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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.
| V781 Tauri: a W Ursae Majoris binary with decreasing period
We analyze light curves of the W UMa type eclipsing binary V781 Taurifrom three epochs and radial velocity curves from two epochssimultaneously, including previously unpublished B and V data. Theoverall time span is from 1983 to 2000 and the solution is donecoherently in time (not phase) with five light curves and two sets ofprimary and secondary velocity curves. Minor systematic differencesamong the individual light curves are not large enough to undermine thevalue of a coherent solution that represents 18 years of observations.Times of minima confirm a period of 0.34491d and the general solutionfinds a small period change, dP/P, of(5.08±{04})×10-11 that represents recentbehavior. The eclipse timings cover the last half-century and find dP/Pabout four times smaller, corresponding to a period change time scale,P/(dP/dt) of about 6 million years. The system is over-contact with afilling factor of 0.205. The solution produces a temperature differenceof about 260 K between the components, an inclination of 65.9dg, and amass ratio M_2/M_1=2.47. Separate solutions of the several light curvesthat incorporate dark spots find parameters that differ little fromcurve to curve. Absolute masses, luminosities, radii and the distanceare derived, with luminosities and distance based on star 1 being oftype G0V. The orbital angular momentum is compared with those of other WUMa type binaries and is normal. The star to star mass flow that one caninfer from dP/dt is opposite to that expected from TRO (ThermalRelaxation Oscillator) theory, but pertains to a time span that is veryshort compared to the time scale of TRO oscillations.
| W Ursae Majoris Contact Binary Variables as X-Ray Sources
We present cross-identification of archived ROSAT X-ray point sourceswith W UMa variable stars found in the All-Sky Automated Survey. A totalof 34 W UMa stars have been found associated with X-ray emission. Wecompute the distances of these W UMa systems and hence their X-rayluminosities. Our data support the ``supersaturation'' phenomenon seenin these fast rotators, namely that the faster a W UMa star rotates, theweaker its X-ray luminosity.
| 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.
| 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.
| On the properties of contact binary stars
We have compiled a catalogue of light curve solutions of contact binarystars. It contains the results of 159 light curve solutions. Theproperties of contact binary stars were studied using the cataloguedata. As is well known since Lucy's (\cite{Lucy68a},b) and Mochnacki's(\cite{Mochnacki81}) studies, primary components transfer their ownenergy to the secondary star via the common envelope around the twostars. This transfer was parameterized by a transfer parameter (ratio ofthe observed and intrinsic luminosities of the primary star). We provethat this transfer parameter is a simple function of the mass andluminosity ratios. We introduced a new type of contact binary stars: Hsubtype systems which have a large mass ratio (q>0.72). These systemsshow behaviour in the luminosity ratio- transfer parameter diagram thatis very different from that of other systems and according to ourresults the energy transfer rate is less efficient in them than in othertypes of contact binary stars. We also show that different types ofcontact binaries have well defined locations on the mass ratio -luminosity ratio diagram. Several contact binary systems do not followLucy's relation (L2/L1 =(M2/M1)0.92). No strict mass ratio -luminosity ratio relation of contact binary stars exists.Tables 2 and 3 are available in electronic form athttp://www.edpsciences.org
| 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.
| Orbital period changes of contact binary systems: direct evidence for thermal relaxation oscillation theory
Orbital period changes of ten contact binary systems (S Ant, ɛCrA, EF Dra, UZ Leo, XZ Leo, TY Men, V566 Oph, TY Pup, RZ Tau and AGVir) are studied based on the analysis of their O-C curves. It isdiscovered that the periods of the six systems, S Ant, ɛ CrA, EFDra, XZ Leo, TY Men and TY Pup, show secular increases. For UZ Leo, itssecular period increase rate is revised. For the three systems, V566Oph, RZ Tau and AG Vir, weak evidence is presented that a periodicoscillation (with periods of 20.4, 28.5 and 40.9yr respectively) issuperimposed on a secular period increase. The cyclic period changes canbe explained by the presence of an unseen third body in the threesystems. All the sample stars studied are contact binaries withM1>=1.35Msolar. Furthermore, orbital periodchanges of 27 hot contact binaries have been checked. It is found that,apart from AW UMa with the lowest mass ratio (q=0.072), none shows anorbital period decrease. The relatively weak magnetic activity in thehotter contact binaries means little angular momentum loss (AML) fromthe systems via magnetic stellar winds. The period increases of these WUMa binaries can be explained by mass transfer from the secondary to theprimary components, which is in agreement with the prediction of thethermal relaxation oscillation (TRO) models. This suggests that theevolution of a hotter W UMa star is mainly controlled by TRO. On theother hand, for a cooler W UMa star(M1<=1.35Msolar), its evolution may be TRO plusAML, which coincides with the recent results of Qian.
| A CCD Photometric Study of the Contact Binary V396 Monocerotis
Complete BV light curves of the W Ursae Majoris binary V396 Mon arepresented. The present CCD photometric observations reveal that thelight curves of the system are obviously asymmetric, with the primarymaximum brighter than the secondary maximum (the ``O'Connell effect'').The light curves are analyzed by means of the latest version of theWilson-Devinney code. The results show that V396 Mon is a W-subtype WUMa contact binary with a mass ratio of 0.402. The asymmetry of thelight curves is explained by a cool spot on the secondary component. Thenature of the overluminosity of the secondary of a W UMa-type system isanalyzed. It is shown that the overluminosity of the secondary isclearly related to the mass of the primary and that, for a W UMa system,the higher the mass of the primary, the greater the overluminosity ofthe secondary. In addition, the overluminosity of the secondary is alsorelated to its own density: the lower the density of the secondary, thegreater its overluminosity.
| Multicolour photometry of the eclipsing binaries AQ Tuc and AY Vel
First multicolour photoelectric light curves of the eclipsing binariesAQ Tuc and AY Vel obtained in 1965 and 1969 at the Leiden SouthernStation using Walraven VBLU filters are presented.
| Analysis of multicolour light curves of the eclipsing binaries AQ Tuc and AY Vel
First multicolour photoelectric light curves of the eclipsing binariesAQ Tuc and AY Vel obtained in 1965 and 1969 at the Leiden SouthernStation using Walraven VBLU filters were analyzed by theWilson-Devinney's code. Our analysis confirmed the contact configurationfor AQ Tuc and revealed that AY Vel is an almost contact system with qapprox. 3. The absolute radii of the components of AQ Tuc derived fromthe combination of our photometric and available spectroscopic elementsare R1 = 2.03 +/- 0.11 RSun and R2 =1.30 +/- 0.07 RSun.
| ROSAT all-sky survey of W Ursae Majoris stars and the problem of supersaturation
From ROSAT all-sky survey (RASS) data we obtained X-ray fluxes for 57 WUMa type contact systems. In our sample we detected three stars whichare the shortest period main sequence binaries ever found as X-raysources. For stars with (B-V)_0 < 0.6 the normalized X-ray fluxdecreases with a decreasing color index but for (B-V)_0 > 0.6 aplateau is reached, similar to the saturation level observed for single,rapidly rotating stars. The X-ray flux of W UMa stars is about 4-5 timesweaker than that of the fastest rotating single stars. Because earlytype, low activity variables have longer periods, an apparentperiod-activity relation is seen among our stars, while cool stars with(B-V)_0 > 0.6 and rotation periods between 0.23 and 0.45 days do notshow any such relation. The lower X-ray emission of the single, ultrafast rotators (UFRs) and W UMa stars is interpreted as the result of adecreased coronal filling factor. The physical mechanisms responsiblefor the decreased surface coverage differs for UFRs and W UMa systems.For UFRs we propose strong polar updrafts within a convection zone,driven by nonuniform heating from below. The updrafts should beaccompanied by large scale poleward flows near the bottom of theconvective layer and equatorward flows in the surface layers. The flowsdrag dynamo generated fields toward the poles and create a field-freeequatorial region with a width depending on the stellar rotation rate.For W UMa stars we propose that a large scale horizontal flow embracingboth stars will prevent the magnetic field from producing long-livedstructures filled with hot X-ray emitting plasma. The decreased activityof the fastest rotating UFRs increases the angular momentum loss timescale of stars in a supersaturated state. Thus the existence of a periodcutoff and a limiting mass of W UMa stars can be naturally explained.
| The W Ursae Majoris system AK Herculis
A detailed study of the period and the light-curve of the eclipsingbinary AK Her is presented. Based on the study of the (O-C) curve, weind that the period variation of the system contains a component of along-term decrease, and three other components of periodical variation.Our result is very different from that of other investigators. Wecompare light curves obtained by other groups and find that the lightcurve of the system has changed considerably. Based on the analysis, weinvestigate the physical mechanisms which may underlie the variations ofthe period and the light curve and obtain some new conclusions.According to the characteristics of rapid light variation of the system,we conclude that the rapid change is probably caused by pulsation of thecommon envelope, and that the physical mechanism causing the pulsationmay be mass transfer between the two components. In addition, we findthat the amplitude of the light curve variation is almost proportionalto the rate of the period variation. Finally, the trends in theevolution of the system are discussed. Table 3 is only available inelectronic form at http://www.edpsciences.org
| 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.
| The properties of W Ursae Majoris contact binaries: new results and old problems.
The physical properties of W UMa binary systems are revisited on thebasis of the observational data published in the last decade and of therecent theoretical studies on angular-momentum-loss-driven secularevolution. The absolute elements (masses, radii, luminosities) arederived by an inference method and a calibration based on the availablehigh quality spectroscopic orbits. The derived age (8Gy) agrees with theestimate of Guinan and Bradstreet from space motions. The analysis ofthe resulting physical parameters shows little correlation between thestandard classification in A and W subtype (first proposed by Binnendijk(1970) and only related to the light curve morphology) and theevolutionary status and origin of the systems. Most A-subtype systemsseem to have no evolutionary link with W-subtype ones. The relationbetween total mass and mass ratio for the "bona fide" sample alsosuggests that mass loss from the system may play an important role.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Are Contact Binaries Undergoing Thermal Relaxation Oscillations with Contact Discontinuity?
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110..782W&db_key=AST
| The thermal relaxation oscillation states of contact binaries
A contact system almost certainly cannot exist in a state of staticequilibrium undergoing periodic thermal relaxation oscillation (TRO). Inthis paper the TRO evidence is found by the calculation of 22 contactsystems: A-sub and W-sub types are in expanding and contracting TROstates at the velocities of 25.04 and 3.10 m/yr, respectively. It ispointed out that the W-phenomenon is phase-dependent and correspondingto the contracting TRO phase. The corrected period-color diagram impliesthat the two kind systems have the same physical structure.
| The interaction between the secondary and the common convective envelope in a contact binary
It has been suggested that a contact system almost certainly cannotexist in static equilibrium undergoing periodic thermal relaxationoscillation. The energy transfer in a common convective envelope (CCE)makes the secondary have a complex structure, so the interaction betweenthe secondary and CCE may play an important role in the structure andevolution of the contact system. The present paper tests the ThermalRelaxation Oscillation (TRO) theory and investigates this interactionwith polytropic stellar model from the observational datum of 22 contactsystems directly. It shows that the A-type systems are expanding with avelocity of 25.04 m/yr, and the W-type systems are contracting atvelocity of 3.10 m/yr by the calculations about these contact systems.Also, we calculate the ratio of energy transfer and the interactioncoefficient for them. The HS (hot secondary) model is supported by ourcalculations. These results may help to understand the TRO theory andthe W-phenomenon.
| The intractable W UMa system AE Phe - Light curve synthesis and mass-ratio problem
Four B,V light curves of AE Phe observed between 1970-1978 were analyzedwith the Wilson-Devinney code. Consistent system parameters wereobtained; only the temperature difference undergoes small variations. Anobvious discrepancy between the photometrically and spectroscopicallydetermined mass-ratio, which also occurs in other totally eclipsing WUMa systems of all spectral types in a systematic way, may be due to theinfluence of a global circulation pattern on the measured radialvelocities.
| Spectroscopic binaries - 15th complementary catalog
Published observational data on the orbital characteristics of 436spectroscopic binaries, covering the period 1982-1986, are compiled intables. The data sources and the organization of the catalog are brieflydiscussed, and notes are provided for each item.
| A note on thermally decoupled W Ursae Majoris systems
The thermal decoupling degree of short-period contact or near-contactsystems is studied. Statistics of well-observed W UMa systems includingnew beta-light-curve objects was made for thermal-decoupling degree,spectral type, and orbital period. W UMa systems of type A and W arefound to be well characterized by these parameters. W-type objects showa good (linear) correlation in the spectral type vs. thermal-decouplingparameter diagram. This extends to the lower border of the diagram forA-type systems, otherwise scattered in an area of large thermaldecoupling. These empirical facts are analyzed in terms of contact ornoncontact configurations.
| The evolutionary state of contact and near-contact binary stars
A compilation is presented of the masses, radii, and luminosities of thecomponents of 31 F-K type binary systems which have been found to be incontact or near-contact states. Comparisons of these data with thoseexpected for single stars demonstrates that: (1) the primary componentsof the shallow-contact W-type WUMa systems are unevolved main-sequencestars, while those of the deeper-contact A-type systems are near to theterminal-age main sequence; (2) the secondary components of the W-typesystems have radii of the order of 1.5 times larger than expected fortheir ZAMS masses, while those of the A-type systems have radii of theorder of three times larger; (3) the nine systems in the sample which donot display EW-type light curves can be divided into three marginalcontact systems, five semidetached systems, and one detached system. Theimplications of these findings for the types of evolution into contactare addressed.
| Contact and near-contact binary systems. IV - RT Scl and AQ TUC
Reticon spectroscopic observations are presented for the short-periodeclipsing binary systems RT Scl and AQ Tuc. Analysis of these datatogether with new analyses of previously published light curves showthat RT Scl is composed of a main-sequence primary component, virtuallyin contact with its Roche lobe, and a detached secondary component whichis ≡40 per cent larger than expected for its mass. The observeddecrease in orbital period and the asymmetry in the light curve may beunderstood in terms of mass transfer from the primary component at arate of 10-8M_sun;yr-1 via a stream from the innerLagrangian point which hits directly the surface of the oversizedsecondary. The system AQ Tuc, which has the same total mass and specificorbital angular momentum as RT Scl, is confirmed to be an A-type W UMacontact system. There is some disagreement between the spectroscopic andphotometric determinations of the mass ratio. The best solutions of thelight curves are obtained with a convective value (β = 0.03) forthe gravity-darkening exponent. These findings support the conclusionsreached by Eaton that convective (or turbulent) atmospheres extend toearlier spectral types amongst contact systems than amongst singlestars.
| General properties of W Ursae Majoris systems
The light curves of a sample of 42 W Ursae Majoris binary systems (21W-type, 21 A-type) have been synthesized using the computer code ofWilson and Devinney (1971). The masses, radii and luminosities of thestars have been derived assuming the global properties of a contactbinary system are the same as those of an analogous detached system. Atable listing the main photometric data is given. Substantial continuitywas observed in the physical properties of the A-type and the W-typesystems, suggesting a scenario in which almost all of the A-type systemsare the evolved counterparts of the W-types. The existence of aninhomogeneous group, probably evolved into contact from a detachedconfiguration, is confirmed. An upper limit for the primary mass of theunevolved objects is derived.
| Statistics of categorized eclipsing binary systems Lightcurve shapes, periods, and spectral types
The statistics of the light curve morphologies, eclipse depths, orbitalperiods, and spectral types of about 1000 eclipsing binary systems areexamined, after attempting to subdivide these binaries into variousbasic evolutionary categories. The applicability of statisticalcriteria, based on light curve morphologies and eclipse depths, for thecategorization of eclipsing binaries has been found more limited thanpreviously believed. In particular, EW-type light curves turn out to begood indicators of contact systems (though not conversely), while EA-and EB-type light curves have little physical significance. Moreover,the study reveals a strong deficit of short-period noncontact systems inthe whole spectral range, together with an underabundance of early-typecontact binaries (compared with the number of late-type contact pairs).Interestingly, the distribution of evolved Algol-type systems isshifted, on average, to periods longer than those of unevolved detachedsystems in the OB and early A spectral range (and to shorter periods inthe F spectral range).
| Violet and ultraviolet continua of W UMa systems on the basis of UVBY photometry observations
New observations of 17 southern WUMa systems are discussed together withprevious uvby data for 44 systems to determine properties of violet andultraviolet spectral distributions and to relate them to theperiod-color relation. The interstellar-reddening-corrected delta(m1)values extend from -0.02 to +0.10, which could be interpreted by aplausible range of metallicities; the most positive values of delta(m1)and largest ultraviolet excesses are observed for systems having theshortest periods at a given spectral type. The reddening-correcteddelta(c1) values are close to zero and are only slightly positive forearlier spectral types - mean delta (cl) = +0.04 for (b-y)O less than0.31 - indicating only very slight evolutionary advancement. Traces of adelta(cl) = -delta(ml) correlation for least evolved systems - smallestdelta(cl) - leave the possibility of intrinsic excesses still open.
| Estimated absolute dimensions and the inferred lifetime and angular momentum of W Ursae Majoris contact binaries
The masses, radii, spectral types, and total specific angular momenta ofthe primary components of 47 W UMa contact binaries are estimated fromthe observed system spectral types and from an empirical spectraltype-mass relation. The binaries examined include 25 W-type and 22A-type systems. The absolute lifetimes of the primaries and theirfractional lifetimes with respect to the time required for crossing themain-sequence band are determined by finding the positions of theprimaries in theoretical evolutionary sequences for single stars. Afurther subdivision of the classical A- and W-type groups is discoveredin which each subclass corresponds to a characteristic origin andevolutionary state.
| Determination of parameters of W UMa systems. I - AE Phe, AQ Tuc, 44 i Boo
Multicolor lightcurves of three W UMa systems are solved using theWilson-Devinney computer code, modified in order to run on a medium-sizeminicomputer. The solution confirms the contact hypothesis for thesesystems, one of which (AQ Tuc) has turned out to be of Binnendijk'sA-type (deeper minimum resulting from the eclipse of the more massivestar) and the other two (AE Phe and 44 i Boo) of W type. A comparison ismade with previous solutions. The main features of such systems areconsidered to be (1) a small degree of contact and (2) the fact that theless massive star is hotter than the companion.
| The eclipsing variable AQ Tucanae.
Abstract image available at:http://adsabs.harvard.edu/abs/1978A&AS...34..207W
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