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165. List of Timings of Minima Eclipsing Binaries by BBSAG Observers
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| The Case for Third Bodies as the Cause of Period Changes in Selected Algol Systems
Many eclipsing binary star systems show long-term variations in theirorbital periods, evident in their O-C (observed minus calculated period)diagrams. With data from the Robotic Optical Transient Search Experiment(ROTSE-I) compiled in the SkyDOT database, New Mexico State University 1m data, and recent American Association of Variable Star Observers(AAVSO) data, we revisit Borkovits and Hegedüs's best-casecandidates for third-body effects in eclipsing binaries: AB And, TV Cas,XX Cep, and AK Her. We also examine the possibility of a third bodyorbiting Y Cam. Our new data support their suggestion that a third bodyis present in all systems except AK Her, as is revealed by thesinusoidal variations of the O-C residuals. Our new data suggest that athird body alone cannot explain the variations seen in the O-C residualsof AK Her. We also provide a table of 143 eclipsing binary systems thathave historical AAVSO O-C data with new values computed from the SkyDOTdatabase.
| 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.
| 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.
| 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 Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| Photoelectric Minima of Some Eclipsing Binary Stars
We present 70 minima times of 35 eclipsing binaries.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| Photoelectric Minima of Some Eclipsing Binary Stars
We present 24 minima times of 18 eclipsing binaries.
| Beobachtungssergebnisse Bundesdeutsche Arbeitsgemeinschaft fuer Veraenderliche Sterne e.V.
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| Radial Velocity Studies of Close Binary Stars. X.
Radial velocity measurements and sine-curve fits to orbital velocityvariations are presented for the ninth set of 10 close binary systems:V395 And, HS Aqr, V449 Aur, FP Boo, SW Lac, KS Peg, IW Per, V592 Per, TUUMi, and FO Vir. The first three are very close, possibly detached,early-type binaries, and all three require further investigation.Particularly interesting is V395 And, whose spectral type is as early asB7/8 for a 0.685 day orbit binary. KS Peg and IW Per are single-linebinaries, with the former probably hosting a very low mass star. We havedetected a low-mass secondary in an important semidetached system, FOVir, at q=0.125+/-0.005. The contact binary FP Boo is also a very smallmass ratio system, q=0.106+/-0.005. The other contact binaries in thisgroup are V592 Per, TU UMi, and the well-known SW Lac. V592 Per and TUUMi have bright tertiary companions; for these binaries, and for V395And, we used a novel technique of arranging the broadening functionsinto a two-dimensional image in phase. The case of TU UMi turned out tobe intractable even using this approach, and we have not been able toderive a firm radial velocity orbit for this binary. Three systems ofthis group were observed spectroscopically before: HS Aqr, SW Lac, andKS Peg.Based on the data obtained at the David Dunlap Observatory, Universityof Toronto.
| Wer beobachtet mit: AH Virginis.
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| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderlichen Serne e.V.
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| Radial Velocity Studies of Close Binary Stars. IX.
Radial velocity measurements and sine-curve fits to the orbital velocityvariations are presented for the eighth set of 10 close binary systems:AB And, V402 Aur, V445 Cep, V2082 Cyg, BX Dra, V918 Her, V502 Oph, V1363Ori, KP Peg, and V335 Peg. Half of the systems (V445 Cep, V2082 Cyg,V918 Her, V1363 Ori, and V335 Peg) were discovered photometrically bythe Hipparcos mission, and all systems are double-lined (SB2) contactbinaries. The broadening function method permitted improvement of theorbital elements for AB And and V502 Oph. The other systems have beenobserved for radial velocity variations for the first time; in thisgroup are five bright (V<7.5) binaries: V445 Cep, V2082 Cyg, V918Her, KP Peg, and V335 Peg. Several of the studied systems are primecandidates for combined light and radial velocity synthesis solutions.Based on the data obtained at the David Dunlap Observatory, Universityof Toronto.
| 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
| 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.
| Photoelectric Minima of Selected Eclipsing Binaries
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| The First Eclipsing Binary Observations at the Ulupinar Astrophysics Observatory
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| 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.
| A Possible Explanation of the O'Connell Effect in Close Binary Stars
A theoretical model for explaining the O'Connell effect of close binarystars is given based on the hypothesis that the circumstellar materialof a binary system is captured by its components. The results inferredfrom the model suggest that late-type and/or short-period binaries caneasily produce obvious O'Connell effect and that the occurrence ofO'Connell effect has no relation with the type of binaries. Theseconclusions are in agreement with the observed results. The observedO'Connell effects of six binary systems are examined by the model. Forthree W-subtype W UMa binaries (YY Eri, BX Per and SW Lac), thedensities of the materials captured by the two components are assumed tobe equal, and the calculated O'Connell effect is found to be almostequal to the observed effect. For three A-subtype W UMa systems (CNAnd, FG Hya and AU Ser), the two densities are assumed to be different,and are calculated separately. The calculated O'Connell effect turns outto agree better with the observed effect than that was formerlyobtained.
| Zur qualitat der visuellen Beobachtung kurzperiodisch Veranderlicher.
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| Beobachtungsegebnisse Bundesdeutsche Arbeitsgemainschaft fur Veranderliche Sterne e.V.
Not Available
| The Hamburg/RASS Catalogue of optical identifications. Northern high-galactic latitude ROSAT Bright Source Catalogue X-ray sources
We present the Hamburg/RASS Catalogue (HRC) of optical identificationsof X-ray sources at high-galactic latitude. The HRC includes all X-raysources from the ROSAT Bright Source Catalogue (RASS-BSC) with galacticlatitude |b| >=30degr and declination delta >=0degr . In thispart of the sky covering ~ 10 000 deg2 the RASS-BSC contains5341 X-ray sources. For the optical identification we used blue Schmidtprism and direct plates taken for the northern hemisphere Hamburg QuasarSurvey (HQS) which are now available in digitized form. The limitingmagnitudes are 18.5 and 20, respectively. For 82% of the selectedRASS-BSC an identification could be given. For the rest either nocounterpart was visible in the error circle or a plausibleidentification was not possible. With ~ 42% AGN represent the largestgroup of X-ray emitters, ~ 31% have a stellar counterpart, whereasgalaxies and cluster of galaxies comprise only ~ 4% and ~ 5%,respectively. In ~ 3% of the RASS-BSC sources no object was visible onour blue direct plates within 40\arcsec around the X-ray sourceposition. The catalogue is used as a source for the selection of(nearly) complete samples of the various classes of X-ray emitters.
| 149 Bedeckungssterne der BAV-Programme. Eine Analyse der Beobachtungstatigkeit seit den Angangen.
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| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veraenderliche Sterne e.V.
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| Starspots and photometric noise on observed minus calculated (O-C) diagrams
The effects of starspots on the O-C diagrams of eclipsing binaries areinvestigated, with a special emphasis on contact binaries. It is shownthat starspots modulate the O-C differences in a fundamentally differentway than real orbital period variations. Migrating starspots can onlyintroduce high frequency, low amplitude disturbances (generally lessthan 0.01 d), whose characteristics are numerically specified fortypical contact binaries. It becomes evident that the observedsystematic short timescale variations of the O-C diagrams of activecontact binaries (even those like VW Cep) cannot be attributed tostarspots. Furthermore, the basic property of non-linear modulation ofO-C differences is emphasised. This non-linearity has seriousconsequences for the widespread traditional method of O-C diagramanalysis. This traditional method is found inappropriate even on afundamental level, and its mathematical and physical inconsistencies arereviewed.
| 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.
| 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.
| A CCD Photometric Study of the Contact Binary V396 Monocerotis
Complete BV light curves of the W Ursae Majoris binary V396 Mon arepresented. The present CCD photometric observations reveal that thelight curves of the system are obviously asymmetric, with the primarymaximum brighter than the secondary maximum (the ``O'Connell effect'').The light curves are analyzed by means of the latest version of theWilson-Devinney code. The results show that V396 Mon is a W-subtype WUMa contact binary with a mass ratio of 0.402. The asymmetry of thelight curves is explained by a cool spot on the secondary component. Thenature of the overluminosity of the secondary of a W UMa-type system isanalyzed. It is shown that the overluminosity of the secondary isclearly related to the mass of the primary and that, for a W UMa system,the higher the mass of the primary, the greater the overluminosity ofthe secondary. In addition, the overluminosity of the secondary is alsorelated to its own density: the lower the density of the secondary, thegreater its overluminosity.
| The long-period companions of multiple stars tend to have moderate eccentricities
We examined the statistics of an angle gamma between the radius vectorof a visual companion of a multiple star and the vector of its apparentrelative motion in the system. Its distribution f(gamma ) is related tothe orbital eccentricity distribution in the investigated sample. Wefound that for the wide physical subsystems of the 174 objects from theMultiple Star Catalogue f(gamma ) is bell-shaped. The Monte-Carlosimulations have shown that our f(gamma ) corresponds to the populationof the moderate-eccentricity orbits and is not compatible with thelinear distribution f(e)=2e which follows from stellar dynamics andseems to hold for wide binaries. This points to the absence of highlyelongated orbits among the outer subsystems of multiple stars. Theconstraint of dynamical stability of triple systems is not sufficient toexplain the ``rounded-off'' outer orbits; instead, we speculate that itcan result from the angular momentum exchange in multiple systems duringtheir early evolution.
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