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An Orbital Period Investigation of the Solar-Type Overcontact Binary V700 Cygni
Not Available
| An Orbital Period Investigation of the Semi-Detached Near-Contact Binary DD Monocerotis
Not Available
| On Period Variations of the K-Type Eclipsing Binary BM Ursae Majoris
From new CCD observations, 11 light minimum times are presented in thispaper. The orbital period change of a W UMa-type eclipsing binary, BMUrase Majoris, was investigated, based on all available times of lightminimum. It was discovered that the orbital period of the binary showscyclic oscillation, superimposed on a secular period decrease. Theamplitude and the period of the cyclic variation are A =0.0101(±0.0004)d and P3 = 30.8(±0.2)yr,respectively. This kind of cyclic variation may be due to a light-timeeffect via an unseen third body. If the existence of an additional bodyis true, it may remove a great amount of angular momentum from thecentral system, and may play an important role in the formation of closebinary. The orbital period continuously decreases at a rate of dP/dt =‑7.49(±0.16) × 10-8d yr-1,which may be due to mass transfer from the primary to the secondary,accompanying mass and angular-momentum loss from the binary system. Theorbital period decrease, accompanying mass and angular momentum loss,would cause the contact degree to increase. Therefore, this binary willevolve into a deep contact configuration.
| Orbital Period Changes and Their Evolutionary Status for Weak-Contact Binaries. II. CC Comae Berenices and BV Draconis
Based on O - C curves, we present detailed period investigationsof two weak-contact binaries CC Com and BV Dra. It is found that theperiods of these two binaries have varied in a cyclic variation waysuperposed on a secular period change. The periods and amplitudes of thecyclic variations are P 3 = 23.6(±0.4) yr and A =0fd0028(±0fd0003) for CC Com and P 3 =23.8(±0.6) yr and A = 0fd0029(±0fd0003) for BV Dra. Thecyclic oscillations for these two stars may be attributed to thelight-time effect via an unseen third body, which could extract angularmomentum from the central system. If the existence of the additionalbody is true, CC Com and BV Dra may be triple system stars. For CC Com,the secular period decrease rate is dP/dt = -0.20 ×10-7 d yr-1, which suggests that themass transfers from the more massive component to the less massive one,accompanied with the angular momentum loss due to mass outflow from L2. A decrease in its orbital period will result in theshrinking of the inner and outer critical Roche lobes, and then causethe contact degree to increase. This kind of weak-contact binary with along-term period decrease may evolve into a deep contact configuration.For BV Dra, the continuous period increase rate is dP/dt = +0.29 ×10-7 d yr-1, indicating that the masstransfers from the less massive component to the more massive one. Anincrease in its orbital period may cause the separation between bothcomponents to increase, and thus the contact configuration will break,as predicted by thermal relaxation oscillation theory. Therefore, thiskind of weak-contact binary with a secular period increase will evolveinto a broken-contact configuration.
| B.R.N.O. Contributions #36, Times of minima
Not Available
| A New Photometric Investigation of the W UMa-Type Binary BI CVn
New photometric observations and their investigation of the W UMa-typebinary, BI CVn, are presented. The variations of the orbital period wereanalyzed based on 12 new determined times of light minimum together withthe others compiled from the literature. It is discovered that theperiod of BI CVn shows a long-term period decrease at a rate of\dot{P}=-1.51(\pm 0.12)\times {10^{-7}} daysyear-1 while it undergoes a cyclic variation with aperiod of 27.0 years and an amplitude of 0fd0151. Photometricsolutions determined with the Wilson-Devinney method suggest that BI CVnis a contact binary with a degree of contact of 18.0(±1.7)%. Theasymmetry of the light curves was interpreted by the presence of darkspots on both components, and absolute parameters were determined bycombining the photometric elements with the spectroscopic solutionsgiven by Lu. The observed period decrease can be plausibly explained bya combination of the mass transfer from the primary to the secondary andangular momentum loss via magnetic braking. The cyclic periodoscillation suggests that BI CVn is a triple system containing atertiary component with a mass no less than 0.58 M sun in a27.0 year orbit. As in the cases of the other contact binaries (e.g., AHCnc, AP Leo, AD Cnc, and UX Eri), it is possible that this tertiarycompanion played an important role for the formation and evolution ofthe contact system by removing angular momentum from the central systemvia Kozai oscillation or a combination of Kozai cycle and tidalfriction, which causes the eclipsing pair to have a short initialorbital period (e.g., P < 5d). In that case, can theinitially detached system evolve into the present contact configurationvia a combination of magnetic torques from stellar winds and a case Amass transfer?
| Angular momentum and mass evolution of contact binaries
Various scenarios of contact binary evolution have been proposed in thepast, giving hints of (sometimes contradictory) evolutionary sequencesconnecting A- and W-type systems. As the components of close detachedbinaries approach each other and contact binaries are formed, followingevolutionary paths transforms them into systems of two categories:A-type and W-type. The systems evolve in a similar way but underslightly different circumstances. The mass/energy transfer rate isdifferent, leading to quite different evolutionary results. Analternative scenario of evolution in contact is presented and discussed,based on the observational data of over one hundred low-temperaturecontact binaries. It results from the observed correlations amongcontact binary physical and orbital parameters. Theoretical tracks arecomputed assuming angular momentum loss from a system via stellar wind,accompanied by mass transfer from an advanced evolutionary secondary tothe main-sequence primary. A good agreement is seen between the tracksand the observed graphs. Independently of details of the evolution incontact and a relation between A- and W-type systems, the ultimate fateof contact binaries involves the coalescence of both components into asingle fast rotating star.
| V802 Aquilae: A Short-Period Eclipsing Binary with Magnetic Activity
New CCD observations for V802 Aql were observed from 2004 to 2007, andseven light minimum timings were obtained. Using the Wilson-Devinneycode, the photometric solution was deduced from R-band observations. Theresults show that the mass-ratio and the contact degree are q =0.1443±0.0059 and f = 34.9%±7.6%, respectively. Comparingthe parameters of the dark spot from our results with those from Samecet al., it is found that the magnetic activity of the primary componentmay have been migrating towards its equator from 2002 to 2005. Anorbital period analysis weakly suggests that the orbital period mayundergo a cyclic variation with a period of P3 = 8.32yr andan amplitude of A = 0d.0196. The periodic oscillation of thisbinary may be more plausibly explained as being the result of magneticactivity cycles. Therefore, the eclipsing star V802 Aql may becoalescing via magnetic breaking.
| a Photometric Study of the Neglected Eclipsing Binary BS Cassiopeiae
We present multicolor charge-coupled device (CCD) photometry for theeclipsing binary BS Cassiopeiae, observed on four nights between 2007December and 2008 January. Using the Wilson-Devinney program, thephotometric solution was derived from our BVR observations. Photometricresults indicated that BS Cas is a W-subtype binary, whose mass ratioand overcontact degree are q = 0.2834(±0.0010) and f =31.6%(±1.1%), respectively. Light curves of BS Cas present atypical O'Connell effect, which may be attributed to dark spot activityof the primary component. A detailed period analysis reveals that thereexists a cyclic variation overlaying a secular period decrease, based oneither all available light minimum times or recent light minimum timessince 1989. The low-amplitude cyclic variation with a period of about 13yr can be explained by either the light-time effect or cyclic magneticactivity of both components. The long-term orbital period decreasesuggests that BS Cas is undergoing mass transfer from the primarycomponent to the secondary one. With its mass transfer and accompanyingangular momentum loss, this binary will evolve into a deeper contactconfiguration.
| The evolutionary status of W Ursae Majoris-type systems
Well-determined physical parameters of 130 W Ursae Majoris (W UMa)systems were collected from the literature. Based on these data, theevolutionary status and dynamical evolution of W UMa systems areinvestigated. It is found that there is no evolutionary differencebetween W- and A-type systems in the M-J diagram, which is consistentwith the results derived from the analysis of observed spectral type andof M-R and M-L diagrams of W UMa systems. M-R and M-L diagrams of W- andA-type systems indicate that a large amount of energy should betransferred from the more massive to the less massive component, so thatthey are not in thermal equilibrium and undergo thermal relaxationoscillation. Moreover, the distribution of angular momentum, togetherwith the distribution of the mass ratio, suggests that the mass ratio ofthe observed W UMa systems decreases with decreasing total mass. Thiscould be the result of the dynamical evolution of W UMa systems, whichsuffer angular momentum loss and mass loss as a result of the magneticstellar wind. Consequently, the tidal instability forces these systemstowards lower q values and finally to rapidly rotating single stars.
| Times of Minima for Neglected Eclipsing Binaries 2006-2007
CCD minima observations of eclipsing binaries during 2006-2007 for anumber of neglected eclipsing binaries are presented.
| AD Cancri: A Shallow Contact Solar-Type Eclipsing Binary and Evidence for a Dwarf Third Component and a 16 Year Magnetic Cycle
CCD photometric observations of AD Cancri obtained from 2000 March 7 to2004 December 20 are presented. Variations of the light levels at theprimary minimum and both maxima are found. Uniform solutions of foursets of photometric data were derived by using the Wilson-Devinneymethod. The solutions suggest that AD Cancri is a shallow W-type contactbinary (f=8.3%+/-1.3%) with a high mass ratio of 1/q=0.770+/-0.002. Thelong-term variation of the light curve is explained by variabledark-spot models of the more massive component star with a possible 17yr cycle. Our 13 times of light minimum over 5 years, including otherscollected from the literature, have been used for the period study. Thecomplex period changes can be sorted into a long-term period increase atrate of dP/dt=+(4.94+/-0.16)×10-7 days yr-1,a 16.2 yr periodic component (A3=0.0155 days), and a verysmall amplitude period oscillation (A4=0.0051 days,P4=6.6 yr). The existence of third light may indicate thatthere is a tertiary component in the binary system. Solving thefour-band light curves of Samec & Bookmyer, it is found that thecontribution of the tertiary component to the total light of the triplesystem increases with wavelength, which suggests that it is very cooland may be a very red main-sequence star. The small-amplitude periodoscillation may be caused by the light-time effect of the cool tertiarycomponent (M3~0.41 Msolar). The 16.2 yr periodiccomponent in the orbital period and the 17 yr cyclic activity of thedark spot on the more massive component both may reveal that the moremassive component displays solar-type magnetic activity with a cyclelength of about 16 yr.
| Contact Binaries with Additional Components. III. A Search Using Adaptive Optics
We present results of the Canada-France-Hawaii Telescope adaptive optics(AO) search for companions of a homogeneous group of contact binarystars, as a contribution to our attempts to prove the hypothesis thatthese binaries require a third star to become as close as observed. Inaddition to directly discovering companions at separations of>=1″, we introduced a new method of AO image analysis utilizingdistortions of the AO diffraction ring pattern at separations of0.07″-1″. Very close companions, with separations in thelatter range, were discovered in the systems HV Aqr, OO Aql, CK Boo, XYLeo, BE Scl, and RZ Tau. More distant companions were detected in V402Aur, AO Cam, and V2082 Cyg. Our results provide a contribution to themounting evidence that the presence of close companions is a very commonphenomenon for very close binaries with orbital periods <1 day.Based on observations obtained at the Canada-France-Hawaii Telescope,which is operated by the National Research Council of Canada, theInstitut National des Sciences de l'Univers of the Centre National de laRecherche Scientifique of France, and the University of Hawaii.
| Ternarity, Activity, and Evolutionary State of the W UMa-Type Binary UX Eridani
Charge-coupled device photometric observations of the W UMa-type binarystar UX Eridani are presented. Comparing the B light curve with thatobtained by Binnendijk in 1964-1965, the variation of the light curvearound the primary minimum was found. Photometric solutions ofBinnendijk's and our light curves were derived by using the new versionof the Wilson-Devinney program. Our solutions confirmed that UX Eri is amarginal W-type overcontact binary system with a very low degree ofovercontact, f < 15%. The change of the light curve around theprimary minimum was explained as the disappearance of a dark spot on themore massive component star. This suggests that UX Eri shows strongmagnetic activity, which is in agreement with its having the highestX-ray flux among 57 W UMa-type binary stars studied by Stepien et al.The high level of magnetic activity was interpreted as the result of ashallow common convective envelope. Orbital period changes were analyzedusing several newly determined CCD times of light minimum together withothers collected from the literature. A cyclic period change (T = 45.3yr) was found to be superimposed on a long-term increase (dP/dt = +7.7× 10-8 days yr-1). The period oscillationand the existence of third light both confirm that UX Eri contains atertiary component. Since no spectroscopic companion was found, it isestimated that the mass of the third body is M3 < 0.56Modot. The tertiary component star is moving in an eccentricorbit (e' = 0.72) with an orbital inclination of i' > 44.5°. Thetertiary component may have played an important role in the formation ofthe progenitor of UX Eri by transferring angular momentum during theKozai oscillation. In that way, the detached progenitor could evolveinto overcontact configuration via magnetic braking. It was found thatthe timescale of the period increase is close to the thermal timescaleof the less massive component, which suggests that UX Eri is in anevolutionary state of thermally conservative mass transfer from the lessmassive component to the more massive one.
| B.R.N.O. Contributions #34
Not Available
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| New Times of Minima of Some Eclipsing Binary Stars
Not Available
| Orbital Period Changes for the Weak-Contact Binary TY Bootis
We present a detailed period analysis of TY Bootis, based on allavailable light minimum times covering about 80 years. We discoveredthat there exists a cyclic variation overlaying a secular perioddecrease from the distorted (O-C) diagram. A long-term decrease with asinusoidal oscillation (i.e., eq. [2]) or with a light-time effect(i.e., eq. [3]) may be reasonable due to the smaller difference betweentheir sum of residuals. The sinusoidal change with a period of 59.7 yrfor equation (2) can be attributed to either a light-time effect orcyclic magnetic activity of both components. For the assumed third body,the period and eccentricity of the light-time orbit areP3=58.6 yr and e'=0.1744, respectively. If theexistence of an additional unseen body is true, this binary may be atertiary system. The long-term orbital period decrease suggests that TYBoo is undergoing a mass transfer from the primary component to thesecondary component at a rate of dm/dt=-3.15×10-8Msolar yr-1 for equation (2) ordm/dt=-2.90×10-8 Msolar yr-1 forequation (3). As its mass transfers, accompanied by angular momentumloss due to mass outflow L2, this binary will evolve into adeep contact configuration.
| CCD Photometric Study of the Contact Binary TX Cnc in the Young Open Cluster NGC 2632
TX Cnc is a member of the young open cluster NGC2632. In the presentpaper, four CCD epochs of light minimum and a complete V light curve ofTX Cnc are presented. A period investigation based on all availablephotoelectric or CCD data showed that it is superimposed on a long-termincrease (dP/dt=+3.97×10-8) and weak evidence suggeststhat it includes a small-amplitude period oscillation(A3=0d.0028; T3=26.6yr). The lightcurves in the V band obtained in 2004 were analyzed with the 2003version of the W-D code. It was shown that TX Cnc is an overcontactbinary system with a degree of contact factor f=24.8%. The absoluteparameters of the system were calculated:M1=1.319±0.007Mȯ,M2=0.600±0.01Mȯ;R1=1.28±0.19Rȯ,R2=0.91±0.13Rȯ. TX Cnc may be on theTRO-controlled stage of the evolutionary scheme proposed by Qian (2001a,b, 2003a), and may contain an invisible tertiary component(m3≈0.097Mȯ). If this is true, thetertiary component has played an important role in the formation andevolution of TX Cnc by removing angular momentum from the central system(Pribulla & Rucinski 2006). In this way the contact binaryconfiguration can be formed in the shortlife time of a young opencluster via AML.
| Formation and Evolution of W Ursae Majoris Contact Binaries
The origin and evolution of W UMa systems are discussed based on All SkyAutomated Survey (ASAS) data and the mean kinematic ages of foursubgroups of 97 field contact binaries (FCBs). The period distributionof eclipsing binaries discovered by ASAS suggests that a period limit totidal locking for the close binaries is about 2.24 days, so that most WUMa systems might be formed from detached binaries with periodsP<~2.24 days, and a maximum advanced time from a detached system to aW UMa is about 3.23 Gyr. Moreover, the secular evolution of the angularmomentum (AM), the system mass, and the orbital period of 97 FCBs wereinvestigated according to the mean kinematic ages, which were setaccording to AM bins. AMs, systemic masses, and orbital periods wereshown to be decreasing with kinematic age. Their first-order decreasingrates have been determined as J˙/J=1.86×10-10yr-1, M˙/M=0.95×10-10 yr-1,and P˙/P=1.24×10-10 yr-1, and theaverage amplification (A¯=dlnJ/dlnM) is derived to be 1.96. Theseare lower than those derived from detached chromospherically activebinaries (CABs). This suggests that the magnetic activity level of FCBsis indeed weaker than that of CABs. Meanwhile, the decreasing rate of AMof FCBs is found to be equal to an average value in a cycle of a cyclicmodel of contact binaries. This might suggest that the evolution of FCBsundergoes thermal relaxation oscillation (TRO) and that the coalescenceof W UMa systems is a very long process, which is also indicated by thedynamical evolution of FCBs.
| Photoelectric Minima of Some Eclipsing Binary Stars
We present 119 minima times of 47 eclipsing binaries.
| A New CCD Photometric Investigation of the Short-Period Close Binary AP Leonis
New CCD photometric light curves in the B, V, and R bands of theshort-period close binary AP Leonis are presented. A photometricanalysis with our symmetric light curves suggests that AP Leo is anovercontact binary with a degree of overcontact of 24.9%. Since the O-Cvalues of photographic and visual times of light minimum showed a largescatter (up to 0.06 days), all of the period changes proposed for theeclipsing binary by previous investigators are not reliable. In thispaper the orbital period changes of AP Leo are analyzed based on allpublished CCD and photoelectric eclipse times. A small-amplitude cyclicoscillation, with a period of 22.4 yr and an amplitude of 0.0049 days,is discovered to be superposed on a secular period decrease at a rate ofdP/dt=-1.08×10-7 days yr-1. The continuousperiod decrease may be caused by angular momentum loss or a combinationof the mass transfer from the primary to the secondary and angularmomentum loss. The cyclic period change may indicate that AP Leo is atriple system containing a cool dwarf third component. If this is true,it is possible that this third component plays an important role in theorigin and evolution of the overcontact system by removing angularmomentum from the central system, and that it makes the eclipsing pairhave a low angular momentum and a short initial orbital period (e.g.,P<5 days). In that case, the initially detached system evolves intoan overcontact configuration via magnetic torques from stellar winds. Onthe other hand, the rapid rotation of the solar-type components(spectral type G0) and the variations of the light curve indicate a highdegree of magnetic activity from the spin-up of the components. Both thelong-term period decrease and the oscillation can plausibly beinterpreted by magnetic activity (i.e., enhanced magnetic stellar windand activity cycles).
| Dynamical evolution of active detached binaries on the logJo-logM diagram and contact binary formation
Orbital angular momentum (OAM, Jo), systemic mass (M) andorbital period (P) distributions of chromospherically active binaries(CAB) and W Ursae Majoris (W UMa) systems were investigated. Thediagrams of and logJo-logM were formed from 119 CAB and 102 WUMa stars. The logJo-logM diagram is found to be mostmeaningful in demonstrating dynamical evolution of binary star orbits. Aslightly curved borderline (contact border) separating the detached andthe contact systems was discovered on the logJo-logM diagram.Since the orbital size (a) and period (P) of binaries are determined bytheir current Jo, M and mass ratio, q, the rates of OAM loss(dlogJo/dt) and mass loss (dlogM/dt) are primary parametersto determine the direction and the speed of the dynamical evolution. Adetached system becomes a contact system if its own dynamical evolutionenables it to pass the contact border on the logJo-logMdiagram. The evolution of q for a mass-losing detached system is unknownunless the mass-loss rate for each component is known. Assuming q isconstant in the first approximation and using the mean decreasing ratesof Jo and M from the kinematical ages of CAB stars, it hasbeen predicted that 11, 23 and 39 per cent of current CAB stars wouldtransform to W UMa systems if their nuclear evolution permits them tolive 2, 4 and 6 Gyr, respectively.
| CCD Times of Minima of Selected Eclipsing Binaries
374 CCD minima observations of 187 eclipsing binaries are presented. Theobserved stars were chosen mainly from catalogue BRKA of observingprogramme of Variable Star Section of CAS.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Contact Binaries with Additional Components. I. The Extant Data
We have attempted to establish observational evidence for the presenceof distant companions that may have acquired and/or absorbed angularmomentum during the evolution of multiple systems, thus facilitating orenabling the formation of contact binaries. In this preliminaryinvestigation we use several techniques (some of themdistance-independent) and mostly disregard the detection biases ofindividual techniques in an attempt to establish a lower limit to thefrequency of triple systems. While the whole sample of 151 contactbinary stars brighter than Vmax=10 mag gives a firm lowerlimit of 42%+/-5%, the corresponding number for the much better observednorthern-sky subsample is 59%+/-8%. These estimates indicate that mostcontact binary stars exist in multiple systems.
| 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.
| Precise CCD Times of Minima of Selected Eclipsing Binaries
We present 135 precise CCD minima timings for 93 eclipsing binariesobtained at Ondrejov observatory during 2003-2004.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Photoelectric Minima of Some Eclipsing Binary Stars
We present 70 minima times of 35 eclipsing binaries.
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