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Trigonometric Parallaxes of Central Stars of Planetary Nebulae
Trigonometric parallaxes of 16 nearby planetary nebulae are presented,including reduced errors for seven objects with previous initial resultsand results for six new objects. The median error in the parallax is0.42 mas, and 12 nebulae have parallax errors of less than 20%. Theparallax for PHL 932 is found here to be smaller than was measured byHipparcos, and this peculiar object is discussed. Comparisons are madewith other distance estimates. The distances determined from theseparallaxes tend to be intermediate between some short distance estimatesand other long estimates; they are somewhat smaller than those estimatedfrom spectra of the central stars. Proper motions and tangentialvelocities are presented. No astrometric perturbations from unresolvedclose companions are detected.
| 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).
| Discovery of magnetic fields in central stars of planetary nebulae
For the first time we have directly detected magnetic fields in centralstars of planetary nebulae by means of spectro-polarimetry with FORS1 atthe VLT. In all four objects of our sample we found kilogauss magneticfields, in NGC 1360 and LSS 1362 with very highsignificance, while in EGB 5 and Abell 36 the existence ofa magnetic field is probable but with less certainty. This discoverysupports the hypothesis that the non-spherical symmetry of mostplanetary nebulae is caused by magnetic fields in AGB stars. Our highdiscovery rate demands mechanisms to prevent full conservation ofmagnetic flux during the transition to white dwarfs.Based on observations collected at the European Southern Observatory,Paranal, Chile, under programme ID 072.D-0089.
| The distances of highly evolved planetary nebulae
The central stars of highly evolved planetary nebulae (PNe) are expectedto have closely similar absolute visual magnitudes MV. Thisenables us to determine approximate distances to these sources where oneknows their central star visual magnitudes, and levels of extinction. Wefind that such an analysis implies values of D which are similar tothose determined by Phillips; Cahn, Kaler & Stanghellin; Acker, andDaub. However, our distances are very much smaller than those of Zhang;Bensby & Lundstrom, and van de Steene & Zijlstra. The reasonsfor these differences are discussed, and can be traced to errors in theassumed relation between brightness temperature and radius.Finally, we determine that the binary companions of such stars can be nobrighter than MV~ 6mag, implying a spectral type of K0 orlater in the case of main-sequence stars.
| 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.
| 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.
| The Use of Line Excitation Mapping to Investigate Planetary Nebula Morphologies
It is now well established that circular, elliptical, and bipolarplanetary nebulae (PNe) possess differing physical and spatialcharacteristics. Not only are their structures quite distinct, but theyalso appear to possess differing Zanstra temperatures, abundances,expansion velocities, brightness temperatures, and scale heights abovethe Galactic plane. We report here a further sensitive way in which thedifferences between these outflows may be illustrated. We shall notethat the nebulae posses varying ranges of emission line ratio, and thatthis is likely to arise as a consequence of their differing progenitormasses. Similarly, we point out the potential of line-ratio mapping foranalyzing other morphological classes, as well as for establishing theuniqueness of their populations, and their relative progenitor masses.Thus we find that sources containing jets often possess low lineemission intensities relative to hydrogen, suggesting that theirprogenitors may have low overall masses. This conclusion is supported bya variety of independent observational evidence. We also show thatirregular sources appear to represent a distinct class of outflows. Itis likely that their mean progenitor masses are greater than those ofelliptical PNe, but less than thoseof the bipolar outflows.
| On the discovery of an enormous ionized haloaround the hot DO white dwarf PG 1034+001
The discovery of the largest known planetary nebula on the skysurrounding the DO white dwarf PG 1034+001 with anapparent diameter of about 2 °, corresponding to a linear diameterof 3.5-7.0 pc at the likely distance of 100-200 pc, has been reported byHewett et al. (\cite{Hewett03}). A careful inspection of available skysurvey data has now shown that this planetary nebula, Hewett1, is surrounded by an elliptical emission shell with anapparent diameter of 6 ° × 9°(16.2+6.1-4.5 ×24.3+9.1-6.8 pc at d =155+58-43 pc). A further emission structure,detected northeast of the central star, may indicate another shell witha size of 10 ° × 16 °. From presently availableobservational data we do not have indications revealing whether theemission arises from material ejected from PG1034+001 or from ionized ambient ISM.Improved proper motion data combined with radial velocity and distancedata from the literature have enabled us to derive a Galactic orbit forthe central star PG 1034+001. Its thin disk orbit andthe morphology of the first halo suggest that the nebula is in anadvanced stage of interaction with the interstellar medium.
| 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}
| X-ray and UV Views of Hot Gas in Planetary Nebulae (invited review)
Not Available
| Temperature Scale and Iron Abundances of Very Hot Central Stars of Planetary Nebulae (invited review)
The determination of effective temperatures of very hot central stars(Teff>70000K) by model atmosphere analyses of optical H and He lineprofiles is afflicted with considerable uncertainty, primarily due tothe lack of neutral helium lines. Ionization balances of metals,accessible only with UV lines, allow more precise temperature estimates.The potential of iron lines is pointed out. At the same time iron andother metal abundances, hardly investigated until today, may be derivedfrom UV spectra. We describe recent HST spectroscopy performed for thispurpose. A search for iron lines in FUV spectra of the hottestH-deficient central stars (PG1159-type, Teff>100000K) taken with FUSEwas unsuccessful. The derived deficiency is interpreted in terms of irondepletion due to n-capture nucleosynthesis in intershell matter, whichis now exposed at the stellar surface as a consequence of a late Heshell flash.
| The 5° Diameter Ionized Halo of the Planetary Nebula Abell 36
We have observed an ionized halo surrounding the planetary nebula Abell36. It is barrel-shaped, with dimensions 4°×5°, which is17 pc×21 pc at a distance of 240 pc. With an average Hαsurface brightness of 0.8+/-0.2 rayleighs, the halo's total Hαflux, 8.3×10-10 ergs cm-2 s-1,exceeds that of the previously known inner part of the nebula by afactor of 30. The ionized mass of the halo is 48sqrt(ɛ)Msolar, where ɛ is the filling factor of the ionizedgas. Velocity-resolved Hα spectra indicate that the halo isambient interstellar matter and not matter ejected from the planetarynebula. The edges of the halo are evident in both 100 μm emission andred optical continuum.
| ROSAT Observations of X-Ray Emission from Planetary Nebulae
We have searched the entire ROSAT archive for useful observations tostudy X-ray emission from Galactic planetary nebulae (PNs). The searchyields a sample of 63 PNs, which we call the ROSAT PN sample. About20%-25% of this sample show X-ray emission; these include 13 definitedetections and three possible detections (at a 2 σ level). AllX-ray sources in these PNs are concentrated near the central stars. OnlyA30, BD +30°3639, and NGC 6543 are marginally resolved by the ROSATinstruments. Three types of X-ray spectra are seen in PNs. Type 1consists of only soft X-ray emission (<0.5 keV), peaks at 0.1-0.2keV, and can be fitted by blackbody models at temperatures1-2×105 K. Type 2 consists of harder X-ray emission,peaks above 0.5 keV, and can be fitted by thin plasma emission models attemperatures of a few times 106 K. Type 3 is a composite of abright type 1 component and a fainter type 2 component. Unresolved softsources with type 1 spectra or the soft component of type 3 spectra aremost likely photospheric emission from the hot central stars. Absorptioncross sections are large for these soft-energy photons; therefore, onlylarge, tenuous, evolved PNs with hot central stars and small absorptioncolumn densities have been detected. The origin of hard X-ray emissionfrom PNs is uncertain. PNs with type 2 spectra are small, dense, youngnebulae with relatively cool (<<105 K) central stars,while PNs with type 3 X-ray spectra are large, tenuous, evolved nebulaewith hot central stars. The hard X-ray luminosities are also differentbetween these two types of PNs, indicating perhaps different origins oftheir hard X-ray emission. Future Chandra and XMM observations with highspatial and spectral resolution will help to understand the origin ofhard X-ray emission from PNs.
| The Rise and Fall of V4334 Sagittarii (Sakurai's Object)
CCD UBVRi photometry of the final helium flash object V4334 Sgr(Sakurai's object) carried out during 1997-1999 is presented, and thelight curve from its prediscovery rise to the dust obscuration phase isconstructed. The optical light curve can be divided into four sections,the rise to maximum, the maximum, the dust onset, and the massive dustshell phase. The color indices show a general increase with time, firstbecause of the photospheric expansion and cooling and later because ofthe dust-forming events. The energy distributions for the years1996-1999 show that an increasing part of the energy is radiated atinfrared wavelengths. In 1996 the infrared excess is likely caused byfree-free radiation in the stellar wind. Starting from 1997 or 1998 atthe latest, carbon dust grains are responsible for the more and moredramatic decrease of optical radiation and the growing infrared excess.Its photometric behavior in 1998-1999 mimics the ``red declines'' of RCrB variables; the amplitude, however, is more extreme than any fadingever observed in an R CrB star. Evidence is given that a complete dustshell has formed around V4334 Sgr. It therefore shows similarities withdust-forming classical novae, although it is evolving ~20 times moreslowly. Its luminosity increased by a factor 4 between 1996 and 1998. Acomparison of timescales of the final helium flash objects FG Sge, V605Aql, and V4334 Sgr shows that the observed photometric and spectroscopicfeatures are similar, while V4334 Sgr is the most rapidly evolvingobject to date.
| Monochromatic morphologies of Abell planetary nebulae
Monochromatic (Delta lambda <= 10 Ä) images have been obtainedfor seven large (2-10 arcmin) Abell planetary nebulae. From this deepsurvey, we found 4 to have normal bipolar shapes, whereas 3 have trulyspherical shells. The structures of these nebulae are discussed usingthe absolutely calibrated intensity maps in Hα , [N ii], and [Oiii]. An attempt to derive ionized mass using our (dereddened) measuredabsolute flux as a function of distance to the PN is also given. Theobservations were carried out at the Observatoire de Haute Provence120-cm telescope - CNRS, St Michel l'Observatoire, France.
| The iron abundance in hot central stars of planetary nebulae derived from IUE spectra
We present the first attempt to determine the iron abundance in hotcentral stars of planetary nebulae. We perform an analysis with fullymetal-line blanketed NLTE model atmospheres for a sample of ten stars(T_eff >~ 70 000 K) for which high-resolution UV spectra areavailable from the IUE archive. In all cases lines of Fe Vi or Fe Viican be identified. As a general trend, the iron abundance appears to besubsolar by 0.5-1 dex, however, the S/N of the IUE spectra is notsufficient to exclude a solar abundance in any specific case. Improvedspectroscopy by either FUSE or HST is necessary to verify thepossibility of a general iron deficiency in central stars. The suspecteddeficiency may be the result of gravitational settling in the case ofthree high-gravity objects. For the other stars with low gravity andhigh luminosity dust fractionation during the previous AGB phase is aconceivable origin. Based on observations with the InternationalUltraviolet Explorer (IUE) satellite.
| Possible trends in expansion velocities of planetary nebulae evolved from common envelope binary systems
Not Available
| Electron densities in planetary nebulae, and the unusual characteristics of the [S BT II] emission zone} ] densities in planetary nebulae
We investigate the radial variation of electron densities in planetarynebulae, using values of ne deriving from the [S ii]<~mbda6717/<~mbda6730 line ratio. As a result, we are able to showthat there is a sharp discontinuity in densities of order 1.4 dex closeto nebular radii R=0.1 pc. It is proposed, as a consequence, that mostnebulae contain two primary [S ii] emission zones, with densitiesdiffering by a factor ~ 10(2) . The intensity of emission from thedenser component increases by an order of magnitude where nebulae passfrom radiation to density-bound expansion regimes, resulting in acorresponding discontinuous jump in [S ii]/Hβ line ratios. Theorigins of these changes are not entirely clear, although one mechanismis investigated whereby the superwind outflows shock interact withexterior AGB envelopes. Finally, the derived trends in ne(R)are used to determine distances for a further 262 nebulae. The resultingdistance scale appears to be comparable to that of Daub (1982) and Cahnet al. (1992).
| The kinematics of 867 galactic planetary nebulae
We present a compilation of radial velocities of 867 galactic planetarynebulae. Almost 900 new measurements are included. Previously publishedkinematical data are compared with the new high-resolution data toassess their accuracies. One of the largest samples in the literatureshows evidence for a systematic velocity offset. We calculate weightedaverages between all available data. Of the final values in thecatalogue, 90% have accuracies better than 20 km s(-1) . We use thiscompilation to derive kinematical parameters of the galacticdifferential rotation obtained from least-square fitting and toestablish the Disk rotation curve; we find no significal trend for thepresence of an increasing external rotation curve. We examine also therotation of the bulge; the derived curve is consistent with a linearlyincreasing rotation velocity with l: we find V_b,r=(9.9+/-1.3)l -(6.7+/-8.5) km s(-1) . A possible steeper gradient in the innermostregion is indicated. Table 2 is available in electronic form only, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| A sample of planetary nebulae observed by HIPPARCOS
By using HIPPARCOS data (magnitudes, parallaxes, proper motions), (1) wedetermine new values of the apparent luminosity of the central stars of19 planetary nebulae, (2) we discuss their distance and position on theT/L diagram. By comparison with the distances determined by individualor statistical methods, we see that most of these ``ground" distanceslook overestimated when we trust the HIPPARCOS trigonometric parallaxes.It seems that for compact nebulae, the nebula itself could influence theparallax measurement. In particular, the very small HIPPARCOS distancesto SwSt 1 and Hu 2-1 are unexpected and are not trustworthy. Peculiarmotions are analyzed, in terms of astrophysical parameters of the binarysystem A 35, and in relation with asymmetric morphology.
| Planetary Nebulae in the NRAO VLA Sky Survey
The 1.4 GHz NRAO VLA Sky Survey (NVSS) images and source catalog wereused to detect radio emission from the 885 planetary nebulae north ofJ2000 declination delta = -40 deg in the Strasbourg-ESO Catalogue ofGalactic Planetary Nebulae. We identified 680 radio sources brighterthan about S = 2.5 mJy beam-1 (equivalent to T ~ 0.8 K in the 45" FWHMNVSS beam) with planetary nebulae by coincidence with accurate opticalpositions measured from Digitized Sky Survey (DSS) images. Totalextinction coefficients c at lambda = 4861 Angstroms were calculated forthe 429 planetary nebulae with available H beta fluxes and low free-freeoptical depths at 1.4 GHz. The variation of c with Galactic latitude andlongitude is consistent with the extinction being primarily interstellarand not intrinsic.
| A comparison of HIPPARCOS parallaxes with planetary nebulae spectroscopic distances
The Hipparcos satellite has measured the parallax of a small sample ofplanetary nebulae. In this paper we consider the results for 3 planetarynebulae (PN) for which spectroscopic distances have also been determinedfrom stellar gravities. These gravities in turn have been derived fromprofile fitting of selected hydrogen and helium lines (Mendez et al.,1988 a, b, 1992). A comparison of these distances shows that theHipparcos distances are all considerably smaller. This same effect hasbeen found in two other PN central stars, whose distance has beendetermined from the VLA measured nebular expansion. The question of themass of the central star of PHL 932 is also discussed.
| On the mass distribution of planetary nebulae central stars.
We apply a method, described in Gorny et al. (1997A&A...318..256G),to derive the masses of 125 central stars of planetary nebulae (PN).This method is self-consistent and distance-independent. It requires theknowledge of the nebular Hβ fluxes, angular radii and expansionvelocities, as well as the stellar visual magnitudes. This method isbased on a simple model for the evolution of planetary nebulae, in whichthe central stars evolve according to the theoretical models of Bloecker(1995A&A...299..755B) and Schoenberner (1983ApJ...272..708S). Theresults are dependent on the assumed total nebular mass. Nevertheless,for any reasonable total nebular mass distribution, we find that therange in planetary nebulae central star masses is very restricted: morethan 80% of the objects have a central star mass between 0.55 and0.65Msun_. We show how to convert, in this mass range, theobserved PN central star mass distribution into a zero-age post-AGB starmass distribution.
| Properties That Cannot Be Explained by the Progenitors of Planetary Nebulae
I classify a large number of planetary nebulae (458) according to theprocess that caused their progenitors to blow axisymmetrical winds. Theclassification is based primarily on the morphologies of the differentplanetary nebulae, assuming that binary companions, stellar orsubstellar, are necessary in order to have axisymmetrical mass loss onthe asymptotic giant branch. I propose four evolutionary classes,according to the binary-model hypothesis: (1) Progenitors of planetarynebula that did not interact with any companion. These amount to ~10% ofall planetary nebulae. (2) Progenitors that interact with stellarcompanions that avoided a common envelope, 11^{+2}_{-3}% of all nebulae.(3) Progenitors that interact with stellar companions via a commonenvelope phase, 23^{+11}_{-5}% of all nebulae. (4) Progenitors thatinteract with substellar (i.e., planets and brown dwarfs) companions viaa common envelope phase, 56^{+5}_{-8}% of all nebulae. In order todefine and build the different classes, I start with clarifying somerelevant terms and processes related to binary evolution. I then discusskinematical and morphological properties of planetary nebulae thatappear to require the interaction of the planetary nebula progenitorsand/or their winds with companions, stellar or substellar.
| The Edinburgh-Cape Blue Object Survey - II. Zone 1 - the North Galactic CAP
Results for Zone 1 of the Edinburgh-Cape (EC) Blue Object Survey arepresented. This zone covers that part of the North Galactic Cap morethan ~30 deg from the Galactic plane and south of about -12^ deg_.3declination (although a few fields north of this declination areincluded). The zone effectively complements the Palomar-Green Survey inthe North Galactic Cap, although the EC Survey should be more completeto a fainter limit (B=16.5 mag) and to somewhat redder stars (U-B bluerthan about -0.4). Zone 1 covers approximately 1560 deg^2 and contains675 blue objects for which we list equatorial coordinates accurate to ~1arcsec, UBV photoelectric photometry, and spectral types determined frommoderate-dispersion (100 A mm^-1) spectrograms.
| X-ray emission from Planetary Nebulae
Not Available
| An Atlas of Ancient Planetary Nebulae and Their Interaction with the Interstellar Medium
Abstract image available at:http://adsabs.harvard.edu/abs/1996ApJS..107..255T
| ROSAT X-Ray Observations of Four Planetary Nebulae
Abstract image available at:http://adsabs.harvard.edu/abs/1996ApJ...466..352L
| Local space density and formation rate of planetary nebulae.
Individual distances of 50 nearby planetary nebulae are determined usinga variety of methods, but excluding statistical methods or distancescales. These distances, together with a discussion of the samplecompleteness, are used to determine local PN formation rate. Togetherwith the brightness of the nebula, its ionized mass is derived. Theevolution of the ionized mass is discussed. As a by-product, the Zanstratemperature of the central stars of the optically thick nebulae isfound. Interestingly this temperature indicates that the DA white dwarfsin the sample are considerably hotter than previously thought. Finally,with the help of the galactic bulge PN, a luminosity function for PN inthe galaxy is derived.
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