Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
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.
| Infrared Spectroscopy of Symbiotic Stars. V. First Orbits for Three S-Type Systems: Henize 2-173, CL Scorpii, and AS 270
Infrared radial velocities have been used to compute first orbits of theM giants in three southern S-type symbiotic systems. Of the three, Hen2-173 has the longest orbital period, 911 days, and also has anoncircular orbit with an eccentricity of 0.21. The large value of itsmass function suggests that Hen 2-173 may be an eclipsing system. For CLSco our spectroscopic orbital period of 626 days is essentiallyidentical to the previously determined light variability period of 625days, and we have adopted the latter. AS 270 has an orbital period ofsimilar length, 671 days, and both CL Sco and AS 270 have circularorbits. Only CL Sco has been extensively investigated previously, and wecompare our results with the conclusions of Kenyon & Webbink. Wealso have examined the period-eccentricity relation for 30 S-typesymbiotics. Circular orbits are found for 81% of the systems withorbital periods up to 800 days, while they occur for only 22% withperiods greater than 800 days. This distribution is quite unlike thatfor G and K giants; rather, it is similar to that for barium stars,another type of mass-transfer binary, which also consists of a late-typegiant and a white dwarf companion.
| 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.
| Not Available
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.
| The Non-Standard Multifrequency Behavior of AG DRA
We summarize the behavior of AG Dra during the last 25 years,characterized by a sequence of 5 active phases (with 14 light maxima).Cool and hot outbursts are discussed. In general, during bursts theX-ray flux weakens or vanishes, which should be mostly due to anincrease of the high energy opacity of the envelope, rather than to adecrease of the source temperature. An explanation is suggested for thedifferent behavior of the He II Zanstra temperature during the two bursttypes, and the possibility is considered that during all the burstevents AG Dra first passes through a hot phase, and that only in thestrongest bursts it evolves towards the cool burst phase.
| 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.
| High-Ionization Forbidden Lines in the UV Spectrum of AG Draconis
High-ionization forbidden lines from Ca VII, Fe VII, Mg V, Mg VI, MgVII, and Si VII are found in recent Hubble Space Telescope STISultraviolet spectra of the symbiotic star AG Draconis. These specieshave ionization potentials between 99 and 205 eV, which are unexpecteddue to the high density (~1010 cm-3) of the AG Dranebula. The identification of the Mg VII λλ2510, 2629lines is the first in astrophysical or laboratory spectra, and revisedrest wavelengths are suggested from the STIS spectra. Plasma diagnosticsfrom Mg V-VII are applied, but do not provide a consistent constraint ontemperature or density. A density >=108 cm-3 isconfirmed, however. The lines show double-peaked profiles with widths~100-160 km s-1, suggestive of an origin in an accretiondisk. However, the line widths, if identified with motion in a Kepleriandisk, indicate radii much smaller than sizes inferred from the linefluxes themselves. The source of these high-ionization forbidden linesremains unidentified.
| 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).
| Aus der Sektion Kataklysmische Sterne Juli - November 2006.
Not Available
| Emission line variability of RS Ophiuchi*
We report that the Hα emission line of RS Oph was stronglyvariable during our 2004 observations on a time-scale of one month. Theline consisted of both a double-peaked central narrow component [fullwidth at half-maximum (FWHM) ~ 220 kms-1] and a stronglyvariable broad one (FWHM > 2000 kms-1). The base of theHα line was very broad, with full width at zero intensity ~4600kms-1 on all spectra from 1986 to 2004. The variability ofthe broad component extends from -2000 to +2000 kms-1. Mostprobably this is due either to blobs ejected from the white dwarf (witha typical blob mass estimated to be ~10-10Msolar)or to a variable accretion disc wind. We also detected variability ofthe HeIIλ4686 line on a time-scale shorter than 1 d. The possibleorigin is discussed.
| On metal-deficient barium stars and their link with yellow symbiotic stars
This paper addresses the question of why metal-deficient barium starsare not yellow symbiotic stars (YSyS). Samples of (suspected)metal-deficient barium (mdBa) stars and YSyS have been collected fromthe literature, and their properties reviewed. It appears in particularthat the barium nature of the suspected mdBa stars needs to beascertained by detailed abundance analyses. Abundances are thereforederived for two of them, HD 139409 and HD 148897, which reveal that HD148897 should not be considered a barium star. HD 139409 is a mildbarium star, with overabundances observed only for elements belonging tothe first s-process peak (Y and Zr). It is only moderately metal-poor([Fe/H] = -0.4). The evidence for binarity among mdBa stars is thenreviewed, using three different methods: (i) radial-velocity variations(from CORAVEL observations), (ii) Hipparcos astrometric data, and (iii)a method based on the comparison between the Hipparcos and Tycho-2proper motions. An orbit is obtained for HIP 55852, whereas evidence forthe (so far unknown) binary nature of HIP 34795, HIP 76605, HIP 97874and HIP 107478 is presented. No conclusion regarding the binary natureof HIP 11595, HIP 25161 could be reached. Two stars with no evidence forbinarity whatsoever (HIP 58596 and BD +3°2688) are candidateslow-metallicity thermally-pulsing asymptotic giant branch stars, asinferred from their large luminosities. The reason why mdBa stars arenot YSyS is suggested to lie in their different orbital perioddistributions: mdBa stars have on average longer orbital periods thanYSyS, and hence their companion accretes matter at a lower rate, for agiven mass loss rate of the giant star. The definite validation of thisexplanation should nevertheless await the determination of the orbitalperiods for the many mdBa stars still lacking periods, in order to makethe comparison more significant.
| 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.
| Bipolar jet growth and decline in Hen 3-1341: a direct link to fast wind and outburst evolution*
We report on and investigate the evolution and disappearance in thesymbiotic star Hen 3-1341 of collimated bipolar jets, which take theform of symmetrically displaced components of emission lines. Frommodelling of the emission-line spectrum it turns out that the accretingwhite dwarf (WD) in quiescence has TWD~ 1.2 ×105 K and RWD~ 0.14 Rsolar, for aluminosity of 3.8 × 103 Lsolar, and it isstably burning hydrogen on the surface at a rate of , feeding ionizingphotons to a radiation bounded circumstellar nebula extending for ~17au. The WD underwent a multimaxima outburst lasting from 1998 to 2004during which its H-burning envelope reacted to a probable small increasein the mass accretion by expanding and cooling to Teff~ 1× 104 K and R~ 20 Rsolar, mimicking anA-type giant that radiated a total of ~6 × 1044 erg, atan average rate of ~1 × 103 Lsolar. Bipolarjets developed at the time of outburst maximum and their strengthdeclined in parallel with the demise of the fast wind from the inflatedWD, finally disappearing when the wind stopped halfway to quiescence,marking a 1:1 correspondence between jets presence and feeding action ofthe fast wind. The total mass in the jets was Mjet~ 2.5× 10-7 Msolar for a kinetic energy ofEkinjet~ 1.7 × 1042(sini)-1 erg, corresponding to ~0.3(sini)-1 percent of the energy radiated during the whole outburst. We suggest thatthe spectroscopic search for jets in symbiotic stars could pay higherdividends if focused on the outburst phases characterized by maximumwind intensity.
| AS 325: Discovery of Eclipses in an Enigmatic Emission Line Star
AS 325 (= NSV 24607 = CD -26 13521 = CPD -26 6567 = He 3-1728; 18h 50m03.57s -26deg 24' 15.4" (2000.0)) is found to be an eclipsing binarywith a period of 513 days using ASAS-3 data. This discovery, in additionto the presence of out of eclipse variations and a long term brighteningtrend in the light curve, support the symbiotic classification of thissystem. A call for observations at the next eclipse between June anAugust 2005 is made.
| 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.
| Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters
The availability of the Hipparcos Catalogue has triggered many kinematicand dynamical studies of the solar neighbourhood. Nevertheless, thosestudies generally lacked the third component of the space velocities,i.e., the radial velocities. This work presents the kinematic analysisof 5952 K and 739 M giants in the solar neighbourhood which includes forthe first time radial velocity data from a large survey performed withthe CORAVEL spectrovelocimeter. It also uses proper motions from theTycho-2 catalogue, which are expected to be more accurate than theHipparcos ones. An important by-product of this study is the observedfraction of only 5.7% of spectroscopic binaries among M giants ascompared to 13.7% for K giants. After excluding the binaries for whichno center-of-mass velocity could be estimated, 5311 K and 719 M giantsremain in the final sample. The UV-plane constructed from these datafor the stars with precise parallaxes (σπ/π≤20%) reveals a rich small-scale structure, with several clumpscorresponding to the Hercules stream, the Sirius moving group, and theHyades and Pleiades superclusters. A maximum-likelihood method, based ona Bayesian approach, has been applied to the data, in order to make fulluse of all the available stars (not only those with precise parallaxes)and to derive the kinematic properties of these subgroups. Isochrones inthe Hertzsprung-Russell diagram reveal a very wide range of ages forstars belonging to these groups. These groups are most probably relatedto the dynamical perturbation by transient spiral waves (as recentlymodelled by De Simone et al. \cite{Simone2004}) rather than to clusterremnants. A possible explanation for the presence of younggroup/clusters in the same area of the UV-plane is that they have beenput there by the spiral wave associated with their formation, while thekinematics of the older stars of our sample has also been disturbed bythe same wave. The emerging picture is thus one of dynamical streamspervading the solar neighbourhood and travelling in the Galaxy withsimilar space velocities. The term dynamical stream is more appropriatethan the traditional term supercluster since it involves stars ofdifferent ages, not born at the same place nor at the same time. Theposition of those streams in the UV-plane is responsible for the vertexdeviation of 16.2o ± 5.6o for the wholesample. Our study suggests that the vertex deviation for youngerpopulations could have the same dynamical origin. The underlyingvelocity ellipsoid, extracted by the maximum-likelihood method afterremoval of the streams, is not centered on the value commonly acceptedfor the radial antisolar motion: it is centered on < U > =-2.78±1.07 km s-1. However, the full data set(including the various streams) does yield the usual value for theradial solar motion, when properly accounting for the biases inherent tothis kind of analysis (namely, < U > = -10.25±0.15 kms-1). This discrepancy clearly raises the essential questionof how to derive the solar motion in the presence of dynamicalperturbations altering the kinematics of the solar neighbourhood: doesthere exist in the solar neighbourhood a subset of stars having no netradial motion which can be used as a reference against which to measurethe solar motion?Based on observations performed at the Swiss 1m-telescope at OHP,France, and on data from the ESA Hipparcos astrometry satellite.Full Table \ref{taba1} is only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/430/165}
| High-resolution spectroscopic observations of the D'-type symbiotic stars HD 330036 and AS 201
We present high-resolution spectroscopic analyses of two starsclassified as D'-type symbiotic stars, HD 330036 and AS 201. These twostars display both rapid rotation and enhancements of the s-processelements that are synthesized via slow neutron captures during stellarevolution along the asymptotic giant branch (AGB). Both characterisiticsof rapid rotation and s-process overabundances have also been discoveredrecently in another D'-type symbiotic, S190. The stellar parametersderived here for HD 330036 are Teff=6200 K and log g=2.4,while AS 201 has Teff=6000 K and log g=2.3. Resultingluminosity and distance estimates are 650 Lȯ and 2.3 kpcfor HD 330036, and 700 Lȯ and 4.3 kpc for AS 201. BothHD 330036 and AS 201 have evolved away from the main sequence and areapproaching the base of the red-giant branch. These stars havenear-solar abundances of iron and calcium, but substanial enhancements(by about +0.9 dex for HD 330036 and +1.7 dex for AS 201) of thes-process element barium. The observed barium overabundances in thecurrent cool-star members of these two binary systems probably resultedfrom mass-transfer when the current white dwarf was an AGB star. Therapid rotation found in the cool stars may also be due to mass-transfer,with the mass-gaining stars being spun up with the transfer of angularmomentum from the AGB winds. As only a few (six) D'-type symbiotics areknown, the fact that the 3 studied to date at high-spectral resolutionall display rapid rotation and s-process elemental overabundances mayindicate that these two traits are signatures of these rare binarysystems.Based on observations made with the 1.52 m telescope at the EuropeanSouthern Observatory (La Silla, Chile) under the agreement with theCNPq-Observatório Nacional (Brazil).
| Spectral investigations of the symbiotic star CH Cygni.
Not Available
| Ubernahme der AFOEV Daten in die Einzelbeobachtungsdatenbank der BAV.
Not Available
| 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.
| Spreading of Accreted Material on White Dwarfs
When a white dwarf (WD) is weakly magnetized and its accretion disk isthin, accreted material first reaches the WD's surface at its equator.This matter slows its orbit as it comes into corotation with the WD,dissipating kinetic energy into thermal energy and creating a hot bandof freshly accreted material around the equator. Radiating in theextreme-ultraviolet and soft X-ray, this material moves toward the poleas new material piles up behind it, eventually becoming part of the WDonce it has a temperature and rotational velocity comparable to those atthe surface. We present a set of solutions that describe the propertiesof this ``spreading layer'' in the steady state limit on the basis ofthe conservation equations recently derived by Inogamov and Sunyaev foraccreting neutron stars. Our analysis and subsequent solutions show thatthe case of WDs is qualitatively different. We investigate examplesolutions of the spreading layer for a WD of mass M=0.6Msolarand radius R=9×108cm. These solutions show that thespreading layer typically extends to an angle ofθSL~0.01-0.1 (with respect to the equator), dependingon accretion rate and the magnitude of the viscosity. At low accretionrates, M˙<~1018gs-1, the amount ofspreading is negligible, and most of the dissipated energy is radiatedback into the accretion disk. When the accretion rate is high, such asin dwarf novae, the material may spread to latitudes high enough to bevisible above the accretion disk. The effective temperature of thespreading layer is ~(2-5)×105K with approximatelyTeff~M˙9/80. This power-law dependence onM˙ is weaker than for a fixed radiating area and may help explainextreme-ultraviolet observations during dwarf novae. We speculate aboutother high accretion rate systems(M˙>~1018gs-1) that may show evidence for aspreading layer, including symbiotic binaries and supersoft sources.
| Long-term photometric and spectroscopic behaviour of symbiotic system AG Dra
The general behaviour of AG DRA was studied in the context of thelong-term photometry and radial velocity analysis.
| Symbiotic Stars in the Magellanic Clouds
Orbital periods and other parameters of symbiotic binary systems in theLMC and SMC are presented and discussed. In particular, the symbioticstars in the MCs are compared with those in the Milky Way.
| Searching for periods in X-ray observations using Kuiper's test. Application to the ROSAT PSPC archive
We use Kuiper's test to detect periodicities in X-ray and gamma-rayobservations. Like Rayleigh's test, it uses the individual photonarrival times, and is therefore well suited to the analysis of faintsources. Our method makes it possible to take into account thediscontinuities in the observation, and to completely get rid of thecontamination that results from them. This makes it particularly adaptedto the search of periods long compared to the total observationduration. We propose a semi-analytical approach to determine theeffective number of trial frequencies when searching for unknown periodsover a frequency range. This approach can be easily adapted to othertests. We show that, using Kuiper's test, we can recover periods infrequency domains where other tests are completely confused bycontamination. We finally search the entire ROSAT Position-SensitiveProportional Counter (PSPC) archive for long periods, and find 28 newperiodic-source candidates.Appendices A and B are only available in electronic form athttp://www.edpsciences.org
| 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.
|
Enviar un nou article
Enllaços Relacionats
- - No s'ha trobat enllaços -
Enviar un nou enllaç
Membre dels grups següents:
|
Dades d'Observació i Astrometria
| Constel·lació: | Draco |
| Ascensió Recta: | 16h01m41.01s |
| Declinació: | +66°48'10.1" |
| Magnitud Aparent: | 9.795 |
| Moviment propi RA: | -7.3 |
| Moviment propi Dec: | -5.8 |
| B-T magnitude: | 11.519 |
| V-T magnitude: | 9.938 |
Catàlegs i designacions:
|
INHABITED SKY
