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Orbital Evolution of Algol Binaries with a Circumbinary Disk
It is generally thought that conservative mass transfer in Algolbinaries causes their orbits to be wider, so that the less massive staroverflows its Roche lobe. The observed decrease in the orbital periodsof some Algol binaries suggests orbital angular momentum loss during thebinary evolution, and the magnetic braking mechanism is often invoked toexplain the observed orbital shrinkage. Here we suggest an alternativeexplanation, in which a small fraction of the transferred mass forms acircumbinary disk, which extracts orbital angular momentum from thebinary through tidal torques. We also perform numerical calculations ofthe evolution of Algol binaries with typical initial masses and orbitalperiods. The results indicate that, for reasonable input parameters, thecircumbinary disk can significantly influence the orbital evolution, andcause the orbit to shrink on a sufficiently long timescale. Rapid masstransfer in Algol binaries with low mass ratios can also be accountedfor in this scenario.
| The Near-Contact Binary RU Ursae Minoris
The near-contact binary RU UMi with an F0-type primary and a K-typesecondary was observed in 2003. With the latest version of theWilson-Devinney code, the photometric elements were computed. Theresults reveal that RU UMi is a semi-detached system with the secondarycomponent filling its Roche lobe, which should lead to an increase ofthe period for conservative mass transfer between the two components.However, an orbital period analysis shows that the orbital period ofthis system undergoes a continuous decrease at a rate ofdP/dt=-1.72×10-8d yr-1. Therefore, thecontinuous period decrease may demonstrate that the system isnonconservative. This can result from a combined effect of mass transferfrom the secondary component to the primary one and mass and angularmomentum loss from the system. With the secular mass and angularmomentum losses, RU UMi may evolve from the present short-periodnear-contact system into an A-type contact binary.
| 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.
| Photoelectric Times of Minima of Some Eclipsing Binaries
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| Automatic classification of eclipsing binaries light curves using neural networks
In this work we present a system for the automatic classification of thelight curves of eclipsing binaries. This system is based on aclassification scheme that aims to separate eclipsing binary systemsaccording to their geometrical configuration in a modified version ofthe traditional classification scheme. The classification is performedby a Bayesian ensemble of neural networks trained with Hipparcos data ofseven different categories including eccentric binary systems and twotypes of pulsating light curve morphologies.
| Gravity-darkening exponents in semi-detached binary systems from their photometric observations. II.
This second part of our study concerning gravity-darkening presents theresults for 8 semi-detached close binary systems. From the light-curveanalysis of these systems the exponent of the gravity-darkening (GDE)for the Roche lobe filling components has been empirically derived. Themethod used for the light-curve analysis is based on Roche geometry, andenables simultaneous estimation of the systems' parameters and thegravity-darkening exponents. Our analysis is restricted to theblack-body approximation which can influence in some degree theparameter estimation. The results of our analysis are: 1) For four ofthe systems, namely: TX UMa, β Per, AW Cam and TW Cas, there is avery good agreement between empirically estimated and theoreticallypredicted values for purely convective envelopes. 2) For the AI Drasystem, the estimated value of gravity-darkening exponent is greater,and for UX Her, TW And and XZ Pup lesser than corresponding theoreticalpredictions, but for all mentioned systems the obtained values of thegravity-darkening exponent are quite close to the theoretically expectedvalues. 3) Our analysis has proved generally that with the correction ofthe previously estimated mass ratios of the components within some ofthe analysed systems, the theoretical predictions of thegravity-darkening exponents for stars with convective envelopes arehighly reliable. The anomalous values of the GDE found in some earlierstudies of these systems can be considered as the consequence of theinappropriate method used to estimate the GDE. 4) The empiricalestimations of GDE given in Paper I and in the present study indicatethat in the light-curve analysis one can apply the recent theoreticalpredictions of GDE with high confidence for stars with both convectiveand radiative envelopes.
| Spaeter Einstieg in die Veraenderlichenbeobachtung.
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| Notices to investigation of symbiotic binaries. III. Approximation of the Roche lobe parameters for asynchronously rotating star in a binary system
We derive approximative analytical formulas for the basic parameters ofthe Roche lobe, its radius and the position of the L1-point,for asynchronously rotating component in a binary system. Our solutionis valid in the range of the mass ratio 0.1 < q < 10 and theparameter 1 ≤ p ≤ 20 (p = Porb/Prot).Deviations between numerical solution and that given by our analyticalapproximation are less than 7%.
| Catalogue of Algol type binary stars
A catalogue of (411) Algol-type (semi-detached) binary stars ispresented in the form of five separate tables of information. Thecatalogue has developed from an earlier version by including more recentinformation and an improved layout. A sixth table lists (1872) candidateAlgols, about which fewer details are known at present. Some issuesrelating to the classification and interpretation of Algol-like binariesare also discussed.Catalogue is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/417/263
| Doppler tomography of Algols
The technique of Doppler tomography has been influential in the study ofmass transfer in Algol-type interacting binaries. The Algols contain ahot blue dwarf star with a magnetically-active late-type companion. Inthe close Algols, the gas stream flows directly into the photosphere ofthe blue mass-gaining star because it does not have enough room to avoidimpact with that star. Doppler tomograms of the Algols have beenproduced from over 2500 time-resolved spectra at wavelengthscorresponding to Hα, Hβ, He I (6678 Å), Si II (6371Å) and Si IV (1394 Å). These tomograms display images ofaccretion structures that include a gas stream, accretion annulus,accretion disk, stream-star impact region, and occasionally a source ofchromospheric emission associated with the cool, mass-losing companion.Some Algol systems alternate between stream-like and disk-like states,and provide direct evidence of active mass transfer within the Algols.This work produced the very first images of the gas stream for theentire class of interacting binaries, and demonstrated that the Algolsare far more active than formerly believed, with variability on timescales of weeks to months.
| CCD Times of Minima of Some Eclipsing Binaries in 2003
We present CCD observations of minima of 31 eclipsing binaries observedby SAVS sky survey in 2003.
| TX UMa-Karte (BAV-Standardprogramm): Vergleichsstern fehlt !
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| Photoelectric Minima of Selected Eclipsing Binaries
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| The Hamburg/RASS Catalogue of optical identifications. Northern high-galactic latitude ROSAT Bright Source Catalogue X-ray sources
We present the Hamburg/RASS Catalogue (HRC) of optical identificationsof X-ray sources at high-galactic latitude. The HRC includes all X-raysources from the ROSAT Bright Source Catalogue (RASS-BSC) with galacticlatitude |b| >=30degr and declination delta >=0degr . In thispart of the sky covering ~ 10 000 deg2 the RASS-BSC contains5341 X-ray sources. For the optical identification we used blue Schmidtprism and direct plates taken for the northern hemisphere Hamburg QuasarSurvey (HQS) which are now available in digitized form. The limitingmagnitudes are 18.5 and 20, respectively. For 82% of the selectedRASS-BSC an identification could be given. For the rest either nocounterpart was visible in the error circle or a plausibleidentification was not possible. With ~ 42% AGN represent the largestgroup of X-ray emitters, ~ 31% have a stellar counterpart, whereasgalaxies and cluster of galaxies comprise only ~ 4% and ~ 5%,respectively. In ~ 3% of the RASS-BSC sources no object was visible onour blue direct plates within 40\arcsec around the X-ray sourceposition. The catalogue is used as a source for the selection of(nearly) complete samples of the various classes of X-ray emitters.
| 162-nd List of Minima Timings of Eclipsing Binaries by BBSAG Observers
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| The HRX-BL Lac sample - Evolution of BL Lac objects
The unification of X-ray and radio selected BL Lacs has been anoutstanding problem in the blazar research in the past years. Recentinvestigations have shown that the gap between the two classes can befilled with intermediate objects and that apparently all differences canbe explained by mutual shifts of the peak frequencies of the synchrotronand inverse Compton component of the emission. We study the consequencesof this scheme using a new sample of X-ray selected BL Lac objectscomprising 104 objects with z<0.9 and a mean redshift bar {z} = 0.34.77 BL Lacs, of which the redshift could be determined for 64 (83%)objects, form a complete sample. The new data could not confirm ourearlier result, drawn from a subsample, that the negative evolutionvanishes below a synchrotron peak frequency log nupeak =16.5. The complete sample shows negative evolution at the 2sigma level(< Ve/Va > = 0.42 +/- 0.04). We concludethat the observed properties of the HRX BL Lac sample show typicalbehaviour for X-ray selected BL Lacs. They support an evolutionarymodel, in which flat-spectrum radio quasars (FSRQ) with high energeticjets evolve towards low frequency peaked (mostly radio-selected) BL Lacobjects and later on to high frequency peaked (mostly X-ray selected) BLLacs.Appendix (Tables 8 and 9, Fig. 8) is only available in electronic format http://www.edpsciences.org
| CCD Times of Minima of Some Eclipsing Binaries in 2002
We present CCD observations of minima of 11 eclipsing binaries.
| Evolution of Wolf-Rayet Stars in Binary Systems: An Analysis of the Mass and Orbital-Eccentricity Distributions
We have undertaken a statistical study of the component mass ratios andthe orbital eccentricities of WR + O close binary, detachedmain-sequence (DMS), contact early-type (CE), and semidetached (SD)systems. A comparison of the characteristics of WR + O systems and ofDMS, CE, and SD systems has enabled us to draw certain conclusions aboutthe evolutionary paths of WR + O binaries and to demonstrate that up to90% of all known WR + O binaries formed as a result of mass transfer inmassive close O + O binary systems. Since there is a clear correlationbetween the component masses in SD systems with subgiants, the absenceof an anticorrelation between the masses of the WR stars and O stars inWR + O binaries cannot be considered evidence against the formation ofWR + O binaries via mass transfer. The spectroscopic transitionalorbital period P tr sp corresponding to the transition from nearlycircular orbits (e sp<0.1) to elliptical orbits (e sp≥0.1) is14d for WR + O systems and 2d 3d for OB + OB systems. Theperiod range in which all WR + O orbits are circular &$(1mathop dlimits_. 6 ≤slant P ≤slant 14(d) ); is close to the range for SD systems with subgiants, &0mathop dlimits_. 7 ≤slant P ≤slant 15(d); . The large difference between the P tr sp values for WR + O and OB +OB systems suggests that a mechanism of orbit circularization additionalto that for OB + OB systems at the DMS stage (tidal dissipation of theorbital energy due to radiative damping of the dynamical tides) acts inWR + O binaries. It is natural to suggest mass transfer in the parent O+ O binaries as this supplementary orbit-circularization mechanism.Since the transitional period between circular and elliptical orbits forclose binaries with convective envelopes and ages of 5×109 yearsis &P_{tr} = 12mathop dlimits_. 4$; , the orbits of most known SD systems with subgiants had enough timeto circularize during the DMS stage, prior to the mass transfer. Thus,for most SD systems, mass transfer plays a secondary role incircularization of their orbits. In many cases, the initial orbitaleccentricities of the O + O binary progenitors of WR + O systems arepreserved, due to the low viscosity of the O-star envelopes and theshort timescale for their nuclear evolution until the primary O starfills its Roche lobe and the mass transfer begins. The mass transfer inthe parent O + O systems is short-lived, and the number of orbitalcycles during the early mass-transfer stage is relatively low (lowerthan for the progenitors of SD systems by three or four orders ofmagnitude). The continued transfer of mass from the less massive to themore massive star after the component masses have become equal leads tothe formation of a WR + O system, and the orbit's residual eccentricityincreases to the observed value. The increase of the orbitaleccentricity is also facilitated by variable radial mass loss via thewind from the WR star in the WR + O system during its motion in theelliptical orbit. The result is that WR + O binaries can haveconsiderable orbital eccentricities, despite their intense masstransfer. For this reason, the presence of appreciable eccentricitiesamong WR + O binaries with large orbital periods cannot be consideredfirm evidence against mass transfer in the parent O + O binary systems.Only for the WR + O binaries with the longest orbital periods (4 of 35known systems, or 11 %) can the evolution of the parent O + O binariesoccur without filling of the Roche lobe by the primary O star, beinggoverned by radial outflow in the form of the stellar wind and possiblyby the LBV phenomenon, as in the case of HD 5980.
| Beobachtungsegebnisse Bundesdeutsche Arbeitsgemainschaft fur Veranderliche Sterne e.V.
Not Available
| Orbital Period Studies of Two Algol-Type Eclipsing Binary Systems: TY Pegasi and X Trianguli
O-C curves of two EA-type eclipsing binaries, TY Peg and X Tri, areformed and studied in detail based on all available times of lightminimum. For TY Peg, it was discovered that the general trend of the O-Ccurve showed a downward parabolic variation, which indicates a secularperiod decrease with rate at dP/dt=-1.16×10-6 daysyr-1. When the secular decrease is removed from the O-Ccurve, the residuals can be described by several linear ephemerides,suggesting several sudden period jumps. For the other one, X Tri, it isfound that the general O-C trend also indicates a secular perioddecrease (dP/dt=-1.42×10-7 days yr-1), andseveral irregular period jumps are found to superpose on the long-timeperiod decrease. This kind of period change, irregular sudden jumpssuperposed on secular decrease, is typical for many other Algol-typebinary systems such as TU Her, UU And, Z Per, Y Psc, BO Mon, FH Ori, RTPer, and TX UMa. The period changes of these systems may be caused byorbital angular momentum loss via variable magnetic coupling and gravitycoupling between the components.
| Hα spectroscopy and BV photometry of RT Lacertae
Contemporaneous spectroscopic and photometric B V observations of the RSCVn type eclipsing binary RT Lacertae were performedin summer 2000. The photometric observations were obtained at the EgeUniversity Observatory, while the spectroscopic ones were carried out atCatania Astrophysical Observatory in the spectral range 5860-6700Å. We obtained a high quality radial velocity curve of the systemthat allowed us to give more accurate values of the orbital parameters.A steady decrease of the barycentric velocity from 1920 to 2000 has beenpointed out and has been discussed in the context of a third bodyhypothesis. Through the subtraction of a ``synthetic'' spectrum, builtup with spectra of inactive standard stars, we detected Hα excessemission which fills in the photospheric absorption profiles of bothcomponents. With the exception of a few spectra, taken close to theeclipses, in which some extra absorption or a faint double-peaked broademission appears, there is no further evidence of circumstellar matterin this system, as suggested in previous works. The hotter and moremassive star appears also as the more active at a chromospheric level,since it has a Hα flux about ten times greater than the companion,on average. Rotational modulation of the Hα emission has beendetected in both stars. The hemisphere of the more massive star facingthe observer at phase 0fp75 appears brighter (in Hα ) than thatseen at phase 0fp25 , while for the less massive G9 IV star the maximumHα emission is seen around phase 0fp0-0fp1 . From the analysis ofthe contemporaneous light curve (Lanza et al. \cite{Lanza2001}), themore massive G5 IV star results to be more active than the companion ata photospheric level, in agreement with the chromospheric behaviourobserved in Hα . In addition, the starspots of the G5 IV star aremainly located in the Hα brighter hemisphere, suggesting a closespatial association of spots and plages in this star. The G9 IV stardisplays instead the maximum Hα emission at the phase of maximumvisibility of the smaller spotted area found from the light-curveanalysis. The minimum Hα emission occurs when the more heavilyspotted region is visible. Based on observations collected at CataniaAstrophysical Observatory, Italy, and at Ege University Observatory,Turkey. Table 1 only available 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/388/298
| Problems in modeling evolutionary processes in close binaries
In modeling the evolutionary processes of interacting binaries, a numberof assumptions are invoked by many workers concerning the manner of themass flow between the two stars. This article reviews the validity ofthe four assumptions most commonly used, namely, assumptions concerning(A) the critical Roche equipotential surface (the so-called Roche lobe),(B) accretion of matter from one star to its companion, (C) mass lossfrom the binary system, and (D), which is related to the last two items,whether the mass flow in a binary system is conservative or not. A largenumber of workers in this field appear to assume that the critical Rocheequipotential surfaces (Roche lobes, in their lexicon) control the massflow with the Lagrangian 1 point acting like a nozzle, channeling arather well collimated jet of gas. Similarly, they also assume thataccretion `disks' are formed in this process and those `disks' haveproperties very similar to solid disks with well defined surfaces andwith precession, nutation etc. Finally, they assume, except in the mostextreme case of rapid mass flow, conservative mass flow in which allmass lost by one star is completely accreted by the companion. Thesecommonly invoked assumptions are critically examined from bothobservational data and relevant physics and are shown to be lackingrealistic justification. We show what the concept of Roche equipotentialsurfaces actually tells us, and examine the manners of actual mass flowobserved in selected binaries.
| The Origin of Cyclic Period Changes in Close Binaries: The Case of the Algol Binary WW Cygni
Year- to decade-long cyclic orbital period changes have been observed inseveral classes of close binary systems, including Algol, W UrsaeMajoris, and RS Canum Venaticorum systems and the cataclysmic variables.The origin of these changes is unknown, but mass loss, apsidal motion,magnetic activity, and the presence of a third body have all beenproposed. In this paper, we use new CCD observations and thecentury-long historical record of the times of primary eclipse for WWCygni to explore the cause of these period changes. WW Cyg is an Algolbinary whose orbital period undergoes a 56 yr cyclic variation with anamplitude of ~0.02 days. We consider and reject the hypotheses of masstransfer, mass loss, apsidal motion, and the gravitational influence ofan unseen companion as the cause for these changes. A model proposed byApplegate, which invokes changes in the gravitational quadrupole momentof the convective and rotating secondary star, is the most likelyexplanation of this star's orbital period changes. This finding is basedon an examination of WW Cyg's residual O-C curve and an analysis of theperiod changes seen in 66 other Algols. Variations in the gravitationalquadrupole moment are also considered to be the most likely explanationfor the cyclic period changes observed in several different types ofbinary systems.
| 149 Bedeckungssterne der BAV-Programme. Eine Analyse der Beobachtungstatigkeit seit den Angangen.
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| Bedeckungsveraenderliche mit Apsidendrehung.
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| Das Brunner Punktesystem.
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| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veraenderliche Sterne e.V.
Not Available
| Possible Mass and Angular Momentum Loss in Algol-Type Binaries. V. RT Persei and TX Ursae Majoris
The changes in the orbital periods of two EA-type eclipsing binaries, RTPer and TX UMa, are studied in detail, based on the analysis of theirtimes of minimum light. For RT Per, it is shown that the trend of theO-C curve can be described by a parabola opening at the bottom, whichindicates a secular period decrease at the ratedP/dt=-9.29×10-8 days yr-1. By subtractingthe secular decrease in the O-C curve, the residuals display anoscillatory variation that can either be described by a continuousperiodic change, indicating the presence of a third body, or by severallinear ephemerides, indicating several sudden period jumps. Since theoscillatory change is not strictly periodic, the latter is moreplausible, which suggests that several irregular period jumps aresuperposed on the long-term period decrease. For the other object, TXUMa, it is discovered that the O-C trend also suggests a secular perioddecrease (dP/dt=-7.13×10-7 days yr-1), andfive irregular period jumps are found superposed on the secular perioddecrease. This kind of period is not unique for Algol-type binarysystems. The period changes, both the secular decrease and the suddenjumps, can be plausibly explained by orbital angular momentum loss viamagnetic coupling and gravity coupling between the components.
| Detection of the Secondary minima in TX UMa
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| A Complete Survey of Case A Binary Evolution with Comparison to Observed Algol-type Systems
We undertake a comparison of observed Algol-type binaries with a libraryof computed Case A binary evolution tracks. The library consists of 5500binary tracks with various values of initial primary massM10, mass ratio q0, and period P0,designed to sample the phase-space of Case A binaries in the range-0.10<=logM10<=1.7. Each binary is evolved using astandard code with the assumption that both total mass and orbitalangular momentum are conserved. This code follows the evolution of bothstars to the point where contact or reverse mass transfer occurs. Theresulting binary tracks show a rich variety of behavior that we sortinto several subclasses of case A and case B. We present the results ofthis classification, the final mass ratio, and the fraction of timespent in Roche Lobe overflow for each binary system. The conservativeassumption under which we created this library is expected to hold for abroad range of binaries, where both components have spectra in the rangeG0 to B1 and luminosity classes III to V. We gather a list of relativelywell-determined, observed hot Algol-type binaries meeting thiscriterion, as well as a list of cooler Algol-type binaries, for which weexpect significant dynamo-driven mass loss and angular momentum loss. Wefit each observed binary to our library of tracks using aχ2-minimizing procedure. We find that the hot Algolsdisplay overall acceptable χ2, confirming theconservative assumption, while the cool Algols show much less acceptableχ2, suggesting the need for more free parameters, such asmass and angular momentum loss.
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