Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
High- and low-resolution spectroscopic observations of the peculiar planetary-nebula HD 149427 (=PC 11)
Aims: We discuss the status of the A-type component of the binarycentral star in the peculiar planetary nebula HD 149427. Methods:We acquired low and high spectral resolution optical spectroscopy forthe range 4500-9000 Å. Results: The analysis of the highresolution spectrum shows that the A-type star has an effectivetemperature of Teff = 8700 ± 150 K and a surfacegravity of log g = 2.3 ± 0.4, corresponding to a spectral typeA3-A4 II. These parameters infer a luminosity estimate oflog(L/L?) = 3.69 ± 0.32, implying a distance of10 ± 0.6 kpc. The A-type star is slightly metal-poor; barium andstrontium, two key elements for monitoring the s-processnucleosynthesis, are not enriched; nitrogen is enriched relative to Sun;while carbon and oxygen are underabundant. The photospheric abundance ofthe A-type giant star in HD 149427 is compared with the abundance inother types of stars at different evolutionary stages.ARRAY(0x382e430)
| Comparing Symbiotic Nebulae and Planetary Nebulae Luminosity Functions
We compare the observed symbiotic nebulae (SyN) luminosity function(SyNLF) in the [O III] ?5007 Å line to the planetarynebulae (PN) luminosity function (PNLF) and find that the intrinsicSyNLF (ISyNLF) of galactic SyNs has—within its uncertainty of0.5-0.8 mag—very similar cutoff luminosity and general shape tothose of the PNLF. The [O III]/(H?+[N II]) line ratios of SyNs andPNs are shown to be also related. Possible implications of these resultsfor the universality of the PNLF are briefly outlined.
| High-resolution spectroscopic observations of the peculiar planetary nebula Me 1-1
Aims:We determined the atmospheric parameters and evolutionary state ofthe cool stellar component of the peculiar planetary nebula Me 1-1 andanalyzed its spatio-kinematic structure. Methods: High-resolutionoptical spectroscopy was used in an abundance analysis of the coolcomponent in Me 1-1. Narrow-band images were used to study the nebula.Results: The stellar parameters derived for the cool star in Me1-1 are T_eff = 4500 K and log g = 2.0, which correspond to a spectraltype of K(1-2) II. This star is rapidly rotating with a projectedrotational velocity of V_rot = 90 km s-1. Its estimated massis 3.5 Mȯ with a distance of 6 kpc and a luminosity of370 Lȯ. The cool star in Me 1-1 has nearly solar ironand calcium abundances. Barium, a monitor of s-process nucleosynthesis,is not enriched. We show that this cool star has reached the base of theRGB and its accreted matter has been diluted by the deepening convectiveenvelope. The images strongly suggest that Me 1-1 is an edge-on ringwith incipient bipolar lobes. The central star is displaced ~400 AU fromthe center of the nebula. The expansion velocity of the ring ranges from10 and 13 km s-1 in the different emission lines. Broad(≃600 km s-1) wings are detected in the Hαemission, probably with a stellar origin. A comparison of Me 1-1 withother ring-like planetary nebula shows that most of them host off-centerbinary central stars.Based on observations collected at the Centro Astronómico HispanoAlemán (CAHA) at Calar Alto, operated jointly by the Max-PlanckInstitut für Astronomie and the Instituto de Astrofísica deAndalucía (CSIC).
| Gas and dust spectra of the D' type symbiotic star HD 330036
Aims:We present a comprehensive and self-consistent modelling of the D'type symbiotic star (SS) HD 330036 from radio to UV. Methods:Within a colliding-wind scenario, we analyse the continuum, line, anddust spectra by means of SUMA, a code that simulates the physicalconditions of an emitting gaseous cloud under the coupled effect ofionisation from an external radiation source and shocks. Results:We find that the UV lines are emitted from high-density gas betweenthestars downstream of the reverse shock, while the optical lines areemitted downstream of the shock propagating outwards from the system. Asregards the continuum SED, three shells are identified in the IR, at 850K, 320 K, and 200 K with radii r = 2.8 × 1013 cm, 4× 1014 cm, and 1015 cm, respectively, afteradopting a distance to Earth of d=2.3 kpc. Interestingly, all theseshells appear to be circumbinary. Analysis of the unexploited ISO-SWSspectrum reveals that both PAHs and crystalline silicates coexist in HD330036, with PAHs associated to the internal shell at 850 K, andcrystalline silicates stored in the cool shells at 320 K and 200 K.Strong evidence that crystalline silicates are shaped in a disk-likestructure is derived on the basis of the relative band strengths.Finally, we suggest that shocks can be a reliable mechanism foractivating the annealing and the consequent crystallisation processes. Conclusions: We show that a consistent interpretation of gas anddust spectra emitted by SS can be obtained by models that account forthe coupled effect of the photoionising flux and of shocks. TheVLTI/MIDI proposal recently accepted by ESO aims to verify and betterconstrain some of our results by means of IR interferometricobservations.
| The symbiotic star H1-36. A composite model of line and continuum spectra from radio to ultraviolet
Aims:In this paper, we analyse the spectra of D-type SS H1-36 within acolliding-wind scenario. We aim to analyse the properties of this objectby taking the observational data along the whole electromagneticspectrum into account, in order to derive a self-consistent picture ableto interpret the nature of the system as a whole. Methods: Afterconstraining the relative physical conditions by modelling more than 40emission lines from radio to UV, we are able to explain the continuumspectral energy distribution by considering all the emittingcontributions arising from both the stars, the dust shells, and thegaseous nebulæ. Results: A comprehensive model of the radiospectra allows reproduction of the different slopes of the radio profileand the turnover frequency, as well as the different sizes of theobserved shocked envelope at different frequencies in the light of thecontributions from the expanding and reverse nebulæ. The IRcontinuum unveils the presence of two dust shells with different radiiand temperatures, which might be a distinctive feature of D-typesymbiotic systems as a class of objects. The broad profiles of IR linesdirect us to investigate whether an X-ray jet may be present. Conclusions: This insight leads us to indicate H1-36 as a promisingX-ray target and to encourage observations and studies that consistentlytake the complex nature of symbiotic stars into account throughout thewhole electromagnetic spectrum.
| Silicates in D-Type Symbiotic Stars: An Infrared Space Observatory Overview
We investigate the IR spectral features of a sample of D-type symbioticstars in order to constrain the emitting properties of coupled dust-gasparticles across the whole system. In particular, by analyzingunexploited ISO Short Wavelength Spectrometer data, deriving the basicobservational parameters of dust bands, and comparing them with respectto those observed in other astronomical sources, we try to highlight theeffect of environment on grain chemistry and physics. We find strongamorphous silicate emission bands at ~10 and ~18 μm in a largefraction of the sample. The analysis of the ~10 μm band, along with adirect comparison with several astronomical sources, reveals thatsilicate dust in symbiotic stars shows features between thecharacteristic circumstellar environments and the interstellar medium.This indicates an increasing reprocessing of grains in relation tospecific symbiotic behavior of the objects. A correlation between thecentral wavelengths of the ~10 and ~18 μm dust bands is found. Bymodeling IR spectral lines we also investigate dust grain conditionswithin the shocked nebulae. Both the unusual depletion values and thehigh sputtering efficiency might be explained by the formation of SiOmolecules, which are known to be a very reliable shock tracer. Weconclude that the signature of dust chemical disturbance due tosymbiotic activity should be looked for in the outer, circumbinary,expanding shells where the environmental conditions for grain processingmight be achieved. Symbiotic stars are thus attractive targets for newmid-IR and millimeter observations.
| 2MASS near-infrared photometry of symbiotic stars
We present Two Micron All Sky Survey photometry for 216 symbiotic andpossible symbiotic stars. This represents the most comprehensivenear-infrared photometry for these sources which has been published todate. The results are used to define the statistics of S- and D-typestars; to investigate the photometric properties of Magellanic S-typesymbiotics; and to define the possible evolution of D-type symbioticswithin the J - H/H - KS colour plane. It appears that thecolours of D-type symbiotics are consistent with differing mass-lossrates dM/dt, provided that the grains have a silicate-like composition,and maximum temperatures of the order of ~800 K.
| Further 2MASS mapping of hot dust in planetary nebulae
We have used 2 Micron All Sky Survey (2MASS) mapping results toinvestigate the distribution of hot dust continua in 12 planetarynebulae (PNe). The nature of this emission is unclear, but it ispossible that where the continuum is extended, as is the case for M 1-12and NGC 40, then the grains concerned may be very small indeed. Theabsorption of individual photons by such grains may lead to sharp spikesin temperature, as has previously discussed for several other suchoutflows. Other sources (such as MaC 1-4, He 2-25, B1 2-1 and K 3-15)appear to be relatively compact, and the high temperatures observed areunderstandable in terms of more normal heating processes. It is possiblethat the grains in these cases are experiencing high radiant fluxlevels.Finally, it is noted that whilst the core of M 2-2 appears to show hotgrain emission, this is less the case for its more extended envelope.The situation may, in this case, be similar to that of NGC 2346, inwhich much of the emission is located within an unresolved nucleus.Similarly, it is noted that in addition to hot dust and gas thermalcontinua, the emission in the interior of NGC 40 may be enhanced throughrotational-vibrational transitions of H2, and/or the2p3P0-2s3S transition of HeI.
| Spectroscopic observations of the rapid rotating post-AGB star IRAS 05381+1012
We report on the high-resolution stellar parameters and abundanceanalysis of the rapidly rotating post-AGB star IRAS 05381+1012. Analysisof high-resolution spectra shows that IRAS 05381+1012 has an effectivetemperature of T_eff=5200± 100 K and a surface gravity of logg=1.0± 0.5 corresponding to a spectral type G(2-3)I. Theseparameters result in an estimated luminosity of 970 Lȯand a distance of 2700 pc. We also show that IRAS 05381+1012 has aprojected rotational velocity vsin i=40± 10 km s-1.The abundance analysis based on a few available lines reveals that thisstar is an iron-deficient object with [Fe/H]=-0.8. We also analyze theabundance pattern and compare it to other classes of stars with similarstellar parameters.
| Rotational velocities of the giants in symbiotic stars - I. D'-type symbiotics*
We have measured the rotational velocities (v sini) of the mass donorsin a number of D'-type symbiotic stars (SSs), using thecross-correlation function method. Four out of five D' SSs with known vsini appeared to be very fast rotators compared with the catalogues of vsini for the corresponding spectral types. At least three of these starsrotate at a substantial fraction (>~0.5) of the critical velocity.This means that at least in D'-type SSs the cool components rotatefaster than isolated giants. If these binary stars are synchronized,their orbital periods should be relatively short (4-60 d). We alsobriefly discuss the possible origin of the rapid rotation and itsconnection with mass loss and dust formation.
| Hot dust haloes in planetary nebulae
We point out that many planetary nebulae (PNe) have large infraredindices (H-KS), and that this is likely to result from thepresence of hot grains, and/or H2 S(1) line emission atλ= 2.122μm. We are able to identify two groups of sourcesassociated with each of these mechanisms, both of which appear topossess distinct physical characteristics. One difference between thesegroups concerns the near-infrared dimensions of the sources. It appearsthat hot dust outflows frequently have sizes θ(KS)> θ(H) > θ(J). Four of the sources are particularlyextreme in this regard, and show emission extending well outside of theprimary shells. We propose that this is likely to arise fromhigh-temperature grains located in low-density haloes. The location ofsuch grains at large distances from the central stars represents achallenge for any mechanism purporting to explain this phenomenon. Themost likely explanation appears to be in terms of photon heating of verysmall grains.
| On metal-deficient barium stars and their link with yellow symbiotic stars
This paper addresses the question of why metal-deficient barium starsare not yellow symbiotic stars (YSyS). Samples of (suspected)metal-deficient barium (mdBa) stars and YSyS have been collected fromthe literature, and their properties reviewed. It appears in particularthat the barium nature of the suspected mdBa stars needs to beascertained by detailed abundance analyses. Abundances are thereforederived for two of them, HD 139409 and HD 148897, which reveal that HD148897 should not be considered a barium star. HD 139409 is a mildbarium star, with overabundances observed only for elements belonging tothe first s-process peak (Y and Zr). It is only moderately metal-poor([Fe/H] = -0.4). The evidence for binarity among mdBa stars is thenreviewed, using three different methods: (i) radial-velocity variations(from CORAVEL observations), (ii) Hipparcos astrometric data, and (iii)a method based on the comparison between the Hipparcos and Tycho-2proper motions. An orbit is obtained for HIP 55852, whereas evidence forthe (so far unknown) binary nature of HIP 34795, HIP 76605, HIP 97874and HIP 107478 is presented. No conclusion regarding the binary natureof HIP 11595, HIP 25161 could be reached. Two stars with no evidence forbinarity whatsoever (HIP 58596 and BD +3°2688) are candidateslow-metallicity thermally-pulsing asymptotic giant branch stars, asinferred from their large luminosities. The reason why mdBa stars arenot YSyS is suggested to lie in their different orbital perioddistributions: mdBa stars have on average longer orbital periods thanYSyS, and hence their companion accretes matter at a lower rate, for agiven mass loss rate of the giant star. The definite validation of thisexplanation should nevertheless await the determination of the orbitalperiods for the many mdBa stars still lacking periods, in order to makethe comparison more significant.
| Evolution from AGB to planetary nebula in the MSX survey
We investigate the evolution of oxygen- and carbon-rich AGB stars,post-AGB objects, and planetary nebulae using data collected mainly fromthe MSX catalogue. Magnitudes and colour indices are compared with thosecalculated from a grid of synthetic spectra that describe the post-AGBevolution beginning at the onset of the superwind. We find that carbonstars and OH/IR objects form two distinct sequences in the (K-[8.3])×([8.3]-[14.7]) MSX colour diagram. OH/IR objects are distributedin two groups: the bluest ones are crowded near [14.7]-[21.3]≃ 1and [8.3]-[14.7]≃ 2, and a second, redder group is spread over alarge area in the diagram, where post-AGB objects and planetary nebulaeare also found. High mass-loss rate OH/IR objects, post-AGB stars, andplanetary nebulae share the same region in the (K-[8.3])×([8.3]-[14.7]) and [14.7]-[21.3]×([8.3]-[14.7]) colour-colourdiagrams. This region in the diagram is clearly separated from a bluerone where most OH/IR stars are found. We use a grid of models ofpost-AGB evolution, which are compared with the data. The gap in thecolour-colour diagrams is interpreted as the result of the rapidtrajectory in the diagram of the stars that have just left the AGB.Based on results obtained by the MSX survey.Tables 1 to 3 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/565
| High-resolution spectroscopic observations of the D'-type symbiotic stars HD 330036 and AS 201
We present high-resolution spectroscopic analyses of two starsclassified as D'-type symbiotic stars, HD 330036 and AS 201. These twostars display both rapid rotation and enhancements of the s-processelements that are synthesized via slow neutron captures during stellarevolution along the asymptotic giant branch (AGB). Both characterisiticsof rapid rotation and s-process overabundances have also been discoveredrecently in another D'-type symbiotic, S190. The stellar parametersderived here for HD 330036 are Teff=6200 K and log g=2.4,while AS 201 has Teff=6000 K and log g=2.3. Resultingluminosity and distance estimates are 650 Lȯ and 2.3 kpcfor HD 330036, and 700 Lȯ and 4.3 kpc for AS 201. BothHD 330036 and AS 201 have evolved away from the main sequence and areapproaching the base of the red-giant branch. These stars havenear-solar abundances of iron and calcium, but substanial enhancements(by about +0.9 dex for HD 330036 and +1.7 dex for AS 201) of thes-process element barium. The observed barium overabundances in thecurrent cool-star members of these two binary systems probably resultedfrom mass-transfer when the current white dwarf was an AGB star. Therapid rotation found in the cool stars may also be due to mass-transfer,with the mass-gaining stars being spun up with the transfer of angularmomentum from the AGB winds. As only a few (six) D'-type symbiotics areknown, the fact that the 3 studied to date at high-spectral resolutionall display rapid rotation and s-process elemental overabundances mayindicate that these two traits are signatures of these rare binarysystems.Based on observations made with the 1.52 m telescope at the EuropeanSouthern Observatory (La Silla, Chile) under the agreement with theCNPq-Observatório Nacional (Brazil).
| Radial-Velocity Survey of Central Stars of Southern Planetary Nebulae .
We have monitored selected southern-hemisphere planetary-nebula nuclei(PNNi) in order to search for radial-velocity (RV) variations. Theobservations have been carried out regularly since early 2003 with theSMARTS Consortium 1.5-m telescope and Cassegrain spectrograph at CerroTololo Inter-American Observatory, Chile. This study is a followup to anearlier survey of northern PNNi made by \citet{demarco04}, whichsuggested that there is a high incidence of RV variability among PNNi.If the variations are due to motion in binary orbits, the fraction ofclose binaries among PNNi must be very high, suggesting that mostplanetary nebulae are ejected through binary-star processes, such ascommon-envelope interactions. We presente here the results of thesouthern portion of our RV survey. Preliminary results indicate that thefraction of variable RVs is also very high among southern PNNi.
| Symbiotic Stars as Laboratories for the Study of Accretion and Jets: A Call for Optical Monitoring
Symbiotic binary stars typically consist of a white dwarf (WD) thataccretes material from the wind of a companion red giant. Orbitalperiods for these binaries are on the order of years, and theirrelatively small optical outbursts tend to occur every few years todecades. In some symbiotics, material that is transferred from the redgiant to the WD forms a disk around the WD. Thus, symbiotic stars are abit like overgrown cataclysmic variables (CVs), but with less violenteruptions. Symbiotic stars are not as well understood as CVs, in partbecause their longer variability time scales mean that observations overmany years are required to cover different outburst states and orbitalphases. The recent discovery of collimated outflows ("jets") from anumber of symbiotics provides a new motivation for such long-term studyof these objects. Astrophysical jets are observed in almost every typeof accretion-powered system, and symbiotic stars may help us understandthese structures. Optical monitoring by amateurs can identify systemsin outburst, and also help to build a comprehensive database of outburstand quiescent symbiotic light curves. Together with radio through X-rayobservations that will be performed when new outbursts are found,long-term optical light curves will improve understanding of symbioticoutbursts, jet production, and the connection between outbursts, jets,and accretion disks in symbiotic stars.
| The relation between Zanstra temperature and morphology in planetary nebulae
We have created a master list of Zanstra temperatures for 373 galacticplanetary nebulae based upon a compilation of 1575 values taken from thepublished literature. These are used to evaluate mean trends intemperature for differing nebular morphologies. Among the most prominentresults of this analysis is the tendency forη=TZ(HeII)/TZ(HeI) to increase with nebularradius, a trend which is taken to arise from the evolution of shelloptical depths. We find that as many as 87 per cent of nebulae may beoptically thin to H ionizing radiation where radii exceed ~0.16 pc. Wealso note that the distributions of values η and TZ(HeII)are quite different for circular, elliptical and bipolar nebulae. Acomparison of observed temperatures with theoretical H-burning trackssuggests that elliptical and circular sources arise from progenitorswith mean mass ≅ 1 Msolar(although the elliptical progenitors are probably more massive).Higher-temperature elliptical sources are likely to derive fromprogenitors with mass ≅2 Msolar, however, implying thatthese nebulae (at least) are associated with a broad swathe ofprogenitor masses. Such a conclusion is also supported by trends in meangalactic latitude. It is found that higher-temperature ellipticalsources have much lower mean latitudes than those with smallerTZ(HeII), a trend which is explicable where there is anincrease in with increasing TZ(HeII).This latitude-temperature variation also applies for most other sources.Bipolar nebulae appear to have mean progenitor masses ≅2.5Msolar, whilst jets, Brets and other highly collimatedoutflows are associated with progenitors at the other end of the massrange (~ 1 Msolar). Indeed it ispossible, given their large mean latitudes and low peak temperatures,that the latter nebulae are associated with the lowest-mass progenitorsof all.The present results appear fully consistent with earlier analyses basedupon nebular scale heights, shell abundances and the relativeproportions of differing morphologies, and offer further evidence for alink between progenitor mass and morphology.
| Galactic Planetary Nebulae and their central stars. I. An accurate and homogeneous set of coordinates
We have used the 2nd generation of the Guide Star Catalogue (GSC-II) asa reference astrometric catalogue to compile the positions of 1086Galactic Planetary Nebulae (PNe) listed in the Strasbourg ESO Catalogue(SEC), its supplement and the version 2000 of the Catalogue of PlanetaryNebulae. This constitutes about 75% of all known PNe. For these PNe, theones with a known central star (CS) or with a small diameter, we havederived coordinates with an absolute accuracy of ~0\farcs35 in eachcoordinate, which is the intrinsic astrometric precision of the GSC-II.For another 226, mostly extended, objects without a GSC-II counterpartwe give coordinates based on the second epoch Digital Sky Survey(DSS-II). While these coordinates may have systematic offsets relativeto the GSC-II of up to 5 arcsecs, our new coordinates usually representa significant improvement over the previous catalogue values for theselarge objects. This is the first truly homogeneous compilation of PNepositions over the whole sky and the most accurate one available so far.The complete Table \ref{tab2} is only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/408/1029}
| Angular dimensions of planetary nebulae
We have measured angular dimensions of 312 planetary nebulae from theirimages obtained in Hα (or Hα + [NII]). We have appliedthree methods of measurements: direct measurements at the 10% level ofthe peak surface brightness, Gaussian deconvolution and second-momentdeconvolution. The results from the three methods are compared andanalysed. We propose a simple deconvolution of the 10% levelmeasurements which significantly improves the reliability of thesemeasurements for compact and partially resolved nebulae. Gaussiandeconvolution gives consistent but somewhat underestimated diameterscompared to the 10% measurements. Second-moment deconvolution givesresults in poor agreement with those from the other two methods,especially for poorly resolved nebulae. From the results of measurementsand using the conclusions of our analysis we derive the final nebulardiameters which should be free from systematic differences between small(partially resolved) and extended (well resolved) objects in our sample.Table 1 is only available in electronic form athttp://www.edpsciences.org
| Infrared low-resolution spectra of symbiotic stars
The IRAS low-resolution spectra (LRS) of 29 symbiotic stars arepresented in this paper. It is found that silicate dust is commonmaterial in the circumstellar shells of symbiotic stars. From the IRASlow-resolution spectra, IRAS colors, symbiotic types and spectral types,some physical properties of symbiotic stars with the LRS spectra arealso discussed.
| A Catalogue of IJK Photometry of PNe with DENIS
Near-infrared photometry of planetary nebulae (PNe) allows theclassification of those objects (Whitelock 1985; Peña &Torres-Peimbert 1987). We present the largest homogeneous sample.
| A multi-epoch spectrophotometric atlas of symbiotic stars
A multi-epoch, absolute-fluxed spectral atlas extending from about 3200to 9000 Å is presented for 130 symbiotic stars, including membersof the LMC, SMC and Draco dwarf galaxies. The fluxes are accurate tobetter than 5% as shown by comparison with Tycho and ground-basedphotometric data. The spectra of 40 reference objects (MKK cool giantstandards, Mira and Carbon stars, planetary nebulae, white dwarfs, hotsub-dwarfs, Wolf-Rayet stars, classical novae, VV Cep and Herbig Ae/Beobjects) are provided to assist the interpretation of symbiotic starspectra. Astrometric positions and counterparts in astrometriccatalogues are derived for all program symbiotic stars. The spectra areavailable in electronic form from the authors. Based on observationscollected with the telescopes of the European Southern Observatory (ESO,Chile) and of the Padova & Asiago Astronomical Observatories(Italy). Tables 2 and 3 are only available in electronic form (a) at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/383/188, and (b) from thepersonal home page http://ulisse.pd.astro.it/symbio_atlas/ Figures 4-256are only available in electronic form (a) at http://www.edpsciences.organd (b) from the personal home pagehttp://ulisse.pd.astro.it/symbio_atlas/
| Version 2000 of the Catalogue of Galactic Planetary Nebulae
The ``Catalogue of Galactic Planetary Nebulae (Version 2000)'' appearsin Abhandlungen aus der Hamburger Sternwarte, Band XII in the year 2001.It is a continuation of CGPN(1967) and contains 1510 objects classifiedas galactic PNe up to the end of 1999. The lists of possible pre-PNe andpossible post-PNe are also given. The catalogue is restricted only tothe data belonging to the location and identification of the objects. Itgives identification charts of PNe discovered since 1965 (published inthe supplements to CGPN) and those charts of objects discovered earlier,which have wrong or uncertain identification. The question ``what is aplanetary nebula'' is discussed and the typical values of PNe and oftheir central stars are summarized. Short statistics about thediscoveries of PNe are given. The catalogue is also available in theCentre de Données, Strasbourg and at Hamburg Observatory viainternet. The Catalogue is only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/378/843
| Optical Coordinates of Southern Planetary Nebulae
A homogeneous set of new measurements of nearly all (995 out of 1007)objects from the Strasbourg-ESO Catalogue of Galactic Planetary Nebulaeor in the first supplement of this catalogue in the area covered by theDENIS survey (δ < +2 degrees) is given here. A list of 24 newand 27 wrong crossidentifications with sources in the IRAS PSC catalogueand some confusion in the literature is listed as well.
| Spectroscopic verification of suspected planetary nebulae. IV.
Verification of 7 objects as PNe (Table 1/A) as well asmisclassification of 5 objects as PNe (Table 1/C) are discussedaccording to our CCD spectra; the status of 4 objects (Table 1/B)remains uncertain. In Table we give the estimates of line-strengths andthe measured intensities of emission lines as well as the derived hel.radial velocities and their standard deviations.
| 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.
| A catalogue of symbiotic stars
We present a new catalogue of symbiotic stars. In our list we include188 symbiotic stars as well as 30 objects suspected of being symbiotic.For each star, we present basic observational material: coordinates, Vand K magnitudes, ultraviolet (UV), infrared (IR), X-ray and radioobservations. We also list the spectral type of the cool component, themaximum ionization potential observed, references to finding charts,spectra, classifications and recent papers discussing the physicalparameters and nature of each object. Moreover, we present the orbitalphotometric ephemerides and orbital elements of known symbioticbinaries, pulsational periods for symbiotic Miras, Hipparcos parallaxesand information about outbursts and flickering.
| 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
| Spectral classification of the cool giants in symbiotic systems
We derive the spectral types of the cool giants in about 100 symbioticsystems. Our classification is mainly based on near IR spectra in orderto avoid the contamination of the spectrum by the nebula and the hotcomponent in the visual region. The accuracy of our spectral types isapproximately one spectral subclass, similar to previous near IRclassification work, and much better than visual spectral typeestimates. Strong, intrinsic spectral type variations (>2 spectralsubtypes) are only seen in systems containing pulsating mira variables.We present a catalogue of spectral types for cool giants in symbioticsystems which also includes determinations taken from the literature.The catalogue gives spectral types for the cool giants in about 170systems which is nearly the full set of confirmed symbiotics. Based onour classifications we discuss the distribution of spectral types of thecool giants in galactic symbiotic binaries. We find that the spectraltypes cluster strongly between M3 and M6, with a peak at M5. Thedistribution of systems with a mira variable component peaks even later,at spectral types M6 and M7. This is a strong bias towards late spectraltypes when compared to red giants in the solar neighbourhood. Also thefrequency of mira variables is much larger among symbiotic giants. Thispredominance of very late M-giants in symbiotic systems seems toindicate that large mass loss is a key ingredient for triggeringsymbiotic activity on a white dwarf companion. Further we find forsymbiotic systems a strong correlation between the spectral type of thecool giant and the orbital period. In particular we find a tightrelation for the minimum orbital period for symbiotic systems with redgiants of a given spectral type. This limiting line in the spectral type- orbital period diagram seems to be equivalent with the relationR<=l_1/2, where R is the radius of the red giant and l_1 the distancefrom the center of the giant to the inner Lagrangian point L_1. Thiscorrelation possibly discloses that symbiotic stars are - with probablyonly one exception in our sample - well detached binary systems. Basedon observations obtained with the 1.52~m and 3.6~m telescopes of theEuropean Southern Observatory (ESO), the 1.93~m telescope of theObservatoire de Haute-Provence (OHP), the 2.3~m telescope of theAustralian National University (ANU) at Siding Spring, and the WilliamHerschel Telescope (WHT) at La Palma. This research has made use of theAFOEV database, operated at CDS, France.
| A Survey of Planetary Nebulae in the Southern Galactic Bulge
We present the results of a deep and uniform narrowband Hα imagingsurvey for planetary nebulae (PNs) in the southern Galactic bulge. Inour survey, we have found 56 new PNs and have rediscovered 45 known PNs.We have measured the radial velocities of this uniformly selected sampleand have also remeasured radial velocities for a subset of 317 PNs fromthe Acker catalog. Using the COBE/DIRBE 1.25, 2.2, and 3.5 μm images,we show that there is a similar longitude distribution of the PNs andthe COBE light in the zone of our deep survey. Also, we find that theextinction in our surveyed fields is not severe and that itsdistribution is fairly uniform. Finally, we present Hα fluxes for47 of our 56 newly discovered PNs and estimate the survey detectionlimit.
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Cetvel |
| Sað Açýklýk: | 15h51m15.94s |
| Yükselim: | -48°44'58.7" |
| Görünürdeki Parlaklýk: | 11.319 |
| özdevim Sað Açýklýk: | -2.4 |
| özdevim Yükselim: | -3 |
| B-T magnitude: | 13.703 |
| V-T magnitude: | 11.516 |
Kataloglar ve belirtme:
|
INHABITED SKY
