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Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| 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.
| 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.
| Analysis of Van Houten's Estimates of Variable Stars From Photographic Plates
Huge amount of observations from photogrphic plates made by C. J. vanHouten remained unprocessed and unpublished after his death. The datawere obtained during the first half of the 20th century. All of thestars are situated on the southern hemisphere a most of them areeclipsing binaries. These times of minima can do a great job for O-Canalysis of these objects. The aim of this paper is to introduce thisproject.
| 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.
| CCD Minima for Selected Eclipsing Binaries in 2005
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| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| 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.
| 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.
| Photoelectric Minima of Some Eclipsing Binary Stars
We present 24 minima times of 18 eclipsing binaries.
| 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
| Times of Minima for Neglected Eclipsing Binaries in 2003
Times of minima for a number of neglected eclipsing binaries arepresented.
| 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.
| 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.
| New Times of Minima of Eclipsing Binary Systems
We present 58 photoelectric minima observations of 19 eclipsingbinaries.
| Photometric study of the over-contact binary star GSC 3822-1056
Here we present the first Johnson-Cousins VRC light curves ofthe over-contact binary star GSC 3822-1056. A periodstudy and the light curve solution are also given. An extremely highrate of period increase (+11.6 s/century) was found. The origin of thisperiod change can be: (i) partly covered light-time effect due to theorbital motion around the mass center of a possible third body; (ii)mass transfer between the components.The light curve was solved using the 1998 Wilson-Devinney Code. Weexamined the light curve with and without third light. Both solutionsyielded a contact configuration with high temperature difference betweenthe components. Despite the high degree of the contact (f=0.57), thetemperature difference between the components DeltaT=Tprimary-Tsecondary=1045 K.The high mass ratio of the system and its other unusual propertiessuggest that GSC 3822-1056 may be a recently formedcontact binary.Observations were made by the 80 cm ``IAC80'' telescope at Observatoriodel Teide in Tenerife, Spain, operated by Instituto de Astrofisica deCanarias.Tables 2a-c are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/403/637
| 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.
| 149 Bedeckungssterne der BAV-Programme. Eine Analyse der Beobachtungstatigkeit seit den Angangen.
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| Orbital period changes of contact binary systems: direct evidence for thermal relaxation oscillation theory
Orbital period changes of ten contact binary systems (S Ant, ɛCrA, EF Dra, UZ Leo, XZ Leo, TY Men, V566 Oph, TY Pup, RZ Tau and AGVir) are studied based on the analysis of their O-C curves. It isdiscovered that the periods of the six systems, S Ant, ɛ CrA, EFDra, XZ Leo, TY Men and TY Pup, show secular increases. For UZ Leo, itssecular period increase rate is revised. For the three systems, V566Oph, RZ Tau and AG Vir, weak evidence is presented that a periodicoscillation (with periods of 20.4, 28.5 and 40.9yr respectively) issuperimposed on a secular period increase. The cyclic period changes canbe explained by the presence of an unseen third body in the threesystems. All the sample stars studied are contact binaries withM1>=1.35Msolar. Furthermore, orbital periodchanges of 27 hot contact binaries have been checked. It is found that,apart from AW UMa with the lowest mass ratio (q=0.072), none shows anorbital period decrease. The relatively weak magnetic activity in thehotter contact binaries means little angular momentum loss (AML) fromthe systems via magnetic stellar winds. The period increases of these WUMa binaries can be explained by mass transfer from the secondary to theprimary components, which is in agreement with the prediction of thethermal relaxation oscillation (TRO) models. This suggests that theevolution of a hotter W UMa star is mainly controlled by TRO. On theother hand, for a cooler W UMa star(M1<=1.35Msolar), its evolution may be TRO plusAML, which coincides with the recent results of Qian.
| V842 Her: a W UMa Star with Constant Period
Times of minima of V842 Herculis were collected from the literature andtwo new moments of minima are published. A period determination wascarried out based on these minima and constant period was suspected(between 2490000-2520000). We commend the observation of V842 Herculis.
| 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.
| A photometric study of BO Canum Venaticorum
Photometric BV light curves of BO CVn obtained in 1992 and new times ofminima are presented. The primary minimum shows a transit, whereas thesecondary minimum, shows an occultation. The system may be classified asan A-type W UMa system. A complete study of minima allows one to detecta possibly increasing period by about 0.037 s/yr. This indicates thatthe conservative mass transfer rate from the less massive component tothe more massive one is 1.57 10 - 10Msun /yr. Because of the variableperiod, the new ephemeris is determined for future observations. Usingthe Wilson-Devinney code a simultaneous solution of the B and V lightcurves is also performed. The analysis shows that the system is in acontact configuration with q = 0.205 +/- 0.001 and fillout factor (f) =0.18, T1 = 7240 K (fixed), T2 = 7150 +/- 10 K. The high orbitalinclination i = 87.54 deg +/- 0.26 was con firmed by photometricobservations of the secondary minimum.
| 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.
| Period changes in W UMa-type eclipsing binaries: DK Cygni, V401 Cygni, AD Phoenicis and Y Sextantis
We present a period analysis of the four well-known W UMa-type eclipsingbinaries DK Cyg (P = 0fd47 ), V401 Cyg (0fd58 ), AD Phe (0fd38 ) and YSex (0fd42 ). Several new times of minimum light, recordedphotoelectrically, have been gathered. Analysis of all available eclipsetimings of the DK Cygni and V401 Cygni has confirmed a significantincrease in period of 1.15 10-10 and 1.48 10-10day cycle-1, respectively. A simultaneous solution of the B,V and R light curves was computed for V401 Cyg using the Binary Maker2.0 synthetic lightcurve software. This solution indicates that V401 Cygis in contact with a filing factor of 46%. The period of AD Phe seems tobe constant. Period changes of Y Sex could be explain by a light-timeeffect caused by a third body in an eccentric orbit with a period of 58years. Some of the observations reported in this paper were obtained atthe South Africa Astronomical Observatory, Sutherland, South Africa.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| HV Ursae Majoris, a new contact binary with early-type components
We present the first UBV and uvby photometric observations for the shortperiod variable star HV Ursae Majoris classified as a field RRcvariable. The observed differences between the consecutive minima andthe lack of colour variations disagree with the RRc-classification andsuggest the possible binary nature of HV UMa. In order to reveal thereal physical status of this star, we took medium resolution (lambda/Delta lambda ~ 11000) spectra in the red spectral region centered at6600 Ä. Spectra obtained around the assumed quadratures clearlyshowed the presence of the secondary component. An improved ephemeriscalculated using our and Hipparcos epoch photometry is Hel.JD_min=2451346.743+/-0.001, P=0fd7107523 (3). A radial velocity curvewas determined by modelling the cores of Hα profiles with twoGaussian components. This approximative approach gave a spectroscopicmass ratio of q_sp=0.19+/-0.03. A modified Lucy model containing atemperature excess of the secondary was fitted to the V light curve. Theobtained set of physical parameters together with the parallaxmeasurement indicate that this binary lies far from the galactic plane,and the primary component is an evolved object, probably a subgiant orgiant star. The large temperature excess of the secondary may suggest apoor thermal contact between the components due to a relatively recentformation of this contact system. Based on the data obtained at theDavid Dunlap Observatory, University of Toronto
| Doppler Imaging of VW Cephei: Distribution and Evolution of Starspots on a Contact Binary
We present maximum entropy Doppler images of the contact binary VWCephei, produced from seven data sets of simultaneous spectroscopic andphotometric data at epochs from 1991 March to 1993 May. The geometricand orbital parameters of the contact binary were fitted, along withthird-light characteristics, at the same time as spots, using both thespectroscopic and photometric data to constrain the models. The Dopplerimages indicated the presence of large polar spots on both components.The polar spot on the primary was about 50 deg in diameter and slightlyoff-center, similar to polar spots on other unevolved systems, while thepolar spot on the secondary was 30 deg in diameter. A number of lowerlatitude features were also present. Spots were found to migrate aroundthe primary component in the same direction as the orbital motion of thesystem. Slow differential rotation of the primary component wasobserved, with spots at higher latitudes moving at higher angular rates.The spot distribution on the secondary appeared to be quite stable, withspots congregating at active longitudes, and with no organized patternof migration. The spot coverage on both components was extremely high,though not unrealistic compared to spot coverages of some RS CVnsystems. Spots covered 66% of the surface area of the primary and 55% ofthe secondary. The spot coverage was much greater than that suggested byasymmetry of the light curves. Our Doppler images were modeled inagreement with the Mullan starspot model. However, they also explainedthe success of the hot secondary model, since the bolometricflux-weighted mean surface temperature of the primary was less than thatof the secondary, owing to the large numbers of nonblack spots. Themodels indicated the presence of a great number of unresolved spots. Wediscuss the implications of this to the field of Doppler imaging andargue in favor of the use of two-temperature photosphere models for theDoppler imaging of all rapidly rotating systems. We detected threeflares at Hα and estimate that one such detectable flare occurs onVW Cep every 35+/-20 hr. We also noted that the distribution ofchromospheric emission at Hα over the primary of VW Cep may varyfrom epoch to epoch.
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Dades d'Observació i Astrometria
| Constel·lació: | Leo |
| Ascensió Recta: | 10h40m33.18s |
| Declinació: | +13°34'00.8" |
| Magnitud Aparent: | 9.759 |
| Moviment propi RA: | -23.5 |
| Moviment propi Dec: | -2.5 |
| B-T magnitude: | 10.205 |
| V-T magnitude: | 9.796 |
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INHABITED SKY
