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The Origin and Shaping of Planetary Nebulae: Putting the Binary Hypothesis to the Test
Planetary nebulae (PNs) are circumstellar gas ejected during an intensemass-losing phase in the lives of asymptotic giant branch stars. PNshave a stunning variety of shapes, most of which are not sphericallysymmetric. The debate over what makes and shapes the circumstellar gasof these evolved, intermediate mass stars has raged for two decades.Today the community is reaching a consensus that single stars cannottrivially manufacture PNs and impart to them nonspherical shapes andthat a binary companion, possibly even a substellar one, might be neededin a majority of cases. This theoretical conjecture has, however, notbeen tested observationally. In this review we discuss the problem fromboth the theoretical and observational standpoints, explaining theobstacles that stand in the way of a clean observational test and waysto ameliorate the situation. We also discuss indirect tests of thishypothesis and its implications for stellar and galactic astrophysics.
| Galactic planetary nebulae and their central stars. II. Proper motions
Context: More than 1500 Galactic planetary nebulae (PNe) are known butonly a tiny fraction of them have measured proper motions. To date, thelargest set of proper motion (PM) data for PNe is the one by Cudworth(1974), which includes 62 objects 25 of which have PM with significancebetter than 3σ in at least one component. Aims: With our newcompilation of 234 PNe we enlarge - compared to Cudworth's 25 - byalmost an order of magnitude the number of PNe and central stars (CSs)with reliably measured proper motion (i.e. with significance better than3σ in at least one component) and confirm some previousmeasurements. Methods: We have used all-sky astrometric cataloguesavailable via the Vizier database to collect proper motion informationfor a sample of objects selected from the catalogue of PNe positions ofKerber et al. (2003a, A&A, 408, 1029). Results: We have derivedproper motion information for a total of 234 PNe (274 when including 40doubtful candidates). We include all PNe for which a confidence level ofat least 3σ was achieved in at least one proper motion component.For many objects PM data are available from more than one catalogue andagreement between different catalogues is usually very reasonableproviding independent confirmation of the results. For comparison withCudworth's results we use the proper motion modulus as a metric. Wecross-correlated his 62 objects with our master catalogue and found 12matching objects out of the 18 with >3σ in his list. For thesewe find good agreement for 10 out of the 12 objects, while we findsignificant PM for another five objects with PM σ ≤3 reportedby Cudworth. The number of objects we have in common was limited byseveral factors discussed in the paper. Conclusions: With 234 (274including doubtful candidates) entries our work is the largest availablecompilation of proper motion data for PNe and their CSs. Thiscompilation opens new opportunities for studies of orbital kinematics ofPNe in the Galaxy.Table 3 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/479/155
| Bayesian posterior classification of planetary nebulae according to the Peimbert types
Context: Galactic planetary nebulae are observed with a wide variety ofkinematic properties, spatial distribution, chemical composition andmorphologies, comprising members of the dominant stellar populations ofour Galaxy. Due to their broad astrophysical interest, a propercharacterization of these populations is of major importance. Aims: Inthis paper we present a re-analysis of the criteria used to characterizethe Peimbert classes I, IIa, IIb, III and IV, through a statisticalstudy of a large sample of planetary nebulae previously classifiedaccording to these groups. In the original classification, it is usualto find planetary nebulae that cannot be associated with a single type;these most likely have dubious classifications into two or three types.Statistical methods can greatly contribute in providing a bettercharacterization of planetary nebulae groups. Methods: We use the BayesTheorem to calculate the posterior probabilities for an object to bemember of each of the types I, IIa, IIb, III and IV. This calculation isparticularly important for planetary nebulae that are ambiguouslyclassified in the traditional method. The posterior probabilities aredefined from the probability density function of classificatoryparameters of a well-defined sample, composed only by planetary nebulaeunambiguously fitted into the Peimbert types. Because the probabilitiesdepend on the available observational data, they are conditionalprobabilities, and, as new observational data are added to the sample,the classification of the nebula can be improved, to take into accountthis new information. Results: This method differs from the originalclassificatory scheme, because it provides a quantitative result of therepresentativity of the object within its group. Also, through the useof marginal distributions it is possible to extend the Peimbertclassification even to those objects for which only a few classificatoryparameters are known. Conclusions: We found that ambiguities in theclassification of planetary nebulae into the Peimbert types, should beassociated to difficulties in defining sharp boundaries for theprogenitor star mass for each of these types. Those can be at leastpartially explained by real overlaps of some of the parameters thatcharacterize the different stellar populations. Those results suggestthe need of a larger number of classificatory parameters for a reliablephysical classification of planetary nebulae.Tables [see full textsee full text] and [see full textsee full text] areonly available in electronic form at http://www.aanda.org
| Progenitors of type Ia supernovae: Binary stars with white dwarf companions
Type Ia SNe (SNe Ia) are thought to come from carbon oxygen white dwarfsthat accrete mass from binary companions until they approach theChandrasekhar limit, ignite carbon, and undergo complete thermonucleardisruption. A survey of the observed types of binaries that containwhite dwarfs is presented. We propose that certain systems that seemmost promising as SN Ia progenitors should be more intensively observedand modeled, to determine whether the white dwarfs in these systems willbe able to reach the Chandrasekhar limit. In view of the number ofpromising single-degenerate systems and the dearth of promisingdouble-degenerate systems, we suspect that single-degenerates producemost or perhaps all SNe Ia, while double-degenerates produce some orperhaps none.
| Binary Life after the AGB -- Towards a Unified Picture
We attempt to construct a unified evolutionary scheme that includespost-AGB systems, barium stars, symbiotics and related systems,explaining their similarities as well as their differences. Specialattention is given to the comparison of the barium pollution andsymbiotic phenomena. Finally, we outline a `transient torus'evolutionary scenario that makes use of the various observational andtheoretical hints and aims at explaining the observed characteristics ofthe relevant systems.
| The shaping of planetary nebula Sh2-188 through interactionwith the interstellar medium
Sh2-188 is an example of strong interaction between a planetary nebula(PN) and the interstellar medium (ISM). It shows a single arc-likestructure, consisting of several filaments, which is postulated to bethe result of motion through the ISM. We present new Hα imagesfrom the Isaac Newton Telescope Photometric Hα Survey of theNorthern Galactic Plane which reveal structure behind the filamentarylimb. A faint, thin arc is seen opposite the bright limb, in combinationforming a closed ring. Behind the faint arc a long wide tail isdetected, doubling the size of the nebula. The nebula extends 15 arcminon the sky in total. We have developed a `triple-wind' hydrodynamicalmodel, comprising of the initial `slow' asymptotic giant branch (AGB)wind and the later `fast' stellar wind (the interacting stellar windsmodel), plus a third wind reflecting the motion through the ISM.Simulations at various velocities of the central star relative to theISM indicate that a high velocity of 125 kms-1 is required toreproduce the observed structure. We find that the bright limb and thetail already formed during the AGB phase, prior to the formation of thePN. The closure of the ring arises from the slow-fast wind interaction.Most of the mass lost on the AGB has been swept downstream, providing apotential explanation of the missing-mass problem in PNe. We report aproper motion for the central star of 30 +/- 10masyr -1 inthe direction of the bright limb. Assuming the central star is moving at125 +/- 25kms-1, the distance to the nebula is estimated tobe 850+500-420 pc, consistent with a spectroscopicdistance to the star. Expansion velocities measured from spectroscopicdata of the bright filaments are consistent with velocities measuredfrom the simulation. Sh2-188 is one of the largest PNe known, with anextent of 2.8 pc. The model shows that this size was already set duringthe AGB phase.
| Precatalysmic binary systems.
Not Available
| The distances of highly evolved planetary nebulae
The central stars of highly evolved planetary nebulae (PNe) are expectedto have closely similar absolute visual magnitudes MV. Thisenables us to determine approximate distances to these sources where oneknows their central star visual magnitudes, and levels of extinction. Wefind that such an analysis implies values of D which are similar tothose determined by Phillips; Cahn, Kaler & Stanghellin; Acker, andDaub. However, our distances are very much smaller than those of Zhang;Bensby & Lundstrom, and van de Steene & Zijlstra. The reasonsfor these differences are discussed, and can be traced to errors in theassumed relation between brightness temperature and radius.Finally, we determine that the binary companions of such stars can be nobrighter than MV~ 6mag, implying a spectral type of K0 orlater in the case of main-sequence stars.
| Unresolved Hα Enhancements at High Galactic Latitude in the WHAM Sky Survey Maps
We 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 stars
This paper presents new investigations on coherent scattering in theforward direction (orders of magnitude; conservation of energy;dependence of scattered light on geometry and wavelength), and on howscattered light contamination in the spectrum of reddened stars ispossibly related to as yet unexplained observations (the diminution ofthe 2200 Å bump when the obscuring material is close to the star,the difference between Hipparcos and photometric distances). This paperthen goes on to discuss the fit of the extinction curve, a possible roleof extinction by the gas in the far-UV, and the reasons of theinadequacy of the Fitzpatrick and Massa [ApJSS, 72 (1990) 163] fit.
| The Low- and Intermediate-Mass Stellar Population in the Small Magellanic Cloud: The Central Stars of Planetary Nebulae
We present a study on the central stars (CSs) of planetary nebulae (PNs)observed in the Small Magellanic Cloud (SMC) with the Space TelescopeImaging Spectrograph (STIS) instrument on board the Hubble SpaceTelescope (HST). The stellar magnitudes have been measured usingbroadband photometry, and Zanstra analysis of the nebulae provided thestellar temperatures. From the location of the CSs on the H-R diagram,and by comparing the observed CSs with current models of stellarevolution, we infer the CS masses. We examine closely the possibility oflight contamination in the bandpass from an unrecognized stellarcompanion, and we establish strong constraints on the existence andnature of any binary companion. We find an average mass of 0.63Msolar, which is similar to the mass obtained for a sample ofCSs in the LMC (0.65 Msolar). However, the SMC and LMC CSmass distributions differ slightly, with the SMC sample lacking anintermediate-mass stellar population (0.65-0.75 Msolar). Wediscuss the significance and possible reasons for the difference betweenthe two mass distributions. In particular, we consider the differencesin the star formation history between the clouds and the mass-loss ratedependence on metallicity.Based on observations made with the NASA/ESA Hubble Space Telescopeobtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc., underNASA contract NAS 5-26555.
| Me 1-1: A PN containing a cool star
We report the detection of a cool stellar component at the center of theplanetary nebula (PN) Me 1-1 and present optical spectra of the system.From measurements of nebular emission lines, we have derived electrontemperature, density and chemical composition. Heavy elementalabundances deduced from collisionally excited lines (CELs) are comparedwith those derived from optical recombination lines (ORLs). The electrontemperature and density deduced from the nebular analysis were used tocalculate the nebular continuum emission, which was then subtracted fromthe observed spectrum in order to obtain the spectrum of the coolstellar component apparent in the observed spectrum. We calculate B andV magnitudes of the cool companion and obtain a color index of B-V=1.20.By comparing the spectrum of the cool star with standard spectra inPickles's 1998 Stellar Flux Library, we find that the cool component hasthe spectral type of a K3-4 bright giant. Our analysis suggests that Me1-1 is probably a yellow symbiotic system.
| Differential rotation of cool active stars
The surface differential rotation of active solar-type stars can beinvestigated by means of Doppler and Zeeman-Doppler Imaging, bothtechniques enabling one to estimate the short-term temporal evolution ofphotospheric structures (cools spots or magnetic regions). Afterdescribing the main modeling tools recently developed to guarantee aprecise analysis of differential rotation in this framework, we detailthe main results obtained for a small number of active G and K fastrotating stars. We evoke in particular some preliminary trends that canbe derived from this sample, bearing the promise that major advances inthis field will be achieved with the new generation ofspectropolarimeters (ESPaDOnS/CFHT, NARVAL/TBL).
| 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}
| Properties of Galactic and MC CSPN disclosed by Far-Ultraviolet Spectroscopy
We are performing a comprehensive spectral analysis of FUSE, IUE, HSTand ground-based data of Galactic, and Large and Small Magellanic Cloud(LMC and SMC) central stars of planetary nebulae (CSPN), with the aim ofunderstanding the overall evolution of PN in environments of differingmetallicities. We determine the parameters of the central stars as wellas the characteristics of the circumstellar environment.
| WeBo 1: A Young Barium Star Surrounded by a Ringlike Planetary Nebula
WeBo 1 (PN G135.6+01.0), a previously unrecognized planetary nebula witha remarkable thin-ring morphology, was discovered serendipitously onDigitized Sky Survey images. The central star is found to be a late-typegiant with overabundances of carbon and s-process elements. The giant ischromospherically active and photometrically variable, with a probableperiod of 4.7 days; this suggests that the star is spotted, and that 4.7days is its rotation period. We propose a scenario in which onecomponent of a binary system became an asymptotic giant branch (AGB)star with a dense stellar wind enriched in C and s-process elements; aportion of the wind was accreted by the companion, contaminating itsatmosphere and spinning up its rotation. The AGB star has now become ahot subdwarf, leaving the optical companion as a freshly contaminatedbarium star inside an ionized planetary nebula.
| The Binary Central Star of the Planetary Nebula A35
Using new Far Ultraviolet Spectroscopic Explorer (FUSE) observations inconjunction with Space Telescope Imaging Spectrograph (STIS) andInternational Ultraviolet Explorer archive data, we have modeled bothcomponents of the binary central star of the planetary nebula A35. Thewhite dwarf (the ionizing star) was modeled using the non-LTE,plane-parallel code TLUSTY. We find its parameters to beTeff=80+/-3 kK, logg=7.70+0.13-0.18 cms-2, and [He/H]=-4+/-1 and C, N, O, Si, and Fe to beunderabundant by 2 orders of magnitude with respect to their solarvalues. This confirms its classification as a DAO white dwarf, and usingthe Hipparcos distance D=163 pc, we derive a radius ofRWD~=1.65×10-2 Rsolar and a massof M~=0.5 Msolar. The modeling of the far-ultraviolet spectraalso constrains the extinction value; EB-V=0.04+/-0.01.Furthermore, the FUSE and STIS data allow us to measure the molecularhydrogen (H2) and neutral hydrogen (H I) columndensities along the sight line, the majority of which we believe isassociated with the circumstellar material. The FUSE spectrum is bestfitted with a two-component model for H2,consisting of a cool component (T=200 K) withlogN(H2,cool)=19.6+0.1-0.2cm-2 and a hot component (T~=1250 K) withlogN(H2,hot)=17.4+0.3-0.4cm-2. The H I column density is logN(HI)=20.9+/-0.1cm-2. Assuming a typical gas/dust ratio for the interstellarmedium, our value of EB-V implies that logN(HI)=20.8cm-2 of this is circumstellar. Our low extinction value andthe measured column densities imply that there is essentially no dust inthe nebula. Assuming that the neutral and molecular hydrogen iscontained in a sphere of comparable dimensions to the ionized shell, wederive the combined mass of the circumstellar H I andH2 to be ~2.7 Msolar. Other geometries,such as a shell surrounding the ionized region, can be excluded. Themass of the ionized hydrogen is <~1% that of the neutral material.From comparison with evolutionary calculations, we estimate theprogenitor mass to be ~3.2 Msolar. Based on observations madewith the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer. FUSE isoperated for NASA by Johns Hopkins University under NASA contractNAS5-32985.
| Doppler images of starspots
I present a literature survey of the currently available Doppler imagesof cool stars. The 65 individual stars with Doppler images consist of 29single stars and 36 components in close binaries. Out of the total, 31were observed only once but 12 stars are (or were) being monitored foryears. Each image for each star is identified with the time when it wasobserved, whether photometry was used in the imaging, the inclination ofthe stellar rotation axis, the vsin i, the stellar rotation period, andwhether a polar spot and/or a high-latitude or low-latitude spot wasseen. The type of variable star and its M-K spectral classification isalso listed to identify the evolutionary status. The sample consists of3 classical T Tauri stars, 8 weak-lined T Tauri's, 27 main-sequencestars, 9 subgiants, and 18 giants. The total number of Doppler images is245 as of June 2002.
| Measuring starspots on magnetically active stars with the VLTI
We present feasibility studies to directly image stellar surfacefeatures, which are caused by magnetic activity, with the Very LargeTelescope Interferometer (VLTI). We concentrate on late typemagnetically active stars, for which the distribution of starspots onthe surface has been inferred from photometric and spectroscopic imaginganalysis. The study of the surface spot evolution during consecutiverotation cycles will allow first direct measurements (apart from theSun) of differential rotation which is the central ingredient ofmagnetic dynamo processes. The VLTI will provide baselines of up to 200m, and two scientific instruments for interferometric studies at near-and mid-infrared wavelengths. Imaging capabilities will be made possibleby closure-phase techniques. We conclude that a realistically modeledcool surface spot can be detected on stars with angular diametersexceeding ~ 2 mas using the VLTI with the first generation instrumentAMBER. The spot parameters can then be derived with reasonable accuracy.We discuss that the lack of knowledge of magnetically active stars ofthe required angular size, especially in the southern hemisphere, is acurrent limitation for VLTI observations of these surface features.
| X-Ray Emission from Central Binary Systems of Planetary Nebulae
We study the conditions under which a main-sequence binary companion tothe central ionizing star of a planetary nebula (PN) might becomemagnetically active and thereby display strong X-ray luminosity,LX>~5×1029 ergs s-1. Sincemost PNs are older than few billion years, any main-sequence companionwill rotate too slowly to have magnetic activity and hence bright X-rayemission unless it is spun up. We demonstrate that if the orbitalseparation during the asymptotic giant branch (AGB) phase of the PNprogenitor is a<~30-60 AU, main-sequence companions in the spectraltype range F7-M4 (mass range0.3Msolar<~M2<~1.3Msolar) willaccrete enough angular momentum from the AGB wind to rotate rapidly,become magnetically active, and exhibit X-ray luminositiesLX>~5×1029 ergs s-1. Lowermass M stars and brown dwarfs can also become magnetically active, butthey should have small orbital separations and hence are less likely tosurvive the AGB phase of the progenitor. For orbital separation ofa<~0.3 AU, i.e., for a binary systems that went through a commonenvelope phase, the fast wind from the central white dwarf (WD) starwill interact with (and potentially disrupt) the companion's corona onthe side facing the central star, while for a<~6 Rsolar,i.e., an orbital period of Porb<~30 hr, the WD's fast windwill compress a dense small region near the surface of the companion.This region may thermally emit X-rays with nonnegligible luminosity. Weestimate that 20%-30% of elliptical PNs and 30%-50% of bipolar PNs arelikely to have magnetically active companions that will revealthemselves in X-ray observations. Reanalysis of Chandra spectroscopy ofthe compact central source of NGC 7293 indicates that the emittingregion of this object possesses abundance anomalies similar to those ofcoronally active main-sequence stars. High-resolution X-ray spectroscopyof this and other compact sources in PNs are necessary to confirm acoronal origin for the X-ray emission.
| HST Observations of Sakurai's Object (V4334 Sgr) and Related Stars
We describe our ongoing program of HST observations of Sakurai's Object(V4334 Sgr). Direct WFPC2 imaging from August 1996 through August 2000reveals no transient features (such as light echoes), and documents thedecline of the star to below 24th visual magnitude in 2000. Thesurrounding planetary nebula has shown no changes from 1996 through2000. There are no obvious peculiar features (such as blobs or knots) inthe immediate vicinity of the star. We also have in place atarget-of-opportunity program to obtain UV spectra with HST in the eventthat the star begins to retrace its evolution back to high surfacetemperature. We also present older HST FOC imaging of V605 Aql. Thecentral object is a resolved nebula that emits in [O III] (but not inhydrogen), whose 0''.6 diameter is consistent with a dust cloud ejectedduring the 1919 outburst. The central star itself is not seen due to itsbeing embedded in the nebula. Several other central stars (including H3-75, IC 2120, and Abell 14) have late-type nuclei and no evidence forhot companions. They may be further candidates for `born-again'red-giant nuclei.
| 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.
| A Catalog and Atlas of Cataclysmic Variables: The Living Edition
The Catalog and Atlas of Cataclysmic Variables (Edition 1: Downes &Shara; Edition 2: Downes, Webbink, & Shara) has been a valuablesource of information for the cataclysmic variable community. However,the goal of having a central location for all objects is slowly beinglost as each new edition is generated. There can also be a long timedelay between new information becoming available on an object and itspublication in the catalog. To eliminate these concerns, as well as tomake the catalog more accessible, we have created a Web site which willcontain a ``living'' edition of the catalog. We have also added orbitalperiod information, as well as finding charts for novae, to thecatalog.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| PN G218.9-10.7: a galactic emission nebula of unique morphology
We present an Hα + [N II] narrow band image and optical spectra ofthe galactic nebula PN G218.9-10.7 that has been hardly studied up tonow and is suspected to be a planetary nebula. Its morphology is quiteunusual: the nebula appears to consist of both symmetric components andasymmetric diffuse ones, and also displays long straight filaments inthe east. It rather looks like a combination of morphological featuresfound in HII regions, supernova remnants and planetary nebulae. Thenebula has very low [O III] emission, and is close to a very blue faintstar that has been supposed to be of high gravity nature. Detaileddescription and attempt to give an interpretation of the morphology forthis nebula are discussed. The spectral results of the object have beenderived, such as the interstellar extinction, excitation class, electrontemperature, and electron density. Based on observations obtained at theEuropean Southern Observatory and the Las Campanas Observatory
| Infrared Planetary Nebulae in the NRAO VLA Sky Survey
In order to construct a sample of planetary nebulae (PNe) unbiased bydust extinction, we first selected the 1358 sources in the IRAS PointSource Catalog north of J2000 declination delta=-40^deg having measuredS(25 μm)>=1 Jy and colors characteristic of PNe: detections orupper limits consistent with both S(12 μm)<=0.35S(25 μm) andS(25 μm)>=0.35S(60 μm). The majority are radio-quietcontaminating sources such as asymptotic giant branch stars. Free-freeemission from genuine PNe should make them radio sources. The 1.4 GHzNRAO VLA Sky Survey (NVSS) images and source catalog were used to rejectradio-quiet mid-infrared sources. We identified 454 IRAS sources withradio sources brighter than S~2.5 mJy beam^-1 (equivalent to T~0.8 K inthe 45" FHWM NVSS beam) by positional coincidence. They comprise 332known PNe in the Strasbourg-ESO Catalogue of Galactic Planetary Nebulaeand 122 candidate PNe, most of which lie at very low Galactic latitudes.Exploratory optical spectroscopic observations suggest that most ofthese candidates are indeed PNe optically dimmed by dust extinction,although some contamination remains from H II regions, Seyfert galaxies,etc. Furthermore, the NVSS failed to detect only 4% of the known PNe inour infrared sample. Thus it appears that radio selection can greatlyimprove the reliability of PN candidate samples withoutsacrificingcompleteness.
| Classification and spectral analysis of faint central stars of highly excited planetary nebulae
We present narrow-band images of nine planetary nebulae (PN) and aspectral analysis of four of their central stars (CSPN) by means ofmodel atmosphere techniques based on medium-resolution optical spectra.Four of our CSPN are unambiguously identified. They are very hot (T_eff,>100 kK) and have about 1 - 2 times solar He/H abundance ratios. (theexciting stars of PN G214.9+07.8, PNG231.8+04.1, PN G283.6+25.3, PNG293.6+10.9). Three other of our PN are candidates forAbell 35-like objects: The supposed central stars ofPN G257.5+00.6 and PN G277.1-03.8exhibit F-type spectra while probably the hotter exciting star escapesdetection in the optical. Absorption features is the spectrum of thecentral star of PN G283.6+25.3 suggest the presenceof a cool companion. The images of PN G277.1-03.8display two close stars at its center which both show F-type spectra. Itappears likely that this is a binary system but better spectra andadditional UV spectra are required in order to successfully identify theexciting central star. Based on observations collected at the EuropeanSouthern Observatory, La Silla, Chile (proposals 56.D-0717, 57.D-0148)
| AGB stars in binaries and their progeny
An AGB star in a binary system is likely to pollute its companion withcarbon- and s-process-rich matter. After the AGB star has faded into anunconspicuous white dwarf, the polluted companion enters the zoo ofstars with chemical peculiarities. In this paper, the progeny of AGBstars in binary systems are identified among existing spectroscopicclasses (Abell 35-like, binary post-AGB, WIRRing, dwarf Ba and C,subgiant CH, Ba, CH, S, yellow symbiotics) and their filiation isdiscussed from the properties of their eccentricity -- period diagrams.
| Emerging trends of optical interferometry in astronomy
The current status of the high spatial resolution imaging interferometryin optical astronomy is reviewed in the light of theoreticalexplanation, as well as of experimental constraints that exist in thepresent day technology. The basic mathematical interlude pertinent tothe interferometric technique and its applications in astronomicalobservations are presented in detail. An elaborate account of the randomrefractive index fluctuations of the atmosphere producing randomaberrations in the telescope pupil, elucidating the trade offs betweenlong-exposure and short-exposure imaging is given. Further, the othermethods viz., (i) speckle spectroscopy, (ii) speckle polarimetry, (iii)phase closure, (iv) aperture synthesis, (v) pupil plane interferometry,(vi) differential speckle interferometry etc., using single moderate orlarge telescopes are described as well. The salient features of variousdetectors that are used for recording short-exposure images aresummarized. The mathematical intricacies of the data processingtechniques for both Fourier modulus and Fourier phase are analyzed; thevarious schemes of image restoration techniques are examined as wellwith emphasis set on their comparisons. The recent technologicalinnovation to compensate the deleterious effects of the atmosphere onthe telescope image in real-time is enumerated. The experimentaldescriptions of several working long baseline interferometers in thevisible band are summarized. The astrophysical results obtained tilldate are highlighted.
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| özdevim Sað Açýklýk: | -60 |
| özdevim Yükselim: | -14.1 |
| B-T magnitude: | 10.823 |
| V-T magnitude: | 9.796 |
Kataloglar ve belirtme:
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INHABITED SKY
