Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
New Times of Minima of Some Eclipsing Binary Stars
Not Available
| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderliche Sterne e.V.
Not Available
| The Case for Third Bodies as the Cause of Period Changes in Selected Algol Systems
Many eclipsing binary star systems show long-term variations in theirorbital periods, evident in their O-C (observed minus calculated period)diagrams. With data from the Robotic Optical Transient Search Experiment(ROTSE-I) compiled in the SkyDOT database, New Mexico State University 1m data, and recent American Association of Variable Star Observers(AAVSO) data, we revisit Borkovits and Hegedüs's best-casecandidates for third-body effects in eclipsing binaries: AB And, TV Cas,XX Cep, and AK Her. We also examine the possibility of a third bodyorbiting Y Cam. Our new data support their suggestion that a third bodyis present in all systems except AK Her, as is revealed by thesinusoidal variations of the O-C residuals. Our new data suggest that athird body alone cannot explain the variations seen in the O-C residualsof AK Her. We also provide a table of 143 eclipsing binary systems thathave historical AAVSO O-C data with new values computed from the SkyDOTdatabase.
| 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.
| 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.
| An XMM-Newton and Chandra study of the starburst galaxy IC 10
We present an X-ray study of our nearest starburst galaxy IC 10, basedon XMM-Newton and Chandra observations. A list of 73 XMM-Newton and 28Chandra detections of point-like X-ray sources in the field is provided;a substantial fraction of them are likely stellar objects in the MilkyWay due to the low Galactic latitude location of IC 10. The brightestsource in the IC 10 field, X-1, has a mean 0.3-8.0 keV luminosity of~1.2 × 1038ergs-1 and shows a largevariation by a factor of up to ~6 on time-scales of ~104 sduring the XMM-Newton observation. The X-ray spectra of the sourceindicate the presence of a multicolour blackbody accretion disc with aninner disc temperature Tin~ 1.1 keV. These results areconsistent with the interpretation of the source as a stellar mass blackhole (BH), probably accreting from a Wolf-Rayet (W-R) star companion. Weinfer the mass of this BH to be ~4Msolar if it is notspinning, or a factor of up to ~6 higher if there is significantspinning. We also detect an apparent diffuse soft X-ray emissioncomponent of IC 10. An effective method is devised to remove the X-rayCCD-readout streaks of X-1 that strongly affect the study of the diffusecomponent in the XMM-Newton and Chandra observations. We find that thediffuse X-ray morphology is oriented along the optical body of thegalaxy and is chiefly associated with starburst regions. The diffusecomponent can be characterized by an optically thin thermal plasma witha mean temperature of ~4 × 106 K and a 0.5-2 keVluminosity of ~8 × 1037ergs-1, representingonly a small fraction of the expected mechanical energy inputs frommassive stars in the galaxy. There is evidence that the hot gas isdriving outflows from the starburst regions; therefore, the bulk of theenergy inputs may be released in a galactic wind.
| New Times of Minima of Some Eclipsing Binary Stars
Not Available
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| New Times of Minima of Eclipsing Binary Stars
Not Available
| Photoelectric Minima of Some Eclipsing Binary Stars
Not Available
| Die Geschichte und Literatur des Lichtwechsels veraenderlicher Sterne G.u.L.
Not Available
| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderlichen Serne e.V.
Not Available
| 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
| Beobachtungsegebnisse Bundesdeutsche Arbeitsgemainschaft fur Veranderliche Sterne e.V.
Not Available
| Gravity-darkening exponents in semi-detached binary systems from their photometric observations: Part I
From the light curve analysis of several semi-detached close binarysystems, the exponent of the gravity-darkening (GDE) for the Roche lobefilling components has been empirically estimated. The analysis, basedon Roche geometry, has been made using the latest improved version ofour computer programme. The present method of the light-curve analysisenables simultaneous estimation of the systems' parameters and thegravity-darkening exponents. The reliability of the method has beenconfirmed by its application to the artificial light curves obtainedwith a priori known parameters. Further tests with real observationshave shown that in the case of well defined light curves the parametersof the system and the value of the gravity-darkening exponent can bereliably estimated. This first part of our analysis presents the resultsfor 9 of the examined systems, that could be briefly summarised asfollows: 1) For four of the systems, namely: ZZ Cru, RZ Dra, XZ Sgr andW UMi, there is a very good agreement between empirically estimated andtheoretically predicted values for purely radiative and convectiveenvelopes. 2) For the rest five, namely: TT Aur, V Pup, TV Cas, LT Her,and VV UMa, the estimated values of the gravity-darkening exponents werededuced to be larger than theory expects for purely radiative orconvective envelopes, respectively. Moreover, it is worthwhile tomention that these values -although greater than theoreticalpredictions- are: a) Smaller compared to those found by others. b) Intwo cases, (TV Cas & LT Her), they are normal if some kind of solartype activity (i.e. by employing the Roche model involving a spottedarea on the surface of the secondary star) is assumed. 3) The largevalues derived for the two early type systems TT Aur & V Pup, arevery possibly connected with the effects of rotation laws, and in somedegree with the large contribution of the radiative pressure in thetotal potential, leading by that to considerable deviations of thestellar surfaces from the assumed classical Roche geometry. 4) Finally,in the VV UMa case, the estimated value of the gravity-darkeningexponent - although almost double than the expected for stars withconvective envelopes - still it is low in comparison with that estimatedby others who have analysed the same data. But, since for thisparticular binary the anomalous GDE is not supported by recentsimultaneous uvby observations (Lazaro et al. \cite{lazaro}), theestimated higher value may be due to the old observational materialused.
| Times of Minima of Eclipsing Binaries
19 times of minima of ten eclipsing binary stars are reported. Apreliminary ephemeris of EV Cnc is given.
| 149 Bedeckungssterne der BAV-Programme. Eine Analyse der Beobachtungstatigkeit seit den Angangen.
Not Available
| Wer beobachtet mit ? TV Cas.
Not Available
| Das Brunner Punktesystem.
Not Available
| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veraenderliche Sterne e.V.
Not Available
| 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 New Elements for Several Stars
Not Available
| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veraenderliche Sterne e.V.
Not Available
| 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 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.
| 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.
| Do the physical properties of Ap binaries depend on their orbital elements?
We reveal sufficient evidence that the physical characteristics of Apstars are related to binarity. The Ap star peculiarity [represented bythe Δ(V1-G) value and magnetic field strength] diminishes witheccentricity, and it may also increase with orbital period(Porb). This pattern, however, does not hold for largeorbital periods. A striking gap that occurs in the orbital perioddistribution of Ap binaries at 160-600d might well mark a discontinuityin the above-mentioned behaviour. There is also an interestingindication that the Ap star eccentricities are relatively lower thanthose of corresponding B9-A2 normal binaries for Porb>10d.All this gives serious support to the pioneering idea of Abt &Snowden concerning a possible interplay between the magnetism of Apstars and their binarity. Nevertheless, we argue instead in favour ofanother mechanism, namely that it is binarity that affects magnetism andnot the opposite, and suggest the presence of a newmagnetohydrodynamical mechanism induced by the stellar companion andstretching to surprisingly large Porb.
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Zincirli Prenses |
| Sað Açýklýk: | 00h19m18.74s |
| Yükselim: | +59°08'20.5" |
| Görünürdeki Parlaklýk: | 7.311 |
| Uzaklýk: | 254.453 parsek |
| özdevim Sað Açýklýk: | 33.9 |
| özdevim Yükselim: | -0.8 |
| B-T magnitude: | 7.363 |
| V-T magnitude: | 7.316 |
Kataloglar ve belirtme:
|
