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Abstracts
M. Baes1, E. Vidal1, H. van Winckel2, P. Deroo2, C. Gielen2 1 Ghent University, Belgium 2 Instituut voor Sterrenkunde, K.U. Leuven, Belgium We present SKIRT, an efficient 3D Monte Carlo radiative transfer code designed to treat continuum radiative transfer problems in dusty systems. In particular, we are using SKIRT to investigate the geometry, composition and formation of circumbinary dust disks around post-AGB stars. The main novelty in SKIRT is the use of partly polychromatic photon packages, which allow to a very efficient radiative transfer algorithm. We test the accuracy and the numerical requirements of the SKIRT code by comparing its results with recent 1D and 2D benchmark calculations. We demonstrate that the common belief that Monte Carlo radiative transfer is slow, is not valid for state-of-the-art Monte Carlo codes where modern optimization techniques are included. Moreover, the very limited memory requirements of Monte Carlo radiative transfer make high-resolution three-dimensional radiative transfer simulations possible, while this might be more challenging for traditional grid-based codes.
Valentin Bujarrabal Observatorio Astronomico Nacional, Spain Molecular gas often appears in nebulae around post-AGB stars, being the main component of relatively young objects. Molecules are rare in evolved planetary nebulae (PNe), because the relatively hot star and diffuse nebula yield strong photodissociation. In these objects, molecules are often found just in certain parts of the nebulae, like equatorial tori or axial clumps; PDRs and HII regions are well developed in these sources. In young PNe, however, the molecular emission, particularly of CO, probes most of the nebular material, and many species are observed. In some intermediate-evolution nebulae, photo- or shock-induced chemistry produces high abundances of radicals and large molecules. The chemistry of different kinds of objects is discussed, including standard PNe, yellow super/hypergiants, and rotating disks around post-AGB stars.
Marcin Cikala and Cezary Galan Centrum Astronomii Uniwersytetu Mikolaja Kopernika w Toruniu, Poland
G. Cherini, A. Siviero et al. INAF - Astronomical Observatory of Padova, Italy The recent behaviour of the yellow, low excitation symbiotic star V471 Per is investigated on the basis of absolute spectrophotometry, high resolution Echelle spectroscopy and UBVRI CCD photometry. A photoionizated modeling of the circumstellar nebula is performed.
Romano L.M. Corradi Isaac Newton Group of Telescopes, Spain I present IPHAS, the Halpha imaging survey of the Northern Galactic Plane that we are carrying on at the 2.5m INT telescope at La Palma. The survey is expected to discover about 50000 new Hα emitting stars and nebulae, including a number of new symbiotic stars. I discuss the color-color diagrams used to distinguish among the different classes of objects, and present the first discoveries of new symbiotic stars by IPHAS.
Cian Crowley Trinity College Dublin, Ireland I will discuss the results of an analysis of high-resolution ultraviolet and optical datasets of a sample of eclipsing symbiotic systems. These binaries contain giants differing in spectral type and abundances. The optical data provides information on the photospheric abundances and conditions, while the variable absorption features in the ultraviolet spectra (taken at a number of different orbital phases) diagnose the outflowing material in the cool wind of the giant star. It is found that giants of differing evolutionary status possess similar wind conditions and most likely the same wind-driving mechanism. This information provides vital spatially-resolved constraints which are required for the modelling of these winds. Preliminary models using the Phoenix stellar atmosphere code are also presented.
Pieter Deroo Instituut voor Sterrenkunde - K.U.Leuven, Belgium In recent years it became clear that among post-AGB stars binarity is a widespread phenomenon. These binaries have distinct observational characteristics including a broad infrared excess pointing to the presence of both hot and cool dust in a disc geometry around the central object. Kinematical information of several objects by CO measurements confirms the presence of a Keplerian circumbinary disc. Although the presence of a circumbinary disc is now well established, its actual structure but also its formation, stability and evolution remain largely unknown. We therefore used the VLTI/MIDI interferometer to observe the discs around a sample of post-AGB binaries. These measurements show the very compact nature of the circumstellar environment around binary post-AGBs and confirm the disc interpretation of their SED. In addition, for some objects a lower visibility is observed in the continuum radiation than in the emission feature originating from crystalline silicates. This is interpreted as a geometrical difference between the compact highly crystalline emission emerging from close to the star and the larger continuum emitting total disc surface. Whether this is a result of the formation process of the disc, or due to annealing during the long storage time in the disc is not clear.
M. Eriksson1, H. Veenhuizen2, H. Nilsson3 1 Space Telescope Science Institute, 3700 San Martin drive, Baltimore, MD 21218, US 2 University of Kalmar, 391 82 Kalmar, Sweden 3 Lund Observatory, Lund University, Box 43, 221 00 Lund, Sweden A set of equations are put into a code forming a procedure to derive intensities of fluorescence lines based on both physical properties of the fluorescent plasma as well at its location relative to the origin of the pumping emission. In a first test, the code is applied to symbiotic stars and effort is made on explaining under which circumstances the two known Fe II channels pumped by C IV are activated. For the channel at 1548.204 Å, which is the most frequently observed to be active, there is good agreement between results of the code and observed resulting Fe II line strengths. Fluorescence lines resulting from pumping through the other channel at 1548.411 Å can, according to the results of the code, only occur in systems where a fast outflow from the white dwarf wind is present. Interestingly, discussions or conclusions about white dwarf winds are found in literature for all symbiotic systems in which observation of Fe II fluorescence lines from the w2D3/2 level is reported.
Adam Frankowski IAA, Universite Libre de Bruxelles, Belgium N.Copernicus Astronomical Center, Poland A unified evolutionary scheme that includes post-AGB systems, barium stars, symbiotics, and related systems, explaining their similarites as well as differences. Can we construct it? One of the main issues involved is: how to reproduce orbital period distributions for these families of evolved binaries? We compare these various classes of objects and suggest that important clues are offered by a handful of a bit awkward members of the stellar families in question. Among these telling cases is 56 Peg, a barium star that has recently been found to be a rather special spectroscopic binary. Another example is WeBo 1, a Planetary Nebula hosting a barium star in the center. A quite peculiar subclass of symbiotics, the d'-types, notable for their spectral properties and high spin rates, seems also relevant. We analyze the characteristics of both 'average' and 'extreme' objects and show how they bring us closer to a consistent evolutionary picture.
M. Friedjung1, R.F. Viotti2, C. Rossi3, R. Gonzalez-Riestra4, T. Iijima5, F. Montagni6 1 IAP, Paris 2 INAF-IASF, Roma 3 La Sapienza University, Roma 4 XMM SOC, VILSPA, Madrid 5 INAF-Padova Observatory, Asiago Section 6La Sapienza University, Roma We present a review of the multifrequency observations of the symbiotic star AG Dra during the last quarter of century, which were characterised by a sequence of 5 ?active phases? and long lasting periods of quiescence. We discuss the results of UV and X-ray observations and compare with the coordinated optical ones. In several cases the behaviour of AG Dra appears unexpected (such as the strong decline of the X-ray flux during the outbursts) which requires new ways to approach the problem of the violent events in cataclysmic stars. Suggestions for future studies are given.
Clio Gielen Institute of Astronomy, Katholieke Universiteit Leuven, Belgium The number of binary post-AGB stars known in the galaxy is significant, yet their evolutionary status is far from understood. The orbital elements of our sample indicate that these objects must have undergone severe binary interaction when the primary was at giant dimension. Evidence is growing that all these evolved binaries are surrounded by circumbinary Keplerian dusty disks. We present the first results of our SED-modelling and detailed study of the mineralogy using Spitzer-IRS and TIMMI2 spectra. We find the dust to be O-rich and highly crystalline. Features of crystalline olivine and pyroxene, forsterite and enstatite, dominate the spectra. Our SED-modelling shows the presence of large grains,to account for the 850 micron flux. This together with the crystallinity is evidence for efficient dust processing in a stable Keplerian disk.
M. Gromadzki1, J. Mikolajewska1, M. Borawska2, A. Lednicka2 1 N. Copernicus Astronomical Center, Poland 2 Warsaw University Observatory, Poland We identified 126 symbiotic stras in ASAS, OGLE and MACHO databases. The light curves of 74 systems were good enough to perform search for periodic changes. We will present and discuss preliminary results of our search.
Marcin Hajduk1, Ryszard Szczerba2, Krzysztof Gesicki1 1Centrum Astronomii UMK, ul. Gagarina 11, 87-100 Torun, Poland 2N. Copernicus Astronomical Center, ul.Rabianska 8, 87-100 Torun, Poland Mixed chemistry (simultaneus presence of O- and C-rich gas and/or dust) is still unsolved problem. [WR] planetary nebulae beeing C-rich show at the same time the presence of crystaline silicates. We perform radiative transfer modelling of ISO spectrum for M2-43 to determine spatial location of PAH and crystaline silicates inside the nebula. This allows us to discuss the origin of mixed chemistry in [WR] planetary nebulae.
Tomislav Jurkic Dept. of Physics, University in Rijeka, Croatia We present a model of inner dust regions around the the cool Mira component of the symbiotic nova RR Tel based on observations in the near IR from 1975 to 2002. The JHKL magnitudes taken at the South African Astronomical Observatory and corrected for Mira pulsations were modeled by DUSTY code. The code solves radiative transfer by assuming spherical dust distribution in the innermost regions around Mira. Dust temperature, grain size, density distribution and optical depth during intervals with and without obscuration have been obtained.
Mariko Kato Keio University, Japan RS Oph is a symbiotic recurrent nova that has underwent the 6th recorded outburst on 2006 February 12. We have observed RS Oph with moderately narrow y-band filters and detect the extinguish epoch of hydrogen shell burning about 80 days after the optical peak. We have revised our RS Oph model which consists of a white dwarf, an irradiated red-giant companion, and a remaining irradiated (accretion) disk. In our new light curve model, free-free emission from the optically thin ejecta dominates the continuum flux in the early phase and an irradiated (accretion) disk dominates in the later phase (from 60 days after the optical peak). Our modeled light curve suggests the white dwarf mass of RS Oph to be 1.34-1.35 Msol for the hydrogen abundance of X=0.35-0.50, and reasonably explains the characteristic time scales of nova for various wavelength light curves such as supersoft X-ray, UV, or radio. We also discuss the distance to the star.
Edwin Kellogg Harvard/Smithsonian Center for Astrophysics, USA Results from three Chandra observations, year 2000 to 2005, XMM in 2005 and FUSE in 2004, of the central source and bipolar outflows extending from 800 to 6000 AU from the central star shows a rich variety of phenomena. There are thermal outer lobes at 1.2e6 K, moving at ~600 km/s.; also new nonthermal inner lobes extending out from the central binary, that has a spectrum reminiscent of an AGN, with a very soft component plus hard optically thin thermal emission at ~8e7 K, and Fe Kα from cold gas. Interpretation and preliminary modeling including shocks in the outer lobes is presented.
between 4010-8790 Å V.Klochkova, E.Chentsov, V.Panchuk, N.Tavolganskaya, M.Shapovalov Special Astrophysical Observatory RAS, Russia We present an atlas of the optical spectrum of the well known post-AGB star HD56126 associated with the IR-source IRAS07134+1005 in comparison to the standard alpha Per. The spectra were obtained with 2 echelle spectrometers at the 6-m telescope of the RAS in the spectral range 4010 to 8790 Å, with a high spectral-resolution R=75000 (R=25000 for λ > 6800 Å). We have identified 1700 spectral lines, molecular features and DIBs. Specific behaviour of selected lines (Hα, Hβ and spectral features identified with FeII(42), C2, CN, DIBs is described. The variable differential motions in atmosphere are revealed.
Valentina Klochkova and Tony Kipper Special Astrophysical Observatory RAS, Russia Using the echelle spectrograph PFES of the 6m telescope, we obtained moderate resolution CCD-spectra of a post-AGB star CGCS6857 associated with an IR-source IRAS20000+3239 having the emission IR-feauture at 21mkm. Despite numerous remarkable properties, the star CGCS6857 is still poorly studied due to its weakness (B=16.13, V=13.39). We revealed the bands of the C2 and CN molecules, but no C3, in the optical spectrum. The model atmospheric parameters adopted are: the effective temperature Teff=5000±200K, the logarithmic gravity log g=1.0±0.3 and the microturbulent velocity ξt=9.0±1.0 km/s. We obtained the low metallicity [Fe/H]=-1.4, the C/O-ratio close to 1 together with the large overabundances of s-process elements Y, Zr, Ba, La, Ce, Pr, Sm with the average value [s/Fe]=+1.4. The heliocentric radial velocity from metallic lines is equal to Vr(met)=-15±2 km/s.
D. Kotnik-Karuza1 , T. Jurkic1 , M. Friedjung2 1 Dept. of Physics, University in Rijeka, Croatia 2 IAP, Paris We present a study of the properties of circumstellar dust in symbiotic Miras during sufficiently long time intervals, including observed obscuration events. The published JHKL magnitudes of o Ceti, RX Pup, KM Vel, V366 Car, V835 Cen, HM Sge, V1016 Cyg, RR Tel, V407 Cyg, R Aqr have been collected. In order to follow the evolution of their colours in time, we removed the Mira pulsations to correct their light curves. Assuming spherical distribution of the dust in the close neighbourhood of the Mira, the DUSTY code was used to solve the radiative transfer in order to determine the dust temperature and its properties in each particular case. The preliminary results of this first systematic study of dust envelopes in symbiotic stars with Miras as cool components provide information on common nature of dust in these objects.
Laurits Leedjarv and Mari Burmeister Tartu Observatory, Estonia CH Cygni has caused headache to its investigators for a long time. On one hand, with its cool component as a semiregular M6-M7III variable of solar chemical composition, it fits well into the classification schemes (S- and D-type). On the other hand, its activity behaviour is different from most of the other symbiotic stars. We will describe some aspects of recent spectroscopic and photometric variability of CH Cyg. Some characteristics of CH Cyg in comparison with other symbiotic stars will be reviewed. An attempt will be made to explain most of the peculiarities of CH Cyg as a consequence of extremely long orbital period (~5300 d) for an S-type symbiotic star.
G. J. M. Luna, R. D. D. Costa & J. Sokoloski SAO/CfA, USA IAG/USP, Brazil We present relative elemental abundances for a representative sample of 53 symbiotic stars in our galaxy. We derive the He abundances taking into account self-absorption effects in the Balmer lines. Our results for N/O, Ne/O, Ar/O and He/H show that symbiotic stars follow the same trend as such other well-known tracers of galactic chemical evolution as Planetary Nebulae. The increasing number of suspected symbiotic stars being discovered at both X-ray and optical wavelengths suggest that symbiotics may play a key role in late-time galaxy evolution.
G. J. M. Luna & J. Sokoloski SAO/CfA, USA IAG/USP, Brazil Novae, some of which occur in symbiotic stars, play an important role in the chemical evolution of the Galaxy and the symbiotic stars themselves. A common feature of symbiotic recurrent novae (RNe) is rapid optical flickering. At least one symbiotic RN (T CrB) has also produced very hard X-ray emission. RT Cru produces optical flickering, has an optical spectrum like that of T CrB, and has recently been discovered by Integral to produce X-ray emission out to ~60 keV. It is thus a RN candidate. We have analyzed X-ray observations of RT Cru from the Chandra and Swift satellites. It clearly shows both thermal and non-thermal X-ray emission. Absorption of soft X-rays that is variable on a time scale of months suggests occultation by the red giant. We discuss two possible models for RT Cru: a jet-producing system viewed nearly edge on, or a magnetic white dwarf viewed pole on.
A. Maitan and U. Munari et al. INAF Astronomical Observatory of Padova-Asiago, Italy The symbiotic star GH Gem has been so far neglected in literature. We present absolute spectrophotometry, high resolution spectroscopy and UBVRI photometry collected during recent years that allows to reconstruct the recent photometric and spectroscopic history and to frame the physical properties of GH Gem.
Mikako Matsuura National Astronomical Observatory of Japan, Japan A high fraction of post-AGB stars and planetary nebulae (PNe) show asymmetric shapes in their circumstellar envelopes, such as elliptical and bipolar, while typically, the AGB wind is spherically symmetric. One of the hypotheses about the formation of the bipolar shape invokes a binary disk scenario. Part of the material lost during the intensive AGB mass-loss wind is trapped in the binary system, and a circumbinary disk is formed in the plane of the binary orbit. The disk restricts the direction of the low density but high velocity post-AGB and PN wind in the equatorial plane, and focuses the wind towards two poles OH 231.8+4.2 is one of the well-studied post-AGB candidates. The outflow is strongly bipolar. We have observed OH 231.8+4.2, using the mid-infrared interferometer MIDI and the infrared camera with the adaptive optics system NACO on the Very Large Telescope. An unresolved core (>200 mas in FWHM) is found at the centre of the OH 231.8+4.2 in the 3.8 micron image. This compact source is resolved with the interferometer. The fringes from the four baselines consistently show the presence of a compact circumstellar object with an inner radius of 30-40 mas, which is equivalent to 40-50 AU at 1.3 kpc. The measured size of the circumstellar material is consistent with the size of such disks calculated by hydrodynamic models, implying the circumstellar material may have a disk configuration.
Joanna Mikalajewska N. Copernicus Astronomical Center, Poland I will review current knowledge of symbiotic binaries, with special emphasize on their orbital and stellar parametrers.
U. Munari and G. Sostero et al. INAF Astronomical Observatory of Padova-Asiago, Italy Absolute spectrophotometry, polarimetry, high-resolution spectroscopy and UBVRI photometry are used to document in detail and discuss the evolution of the 2006 outburst of the recurrent nova and symbiotic binary RS Oph. Comparsion is carried out with respect to previous outbursts and multi-wavelength properties.
Nathan Netzer ORT Braude College, Israel We present results of model calculation of radiation driven stellar outflows. The radiative transfer equation is expanded in terms of a Legendre series. The results that we present cover a wide range of model stars, early-type, late-type, AGB and post-AGB stars. The models refer to the case of time variation of the outflow, yet, for the time being, there is not yet a model for departure from spherical symmetry.
Juan R. Pardo Instituto De Estructuta De La Materia - CSIC, Spain We will present the complete data set, model and line identification of a survey of the emission from the C-rich protoplanetary nebula CRL 618 performed with the IRAM-30m telescope in the following frequency ranges: 80.25-115.75 GHz, 131.25-179.25 GHz, and 204.25-275.250 GHz. A selection of lines from different species has been used to derive the structure of the source, its physical parameters and the chemical abundances in the different gas regions. Then, a global simulation of the spectrum has been performed in order to ease the task of line identification. The total number of lines that have a correspondence in both data and model is ~3200. Of all the lines that we have been able to label, ~50 % of them belong to the different forms of HC3N, and ~34 % to those of HC5N. The density of remaining unidentified features above the 3 sigma limit is only one per ~2.1 GHz (72 features), which is unprecedented in the analysis of this type of large millimeter-wave line surveys.
Philipp Podsiadlowski University of Oxford, UK Symbiotic binaries form a diverse class of interacting binaries. In this review I will summarize the main evolutionary paths and some of the remaining puzzles in their evolution. Recent observations of Mira suggest that even very wide symbiotics experience a new form of Roche-lobe overflow. I will present preliminary hydrodynamical simulations of this type of mass transfer and discuss its implications for the shaping of planetary nebulae and potentially Type Ia supernova progenitors.
Marta Pulecka N. Copernicus Astronomical Center, Poland We have observed with the IRAM radio-telescope two carbon stars: IRAS 04130+3918 and IRAS 06238+0904 with OH maser emission towards them . We have detected rotational transitions of HCN J=1-0, CS J=3-2, CS J=5-4, SiO J=3-2. Physical model of the envelope was found by modeling of the spectral energy distribution. Chemical model was developed for reconstruction of molecular distribution in circumstellar shell assuming that IRAS 06238+0904 are genuine carbon star. Observed emissions were fitted with the non-LTE code. The formulation of the radiative transfer problem in molecular lines were done in Large Velocity Gradient (LVG) approximation. The aim of the work was to examine if the observed abundance of the SiO molecule can be explained by chemistry in envelopes around C-stars or rather by existence of the reservoir of O-based material (known to be present in "silicate" C-stars) is necessary.
Maarten Reyniers Instituut voor Sterrenkunde, K.U.Leuven, Belgium V Tauri stars are a heterogeneous subclass of the Pop. II Cepheids, showing alternating deep and shallow minima in their light curves. Since many of these stars show infrared excesses, they are believed to be post-AGB stars. Many RV Tauri stars show some degree of depletion in their photospheres, which is caused by a gas-dust separation in the circumstellar environment and a subsequent gas accretion, making the photosphere devoid of refractory elements. The most favourable circumstance for this process to occur is, if the circumstellar dust is trapped in a disc. The presence of a disc in evolved objects is likely to be related to binarity. In this contribution, we present the first results of our abundance study of RV Tauri stars in the Large Magellanic Cloud, based on high-resolution VLT-UVES spectra. While our analysis is still ongoing, it is clear that also in the LMC depletion occurs, and seems to be even quite common amongst LMC RV Tauri objects.
A. Rutkowski1, J. Mikolajewska1, P.A. Whitelock2,3,4 1 N. Copernicus Astronomical Center, Poland 2 SAAO, South Africa 3 Astronomy Department, University of Cape Town, South Africa 4 National Astrophysics and Space Science Programme, Department of Mathematics and Applied Mathematics, University of Cape Town, South Africa Near infrared light curves of some well-studied symbiotic stars show a modulation with half-orbital period as expected for an ellipsoidal variability in the red giant. We will present and discuss preliminary results of modelling a few symbiotic systems with such variability.
C. Quiroga1, E. Brandi1, K. Hinkle2, J. Mikolajewska3, L.G. Garcia1, O. E. Ferrer1 1 Facultad Ciencias Astronomicas y Geofisicas - UNLP, Argentina 2 NOAO, USA 3 N. Copernicus Astronomical Center, Poland The study of photospheric abundances for the symbiotic giants provide information about the population and the past history of the systems and allows to address properly the role of etallicity on the symbiotic phenomenon. We propose a direct high resolution pectroscopic determination of the photospheric chemical abundances of red symbiotic giants in our galaxy based on high-resolution, near-infrared 2.3 micron spectra obtained with the Phoenix spectrometer on Gemini South telescope. We determine the carbon elemental and isotopic abundances in a sample of 10 symbiotic stars and using the method of standard LTE analysis and atmosphere models, and spectrum synthesis.
Miguel Santander-García Instituto de Astrofísica de Canarias, Spain Currently, there are a dozen known spatially resolved nebulae around symbiotic stars. We summarize their properties, focusing on their dynamical properties. Then, new results about the determination of the expansion in the plane of the sky of the nebulae around Hen 2-104 and Hen 2-147, which allows to gain important information about their dynamics and to discuss their distance via the expansion parallax method, will be described. Finally, discussion will be extended to bipolar nebulae presently classified as planetary nebulae, but which might instead host a symbiotic star, and in particular to the remarkable cases of Mz 3 and M 2-9.
Miroslaw Schmidt N. Copernicus Astronomical Center, Poland The photospheric abundances for the cool component of the symbiotic star were calculated for the first time using high-resolution near-infrared spectra and the method of of standard LTE analysis and atmospheric models. The iron abundance for CH Cyg was found to be solar, [Fe/H] = 0.0 ± 0.19. The atmospheric parameters ( Teff = 3100 K, log g = 0.0 (cgs), ξt = 2.2 km s-1) and metallicity for CH Cyg are found to be approximately equal to those for nearby field M7 giants. The calculated [C/H] = -0.15, [N/H] = +0.16, [O/H] = -0.07, and the isotopic ratios of 12C/13C and 16O/17O are close to the mean values for single M giants that have experienced the first dredge-up. The emission line technique was explored for estimating CNO ratios in the wind of the giant. The analysis of spectroscopic variability in photometric K band during 7 years period of observations is presented.
Sergey Shugarov Sternberg Astronomical Institute,Russia The results of the UBVRIJHKLM photometrical observations of the symbiotic mira V407 Cyg obtained in 1984 – 2006 are presented. Brightness variability on the different time scales was analyzed both in quiescent and active states of the star. We confirm that cool component of V407 Cyg is lithium mira with P~763d. This mira passes through "hot bottom base" evolutionary stage. We consider variations of the flicker effect during outburst’s evolution.
Edward Sion Villanova University, USA Multi-component synthetic spectral analyses of the FUSE, HST and IUE spectra of symbiotic variables are presented for a number of systems from "weak" symbiotics like Mira AB to systems like AG Dra, AE Ara, AR Pav, SY Mus and CH Cyg. In some cases, FUSE spectra are combined with HST and IUE spectra taken at the same orbital phase and brightness level to extend the wavelength coverage. The nature of the hot accreting component is discussed for each case.
A. Siviero, S. Moretti et al. INAF - Astronomical Observatory of Padova, Italy The total eclipse of the symbiotic nova AS 338 occurred during the summer of 2005 has been monitored in detail in UBVRI bands resulting in accurate multi-color eclipse profiles. These eclipse profiles are modelled to derive absolute dimension and properties of the inflated and outbursting WD component and to compare it with theoretical expectations.
Jennifer Sokoloski Harvard-Smithsonian Center for Astrophysics, USA Nuclear burning occurs to some degree in the eruptions of both classical symbiotic stars and symbiotic recurrent novae. During both types of outbursts, processed material can be ejected into the surrounding environment with simultaneous shell-like and bi-polar structures. I will present recent work on: 1) classical symbiotic outbursts; 2) the 2006 eruption of the symbiotic recurrent nova RS Oph; and 3) mass ejection during both types of events. Extensive multi-wavelength observations of Z And suggest that classical symbiotic outbursts are "combination novae", in which an accretion disk instability triggers enhanced thermonuclear shell burning on the surface of the white dwarf. X-ray through radio observations of the recent outburst of RS Oph reveal a decelerating, asymmetric blast wave and synchrotron-emitting jets. The RS Oph observations have implications for the WD mass, which is close to the Chandrasekhar limit, the detailed nature of the thermonuclear explosion, and the circum-binary environment.
Ryszard Szczerba N. Copernicus Astronomical Center, Poland Already, due to the IRAS observations it was known that there is a group of C-stars with features typical for oxygen-rich environment. A surprising ISO result, as far as late stages of stellar evolution is concerned, was discovery that coexistence of O-rich and C-rich material is much more common than previously believed. I will describe and discuss konown groups of evolutionary advanced stars (among them proto-planetary nebulae) which shows signatures of mixed chemistry with emphasis on the scenarios which try to explain this phenomenon.
T. Szymanski1, J. Mikolajewska2, P.A. Whitelock3,4,5 1 Jagiellonian University, Poland 2 N. Copernicus Astronomical Center, Poland 3 SAAO, South Africa 4 Astronomy Department, University of Cape Town, South Africa 5 National Astrophysics and Space Science Programme, Department of Mathematics and Applied Mathematics, University of Cape Town, South Africa Near infrared light curves of BX Mon show pronounced minina at the time of spectroscopic conjunction with the M giant behind the hot component. These light curves could be explained in terms of ellipsoidal variability of the cool giant which fills its tidal lobe during the periastron passage on its highly eccentric (e=0.45) orbit.
E. Vidal1, M. Baes1, H. van Winckel2, P. Deroo2, C. Gielen2 1 Ghent University, Belgium 2 Instituut voor Sterrenkunde, K.U. Leuven, Belgium Circumstellar dusty discs seem to be a ubiquitous feature around stars in different phases of their evolution, including post-AGB stars. We present 3D radiative transfer simulations of circumstellar discs with an inhomogeneous dust distribution to investigate the effect of a clumpy medium on the dust temperature distribution. Our initial results indicate that the structure of the dust temperature distribution is rather insensitive to the structure of the ISM, but nevertheless we find a systematic dependence on the parameters describing the structure of the clumpiness of the dust medium.
Klaus Werner University of Tuebingen, Germany The hydrogen-deficiency in extremely hot post-AGB stars of spectral class PG1159 is probably caused by a (very) late helium-shell flash or a AGB final thermal pulse that consumes the hydrogen envelope, exposing the usually-hidden intershell region. Thus, the photospheric element abundances of these stars allow to draw conclusions about details of nuclear burning and mixing processes in the precursor AGB stars. We compare predicted element abundances to those determined by quantitative spectral analyses performed with advanced non-LTE model atmospheres. A good qualitative and quantitative agreement is found for many species (He, C, N, O, Ne, F, Si) but discrepancies for others (P, S, Fe) point at shortcomings in stellar evolution models for AGB stars.
Hans van Winckel Instituut voor Sterrenkunde, KULeuven, Belgium
The first few binary post-AGB stars were serendipitously discovered. It
was realised that the objects showed a distinct common observational
characteristic: their dust excess starts already at the H or K.
This hot dust is remarkable, because the central stars are of
spectral type F or G are not thought to be actual or very recent
dust producers. It was postulated that this indicates the presence
of gravitationally-bound circumstellar material in the system.
The most famous example is the Red Rectangle, and in this object,
the Keplerian kinematics have indeed been resolved by
interferometric CO measurements.
A. Zajczyk1, T. Tomov1, M. Mikolajewski1, M. Cikala1, G. Galazutdinov2 1 Centrum Astronomii Uniwersytetu Mikolaja Kopernika w Toruniu, Poland 2 Korea Astronomy and Space Science Institute, Republic of Korea We will present the results of high resolution spectroscopy observations of RS Oph during 2004-2005. We analyzed profiles of absorption lines of TiII and FeII and emission line of HeI. In the structure of TiII profiles two components are visible. The one which radial velocity is almost constant in time and the second with radial velocity variable with amplitude about 10 km/s.
Albert Zijlstra University of Manchester, School of Physics & Astronomy, UK The high luminosity of post-AGB stars makes it difficult to detect binary companions. However, a significant fraction is expected to have binary nuclei. The talk will focus on the effect of binarity on mass loss, and on the properties of the nebulae.
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