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Публикации по объекту
Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| Bericht über die 2. Veraenderlichen-Beobachtungswoche an der VdS-Sternwarte Kirchheim 2005.
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| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderliche Sterne e.V.
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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.
| 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.
| 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.
| New Times of Minima of Some Eclipsing Binary Stars
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| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| Sektion Bedeckungsveraenderliche: Lichtkurven in allen Phasen.
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| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderlichen Serne e.V.
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| 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
| New Times of Minima of Some Selected Eclipsing Binary Systems
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| The First Eclipsing Binary Observations at the Ulupinar Astrophysics Observatory
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| Beobachtungsegebnisse Bundesdeutsche Arbeitsgemainschaft fur Veranderliche Sterne e.V.
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| 149 Bedeckungssterne der BAV-Programme. Eine Analyse der Beobachtungstatigkeit seit den Angangen.
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| Das Brunner Punktesystem.
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| 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.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veraenderliche Sterne e.V.
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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.
| Survey of Hα Mass Transfer Structures in Classical Algol-Type Binaries
Five years of Hα survey data for 37 ``classical'' Algol-typebinaries are presented. All these systems have primaries with a spectraltype of A or B, have a period of less than 5 days, and are visible inthe Northern Hemisphere. Data were collected with the 1.02 m reflectorat the US Naval Observatory, Flagstaff Station. The survey consists ofover 460 system spectra. Each system was observed at least once duringthe 5 years, with many systems observed several times over severalepochs. Difference profiles are calculated for most spectra by modelingand subtracting the spectrum of the photospheres of the stellarcomponents. We examined each spectrum for the presence of mass transfer,stream-star and stream-disk interaction, a disk or circumstellar bulge,and chromospheric emission. We present information on the prevalence ofmass transfer activity, disk presence, and system states associated withparticular mass transfer structures. We show that no currently publishedstudy, including this one, has enough data for a rigorous statisticalidentification of system states.
| Possible Mass and Angular Momentum Loss in Algol-Type Binaries. III. TU Cancri, FZ Delphini, AY Geminorum, VZ Leonis, FH Orionis, IU Persei, XZ Persei, and BE Vulpeculae
Orbital period variations of eight Algol-type binaries, TU Cnc, FZ Del,AY Gem, VZ Leo, FH Ori, IU Per, XZ Per, and BE Vul, are studied based onthe analysis of the O-C observations. It is discovered that the periodsof three systems, TU Cnc, FH Ori, and IU Per, show secular decrease. ForAY Gem and XZ Per, the orbital periods can be described by a suddendecrease or by two sudden changes superposed on a secular decrease. Weakevidence also shows that the orbital periods of the other three systems,FZ Del, VZ Leo, and BE Vul, are decreasing. As in other systems proposedby Qian, the decrease in the orbital periods of these systems, combinedwith their semidetached configurations, suggests that they may beundergoing secular mass and angular momentum loss due to magneticbraking. The irregular period jumps superposed on the secular decrease(e.g., in AY Gem, FH Ori, XZ Per, and BE Vul) can be explained byvariable magnetic coupling and gravity coupling between the twocomponents. However, the present secular period decrease of thesesystems may be part of a long-period periodic change (as in TT Del),which needs further investigation.
| 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
| New labour on Algols: conservative or liberal?
I consider three topics related to the influence of magnetic braking,combined with tidal friction, on the orbital evolution of CVs. Firstly,I attempt to show that properties of Algols are roughly consistent withthe view that angular momentum loss (AML) takes place in systems withcool (G/K) components, but not in systems with hot (B/A) components.This is what one might expect if the AML requires an active dynamo asseen in the Sun and other cool stars. The timescale required is roughlyof the order of what might be expected by magnetic braking. Someenhanced mass loss (ML), presumably by stellar wind, also seems to benecessary in the more evolved Algol systems. Secondly, I urge thattheorists adopt a recipe for magnetic braking that is more on the linesof Stȩpień (1995) than of Skumanich (1972). Thirdly, Iargue that `interrupted magnetic braking', a mechanism often invoked toexplain the upper edge of the period gap in CVs, is not in accord withobserved properties of late M dwarfs and brown dwarfs, and that someother mechanism should be sought.
| AV Hydrae: a near-contact semi-detached binary with possible mass and angular momentum loss.
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| Possible Mass and Angular Momentum Loss in Algol-Type Binaries. II. TT Delphini, BO Monocerotis, and Y Piscium
The period variations of three Algol-type binaries, TT Del, BO Mon, andY Psc, are studied based on the analysis of the O-C observations. Theorbital period of TT Del is discovered to be decreasing at a ratedP/dt=-2.20×10-6 days yr-1, while theorbital periods of BO Mon and Y Psc vary in some complex ways. For BOMon, three abrupt changes in its orbital period are found while itundergoes secular decrease at a rate dP/dt=-2.36×10-6days yr-1. For the remaining one, Y Psc, two jumps in theorbital period are found to superpose on a rapid period decrease(dP/dt=-4.90×10-6 days yr-1). As in the caseof TU Her (Paper I), the rapid decrease in the orbital periods of thesesystems, combined with their semidetached configurations, suggests thatthey may be undergoing rapid mass and angular momentum loss (AML) due tomagnetic braking. With the present decrease rate, after(7-9)×105 yr they will evolve into contact binaries.The abrupt changes that are superposed on the rapid period decrease maybe caused by the interplay between the variable AML and variablemagnetic coupling.
| Orbital Period Changes and Possible Mass and Angular Momentum Loss in Two Algol-Type Binaries: RW Coronae Borealis and TU Herculis
The orbital period of two Algol-type binaries, RW CrB and TU Her, arestudied. It is discovered that the orbital period of RW CrB shows asecular decrease at the rate of dP/dt=-4.29x10-8 daysyr-1, while the orbital period of TU Her varies in somecomplex way. Two jumps in the orbital period are found while itundergoes secular decrease at a rate of dP/dt=-2.92x10-6 daysyr-1. The rates of decrease of the orbital periods dP/dt inother Algol-type binaries are revised and the statistical relationbetween the orbital period P and its rate of change dP/dt is alsodiscussed. The properties of the changes in the orbital period of thesesystems, combined with their semidetached configurations, demonstratethat they may be undergoing secular mass and angular momentum loss (AML)during their evolution. The irregular abrupt changes that are superposedon the secular decrease of the orbital period may be caused by someinstabilities during the mass transfer and AML.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| Limb-darkening coefficients of illuminated atmospheres. I. Results for illuminated line-blanketed models with 3 700 K < T_eff < 7 000 K
The effect of mutual illumination in a close binary on thelimb-darkening coefficients is studied using the UMA (Uppsala ModelAtmosphere) code in convective line-blanketed atmospheres illuminated byline-blanketed fluxes, for 3 700 K
| The gravity-brightening effect and stellar atmospheres. II Results for illuminated models with 3 700 K < T_eff < 7 000 K
The influence of the so-called ``reflection effect'' (mutualillumination in a close binary) on the gravity-brightening exponent(beta ) is studied using the UMA (Uppsala Model Atmosphere) code. Themodel is applied to convective grey (in the sense ofcontinuum-only-opacity) and non-grey (line-blanketed) atmospheres with 3700 K < T_eff < 7 000 K, illuminated by grey and non-grey fluxes.The results for grey atmospheres illuminated by grey or non-grey fluxesare very similar. In this case beta mostly depends on the amount ofincident energy and on the illumination direction, apart from thedependence on the effective temperature already discussed fornon-illuminated models in a previous work (Alencar & Vaz\cite{paper1}). The existence of a maximum in the beta (T_eff) relationis due to the interplay between the convection and opacity properties ofthe models. The external illumination increases the values of beta ,that is, the larger the amount of incident flux the larger the value ofthe exponent. This effect is caused by the ``quenching'' of convectionas the external illumination heats the surface layers of the illuminatedstar, thus bringing it closer to radiative equilibrium, where beta isclose to unity. We provide a polynomial fit to the variation of betawith the fundamental parameters, in order to make it possible to easilyaccount for the effect in light curve synthesis programs. Forline-blanketed illuminated atmospheres there is an additional dependenceon the effective temperature of the incident flux (the heatingtemperature). This is related to the overall wavelength dependence ofthe spectral line opacity. Particularly in the UV, the line opacity isso strong that it prevents a significant amount of the incident fluxfrom penetrating to the continuum formation layers. The quenching ofconvection by the external illumination and the related increase of betaare thus partly prevented.
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Наблюдательные данные и астрометрия
| Созвездие: | Пегас |
| Прямое восхождение: | 22h13m23.52s |
| Склонение: | +08°25'30.9" |
| Видимая звёздная величина: | 9.022 |
| Собственное движение RA: | -16.8 |
| Собственное движение Dec: | -16.7 |
| B-T magnitude: | 9.257 |
| V-T magnitude: | 9.042 |
Каталоги и обозначения:
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