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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).
| 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.
| 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}
| 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.
| 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.
| 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.
| 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.
| High-Velocity Jets from Symbiotic Stars and Other Astrophysical Systems
Among about 200 known symbiotic stars there are at least 6--7 objectswhich have exhibited high-velocity, collimated, bipolar jets. Thepossibility that those jet sources contain hot components with lowerluminosities (Lhot 1--102 Lȯ)than in most other symbiotic stars is discussed. This implies that thoseobjects are powered by accretion rather than by thermonuclear reactions.Other types of jet sources and relations of symbiotic stars to them arebriefly discussed.
| 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.
| 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.
| Synthetic Spectral Analysis of the Hot Component in the S-Type Symbiotic Variable EG Andromedae
We have applied grids of non-LTE (NLTE) high-gravity model atmospheresand optically thick accretion disk models for the first time to archivalIUE and FUSE spectra of the S-type symbiotic variable EG Andromedaetaken at superior spectroscopic conjunction, when Rayleigh scatteringshould be minimal and the hot component is viewed in front of the redgiant. For EG And's widely accepted, published hot-component mass,orbital inclination, and distance from the Hipparcos parallax, we findthat hot, high-gravity, NLTE photosphere model fits to the IUE spectrayield distances from the best-fitting models that agree with theHipparcos parallax distance, but at temperatures substantially lowerthan the modified Zanstra temperatures. NLTE fits to an archival FUSEspectrum taken at the same orbital phase as the IUE spectra yield thesame temperature as the IUE temperature (50,000 K). However, for thesame hot-component mass, inclination, and parallax-derived distance,accretion disk models at moderately high inclinations, ~60°-75°,with accretion rates M from 1×10-8 to1×10-9 Msolar yr-1 for whitedwarf masses Mwd=0.4 Msolar yield distancesgrossly smaller than the distance from the Hipparcos parallax.Therefore, we rule out an accretion disk as the dominant source of thefar-UV flux. Our findings support a hot bare white dwarf as the dominantsource of far-UV flux.
| 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.
| 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.
| Reprocessing the Hipparcos Intermediate Astrometric Data of spectroscopic binaries. II. Systems with a giant component
By reanalyzing the Hipparcos Intermediate Astrometric Data of a largesample of spectroscopic binaries containing a giant, we obtain a sampleof 29 systems fulfilling a carefully derived set of constraints andhence for which we can derive an accurate orbital solution. Of these,one is a double-lined spectroscopic binary and six were not listed inthe DMSA/O section of the catalogue. Using our solutions, we derive themasses of the components in these systems and statistically analyzethem. We also briefly discuss each system individually.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997) and on data collected with theSimbad database.
| Hipparcos red stars in the HpV_T2 and V I_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibratedinstantaneous (epoch) Cousins V - I color indices using newly derivedHpV_T2 photometry. Three new sets of ground-based Cousins V I data havebeen obtained for more than 170 carbon and red M giants. These datasetsin combination with the published sources of V I photometry served toobtain the calibration curves linking Hipparcos/Tycho Hp-V_T2 with theCousins V - I index. In total, 321 carbon stars and 4464 M- and S-typestars have new V - I indices. The standard error of the mean V - I isabout 0.1 mag or better down to Hp~9 although it deteriorates rapidly atfainter magnitudes. These V - I indices can be used to verify thepublished Hipparcos V - I color indices. Thus, we have identified ahandful of new cases where, instead of the real target, a random fieldstar has been observed. A considerable fraction of the DMSA/C and DMSA/Vsolutions for red stars appear not to be warranted. Most likely suchspurious solutions may originate from usage of a heavily biased color inthe astrometric processing.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).}\fnmsep\thanks{Table 7 is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/397/997
| The symbiotic star CH Cygni - IV. Basic kinematics of the circumstellar matter during active phases
We give a brief summary of common basic characteristics of active phasesduring the whole (1963-2000) observed symbiotic life of CH Cygni. Weidentify two types of outbursts: (1) those with pronounced signatures ofa high-velocity mass outflow, and (2) those displaying signatures ofonly a mass inflow to the central star. On the basis of the observedHα emission, we investigate mass loss from the active star duringthe period from when radio jets appeared (1984.6) to the most recentactivity (1998-2000). A simple expression, which relates the observedHα luminosity to the mass-loss rate, is derived. We obtainedmass-loss rates of and 1.8 +/- 0.7 × 10-6Msolar yr-1 in 1984 October, 1992 August and 1998September, respectively. Our values are in very good agreement withradio mass-loss rates determined previously. Mass loss from CH Cygni isa transient effect connected only with active phases of type (1), and isvery variable. The ejected material, which is accelerated to the samev&infy; at a distance of ~ 100 Rsolar, is heavilydecelerated at much larger distances (~ 1000 au). The most recent ejectareflect a larger deceleration.
| Photometry of symbiotic stars. X. EG And, Z And, BF Cyg, CH Cyg, V1329 Cyg, AG Dra, RW Hya, AX Per and IV Vir
We present new photometric observations of EG And, Z And, BF Cyg, CHCyg, V1329 Cyg, AG Dra, RW Hya, AX Per and IV Vir made in the standardJohnson UBVR system. The current issue summarizes observations of theseobjects to 2001 December. The main results can be summarized as follows:EG And: A periodic double-wave variation in all bands as a function ofthe orbital phase was confirmed. A maximum of the light changes wasobserved in U (Delta U ~ 0.5 mag). Z And: Our observations cover anactive phase, which peaked around 8.4 in U at the beginning of 2000December. Consequently, a gradual decrease in the star's brightness hasbeen observed. BF Cyg: A periodic wave-like variation in the opticalcontinuum reflects a quiescent phase of this star. A complex light curve(LC) profile was observed. CH Cyg: The recent episode of activity endedin Spring 2000. We determined the position of an eclipse in the outerbinary at JD 2451426 +/- 3. Recent observations indicate a slow increasein the star's brightness. V1329 Cyg: Observations were made around amaximum at 2001.2. AG Dra: Our measurements from the Autumn of 2001revealed a new eruption, which peaked at ~JD 2452217. RW Hya: The lightminimum in our mean visual LC precedes the time of the spectroscopicconjunction of the giant in the binary. AX Per: A periodic wave-likevariation was observed. Our recent observations revealed a secondaryminimum at the orbital phase 0.5, seen best in the V and B bands. IVVir: The LC displays a double-wave throughout the orbital cycle.
| Infrared low-resolution spectra of symbiotic stars
The IRAS low-resolution spectra (LRS) of 29 symbiotic stars arepresented in this paper. It is found that silicate dust is commonmaterial in the circumstellar shells of symbiotic stars. From the IRASlow-resolution spectra, IRAS colors, symbiotic types and spectral types,some physical properties of symbiotic stars with the LRS spectra arealso discussed.
| A multi-epoch spectrophotometric atlas of symbiotic stars
A multi-epoch, absolute-fluxed spectral atlas extending from about 3200to 9000 Å is presented for 130 symbiotic stars, including membersof the LMC, SMC and Draco dwarf galaxies. The fluxes are accurate tobetter than 5% as shown by comparison with Tycho and ground-basedphotometric data. The spectra of 40 reference objects (MKK cool giantstandards, Mira and Carbon stars, planetary nebulae, white dwarfs, hotsub-dwarfs, Wolf-Rayet stars, classical novae, VV Cep and Herbig Ae/Beobjects) are provided to assist the interpretation of symbiotic starspectra. Astrometric positions and counterparts in astrometriccatalogues are derived for all program symbiotic stars. The spectra areavailable in electronic form from the authors. Based on observationscollected with the telescopes of the European Southern Observatory (ESO,Chile) and of the Padova & Asiago Astronomical Observatories(Italy). Tables 2 and 3 are only available in electronic form (a) at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/383/188, and (b) from thepersonal home page http://ulisse.pd.astro.it/symbio_atlas/ Figures 4-256are only available in electronic form (a) at http://www.edpsciences.organd (b) from the personal home pagehttp://ulisse.pd.astro.it/symbio_atlas/
| Long-Term VRI Photometry of Small-Amplitude Red Variables. I. Light Curves and Periods
We report up to 5000 days of VRI photometry, from a robotic photometrictelescope, of 34 pulsating red giants, namely, TV Psc, EG And, Z Psc, RZAnd, 4 Ori, RX Lep, UW Lyn, η Gem, μ Gem, ψ1 Aur,V523 Mon, V614 Mon, HD 52690, Y Lyn, BC CMi, X Cnc, UX Lyn, RS Cnc, VYUMa, ST UMa, TU CVn, FS Com, SW Vir, 30 Her, α1 Her,V642 Her, R Lyr, V450 Aql, V1293 Aql, δ Sge, EU Del, V1070 Cyg, WCyg, and μ Cep, as well as a few variable comparison stars. V, R, andI variations are generally in phase. The length and density of the dataenable us to look for variations on timescales ranging from days toyears. We use both power-spectrum (Fourier) analysis and autocorrelationanalysis, as well as light-curve analysis; these three approaches arecomplementary. The variations range from regular to irregular, but inmost of the stars, we find a period in the range of 20-200 days, whichis probably due to low-order radial pulsation. In many of the stars, wealso find a period which is an order of magnitude longer. It may be dueto rotation, or it may be due to a new kind of convectively inducedoscillatory thermal mode, recently proposed by P. Wood.
| Raman Scattering in Symbiotic Stars
Not Available
| A search for rapid photometric variability in symbiotic binaries
We report on our survey for rapid (time-scale of minutes) photometricvariability in symbiotic binaries. These binaries are becoming anincreasingly important place to study accretion on to white dwarfs,since they are candidate Type Ia supernova progenitors. Unlike in mostcataclysmic variables, the white dwarfs in symbiotics typically accretefrom a wind, at rates greater than or equal to10-9Msolaryr-1. In order to elucidatethe differences between symbiotics and other white dwarf accretors, aswell as to search for magnetism in symbiotic white dwarfs, we havestudied 35 symbiotic binaries via differential optical photometry.Included in our sample are all but one of the symbiotics from the listsof Kenyon and Downes & Keyes with published V magnitudes less than14 and declinations greater than -20°. Our study is the mostcomprehensive to date of rapid variability in symbiotic binaries. Wehave found one magnetic accretor, Z And, previously reported bySokoloski & Bildsten. In four systems (EG And, BX Mon, CM Aql and BFCyg), some evidence for flickering at a low level (roughly 10mmag) isseen for the first time. These detections are, however, marginal. For 25systems, we place tight upper limits on both aperiodic variability(flickering) and periodic variability, highlighting a major differencebetween symbiotics and cataclysmic variables. The remaining five of theobjects included in our sample (the two recurrent novae RS Oph and TCrB, plus CH Cyg, o Ceti and MWC 560) had previous detections of opticalflickering. We discuss our extensive observations of these previouslyknown flickering systems in a separate paper. Five new variable starswere discovered serendipitously in the fields of the survey objects, andthe observations of these stars are also presented elsewhere. We discussthe impact of our results on the `standard' picture of wind-fedaccretion, and speculate on the possibility that light from quasi-steadynuclear burning on the surface of the white dwarf hides the fluctuatingemission from accretion.
| Periods of 25 Pulsating Red Giants
We report periods and amplitudes of 25 pulsating red giants: T Cet, EGAnd, AK Hya, TV UMa, GK Com, SW Vir, FH Vir, EV Vir, tau-4 Ser, AZ Dra,V973 Cyg, V1070 Cyg, and also HR 211, 284, 648, 2286, 2999, 3521, 4267,4483, 5331, 5352, 6543, 6815, and 7009, determined from AmericanAssociation of Variable Stars (AAVSO) photoelectric photometry over upto 5800 days.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| High resolution spectroscopy of symbiotic stars. VI. Orbital and stellar parameters for AR Pavonis
We present new dynamical parameters of the AR Pav binary system. Ourobservations consist of a series of high resolution optical/NIR spectrafrom which we derive the radial velocity curve of the red giant as wellas its rotation velocity. Assuming co-rotation, we determine the stellarradius (130 Rsun) of the red giant. Based on this we derivethe red giant's luminosity and mass (2.0 Msun) as well as thedistance of the system (4.9 kpc). The binary mass function finallyyields the companion's mass (0.75 Msun) and the binaryseparation (1.95 AU). We find that the red giant does not fill its Rochelobe. We review the radial velocity data of Thackeray & Hutchings(\cite{Thacker74}), and compare it with our red giant's orbit. We findthat their RV curves of the blue absorption system and the permittedemission lines are in anti-phase with the red giant, and that theforbidden emission lines are shifted by a quarter of a period. The blueabsorptions and the permitted emission lines are associated with the hotcompanion but not in a straightforward way. The blue absorption systemonly tracks the hot component's orbital motion whilst it is in front ofhe red giant, whereas at other phases line blanketing by interbinarymaterial leads to perturbations. We finally present UV light curvesbased on IUE archive spectra. We clearly detect eclipses in thecontinuum at all wavelengths. The eclipse light curves are unusual inthat they show a slow and gradual decline prior to eclipse which isfollowed by a sharp increase after eclipse. Based on observationsobtained at the European Southern Observatory, La Silla, Chile; theobservations were granted for the ESO programs 47.7-081, 48.7-083,49.7-041, 50.7-129, 51.7-093, 52.7-068, 53.7-083, 54.E-061, 55.E-446,56.E-526.
| What mimics the reflection effect in symbiotic binaries?
We discuss the origin of a periodic wave-like variation as a function ofthe orbital phase observed in the light curves (LC) of symbiotic stars.It is shown that this type of variability cannot be ascribed to areflection effect. For example, the observed amplitudes of the LCs arefar larger than those calculated within a model of the reflectioneffect. Here, the nature of the orbitally related changes in the opticalcontinuum is outlined within an ionization model of symbiotic binaries.Appendices A, B, C are only available in electronic form athttp://www.edpsciences.org
| Spectroscopic Diagnostics of Symbiotic Stars III. Radial Velocity Analyses of HBV 475
We present highly resolved spectroscopic data of HBV 475 (= V 1329 Cyg)in the optical region, which have been obtained during the past 10 yearsat the Okayama Astrophysical Observatory. We analyzed line profiles ofHα , Hγ , He II lambda 4686, [O III] lambda 5007, and [Fe VII]lambda 6086 using Gaussian de-convolution method, and investigated thevariation of individual components of the profiles as a function of theorbital phase. We revised the mass function obtained from the orbitalelements of the hot star as f_h(M) ~ 1.2 +/- 0.3 MO . It differsconsiderably from previously published values, which were larger than 20MO . However, our new mass function is more reasonable for a symbioticsystem consisting of a red giant and a hot star, which is currentlypresumed to be a white dwarf. Finally, we suggest a descriptive model ofline-emitting regions in the HBV 475 binary, which explains the basicvariation in the line profiles and agrees with the main features of theHST image.
| Notices to investigation of symbiotic binaries. I. Effective temperatures of cool components
A comparison of synthetic spectra for cool giants with the observedbroad-band optical/IR photometry is suggested to estimate the effectivetemperature, T_eff, of cool components in symbiotic binaries. Theuncertainties of such estimates are within a range of 100-300 K. Here wedemonstrated this approach on EG And and AX Per, and found T_eff (EGAnd) = 3 500 +200/-100 K and T_eff (AX Per) = 3 400 +/- 150 K. Theseresults agree well with those obtained from empirically determineddependencies of effective temperature upon spectral type.
| Contemporaneous Ultraviolet and Optical Observations of Direct and Raman-scattered O VI Lines in Symbiotic Stars
Symbiotic stars are binary systems consisting of a hot star, typically awhite dwarf, and a cool giant companion. The wind from the cool star isionized by the radiation from the hot star, resulting in thecharacteristic combination of sharp nebular emission lines and stellarmolecular absorption bands in the optical spectrum. Most of the emissionlines are readily identifiable with common ions. However, two strong,broad emission lines at 6825 and 7082 Å defied identification withknown atoms and ions. In 1989 Schmid made the case that these longunidentified emission lines resulted from the Raman scattering of the OVI resonance photons at 1032, 1038 Å by neutral hydrogen. Wepresent contemporaneous far-UV and optical observations of direct andRaman-scattered O VI lines for nine symbiotic stars obtained with theHopkins Ultraviolet Telescope (Astro-2) and various ground-based opticaltelescopes. The O VI emission lines are present in every instance inwhich the λλ6825, 7082 lines are present, in support ofthe Schmid Raman-scattering model. We calculate the scatteringefficiencies and discuss the results in terms of the Raman-scatteringmodel. Additionally, we measure the flux of the Fe II fluorescence lineat 1776 Å, which is excited by the O VI line at 1032 Å, andcalculate the first estimates of the conversion efficiencies for thisprocess.
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