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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.
| Symbiotisch Veraenderliche von Typ Z And.
Not Available
| Summary of the Conference
After showing how ideas about the nature of symbiotic binaries and theirrelation with other classes of objects, also examined at this meeting,have become more precise, personally selected highlights of theconference are mentioned. A few lessons for the future are drawn.
| 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.
| 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.
| UBV(RI)C photometric sequences for symbiotic stars. III
We present accurate UBV(RI)C photometric sequences andastrometric positions for a final set of 41 symbiotic stars. In asimilar manner to the 40 targets of Papers I and II, these sequencesextend over wide brightness and color ranges and are suited to coveringboth quiescence and outburst phases. They are intended to assist boththe CCD photometric monitoring of current variability and exploitationof old photographic plates from historical archives.
| Broad Hα wings from the optically thin stellar wind of the hot components in symbiotic binaries
Aims.To model broad Hα wings observed in symbiotic binaries by anoptically thin, bipolar stellar wind from their hot components as analternative to that considering the Raman scattering of Lyβ photonson atomic hydrogen. Methods: .Profile-fitting analysis. Comparisonof the observed broad Hα wings and their luminosity with thosepredicted by the model. Results: .Synthetic Hα profiles fitexcellently the observed wings for | Δ v | 200 kms-1 in our sample of 10 symbiotic stars during the quiescentas well as active phases. The wing profile formed in the stellar windcan be approximated by a function f(Δ v) ∝ Δv-2, which is of the same type as that arising from the Ramanscattering. Therefore it is not possible to distinguish between thesetwo processes only by modeling the line profile. Some observationalcharacteristics of the Hα-emission, its relationship with theemission measure of the symbiotic nebula and a steep radio spectrum at1.4-15 GHz suggest the ionized stellar wind from the hot component to bethe dominant source contributing to the Hα wings during activephases. The model corresponding mass-loss rates from the hot componentsare of a few × 10-8 Mȯ yr-1and of a few × (10-7 - 10-6)Mȯ yr-1 during quiescent and active phases,respectively.
| The nature of ultraviolet spectra of AG Pegasi and other symbiotic stars: locations, origins, and excitation mechanisms of emission lines
A detailed study of ultraviolet spectra of the symbiotic star AG Peg hasbeen undertaken to derive the atomic excitation mechanisms and origin offormation for the lines common in symbiotic systems. More than 600emission lines are observed in spectra from {IUE}, {HST} and {FUSE} ofwhich 585 are identified. Population mechanisms and origin of formationare given for a majority of those lines. Based on the understanding ofthe AG Peg spectra {IUE} data of 19 additional symbiotic stars areinvestigated and differences and similarities of their spectra arediscussed. Fe II fluorescence lines pumped by strong emission linesbetween 1000 and 2000 Å are observed in 13 of these systems. Someof the symbiotic systems belonging to the subclass symbiotic novae havemore than 100 Fe II fluorescence lines in the ultraviolet wavelengthregion. Forbidden lines are detected for 13 of the stars, mostly fromhighly-ionized spectra such as Ar V, Ne V and Mg V. Further, [Mg VI] and[Mg VII] lines are observed in a symbiotic star (AG Dra) for the firsttime. Five of the symbiotic stars have broad white-dwarf wind profiles({FWHM} > 400 km s-1) for a few lines in their spectra.The stars with no such broad lines can be divided into two similarlysized groups, one where all lines have FWHM less than 70 kms-1 and the other where one, a few or all of the broad({FWHM} > 400 km s-1) lines of AG Peg have an enhancedbroad wing (110-140 km s-1).
| Multiperiodic variations in the last 104-yr light curve of the symbiotic star BF Cyg
We analyse a light curve (LC) of the symbiotic star BF Cyg, covering114yr of its photometric history. The star had a major outburst aroundthe year 1894. Since then the mean optical brightness of the system isin steady decline, reaching only in the last few years its pre-outburstvalue. Superposed on this general decline are some six less intenseoutbursts of 1-2mag and duration of 2000-5000d. We find a cycle of6376d, or possibly twice this period, in the occurrence of theseoutbursts. We suggest that the origin of the system outbursts is in somemagnetic cycle in the outer layers of the giant star of the system, akinto the less intense 8000-d magnetic cycle of our Sun. We further find,that in addition to its well-known binary period of 757.3d, BF Cygpossesses also another photometric period of 798.8 d. This could be therotation period of the giant star of the system. If it is, the beatperiod of these two periodicities, 14580d, is the rotation period of atidal wave on the surface of the giant. A fourth period of 4436d, thebeat period of the 14580-d and the 6376-d cycles is possibly alsopresent in the LC. We predict that BF Cyg will be at the peak of itsnext outburst around the month of May in the year 2007. The newlydiscovered 798.8-d period explains the disappearance of the orbitalmodulation at some epochs in the LC. The 757.3-d oscillations will bedamped again around the year 2013.
| Nonradial pulsations of the hot component of the symbiotic star CH Cyg during its active phase
We observed the symbiotic star CH Cyg with the 70 cm telescope of theCrimean Astrophysical Observatory in 1982, during its active phase, whenit was brighter than 6m in the V band. We simultaneously detected thecontinuum brightness at wavelengths of 3737, 5092, and 5500 Å witha time resolution of 20 s. We present light curves for these wavelengthsfor four nights between July 13 and August 22, demonstrating thecharacter of the star’s rapid variations. Variousfrequency-analysis methods were applied to the data series at 3737 and5092 Å, where the light from the hot component made an appreciablecontribution. For both series, we find some 20 similar frequenciescorresponding to periods ranging from 150 to 6000 s. Our estimates ofthe significance of the identified frequencies indicate that thesignificance level exceeds 3 σ in all cases, and is even higher inmost cases. For many of the oscillations, the amplitudes varied on timescales shorter than one day. Multiperiodicity and variable oscillationamplitudes are characteristic of nonradial pulsations. We conclude thatnonradial oscillations typical of a white dwarf’s g modes wereexcited during the symbiotic star’s state of highest activity.
| A ``Combination Nova'' Outburst in Z Andromedae: Nuclear Shell Burning Triggered by a Disk Instability
We describe observational evidence for a new kind of interacting binarystar outburst that involves both an accretion instability and anincrease in thermonuclear shell burning on the surface of an accretingwhite dwarf. We refer to this new type of eruption as a combinationnova. In late 2000, the prototypical symbiotic star Z Andromedaebrightened by roughly 2 mag in the optical. We observed the outburst inthe radio with the VLA and MERLIN, in the optical both photometricallyand spectroscopically, in the far-ultraviolet with FUSE, and in theX-rays with both Chandra and XMM-Newton. The 2 year long event had threedistinct stages. During the first stage, the optical rise closelyresembled an earlier, small outburst that was caused by an accretiondisk instability. In the second stage, the hot component ejected anoptically thick shell of material. In the third stage, the shell clearedto reveal a white dwarf whose luminosity remained on the order of104 Lsolar for approximately 1 yr. The eruptionwas thus too energetic to have been powered by accretion alone. Wepropose that the initial burst of accretion was large enough to triggerenhanced nuclear burning on the surface of the white dwarf and theejection of an optically thick shell of material. This outbursttherefore combined elements of both a dwarf nova and a classical nova.Our results have implications for the long-standing problem of producingshell flashes with short recurrence times on low-mass white dwarfs insymbiotic stars.
| Disentangling the composite continuum of symbiotic binaries. I. S-type systems
We describe a method of disentangling the composite, 0.12-5 μmcontinuum of symbiotic binaries. The observed SED is determined by theIUE/HST archival spectra and flux-points corresponding to the opticalUBVRI and infrared JHKLM photometric measurements. The modeled SED isgiven by superposition of fluxes from the cool giant, hot stellar sourceand nebula including the effect of the Rayleigh scattering process andconsidering influence of the iron curtain absorptions. We applied thismethod to 21 S-type symbiotic stars during quiescence, activity andeclipses. We isolated four main components of radiation and determinedtheir properties. (i) Stellar radiation from the giant corresponds to aunique luminosity class - normal giants. Characteristic luminosities are1600 ± 200 and 290 ± 30 Lȯ for red andyellow giants, respectively in our sample of objects. (ii) Hot objectradiation during quiescence consists of the nebular and stellarcomponent. The former radiates at a mean electron temperature of 19 000K and its amount of emission suggests a mass-loss rate from giants viathe wind at dot MW = a few × 10-7Mȯ yr-1. Radiation of the latter conformswell with that of a black-body photosphere at a characteristictemperature of 105 000 K. The corresponding effective radii are a factorof 10 larger than those of white dwarfs, which thus precludes observingthe accretor's surface. Extreme cases of AX Per and V443 Her, for whichthe hot star temperature from the fit is not capable of producing thenebular emission, signal a disk-like structure of the hot stellar sourceeven during quiescence. (iii) Hot object radiation during activityconsists of three components - the stellar and the low- andhigh-temperature nebular radiation. The stellar radiation satisfies thatof a black-body photosphere at a low characteristic temperature of 22000 K (we call it the 1st type of outbursts) or at a very highcharacteristic temperature of ≈165 000 K (2nd type of outbursts). Allthe active objects with a high orbital inclination show features of the1st-type of outbursts (here Z And, AE Ara, CD-43circ14304, TXCVn, BF Cyg, CH Cyg, CI Cyg, AR Pav, AX Per), while AG Dra representsthe 2nd-type. The presence of a two-temperature type of UV spectrum andan enlargement of effective radii of the stellar source by a factor of 10 with respect to the quiescent values during the 1st-type of outburstsuggest an expansion of an optically thick medium at the orbital planein the form of a disk. The low-temperature nebula radiates at a meanelectron temperature of 14 000 K and is subject to eclipses, while thehigh-temperature nebula, which is seen during eclipses as the onlycomponent, is characterized by Te > 30 000 K. Radiativeand geometric properties of the main sources of radiation allowed us toreconstruct a basic structure of the hot object during the 1st-type ofoutburst. There is an edge-on disk around the accretor. Its outer flaredrim represents a warm pseudophotosphere of the hot stellar source, whoseradiation is Rayleigh attenuated and affected by the iron curtainabsorptions in the neutral gas concentrated at the orbital plane. Thelow-temperature nebula is placed just above/below the disk with aconcentration at its edge as to be subject to eclipses and to“see” well the central ionizing source. High above/below theorbital plane, there is a hot nebular emitting region.
| Bowen excitation of N III lines in symbiotic stars
We present a semi-empirical equation for prediction of the strengths ofthose N III lines that are generated by the Bowen mechanism and observedin spectra of symbiotic stars. The equation assumes that the Bowenmechanism is the only source populating the 3d state in N III, andcomparisons with observations of the 3s-3p and 3p-3d transitions serveas a test of this assumption. In an ongoing study of symbiotic stars theequation has been applied to two symbiotic novae, RR Tel and AG Peg, bycomparing the predicted N III line strengths to observed lineintensities. It is clear that besides the Bowen mechanism there isanother process, most likely radiative recombination, that contributesto the N III 3d population in AG Peg and is the main population processof this state in RR Tel. It is also clear that a second, not previouslyconsidered, N III channel, 2p 2P{1/2}-3d 2D{3/2}at 374.198 Å, is pumped by O III in both RR Tel and AG Peg.
| Astrophysics in 2004
In this 14th edition of ApXX,1 we bring you the Sun (§ 2) and Stars(§ 4), the Moon and Planets (§ 3), a truly binary pulsar(§ 5), a kinematic apology (§ 6), the whole universe(§§ 7 and 8), reconsideration of old settled (§ 9) andunsettled (§ 10) issues, and some things that happen only on Earth,some indeed only in these reviews (§§ 10 and 11).
| Colliding Winds in Symbiotic Binary Systems. I. Analytic and Numerical Solutions
We present new formulations of binary colliding wind models appropriateto symbiotic star systems. The derived models differ from previousformulations in assuming mixing of the shocked material from bothincoming streams, rather than postulating a self-sustaining contactdiscontinuity. The CWb model (colliding winds, binary) extends the workof Girard and Willson by the derivation of an adiabatic temperature, theconsideration of radiative cooling, the inclusion of thermal pressuresin the incoming winds, and the treatment of interaction shells of finitethickness and density. The finite thickness of the interaction shellallows for calculation of its radiative intensity distribution. The CWcmodel (colliding winds, concentric) is a similar extension of the modelof Kwok, Purton, and Fitzgerald. It is derived in a manner parallel tothat of the CWb model, thereby facilitating a unification of the twomodels. A unified model is desired since wind collisions in symbioticsystems should include aspects of both CWb and CWc interactions. Twoexamples of model applications are presented: a comparison of the fluxdensities arising from colliding winds (CWb model) with those arisingfrom the ionization of the surrounding medium (STB model) in thegalactic population of symbiotic stars, and model imaging of thesymbiotic nova HM Sge.
| Far Ultraviolet Spectroscopic Explorer Observations of the Symbiotic Star AG Draconis
Spectra of the bright symbiotic star AG Draconis (BD +67°922) in thewavelength range 905-1187 Å obtained with the Far UltravioletSpectroscopic Explorer (FUSE) are presented. The spectra show a numberof narrow, nebular emission lines, together with a uniform continuumfrom the hot component of the system, and numerous interstellarabsorption lines. We infer the existence of Ne VIII in the AG Dra nebulathrough the identification of the Ne VII λ973.3 recombinationline. The emission-line spectrum is dominated by intense lines of O VIbut also shows weaker lines from highly ionized ions including Ne V, NeVI, S IV, and S VI. Members of the He II Balmer series can be identifiedup to n=20. Lines of Fe II and Fe III fluoresced by O VI λ1032are identified at wavelengths 1141.172 and 1142.429 Å,respectively. The emission lines are shown to be produced in a plasmawith an electron temperature of 20,000-30,000 K, photoionized by thewhite dwarf. The Ne VI λ997/λ999 ratio shows that this ionand all others except perhaps Ne VII are formed at least 300 white dwarfradii from the white dwarf. Revised wavelengths for the Ne V2s22p23P0,1-2s2p3 5S2and Ne VI 2s22p 2P-2s2p2 4Ptransitions are published.
| Spectral investigations of the symbiotic star CH Cygni.
Not Available
| Ubernahme der AFOEV Daten in die Einzelbeobachtungsdatenbank der BAV.
Not Available
| Self-Correlation Analysis of the Brightness Variability of Symbiotic Stars: A Pilot Project
About one-third of pulsating red giants show secondary periods which arean order of magnitude longer than the main pulsation period. The causesof the long secondary periods (LSPs) are unknown, but some may resultfrom the effects of a binary companion. We have carried outself-correlation analysis of EG And, AX Per, CH Cyg, CL Cyg, AG Peg, andZ And, using both visual and photoelectric data. Five of the stars showvariability which is orbit related: the time scale is equal to theorbital period, or half the orbital period. However, the pulsationalvariability, if any, is very low amplitude, compared with normal redgiants of the same spectral type.
| Spectral and Luminosity Classification of Symbiotic Star Cool Components with Near-Infrared Photometry
We have used the absolutely calibrated Wing eight-color near-infraredphotometric system to quantitatively derive spectral types andluminosity classes for the cool components of 12 symbiotic stars. Weexamine the advantages and limitations of the system as applied tosymbiotic systems. We find that three systems, CI Cyg, T CrB, and S149,have CN strengths corresponding to luminosity class II. For severalsystems there is a correlation between photometric phase and measuredspectral type.
| Fe II fluorescence in symbiotic stars
Fe 0 fluorescence by PAR has been investigated in eight symbiotic starshaving a wide range in temperature of the hot component and orbitalperiod. The data used are spectra obtained from the IUE archive. Allpumping lines investigated in this work are in the short wavelengthregion of IUE (1200-2000 Å), except for He 0 λ 1084.942 andO 0 λ 1032.041. The resulting Fe 0 fluorescence lines are mainlyin the long wavelength region (2000-3300 Å), but a few fall in thesame region as the pumping lines. The aim is to understand the optimalconditions for formation of Fe 0 fluorescence lines caused by PAR. Threeof the selected systems, RR Tel, AG Peg and V1016 Cyg, have 10-30 activeFe 0 channels. Two conditions connect those systems to each other: Thehot component is a white dwarf of extreme temperature (80 .103-150 . 103 K) and all three systems are socalled symbiotic novae and have had outbursts during the last 150 years.Three systems, AG Dra, RW Hya and R Aqr, have only 2-3 active Fe 0channels. In the two remaining systems, CI Cyg and T CrB, Fe 0fluorescence lines were totally absent. These two systems have twofeatures in common: The emission strength of highly ionized elements isless than in most symbiotic systems, and the hot component is suspectedto be an accreting main sequence star rather than a white dwarf.
| Modeling the wind structure of AG Peg by fitting of C IV and N V resonance doublets
The latest outburst of AG Peg has lasted for 150 years, which makes itthe slowest nova eruption ever recorded. During the time of IUEobservations (1978-1995) line profiles and intensity ratios of the N Vand C IV doublet components changed remarkably, and we discuss plausiblereasons. One of them is radiative pumping of Fe II which is investigatedby studying the fluorescence lines from pumped levels. Three Fe IIchannels are pumped by C IV and one by N V. The pumping rates of thoseFe II channels as derived by the modeling agree well with the strengthsof the Fe II fluorescence lines seen in the spectra. We model the C IVand N V resonance doublets in IUE spectra recorded between 1978 and 1995in order to derive optical depths, expansion velocities, and theemissivities of the red giant wind, the white dwarf wind and theircollision region. The derived expansion velocities are 60 kms-1 for the red giant wind and 700 km s-1 forthe white dwarf wind. We also suggest a fast outflow from the system at150 km s-1. The expansion velocity is slightly higherfor N V than for C IV. Emission from the collision region stronglyaffects the profile of the N V and C IV resonance doublets indicatingits existence.
| Spectroscopic Diagnostics of Symbiotic Stars. II. Statistical Analyses of Highly Resolved Emission-Line Profiles
We obtained highly resolved spectroscopic data of 34 symbiotic stars atHα, He II λ 4686, and [O III ] λ 5007. We analyzed the line profilesstatistically to obtain clear common characteristics of the emissionnebulae in symbiotic stars. We first carried out coarse analyses, whichsuggested differences in the line profiles between the quiescent andoutburst phases. Second, we de-convolved the line profiles with multipleGaussian components, and statistically dealt with each component inorder to extract certain characteristics as a group. In the case ofalmost edge-on binary orbits, the relation between the characteristicvelocities of the main, the broad wing, and the absorption components ofHα versus the orbital phase can be explained by the existence andinteraction of stellar winds from cool and hot stars. The difference inthe width of the main component of He II λ4686 between the quiescent and the outburst phases and the changes intheir radial velocities with the orbital phase support the idea thatHe++ gas would distribute around a hot star. Double-peakedprofiles of [O III ] λ 5007 lines and theirrelation to the orbital phase can be explained by bi-conical flows.
| Classification of Spectra from the Infrared Space Observatory PHT-S Database
We have classified over 1500 infrared spectra obtained with the PHT-Sspectrometer aboard the Infrared Space Observatory according to thesystem developed for the Short Wavelength Spectrometer (SWS) spectra byKraemer et al. The majority of these spectra contribute to subclassesthat are either underrepresented in the SWS spectral database or containsources that are too faint, such as M dwarfs, to have been observed byeither the SWS or the Infrared Astronomical Satellite Low ResolutionSpectrometer. There is strong overall agreement about the chemistry ofobjects observed with both instruments. Discrepancies can usually betraced to the different wavelength ranges and sensitivities of theinstruments. Finally, a large subset of the observations (~=250 spectra)exhibit a featureless, red continuum that is consistent with emissionfrom zodiacal dust and suggest directions for further analysis of thisserendipitous measurement of the zodiacal background.Based on observations with the Infrared Space Observatory (ISO), aEuropean Space Agency (ESA) project with instruments funded by ESAMember States (especially the Principle Investigator countries: France,Germany, Netherlands, and United Kingdom) and with the participation ofthe Institute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| Photometry of symbiotic stars. XI. EG And, Z And, BF Cyg, CH Cyg, CI Cyg, V1329 Cyg, TX CVn, AG Dra, RW Hya, AR Pav, AG Peg, AX Per, QW Sge, IV Vir and the LMXB V934 Her
We present new photometric observations of EG And, Z And, BF Cyg, CHCyg, CI Cyg, V1329 Cyg, TX CVn, AG Dra, RW Hya, AG Peg, AX Per, IV Virand the peculiar M giant V934 Her, which were made in the standardJohnson UBV(R) system. QW Sge was measured in the Kron-Cousin B, V,RC, IC system and for AR Pav we present its newvisual estimates. The current issue gathers observations of theseobjects to December 2003. The main results can be summarized as follows:EG And: The primary minimum in the U light curve (LC) occurred at theend of 2002. A 0.2 -- 0.3 mag brightening in U was detected in theautumn of 2003. Z And: At around August 2002 we detected for the firsttime a minimum, which is due to eclipse of the active object by the redgiant. Measurements from 2003.3 are close to those of a quiescent phase.BF Cyg: In February 2003 a short-term flare developed in the LC. Adifference in the depth of recent minima was detected. CH Cyg: This starwas in a quiescent phase at a rather bright state. A shallow minimumoccurred at JD 2 452 730, close to the position of the inferiorconjunction of the giant in the inner binary of the triple-star model ofCH Cyg. CI Cyg: Our observations cover the descending branch of a broadminimum. TX CVn: At/around the beginning of 2003 the star entered abright stage containing a minimum at JD 2 452 660. AG Dra: Newobservations revealed two eruptions, which peaked in October 2002 and2003 at 9.3 in U. AR Pav: Our new visual estimates showed atransient disappearance of a wave-like modulation in the star'sbrightness between the minima at epochs E = 66 and E = 68 and itsreappearance. AG Peg: Our measurements from the end of 2001 showedrather complex profile of the LC. RW Hya: Observations follow behaviourof the wave-like variability of quiet symbiotics. AX Per: In May 2003 a0.5 mag flare was detected following a rapid decrease of the light to aminimum. QW Sge: CCD observations in B, V, RC, ICbands cover a period from 1994.5 to 2003.5. An increase in the star'sbrightness by about 1 mag was observed in all passbands in 1997. Lesspronounced brightening was detected in 1999/2000. V934 Her: Ourobservations did not show any larger variation in the optical as areaction to its X-ray activity.
| Hα variability of the recurrent nova T Coronae Borealis
We analyze Hα observations of the recurrent nova TCrB obtained during the last decade. For the first time theHα emission profile is analyzed after subtraction of the red giantcontribution. Based on our new radial velocity measurements of theHα emission line we estimate the component masses of TCrB. It is found that the hot component is most likely amassive white dwarf. We estimate the inclination and the componentmasses to be i≃67o,MWD≃1.37±0.13 Mȯ andMRG≃1.12±0.23 Mȯ, respectively. The radial velocity of the central dip in the Hα profile changesnearly in phase with that of the red giant's absorption lines. Thissuggests that the dip is most likely produced by absorption in thegiant's wind.Our observations cover an interval when the Hα and the U-band fluxvary by a factor of 6, while the variability in B and V is muchsmaller. Based on our observations, and archival ultraviolet and opticaldata we show that the optical, ultraviolet and Hα fluxes stronglycorrelate. We argue that the presence of an accretion disc can accountfor most of the observed properties of T CrB.Based on observations obtained at Rozhen National AstronomicalObservatory, Bulgaria.
| Symbiotic Stars as Laboratories for the Study of Accretion and Jets: A Call for Optical Monitoring
Symbiotic binary stars typically consist of a white dwarf (WD) thataccretes material from the wind of a companion red giant. Orbitalperiods for these binaries are on the order of years, and theirrelatively small optical outbursts tend to occur every few years todecades. In some symbiotics, material that is transferred from the redgiant to the WD forms a disk around the WD. Thus, symbiotic stars are abit like overgrown cataclysmic variables (CVs), but with less violenteruptions. Symbiotic stars are not as well understood as CVs, in partbecause their longer variability time scales mean that observations overmany years are required to cover different outburst states and orbitalphases. The recent discovery of collimated outflows ("jets") from anumber of symbiotics provides a new motivation for such long-term studyof these objects. Astrophysical jets are observed in almost every typeof accretion-powered system, and symbiotic stars may help us understandthese structures. Optical monitoring by amateurs can identify systemsin outburst, and also help to build a comprehensive database of outburstand quiescent symbiotic light curves. Together with radio through X-rayobservations that will be performed when new outbursts are found,long-term optical light curves will improve understanding of symbioticoutbursts, jet production, and the connection between outbursts, jets,and accretion disks in symbiotic stars.
| HST/WFPC2 snapshot imaging of symbiotic stars
The results of a HST/WFPC2 snapshot imaging survey of selected symbioticstars in 1999/2000 are presented. Seven sources - HD 149427 (PC 11), PUVul, RT Ser, He2-104 (Southern Crab), V1329 Cyg (HBV 475), V417 Cen andAS 201 - were observed in filters F218W (ultraviolet continuum), F502N([O III]λλ 4959, 5007) and F656N (Hαλ 6563);an eighth source, RS Oph, was observed in F437N ([O III]λ 4363),F502N and F656N. The presence of extended emission was detected inHe2-104, V1329 Cyg and possibly HD 149427. In He2-104, we detected the[O III] and Hα counterparts to the inner lobes found in [N II] byCorradi et al. For V1329 Cyg, comparison with previously publishedHST/FOC results indicates expanding ejecta which may be associated withan ejection event in 1982 (+/-2 yr) at a velocity of 260 +/- 50 kms-1 in the plane of the sky and at an assumed distance of 3.4kpc. We also present previously unpublished radio images of HD 149427,which we have obtained from the archives of the Australia TelescopeCompact Array and which reveal the presence of extended emission at asimilar orientation to that of the possible optical extension. Finally,we also include HST/WFPC2 GO observations of AG Peg and detect possibleextended emission in the F218W filter.
| Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type stars
This paper presents the catalogue and the method of determination ofaveraged quadratic effective magnetic fields < B_e > for 596 mainsequence and giant stars. The catalogue is based on measurements of thestellar effective (or mean longitudinal) magnetic field strengths B_e,which were compiled from the existing literature.We analysed the properties of 352 chemically peculiar A and B stars inthe catalogue, including Am, ApSi, He-weak, He-rich, HgMn, ApSrCrEu, andall ApSr type stars. We have found that the number distribution of allchemically peculiar (CP) stars vs. averaged magnetic field strength isdescribed by a decreasing exponential function. Relations of this typehold also for stars of all the analysed subclasses of chemicalpeculiarity. The exponential form of the above distribution function canbreak down below about 100 G, the latter value representingapproximately the resolution of our analysis for A type stars.Table A.1 and its references are 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/407/631 and Tables 3 to 9are only available in electronic form at http://www.edpsciences.org
| Mass ejection by the symbiotic binary Z And during its 2000-2002 outburst
Broad-band UBVJHKLM data have been obtained at the time of the quiescentorbital photometric maximum of the classical symbiotic binary system ZAnd, and at some epochs of its 2000-2002 active phase. The data of theactive phase are related to the time of the optical maximum and after itwhen the star was returning to quiescence. Broad-band quiescent RIphotometry from the literature was also used to obtain the parameters ofthe cool component of this binary. All of these data suggest that thehot compact component has undergone a major expansion and the emissionmeasure of the circumbinary nebula has also increased. Some mechanismsfor interpretation of the outburst are reviewed.Based on observations collected at the National Astronomical ObservatoryRozhen, Bulgaria and the Crimean Station of the Sternberg AstronomicalInstitute, Ukraine.
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Osservazione e dati astrometrici
| Costellazione: | Pegaso |
| Ascensione retta: | 21h51m01.97s |
| Declinazione: | +12°37'32.1" |
| Magnitudine apparente: | 8.699 |
| Distanza: | 10000000 parsec |
| Moto proprio RA: | -1 |
| Moto proprio Dec: | -3.5 |
| B-T magnitude: | 10.183 |
| V-T magnitude: | 8.822 |
Cataloghi e designazioni:
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