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WZ Cephei: A Close Binary at the Beginning of Contact Phase
Photometric photoelectric data of the short-period close binary system,WZ Cephei, are presented. A new photometric analysis with the 2003version of the Wilson-Devinney method confirmed that it is a shallowcontact binary (f ~ 13.3%) with a high level of spot activity on theprimary component. Combining new determined times of light minimum withthe others published in the literature, the period change of the binarystar is investigated. A periodic variation, with a period of 34.2 yearsand an amplitude of 0fd013, was discovered to be superimposed on along-term period decrease (dP/dt = –8.8 ×10–8 days year–1). Both the secularperiod decrease and the shallow contact configuration suggest that thisbinary system is at the beginning of contact phase. It is on the way toevolving into a normal overcontact phase via secular angular momentumloss and/or mass transfer from the more massive component to the lessmassive one. The period oscillation can be explained either by thelight-time effect due to the presence of a third body or by magneticactivity. On the one hand, if it is caused by the light-time effect, themass and the orbital radius of the additional body should be m3 = 0.17 M sun and a 3 = 26.6 AU,respectively, when this body is coplanar to the orbit of the eclipsingpair. On the other hand, since the system shows high levels of spotactivity, the period oscillation may be explained as a consequence ofmagnetic cycles. In this case, the required variation of the quadrupolemoment is calculated to be 9.2 × 1049 g cm2.
| Radial Velocity Studies of Close Binary Stars. XIV
Radial velocity (RV) measurements and sine curve fits to the orbital RVvariations are presented for 10 close binary systems: TZ Boo, VW Boo, ELBoo, VZ CVn, GK Cep, RW Com, V2610 Oph, V1387 Ori, AU Ser, and FT UMa.Our spectroscopy revealed two quadruple systems, TZ Boo and V2610 Oph,while three stars showing small photometric amplitudes, EL Boo, V1387Ori, and FT UMa, were found to be triple systems. GK Cep is a closebinary with a faint third component. While most of the studied eclipsingsystems are contact binaries, VZ CVn and GK Cep are detached orsemidetached double-lined binaries, and EL Boo, V1387 Ori, and FT UMaare close binaries of uncertain binary type. The large fraction oftriple and quadruple systems found in this sample supports thehypothesis of formation of close binaries in multiple stellar systems;it also demonstrates that low photometric amplitude binaries are afertile ground for further discoveries of multiple systems.Based on the data obtained at the David Dunlap Observatory, Universityof Toronto, Canada.
| B.R.N.O. Times of minima
Not Available
| 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.
| 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.
| Deep, Low Mass Ratio Overcontact Binary Systems. VII. QX Andromedae in the Intermediate-Age Open Cluster NGC 752
QX Andromedae is a short-period eclipsing binary in the intermediate-ageopen cluster NGC 752. Charge-coupled device photometric observations ofthe close binary system obtained from 2004 November 13 to 2006 November18 are presented. It is confirmed that the light curves show partialeclipses, and night-to-night intrinsic variations are seen. As in thecase of AH Cancri in the old open cluster M67, the light curve of QX Andseems to change between A and W types. Both the short- and long-termlight variations suggest that QX And shows strong magnetic activity,which is in agreement with its X-ray observations. The symmetric lightcurves in B and V bands obtained the night of 2004 November 13 wereanalyzed with the new version of the W-D code. It is found that QX Andis a deep overcontact binary system with a high degree of overcontact off = 55.9% and a low mass ratio of q = 0.2327, suggesting that it is inthe late stage of overcontact evolution. Based on our 23 times of lightminimum, including four recently published eclipse times, the orbitalperiod of the eclipsing binary was revised. It was discovered that theorbital period shows a continuous period increase at a rate of dP/dt =+2.48 × 10-7 days yr-1, which can beinterpreted as a mass transfer from the less massive component to themore massive one. As the period increases, the mass ratio of the systemwill decrease. It may finally evolve into a rapid-rotating single starwhen it meets the more familiar criterion that the orbital angularmomentum is less than 3 times the total spin angular momentum. Theexistence of QX And in the late evolutionary stage of an overcontactbinary in the intermediate-age open cluster NGC 752 indicates that itmay undergo strong cluster stellar interaction. This means it had a veryshort initial orbital period and could have evolved into the presentevolutionary state within the cluster age. By comparing with theevolutionary state of TX Cnc in M44, it is estimated that the lifetimeof overcontact binaries may be no less than 1 Gyr.
| New Times of Minima of Some Eclipsing Binary Stars
Not Available
| 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.
| 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.
| 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.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Variation in the orbital period of W UMa-type contact systems
The secular variation in the orbital period Porb is studiedas a function of the mass ratio q of the components in a sample of 73contact systems of class W UMa constructed from a survey of current(1991–2003) published photometric and spectroscopic data. Almostall the W UMa-systems (>93% of this sample) are found to have avariation in their orbital periods Porb which alternates insign independently of their division into A-and Wsubclasses. Astatistical study of this sample in terms of the observedcharacteristics dPorb/dt and q showed that on the average thenumbers of increases (35 systems) and decreases (33 systems) in theperiods are the same, which indicates the existence of flows directedalternately from one component to the other and illustrates the cyclicalcharacter of the thermal oscillations. An analysis of the behavior ofdPorb/dt as a function of the mass interval of the primarycomponent yields a more accurate value for the mass ratio, q ≈ 0.4÷ 0.45 at which contact binaries are separated into A-andW-subclasses. No correlations were observed between the fill-out factorfor the outer contact configuration, the total mass of the contactsystem, and the mass ratio of the components, on one hand, and the signof the secular variation in the period. The physical properties andevolutionary features of these systems are discussed.
| HL Aurigae: A pre-contact binary system with a solar-mass companion
Orbital period changes of the near-contact binary (NCB) system, HLAurigae, are analyzed based upon all the published CCD and photoelectrictimes of light minimum. It is found that the period of HL Aurigae showsa small-amplitude cyclic oscillation with a period of 6.5 years and anamplitude of 0.d0058 while it undergoes a secular decrease ata rate of dP/dt = ‑1.08 × 10‑7 days/year.The cyclic period oscillation can be interpreted either by thelight-time effect of a third body or by magnetic activity cycles of thecomponents. Since the third-body assumption is in agreement with thepresence of a large amount of third light in the system discovered by ,we think that HL Aurigae may be a true triple system. In order to deducea G2-type third companion as proposed by , the orbital inclination ofthe third body should be i′ = 40°, which is much smaller thanthat of the eclipsing pair (i = 85.°7). This suggests that the thirdcompanion is not coplanar with the eclipsing binary. This may indicatethat the solar-mass component may be captured by the eclipsing binarysystem in some previous stages of its formation and evolution. HLAurigae is a short-period NCB with a F1V-type primary and a G9V-typesecondary component and both of the components are filling or nearlyfilling their Roche lobes. As the period is decreasing, the shrinking ofthe Roche lobe will finally cause it to evolve into a contact binarysystem in the timescale of 2.1 × 106 years. Theperiod decrease may be caused by mass transfer or/and by angularmomentum loss via magnetic braking.
| 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.
| A ROSAT Survey of Contact Binary Stars
Contact binary stars are common variable stars that are all believed toemit relatively large fluxes of X-rays. In this work we combine a largenew sample of contact binary stars derived from the ROTSE-I telescopewith X-ray data from the ROSAT All Sky Survey (RASS) to estimate theX-ray volume emissivity of contact binary stars in the Galaxy. Weobtained X-ray fluxes for 140 contact binaries from the RASS, as well astwo additional stars observed by the XMM-Newton observatory. From thesedata we confirm the emission of X-rays from all contact binary systems,with typical luminosities of approximately 1.0×1030ergs s-1. Combining calculated luminosities with an estimatedcontact binary space density, we find that contact binaries do not havestrong enough X-ray emission to account for a significant portion of theGalactic X-ray background.
| A Catalog of 1022 Bright Contact Binary Stars
In this work we describe a large new sample of contact binary starsextracted in a uniform manner from sky patrol data taken by the ROTSE-Itelescope. Extensive ROTSE-I light-curve data are combined with J-, H-,and K-band near-infrared data taken from the Two Micron All Sky Surveyto add color information. Contact binary candidates are selected usingthe observed period-color relation. Candidates are confirmed by visualexamination of the light curves. To enhance the utility of this catalog,we derive a new J-H period-color-luminosity relation and use this toestimate distances for the entire catalog. From these distance estimateswe derive an estimated contact binary space density of(1.7+/-0.6)×10-5 pc-3.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| 164. List of Timings of Minima Eclipsing Binaries by BBSAG Observers
Not Available
| Deep, Low Mass Ratio Overcontact Binary Systems. V. The Lowest Mass Ratio Binary V857 Herculis
Charge-coupled device (CCD) photometric light curves in the B, V, and Rbands of the complete eclipsing binary star V857 Her are presented. Itis shown that the light curves of the W UMa-type binary are symmetricand of A type according to Binnendijk's classification. Our four epochsof light minimum along with others compiled from the literature wereused to revise the period and study the period change. Weak evidenceindicates that the orbital period of V857 Her may show a continuousincrease at a rate of dP/dt=+2.90×10-7 daysyr-1. The photometric parameters of the system weredetermined with the 2003 version of the Wilson-Devinney code. It isshown that V857 Her is a deep overcontact binary system withf=83.8%+/-5.1%. The derived mass ratio of q=0.06532+/-0.0002 suggeststhat it has the lowest mass ratio among overcontact binary systems. Asthe orbital period increases, the decrease of the mass ratio will causeit to evolve into a single rapidly rotating star when it meets the morefamiliar criterion that the orbital angular momentum be less than 3times the total spin angular momentum. To understand the evolutionarystate of the system, long-term photometric monitoring and spectroscopicobservations will be required.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Kinematics of W Ursae Majoris type binaries and evidence of the two types of formation
We study the kinematics of 129 W UMa binaries and we discuss itsimplications on the contact binary evolution. The sample is found to beheterogeneous in the velocity space. That is, kinematically younger andolder contact binaries exist in the sample. A kinematically young (0.5Gyr) subsample (moving group) is formed by selecting the systems thatsatisfy the kinematical criteria of moving groups. After removing thepossible moving group members and the systems that are known to bemembers of open clusters, the rest of the sample is called the fieldcontact binary (FCB) group. The FCB group is further divided into fourgroups according to the orbital period ranges. Then, a correlation isfound in the sense that shorter-period less-massive systems have largervelocity dispersions than the longer-period more-massive systems.Dispersions in the velocity space indicate a 5.47-Gyr kinematical agefor the FCB group. Compared with the field chromospherically activebinaries (CABs), presumably detached binary progenitors of the contactsystems, the FCB group appears to be 1.61 Gyr older. Assuming anequilibrium in the formation and destruction of CAB and W UMa systems inthe Galaxy, this age difference is treated as an empirically deducedlifetime of the contact stage. Because the kinematical ages (3.21, 3.51,7.14 and 8.89 Gyr) of the four subgroups of the FCB group are muchlonger than the 1.61-Gyr lifetime of the contact stage, the pre-contactstages of the FCB group must dominantly be producing the largedispersions. The kinematically young (0.5 Gyr) moving group covers thesame total mass, period and spectral ranges as the FCB group. However,the very young age of this group does not leave enough room forpre-contact stages, and thus it is most likely that these systems wereformed in the beginning of the main sequence or during thepre-main-sequence contraction phase, either by a fission process or mostprobably by fast spiralling in of two components in a common envelope.
| 163. List of Minima Timings of Eclipsing Binaries by BBSAG Observers
Not Available
| On the Period Variation of the Neglected W UMa-type Binary System V714 Monocerotis
Some new CCD times of the light minimum for a neglected W UMa-typebinary star, V714 Monocerotis, observed in 2002 and 2003, are presented.By considering the general trend of the O ‑ C variation, aplausible O ‑ C curve was formed and a mean linear ephemeris wasobtained. It was found that the period of the binary star shows acontinuous decrease with rate of dP/dt = ‑1.48 ×10-7 d yr-1. In order to understand theevolutionary state of the binary system, new photometric andspectroscopic observations and a careful investigation on those data arerequired.
| Up-to-Date Linear Elements of Eclipsing Binaries
About 1800 O-C diagrams of eclipsing binaries were analyzed and up-todate linear elements were computed. The regularly updated ephemerides(as a continuation of SAC) are available only in electronic form at theInternet address: http://www.as.ap.krakow.pl/ephem/.
| CCD Minima for Selected Eclipsing Binaries in 2003
Not Available
| Photoelectric Minima of Selected Eclipsing Binaries
Not Available
| 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.
| Are overcontact binaries undergoing thermal relaxation oscillation with variable angular momentum loss?
Orbital period variations of five W-type overcontact binaries, GW Cep,VY Cet, V700 Cyg, EM Lac and AW Vir, are presented based on the analysisof all available times of light minimum. It is discovered that theperiod of GW Cep is decreasing at a rate of dP/dt=-6.62×10-8 d yr-1. For VY Cet and V700 Cyg, acyclic oscillation is found superimposed on a secular period increase,which can be explained either by the light-time effect of an assumedthird body or by magnetic activity cycles. For the other two, EM Lac andAW Vir, the periods show a secular increase. GW Cep is a low mass ratiosystem with q= 0.37, while the others are high mass ratio systems (q=0.67, 0.65, 0.63 and 0.76, respectively). The period changes of the fivesample stars are in good agreement with Qian's conclusion that low massratio overcontact binaries usually show a decreasing period, while theperiods of high mass ratio systems are increasing.Based on the period variations of 59 overcontact binaries, a statisticalinvestigation of period change is given. It is confirmed that the periodchange of a W UMa-type binary star is correlated with the mass ratio (q)and with the mass of the primary component (M1). Meanwhile,some statistical relations (M1-P,Js-M1, Js-M2 andJs-P) for overcontact binaries are presented using theabsolute parameters of 78 systems. From these relations, the followingresults may be drawn: (i) free mass transfer in both directions existsbetween the components, which is assumed by thermal relaxationoscillation (TRO) theory; (ii) angular momentum loss (AML) can make a WUMa-type star maintain shallow overcontact and not evolve fromovercontact to semidetached configurations as proposed by Rahunen; (iii)the evolution of the W UMa-type systems may be oscillation around acritical mass ratio, while the critical mass ratio varies with the massof the primary component. These results can be plausibly explained bythe combination of the TRO and the variable AML via a change of depth ofthe overcontact, which is consistent with the X-ray and IUEobservations.
| Photoelectric Minima of Some Eclipsing Binary Stars
We present 48 minima times of 10 eclipsing binaries.
| Catalogue of the field contact binary stars
A catalogue of 361 galactic contact binaries is presented. Listedcontact binaries are divided into five groups according to the type andquality of the available observations and parameters. For all systemsthe ephemeris for the primary minimum, minimum and maximum visualbrightness and equatorial coordinates are given. If available,photometric elements, (m1+m2)sin3i,spectral type, parallax and magnitude of the O'Connell effect are alsogiven. Photometric data for several systems are augmented by newobservations. The quality of the available data is assessed and systemsrequiring modern light-curve solutions are selected. Selectedstatistical properties of the collected data are discussed.
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