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s-Process Abundances in Planetary Nebulae
The s-process should occur in all but the lower mass progenitor stars ofplanetary nebulae, and this should be reflected in the chemicalcomposition of the gas that is expelled to create the current planetarynebula shell. Weak forbidden emission lines are expected from severals-process elements in these shells and have been searched for and insome cases detected in previous investigations. Here we extend thesestudies by combining very high signal-to-noise ratio echelle spectra ofa sample of PNe with a critical analysis of the identification of theemission lines of Z>30 ions. Emission lines of Br, Kr, Xe, Rb, Ba,and Pb are detected with a reasonable degree of certainty in at leastsome of the objects studied here, and we also tentatively identify linesfrom Te and I, each in one object. The strengths of these lines indicateenhancement of s-process elements in the central star progenitors, andwe determine the abundances of Br, Kr, and Xe, elements for which atomicdata relevant for abundance determination have recently becomeavailable. As representative elements of the ``light'' and ``heavy''s-process peaks, Kr and Xe exhibit similar enhancements over solarvalues, suggesting that PN progenitors experience substantial neutronexposure.
| 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).
| Fluorine Abundances in Planetary Nebulae
We 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.
| 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.
| Planetary nebula distances re-examined: an improved statistical scale
The distances of planetary nebulae (PNe) are still quite uncertain.Although observational estimates are available for a small proportion ofPNe, based on statistical parallax and the like, such distances are verypoorly determined for the majority of galactic PNe. In particular,estimates of so-called `statistical' distance appear to differ byfactors of ~2.7.We point out that there is a well-defined correlation between the 5-GHzluminosity of the sources, L5, and their brightnesstemperatures, TB. This represents a different trend to thoseinvestigated in previous statistical analyses, and permits us todetermine independent distances to a further 449 outflows. Thesedistances are shown to be closely comparable to those determined using aTB-R correlation, providing that the latter trend is taken tobe non-linear.This non-linearity in the TB-R plane has not been noted inprevious analyses, and is likely responsible for the broad (andconflicting) ranges of distance that have previously been published.Finally, we point out that there is a close accord between observedtrends within the L5-TB and TB-Rplanes, and the variation predicted through nebular evolutionarymodelling. This is used to suggest that observational biases areprobably modest, and that our revised distance scale is reasonablytrustworthy.
| Sulfur, Chlorine, and Argon Abundances in Planetary Nebulae. IV. Synthesis and the Sulfur Anomaly
We have compiled a large sample of O, Ne, S, Cl, and Ar abundances thathave been determined for 85 Galactic planetary nebulae in a consistentand homogeneous manner using spectra extending from 3600 to 9600Å. Sulfur abundances have been computed using the near-IR lines of[S III] λλ9069, 9532 along with [S III] temperatures. Wefind average values, expressed logarithmically with a standarddeviation, of log(S/O)=-1.91+/-0.24, log(Cl/O)=-3.52+/-0.16, andlog(Ar/O)=-2.29+/-0.18, numbers consistent with previous studies of bothplanetary nebulae and H II regions. We also find a strong correlationbetween [O III] and [S III] temperatures among planetary nebulae. Inanalyzing abundances of Ne, S, Cl, and Ar with respect to O, we find atight correlation for Ne-O, and loose correlations for Cl-O and Ar-O.All three trends appear to be colinear with observed correlations for HII regions. S and O also show a correlation, but there is a definiteoffset from the behavior exhibited by H II regions and stars. We suggestthat this S anomaly is most easily explained by the existence ofS+3, whose abundance must be inferred indirectly when onlyoptical spectra are available, in amounts in excess of what is predictedby model-derived ionization correction factors in PNe. Finally for thedisk PNe, abundances of O, Ne, S, Cl, and Ar all show gradients whenplotted against Galactocentric distance. The slopes are statisticallyindistinguishable from one another, a result which is consistent withthe notion that the cosmic abundances of these elements evolve inlockstep.
| 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}
| Gas temperature and excitation classes in planetary nebulae
Empirical methods to estimate the elemental abundances in planetarynebulae usually use the temperatures derived from the [O III] and [N II]emission-line ratios, respectively, for the high- and low-ionizationzones. However, for a large number of objects these values may not beavailable. In order to overcome this difficulty and allow a betterdetermination of abundances, we discuss the relationship between thesetwo temperatures. Although a correlation is not easily seen when asample of different PNe types is used, the situation is improved whenthey are gathered into excitation classes. From [OII]/[OIII] andHeII/HeI line ratios, we define four excitation classes. Then, usingstandard photoionization models which fit most of the data, a linearrelation between the two temperatures is obtained for each of the fourexcitation classes. The method is applied to several objects for whichonly one temperature can be obtained from the observed emission linesand is tested by recalculation of the radial abundance gradient of theGalaxy using a larger number of PNe. We verified that our previousgradient results, obtained with a smaller sample of planetary nebulae,are not changed, indicating that the temperature relation obtained fromthe photoionization models are a good approximation, and thecorresponding statistical error decreases as expected. Tables 3-5, 7 and9 are only available in electronic form at http://www.edpsciences.org
| Sulfur, Chlorine, and Argon Abundances in Planetary Nebulae. IIB. Abundances in a Southern Sample
We have undertaken a large spectroscopic survey of over 80 planetarynebulae with the goal of providing a homogeneous spectroscopic databasebetween 3600 and 9600 Å, as well as a set of consistentlydetermined abundances, especially for oxygen, sulfur, chlorine, andargon. In the current paper we calculate and report the S/O, Cl/O, andAr/O abundance ratios for 45 southern planetary nebulae (predominantlytype II), using our own recently observed line strengths published in acompanion paper. One of the salient features of our work is the use ofthe near-IR lines of [S III] λλ9069, 9532 coupled with the[S III] temperature, to determine the S+2 ionic abundance. Wefind the following average abundances for these objects:S/O=0.011+/-0.0064, Cl/O=0.00031+/-0.00012, and Ar/O=0.0051+/-0.0020.
| Sulfur, Chlorine, and Argon in Planetary Nebulae. IIA. Observations of a Southern Sample
In this paper we present fully reduced and dereddened emission linestrengths for a sample of 45 southern type II planetary nebulae(PNs).The spectrophotometry for these PNs covers an extendedoptical/near-IR range from 3600 to 9600 Å. This PN study andsubsequent analysis (presented in a companion paper), together with asimilar treatment for a northern PN sample, is aimed at addressing thelack of homogeneous, consistently observed, reduced, and analyzed datasets that include the near-IR [S III] lines at 9069 and 9532 Å.The use of type II objects only is intended to select disk nebulae thatare uncontaminated by nucleosynthetic products of the progenitor star.Extending spectra redward to include the strong [S III] lines enables usto look for consistency between S+2 abundances inferred fromthese lines and from the more accessible, albeit weaker, [S III] line atλ6312.
| Helium contamination from the progenitor stars of planetary nebulae: The He/H radial gradient and the ΔY / ΔZ enrichment ratio
In this work, two aspects of the chemical evolution of 4He inthe Galaxy are considered on the basis of a sample of disk planetarynebulae (PN). First, an application of corrections owing to thecontamination of 4He from the evolution of the progenitorstars shows that the He/H abundance by number of atoms is reduced by0.012 to 0.015 in average, leading to an essentially flat He/H radialdistribution. Second, a determination of the helium to heavy elementenrichment ratio using the same corrections leads to values in the range2.8 < ΔY / ΔZ < 3.6 for Y p = 0.23 and 2.0< ΔY / ΔZ < 2.8 for Y p = 0.24, in goodagreement with recent independent determinations and theoretical models.
| The Galactic disc distribution of planetary nebulae with warm dust emission features - I
We investigate the Galactic disc distribution of a sample of planetarynebulae characterized in terms of their mid-infrared spectral features.The total number of Galactic disc PNe with 8-13μm spectra is broughtup to 74 with the inclusion of 24 new objects, the spectra of which wepresent for the first time. 54 PNe have clearly identified warm dustemission features, and form a sample that we use to construct thedistribution of the C/O chemical balance in Galactic disc PNe. The dustemission features complement the information on the progenitor massesbrought by the gas-phase N/O ratios: PNe with unidentified infraredemission bands have the highest N/O ratios, while PNe with the silicatesignature have either very high N enrichment or close to none. We find atrend for a decreasing proportion of O-rich PNe towards the third andfourth Galactic quadrants. Two independent distance scales confirm thatthe proportion of O-rich PNe decreases from 30\pm 9 per cent inside the solar circle to 14\pm 7 per cent outside. PNe with warm dustare also the youngest. PNe with no warm dust are uniformly distributedin C/O and N/O ratios, and do not appear to be confined to C/O\sim 1. They also have higher 6-cmfluxes, as expected from more evolved PNe. We show that the IRAS fluxesare a good representation of the bolometric flux for compact andIR-bright PNe, which are probably optically thick. Selection of objectswith \fontshape{it}{F}(12\hphantom{0}\mu m)>0.5\hphantom{0} Jyshould probe a good portion of the Galactic disc for these young, denseand compact nebulae, and the dominant selection effects are rooted inthe PN catalogues.
| Gravity distances of planetary nebulae II. Aplication to a sample of galactic objects.
Not Available
| On the abundance gradient of the galactic disk
Estimates of the gas temperature in planetary nebulae obtained from the[O III] emission line ratio and from the Balmer discontinuity indicatedifferences reaching up to 6000 K (Liu & Danziger 1993). The [O III]temperature is commonly used to obtain the ionic fractions of highlyionized ions, particularly the O++ and Ne++ ions when using theempirical method to calculate the elemental abundances of photoionizedgas from the observed emission line intensities. However, if the gastemperature is overestimated the elemental abundances may beunderestimated. In particular this may lead to an incorrect elementalabundance gradient for the Galaxy, usually used as a constraint for thechemical evolution models. Using Monte Carlo simulations, we calculatethe systematic error introduced in the abundance gradient obtained fromplanetary nebulae by an overestimation of the gas temperature. Theresults indicate that the abundance gradient in the Galaxy should besteeper than previously assumed.
| Distances of Galactic Planetary Nebulae Based on a Relationship Between the Central Star Mass and the N/O Abundance
In this paper, we propose a method to determine distances of Galacticplanetary nebulae on the basis of a relationship between the centralstar mass and the nebular N/O abundance ratio. This relationship is usedin combination with some basic parameters of the central stars, such asthe lambda 5480 flux, surface gravity and visual magnitude in order toobtain distances to a sample of a hundred Galactic planetary nebulae.
| The dust content of planetary nebulae: a reappraisal
We have performed a statistical analysis using broad band IRAS data onabout 500 planetary nebulae with the aim of characterizing their dustcontent. Our approach is different from previous studies in that it usesan extensive grid of photoionization models to test the methods forderiving the dust temperature, the dust-to-gas mass ratio and theaverage grain size. In addition, we use only distance independentdiagrams. With our models, we show the effect of contamination by atomiclines in the broad band IRAS fluxes during planetary nebula evolution.We find that planetary nebulae with very different dust-to-gas massratios exist, so that the dust content is a primordial parameter for theinterpretation of far infrared data of planetary nebulae. In contrastwith previous studies, we find no evidence for a decrease in thedust-to-gas mass ratio as the planetary nebulae evolve. We also showthat the decrease in grain size advocated by Natta & Panagia(\cite{NattaPanagia}) and Lenzuni et al. (\cite{Lenzuni}) is an artefactof their method of analysis. Our results suggest that the timescale fordestruction of dust grains in planetary nebulae is larger than theirlifetime. Table~1 is only accessible in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| First Extragalactic Direct Detection of Large-Scale Molecular Hydrogen in the Disk of NGC 891
We present direct observations of molecular hydrogen in the disk of thenearby edge-on spiral galaxy NGC 891. With Infrared Space Observatory'sShort-Wavelength Spectrometer (SWS) it has been possible, for the firsttime, to observe the lowest pure rotational lines of H_2 [S(0) at 28.2μm and S(1) at 17.0 mum] at eight positions throughout the stellardisk of NGC 891. Both lines have been detected at all the surveyedpositions out to 11 kpc north of the center of the galaxy. An H_2rotation curve is derived, and we compare H_2 radial profiles with COand H I data. The observed line ratios indicate relatively warm(T=150-230 K) molecular clouds scattered throughout the disk in additionto a massive cooler (T=80-90 K) component which dominates the signal inthe outer regions. For H_2 ortho/para ratios of 2-3, the cool gas hastypical edge-on column densities (1-3)x10^23 cm^-2 (or ~3000 M_solarpc^-2), in which case it outweighs the H I by a factor of 5-15. Thisfactor matches well the mass required to resolve the problem of themissing matter of spiral galaxies within at least the optical disk. Thenewly discovered cool H_2 component would be less massive in the case inwhich its dominant ortho/para ratio is near unity. We address thethermal balance of this component by a comparison with [C II] 158 μmdata. When combining the new coolish molecular gas results with recentSCUBA cold dust observations of NGC 891, the total gas-to-dust ratio atr<12 kpc remains around 200.
| Abundance gradients in the outer galactic disk from planetary nebulae
Radial abundance gradients of the element ratios O/H, Ne/H, S/H, andAr/H are determined on the basis of a sample of disk planetary nebulae.The behaviour of the gradients at large distances from the galacticcentre, R > R_0 = 7.6 kpc, is emphasized. It is concluded that thederived gradients are consistent with an approximately constant slope inthe inner parts of the Galaxy, and some flattening for distances largerthan R_0. A comparison is made with previous determinations using bothphotoionized nebulae and young stars, and some consequences ontheoretical models for the chemical evolution of the galactic disk arediscussed. Table~1 is available only electronically at the CDS(anonymousftp 130.79.128.5 or http://cdsweb.u-strasbg.fr/Abstract.html)
| 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
| Inhomogeneous planetary nebulae: carbon and oxygen abundances
We reconsider the problem of the difference between the abundances ofcarbon and oxygen in galactic planetary nebulae (PN) derived from theintensities of the recombination and collisionally excited lines. Thisdiscrepancy can be explained by an inhomogeneity of the PNe and anoverestimation of the weak line intensities. The formulae forcalculation of the nebular line intensities in presence of bothtemperature and density fluctuations are given. The intensities of theforbidden [OIII] lines, the CII, CIII and CIV recombination lines andthe CIII]lambda 1909 UV intercombination doublet for different values ofthe mean electron temperature T_0 in PNe and the rms temperaturevariation t^2, are calculated. Results of these calculations are used tofind the values of T_0 and t^2 which allow to provide the best fit ofthe observed and calculated line intensities (taking into account theobservational errors). In most cases, the obtained values of T_0 appearto be significantly smaller than ordinarily used for the abundancedeterminations T_e([OIII]), while t^2<0.16. The carbon and oxygenabundances for more than 70 PNe are calculated. For these PNe averagechemical abundances are evaluated separately for nebulae of type I, IIand III. For the first, we found C/H=6.67*10(-4) cm(-3) andO/H=5.74*10(-4) 4cm(-3) . For the second they are C/H=8.94*10(-4) cm(-3)and O/H=6.36*10(-4) cm(-3) . For the third we obtained C/H=3.94*10(-4)cm(-3) and O/H=4.79*10(-4) cm(-3) . Results of the fitting of the lineintensities for the NIII lambda 4640 and NIV] lambda 1486 lines are alsogiven.
| Classification and Identification of IRAS Sources with Low-Resolution Spectra
IRAS low-resolution spectra were extracted for 11,224 IRAS sources.These spectra were classified into astrophysical classes, based on thepresence of emission and absorption features and on the shape of thecontinuum. Counterparts of these IRAS sources in existing optical andinfrared catalogs are identified, and their optical spectral types arelisted if they are known. The correlations between thephotospheric/optical and circumstellar/infrared classification arediscussed.
| Southern Emission-Line Flux Standards
We present slitless absolute spectrophotometric observations made athigh dispersion of southern compact (<5" diameter) planetary nebulae(PNs) drawn from the Acker et al. catalog between 7 hr and 17 hr in R.A.A total of 52 nebulae were observed, for which we give accuratepositions. For 50 of these we have measured accurate radial velocities.For the 39 objects observed on more than one occasion, we give absoluteH alpha , H beta , and [O III] line fluxes and equivalent widths and theabsolute fluxes of a number of other emission lines. These data areintended to supply reliable emission-line flux standards for southernhemisphere observers. From our data we have also been able to deriveimproved values for the air wavelengths of the [N II] and [S II] linesin the red.
| The wavelength calibration and resolution of the SWS.
The laboratory wavelength calibration of the SWS has been succesfullytransferred to the in orbit situation. The achieved accuracies for thegrating sections are λ/δλ~10000. Any remainingerrors in the wavelength scale are dominated by uncertainties of therelative position of the target in the 14"-20" wide slits. The gratingspectral profile is very well represented by a Gaussian shape. The widthof the grating spectral profile can be accurately predicted by atheoretical model. The wavelength calibration of the FP's is accurate towithin 1/3 of a resolution element, corresponding toλ/δλ~10^5^. The wavelength stability of the gratingsand FP is excellent, no measurable changes were found during the first 6months of the ISO mission.
| [N II] and [O III] Mean Electron Temperatures in Planetary Nebulae
Mean electron tempertures for 106 planetary nebulae are presented, whichhave been derived using calculations of the values of electrontemperature-sensitive line ratios involving forbidden transitions amongthe 2s^2 2p^2 3P, 1D, and 1S levels of N+ and O++, based on new electronimpact rates and transition probabilities. Comparison of these resultswith values of T_e[N II] and T_e[O III] determined previously by Kalerreveal that the present electron temperatures are systematically lowerfor both ions, and that this discrepancy is correlated with the electrondensity in the nebula. It is also shown that the average differencetween T_e[N II] and T_e[O III] in a planetary nebula is somewhat smallerthan that derived by Kaler, with the present results implying that the NII and O III temperatures disagree on average by 2070 K as opposed tothe 2210 K average found by Kaler. (SECTION: Interstellar Medium andNebulae)
| Classification of planetary nebulae by cluster analysis and artificial neural networks.
According to the chemical composition, a sample of 192 Planetary Nebulaeof different types has been re-classified, and 41 others have beenclassified for the first time, by means of two methods not employed sofar in this field: hierarchical cluster analysis and supervisedartificial neural network. The cluster analysis reveals itself as a goodfirst guess for grouping Planetary Nebulae, while an artificial neuralnetwork provides reliable automated classification of this kind ofobjects.
| Wavelengths of the [NII] ^3P-^1D forbidden lines
The wavelengths of the ^3P-^1D transitions of [NII] have been determinedby observing planetary nebulae with the Ultra-High-Resolution Facilityat the Anglo-Australian Telescope. The accuracy achieved is a factor of5 better than for previous determinations. The combination of a largecollecting area and the most efficient very high-resolution spectrographavailable to the community has made this experiment possible. The newair wavelengths for the ^3P_1-^1D_2 and ^3P_2-^1D_2 lines are6583.454+/-0.007 and 6548.08+/-0.01A respectively.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| A statistical distance scale for Galactic planetary nebulae
A statistical distance scale is proposed. It is based on the correlationbetween the ionized mass and the radius and the correlation between theradio continuum surface brightness temperature and the nebular radius.The proposed statistical distance scale is an average of the twodistances obtained while using the correlation. These correlations,calibrated based on the 1`32 planetary nebulae with well-determinedindividual distances by Zhang, can reproduce not only the averagedistance of a sample of Galactic Bulge planetary nebulae exactly at thedistance to the Galactic center, but also the expected Gaussiandistribution of their distances around the Galactic center. This newdistance scale is applied to 647 Galactic planetary nebulae. It isestimated that this distance scale can be accurate on average to35%-50%. Our statistical distance scale is in good agreement with theone recently proposed by Van de Steene and Zijlstra. The correlationsfound in this study can be attributed to the fact that the core mass ofthe central stars has a very sharp distribution, strongly peaked atapprox. 0.6 solar mass. We stress that the scatter seen in thestatistical distance scale is likely to be real. The scatter is causedby the fact that the core mass distribution, although narrow andstrongly peaked, has a finite width.
| On an alternative statistical distance scale for planetary nebulae. Catalog with statistical distances to planetary nebulae.
We have proposed a statistical method to determine distances toplanetary nebulae. The method is based on an empirical correlationbetween the radio-continuum brightness temperature and radius. Here wepresent a catalog of distance determinations calculated using thismethod.
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