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Recent Minima of 144 Eclipsing Binary Stars
This paper continues the publication of times of minima for eclipsingbinary stars from observations reported to the AAVSO Eclipsing BinarySection. Times of minima from observations made from March 2010 throughSeptember 2010, along with a few unpublished times of minima from olderdata, are presented.
| Do Eclipsing Variable Stars Show Random Cycle-to-cycle Period Fluctuations?
AAVSO observers and others have measured the times of minima of hundredsof eclipsing binaries over many decades. These times can be used toconstruct (O-C) diagrams that can be used to refine the periods of thestars, and to look for changes or fluctuations in the periods. We haveapplied the Eddington-Plakidis (1929) model to the (O-C) data on 100stars in the AAVSO-Eclipsing Binary Program, to determine whether the(O-C) diagrams can be explained by the cumulative effect of random,cycle-to-cycle fluctuations in period. The stars can be divided intothree groups: 25-35% showing (O-C) fluctuations due only to measurementerrors; 40-50% showing small, random cycle-to-cycle period fluctuations(typically a few times 10^4 of a cycle), and 20-30% showing (O-C)variations which do not fit the Eddington-Plakidis model and thereforecannot be explained by the accumulation of random fluctuations. Wediscuss possible explanations for these three groups.
| Physical parameters of 62 eclipsing binary stars using the All Sky Automated Survey-3 data - I
We present a detailed light-curve analysis of publicly available V-bandobservations of 62 binary stars, mostly contact binaries, obtained bythe All Sky Automated Survey (ASAS)-3 project between 2000 and 2009.Eclipsing binaries are important astronomical targets for determiningthe physical parameters of component stars from the geometry of theirorbits. They provide an independent direct method of measuring the radiiof stars. We improved the ASAS determined periods and ephemerides, andobtained the Fourier parameters from the phased light curves of these 62stars. These Fourier parameters were used for preliminary classificationof the stars in our sample. The phased light curves were then analysedwith the aid of the Wilson-Devinney light-curve modelling technique inorder to obtain various geometrical and physical parameters of thesebinaries. The spectroscopic mass ratios as determined from the radialvelocity measurements available in the literature were used as one ofthe inputs to the light-curve modelling. Thus reliable estimations ofparameters of these binaries were obtained with combined photometric andspectroscopic data, and error estimates were made using the heuristicscan method. For several systems in the sample, the solutions wereobtained for the first time and would serve as a good source in thefuture for light-curve analysis based on more precise follow-up CCDphotometric observations. Out of 62 stars in the sample, photometricanalysis of 39 stars is presented here for the first time using the ASASphotometry and precise spectroscopic mass ratios. From the analysis, wefound 54 contact binaries, six semidetached binaries and two detachedbinaries. The Fourier parameters in the a2-a4plane were used for preliminary classification, and the finalclassification was done based on the Roche lobe geometry obtained fromthe light-curve modelling.
| A Multicolour Photometric Study for the W Ursae Majoris Type Binary LR Camelopardalis
A CCD multicolour photometry for the eclipsing binary LR Camelopardalis,obtained on 2008 December 19 and 2010 January 29 and 30 at the XinglongStation of NAOC, is presented. Using the Wilson-Devinney binary code, aphotometric solution was simultaneously derived from BVR light curves.The results show that LR Cam belongs to a W-type contact binary, with amass ratio of q = 0.300(1) and an overcontact degree of f = 23.5(5)%,indicating that LR Cam is a weak-contact binary. The asymmetric lightcurves (i.e., the O'Connell effect) were modeled by a dark spot on themore massive component. From the (O - C) curve of LR Cam, it is foundthat the orbital period shows a sine-like variation superimposed on asecular period increase. The quasi-sinusoidal variation, with A =0.d0039(1), P3 = 5.34(2) yr, and e' = 0.56(3), maymore likely result from a light-time effect via the presence of a thirdbody. The long-term period increases at a rate of dP/dt = +0.65(9)× 10-7 d yr-1, which may be interpreted bymass transfer from the less-massive component to the more-massive one.With mass transferring, LR Cam may evolve into a broken-contact binary.
| Recent Minima of 161 Eclipsing Binary Stars
This paper continues the publication of times of minima for eclipsingbinary stars from observations reported to the AAVSO Eclipsing BinarySection. Times of minima from observations made from March 2009 throughAugust 2009, along with a few unpublished times of minima from olderdata, are presented.
| The Solar-Type Contact Binary BX Pegasi Revisited
We present the results of new CCD photometry for the contact binary BXPeg, made during three successive months beginning on 2008 September. Asdo historical light curves, our observations display an O'Connell effectand the November data by themselves indicate clear evidence for veryshort-term brightness disturbance. For these variations, model spots areapplied separately to the two data sets, Group I (Sep.-Oct.) and GroupII (Nov.). The former is described by a single cool spot on thesecondary photosphere and the latter by a two-spot model with a coolspot on the cool star and a hot one on either star. These aregeneralized manifestations of the magnetic activity of the binarysystem. Twenty light-curve timings calculated from Wilson-Devinney codewere used for a period study, together with all other minimum epochs.The complex period changes of BX Peg can be sorted into a secular perioddecrease caused dominantly by angular momentum loss due to magneticstellar wind braking, a light-travel time (LTT) effect due to the orbitof a low-mass third companion, and a previously unknown short-termoscillation. This last period modulation could be produced either by asecond LTT orbit with a period of about 16 yr due to the existence of afourth body, or by the effect of magnetic activity with a cycle lengthof about 12 yr.
| Close binary and other variable stars in the solar-age Galactic open cluster M 67
We present multi-colour time-series CCD photometry of the solar-agegalactic open cluster M 67 (NGC 2682). About 3600 frames spread over 28nights were obtained with the 1.5 m Russian-Turkish and 1.2 m Mercatortelescopes. High-precision observations of the close binary stars AHCnc, EV Cnc, ES Cnc, the ? Scuti type systems EX Cnc and EW Cnc,and some long-period variables belonging to M 67 are presented. Threefull multi-colour light curves of the overcontact binary AH Cnc wereobtained during three observing seasons. Likewise we gathered threelight curves of EV Cnc, an EB-type binary, and two light curves of ESCnc, a blue straggler binary. Parts of the light change of long-termvariables S1024, S1040, S1045, S1063, S1242, and S1264 are obtained.Period variation analysis of AH Cnc, EV Cnc, and ES Cnc were done usingall times of mid-eclipse available in the literature and those obtainedin this study. In addition, we analyzed multi-colour light curves of theclose binaries and also determined new frequencies for the ? Scutisystems. The physical parameters of the close binary stars weredetermined with simultaneous solutions of multi-colour light and radialvelocity curves. Finally we determined the distance of M 67 as 857(33)pc via binary star parameters, which is consistent with an independentmethod from earlier studies.Based on observations made with the Mercator Telescope, operated on theisland of La Palma by the Flemish Community, at the Spanish Observatoriodel Roque de los Muchachos of the Instituto de Astrofísica deCanarias and TÜB?TAK National Observatory Russian-Turkishtelescope operated at Sakl?kent, Antalya.
| Recent Minima of 154 Eclipsing Binary Stars
This paper continues the publication of times of minima for eclipsingbinary stars from observations reported to the AAVSO Eclipsing BinaryCommittee. Times of minima from observations made from September 2008through February 2009 are presented.
| Radial Velocity Studies of Close Binary Stars. XV
Radial velocity (RV) measurements and sine curve fits to the orbital RVvariations are presented for the last eight close binary systemsanalyzed in the same way as in the previous papers of this series: QXAnd, DY Cet, MR Del, HI Dra, DD Mon, V868 Mon, ER Ori, and Y Sex. Foranother seven systems (TT Cet, AA Cet, CW Lyn, V563 Lyr, CW Sge, LV Vir,and MW Vir), phase coverage is insufficient to provide reliable orbitsbut RVs of individual components were measured. Observations of a fewcomplicated systems observed throughout the David Dunlap Observatory(DDO) close binary program are also presented; among them is anespecially interesting multiple system V857 Her which—in additionto the contact binary—very probably contains one or more subdwarfcomponents of much earlier spectral type. All suspected binaries whichwere found to be most probably pulsating stars are briefly discussed interms of mean RVs and projected rotation velocities (vsin i) as well asspectral-type estimates. In two of them, CU CVn and V752 Mon, thebroadening functions show a clear presence of nonradial pulsations. Thepreviously missing spectral types for Paper I are given here in additionto such estimates for most of the program stars of this paper.Based on the data obtained at the David Dunlap Observatory, Universityof Toronto, Toronto, Canada.
| Recent Minima of 184 Eclipsing Binary Stars
This paper continues the publication of times of minima for eclipsingbinary stars from observations reported to the AAVSO Eclipsing BinaryCommittee. Times of minima from observations made from March 2008through August 2008 are presented.
| Recent Minima of 155 Eclipsing Binary Stars
The AAVSO's publication of times of minima for eclipsing binary stars has shifted from the recent publication series, Observed Minima Timings of Eclipsing Binaries, Number 1-12, back to the JAAVSO. Times of minima fromobservations made in the past eight months are presented. New lightelements for AC CMi have been calculated from recent AAVSO observations:Min(JD) = 2451978.7504 + 0.867216691 E± 0.0004 ± 0.00000024
| Angular momentum and mass evolution of contact binaries
Various scenarios of contact binary evolution have been proposed in thepast, giving hints of (sometimes contradictory) evolutionary sequencesconnecting A- and W-type systems. As the components of close detachedbinaries approach each other and contact binaries are formed, followingevolutionary paths transforms them into systems of two categories:A-type and W-type. The systems evolve in a similar way but underslightly different circumstances. The mass/energy transfer rate isdifferent, leading to quite different evolutionary results. Analternative scenario of evolution in contact is presented and discussed,based on the observational data of over one hundred low-temperaturecontact binaries. It results from the observed correlations amongcontact binary physical and orbital parameters. Theoretical tracks arecomputed assuming angular momentum loss from a system via stellar wind,accompanied by mass transfer from an advanced evolutionary secondary tothe main-sequence primary. A good agreement is seen between the tracksand the observed graphs. Independently of details of the evolution incontact and a relation between A- and W-type systems, the ultimate fateof contact binaries involves the coalescence of both components into asingle fast rotating star.
| Comparative statistics and origin of triple and quadruple stars
The statistics of catalogued quadruple stars consisting of two binaries(hierarchy 2 + 2), is studied in comparison with triple stars, withrespective sample sizes of 81 and 724. Seven representative quadruplesystems are discussed in greater detail. The main conclusions are asfollows. (i) Quadruple systems of ? Lyr type with similar massesand inner periods are common, in 42 per cent of the sample the outermass ratio is above 0.5 and the inner periods differ by less than 10times. (ii) The distributions of the inner periods in triple andquadruple stars are similar and bimodal. The inner mass ratios do notcorrelate with the inner periods. (iii) The statistics of outer periodsand mass ratios in triples and quadruples are different. The medianouter mass ratio in triples is 0.39 independently of the outer period,which has a smooth distribution. In contrast, the outer periods of 25per cent quadruples concentrate in the narrow range from 10 to 100yr,the outer mass ratios of these tight quadruples are above 0.6 and theirtwo inner periods are similar to each other. (iv) The outer and innermass ratios in triple and quadruple stars are not mutually correlated.In 13 per cent of quadruples both inner mass ratios are above 0.85(double twins). (v) The inner and outer orbital angular momenta andperiods in triple and quadruple systems with inner periods above 30dshow some correlation, the ratio of outer-to-inner periods is mostlycomprised between 5 and 104. In the systems with small periodratios the directions of the orbital spins are correlated, while in thesystems with large ratios they are not. The properties of multiple starsdo not correspond to the products of dynamical decay of small clusters,hence the N-body dynamics is not the dominant process of theirformation. On the other hand, rotationally driven (cascade)fragmentation possibly followed by migration of inner and/or outerorbits to shorter periods is a promising scenario to explain the originof triple and quadruple stars.
| a Photometric Study of the Neglected Eclipsing Binary BS Cassiopeiae
We present multicolor charge-coupled device (CCD) photometry for theeclipsing binary BS Cassiopeiae, observed on four nights between 2007December and 2008 January. Using the Wilson-Devinney program, thephotometric solution was derived from our BVR observations. Photometricresults indicated that BS Cas is a W-subtype binary, whose mass ratioand overcontact degree are q = 0.2834(±0.0010) and f =31.6%(±1.1%), respectively. Light curves of BS Cas present atypical O'Connell effect, which may be attributed to dark spot activityof the primary component. A detailed period analysis reveals that thereexists a cyclic variation overlaying a secular period decrease, based oneither all available light minimum times or recent light minimum timessince 1989. The low-amplitude cyclic variation with a period of about 13yr can be explained by either the light-time effect or cyclic magneticactivity of both components. The long-term orbital period decreasesuggests that BS Cas is undergoing mass transfer from the primarycomponent to the secondary one. With its mass transfer and accompanyingangular momentum loss, this binary will evolve into a deeper contactconfiguration.
| The evolutionary status of W Ursae Majoris-type systems
Well-determined physical parameters of 130 W Ursae Majoris (W UMa)systems were collected from the literature. Based on these data, theevolutionary status and dynamical evolution of W UMa systems areinvestigated. It is found that there is no evolutionary differencebetween W- and A-type systems in the M-J diagram, which is consistentwith the results derived from the analysis of observed spectral type andof M-R and M-L diagrams of W UMa systems. M-R and M-L diagrams of W- andA-type systems indicate that a large amount of energy should betransferred from the more massive to the less massive component, so thatthey are not in thermal equilibrium and undergo thermal relaxationoscillation. Moreover, the distribution of angular momentum, togetherwith the distribution of the mass ratio, suggests that the mass ratio ofthe observed W UMa systems decreases with decreasing total mass. Thiscould be the result of the dynamical evolution of W UMa systems, whichsuffer angular momentum loss and mass loss as a result of the magneticstellar wind. Consequently, the tidal instability forces these systemstowards lower q values and finally to rapidly rotating single stars.
| Times of Minima for Neglected Eclipsing Binaries 2006-2007
CCD minima observations of eclipsing binaries during 2006-2007 for anumber of neglected eclipsing binaries are presented.
| Contact Binaries with Additional Components. III. A Search Using Adaptive Optics
We present results of the Canada-France-Hawaii Telescope adaptive optics(AO) search for companions of a homogeneous group of contact binarystars, as a contribution to our attempts to prove the hypothesis thatthese binaries require a third star to become as close as observed. Inaddition to directly discovering companions at separations of>=1″, we introduced a new method of AO image analysis utilizingdistortions of the AO diffraction ring pattern at separations of0.07″-1″. Very close companions, with separations in thelatter range, were discovered in the systems HV Aqr, OO Aql, CK Boo, XYLeo, BE Scl, and RZ Tau. More distant companions were detected in V402Aur, AO Cam, and V2082 Cyg. Our results provide a contribution to themounting evidence that the presence of close companions is a very commonphenomenon for very close binaries with orbital periods <1 day.Based on observations obtained at the Canada-France-Hawaii Telescope,which is operated by the National Research Council of Canada, theInstitut National des Sciences de l'Univers of the Centre National de laRecherche Scientifique of France, and the University of Hawaii.
| B.R.N.O. Contributions #34
Not Available
| Absolute Properties of the Binary System BB Pegasi
We present ground-based photometry of the low-temperature contact binaryBB Peg. We collected all the times of mid-eclipse available in theliterature and combined them with those obtained in this study. Analysesof the data indicate a period increase of(3.0+/-0.1)×10-8 days yr-1. This periodincrease of BB Peg can be interpreted in terms of the mass transfer2.4×10-8 Msolar yr-1 from theless massive to the more massive component. The physical parameters havebeen determined as Mc=1.42 Msolar,Mh=0.53 Msolar, Rc=1.29Rsolar, Rh=0.83 Rsolar,Lc=1.86 Lsolar, and Lh=0.94Lsolar through simultaneous solutions of light and of theradial velocity curves. The orbital parameters of the third body, whichorbits the contact system in an eccentric orbit, were obtained from theperiod variation analysis. The system is compared to the similarbinaries in the Hertzsprung-Russell and mass-radius diagrams.
| New Minima Times of Selected Eclipsing Binaries
We present 169 CCD and photoelectric times of minima of selectedeclipsing binaries obtained from 2005 to 2007 at observatories inSlovakia
| Formation and Evolution of W Ursae Majoris Contact Binaries
The origin and evolution of W UMa systems are discussed based on All SkyAutomated Survey (ASAS) data and the mean kinematic ages of foursubgroups of 97 field contact binaries (FCBs). The period distributionof eclipsing binaries discovered by ASAS suggests that a period limit totidal locking for the close binaries is about 2.24 days, so that most WUMa systems might be formed from detached binaries with periodsP<~2.24 days, and a maximum advanced time from a detached system to aW UMa is about 3.23 Gyr. Moreover, the secular evolution of the angularmomentum (AM), the system mass, and the orbital period of 97 FCBs wereinvestigated according to the mean kinematic ages, which were setaccording to AM bins. AMs, systemic masses, and orbital periods wereshown to be decreasing with kinematic age. Their first-order decreasingrates have been determined as J˙/J=1.86×10-10yr-1, M˙/M=0.95×10-10 yr-1,and P˙/P=1.24×10-10 yr-1, and theaverage amplification (A¯=dlnJ/dlnM) is derived to be 1.96. Theseare lower than those derived from detached chromospherically activebinaries (CABs). This suggests that the magnetic activity level of FCBsis indeed weaker than that of CABs. Meanwhile, the decreasing rate of AMof FCBs is found to be equal to an average value in a cycle of a cyclicmodel of contact binaries. This might suggest that the evolution of FCBsundergoes thermal relaxation oscillation (TRO) and that the coalescenceof W UMa systems is a very long process, which is also indicated by thedynamical evolution of FCBs.
| New Times of Minima of Some Eclipsing Binary Stars
Not Available
| Dynamical evolution of active detached binaries on the logJo-logM diagram and contact binary formation
Orbital angular momentum (OAM, Jo), systemic mass (M) andorbital period (P) distributions of chromospherically active binaries(CAB) and W Ursae Majoris (W UMa) systems were investigated. Thediagrams of and logJo-logM were formed from 119 CAB and 102 WUMa stars. The logJo-logM diagram is found to be mostmeaningful in demonstrating dynamical evolution of binary star orbits. Aslightly curved borderline (contact border) separating the detached andthe contact systems was discovered on the logJo-logM diagram.Since the orbital size (a) and period (P) of binaries are determined bytheir current Jo, M and mass ratio, q, the rates of OAM loss(dlogJo/dt) and mass loss (dlogM/dt) are primary parametersto determine the direction and the speed of the dynamical evolution. Adetached system becomes a contact system if its own dynamical evolutionenables it to pass the contact border on the logJo-logMdiagram. The evolution of q for a mass-losing detached system is unknownunless the mass-loss rate for each component is known. Assuming q isconstant in the first approximation and using the mean decreasing ratesof Jo and M from the kinematical ages of CAB stars, it hasbeen predicted that 11, 23 and 39 per cent of current CAB stars wouldtransform to W UMa systems if their nuclear evolution permits them tolive 2, 4 and 6 Gyr, respectively.
| 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.
| New Times of Minima of Some Eclipsing Binary Systems
We present 42 photoelectric minima observations of 24 eclipsingbinaries.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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.
| 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.
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Observation and Astrometry data
| Constellation: | Pegasus |
| Right ascension: | 22h22m56.89s |
| Declination: | +16°19'27.8" |
| Apparent magnitude: | 11.175 |
| Proper motion RA: | 23.9 |
| Proper motion Dec: | -23.8 |
| B-T magnitude: | 11.797 |
| V-T magnitude: | 11.227 |
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