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# NGC 4361

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 Working with VIMOS-IFU data: Searching and characterizing the faint haloes of planetary nebulaeIn this contribution, we present the VIMOS-IFU data analysis of twoplanetary nebulae: NGC 3242 and NGC 4361. Due to the technical nature ofthe workshop, we emphasize some specific problems of data reduction andanalysis: accuracy in flux calibration, importance of scattered lightand improvement of the S/N ratio. We estimate that accuracy of our fluxcalibration is ˜15% in the spectral range 4200 6100 Å. At˜10″ from the center of a point source, the intensity is≲0.02% of the peak value, indicating that scattered light isnegligible. Some examples of science that we are doing are shown. Inparticular, we have established an apparent temperature gradient acrossthe halo of NGC NGC3242. The structure of planetary nebulae: theory vs. practiceContext.This paper is the first in a short series dedicated to thelong-standing astronomical problem of de-projecting the bi-dimensional,apparent morphology of a three-dimensional mass of gas. Aims.Wefocus on the density distribution in real planetary nebulae (and alltypes of expanding nebulae). Methods. We introduce some basictheoretical notions, discuss the observational methodology, and developan accurate procedure for determining the matter radial profile withinthe sharp portion of nebula in the plane of the sky identified by thezero-velocity-pixel-column (zvpc) of high-resolution spectral images.Results. The general and specific applications of the method (andsome caveats) are discussed. Moreover, we present a series of evolutivesnapshots, combining illustrative examples of both model and trueplanetary nebulae. Conclusions. The zvpc radial-densityreconstruction - added to tomography and 3D recovery developed at theAstronomical Observatory of Padua (Italy) - constitutes a very usefultool for looking more closely at the spatio-kinematics, physicalconditions, ionic structure, and evolution of expanding nebulae. Galactic Planetary Nebulae with Wolf-Rayet Nuclei III. Kinematical Analysis of a Large Sample of NebulaeExpansion 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. Electron temperature fluctuations in planetary nebulaeAn 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 Abundances in Planetary NebulaeWe have determined fluorine abundances from the [F II] λ4789 and[F IV] λ4060 nebular emission lines for a sample of planetarynebulae (PNe). Our results show that fluorine is generally overabundantin PNe, thus providing new evidence for the synthesis of fluorine inasymptotic giant branch (AGB) stars. [F/O] is found to be positivelycorrelated with the C/O abundance ratio, in agreement with thepredictions of theoretical models of fluorine production in thermallypulsing AGB stars. A large enhancement of fluorine is observed in theWolf-Rayet PN NGC 40, suggesting that high mass-loss rates probablyfavor the survival of fluorine. Integral Field Spectroscopy of Faint Halos of Planetary NebulaeWe present the first integral field spectroscopy observations of the twoplanetary nebulae NGC 3242 and NGC 4361 with the VIMOS instrumentattached to VLT-UT3. By co-adding a large number of spaxels, we reach anemission-line detection limit of 5×10-18 ergscm-2 s-1 arcsec-2. In the case of NGC3242, we succeed in determining some properties of the halo. The radialsurface brightness profile in [O III] implies increasing mass lossbefore the formation of the planetary nebula. Traces of the mysteriousrings'' are clearly visible. We find for the first time an apparenttemperature gradient across a halo: from about 16,000 K close to theshell/halo transition to 20,000 K at the halo's outer edge. No lineemission is seen in the suspected halo region of NGC 4361 down to thesensitivity limit. Imaging Fabry-Perot spectrometric studies of velocity fields in gaseous nebulaeIn order to study the spatio-kinematics of extended gaseous nebulae suchas the HII regions associated with giant molecular clouds and planetarynebulae, we had designed and built an Imaging Fabry-Perot Spectrometerfor the 1.2m Mt Abu Telescope. We describe here some of the significantscientific results that came out of these studies in the past one decadeat Mt Abu. Far Ultraviolet Spectroscopic Explorer Measurements of Interstellar FluorineThe source of fluorine is not well understood, although core-collapsesupernovae, Wolf-Rayet stars, and asymptotic giant branch stars havebeen suggested. A search for evidence of the ν-process during Type IIsupernovae is presented. Absorption from interstellar F I is seen inspectra of HD 208440 and HD 209339A acquired with the Far UltravioletSpectroscopic Explorer. In order to extract the column density for F Ifrom the line at 954 Å, absorption from H2 has to bemodeled and then removed. Our analysis indicates that for H2column densities less than about 3×1020cm-2, the amount of F I can be determined from λ954.For these two sight lines, there is no clear indication for enhanced Fabundances resulting from the ν-process in a region shaped by pastsupernovae.Based on observations made with the NASA/CNES/CSA Far UltravioletSpectroscopic Explorer (FUSE), which is operated for NASA by the JohnsHopkins University under NASA contract NAS 5-32985. Unresolved Hα Enhancements at High Galactic Latitude in the WHAM Sky Survey MapsWe have identified 85 regions of enhanced Hα emission at|b|>10deg subtending approximately 1° or less on theWisconsin Hα Mapper (WHAM) sky survey. These high-latitude WHAMpoint sources'' have Hα fluxes of 10-11-10-9ergs cm-2 s-1, radial velocities within about 70km s-1 of the LSR, and line widths that range from less than20 to about 80 km s-1 (FWHM). Twenty-nine of theseenhancements are not identified with either cataloged nebulae or hotstars and appear to have kinematic properties that differ from thoseobserved for planetary nebulae. Another 14 enhancements are near hotevolved low-mass stars that had no previously reported detections ofassociated nebulosity. The remainder of the enhancements are catalogedplanetary nebulae and small, high-latitude H II regions surroundingmassive O and early B stars. Some implications of the introduction of scattered starlight in the spectrum of reddened starsThis 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 NebulaeThe 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. Chemical abundances of planetary nebulae from optical recombination lines - II. Abundances derived from collisionally excited lines and optical recombination linesIn Paper I, we presented spectrophotometric measurements of emissionlines from the ultraviolet (UV) to the far-infrared for 12 Galacticplanetary nebulae (PNe) and derived nebular thermal and densitystructures using a variety of plasma diagnostics. The measurements andplasma diagnostic results are used in the current paper to determineelemental abundances in these nebulae. Abundance analyses are carriedout using both strong collisionally excited lines (CELs) and weakoptical recombination lines (ORLs) from heavy element ions.Assuming electron temperatures and densities derived from HIrecombination spectra (line and continuum), we are able to determine theORL C abundance relative to hydrogen for all the PNe in our sample, Nand O abundances for 11 of them and Ne abundances for nine of them. Inall cases, ORL abundances are found to be systematically higher than thecorresponding values deduced from CELs. In NGC 40, the discrepancybetween the abundances derived from the two types of emission linereaches a factor of 17 for oxygen. For the other 10 PNe, thediscrepancies for oxygen vary from 1.6 to 3.1. In general, collisionallyexcited infrared fine-structure lines, which have excitation energiesless than 103 K and consequently emissivities that areinsensitive to electron temperature and temperature fluctuations, yieldionic abundances comparable to those derived from optical/UV CELs. For agiven nebula, the discrepancies between the ORL and CEL abundances areof similar magnitude for different elements. In other words, relativeabundance ratios such as C/O, N/O and Ne/O deduced from the traditionalmethod based on strong CELs are comparable to those yielded by ORLs, fora wide range of ORL to CEL oxygen abundance ratios, varying from nearunity to over a factor of 20.We have also determined ORL abundances relative to hydrogen for thethird-row element magnesium for 11 nebulae in our sample. In strongcontrast to the cases for second-row elements, Mg abundances derivedfrom the MgII 3d-4f λ4481 ORL are nearly constant for all the PNeanalysed so far and agree within the uncertainties with the solarphotospheric value.In accordance with results from previous studies, the ORL to CELabundance ratio is correlated with the difference between the electrontemperatures derived from the [OIII] forbidden-line ratio, on the onehand, and from the hydrogen recombination Balmer discontinuity, on theother. We find that the discrepancy between the ORL and CEL abundancesis correlated with nebular absolute diameter, surface brightness, theelectron density derived from [SII] CELs, and excitation class. Theresults confirm that the dichotomy of temperatures and heavy elementalabundances determined from the two types of emission line, which hasbeen widely observed in PNe, is a strong function of nebular evolution,as first pointed out by Garnett and Dinerstein.Our analyses show that temperature fluctuations and/or densityinhomogeneities are incapable of explaining the large discrepanciesbetween the heavy elemental abundances and electron temperaturesdetermined from the two types of emission line. Our analyses support thebi-abundance model of Liu et al., who have proposed that PNe containanother previously unseen component of ionized gas which, highlyenriched in heavy elements, has an electron temperature of<~103 K and emits strongly in recombination lines but notin CELs. Our determinations of low average emission temperatures fromthe observed line intensity ratios of HeI and OII ORLs lend furthersupport to this scenario. A deep survey of heavy element lines in planetary nebulae - II. Recombination-line abundances and evidence for cold plasmaIn our Paper I, we presented deep optical observations of the spectra of12 Galactic planetary nebulae (PNe) and three Magellanic Cloud PNe,carrying out an abundance analysis using the collisionally excitedforbidden lines. Here, we analyse the relative intensities of faintoptical recombination lines (ORLs) from ions of carbon, nitrogen andoxygen in order to derive the abundances of these ions relative tohydrogen. The relative intensities of four high-l CII recombinationlines with respect to the well-known 3d-4f λ4267 line are foundto be in excellent agreement with the predictions of recombinationtheory, removing uncertainties about whether the high C2+abundances derived from the λ4267 line could be due tonon-recombination enhancements of its intensity.We define an abundance discrepancy factor (ADF) as the ratio of theabundance derived for a heavy element ion from its recombination linesto that derived for the same ion from its ultraviolet, optical orinfrared collisionally excited lines (CELs). All of the PNe in oursample are found to have ADFs that exceed unity. Two of the PNe, NGC2022 and LMC N66, have O2+ ADFs of 16 and 11, respectively,while the remaining 13 PNe have a mean O2+ ADF of 2.6, withthe smallest value being 1.8.Garnett and Dinerstein found that for a sample of about 12 PNe themagnitude of the O2+ ADF was inversely correlated with thenebular Balmer line surface brightness. We have investigated this for alarger sample of 20 PNe, finding weak correlations with decreasingsurface brightness for the ADFs of O2+ and C2+.The C2+ ADFs are well correlated with the absolute radii ofthe nebulae, although no correlation is present for the O2+ADFs. We also find both the C2+ and O2+ ADFs to bestrongly correlated with the magnitude of the difference between thenebular [OIII] and Balmer jump electron temperatures (ΔT),corroborating a result of Liu et al. for the O2+ ADF.ΔT is found to be weakly correlated with decreasing nebularsurface brightness and increasing absolute nebular radius.There is no dependence of the magnitude of the ADF upon the excitationenergy of the ultraviolet, optical or infrared CEL transition used,indicating that classical nebular temperature fluctuations - i.e. in achemically homogeneous medium - are not the cause of the observedabundance discrepancies. Instead, we conclude that the main cause of thediscrepancy is enhanced ORL emission from cold ionized gas located inhydrogen-deficient clumps inside the main body of the nebulae, as firstpostulated by Liu et al. for the high-ADF PN, NGC 6153. We havedeveloped a new electron temperature diagnostic, based upon the relativeintensities of the OII 4f-3d λ4089 and 3p-3s λ4649recombination transitions. For six out of eight PNe for which bothtransitions are detected, we derive O2+ ORL electrontemperatures of <=300 K, very much less than the O2+forbidden-line and H+ Balmer jump temperatures derived forthe same nebulae. These results provide direct observational evidencefor the presence of cold plasma regions within the nebulae, consistentwith gas cooled largely by infrared fine-structure transitions; at suchlow temperatures, recombination transition intensities will besignificantly enhanced due to their inverse power-law temperaturedependence, while ultraviolet and optical CELs will be significantlysuppressed. Planetary nebula distances re-examined: an improved statistical scaleThe distances of planetary nebulae (PNe) are still quite uncertain.Although observational estimates are available for a small proportion ofPNe, based on statistical parallax and the like, such distances are verypoorly determined for the majority of galactic PNe. In particular,estimates of so-called statistical' distance appear to differ byfactors of ~2.7.We point out that there is a well-defined correlation between the 5-GHzluminosity of the sources, L5, and their brightnesstemperatures, TB. This represents a different trend to thoseinvestigated in previous statistical analyses, and permits us todetermine independent distances to a further 449 outflows. Thesedistances are shown to be closely comparable to those determined using aTB-R correlation, providing that the latter trend is taken tobe non-linear.This non-linearity in the TB-R plane has not been noted inprevious analyses, and is likely responsible for the broad (andconflicting) ranges of distance that have previously been published.Finally, we point out that there is a close accord between observedtrends within the L5-TB and TB-Rplanes, and the variation predicted through nebular evolutionarymodelling. This is used to suggest that observational biases areprobably modest, and that our revised distance scale is reasonablytrustworthy. 12C/13C Ratio in Planetary Nebulae from the IUE ArchivesWe 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. A Survey for Water Maser Emission toward Planetary Nebulae: New Detection in IRAS 17347-3139We report on a water maser survey toward a sample of 27 planetarynebulae (PNe) using the Robledo de Chavela and Medicina single-dishantennas, as well as the Very Large Array (VLA). Two detections havebeen obtained: the already known water maser emission in K3-35, and anew cluster of masers in IRAS 17347-3139. This low rate of detections iscompatible with the short lifetime of water molecules in PNe (~100 yr).The water maser cluster at IRAS 17347-3139 are distributed on a ellipseof size ~=0.2"×0.1", spatially associated with compact 1.3 cmcontinuum emission (simultaneously observed with the VLA). From archiveVLA continuum data at 4.9, 8.4, and 14.9 GHz, a spectral indexα=0.76+/-0.03 (Sν~να) is derivedfor this radio source, which is consistent with either a partiallyoptically thick ionized region or an ionized wind. However, the latterscenario can be ruled out by mass-loss considerations, thus indicatingthat this source is probably a young PN. The spatial distribution andthe radial velocities of the water masers are suggestive of a rotatingand expanding maser ring, tracing the innermost regions of a torusformed at the end of the asymptotic giant branch phase. Given that the1.3 cm continuum emission peak is located near one of the tips of themajor axis of the ellipse of masers, we speculate on a possible binarynature of IRAS 17347-3139, where the radio continuum emission couldbelong to one of the components and the water masers would be associatedwith a companion. The kinematics of the most oxygen-poor planetary nebula PN G 135.9+55.9PN G 135.9+55.9 is a compact, high excitation nebula that has beenidentified recently as the most oxygen-poor halo planetary nebula. Givenits very peculiar characteristics and potential implications in therealms of stellar and Galactic evolution, additional data are needed tofirmly establish its true nature and evolutionary history. Here wepresent the first long-slit, high spectral resolution observations ofthis object in the lines of Hα and He Iilambda 4686. Theposition-velocity data are shown to be compatible with theinterpretation of PN G 135.9+55.9 being a halo planetary nebula. In bothemission lines, we find the same two velocity components thatcharacterize the kinematics as that of an expanding elliptical envelope.The kinematics is consistent with a prolate ellipsoidal model with axisratio about 2:1, a radially decreasing emissivity distribution, avelocity distribution that is radial, and an expansion velocity of 30 kms-1 for the bulk of the material. To fit the observed lineprofiles, this model requires an asymmetric matter distribution, withthe blue-shifted emission considerably stronger than the red-shiftedemission. We find that the widths of the two velocity components aresubstantially wider than those expected due to thermal motions, butkinematic structure in the projected area covered by the slit appears tobe sufficient to explain the line widths. The present data also rule outthe possible presence of an accretion disk in the system that could havebeen responsible for a fraction of the Hα flux, furthersupporting the planetary nebula nature of PN G 135.9+55.9. Fluorine : an elementary mystery.Not Available Characteristics of Planetary Nebulae with [WC] Central StarsWe 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 nebulaeWe 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 coordinatesWe 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} Observations of [S IV] 10.5 μm and [Ne II] 12.8 μm in Two Halo Planetary Nebulae: Implications for Chemical Self-EnrichmentWe have detected the [S IV] 10.5 μm and [Ne II] 12.8 μmfine-structure lines in the halo population planetary nebula (PN) DdDm 1and set upper limits on their intensities in the halo PN H4-1. We alsopresent new measurements of optical lines from various ions of S, Ne, O,and H for DdDm 1, based on a high-dispersion spectrum covering thespectral range 3800 Å to 1 μm. These nebulae have similar O/Habundances, (O/H)~1×10-4, but S/H and Ne/H are abouthalf an order of magnitude lower in H4-1 than in DdDm 1; thus H4-1appears to belong to a more metal-poor population. This supportsprevious suggestions that PNe arising from metal-poor progenitor starscan have elevated oxygen abundances due to internal nucleosynthesis andconvective dredge-up. It is generally accepted that high abundances ofcarbon in many PNe result from self-enrichment. To the extent thatoxygen can also be affected, the use of nebular O/H values to infer theoverall metallicity of a parent stellar population (for example, inexternal galaxies) may be suspect, particularly for low metallicities. 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. Multiwavelength Observations of the Peculiar Planetary Nebula IC 2149We report high- and low-dispersion spectroscopy, optical imaging, andhigh-resolution Very Large Array-A λ3.6 cm continuum observationsof the peculiar planetary nebula IC 2149. These observations show thatbipolar'' is a suitable morphological classification for IC 2149. Mostnebular material is concentrated in a knotty, bright ring seen edge-on,embedded in an apparently oblate ellipsoidal shell from which remnant orincipient bipolar lobes emerge. We confirm the previously reporteddepletion in heavy elements and deduce a very low ejected nebular mass<~0.03 Msolar. All this information indicates that theformation of IC 2149 is the result of the evolution of a low-masscentral star. Electron temperature fluctuations in 30 DoradusWe present an observational study of the spatial variation of theelectron temperature in the 30 Doradus Nebula. Weused the [ion {O}{iii}] (lambda 4959 + lambda 5007)/lambda 4363 ratio toestimate the electron temperature at 135 positions in the nebula acrossthree different directions. We analysed long-slit spectrophotometricdata of high signal-to-noise in the range of 4100 to 5030 Åobtained with the Cassegrain spectrograph attached to the 1.60 mtelescope of the Laboratório Nacional de Astrofísica,Brazil. No large-scale electron temperature gradient was detected in 30Doradus. The electron temperature estimates obtained are fairlyhomogeneous with a mean value of 10 270 +/- 140 (3sigma ) K. Thecompatibility between the present estimates with optical and radiotemperature determinations found in the literature for other positionsor for the entire nebula corroborates this conclusion. Temperaturefluctuations of small amplitude were observed with a variance relativeto the mean of ts2= 0.0025 or equivalently with adispersion of only 5%. The areas with lower surface brightness seem topresent slightly higher electron temperatures. This would indicate thatthe bright arcs of 30 Doradus, which correspond to the densest regions,would have lower electron temperatures than the most diffuse areas. Planetary Nebulae Results from the Infrared Space ObservatoryObservations with the Infrared Space Observatory (ISO) provide a meansto assess important properties of the plasma in gaseous nebulae,including planetary nebulae (PNs). We present some results for averageelectron densities that have been determined from the flux ratios ofseveral fine-structure, infrared emission lines. Because the ISOspectroscopic aperture was always at least as large as 14'' ×20'', these represent macroscopic measurements for our sample of PNs. Wefind some instances of the observed line flux ratio being clearly out ofrange of the theoretical predictions using current atomic data. In thesecases, the ISO data cannot presently be used with these atomic data toderive electron density, but rather provide direction for neededimprovements in the atomic collision strengths. Optical Recombination Lines and Temperature FluctuationsThree decades ago, Peimbert found that in H II regions and planetarynebulae (PNe) Balmer jump temperatures are systematically lower than [OIII] forbidden line temperatures. He suggested that because there arelarge temperature fluctuations in nebulae, as a consequence, heavyelement abundances derived from collisionally excited lines (CELs) havebeen systematically underestimated. In this article, I review the recentabundance determinations for PNe using faint heavy element opticalrecombination lines (ORLs). For all the ionic species studied, ORLsyield higher abundances than CELs. The ratio of ORL to CEL abundancesvaries from object to object and correlates with the difference betweenthe [O III] and Balmer jump temperatures. Temperature and/or densityfluctuations alone are found to be insufficient to explain the verylarge discrepancies between the ORL and CEL abundances observed in asmall number of nebulae. It is suggested that these extreme nebulae maycontain metal-rich inclusions similar to those observed in`born-again'' PN such as Abell30. Are Temperature Fluctuations Out There?The effect of temperature fluctuations in the spectra of ionized nebulaewas firstly explored by Peimbert (1967). Since then, the problem oftheir existence has remained an open question. In fact, there areobservations and models that argue both in favor and against suchfluctuations and these are reviewed in this paper. We also discuss themechanisms that could produce such fluctuations and their possiblepresence and effects in extragalactic objects. Spectroscopic investigations of planetary nebulaeThe morphologies of three selected asymmetrical planetary nebulae (PNe),namely NGC 4361, NGC 1514 and NGC 246, were studied usingspatio-kinematic observations made with an Imaging Fabry-PerotSpectrometer. From the 3D spatio-kinematic models, plaussible nebularformation scenarios were proposed for NGC 4361 and NGC 1514 based on theinteracting binary progenitor model. A few parameters regarding thebinary, viz. the progenitor's mass and the binary separation, weresuggested from this study. The elemental concentration of N and He inthe nebulae were used to get some information regarding theirprogenitors. It is suggested from our study that the binary progenitorhypothesis gives more consistent / explanation of the observedstructures of these PNe than the single star hypothesis. The physicalcondition of a PNe interacting with the ambient interstellar medium hasbeen investigated in NGC 246. Its distorted morphology is attributed toits interaction with the Interstellar Medium (ISM).
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