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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.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| 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.
| CCD Minima for Selected Eclipsing Binaries in 2007
Not Available
| Photoelectric Minima of Some Eclipsing Binary Stars
We present 119 minima times of 47 eclipsing binaries.
| Contact Binaries with Additional Components. II. A Spectroscopic Search for Faint Tertiaries
It is unclear how very close binary stars form, given that during thepre-main-sequence phase the component stars would have been inside eachother. One hypothesis is that they formed farther apart but were broughtin closer after formation by gravitational interaction with a thirdmember of the system. If so, all close binaries should be members oftriple (or higher order) systems. As a test of this prediction, wepresent a search for the signature of third components in archivalspectra of close binaries. In our sample of 75 objects, 23 show evidencefor the presence of a third component, down to a detection limit oftertiary flux contributions of about 0.8% at 5200 Å (consideringonly contact and semidetached binaries, we find 20 out of 66). In ahomogeneous subset of 59 contact binaries, we are fairly confident thatthe 15 tertiaries we have detected are all tertiaries present with massratios 0.28<~M3/M12<~0.75 and implied outerperiods P<~106 days. We find that if the frequency oftertiaries were the same as that of binary companions to solar-typestars, one would expect to detect about 12 tertiaries. In contrast, ifall contact binaries were in triple systems, one would expect about 20.Thus, our results are not conclusive but are sufficiently suggestive towarrant further studies.
| The dynamical stability of W Ursae Majoris-type systems
Theoretical study indicates that a contact binary system would mergeinto a rapidly rotating single star due to tidal instability when thespin angular momentum of the system is more than a third of its orbitalangular momentum. Assuming that W Ursae Majoris (W UMa) contact binarysystems rigorously comply with the Roche geometry and the dynamicalstability limit is at a contact degree of about 70 per cent, we obtainthat W UMa systems might suffer Darwin's instability when their massratios are in a region of about 0.076-0.078 and merge into thefast-rotating stars. This suggests that the W UMa systems with massratio q <= 0.076 cannot be observed. Meanwhile, we find that theobserved W UMa systems with a mass ratio of about 0.077, correspondingto a contact degree of about 86 per cent would suffer tidal instabilityand merge into the single fast-rotating stars. This suggests that thedynamical stability limit for the observed W UMa systems is higher thanthe theoretical value, implying that the observed systems have probablysuffered the loss of angular momentum due to gravitational waveradiation (GR) or magnetic stellar wind (MSW).
| Deep, Low Mass Ratio Overcontact Binary Systems. VI. AH Cancri in the Old Open Cluster M67
CCD photometric light curves in the B and V bands obtained in 2001 andin the V band obtained in 2002 of AH Cnc in the old open cluster M67 arepresented. It is shown that AH Cnc is a total-eclipsing binary and itslight curves correspond to a typical A type according to Binnendijk'sclassification. The variations of the light curve around the primaryminimum and second maximum were found. Our nine epochs of light minimummonitored from 2001 to 2005, including others collected from theliterature, were used to create the first study of the period changes ofthe binary system. A cyclic oscillation with a period of 36.5 yr and anamplitude of 0.0237 days was discovered to be superposed on a continuousperiod increase (dP/dt=3.99×10-7 days yr-1).Weak evidence indicates that there exists another small-amplitude periodoscillation (A4=0.0035 days, P4=7.75 yr). Thesymmetric light curves in the B and V bands obtained in 2001 wereanalyzed with the 2003 version of the Wilson-Devinney code. It isconfirmed that AH Cnc is a deep overcontact binary system with a highdegree of overcontact f=58.5%+/-4.5% and a low mass ratio ofq=0.1682+/-0.0012. The existence of the third light and the cyclicperiod oscillation both may suggest that AH Cnc is a triple systemcontaining an unseen third body. The tertiary component may have playedan important role in the origin of the overcontact binary star byremoving angular momentum from the central system, which would cause itto have a short initial orbital period and thus evolve into anovercontact configuration by angular momentum loss. The long-term periodincrease can be interpreted as a mass transfer from the less massivecomponent to the more massive one. As the orbital period increases, thedecrease of the mass ratio will cause it finally to evolve into a singlerapid-rotating star when the system meets the more familiar criterionthat the orbital angular momentum be less than 3 times the total spinangular momentum. Therefore, AH Cnc may be a progenitor of the bluestraggler stars in M67.
| 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.
| Physical Parameters of Components in Close Binary Systems: VI
New high-quality CCD photometric light curves for the W UMa-type systemsV410 Aur, CK Boo, FP Boo, V921 Her, ET Leo, XZ Leo, V839 Oph, V2357 Oph,AQ Psc and VY Sex are presented. The new multicolor light curves,combined with the spectroscopic data recently obtained at David DunlapObservatory, are analyzed with the Wilson-Devinney code to yield thephysical parameters (masses, radii and luminosities) of the components. Our models for all ten systems resulted in a contact configuration. Fourbinaries (V921 Her, XZ Leo, V2357 Oph and VY Sex) have low, while two(V410 Aur and CK Boo) have high fill-out factors. FP Boo, ET Leo, V839Oph and AQ Psc have medium values of the fill-out factor. Three of thesystems (FP Boo, V921 Her and XZ Leo) have very bright primaries as aresult of their high temperatures and large radii.
| 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.
| CCD Minima for Selected Eclipsing Binaries in 2005
Not Available
| 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.
| New Minima of Selected Eclipsing Close Binaries
We present 180 CCD and photoelectric times of minima of selected closeeclipsing binaries.
| Deep, Low Mass Ratio Overcontact Binary Systems. IV. V410 Aurigae and XY Bootis
The complete charge-coupled device (CCD) light curves in the V, R, and Ibands for the eclipsing binary V410 Aur were observed at the YunnanObservatory in China. Four new light minimum times of V410 Aur werederived from new observations. The photometric solution for V410 Aur wasobtained for the first time, while the orbital elements for XY Boo(observed by Binnendijk in 1971) were reanalyzed by using the latestWilson-Devinney code. The third light contributions to the total lightsof the two binaries are obtained. The results reveal that both systemsare A-subtype W UMa binaries with low mass ratios and deep degrees ofovercontact (i.e., qph=0.1428 and f=52.4% for V410 Aur, andqph=0.1855 and f=55.9% for XY Boo). The photometric massratios of the two binaries are very consistent with the spectroscopicmass ratios. By combining the spectroscopic elements with ourphotometric solutions, the absolute photometric parameters for V410 Aurand XY Boo are (re)determined. Analyzing the orbital periods of the twobinaries, it is discovered that their orbital periods show continuousperiod increases, suggesting that the systems are undergoing masstransfer from the less massive component to the more massive one throughthe inner Lagrangian point L1. This kind of binary, with alow mass ratio, a deep degree of overcontact, and a continuous periodincrease, may coalesce into a rapidly rotating single star due to tidalinstability.
| 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
| Photoelectric Minima of Some Eclipsing Binary Stars
We present 70 minima times of 35 eclipsing binaries.
| 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.
| 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.
| Times of Minima for Neglected Eclipsing Binaries in 2004
Times of minima obtained during 2004 for a number of neglected eclipsingbinaries are presented.
| Photoelectric Minima of Some Eclipsing Binary Stars
Not Available
| Key parameters of W UMa-type contact binaries discovered by HIPPARCOS
A sample of W UMa-type binaries which were discovered by the HIPPARCOSsatellite was constructed with the aid of well defined selectioncriteria described in this work. The selection process showed up thatseveral systems of which the variability types have been assigned as EBin HIPPARCOS catalogue are genuine contact binaries of W UMa-type. Thelight curves of the 64 selected systems based on HIPPARCOS photometrywere analyzed with the aid of light curve synthesis method by Rucinskiand their geometric elements (namely mass ratio q, degree of contact f,and orbital inclination i) were determined. The solutions were obtainedfor the first time for many of the systems in the sample and would be agood source for their future light curve analyses based on more precisefollow-up observations.Based on observations made with the ESA HIPPARCOSastrometry satellite.
| Radial Velocity Studies of Close Binary Stars. VIII.
Radial velocity measurements and sine-curve fits to the orbital velocityvariations are presented for the seventh set of 10 close binary systems:V410 Aur, V523 Cas, QW Gem, V921 Her, V2357 Oph, V1130 Tau, HN UMa, HXUMa, HD 93917, and NSV 223. All systems but three (V523 Cas, HD 93917,NSV 223) were discovered photometrically by the Hipparcos mission. Allsystems are double-lined (SB2) binaries, and all but the detached, veryclose system V1130 Tau are contact binaries. The broadening functionpermitted improvement of the orbital elements for V523 Cas, which wasthe only system observed before for radial velocity variations.Spectroscopic/visual companions were detected for V410 Aur and HX UMa.Several of the studied systems are prime candidates for combined lightand radial velocity synthesis solutions.Based on data obtained at the David Dunlap Observatory, University ofToronto.
| 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.
| The long-period companions of multiple stars tend to have moderate eccentricities
We examined the statistics of an angle gamma between the radius vectorof a visual companion of a multiple star and the vector of its apparentrelative motion in the system. Its distribution f(gamma ) is related tothe orbital eccentricity distribution in the investigated sample. Wefound that for the wide physical subsystems of the 174 objects from theMultiple Star Catalogue f(gamma ) is bell-shaped. The Monte-Carlosimulations have shown that our f(gamma ) corresponds to the populationof the moderate-eccentricity orbits and is not compatible with thelinear distribution f(e)=2e which follows from stellar dynamics andseems to hold for wide binaries. This points to the absence of highlyelongated orbits among the outer subsystems of multiple stars. Theconstraint of dynamical stability of triple systems is not sufficient toexplain the ``rounded-off'' outer orbits; instead, we speculate that itcan result from the angular momentum exchange in multiple systems duringtheir early evolution.
| 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.
| Two-colour photometry for 9473 components of close Hipparcos double and multiple stars
Using observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| The Henry Draper Extension Charts: A catalogue of accurate positions, proper motions, magnitudes and spectral types of 86933 stars
The Henry Draper Extension Charts (HDEC), published in the form offinding charts, provide spectral classification for some 87000 starsmostly between 10th and 11th magnitude. This data, being highlyvaluable, as yet was practically unusable for modern computer-basedastronomy. An earlier pilot project (Roeser et al. 1991) demonstrated apossibility to convert this into a star catalogue, using measurements ofcartesian coordinates of stars on the charts and positions of theAstrographic Catalogue (AC) for subsequent identification. We presenthere a final HDEC catalogue comprising accurate positions, propermotions, magnitudes and spectral classes for 86933 stars of the HenryDraper Extension Charts.
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