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Spectral indications of ejection of mass by the symbiotic binary Z Andromedae during its 2000-2002 outburst
High-resolution observations in the region of the lines Hα, HeIIλ4686 and Hγ of the spectrum of the symbiotic binary ZAndromedae were performed in the quiescent state of the system and alsoduring its outburst phase in 2000-2002. The triplet lines of HeI had PCygni profiles indicating stellar wind with a velocity of 60 kms-1 from the hot secondary. This wind created an absorptiondip in the emission profile of the line Hγ. The lines Hγ andHeII λ4686 had a broad emission component, indicating anoptically thin stellar wind with a velocity of about 500 kms-1. The intensity of the broad component reached its maximumtogether with the optical light. To explain the observations, a modelwith an accretion disc was proposed, where the velocity of the wind fromthe accretor is supposed to be 500 km s-1. The accretion discis responsible for the breaking of the stellar wind close to the orbitalplane where its velocity decreases to about 60 km s-1. Themass-loss rate of the accretor at the time of a maximal light wasobtained of 2.4 × 10-7 (d/1.12 kpc)3/2Msolar yr-1 and decreased to 1.0 ×10-7 (d/1.12 kpc)3/2 Msolaryr-1 in 2001 October.Based on observations collected at the National Astronomical ObservatoryRozhen, Bulgaria.E-mail: tomov@astro.bas.bg
| A 3D dynamical model of the colliding winds in binary systems
We present a three-dimensional (3D) dynamical model of theorbital-induced curvature of the wind-wind collision region in binarystar systems. Momentum balance equations are used to determine theposition and shape of the contact discontinuity between the stars, whilefurther downstream the gas is assumed to behave ballistically. AnArchimedean spiral structure is formed by the motion of the stars, withclear resemblance to high-resolution images of the so-called `pinwheelnebulae'. A key advantage of this approach over grid or smoothedparticle hydrodynamic models is its significantly reduced computationalcost, while it also allows the study of the structure obtained in aneccentric orbit. The model is relevant to symbiotic systems andγ-ray binaries, as well as systems with O-type and Wolf-Rayetstars.As an example application, we simulate the X-ray emission fromhypothetical O+O and WR+O star binaries, and describe a method of raytracing through the 3D spiral structure to account for absorption by thecircumstellar material in the system. Such calculations may be easilyadapted to study observations at wavelengths ranging from the radio toγ-ray.
| Chemical Abundances in Symbiotic Stars
We have carried out a study of the chemical abundances of 1H, 4He, 12C, 13C, 14N, 15N, 16O, 17O, 20Ne, and 22Ne in symbiotic stars (SSs) by means of a population synthesiscode. We find that the ratios of the number of O-rich SSs to that ofC-rich SSs in our simulations are between 3.4 and 24.1, depending on thethird dredge-up efficiency λ and the terminal velocity of thestellar wind v(∞). The fraction of SSs with extrinsic C-rich coolgiants in C-rich cool giants ranges from 2.1% to 22.7%, depending onλ, the common envelope algorithm, and the mass-loss rate.Compared with the observations, the distributions of the relativeabundances of 12C/13C vs. [C/H] of the cool giantsin SSs suggest that thermohaline mixing in low-mass stars may exist. Thedistributions of the relative abundances of C/N vs. O/N, Ne/O vs. N/O,and He/H vs. N/O in the symbiotic nebulae indicate that it is quitecommon for the nebular chemical abundances in SSs to be modified by theejected materials from the hot components. Helium overabundance in somesymbiotic nebulae may be relevant to a helium layer on the surfaces ofwhite dwarf accretors.
| 3D simulations of RS Ophiuchi: from accretion to nova blast
Context: The binary star system RS Ophiuchi is a recurrent nova, withoutbursts occurring about every 22 years. It consists of a red giantstar (RG) and a wind accreting white dwarf close to the Chandrasekharlimit. This system is considered a prime candidate for evolving into anSNIa. For its most recent outbursts in 1985 and 2006, exquisitemultiwavelength observational data are available. Aims: Deeper physicalinsight is needed regarding the inter-outburst accretion phase and thedynamical effects of the subsequent nova explosion in order to improvethe interpretation of the observed data and to shed light on whether thesystem is an SNIa progenitor. Methods: We present a 3D hydrodynamicsimulation of the quiescent accretion with the subsequent explosivephase. Results: The computed circumstellar mass distribution in thequiescent phase is highly structured with a mass enhancement in theorbital plane of about a factor of 2 as compared to the polewarddirections. The simulated nova remnant evolves aspherically, propagatingfaster toward the poles. The shock velocities derived from thesimulations agree with those derived from observations. For v_RG = 20 kms-1 and for nearly isothermal flows, we find that 10% of themass lost by the RG is transfered to the WD. For an RG mass loss of10-7~Mȯ yr-1, the orbit of thesystem decays by 3% per million years. With the derived mass transferrate, multi-cycle nova models provide a qualitatively correct recurrencetime, amplitude, and fastness of the nova. Conclusions: Our 3Dhydrodynamic simulations provide, along with the observations and novamodels, the third ingredient for a deeper understanding of the recurrentnovae of the RS Oph type. In combination with recent multi-cycle novamodels, our results suggest that the WD in RS Oph will increase in mass.Several speculative outcomes then seem plausible. The WD may reach theChandrasekhar limit and explode as an SN Ia. Alternatively, the massloss of the RG could result in a smaller Roch volume, a common envelopephase, and a narrow WD + WD system. Angular momentum loss due togravitational wave emission could trigger the merger of the two WDs and- perhaps - an SN Ia via the double degenerate scenario.In the frame of the computing project “Cosmic Engines inGalaxies”.The movie is only available inelectronic form at http://www.aanda.org
| AG Draconis observed with XMM-Newton
Context: AG Draconis is the brightest symbiotic starin X-rays and one of the prototypes of the supersoft X-ray source class. Aims: Study of the X-ray spectrum of this peculiar binary system,covering both quiescence and activity periods, is necessary toinvestigate the physics of the high temperature spectral component, andto unveil the origin of the outbursts. Methods: X-ray and UVobservations with XMM-Newton during 2003-2005 and coordinated opticalspectrophotometric monitoring, together with archive data, are employedto derive the behaviour of the high energy source of the AG Dra systemduring different orbital and activity phases. Results: Duringquiescence the X-ray emission is very soft and is close in strength tothe previous ROSAT observations, with an estimated luminosity of 2600L_ȯ and a radius of 0.06 R_ȯ. We also found a 20% fluxdecrease in June 2005 at the time when a U-band minimum coincided with aV-band maximum. The X-ray flux in the XMM range largely decreases, andeven vanishes near the optical light maxima (bursts). The UV fluxesmeasured with the XMM Optical Monitor is close to the fluxes observedwith the IUE satellite. There is a marked anticorrelation between X-rayfluxes, and ultraviolet and optical fluxes, indicating that duringoutburst the WD is mostly emitting below 0.1 keV. Conversely, the largestrengthening of the He II 4686 Å emission during the October 2003and July 2005 light maxima indicates a marked increase of the far-UVbrightness especially during the early stages of the outbursts. A highenergy 0.5-0.6 keV X-ray excess seems to be present both in quiescenceand outburst. Conclusions: This is the first time that X-ray spectra ofAG Draconis during an active phase are obtained. These data have allowedus to investigate the change of the energy distribution. Theanti-correlation between X-ray and optical/ultraviolet emission appearsto be a general feature of AG Dra independent of the type and strengthof the outburst. We suggest that during outburst the WD radiationincreases, but is strongly absorbed by the circumstellar ionised gas.The newly-found high energy X-ray component is probably an indication ofthe presence of a shocked region produced by interaction of the WD windwith the circumbinary envelope fed by the red giant's wind.
| Activity cycle of the giant star of Z Andromedae and its spin period
We have re-analysed the long-term optical light curve (LC) of thesymbiotic star Z Andromedae, covering 112 yr of mostly visualobservations. Two strictly periodic cycles and one quasi-periodic cyclecan be identified in this LC. A P1 = 7550 d quasi-periodicitycharacterizes the repetition time of the outburst episodes of thissymbiotic star. Six such events have been recorded so far. Duringquiescence states of the system, that is, in time-intervals betweenoutbursts, the LC is clearly modulated by a stable coherent period of P2= 759.1 d. This is the well-known orbital period of the Z Andromedaebinary system that has been measured also spectroscopically. A thirdcoherent period of P3 = 658.4 d is modulating the intense fluctuationsin the optical brightness of the system during outbursts. We attributethe trigger of the outburst phenomenon and the clock that drives it, toa solar-type magnetic dynamo cycle that operates in the convection andthe outer layers of the giant star of the system. We suggest that theintense surface activity of the giant star during maximum phases of itsmagnetic cycle is especially enhanced in one or two antipode regions,fixed in the atmosphere of the star and rotating with it. Such spotscould be active regions around the North Pole and the South Pole of ageneral magnetic dipole field of the star. The P3 periodicity is halfthe beat of the binary orbital period of the system and the spin periodof the giant. The latter is then either 482 or 1790 d. If only one poleis active on the surface of the giant, P3 is the beat period itself, andthe spin period is 352 d. It could also be 5000 d if the giant isrotating in a retrograde direction. We briefly compare these findings inthe LC of Z Andromedae to similar modulations that were identified inthe LC of two other prototype symbiotics, BF Cyg and YY Her.
| A pre-outburst of the classical symbiotic star BF Cyg in 1987 1989
We analyze previously unpublished spectrophotometric data for theclassical symbiotic star BF Cyg obtained in 1982 1989. These data showthat BF Cyg already started a new period of activity in 1987 1989,earlier believed to correspond to quiescence. An optical spectrum takenon September 29, 1987 displays several features characteristic ofactivity in classical symbiotic stars. During the same time interval,excess near-UV radiation was detected, possibly from the accretion disk,and evidence for Rayleigh scattering of the hot component’sradiation on atomic hydrogen was detected in the far-UV, at phasespreviously believed not to be characteristic of this effect. This latterfinding may testify to an enhanced (compared to 1979 1986) rate of massloss from the cool component of BF Cyg. We discuss the interrelationbetween an increased mass-loss rate of the cool component and the hotcomponent’s activity in the context of classical symbiotic stars.
| The remarkable properties of the symbiotic star AE Circinus
We present new optical spectroscopy and photometry, Two-Micron All-SkySurvey (2MASS) infrared observations and 24 yr of combined AmericanAssociation of Variable Star Observers (AAVSO) and Association Francaisedes Observateurs d'Etoiles Variables (AFOEV) photometry of the symbioticstar candidate AECir. The long-term light curve is characterized byoutbursts lasting several years and having a slow decline of ~2 ×10-4 magd-1. The whole range of variability of thestar in the V band is about 4 mag. The periodogram of the photometricdata reveals strong signals at ~342 and 171 d. The presence of theemission feature at λ6830 Å at minimum and the detection ofabsorption lines of a ~K5 type star confirm the symbiotic classificationand suggest that AECir is a new member of the small group of s-typeyellow symbiotic stars. We estimate a distance of 9.4 kpc. Our spectrumtaken at the high state shows a much flatter spectral energydistribution, the disappearance of the λ6830 Å emissionfeature and the weakness of the HeII 4686 emission relative to theBalmer emission lines. Our observations indicate the presence ofemission-line flickering in time-scales of minutes in 2001. The peculiarcharacter of AECir is revealed in the visibility of the secondary starat the high and low state, the light curve resembling a dwarf novasuperoutburst and the relatively short low states. The data are hard toreconciliate with standard models for symbiotic star outbursts.
| Modeling of C IV pumped fluorescence of Fe II in symbiotic stars
Aims.We describe how the C IV λ1548.18 line pumps the 1548.20 and1548.41 Å channels of Fe II in symbiotic stars through the processknown as photo-ionization by accidental resonance (PAR). We describewhere and why Fe II fluorescence arises in symbiotic stars and whetherthe Fe II λ1548.41 channel can only be activated when there is awhite-dwarf wind present in the system. Further, we aim to show how ananalysis of the PAR-pumped lines helps to understand the phyisicalconditions that they manifest. Methods: We calculate intensities of theC IV-pumped Fe
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| The Nature of the Hard X-Ray-Emitting Symbiotic Star RT Cru
We describe Chandra High Energy Transmission Grating Spectrometerobservations of RT Cru, the first of a new subclass of symbiotic starsthat appear to contain white dwarfs (WDs) capable of producing hardX-ray emission out to greater than 50 keV. The production of such hardX-ray emission from the objects in this subclass (which also includes CD-57 3057, T CrB, and CH Cyg) challenges our understanding of accretingWDs. We find that the 0.3-8.0 keV X-ray spectrum of RT Cru emanates froman isobaric cooling flow, as in the optically thin accretion diskboundary layers of some dwarf novae. The parameters of the spectral fitconfirm that the compact accretor is a WD, and they are consistent withthe WD being massive. We detect rapid, stochastic variability from theX-ray emission below 4 keV. The combination of flickering variabilityand a cooling flow spectrum indicates that RT Cru is likely powered byaccretion through a disk. Whereas the cataclysmic variable stars withthe hardest X-ray emission are typically magnetic accretors with X-rayflux modulated at the WD spin period, we find that the X-ray emissionfrom RT Cru is not pulsed. RT Cru therefore shows no evidence formagnetically channeled accretion, consistent with our interpretationthat the Chandra spectrum arises from an accretion disk boundary layer.
| On the effect of emission lines on UBVR photometry
We investigate the effect on the U, B, V, RC andRJ magnitudes of the removal of emission lines from aspectrum. We determined Δm corrections from the ratio of fluxeswith and without emission lines, transmitted from the object through aphotometric filter. An exact and simplified approach for operative usewas applied. The effect was demonstrated for classical symbiotic stars,symbiotic novae and the classical nova V1974 Cyg. It was found thatabout 20–30%, 30–40%, 10% and 26/20% of the observed flux inthe U, B, V and RC/RJ filters, respectively, areradiated in the emission lines of the investigated classical symbioticstars. The largest effect was found for symbiotic novae (RR Tel andV1016 Cyg) and the classical nova V1974 Cyg at 210 days (an average of74%, 79%, 56% and 66/60%), because of their very strong emission linespectrum. In all cases, the line corrected flux points fit thetheoretical continuum well. The difference between Δm correctionsobtained by the accurate calculation and that given by our approximateformula is less than 10%. Deviations up to 30% can exist only in the Upassband. Examples for practical applications are suggested.
| Outer Jet X-Ray and Radio Emission in R Aquarii: 1999.8 to 2004.0
Chandra and VLA observations of the symbiotic star R Aqr in 2004 revealsignificant changes over the 3-4 year interval between theseobservations and previous observations taken in with the VLA in 1999 andwith Chandra in 2000. This paper reports on the evolution of the outerthermal X-ray lobe jets and radio jets. The emission from the outerX-ray lobe jets lies farther away from the central binary than the outerradio jets and comes from material interpreted as being shock-heated to~=106 K, a likely result of collision between high-speedmaterial ejected from the central binary and regions of enhanced gasdensity. Between 2000 and 2004, the northeast (NE) outer X-ray lobe jetmoved out, away from the central binary, with an apparent projectedmotion of ~=580 km s-1. The southwest (SW) outer X-ray lobejet almost disappeared between 2000 and 2004, presumably due toadiabatic expansion and cooling. The NE radio-bright spot also movedaway from the central binary between 2000 and 2004, but with a smallerapparent velocity than the NE X-ray-bright spot. The SW outer lobe jetwas not detected in the radio in either 1999 or 2004. The density andmass of the X-ray-emitting material is estimated. Cooling times, shockspeeds, pressure, and confinement are discussed.
| Colliding Winds in Symbiotic Binary Systems. II. Colliding Winds Geometries and Orbital Motion in the Symbiotic Nova AG Pegasi
AG Pegasi has been observed at high angular resolution and sensitivityat the Very Large Array (VLA) at 5 GHz in four epochs between 1984 and1991. Analysis of the radio visibilities indicate that a mass of4.0+/-0.5×10-5 Msolar is concentrated in theinner nebula and is moving outward at a velocity of 53+/-4 kms-1 (D=600 pc assumed). In order to explain the observedmorphology of the inner nebula, a new colliding winds model is derived,which includes the effects of orbital motion (CWo model). Orbitaleffects cannot be ignored in AG Pegasi since the orbital timescale (2.25yr; Meinunger 1981) is short compared to the likely timescale of windcollision (symbiotic nova eruption beginning ~1850 Merrill 1959). Whenthese effects are considered, the interaction front between binarystellar winds is wrapped into spiral walls whose density decreasesoutward with 1/r2. Distinctive geometries are found to arisedepending on which wind dominates the interaction, the late-type windfrom the symbiotic ``cool component,'' or the high-velocity wind fromthe ``hot component.'' Application of the CWo model to AG Peg suggeststhat the observed transient lobe enhancements of the inner nebula arisedue to changes in the mass-loss rate from the hot component. Hotcomponent mass-loss rates ranging between 2.1 and6.0×10-8 Msolar yr-1 are derived.The model is also successful in reproducing the radio spectrum of thecentral unresolved object of the system. A position angle of-15deg+/-10deg is inferred for the orbital pole asprojected on the plane of the sky.
| Discovery of Rapid Hard X-Ray Variability and New Jet Activity in the Symbiotic Binary R Aquarii
Two Chandra observations of the R Aqr symbiotic binary system taken 3.3yr apart show dramatic changes in the X-ray morphology and spectralcharacteristics in the inner 500 AU of this system. The morphology ofthe soft X-ray emission has evolved from a nearly circular regioncentered on the binary system to an hourglass shape that indicates theformation of a new southwest jet. Synchrotron radiation from the new jetin contemporaneous VLA radio spectra implies the physical conditions inthe early stages of jet development are different from those in the moreextended outer thermal jets known to exist for decades in this system.The central binary source has two X-ray spectral components in each ofthe two epochs, a soft component and a highly absorbed hard componentcharacterized by T~108 K if fit with a thermal plasma model.The spectrum hardened considerably between 2000.7 and 2004.0, primarilydue to increased flux above 5 keV, suggesting a change in the accretionactivity of the white dwarf on a timescale of a few years or less.Point-source Fe K emission is detected at the position of the centralbinary system in both observations. While the earlier observation showsevidence of only a single emission peak near Fe Kα at 6.4 keV, thelater observation shows a more complex emission structure between 6 and7 keV. Finally, we have discovered a modulation in the hard X-ray fluxwith a period of 1734 s at a 95% confidence level in the 2004observation only. The modulation potentially arises from standing shocksin an accretion column, and we have explored the possibility that thewhite dwarf in R Aqr is analogous to the magnetic white dwarfs inIntermediate Polars.
| 2MASS near-infrared photometry of symbiotic stars
We present Two Micron All Sky Survey photometry for 216 symbiotic andpossible symbiotic stars. This represents the most comprehensivenear-infrared photometry for these sources which has been published todate. The results are used to define the statistics of S- and D-typestars; to investigate the photometric properties of Magellanic S-typesymbiotics; and to define the possible evolution of D-type symbioticswithin the J - H/H - KS colour plane. It appears that thecolours of D-type symbiotics are consistent with differing mass-lossrates dM/dt, provided that the grains have a silicate-like composition,and maximum temperatures of the order of ~800 K.
| Variable Stars in NSVS Database I. 86 New Variables in Andromeda
A search for light curves with variability in the NSVS data was carriedout in a 46 square-degree area in Andromeda. The field contains 51955light curves. We found 136 variables, 86 of them were not knownpreviously. Extrapolating the density of the variables in the field tothe whole NSVS, the total number of variables in the survey is estimatedto be 52000 - 61000.
| Bipolar ejection by the symbiotic binary system Z And during its 2006 outburst
High-resolution data in the region of the Hα line have beenobtained at the time of light maximum and after it for the 2006 opticaloutburst of the symbiotic binary Z And. A blueshifted absorptioncomponent indicating an outflow velocity of about 1400 kms-1, as well as additional emission components with similarvelocities, situated on the two sides of the main peak of the line, wereobserved during that time. It is suggested that all of them are spectralsignatures of bipolar outflow, observed for the first time in theoptical spectrum of this binary. The emission measure and the mass ofthe nebular part of the streams have been estimated approximately,reaching values of up to about 6 × 1057 cm-3and 8 × 10-8Msolar.Based on observations collected at the National Astronomical ObservatoryRozhen, Bulgaria.E-mail: tomov@astro.bas.bg
| A Monte Carlo study of polarization structures in the Thomson-scattered line radiation
Thomson scattering is often invoked to explain broad wing features thatare seen in various objects including active galactic nuclei andsymbiotic stars. Despite the wavelength-independent scatteringcross-section of Thomson scattering, the line flux may exhibitwavelength-dependent linear degree of polarization, because variousparts of emission wings are contributed by photons with differentscattering numbers. Specifically, more scattered and hence more weaklypolarized photons tend to fill the farther wing parts from the linecentre, while the neighbourhood of the line centre is dominated byless-scattered photons with higher degree of polarization. Using a MonteCarlo technique, we investigate the polarization structure ofThomson-scattered line radiation. A detailed analysis of polarizationstructure formation is conducted by investigating the dependence of thepolarization and profile width on the scattering number for variousfinite electron scattering slabs. Significantly varying degree ofpolarization is obtained when the scattering medium has Thomson opticaldepth τTh >= 1. We present our high-resolutionspectrum of the symbiotic star V1016 Cyg obtained with the BohyunsanOptical Echelle Spectrograph (BOES) in order to fit the broad profilearound Hα by electron scattering wings adopting an oblatespheroidal geometry with Thomson optical depth τTh = 0.5and electron temperature Te = 6.2 × 104 K.Local maxima in the linear degree of polarization of Thomson-scatteredline radiation are expected to appear in the spectral regionscharacterized by the average scattering number ~=1.
| Evidence for bipolar jets from the optical spectra of the prototypical symbiotic star Z Andromedae
Aims.We have studied optical spectra of the symbiotic star Z And,obtained during its latest outburst started in April 2006, with the aimof finding changes in the spectrum yielding clues to the nature of thehot component and its outbursts. Methods: .The spectroscopicobservations of Z And have been made using the 1.5-m telescope at theTartu Observatory, Estonia, and processed in a standard way.Results: .We have found high velocity satellites to the hydrogen Balmeremission lines. Starting from July 30, 2006, weak additional emissioncomponents at velocities of about ±1150 km s-1 weredetected. Their appearance near the outburst maximum and similarity tothe emission features in another symbiotic star Hen 3-1341 imply fastcollimated outflows from the hot component of Z And. This finding isconsistent with the earlier results by several authors that symbioticstars can emit bipolar jets at certain stages of their outbursts. Asignificant decrease in the temperature of the hot component in initialstages of the outburst was detected by the disappearance of the highexcitation emission lines from the spectrum.
| 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.
| IRAS 12316--6401: a New Symbiotic Mira?
Current observations indicate that IRAS 12316-6401 is a new addition tothe rare class of resolved symbiotic Miras, however future observationsare needed to confirm this.
| Modeling Light Curves of Symbiotic Stars
Near-infrared light curves of some well-studied symbiotic stars show amodulation with half-orbital period as expected for an ellipsoidalvariability in the red giant. We present and discuss preliminary resultsof modeling of three symbiotic systems with such variability: RW Hya, SYMus and AR Pav.
| V407 CYG as a Member of a New Subclass of Symbiotic Stars
We analyze the results of new multicolor UBVRIJHKLM photometricobservations of the symbiotic Mira V407 Cyg, obtained on return toquiescence from its 1998 outburst.
| Symbiotic Stars: Continually Embarrassing Binaries
This paper aims at presenting the state-of-the-art in understanding ofsymbiotic binaries. In particular, we discuss their basic parameters,the mechanisms of mass loss and accretion and the role of theseprocesses in the observed activity of symbiotic systems.
| Recent photometry of symbiotic stars
We present new photometric observations of 15 symbiotic stars coveringtheir last orbital cycle(s) from 2003.9 to 2007.2. We obtained our databy both classical photoelectric and CCD photometry. Main results are: EGAnd brightened by ˜ 0.3 mag in U from 2003. A ˜0.5 mag deepprimary minimum developed in the U light curve (LC) at the end of 2006.Z And continues its recent activity that began during the 2000 autumn. Anew small outburst started in summer of 2004 with a peak U magnitude of˜ 9.2. During the spring of 2006 the star entered a massiveoutburst. It reached its historical maximum at U˜ 8.0 in 2006July. AE Ara erupted in 2006 February with Δ m_vis ˜ 1.2 mag.BF Cyg entered a new active stage in 2006 August. A brightness maximum(U˜ 9.4) was measured during 2006 September. CH Cyg persists in aquiescent phase. During 2006 June-December a ˜ 2 mag decline inall colours was measured. CI Cyg started a new active phase during 2006May-June. After 31 years it erupted by about 2 mag in U. TX CVnmaintains a bright stage with U ˜ 10.5 from 2003. AG Dra entered anew major outburst in 2006 June. It reached its maximum at U ˜ 8.0in 2006 September. AR Pav persists at a low level of the activity. AGPeg's LC profile varies markedly during different orbital cycles. AX Percontinues its quiescent phase.The Tables of this article are available at the CDS viahttp://cdsarc.u-strasbg.fr/ftp/cats/J/other/AN/328.909
| Line formation regions of the UV spectrum of CI Cygni
Aims.They are the interpretation of the emission line formation regionsin CI Cygni Methods: .They involve theexamination of radial velocities and fluxes of ultraviolet emissionlines at different epochs, deduced from archival IUE and GRHS/HSTspectra. Results: .The line fluxes give electron densities andwere in addition used to calculate emission measures, suggesting lineformation in regions rather smaller than the binary separation.Examination of the radial velocities led to us to find a systematicredshift of the high ionization resonance lines with respect to theintercombination, and He II lines. Possible explanations of the redshiftand the high resolution GHRS C IV profile are discussed. We favour thatinvolving resonance line absorption by a circum-binary region mostprobably in an asymmetric wind interaction shell or in a wind from theaccretion disk.
| Multivariate Characterization of Hydrogen Balmer Emission in Cataclysmic Variables
The ratios of hydrogen Balmer emission line intensities in cataclysmicvariables are signatures of the physical processes that produce them. Toquantify those signatures relative to classifications of cataclysmicvariable types, we applied the multivariate statistical analysis methodsof principal components analysis and discriminant function analysis tothe spectroscopic emission data set of Williams (1983). The two analysismethods reveal two different sources of variation in the ratios of theemission lines. The source of variation seen in the principal componentsanalysis was shown to be correlated with the binary orbital period. Thesource of variation seen in the discriminant function analysis was shownto be correlated with the equivalent width of the Hβ line.Comparison of the data scatterplot with scatterplots of theoreticalmodels shows that Balmer line emission from T CrB systems is consistentwith the photoionization of a surrounding nebula. Otherwise, models thatwe considered do not reproduce the wide range of Balmer decrements,including `inverted' decrements, seen in the data.
| The giant star of the symbiotic system YY Her: rotation, tidal wave, solar-type cycle and spots
We analyse the historical light curve of the symbiotic star YY Her, from1890 up to 2005 December. A secular declining trend is detected, at arate of ~.01 mag in 1000 d, suggesting that the system could belong tothe subclass of symbiotic novae. Several outburst events are superposedon this slow decline. Three independent periodicities are identified inthe light curve. A quasi-periodicity of 4650.7 d is detected for theoutburst occurrence. We suggest that it is a signature of a solar-typemagnetic dynamo cycle in the giant component. A period of 593.2 dmodulates the quiescent light curve and it is identified as the binaryperiod of the system. During outburst events, the system shows a stableperiodic oscillation of 551.4 d. We suggest that it is the rotationperiod of the giant. The secondary minima detected at some epochs ofquiescence are probably due to dark spots on the surface of the rotatinggiant.The difference between the frequencies of these two last periods is thefrequency of a tidal wave in the outer layers of the giant. A periodwhich is a beat between the magnetic cycle and the tidal wave period isalso apparent in the light curve. YY Her is a third symbiotic systemexhibiting these cycles in their light curve, suggesting that a magneticdynamo process is prevalent in the giant components of symbiotic stars,playing an important role in the outburst mechanism of some of thesesystems.
| Continuous presence of bipolar jets from Z And during its 2006 outburst
We report on the continuing activity of the symbiotic prototype Z Andduring its 2006 major outburst that began in 2006 April (cf. ATEL 882).The system still keeps its brightness at a high level (U=9.04, B=9.79,V=9.24, Rc=8.58 as measured on 2006 Oct 26.88 at the Skalnate PlesoObservatory), which is comparable with that from 2006 Aug 15.88(U=8.87, B=9.43, V=8.94, Stara Lesna Observatory).
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Observation and Astrometry data
| Constellation: | Ανδρομέδα |
| Right ascension: | 23h33m39.95s |
| Declination: | +48°49'05.9" |
| Apparent magnitude: | 10.959 |
| Proper motion RA: | -1.4 |
| Proper motion Dec: | -6.5 |
| B-T magnitude: | 12.335 |
| V-T magnitude: | 11.073 |
Catalogs and designations:
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INHABITED SKY
