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Planetary Construction Zones in Occultation: Discovery of an Extrasolar Ring System Transiting a Young Sun-like Star and Future Prospects for Detecting Eclipses by Circumsecondary and Circumplanetary Disks
The large relative sizes of circumstellar and circumplanetary disksimply that they might be seen in eclipse in stellar light curves. Weestimate that a survey of ~104 young (~10 million year old)post-accretion pre-main-sequence stars monitored for ~10 years shouldyield at least a few deep eclipses from circumplanetary disks and diskssurrounding low-mass companion stars. We present photometric andspectroscopic data for a pre-main-sequence K5 star (1SWASPJ140747.93-394542.6 = ASAS J140748-3945.7), a newlydiscovered ~0.9 M &sun; member of the ~16 Myr old UpperCentaurus-Lupus subgroup of Sco-Cen at a kinematic distance of 128± 13 pc. This star exhibited a remarkably long, deep, and complexeclipse event centered on 2007 April 29 (as discovered in Super WideAngle Search for Planets (SuperWASP) photometry, and with portions ofthe dimming confirmed by All Sky Automated Survey (ASAS) data). At leastfive multi-day dimming events of >0.5 mag are identified, with a>3.3 mag deep eclipse bracketed by two pairs of ~1 mag eclipsessymmetrically occurring ±12 days and ±26 days before andafter. Hence, significant dimming of the star was taking place on andoff over at least a ~54 day period in 2007, and a strong >1 magdimming event occurring over a ~12 day span. We place a firm lower limiton the period of 850 days (i.e., the orbital radius of the eclipser mustbe >1.7 AU and orbital velocity must be <22 kms-1). The shape of the light curve is similar to thelopsided eclipses of the Be star EE Cep. We suspect that this new staris being eclipsed by a low-mass object orbited by a dense inner disk,further girded by at least three dusty rings of optical depths nearunity. Between these rings are at least two annuli of near-zero opticaldepth (i.e., gaps), possibly cleared out by planets or moons, dependingon the nature of the secondary. For possible periods in the range2.33-200 yr, the estimated total ring mass is ~8-0.4 M Moon(if the rings have optical opacity similar to Saturn's rings), and theedge of the outermost detected ring has orbital radius ~0.4-0.09 AU. Inthe new era of time-domain astronomy opened by surveys like SuperWASP,ASAS, etc., and soon to be revolutionized by Large Synoptic SurveyTelescope, discovering and characterizing eclipses by circumplanetaryand circumsecondary disks will provide us with observational constraintson the conditions that spawn satellite systems around gas giant planetsand planetary systems around stars.
| Random forest automated supervised classification of Hipparcos periodic variable stars
We present an evaluation of the performance of an automatedclassification of the Hipparcos periodic variable stars into 26 types.The sub-sample with the most reliable variability types available in theliterature is used to train supervised algorithms to characterize thetype dependencies on a number of attributes. The most useful attributesevaluated with the random forest methodology include, in decreasingorder of importance, the period, the amplitude, the V-I colour index,the absolute magnitude, the residual around the folded light-curvemodel, the magnitude distribution skewness and the amplitude of thesecond harmonic of the Fourier series model relative to that of thefundamental frequency. Random forests and a multi-stage scheme involvingBayesian network and Gaussian mixture methods lead to statisticallyequivalent results. In standard 10-fold cross-validation (CV)experiments, the rate of correct classification is between 90 and 100per cent, depending on the variability type. The main mis-classificationcases, up to a rate of about 10 per cent, arise due to confusion betweenSPB and ACV blue variables and between eclipsing binaries, ellipsoidalvariables and other variability types. Our training set and thepredicted types for the other Hipparcos periodic stars are availableonline.
| Period switching in the symbiotic star BX Mon
We report on a detailed analysis of the optical light curve (LC) of thesymbiotic system BX Mon, the data of which were gathered from theliterature. The LC covers the period from 1889 December to 2009 March,with a gap of no observations between 1940 March and 1972 February. TheLC is characterized by strong oscillations of peak-to-peak amplitudefrom 2 to >3 mag. Before the gap, the fluctuations were modulatedmainly by a period Pa= 1373 ± 4 d. After the gap, thedominant periodicity became Pb= 1256 ± 16. Higherharmonics as well as a few beats of the two major periodicities can alsobe identified in the LC. We identify one of the beat periods,Pr= 656 d, as the sidereal rotation period of the giantcomponent of the system. The period switching that took place during thegap in the observations was possibly associated with a certaincataclysmic event, hints of which may be recognized in the LC in thefirst 11 yr after the gap.We suggest that the origin of the major oscillations lies in periodicepisodes of mass accretion from the M giant on to the hot component ofthe system. After the gap, they are correlated with the periastronpassage of the system and therefore appear with the binary period.Before the gap, the oscillations appeared with the diurnal cycle of anobserver on the surface of the rotating M giant, whose Sun is the hotcomponent. The event of the period switching is possibly related to anintensive magnetic activity in the outer layers of the giant star.
| The O I] 1641 Å line as a probe of symbiotic star winds
Aims: The neutral oxygen resonance ?1302 Å line can,if the optical depth is sufficiently high, de-excite by anintercombination transition at ?1641 Å to a metastablestate. This has been noted in a number of previous studies but neversystematically investigated as a diagnostic of the neutral red giantwind in symbiotic stars and symbiotic-like recurrent novae. Methods: We used archival IUE high resolution, and HST GHRS and STISmedium and high resolution, spectra to study a sample of symbioticstars. The integrated fluxes were measured, where possible, for the O I?1302 Å and O I] ?1641 Å lines. Results: The intercombination ?1641 Å line is detected in asubstantial number of symbiotic stars with optical depths that givecolumn densities comparable with direct eclipse measures (EG And) andthe evolution of the recurrent nova RS Oph 1985 in outburst. In foursystems (EG And, Z And, V1016 Cyg, and RR Tel), we find that the O I]variations are strongly correlated with the optical light curve andoutburst activity. This transition can also be important for the studyof a wide variety of sources in which an ionization-bounded H II regionis imbedded in an extensive neutral medium, including active galacticnuclei, and not only for evaluations of extinction.
| Masses and luminosities of O- and B-type stars and red supergiants
Massive stars are of interest as progenitors of supernovae, i.e.neutron stars and black holes, which can be sources of gravitationalwaves. Recent population synthesis models can predict neutron star andgravitational wave observations but deal with a fixed supernova rate oran assumed initial mass function for the population of massive stars. Here we investigate those massive stars, which are supernovaprogenitors, i.e. with O- and early B-type stars, and also allsupergiants within 3 kpc. We restrict our sample to those massive starsdetected both in 2MASS and observed by Hipparcos, i.e. only those starswith parallax and precise photometry. To determine the luminositieswe calculated the extinctions from published multi-colour photometry,spectral types, luminosity class, all corrected for multiplicity andrecently revised Hipparcos distances. We use luminosities andtemperatures to estimate the masses and ages of these stars usingdifferent models from different authors. Having estimated theluminosities of all our stars within 3 kpc, in particular for all O- andearly B-type stars, we have determined the median and mean luminositiesfor all spectral types for luminosity classes I, III, and V. Ourluminosity values for supergiants deviate from earlier results: Previouswork generally overestimates distances and luminosities compared to ourdata, this is likely due to Hipparcos parallaxes (generally moreaccurate and larger than previous ground-based data) and the fact thatmany massive stars have recently been resolved into multiples of lowermasses and luminosities. From luminosities and effective temperatureswe derived masses and ages using mass tracks and isochrones fromdifferent authors. From masses and ages we estimated lifetimes andderived a lower limit for the supernova rate of ?20 events/Myraveraged over the next 10 Myr within 600 pc from the sun. These data arethen used to search for areas in the sky with higher likelihood for asupernova or gravitational wave event (like OB associations).
| How to Understand the Light Curves of Symbiotic Stars
I introduce fundamental types of variations observed in the light curvesof symbiotic stars: the orbitally-related wave-like modulation duringquiescent phases, eclipses during active phases, and apparent orbitalchanges indicated during transitions between quiescence and activity. Iexplain their nature with the aid of the spectral energy distribution ofthe composite spectrum of symbiotic stars and their simple ionizationmodel.
| Recent photometry of symbiotic stars
We present new photometric observations of 15 symbiotic stars coveringtheir last orbital cycle(s) from 2003.9 to 2007.2. We obtained our databy both classical photoelectric and CCD photometry. Main results are: EGAnd brightened by ˜ 0.3 mag in U from 2003. A ˜0.5 mag deepprimary minimum developed in the U light curve (LC) at the end of 2006.Z And continues its recent activity that began during the 2000 autumn. Anew small outburst started in summer of 2004 with a peak U magnitude of˜ 9.2. During the spring of 2006 the star entered a massiveoutburst. It reached its historical maximum at U˜ 8.0 in 2006July. AE Ara erupted in 2006 February with Δ m_vis ˜ 1.2 mag.BF Cyg entered a new active stage in 2006 August. A brightness maximum(U˜ 9.4) was measured during 2006 September. CH Cyg persists in aquiescent phase. During 2006 June-December a ˜ 2 mag decline inall colours was measured. CI Cyg started a new active phase during 2006May-June. After 31 years it erupted by about 2 mag in U. TX CVnmaintains a bright stage with U ˜ 10.5 from 2003. AG Dra entered anew major outburst in 2006 June. It reached its maximum at U ˜ 8.0in 2006 September. AR Pav persists at a low level of the activity. AGPeg's LC profile varies markedly during different orbital cycles. AX Percontinues its quiescent phase.The Tables of this article are available at the CDS viahttp://cdsarc.u-strasbg.fr/ftp/cats/J/other/AN/328.909
| 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.
| Rotational velocities of the giants in symbiotic stars - II. Are S-type symbiotics synchronized?
We have measured the projected rotational velocities (vsini) of the massdonors for 29 S-type symbiotic stars (SSs) using high-resolutionspectroscopic observations and the cross-correlation function (CCF)method. The results of the CCF have been controlled with syntheticspectra. The typical rotational velocity of the K and M giants in S-typesymbiotics appeared to be 4.5 < vsini < 11.7 kms-1. Ina subsample of 16 S-type SSs (with known orbital periods andwell-measured vsini), 15 have deviations from synchronization less thanthe 3σ level. This means that we did not find evidence for astatistically significant deviation from the synchronization for any ofthese 15 objects. The deviation from synchronization is statisticallysignificant (at confidence level >99 per cent) only for the recurrentnova RS Oph.For 22 S-type symbiotics we give clues as to what their orbital periodscould be.Based on observations obtained in ESO programmes 073.D-0724A and074.D-0114.E-mail: rkz@astro.bas.bg (RKZ); mfb@astro.livjm.ac.uk (MFB);andreja.gomboc@fmf.uni-lj.si (AG)
| 2MASS near-infrared photometry of symbiotic stars
We present Two Micron All Sky Survey photometry for 216 symbiotic andpossible symbiotic stars. This represents the most comprehensivenear-infrared photometry for these sources which has been published todate. The results are used to define the statistics of S- and D-typestars; to investigate the photometric properties of Magellanic S-typesymbiotics; and to define the possible evolution of D-type symbioticswithin the J - H/H - KS colour plane. It appears that thecolours of D-type symbiotics are consistent with differing mass-lossrates dM/dt, provided that the grains have a silicate-like composition,and maximum temperatures of the order of ~800 K.
| Binary Life after the AGB -- Towards a Unified Picture
We attempt to construct a unified evolutionary scheme that includespost-AGB systems, barium stars, symbiotics and related systems,explaining their similarities as well as their differences. Specialattention is given to the comparison of the barium pollution andsymbiotic phenomena. Finally, we outline a `transient torus'evolutionary scenario that makes use of the various observational andtheoretical hints and aims at explaining the observed characteristics ofthe relevant systems.
| 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.
| 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 Light Curves of Classical Symbiotic Stars
Results of both photoelectric and visual long-term monitoring ofselected classical symbiotic stars (CSS) are presented. We suggest aclassification in which the complex behavior in their light curves canbe basically divided into two groups: (i) periodic and (ii) non-periodicvariations. The possible nature of the observed variations is brieflydiscussed. Comparison of the visual magnitude estimates to thephotoelectric data is provided for individual cases.
| A catalogue of eclipsing variables
A new catalogue of 6330 eclipsing variable stars is presented. Thecatalogue was developed from the General Catalogue of Variable Stars(GCVS) and its textual remarks by including recently publishedinformation about classification of 843 systems and making correspondingcorrections of GCVS data. The catalogue1 represents thelargest list of eclipsing binaries classified from observations.
| 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.
| 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.
| The spectroscopic orbits and other parameters of the symbiotic binary FN Sgr
We present a study of the eclipsing symbiotic binary FN Sgr with aperiod of 568.3 days determined photometrically and confirmedspectroscopically. The hot component underwent a 2.5 mag eruptioncovered by most of our spectroscopic observations. In particular, wehave determined for the first time spectroscopic orbits based on theradial velocity curves for both components. A set of blue absorptionlines resembling an A-F type star is present in all our spectra and theyseem to be associated with the hot component. Based on the light curve,we derive the red giant's radius (140~ Rȯ) and theorbital inclination (i = 80°). We find that FN Sgr is similar toother S-type symbiotic binaries, composed by an M 5-type giant (M_g=1.5Mȯ) and a hot white dwarf (Mh = 0.7~Mȯ, R_h= 0.2~ Rȯ) with a binaryseparation of ~1.6 AU. The red giant is just filling its Roche lobe anda geometrically and optically thick accretion disk is likely to bepresent around the low-mass accretor. The evolution of Th andLh along the active phase argues in favour of accretion diskinstabilities similar to those of Z And. We have also studied spectralchanges and photometric variations as a function of both the hotcomponent activity and the orbital motion.
| SB9: The ninth catalogue of spectroscopic binary orbits
The Ninth Catalogue of Spectroscopic Binary Orbits(http://sb9.astro.ulb.ac.be) continues the series of compilations ofspectroscopic orbits carried out over the past 35 years by Batten andcollaborators. As of 2004 May 1st, the new Catalogue holds orbits for2386 systems. Some essential differences between this catalogue and itspredecessors are outlined and three straightforward applications arepresented: (1) completeness assessment: period distribution of SB1s andSB2s; (2) shortest periods across the H-R diagram; (3)period-eccentricity relation.
| 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.
| 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.
| The SED in the hot continuum of the symbiotic binary AR Pavonis I. Tests with current models
We present the spectral energy distribution (SED) in the continuum ofthe eclipsing symbiotic binary AR Pav between 0.12and 3.4 ?m. This revealed a high luminosity of the hot object in thebinary, Lh~2?200 (d/4.9 kpc)2Lsolar. We introduce a method of disentangling the totalcontinuum spectrum into its individual components of radiation forcurrent models of symbiotic binaries. Applying a standard ionizationmodel we show that the configuration of AR Pav differssignificantly from that typical for symbiotic binaries during theirquiescent phases. The best fit of the observed SED is provided byradiation of a simple blackbody accretion disk with LAD~1700(d/4.9 kpc)2 Lsolar, which is embedded in anextended hot corona with Te=40?000+/-5000 K andLN~500 (d/4.9 kpc)2 Lsolar. This basicconfiguration of the hot object explains also the observedwavelength-dependent depth and width of the eclipse profile. Thestandard thin disk model requires a high accretion rateM&sun;acc>~2×10-4 Msolaryr-1 onto the central star with a radiusRacc>~2 Rsolar to balance the observedluminosity. Even irrespectively to the disk model, the accretion processlimits Racc>0.1 Rsolar forM&sun;acc>1.7×10-5 Msolaryr-1 and Macc=0.75-1.0 Msolar, whichprecludes a white dwarf to be the accreting star. Application of modelswith the disk and the boundary layer shows that the far-UV spectrum isnot consistent with a large amount of a hot radiation from the boundarylayer. However, the presence of such a boundary layer in the system isindirectly indicated through the strong nebular emission. This solutionsuggests that the hotter inner parts of the disk including the boundarylayer are occulted by the disk material in the direction to theobserver.
| H II regions in symbiotic binaries and their radio emission
The slow and dense wind from a symbiotic red giant (RG) can besignificantly deflected toward the orbital plane by the gravitationalpull of the companion star. In such an environment, the ionizingradiation from the companion creates a highly asymmetric H Ii region. Wepresent three-dimensional models of H Ii regions in symbiotic S-typesystems, for which we calculate radio maps and radio spectra. We showthat the standard assumption of spherically symmetric RG wind results inwrong shapes, sizes and spectra of ionized regions, which in turnaffects the observational estimates of orbital separation and mass lossrate. A sample of radio maps and radio spectra of our models ispresented and the results are discussed in relation to observationaldata.
| 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 spectroscopic orbits and the geometrical configuration of the symbiotic binary AR Pavonis
We analyze optical and near infrared spectra of intermediate and highresolution of the eclipsing symbiotic system AR Pavonis. We haveobtained the radial velocity curves for the red and the hot componentfrom the M-giant absorption lines and from the wings of H? ,H? and He II lambda 4686 emission profiles, respectively. From theorbital elements we have derived the masses, Mg=2.5Msun and Mh=1.0 Msun, for the red giantand the hot component, respectively. We also present and discuss radialvelocity patterns in the blue cF absorption spectrum as well as variousemission lines. In particular, we confirm that the blue absorption linesare associated with the hot component. The radial velocity curve of theblue absorption system, however, does not track the hot companion'sorbital motion in a straightforward way, and its departures from anexpected circular orbit are particularly strong when the hot componentis active. We suggest that the cF-type absorption system is formed inmaterial streaming from the giant presumably in a region where thestream encounters an accretion disk or an extended envelope around thehot component. The broad emission wings originate from the inneraccretion disk or the envelope around the hot star. We also suggest thatthe central absorption in H profiles is formed in a neutral portion ofthe cool giant's wind which is strongly concentrated towards the orbitalplane. The nebula in AR Pav seems to be bounded by significant amount ofneutral material in the orbital plane. The forbidden emission lines areprobably formed in low density ionized regions extended in polardirections and/or the wind-wind interaction zone. Based on observationstaken at Complejo Astronómico El Leoncito (CASLEO), operatedunder an agreement between the Consejo Nacional de InvestigacionesCientíficas y Técnicas de la República Argentina,the Secretaría de Ciencia y Tecnología de la Naciónand the National Universities of La Plata, Córdoba and San Juan.
| The historical, 1889-2002, light curve of the eclipsing symbiotic binary AR Pav
We summarized the historical 1889.5-2001.8 light curve of the eclipsingsymbiotic binary AR Pav. Our new photographic and visual estimates coverthe period 1963-71 and 1998-2002, respectively. Strong variations in ournew data are described. It is shown that the active phase of AR Pavsuddenly finished at the epoch 66. Positions of the recent two minimaslightly refined their average linear ephemeris.
| Study of the symbiotic star AR Pavonis
We present a study of the optical spectra and linear polarization of theeclipsing binary AR Pavonis. The optical spectra were obtained between1990 and 1998, and polarimetric data between 1995 and 1998. Fromspectroscopic variations along the orbital motion we analized the natureof the system. Polarimetric studies indicate that AR Pav has intrinsicpolarization.
| 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.
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| A catalogue of symbiotic stars
We present a new catalogue of symbiotic stars. In our list we include188 symbiotic stars as well as 30 objects suspected of being symbiotic.For each star, we present basic observational material: coordinates, Vand K magnitudes, ultraviolet (UV), infrared (IR), X-ray and radioobservations. We also list the spectral type of the cool component, themaximum ionization potential observed, references to finding charts,spectra, classifications and recent papers discussing the physicalparameters and nature of each object. Moreover, we present the orbitalphotometric ephemerides and orbital elements of known symbioticbinaries, pulsational periods for symbiotic Miras, Hipparcos parallaxesand information about outbursts and flickering.
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Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Tavus |
| Sað Açýklýk: | 18h20m27.87s |
| Yükselim: | -66°04'43.0" |
| Görünürdeki Parlaklýk: | 10.63 |
| özdevim Sað Açýklýk: | -3.3 |
| özdevim Yükselim: | -8.4 |
| B-T magnitude: | 11.537 |
| V-T magnitude: | 10.705 |
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INHABITED SKY
