AC Bootis - An Unevolved W-Type Overcontact Eclipsing Binary with a High Mass Transfer Rate
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Energy transfer and its effects on the secondaries in W Ursae Majoris type contact binaries
Based on the physical parameters of 133 W Ursae Majoris (W UMa) typecontact binaries, energy transfer and its effects on the secondaries inW UMa contact binaries are investigated. Relations are given between themass ratio (q) for W UMa contact binaries and the relative energytransfer rates, i.e. U1, the ratio of the transferredluminosity to the surface luminosity of the primary, and U2,the ratio of the transferred luminosity to the nuclear luminosity of thesecondary. The theoretical curves(U1 versus q andU2 versus q) are derived based on various assumptions: thatthe two components in each W UMa system are nearly identical ineffective temperature and just fill their inner Roche lobes, and theprimaries are zero-age main-sequence stars. Although these curves canreflect the distribution of U1 and U2 versus q,some observational systems deviate significantly from these curves. Thisresults mainly from the difference in effective temperatures of thecomponents of W UMa systems. The radius and the density of the secondaryare related to the relative energy transfer rate U2: thehigher U2, the greater the expansion and the lower thedensity of the secondary in a W UMa system. In addition, it is foundthat the temperature difference of W UMa binary components is correlatedwith the relative energy transfer rate U1 and decreases withincreasing U1. This might suggest that there is a thermalcoupling between the two components in W UMa contact binaries, and thatthe classification of W UMa contact binaries into A or W types dependson the energy transfer from the primary to the secondary. Thetemperature difference of W UMa binary components is poorly correlatedwith the mass of the primary. This suggests that the properties of thecommon envelope of a W UMa contact binary might not have a significanteffect on the energy transfer between the two components.
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B.R.N.O. Contributions #36, Times of minima
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BAV-Results of observations - Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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New absolute magnitude calibrations for W Ursa Majoris type binaries
Parallaxes of W UMa stars in the Hipparcos catalogue have been analyzed.31 W UMa stars, which have the most accurate parallaxes(σπ/π<0.15) which are neither associated with aphotometric tertiary nor with evidence of a visual companion, wereselected for re-calibrating the Period-Luminosity-Color (PLC) relationof W UMa stars. Using the Lutz-Kelker (LK) bias corrected (mostprobable) parallaxes, periods ({0.26< P< 0.87}, P in days), andcolors ({0.04<(B-V)0<1.28}) of the 31 selected W UMa,the PLC relation have been revised and re-calibrated. The differencebetween the old (revised but not bias corrected) and the new (LK biascorrected) relations are almost negligible in predicting the distancesof W UMa stars up to about 100 pc. But, it increases and may becomeintolerable as distances of stars increase. Additionally, using(J-H)0 and (H-K_s)0 colors from 2MASS (Two MicronAll Sky Survey) data, a PLC relation working with infrared data wasderived. It can be used with infrared colors in the range-0.01<(J-H)0<0.58, and{-0.10<(H-K_s)0<0.18}. Despite of the fact that the2MASS data refer to single epoch observations which are not guaranteedto be taken at maximum brightness of the W UMa stars, the establishedrelation has been found surprisingly consistent and reliable inpredicting LK corrected distances of W UMa stars.
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Programmsterne: beobachtungen erwuenscht.
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Programmsterne: beobachtungen erwuenscht.
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B.R.N.O. Times of minima
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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.
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A Photometric Study of the W UMa-Type Contact Binary RZ Com
We present results of CCD photometric observations of the short-period WUMa-type contact binary system, RZ Com. The light curve of the binaryhas changed from W-subtype to A-subtype from 1998 to 2003, then back toW-subtype in 2004. An analysis was carried out using the 2003 version ofthe Wilson-Devinney code. It is confirmed that RZ Com is a low-degree,overcontact f = 20.1% (+/-7.4%) binary system with a high inclination ofi = 81.°40 (+/-0.°40), and a mass ratio q = 2.351 (+/-0.031).Combining four newly determined times of light minimum with others inthe literature, the variations in orbital period is examined. Asmall-amplitude oscillation (A=0.0065d), with a period of 41.5 year, isdiscovered superimposed on a long-term increase at rate dP/dt =+3.97×10-8d yr-1. The period oscillation canbe explained either by the light-time effect due to the presence of anunseen third body, or by cycles of magnetic activity on the components.Combining our photometric solution with the spectroscopic elementsobtained by Mclean & Hilditch, the absolute dimensions of RZ Comare: M1 = 1.14 (+/-0.19)Modot, M2 =0.50 (+/-0.09)Modot, R1 = 1.12(+/-0.01)Rodot, R2 = 0.78(+/-0.01)Rodot and A = 2.41 (+/-0.02)Rodot.
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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.
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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.
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Programmsterne: Beobachtungen erwuenscht.
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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.
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B.R.N.O. Contributions #34
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Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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Photoelectric Minima of Some Eclipsing Binary Stars
We present 51 minima times of 19 eclipsing binaries.
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Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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Photoelectric Minima of Some Eclipsing Binary Stars
We present 119 minima times of 47 eclipsing binaries.
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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.
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Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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165. List of Timings of Minima Eclipsing Binaries by BBSAG Observers
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New Times of Minima of Some Eclipsing Binary Stars
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New CCD Times of Minima of Eclipsing Binary Systems
We present a total of 208 CCD timings for 103 eclipsing binaries.
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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.
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Times of Minima for Neglected Eclipsing Binaries in 2005
Times of minima obtained at Rolling Hills Observatory during 2005 for anumber of neglected eclipsing binaries are presented.
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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.
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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.
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Die BAV-Tagung und Mitgliederversammlung 2006.
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BAV-Beobachter-Treffen 2006 in Hartha.
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