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New Times of Minima of Eclipsing Binary Systems
We present 82 photoelectric minima observations of 34 eclipsingbinaries.
| Precise Times of Minimum Light of Neglected Eclipsing Binaries
Not Available
| Pulsations in the eclipsing variable system AS Camelopardalis
We performed photoelectric observations of AS Cam in 2002 2004. Five newtimes of minima were obtained. Their positions are consistent with thepreviously found light equation for the system and with the hypothesisthat the difference between the observed (15°/100 yr) andtheoretical (44°/100 yr) rates of apsidal motion results from thepresence of a third body in the system. A Fourier analysis of twoobservational data sets, 1968 1970 and 2002 2004, reveals, with a highsignificance, periodic light variations with a frequency of ω 0 =1.0950 ± 0.0001d-1 and an amplitude of 0 . m 020, which areprobably caused by the radial pulsations of one of the components. Wefound a seasonal phase shift of these oscillations that may be producedby other periodic processes in the system. We show that the fairly largescatter of observed times of minima about the theoretical curve of thelight equation can be explained by the presence of pulsations. Using the2002 and 2004 observations as an example, we show that including thepulsations reduces this scatter.
| 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.
| Stability of Triple Star Systems with Highly Inclined Orbits
It is well established that certain detached eclipsing binary starsexhibit apsidal motions whose values are in disagreement with calculateddeviations from Keplerian motion based on tidal effects and the generaltheory of relativity. Although many theoretical scenarios have beendemonstrated to bring calculations into line with observations, all haveseemed unlikely for various reasons. In particular, it has beenestablished that the hypothesis of a third star in an orbit almostperpendicular to the orbital plane of the close binary system canexplain the anomalous motion at least in some cases. The stability oftriple star systems with highly inclined orbits has been in doubt,however. We have found conditions that allow the long-term stability ofsuch systems, so that the third-body hypothesis now seems a likelyresolution of the apsidal motion problem. We apply our stabilitycriteria to the cases of AS Cam and DI Her and recommend observations atthe new Keck interferometer, which should be able to directly observethe third bodies in these systems.
| Apsidal motion in eccentric eclipsing binaries: V871 Aql, V345 Lac, V401 Lac and CR Sct
About thirty new times of minimum light recorded with photoelectric orCCD photometers were obtained for several little studied eccentric-orbiteclipsing binaries V871 Aql (P=3.0°, e=0.13), V345 Lac ( 7.5°,0.46), V401 Lac ( 2.0°, 0.16) and CR Sct ( 4.2°, 0.09). TheirO-C diagrams were analyzed using all reliable timings found in theliterature and in all cases an apsidal motion was either discovered orconfirmed. The new values for the elements of the apsidal motion werederived. We find periods of apsidal motion of about 255, 7000, 79.4 and4400 years for V871 Aql, V345 Lac, V401 Lac and CR Sct, respectively.Partly based on photoelectric observations secured at the HvarObservatory, Zagreb University, Croatia.
| Rotating stellar models and dynamic tides in close binaries: A first approach
Rotating stellar models - homogeneous and evolved ones - were introducedfor the first time, in order to investigate the effects of rotationallyinduced changes in the internal structure of stars on the apsidal motionin close binary systems within the framework of the theory of dynamictides. The rotating models are calculated in the quasi-sphericalapproximation under the assumption that the star rotates as a solidbody. The models show that the spectrum of resonances between dynamictides and free oscillation modes is substantially modified by rotation.In particular, the changes in the internal structure of the rotatingmodels yield complex spectra which are more than simple images of thespectra in non-rotating models shifted in the period space. An immediateconsequence of the differences between rotating and non-rotating modelsis that a reconsideration of the global problem of the apsidal-motionmay be in order.
| Modeling dissimilar components of the eclipsing binary EK Cep:. Does the primary star have a rapidly rotating core?
In this study we propose to explain the discrepancy between classicalmodels and the observational data of early type stars in eclipsingbinaries by the existence of a rapidly rotating core in the primary,rather than by invoking a low metal abundance. Our claim is based on theanalysis of the double lined eclipsing binary EK Cep, on which a strongconstraint is put by its apsidal motion. We constructed models both withand without rotation for the components of the system. If the stars donot rotate, then, considering (i) that both components have the samechemical composition and age, and (ii) that the primary star is exactlyat the zero-age main-sequence point, we derive X=0.614 and Z=0.04 forrespectively the hydrogen and heavy element abundances, with amixing-length parameter alpha =1.30, somewhat lower than that calibratedon the Sun. These values satisfy all the observational constraints atthe single age of 26 Myr, except the luminosity and radius of theprimary, and they are also in good agreement with the observed chemicalevolution in the solar neighborhood. Since the observed luminosity andradius of EK Cep A are less than those predicted by a non-rotatingmodel, we deduce that this star must have a rapidly rotating core, whileits envelope is synchronized with the orbital motion due to tidalinteraction. To achieve perfect agreement between the rotating model ofthis star and the observations, the requirement is that the centralregion rotates about 65 times faster than the synchronized envelope,which contains 48% of the star's total mass. We describe the effect ofsuch differential rotation on the location of the star in the HRdiagram, and compare it with that of rotation caused by contractionalone. We confirm also that such rapid rotation may account for thespread which is observed in the isochrones of open clusters.
| Apsidal Motion in Binaries: Rotation of the Components
A sample of 51 separated binary systems with measured apsidal periodsand rotational velocities of the components is examined. The ranges ofthe angles of inclination of the equatorial planes of the components tothe orbital plane are estimated for these systems. The observed apsidalvelocities can be explained by assuming that the axes of rotation of thestars are nonorthogonal to the orbital plane in roughly 47% of thesystems (24 of the 51) and the rotation of the components is notsynchronized with the orbital motion in roughly 59% of the systems (30of 51). Nonorthogonality and nonsynchrony are defined as deviations from90° and a synchronized angular velocity, respectively, at levels of1 or more.
| Determination of the Ages of Close Binary Stars on the Main Sequence from Evolutionary Model Stars of Claret and Gimenez
A grid of isochrones, covering a wide range of stellar ages from thezero-age main sequence to 10 billion years, is calculated in the presentwork on the basis of the model stars of Claret and Gimenez withallowance for convective overshoot and mass loss by the components. Theages of 88 eclipsing variables on the main sequence from Andersen'scatalog and 100 chromospherically active stars from Strassmeier'scatalog are calculated with a description of the method of optimuminterpolation. Comparisons with age determinations by other authors aregiven and good agreement is established.
| Apsidal Motion in Detached Binary Stars: Comparison of Theory and Observations
A list of 62 detached binaries having reliable data on the rotation ofthe line of apsides is considered. Theoretical estimates of the rate ofapsidal motion are obtained. These estimates are compared withobservational data. It is shown that cases in which the theoreticalestimate exceeds the observed value are several times more frequent thancases in which the theoretical value is lower than the observed one.This discrepancy increases when systems with more reliable observationaldata are considered.
| New results on the apsidal-motion test to stellar structure and evolution including the effects of dynamic tides
We revised the current status of the apsidal-motion test to stellarstructure and evolution. The observational sample was increased by about50% in comparison to previous studies. Classical and relativisticsystems were analyzed simultaneously and only systems with accurateabsolute dimensions were considered. New interior models incorporatingrecent opacity tables, stellar rotation, mass loss, and moderate coreovershooting were used as theoretical tools to compare the predictedwith the observed shifts of the position of the periastron. The stellarmodels were computed for the precise observed masses and the adoptedchemical compositions are consistent with the corresponding tables ofopacities to avoid the inherent problems of interpolation in mass and in(X, Z). The derived chemical composition for each individual system wasused to infer the primordial helium content as well as a law ofenrichment. The values found are in good agreement with those obtainedfrom various independent sources. For the first time, the effects ofdynamic tides are taken into account systematically to determine thecontribution of the tidal distortion to the predicted apsidal-motionrate. The deviations between the apsidal-motion rates resulting from theclassical formula and those determined by taking into account theeffects of dynamic tides are presented as a function of the level ofsynchronism. For systems close to synchronisation, dynamic tides causedeviations with respect to the classical apsidal-motion formula due tothe effects of the compressibility of the stellar fluid. For systemswith higher rotational angular velocities, additional deviations due toresonances arise when the forcing frequencies of the dynamic tides comeinto the range of the free oscillation modes of the component stars. Theresulting comparison shows a good agreement between the observed andtheoretical apsidal-motion rates. No systematic effects in the sensethat models are less mass concentrated than real stars and nocorrelations with the evolutionary status of the systems were detected.
| Studies of Intermediate-Mass Stellar Models Using Eclipsing Binaries
Evolutionary computations for intermediate-mass stars are analyzed usingobserved parameters for eclipsing SB2 binaries and theoreticalparameters based on evolutionary tracks. Modern observations cannot beused to distinguish between models with and without convectiveovershooting for stars in the vicinity of the main sequence.Statistically significant discrepancies between the observed andcomputed stellar parameters are associated with systematic errors inphotometric effective temperatures. After taking into account systematiceffects, the theoretical computations fit the observational datauniformly well throughout the entire mass interval studied. Empiricaland semiempirical (i.e., reduced to the ZAMS and with solar elementalabundances) formulas for the mass-luminosity, mass-effectivetemperature, and mass-radius relations are proposed.
| The Third Body in the Eclipsing System RR Lyn
Based on 70 years of published photoelectric observations, we havedetected quasi-periodic cophased oscillations of the times of theprimary and secondary minima of RR Lyn, one of the brightest and nearesteclipsing binaries in the northern sky ( ; r=74 pc). Approximating theseoscillations using the light equation yields estimates of the orbitalparameters of the third body in the system and imposes constraints onits mass, M 3. In the most probable case when the orbits of theeclipsing and triple systems are coplanar, M 3=1.10±0.02M ȯ,and the semimajor axis of the orbit A 3=17.4±3.5 AU, with asubstantial eccentricity, e 3=0.96±0.02. We have carried out adetailed study of the apsidal rotation of this eclipsing and nowmultiple system, which was suggested by Koch as a test of generalrelativity as far back as 1973. Our high-precision W BV R photoelectricphotometry &$(sigma _{obs} ≅ 0mathop mlimits_. 0032)$; has removed some contradictions. At the same time, the proximity ofthe longitude of periastron ω 180°; the close correlationbetween the jointly estimated values of ω, e and thelimb-darkening coefficients for the component disks, u 1 and u 2; andmicrofluctuations in the brightnesses of the stars prevent determinationof the rate of rotation of the elliptical orbit in the system, evenusing the most accurate measurements.
| Orbital Evolution in Binary and Triple Stars, with an Application to SS Lacertae
We present equations governing the way in which both the orbit and theintrinsic spins of stars in a close binary should evolve subject to anumber of perturbing forces, including the effect of a third body in apossibly inclined wider orbit. We illustrate the solutions in somebinary star and triple star situations: tidal friction in a wide buteccentric orbit of a radio pulsar about a B star (0045-7319), the Darwinand eccentricity instabilities in a more massive but shorter periodmassive X-ray binary, and the interaction of tidal friction with Kozaicycles in a triple star, such as β Per at an early stage in thatstar's life, when all three components were zero-age main sequencestars. We also attempt to model in some detail the interesting triplesystem SS Lac, which stopped eclipsing in about 1950. We find that ourmodel of SS Lac is quite constrained by the relatively goodobservational data of this system and leads to a specific inclination(29°) of the outer orbit relative to the inner orbit at epoch zero(1912). We make some predictions about changes to system parameters inthe short term (20-40 yr) and also in the medium term (up to ~3000 yr).Although the intrinsic spins of the stars have little effect on theorbit, the converse is not true: the spin axes can vary theirorientation relative to the close binary by up to 120° on atimescale of about a century.
| Times of Minima of Eclipsing Binaries DI Herculis and V1143 Cygni
Not Available
| Times of Minima of Eclipsing Binaries
Not Available
| 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
| 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.
| CCD Times of Minima of Eclipsing Binary Systems
We present several CCD minima observations of 22 eclipsing binaries.
| Chemical composition of eclipsing binaries: a new approach to the helium-to-metal enrichment ratio
The chemical enrichment law Y(Z) is studied by using detacheddouble-lined eclipsing binaries with accurate absolute dimensions andeffective temperatures. A sample of 50 suitable systems was collectedfrom the literature, and their effective temperatures were carefullyre-determined. The chemical composition of each of the systems wasobtained by comparison with stellar evolutionary models, under theassumption that they should fit an isochrone to the observed propertiesof the components. Evolutionary models covering a wide grid in Z and Ywere adopted for our study. An algorithm was developed for searching thebest-fitting chemical composition (and the age) for the systems, basedon the minimization of a χ2 function. The errors (andbiases) of these parameters were estimated by means of Monte Carlosimulations, with special care put on the correlations existing betweenthe errors of both components. In order to check the physicalconsistency of the results, we compared our metallicity values withempirical determinations, obtaining excellent coherence. Theindependently derived Z and Y values yielded a determination of thechemical enrichment law via weighted linear least-squares fit. Our valueof the slope, ΔY/ΔZ=2.2+/-0.8, is in good agreement withrecent results, but it has a smaller formal error and it is free ofsystematic effects. Linear extrapolation of the enrichment law to zerometals leads to an estimation of the primordial helium abundance ofYp=0.225+/-0.013, possibly affected by systematics in theeffective temperature determination.
| Estimating the ages of eclipsing variable DM-stars on the basis of the evolutionary star models by Maeder and Meynet
A set of isochrones covering a wide range of star ages from5\cdot106 to 1010 yr was built on the basis of thestellar models by A. Maeder and G. Meynet with overshooting and massloss for Population I stars with abundances (X, Y, Z) = 0.70, 0.28,0.02. The isochrones were used to compute the ages of 88 eclipsingvariable stars from the catalog by Andersen which lie on the mainsequence. The influence of initial data errors on the rezultes wasinvestigated. The ages derived are in good agreement with the results ofother authors.
| A third body in the eclipsing binary AS Cam
Not Available
| Post-Newtonian Theory for Precision Doppler Measurements of Binary Star Orbits
The determination of velocities of stars from precise Dopplermeasurements is described here using a relativistic theory ofastronomical reference frames to determine the Keplerian andpost-Keplerian parameters of binary systems. Seven reference frames areintroduced: (1) the proper frame of a particle emitting light, (2) thestar-centered reference frame, (3) the barycentric frame of the binary,(4) the barycentric frame of the Galaxy, (5) the barycentric frame ofthe solar system, (6) the geocentric frame, and (7) the topocentricframe of observer at the Earth. We apply successive Lorentztransformations and the relativistic equation of light propagation toestablish the exact treatment of Doppler effect in binary systems bothin special and general relativity theories. As a result, the Dopplershift is a sum of (1) linear in c^-1 terms, which include the ordinaryDoppler effect and its variation due to the secular radial accelerationof the binary with respect to observer; (2) terms proportional to c^-2,which include the contributions from the quadratic Doppler effect causedby the relative motion of binary star with respect to the solar system,the motion of the particle emitting light and diurnal rotational motionof observer, orbital motion of the star around the binary's barycenter,and the orbital motion of the Earth; and (3) terms proportional to c^-2,which include the contributions from redshifts due to gravitationalfields of the star, the star's companion, the Galaxy, the solar system,and the Earth. After parameterization of the binary's orbit, we findthat the presence of periodically changing terms in the Doppler shiftenables us to disentangle different terms and measure, along with thewell-known Keplerian parameters of the binary, four additionalpost-Keplerian parameters, which characterize (1) the relativisticadvance of the periastron; (2) a combination of the quadratic Dopplerand gravitational shifts associated with the orbital motion of theprimary relative to the binary's barycenter and the companion'sgravitational field, respectively; (3) the amplitude of the``gravitational lensing'' contribution to the Doppler shift; and (4) theusual inclination angle of the binary's orbit, i. We briefly discuss thefeasibility of practical implementation of these theoretical results,which crucially depends on further progress in the technique ofprecision Doppler measurements.
| Studies on stellar rotation. I. The theoretical apsidal motion for evolved rotating stars
The quasi-spherical approximation, with some modifications, wasimplemented in our stellar evolution code to take into account theeffect of rotation on the internal structure of the stars and, inparticular, on the apsidal motion constant. Three models with masses 2,7 and 15 Msun were used since they are representative of themass range where apsidal motion is detected in binary stars. We adoptedtwo limiting cases of angular momentum redistribution: localconservation and rigid body rotation. It was found that the influence ofrotation on internal structure depends strongly on the distortion of theconfiguration characterized by the parameter lambda = 2v(2) /(3gR) atthe surface of the model. Such results make the work of introducing thecorrection for rotation in the apsidal motion analysis an easier tasksince it is sufficient to decrease the theoretical log k_2 by 0.87lambda_s .
| Astrophysics in 1998
From Alpha (Orionis and the parameter in mixing-length theory) to Omega(Centauri and the density of the universe), the Greeks had a letter forit. In between, we look at the Sun and planets, some very distantgalaxies and nearby stars, neutrinos, gamma rays, and some of theanomalies that arise in a very large universe being studied by roughlyone astronomer per 10^7 Galactic stars.
| The Third Body in the Eclipsing Binary AS Camelopardalis
The eclipsing variable AS Cam is a binary system with anomalously slowapsidal motion. We determined the times of minima from 1993 to 1996 andanalyzed them to reveal a "light time" effect with an amplitude of 3minutes and a period of 2.2 years thereby providing evidence for a thirdbody in the system.
| Apsidal Motion in Double Stars. I. Catalog
A catalog of 128 double stars with measured periods of apsidal motion iscompiled. Besides the apsidal periods, the orbital elements of binariesand physical parameters of components (masses, radii, effectivetemperatures, surface gravities) are given. The agreement of the apsidalperiods found by various authors is discussed.
| Orbital circularization in detached binaries with early-type primaries
Extending our previous study, the present paper reports on thediscussion of the orbital circularization in 37 detached binaries withearly-type primaries. From comparison of the theoretical predictionswith the orbital eccentricities of our binary systems, we find thatZahn's circularization theories are substantially consistent with theobserved data for overwhelming majority of our samples. However, we alsonote that three binaries of whom both components are asynchronizedrotators possess circular orbits. How to understand the circularism ofthe three systems remains a problem not only to Zahn's theories, but toall other present circularization mechanisms.We think that studies onthe circularization of pre-main-sequence binary systems could providesome clues for the problem.
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