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Masses and angular momenta of contact binary stars
Results are presented on component masses and system angular momenta forover 100 low-temperature contact binaries. It is found that thesecondary components in close binary systems are very similar in mass.Our observational evidence strongly supports the argument that theevolutionary process goes from near-contact binaries to A-type contactbinaries, without any need of mass loss from the system. Furthermore,the evolutionary direction of A-type into W-type systems with asimultaneous mass and angular momentum loss is also discussed. Theopposite direction of evolution seems to be unlikely, since it requiresan increase of the total mass and the angular momentum of the system.
| 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).
| 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.
| 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.
| Evolutionary Status of Late-Type Contact Binaries
The old model of an unevolved, cool contact binary, in which thesecondary component is strongly oversized due to energy transfer fromthe primary, and the whole system is out of thermal equilibrium,encounters serious problems.I present a new scenario for evolution of contact binaries, which solvesthe problem of thermal nonequilibrium by assuming that contact binariesare past mass exchange with a mass ratio reversal. The scenario isdivided into three phases. In PhaseI loss of angular momentum (AM) dueto magnetized wind of a detached binary is followed until the primarycomponent fills its critical Roche lobe. In Phase II mass transfer takesplace until mass ratio reversal. Arguments are given in favor of such aprocess in pre-contact binaries. In PhaseIII an approximate evolutionarypath of the contact binary is followed until a possible coalescence. AMloss, evolutionary effects of the components and mass transfer to theprimary are taken into account.It is concluded that WUMa type binaries are old objects with secondariesin an advanced evolutionary stage, possibly with small helium cores.Both components fulfill the mass-radius relation for contact binarieswhile being in thermal equilibrium.
| 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.
| 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.
| 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.
| Automatic classification of eclipsing binaries light curves using neural networks
In this work we present a system for the automatic classification of thelight curves of eclipsing binaries. This system is based on aclassification scheme that aims to separate eclipsing binary systemsaccording to their geometrical configuration in a modified version ofthe traditional classification scheme. The classification is performedby a Bayesian ensemble of neural networks trained with Hipparcos data ofseven different categories including eccentric binary systems and twotypes of pulsating light curve morphologies.
| New Minima of Selected Eclipsing Close Binaries
We present 180 CCD and photoelectric times of minima of selected closeeclipsing binaries.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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.
| Deep, Low Mass Ratio Overcontact Binary Systems. III. CU Tauri and TV Muscae
New CCD photometric light curves in the B and V bands of the neglected WUMa-type eclipsing variable star CU Tauri are presented. The O'Connelleffect in the V light curve obtained in 2001 by Yang and Liu was aboutΔV=+0.015, but it vanished in our 2004 observations. Thevariations in the levels of both minima were seen. Our two epochs oflight minimum and others compiled from the literature were used for theperiod study. It is shown that the types of some eclipse times wereincorrect and the values of the period obtained by previousinvestigators were aliases that prevented formation of a plausible O-Ccurve. A new linear ephemeris was derived, and it is discovered that theorbital period of CU Tau shows a continuous decrease at a rate ofdP/dt=-1.81×10-6 days yr-1. The presentsymmetric light curves were solved with the 2003 version of theWilson-Devinney (W-D) code. Both our solutions and those derived by Yangand Liu reveal that CU Tau is a deep (f=50.1%+/-3.2%), low mass ratio(q=0.1770+/-0.0017) overcontact binary system.Meanwhile, the photoelectric light curves in the B, V, R, and I bands ofTV Muscae published by Hilditch and coworkers were reanalyzed with the2003 version of the W-D code. It is shown that the low mass ratio binaryturns out to be a deep overcontact system with f=74.3%+/-11.3%. A periodanalysis with all collected times of light minimum revealed acombination of a long-term period decrease(dP/dt=-2.16×10-7 days yr-1) and a possiblecyclic change with a period of 29.1 yr. The rapid long-term perioddecreases of both systems can be explained as a combination of the masstransfer from the more massive component to the less massive one and theangular momentum loss due to mass outflow from the L2 point. In thatway, the overcontact degrees of the two systems will become deeper astheir periods decrease, and finally they will evolve into a singlerapid-rotation star. However, for CU Tau, the rate of the secular perioddecrease is very large when compared with the other systems of the sametype. This suggests that the long-term period decrease may be part of along-period periodic change, which we need more data to check.
| Deep, Low Mass Ratio Overcontact Binaries. II. IK Persei
BV photometric light curves of the eclipsing binary IK Per were obtainedduring three nights in 2002 December. The photometric elements werecomputed using the Wilson-Devinney code. The results reveal that IK Peris an A-type overcontact binary system with a low mass ratio of q=0.17and a large degree of overcontact of 60%. The asymmetry of the lightcurves (i.e., the O'Connell effect) is explained by spot models. Theobserved long-term orbital period decrease[dP/dt=-(2.5+/-0.09)×10-7 days yr-1] isprobably influenced by the presence of a third body in the system. Thelow mass ratio, high degree of overcontact, and secular orbital decreaseall indicate that the situation of IK Per resembles those of FG Hya, GRVir, and AW UMa. Because of the decrease of their orbital periods, theshrinking of the inner and outer critical Roche lobes will lead thecommon envelopes to overlap more, and finally the systems will evolveinto single rapid-rotation stars.
| 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.
| Improved astrophysical parameters for the overcontact binary FG Hydrae
Photometric data on FG Hya obtained in 2002 and 2004 are presented.Three data sets show the exchange between A-type, W-type and thevariable O'Connell effects. The photometric mass ratio (q= 0.1115 +/-0.0003) derived from B and V light curves is almost the same as thespectroscopic mass ratio (qsp= 0.112 +/- 0.004). The newphotometric solutions reveal that FG Hya is a deep overcontact binarysystem (f= 85.6 +/- 1.8 per cent) with a spotted massive component. Aperiod investigation, based on all available photoelectric or CCD timesof light minimum, shows that the O-C curve of FG Hya can be explained asa combination of a secular period decrease and a cyclic variation with aperiod of 36.4yr and an amplitude of 0.0289 d. By comparing thevariation of the depth of the primary minimum with the change of thecyclic period, it is discovered that both of them may vary with the samecycle length of 36.4yr and in the same phase. The variation of the lightcurve, the spotted primary component and the connection between thecyclic period change and the depth of the primary minimum, all maysuggest that the G0-type component displays solar-type magnetic activitywith a 36.4-yr cycle length. The long-time period decrease isinterpreted by mass transfer from the more massive component to the lessmassive one or/and angular momentum loss due to mass outflow from theouter Lagrangian point.
| Photoelectric Minima of Some Eclipsing Binary Stars
Not Available
| Spectral Classification of Stars in A Supplement to the Bright Star Catalogue
MK spectral types are given for about 584 stars in A Supplement to theBright Star Catalogue. These are compared with Hipparcos parallaxes tocheck the reliability of those classifications. The estimated errors are+/-1.2 subtypes, and 10% of the luminosity classes may be wrong.
| GR Virginis: A Deep Overcontact Binary
Orbital period variations of the low-mass ratio (q=0.122) overcontactbinary system, GR Vir, were investigated by using two new CCD times ofminimum light and other photoelectric data compiled from literatures. Itis found that the O-C residuals of GR Vir show a cyclic variation with aperiod of 19.3 yr and an amplitude of 0.0140 days while they areundergoing a long-term decrease (dP/dt=-4.32×10-7 daysyr-1). Meanwhile, the 1988 photoelectric observations fromCereda et al. were analyzed using the Wilson-Devinney method. Like somelow-mass ratio overcontact binary stars (e.g., AW UMa), GR Vir is anA-type overcontact binary with a high degree of overcontact (f=78.6%).By combining the spectroscopic solutions with the photometric elements,the absolute parameters of the system are determined as follows:M1=1.36Msolar,M2=0.17Msolar, a=2.40Rsolar,R1=1.42Rsolar,R2=0.61Rsolar,L1=2.87Lsolar, andL2=0.48Lsolar. The long-term period decrease isinterpreted as the result of mass transfer from the more massivecomponent to the less massive one in combination with the angularmomentum loss due to mass outflow from the L2 point. Theconditions in GR Vir resemble those in AW UMa. Both systems show a highdegree of overcontact, low mass ratios, and secular shrinking of theirorbits. As their orbital periods decrease, the shrinking of the innerand outer critical Roche lobes will cause the common convective envelopeto become deeper, until finally the formation of single, rapid-rotationstars is inevitable. The period oscillation may by caused either by thepresence of an unseen tertiary component (e.g., a white dwarf) or bymagnetic activity on the part of the primary component.
| 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
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
| A CCD photometric study of the W UMa contact binary Y Sextantis
A V light curve of the W UMa contact binary Y Sex is presented inthis paper. From the observations, two times of minimum light wasdetermined and from the present times of minimum light and thosecollected from the references, the change in the orbital period of thesystem was analyzed with the method of Kalimeris et al. [A&A 282(1994) 775]. The result reveals that the orbital period of the systemoscillates with a cycle of about 50 years and an amplitude of1.1×10-6 days. The light curve was analyzed by means ofthe latest version of the Wilson-Devinney code, which was also used tocorrect photometric effects on the radial-velocity curve obtained byMcLean and Hilditch [MNRAS 203 (1983) 1]. The results suggest that Y Sex is an A-subtypecontact binary with a mass ratio of q=0.180(2). In the new photometricsolution, a positive value of the third light of the system suggeststhat the sinusoidal variation of the period could be caused by a thirdcomponent in the system. The absolute dimensions of Y Sex are found tobe: M1=1.21(18) Msolar, M2=0.22(3)Msolar, R1=1.50(2) Rsolar,R2=0.75(1) Rsolar, L1=3.00(44)Lsolar, L2=0.69(10) Lsolar, A=2.66(11)Rsolar.
| 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.
| 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.
| New Times of Minima of Eclipsing Binary Systems
We present several photoelectric minima observations of 3 eclipsingbinaries.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| New Photoelectric and CCD Minima and Updated Ephemerides of Selected Eclipsing Binaries
This report presents minima times and updated ephemerides of selectedeclipsing binaries
| The 7.5 Magnitude Limit Sample of Bright Short-Period Binary Stars. I. How Many Contact Binaries Are There?
A sample of bright contact binary stars (W UMa type or EW, and related:with β Lyr light curves, EB, and ellipsoidal, ELL-in effect, allbut the detached, EA) to the limit of Vmax=7.5 mag is deemedto include all discoverable short-period (P<1 day) binaries withphotometric variation larger than about 0.05 mag. Of the 32 systems inthe final sample, 11 systems have been discovered by the Hipparcossatellite. The combined spatial density is evaluated at(1.02+/-0.24)×10-5 pc-3. The relativefrequency of occurrence (RFO), defined in relation to the main-sequencestars, depends on the luminosity. An assumption of RFO~=1/500 forMV>+1.5 is consistent with the data, although the numberstatistics is poor with the resulting uncertainty in the spatial densityand the RFO by a factor of about 2. The RFO rapidly decreases forbrighter binaries to a level of 1/5000 for MV<+1.5 and to1/30,000 for MV<+0.5. The high RFO of 1/130, previouslydetermined from the deep OGLE-I sample of disk population W UMa typesystems toward Baade's window, is inconsistent with and unconfirmed bythe new results. Possible reasons for the large discrepancy arediscussed. They include several observational effects but also apossibility of a genuine increase in the contact-binary density in thecentral parts of the Galaxy. Based on data from the Hipparcos satellitemission and from the David Dunlap Observatory, University of Toronto.
| Photometric observations and analysis of V902 Sagittarii
Not Available
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Observation and Astrometry data
| Constellation: | Άρκτος Μεγάλη |
| Right ascension: | 11h30m04.32s |
| Declination: | +29°57'52.7" |
| Apparent magnitude: | 6.917 |
| Distance: | 66.094 parsecs |
| Proper motion RA: | -82.8 |
| Proper motion Dec: | -199.3 |
| B-T magnitude: | 7.344 |
| V-T magnitude: | 6.953 |
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