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Precatalysmic binary systems.
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| Starspot activity in late stars: Methods and results
Three types of methods for studying the surface inhomogeneities of coolstars and the results of their use on type BY Dra, RS CVn, FK Com, and TTau variables are discussed. The current relevance of traditionalphotometric methods and the advantages of the zonal spottedness modelare pointed out. Dependences of the maximum total areas, averagelatitudes, and temperatures of spots on the global parameters of thestars are given. Analogs of the solar cycle in the variations of theareas and latitudes of starspots are examined, as well as the effects ofdifferential rotation and active longitudes.
| Analysis of 26 barium stars. I. Abundances
Context: .We present a detailed analysis of 26 barium stars, includingdwarf barium stars, providing their atmospheric parameters (T_eff, logg, [Fe/H], v_t), and elemental abundances. Aims: .We aim atderiving gravities and luminosity classes of the sample stars, inparticular to confirm the existence of dwarf barium stars. Accurateabundances of chemical elements were derived. We present the abundanceratios between nucleosynthetic processes, by using Eu and Ba asrepresentatives of the r- and s-processes. Methods:.High-resolution spectra were obtained with the FEROS spectrograph atthe ESO-1.52 m Telescope, along with photometric data with Fotrap at theZeiss telescope at the LNA. The atmospheric parameters were derived inan iterative way, with temperatures obtained from colour-temperaturecalibrations. The abundances were derived using spectrum synthesis forLi, Na, Al, α-, iron-peak, s-, and r-element atomic lines, and forC and N molecular lines. Results: .Atmospheric parameters in therange 4300 < T_eff < 6500, -1.2 < [Fe/H] < 0.0, and 1.4≤ log g < 4.6 were derived, confirming that our sample containsgiants, subgiants, and dwarfs. The abundance results obtained for Li,Al, Na, α-, and iron-peak elements for the sample stars show thatthey are compatible with the values found in the literature for normaldisk stars in the same range of metallicities. Enhancements of C, N, andheavy elements relative to Fe, that characterise barium stars, werederived and showed that [X/Ba] vs. [Ba/H] and [X/Ba] vs. [Fe/H] presentdifferent behaviour as compared to [X/Eu] vs. [Eu/H] and [X/Eu] vs.[Fe/H], reflecting the different nucleosynthetic sites for the s- andr-processes.
| 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.
| Zonal Model of Starspots. Application to RS CVn Systems
Model results on starspots in 15 chromospherically active type RS CVnbinary systems are presented. The dependences of the parameters of thespots on the principal characteristics of the stars (spectral class,luminosity class, rotation, Rossby number) are examined. Latitudinaldrift of the spots, cycles in the spot activity, and differentialrotation are found in 9 of the stars.
| Spots, activity cycles, and differential rotation on cool stars
The first results are reported from a search for activity cycles instars similar to the sun based on modelling their spotting with analgorithm developed at the Crimean Astrophysical Observatory. Of themore than thirty program stars, 10 manifested a cyclical variation intheir central latitudes and total starspot area. The observed cycleshave durations of 4-15 years, i.e., analogous to the 11 year Schwabesunspot cycle. Most of the stars have a rough analog of the solarbutterfly pattern, with a reduction in the average latitude of the spotsas their area increases. A flip-flop effect during the epoch of themaximum average latitude is noted in a number of these objects (e.g.,the analog LQ Hya of the young sun or the RS CVn-type variable V711Tau), as well as a reduction in the photometric rotation period of astar as the spots drift toward the equator, an analog of thedifferential rotation effect in the sun. Unlike in the sun, the observedspot formation cycles do not correlate uniquely with other indicators ofactivity chromospheric emission in the CaII HK lines (Be Cet, EKDra, Dx Leo), H line emission (LQ Hya, VY Ari, EV Lac), or cyclicalflare activity (EV Lac). In V833 Tau, BY Dra, EK Dra, and VY Ari shortSchwabe cycles coexist with long cycles that are analogous to theGleissberg solar cycle, in which the spotted area can approach half theentire area of the star.
| 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).
| Kinematics of chromospherically active binaries and evidence of an orbital period decrease in binary evolution
The kinematics of 237 chromospherically active binaries (CABs) werestudied. The sample is heterogeneous with different orbits andphysically different components from F to M spectral-type main-sequencestars to G and K giants and supergiants. The computed U, V, W spacevelocities indicate that the sample is also heterogeneous in velocityspace. That is, both kinematically younger and older systems exist amongthe non-evolved main sequence and the evolved binaries containing giantsand subgiants. The kinematically young (0.95 Gyr) subsample (N= 95),which is formed according to the kinematical criteria of moving groups,was compared with the rest (N= 142) of the sample (3.86 Gyr) toinvestigate any observational clues of binary evolution. Comparing theorbital period histograms between the younger and older subsamples,evidence was found supporting the finding of Demircan that the CABs losemass (and angular momentum) and evolve towards shorter orbital periods.The evidence of mass loss is noticeable on the histograms of the totalmass (Mh+Mc), which is compared between theyounger (only N= 53 systems available) and older subsamples (only N= 66systems available). The orbital period decrease during binary evolutionis found to be clearly indicated by the kinematical ages of 6.69, 5.19and 3.02 Gyr which were found in the subsamples according to the periodranges of logP<= 0.8, 0.8 < logP<= 1.7 and 1.7 < logP<=3, respectively, among the binaries in the older subsample.
| The bipolarity of the highest Galactic latitude planetary nebula, LoTr 5 (PN G339.9+88.4), around IN Com
High-resolution, spatially resolved, long-slit profiles of the [O III]5007-Å emission line of the highest Galactic latitude planetarynebula, LoTr 5, have been obtained with the Manchester EchelleSpectrometer (MES-SPM) on the San Pedro Martir (SPM) 2.1-m telescope.These are compared with a deep narrow-band [O III] 5007-Å mosaicimage obtained with the same system.This faint nebula, at a distance of >=500 pc from the Galactic plane,is found to be expanding asymmetrically. Some form of bipolar structureis suggested by modelling the position-velocity arrays of line profilesand the new [O III] 5007-Å image. Interestingly, the modelledbipolar axis is nearly perpendicular to the orbital plane of the IN Combinary system; this supports the theories which predict that binarysystems play a part in shaping the outflow.Evidence for interaction of the envelope of LoTr 5 with its localinterstellar medium is also considered.
| Rotational Brightness Modulation and Starspots on the RS CVn-type Stars IN Com, IL Com, UX Ari, and V711 Tau
UBVRI photometric observations and models of spotting are presented forfour noneclipsing RS CVn systems: IN Com (G5III/IV), IL Com (F8V+F8V),UX Ari (K01V+G5V), and V711 Tau (K1IV+G5V). A low amplitude variabilitycaused by cold (T=1700K)spots which can occupy up to 19% of the star''ssurface is confirmed for the little-studied star IL Com. Long-term lightcurves are constructed and the stellar magnitudes and color indices ofthe unspotted photospheres are estimated for IN com, UX Ari, and V711Tau. It is shown that UX Ari becomes bluer with decreasing brightness,so its variability cannot be fully explained in terms of cold spots.Models of spotting on In Com and V711 Tau are constructed from the fullset of available photometric observations. The spots on both of thesevariables lie at middle latitudes and occupy up to 22% (In Com) and 33%(V711 Tau) of the stars'' surfaces. Both stars manifest a tendency forthe width of the spots to decrease as their area increases. This is acrude analog of the Maunder butterflies. These stars experience cyclicalspot activity and have a differential rotation of the type found on thesun.
| Unveiling the Morphology and Kinematics of LoTr 5, the Highest Galactic Latitude PN
A deep [O III] lambda 5007 mosaic image of the highest Galacticlatitude planetary nebula, LoTr 5, has been obtained with the ManchesterEchelle Spectrometer (MES) on the San Pedro Mártir telescope.This image is accompanied by high-resolution, spatially-resolved [O III]lambda 5007 long-slit profiles of the nebula.
| X-ray and UV Views of Hot Gas in Planetary Nebulae (invited review)
Not Available
| An Archive of IUE Low-Dispersion Spectra of the White Dwarf Stars
We have produced an archive of the ultraviolet low-dispersion spectrafor the full set of white dwarf stars observed with the InternationalUltraviolet Explorer (IUE) satellite over the course of its 18 yrmission. This archive contains the spectra of 322 individual degeneratestars which have been processed to optimize the signal-to-noise for eachstar. In particular, all spectra have been corrected for residualtemporal and thermal effects and placed on the Hubble Space TelescopeFaint Object Spectrograph absolute flux scale using procedures describedby Massa & Fitzpatrick. Wherever possible, multiple observations ofindividual stars have been co-added to further enhance signal-to-noiseand have been combined into a single spectrum including the full 1150 to3150 Å wavelength region observed by IUE. The contents of thisspectral archive are described and the details of data reductionprocedures are provided, along with the url for access to the electronicfiles of the processed spectra.
| 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.
| Galactic Planetary Nebulae and their central stars. I. An accurate and homogeneous set of coordinates
We have used the 2nd generation of the Guide Star Catalogue (GSC-II) asa reference astrometric catalogue to compile the positions of 1086Galactic Planetary Nebulae (PNe) listed in the Strasbourg ESO Catalogue(SEC), its supplement and the version 2000 of the Catalogue of PlanetaryNebulae. This constitutes about 75% of all known PNe. For these PNe, theones with a known central star (CS) or with a small diameter, we havederived coordinates with an absolute accuracy of ~0\farcs35 in eachcoordinate, which is the intrinsic astrometric precision of the GSC-II.For another 226, mostly extended, objects without a GSC-II counterpartwe give coordinates based on the second epoch Digital Sky Survey(DSS-II). While these coordinates may have systematic offsets relativeto the GSC-II of up to 5 arcsecs, our new coordinates usually representa significant improvement over the previous catalogue values for theselarge objects. This is the first truly homogeneous compilation of PNepositions over the whole sky and the most accurate one available so far.The complete Table \ref{tab2} is only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/408/1029}
| X-Ray 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.
| 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.
| Doppler imaging of stellar surface structure. XVIII. The very active RS CVn binary UZ Librae revisited
We present eight Doppler images of UZ Librae from the years 1994, 1996,1997, 1998 and 2000. These maps indicate a preferred temperaturedistribution from one year to the other and suggest preferred spotlocations for at least the seven years of our observations. Twoequatorial active regions appear facing towards and opposite the(unseen) companion star. A large and cool polar spot, with two or maybethree appendages extending down to a latitude of 40 degr -50 degr , ispresent and causes the long-term light variability of UZ Lib. Theappendages appear at longitudes very similar to the two equatorialactive regions and sometimes are possibly even attached to them. Nocoherent sign of differential rotation is found for the equatorialregions up to a latitude of approximately +50 degr , but the polarappendages may indicate a general acceleration of the polar regions. Ifinterpreted as being due to differential rotation, if real at all, thenUZ Lib clearly exhibits a non-solar flow pattern.
| The Enigmatic X-Ray Point Sources at the Central Stars of NGC 6543 and NGC 7293
Recent Chandra ACIS-S observations have detected a point source at thecentral star of NGC 6543 and confirmed the point-source nature of thehard X-ray emission from NGC 7293. The X-ray spectra of both sourcespeak between 0.5 and 1.0 keV and show line features indicating a thinplasma at temperatures of a few times 106 K. Their X-rayluminosities are 1030 and 3×1029 ergss-1, respectively. We have considered four differentmechanisms to explain the nature of these sources. The X-ray emissionfrom the central star of NGC 6543 may originate from the coronalactivity of an undetected companion star or from shocks in its faststellar wind, while the hard X-ray emission from NGC 7293 might beascribed to an undetected dMe companion. Follow-up observations areneeded to determine the existence and natures of these stellarcompanions.
| The Catania Automatic Photoelectric Telescope on Mt. Etna: a systematic study of magnetically active stars
A photometric monitoring of about 50 magnetically active stars, that arespread almost all over the H-R diagram, was initiated at the mountainstation of Catania Observatory on Mt. Etna (1750-m a.s.l.) in 1992 withan 80-cm robotic telescope (APT-80) built by AutoScope Co. (USA). Thissystematic survey is now approaching its 10th year anniversary. For mostof the stars, quite well defined solar-like spot maps have been derivedfrom UBV data obtained in different epochs. These data have allowed usto investigate some relevant characteristics of spot activity andvariability on stars, and to obtain clear evidence of long-term activitycycles, in the range from a few to about 10 years, on some of theobserved targets. Starspot maps are constructed by using advanced tools,such as massive parallel computing and are based on Maximum Entropy andTikhonov regularization criteria. Selected results are here presented.Our systematic observation program is still underway and a secondAPT80/2, equipped with a CCD camera, will pair the APT80/1 on the samesite. Its operation is foreseen for mid 2002.
| FAUST observations near the North Galactic Pole
We analyse a UV observation with FAUST in the direction of the NorthGalactic Pole. The region includes a cirrus cloud (G251.2+73.3) and adark globule, and the FAUST image contains 75 UV sources. We discuss theUV source detection and their identification with optical counterparts.We use, for the first time, low-resolution spectral information as theprimary means of identifying possible optical counterparts. This iscomplemented, and sometimes modified, by optical information availablefrom existing data bases. The results are interpreted with the help ofmaps of the distribution of far-infrared emission and of the neutralhydrogen gas. We discuss the types of objects found, the degree ofmatching with the predictions of our UV Galaxy model, and the generalbehaviour of the Galactic UV extinction in this Milky Way part. Wecompare the UV results for this region with similar observations in thesame neighbourhood, which are less affected by dust, and attempt toexplain the peculiar distribution of UV magnitudes as a result of apeculiar distribution of foreground dust, which does not follow theaccepted dust-to-gas relation.
| Three-colour Photometry of IN Comae
Not Available
| Linear Polarization of Precataclysmic Variables
The optical linear polarization of three precataclysmic variables wasmeasured in B and R. A noticeable polarization was detected only inBD+50o2869. In the other two cases, the polarization isprobably interstellar in origin.
| ROSAT Observations of X-Ray Emission from Planetary Nebulae
We have searched the entire ROSAT archive for useful observations tostudy X-ray emission from Galactic planetary nebulae (PNs). The searchyields a sample of 63 PNs, which we call the ROSAT PN sample. About20%-25% of this sample show X-ray emission; these include 13 definitedetections and three possible detections (at a 2 σ level). AllX-ray sources in these PNs are concentrated near the central stars. OnlyA30, BD +30°3639, and NGC 6543 are marginally resolved by the ROSATinstruments. Three types of X-ray spectra are seen in PNs. Type 1consists of only soft X-ray emission (<0.5 keV), peaks at 0.1-0.2keV, and can be fitted by blackbody models at temperatures1-2×105 K. Type 2 consists of harder X-ray emission,peaks above 0.5 keV, and can be fitted by thin plasma emission models attemperatures of a few times 106 K. Type 3 is a composite of abright type 1 component and a fainter type 2 component. Unresolved softsources with type 1 spectra or the soft component of type 3 spectra aremost likely photospheric emission from the hot central stars. Absorptioncross sections are large for these soft-energy photons; therefore, onlylarge, tenuous, evolved PNs with hot central stars and small absorptioncolumn densities have been detected. The origin of hard X-ray emissionfrom PNs is uncertain. PNs with type 2 spectra are small, dense, youngnebulae with relatively cool (<<105 K) central stars,while PNs with type 3 X-ray spectra are large, tenuous, evolved nebulaewith hot central stars. The hard X-ray luminosities are also differentbetween these two types of PNs, indicating perhaps different origins oftheir hard X-ray emission. Future Chandra and XMM observations with highspatial and spectral resolution will help to understand the origin ofhard X-ray emission from PNs.
| The UV (IUE) spectrum of the planetary nebula PC 11 (HD 149427)
The UV spectrum of PC 11 is found to show variations in the strength ofthe O III] 1666Ä , N III] 1750Ä and C III] 1909Ä emissionlines. The detection of continuum emission in the wavelength interval2650Ä to 3200Ä indicates that the central star of PC 11 has anearly F-type dwarf companion. The very low level of UV continuum in thewavelength interval 1150Ä to 1900Ä and the non-detection ofthe central star in the UV images recently taken with HST suggest thatthe hot whitedwarf or sub-dwarf like central star may be obscured by adusty disk. The variations in the UV emission lines observed during theperiod 1987 to 1994 may be the consequence of variable emission comingfrom high-velocity jet-like emission visible in optical images alsotaken with HST in the light of [O III]. Based on our UV observations, weconfirm our identification of PC 11 as a planetary nebula with a closebinary central star. Adopting the absolute magnitude of a F0V companionyields a distance of 485 pc to PC 11. If we assume a typical expansionvelocity of 12.5 km s-1 and considering the observed angulardiameter of the nebula (4.1''), we find the age of PC 11 tobe 376 years. The AGB phase of evolution of the central star seems tohave been terminated only recently. Based on observations obtained withthe International Ultraviolet Explorer, retrieved from the IUE FinalArchive at VILSPA and on observations made with the NASA/ESA HubbleSpace Telescope, obtained from the data Archive at the Space TelescopeScience Institute, which is operated by the Association of Universitiesfor Research in Astronomy, Inc., under NASA contract NAS5-26555
| Ultraviolet Evidence for a Binary Nucleus of the Planetary Nebula SH 2-71
Archival IUE spectra of the planetary nebula Sh 2-71 show a variable MgII lambda2800 emission line superposed on a variable stellar continuum.The Mg II feature is thought to be excited in the chromosphere of thecooler component of a binary nucleus, although other causes are alsoplausible.
| The shape of the LoTr 5 planetary nebula
We observed the large and faint planetary nebula around IN Com in Halpha and N II light with a coronagraphic charge-coupled device on theWise Observatory reflector, blocking the light from the central star.Our goal was to provide a second image of the object with which toconfirm the features seen in the only published photograph from thepaper by Longmore & Tritton reporting the discovery of this object.The nebula is extremely faint, but a combination of images totallingabout one and a half hours of exposure shows it fairly well. A novelimage processing algorithm has been applied to the noisy image in orderto reveal faint extended details of the images. The algorithm is basedon a non-linear self-adaptive filter applied to the wavelet transform ofthe image. The nebula is not round or elliptical, but shows a two-lobedor possibly three-lobed morphology, as well as a peculiar hole-likefeature east of the central star. There is definite east-west andslightly less definite north-south asymmetry.
| 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.
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