Visual Minima Timings of Eclipsing Binaries Observed in the Years 1992 - 1996
The paper contains a list of 283 new times of minima and 77 revisedtimes of minima for 63 eclipsing binaries derived by the author fromhis visual observations.
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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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New Times of Minima of Some Eclipsing Binary Stars
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Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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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.
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On the Period Variation of the W UMa-type Contact Binary V502 Ophiuchi
The variation in the orbital period of the W UMa type contact binaryV502 Oph is analyzed. The orbital period exhibits a wavelike variationwith a periodicity of 23.0 years and an amplitude of ΔP =1.24×10-6 days superimposed on secular decrease ofdP/dt = 1.68×10-7 day per year. The long-term decreasemay be accompanied by the contraction of the secondary at a rate of 83 mper year and a mass transfer rate from the primary to the secondary of4.28×10-8Modot per year. The short-termoscillation may be explained by the presence of a third component.Orbital elements of the third body and its possible mass are presented.
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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.
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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.
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Luminosity function of contact binaries based on the All Sky Automated Survey (ASAS)
The luminosity function for contact binary stars of the W UMa type isevaluated on the basis of the All Sky Automated Survey (ASAS)photometric project covering all stars south of δ=+ 28° withina magnitude range 8 < V < 13. Lack of colour indices enforced alimitation to 3374 systems with P < 0.562 d (i.e. 73 per cent of allsystems with P < 1 d) where a simplified MV(logP)calibration could be used. The spatial density relative to themain-sequence FGK stars of 0.2 per cent, as established previously fromthe Hipparcos sample to V= 7.5, is confirmed. While the numbers ofcontact binaries in the ASAS are large and thus the statisticaluncertainties small, derivation of the luminosity function required acorrection for missed systems with small amplitudes and with orbitalperiods longer than 0.562 d; the correction, by a factor of 3, carriesan uncertainty of about 30 per cent.
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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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CCD Minima for Selected Eclipsing Binaries in 2005
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Basic physical properties of the low-temperature contact binary system V781 Tau and the near-contact binary system V836 Cyg
We present a detailed photometric study of the low-temperature contactbinary V781 Tau, and the near-contact binary V836 Cyg. We have combinedthe parameters obtained from the light-curve analysis with those foundby the spectral studies and we have determined the orbital and physicalparameters of the stars. We have collected the times of the mid-eclipsesobtained so far and combined with the times obtained in this study. Byanalysing all these data we determined the mass transfer rate from themassive star to the less massive one for V781 Tau, and from the lessmassive component to the massive one in the case of V836 Cyg. Finally,we have compared the results obtained for V781 Tau and for V836 Cyg withsimilar systems.
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164. List of Timings of Minima Eclipsing Binaries by BBSAG Observers
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Photoelectric Minima of Some Eclipsing Binary Stars
We present 70 minima times of 35 eclipsing binaries.
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Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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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.
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Times of Minima for Neglected Eclipsing Binaries in 2004
Times of minima obtained during 2004 for a number of neglected eclipsingbinaries are presented.
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Photoelectric Minima of Some Eclipsing Binary Stars
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Photoelectric Minima of Some Eclipsing Binary Stars
We present 24 minima times of 18 eclipsing binaries.
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Spectroscopy, Photometry and Micro-arcsec Astrometry of Binaries with the GAIA Space Mission and with the RAVE Experiment
The GAIA astrometric mission of ESA will be very efficient indiscovering binary and multiple stars with any orbital period, fromminutes to millions of years. The main parameters of the revised missiondesign are presented. Next we estimate the fraction of binary starsdiscovered by means of astrometry, photometry and on-board spectroscopy.Finally we summarize observations that confirm the ability to measurephysical parameters like masses, radii and spectroscopic distance fromGAIA data alone. GAIA will fly only in 2010, but the radial velocityexperiment (RAVE) has started this year. We show that its spectroscopicobservations have the capacity to discover a large fraction of so farunknown binary systems.
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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.
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An Assessment of Dynamical Mass Constraints on Pre-Main-Sequence Evolutionary Tracks
We have assembled a database of stars having both masses determined frommeasured orbital dynamics and sufficient spectral and photometricinformation for their placement on a theoretical H-R diagram. Our sampleconsists of 115 low-mass (M<2.0 Msolar) stars, 27pre-main-sequence and 88 main-sequence. We use a variety of availablepre-main-sequence evolutionary calculations to test the consistency ofpredicted stellar masses with dynamically determined masses. Despitesubstantial improvements in model physics over the past decade, largesystematic discrepancies still exist between empirical and theoreticallyderived masses. For main-sequence stars, all models considered predictmasses consistent with dynamical values above 1.2 Msolar andsome models predict consistent masses at solar or slightly lower masses,but no models predict consistent masses below 0.5 Msolar,with all models systematically underpredicting such low masses by5%-20%. The failure at low masses stems from the poor match of mostmodels to the empirical main sequence below temperatures of 3800 K, atwhich molecules become the dominant source of opacity and convection isthe dominant mode of energy transport. For the pre-main-sequence samplewe find similar trends. There is generally good agreement betweenpredicted and dynamical masses above 1.2 Msolar for allmodels. Below 1.2 Msolar and down to 0.3 Msolar(the lowest mass testable), most evolutionary models systematicallyunderpredict the dynamically determined masses by 10%-30%, on average,with the Lyon group models predicting marginally consistent masses inthe mean, although with large scatter. Over all mass ranges, theusefulness of dynamical mass constraints for pre-main-sequence stars isin many cases limited by the random errors caused by poorly determinedluminosities and especially temperatures of young stars. Adopting awarmer-than-dwarf temperature scale would help reconcile the systematicpre-main-sequence offset at the lowest masses, but the case for this isnot compelling, given the similar warm offset at older ages between mostsets of tracks and the empirical main sequence. Over all age ranges, thesystematic discrepancies between track-predicted and dynamicallydetermined masses appear to be dominated by inaccuracies in thetreatment of convection and in the adopted opacities.
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CCD Minima for Selected Eclipsing Binaries in 2003
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Photoelectric Minima of Some Eclipsing Binary Stars
We present 25 minima times of 12 eclipsing binaries.
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162-nd List of Minima Timings of Eclipsing Binaries by BBSAG Observers
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Evaluating GAIA performances on eclipsing binaries . II. Orbits and stellar parameters for V781 Tau, UV Leo and GK Dra
The orbits and physical parameters of three close, double-lined G0eclipsing binaries have been derived combining H_P, V_T, B_T photometryfrom the Hipparcos/Tycho mission with 8480-8740 Å ground-basedspectroscopy. The setup is mimicking the photometric and spectroscopicobservations that should be obtained by GAIA. The binaries consideredhere are all of G0 spectral type, but each with its own complications:V781 Tau is an overcontact system with components of unequaltemperature, UV Leo shows occasional surface spots and GK Dra contains adelta Scuti variable. Such peculiarities will be common among binariesto be discovered by GAIA. We find that the values of masses, radii andtemperatures for such stars can be derived with a 1-2% accuracy usingthe adopted GAIA-like observing mode.
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Photoelectric Minima of Some Eclipsing Binary Stars
We present 18 minima times of 10 eclipsing binaries.
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V781 Tau: Improved Evidence for an Orbital Period Change
V781 Tau (=SAO 077615) is a G0 over-contact binary with an orbitalperiod that is changing with time. Liu and Yang (2000) proposed aquadratic orbital ephemeris with the binary period changing with time.They analysed observations from the literature and added two minimaobtained in 1997 and 1998. These two points proved crucial for thedetermination of the parabolic term of the ephemeris and need robustconfirmation by extending measurements of the times of minima well intothe descending branch of the parabolic approximation. We report here on10 additional minima secured between Nov-2001 and Jan-2003 to the aim ofconfirming the trend and strengthen the solution. Our results fullyconfirm the orbital ephemeris of Liu and Yang.
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INHABITED SKY
