of ≥ 25 kms-1. The present results are compared with currents models for thecreation of 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.

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.

X-ray Observations of Hot Gas in Planetary Nebulae
The formation and shaping of planetary nebulae (PNe) is a complexprocess that involves the action of multiple agents, including faststellar winds and collimated outflows. Both fast stellar winds andcollimated outflows can produce shock-heated gas that emits diffuseX-rays. Hot gas in PN interiors was hinted by ROSAT observations,but unambiguous detections of diffuse X-ray emission were not made untilChandra and XMM-Newton became available. The unprecedentedangular resolution and sensitivity of these new X-ray observations allowus to investigate in detail the physical properties and origin of thehot gas content of PNe and to assess its dynamical effects on theshaping and expansion of PNe. This paper reviews the results from recentX-ray observations of PNe and discusses their implications to ourunderstanding of the formation and evolution of PNe.

Antoine Darquier et la decouverte de la nebuleuse de la Lyre.
Not Available

Caroline Herschel as observer
Not Available

Variable Star near M27
IAUC 8591 available at Central Bureau for Astronomical Telegrams.

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.

Evolution of Asymptotic Giant Branch Stars
The current status of modeling the evolution and nucleosynthesis ofasymptotic giant branch (AGB) stars is reviewed. The principles of AGBevolution have been investigated in recent years leading to improved andrefined models, for example with regard to hot-bottom burning or thethird dredge-up. The postprocessing s-process model yields quantitativeresults that reproduce many observations. However, these and most otherprocesses in AGB stars are intimately related to the physics of stellarmixing. Mixing in AGB stars is currently not well-enough understood foraccurate yield predictions. Several constraints and methods areavailable to improve the models. Some regimes of AGB evolution have notyet been studied in sufficient detail. These include the super-AGB starsand AGB stars at extremely low or ultra low metallicity.

A Map of the Universe
We have produced a new conformal map of the universe illustrating recentdiscoveries, ranging from Kuiper Belt objects in the solar system to thegalaxies and quasars from the Sloan Digital Sky Survey. This mapprojection, based on the logarithm map of the complex plane, preservesshapes locally and yet is able to display the entire range ofastronomical scales from the Earth's neighborhood to the cosmicmicrowave background. The conformal nature of the projection, preservingshapes locally, may be of particular use for analyzing large-scalestructure. Prominent in the map is a Sloan Great Wall of galaxies 1.37billion light-years long, 80% longer than the Great Wall discovered byGeller and Huchra and therefore the largest observed structure in theuniverse.

Electron temperature fluctuations in planetary nebulae
An observational study of the spatial variation of the electrontemperature and density in 10 galactic planetary nebulae is presented.The data consist of long-slit spectra of high signal-to-noise ratio inthe 3100 to 6900 Å range. Electron temperatures were determinedfrom the [O III](λ 4959 + λ 5007)/λ 4363 and [NII](λ 6548 + λ 6583)/λ 5755 ratios and from theBalmer discontinuity. Electron densities were estimated from the [SII]λ 6716/λ 6731, [Cl III]λ 5517/λ 5537, and[Ar IV]λ 4711/λ 4740 ratios. Electron temperaturevariations of low amplitude were found across the nebular surface in theplanetary nebulae studied. The temperature distribution across eachnebula presents a variance relative to the mean corresponding to 0.0003≤ t2s(Bal) ≤ 0.0078, 0.0003 ≤t2s(N II) ≤ 0.0097, and 0.0011 ≤t2s(O III) ≤ 0.0050. A systematic spatialvariation of electron density has been detected in most of objects(NGC 1535, NGC 2438, NGC2440, NGC 3132, NGC3242, NGC 6302, NGC6563, and NGC 7009). The remaining objects(NGC 6781 and NGC 6853) have notshown any significant electron density dependence on position.NGC 2438, NGC 6563, NGC6781, and NGC 6853 are in general the mostdiffuse and probably evolved objects studied here, with low meandensities in the range Ne(S II) ≈ 95-158~cm-3.An anti-correlation between temperature and density was found forNGC 2438 and NGC 3132, with theelectron temperature increasing with the decrease of electron densityand a correlation between temperature and density was found forNGC 2440, NGC 3242, NGC6302, and NGC 7009, with the electrontemperature increasing with the increase of electron density. Theserelationships seem to be associated with the structure of the nebula.The nebulae in which the correlation between temperature and density ispresent are ring shaped. The anti-correlation between temperature anddensity is found in bipolar planetary nebulae that are denser in thecentre of the nebula.

Fluorine in extremely hot post-AGB stars: Evidence for nucleosynthesis
We have discovered lines of highly ionized fluorine (ion{F}{v} andion{F}{vi}) in the far-UV spectra of extremely hot (T_eff = 85 000-150000 K) post-AGB stars. Our sample comprises H-rich central stars ofplanetary nebulae as well as H-deficient PG1159 stars. We performednon-LTE calculations and find strong F overabundances (up to10-4 by mass, i.e., 250 times solar) in a number of PG1159stars, while F is essentially solar in the H-rich stars. Since PG1159stars are believed to exhibit intershell matter of the preceding AGBphase on their surface, their chemical analyses allow for a directinsight into nucleosynthesis processes during the AGB phase. The high Fabundances in PG1159 stars confirm the conclusion from abundancedeterminations in giants, that F is synthesized in AGB stars and thatthe F enrichment in the intershell must be very high.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.

The distances of Type I planetary nebulae
The distances D of planetary nebulae (PNe) are still extremelyuncertain. Although a variety of methods have been used to evaluate thisparameter, these are often in conflict, and subject to large random andsystematic errors. It is therefore important to evaluate D using as manyindependent procedures as possible. We outline here one further way inwhich this parameter may be assessed. It is noted that where the nebularmass range is narrow, then one might expect observed PNe radii to beroughly similar. This, where it occurs, would also result in acorrelation between their angular diameters Θ, and distances D.We find that just such a trend occurs for Type I nebulae, and we employthis to determine distances to a further 44 such outflows. Our meanvalues of D appear similar to those of Zhang [ApJS 98 (1995) 659],implying a relatively long PNe distance scale.

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.

A Uniform Database of 2.2-16.5 μm Spectra from the ISOCAM CVF Spectrometer
We present all ISOCAM circular variable filter (CVF) spectra that covermore than one-third of the 2.2-16.5 μm spectral range of theinstrument. The 364 spectra have been classified according to theclassification system of Kraemer et al., as modified by Hodge et al. toaccount for the shorter wavelength range. Prior to classification, thespectra were processed and recalibrated to create a uniform database.Aperture photometry was performed at each wavelength centered on thebrightest position in each image field and the various spectral segmentsmerged into a single spectrum. The aperture was the same for all scalesizes of the images. Since this procedure differs fundamentally fromthat used in the initial ISOCAM calibration, a recalibration of thespectral response of the instrument was required for the aperturephotometry. The recalibrated spectra and the software used to createthem are available to the community on-line via the ISO Data Archive.Several new groups were added to the KSPW system to describe spectrawith no counterparts in either the SWS or PHT-S databases: CA, E/SA,UE/SA, and SSA. The zodiacal dust cloud provides the most commonbackground continuum to the spectral features, visible in almost 40% ofthe processed sources. The most characteristic and ubiquitous spectralfeatures observed in the CVF spectral atlas are those of theunidentified infrared bands (UIR), which are typically attributed toultraviolet-excited fluorescence of large molecules containing aromatichydrocarbons. The UIR features commonly occur superimposed on thezodiacal background (18%) but can also appear in conjunction with otherspectral features, such as fine-structure emission lines or silicateabsorption. In at least 13 of the galaxies observed, the pattern of UIRemission features has been noticeably shifted to longer wavelengths.Based on observations with the Infrared Space Observatory, a EuropeanSpace Agency (ESA) project with instruments funded by ESA Member States(especially the Principal Investigator countries: France, Germany, theNetherlands, and the United Kingdom) and with the participation of theInstitute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).

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.

PN G000.2+06.1 and PN G002.3+02.2: Two New Type I Planetary Nebulae in the Galactic Bulge
We confirm the planetary nebula nature of two sources: PN G000.2+06.1and PN G002.3+02.2, previously identified by Terzan in a photometricsurvey toward the Galactic center as objects possibly belonging to thisclass. Optical images taken in Hα reveal the extended morphologyof the nebulae, while spectroscopic observations allow us to determinetheir line intensities and physical parameters (electron density andtemperature), as well as their ionic and elemental abundances. Their lowsurface brightness and large apparent size, together with the lack ofinfrared emission, suggest their identification as well-evolvedplanetary nebulae belonging to the old stellar population of the bulge.However, both planetary nebulae show high N/O ratios and He abundances,similar to those observed in type I disk planetary nebulae, usuallyassociated with young, massive progenitor stars. The implications of ourfindings in the context of the study of chemical abundances in Galacticbulge planetary nebulae are discussed.

A reexamination of electron density diagnostics for ionized gaseous nebulae
We present a comparison of electron densities derived from opticalforbidden line diagnostic ratios for a sample of over a hundred nebulae.We consider four density indicators, the [O II]λ3729/λ3726, [S II] λ6716/λ6731, [Cl III]λ5517/λ5537 and [Ar IV] λ4711/λ4740 doubletratios. Except for a few H II regions for which data from the literaturewere used, diagnostic line ratios were derived from our own high qualityspectra. For the [O II] λ3729/λ3726 doublet ratio, we findthat our default atomic data set, consisting of transition probabilitiesfrom Zeippen (\cite{zeippen1982}) and collision strengths from Pradhan(\cite{pradhan}), fit the observations well, although at high electrondensities, the [O II] doublet ratio yields densities systematicallylower than those given by the [S II] λ6716/λ6731 doubletratio, suggesting that the ratio of transition probabilities of the [OII] doublet, A(λ3729)/A(λ3726), given by Zeippen(\cite{zeippen1982}) may need to be revised upwards by approximately 6per cent. Our analysis also shows that the more recent calculations of[O II] transition probabilities by Zeippen (\cite{zeippen1987a}) andcollision strengths by McLaughlin & Bell (\cite{mclaughlin}) areinconsistent with the observations at the high and low density limits,respectively, and can therefore be ruled out. We confirm the earlierresult of Copetti & Writzl (\cite{copetti2002}) that the [O II]transition probabilities calculated by Wiese et al. (\cite{wiese}) yieldelectron densities systematically lower than those deduced from the [SII] λ6716/λ6731 doublet ratio and that the discrepancy ismost likely caused by errors in the transition probabilities calculatedby Wiese et al. (\cite{wiese}). Using our default atomic data set for [OII], we find that Ne([O II])  Ne([S II]) ≈Ne([Cl III])< Ne([Ar IV]).

Knots in Planetary Nebulae
We have studied the closest bright planetary nebulae with the HubbleSpace Telescope's WFPC2 in order to characterize the dense knots alreadyknown to exist in NGC 7293. We find knots in all of the objects, arguingthat knots are common, simply not always observed because of distance.The knots appear to form early in the life cycle of the nebula, probablybeing formed by an instability mechanism operating at the nebula'sionization front. As the front passes through the knots they are exposedto the photoionizing radiation field of the central star, causing themto be modified in their appearance. This would then explain as evolutionthe difference of appearance like the lacy filaments seen only inextinction in IC 4406 on the one extreme and the highly symmetric``cometary" knots seen in NGC 7293. The intermediate form knots seen inNGC 2392, NGC 6720, and NGC 6853 would then represent intermediatephases of this evolution.

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.

The relation between elemental abundances and morphology in planetary nebulae
An investigation of the variation of elemental abundances with planetarynebula morphology is of considerable interest, since it has a bearingupon how such sources are formed, and from which progenitors they areejected. Recent advances in morphological classification now enable usto assess such trends for a statistically significant number of sources.We find, as a result, that the distribution N[log(X/H)] of sources withrespect to elemental abundance (X/H) varies between the differingmorphologies. Circular sources tend to peak towards low abundancevalues, whilst bipolar nebulae (BPNe) peak towards somewhat highervalues. This applies for most elemental species, although it is perhapsleast apparent for oxygen. In contrast, elliptical sources appear todisplay much broader functions N[log(X/H)], which trespass upon thedomains of both circular and elliptical planetary nebulae (PNe).We take these trends to imply that circular sources derive fromlower-mass progenitors, bipolar sources from higher-mass stars, and thatelliptical nebulae derive from all masses of progenitor, high and low.Whilst such trends are also evident in values of mean abundance, they are much less clear. Only in the cases of He/H, N/H,Ne/H and perhaps Ar/H is there evidence for significant abundancedifferences.Certain BPNe appear to possess low abundance ratios He/H and Ar/H, andthis confirms that a few such outflows may arise from lower-massprogenitors. Similarly, we note that ratios are quite modestin elliptical planetary nebulae, and not much different from those forcircular and bipolar PNe; a result that conflicts with the expectationsof at least one model of shell formation.

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.

X-ray and UV Views of Hot Gas in Planetary Nebulae (invited review)
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Observation and Astrometry data

Right ascension:19h59m36.00s
Apparent magnitude:7.6

Catalogs and designations:
Proper NamesDumbbell Nebula
MessierM 27
NGC 2000.0NGC 6853

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