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Публикации по объекту
New Times of Minima of Eclipsing Binary Systems
We present 82 photoelectric minima observations of 34 eclipsingbinaries.
| 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.
| 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.
| New Times of Minima of Eclipsing Binary Systems and of Maximum of SXPHE Type Stars
We present 64 photoelectric minima observations of 31 eclipsingbinaries. We also report three new times of maxima of three SXPHE typepulsating stars.
| 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.
| Photoelectric Minima of Some Eclipsing Binary Stars
We present 70 minima times of 35 eclipsing binaries.
| Photoelectric Minima of Eclipsing Binaries
Not Available
| 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.
| New Times of Minima of Eclipsing Binary Systems
We present 45 photoelectric minima observations of 20 eclipsingbinaries.
| 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
| Times of Minima for Neglected Eclipsing Binaries in 2003
Times of minima for a number of neglected eclipsing binaries arepresented.
| CCD Times of Minima of Some Eclipsing Binaries in 2003
We present CCD observations of minima of 31 eclipsing binaries observedby SAVS sky survey in 2003.
| Period Changes of Two W UMa-Type Contact Binaries: RW Comae Berenices and CC Comae Berenices
From the present times of minimum light and those collected from theliterature, changes in the orbital period of the two W UMa-type contactbinaries RW Com and CC Com are analyzed. The results reveal that theperiod changes of these two systems show the same natures, with ashort-term oscillation superposed on the secular decrease. For RW Com,its period shows a secular decrease at a rate ofdP/dt=0.43×10-7 days yr-1. An oscillationwith a periodicity of 13.7 yr and an amplitude ofΔP=5.4×10-7 days is superposed on the seculardecrease. For CC Com, its period shows a secular decrease at a rate ofdP/dt=0.40×10-7 days yr-1. An oscillationwith a periodicity of 16.1 yr and an amplitude ofΔP=2.8×10-7 days is superposed on the seculardecrease. The period secular decreases of the two systems may beexplained by a mass-transfer rate of dm/dt=0.29×10-7Msolar yr-1 for RW Com anddm/dt=0.52×10-7 Msolar yr-1 forCC Com. The period short-term oscillations of the two systems may beexplained by the magnetic activity cycle model given by Applegate, andthe parameters for the magnetic activity cycle model are presented.
| Times of Minima for Neglected Eclipsing Binaries in 2002
We present several CCD minima observations of eclipsing binaries.
| 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 15 eclipsingbinaries.
| A possible relation between the period change and the mass ratio for W-type contact binaries
Orbital period changes of eight W-type contact binaries (TY Boo, BH Cas,AD Cnc, TX Cnc, RZ Com, LS Del, BB Peg and AA UMa) are presented basedon the analysis of their O-C curves. It is found that the periods of thefive systems TY Boo, TX Cnc, RZ Com, LS Del and AA UMa show secularincrease. For BB Peg, its period increase rate has been revised. For ADCnc, weak evidence also shows that its orbital period is increasing. Forthe remaining BH Cas, the three times of light minimum given by Agerer& Hubscher indicate that, recently, its period has been increasing.However, the properties of the period need further study. The massratios of all the systems are larger than 0.4. The period increases ofthe systems may suggest that the W-type W UMa stars with high mass ratio(q>0.4) usually show their period increase. In order to check thisconclusion, secular period changes of 30 W-type contact binaries havebeen collected from the literature. It is found that systems showingperiod increase usually have a higher mass ratio (q>0.4), and theperiods of low-mass ratio systems (q<0.4) are varying in a seculardecrease. This strongly suggests that a relation between the orbitalperiod variation and the mass ratio for W-type contact binaries mayexist. If the secular period change is caused by conservative masstransfer between the components, this relation may suggest that theevolution of the W-type systems is oscillation around a critical massratio (q~0.4). However this is highly speculative. On the other hand,the relation may be potentially strong observational evidence forRahunen's conclusion that angular momentum loss (AML) may enable thecomponents of a contact binary to remain in good contact throughout thethermal relaxation oscillation (TRO) cycle. This connection could beexplained by the combination of the TRO and the variable AML via thechange of depth of contact, which needs further studies observationallyand theoretically.
| 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.
| Radial Velocity Studies of Close Binary Stars. I.
Radial velocity data are presented for 10 W UMa-type systems-GZ And,V417 Aql, LS Del, EF Dra, V829 Her, FG Hya, AP Leo, UV Lyn, BB Peg, andAQ Psc-together with preliminary circular-orbit determinations ofspectroscopic elements, with the main goal of obtaining mean radialvelocities and mass ratios for these systems. This is the first part ofa series that will contain radial velocity data for northern hemisphere,short-period eclipsing binaries, accessible to medium-resolutionspectroscopic studies with 1.8 m-class telescopes.
| New Times of Minima and Updated Ephemerides of Selected Contact Binaries
We present new times of minima of 44i Boo, AB And, SW Lac, U Peg VW Cepand XY Leo. Besides these stars, we also give updated ephemerides of OOAql, DK Cyg, LS Del and V1073 Cyg.
| Photoelectric times of minima of some eclipsing binary systems
We presented 27 photoelectric minima of 11 eclipsing binaries. Most ofthe minima observations are part of the complete light curve coverages.
| 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.
| Photoelectric Observations and Minima Times of Four W UMa Systems: LS Del, SW Lac, V839 Oph and AQ Psc
Not Available
| Stroemgren photometry of F- and G-type stars brighter than V = 9.6. I. UVBY photometry
Within the framework of a large photometric observing program, designedto investigate the Galaxy's structure and evolution, Hβ photometryis being made for about 9000 stars. As a by-product, supplementary uvbyphotometry has been made. The results are presented in a cataloguecontaining 6924 uvby observations of 6190 stars, all south ofδ=+38deg. The overall internal rms errors of one observation(transformed to the standard system) of a program star in the interval6.5
| Times of Minima for Some Eclipsing Binaries
Not Available
| 1990 photometry of a small amplitude W UMA system LS Delphini
Differential UBV observations, carried out in 1990 observing season, ofa small amplitude (0.15 m in V and B) W UMa system LS Del = HD 199497are presented. Wavelength-dependent light variations from cycle to cycleindicate that the system is in a very active phase, probably due tomagnetic flare activity or mass transfer in the system. An analysis ofthe minima times indicate a probable secular increase of the photometricperiod which requires a mass transfer from less massive to more massivecomponent. If this is true then the reverse-algol model by Liu et al.(1988) for this system would not be valid.
| Light curve and period variations of a W Ursae Majoris system LS Delphini
Differential UBV observations, carried out between 1987 and 1989, of asmall amplitude W UMa system LS Del=HD 199497 are presented. Lightcurves and photometric periods of the system are found strongly variablefrom cycle to cycle. Wavelength-dependent light variations indicate thatthe system is in a very active phase. It was found, by Fourier analysis,that the light variation is dominated by an ellipticity effect but, thatabout 20 percent of the variation in B band is due to 'reflection'. Bycomparing the light curves, evidence was also found that the apparentlylarge 'reflection' effect may be induced by a variable emission from ahot region in the neck of the system.
| A Photometric Study of LS Delphini
Not Available
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Дельфин |
| Прямое восхождение: | 20h57m10.29s |
| Склонение: | +19°38'59.2" |
| Видимая звёздная величина: | 8.663 |
| Собственное движение RA: | 145.6 |
| Собственное движение Dec: | 83.9 |
| B-T magnitude: | 9.287 |
| V-T magnitude: | 8.715 |
Каталоги и обозначения:
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