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Recent Minima of 146 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 Times of minima from observations made from October 2010 thruMarch 2011, along with a few unpublished times of minima from olderdata, are presented.
| Random forest automated supervised classification of Hipparcos periodic variable stars
We present an evaluation of the performance of an automatedclassification of the Hipparcos periodic variable stars into 26 types.The sub-sample with the most reliable variability types available in theliterature is used to train supervised algorithms to characterize thetype dependencies on a number of attributes. The most useful attributesevaluated with the random forest methodology include, in decreasingorder of importance, the period, the amplitude, the V-I colour index,the absolute magnitude, the residual around the folded light-curvemodel, the magnitude distribution skewness and the amplitude of thesecond harmonic of the Fourier series model relative to that of thefundamental frequency. Random forests and a multi-stage scheme involvingBayesian network and Gaussian mixture methods lead to statisticallyequivalent results. In standard 10-fold cross-validation (CV)experiments, the rate of correct classification is between 90 and 100per cent, depending on the variability type. The main mis-classificationcases, up to a rate of about 10 per cent, arise due to confusion betweenSPB and ACV blue variables and between eclipsing binaries, ellipsoidalvariables and other variability types. Our training set and thepredicted types for the other Hipparcos periodic stars are availableonline.
| 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 Times of minima from observations made from March 2010 throughSeptember 2010, along with a few unpublished times of minima from olderdata, are presented.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.
| BAV-Results of Observations - Photoelectric minima of selected eclipsing binaries and maxima of pulsating stars.
Not Available
| The most plausible explanation of the cyclic period changes in close binaries: the case of the RS CVn-type binary WW Dra
Cyclic period changes are a fairly common phenomenon in close binarysystems and are usually explained as being caused either by the magneticactivity of one or both components or by the light travel time effect(LTTE) of a third body. We searched the orbital period changes in 182EA-type (including the 101 Algol systems used by Hall), 43 EB-type and53 EW-type binaries with known mass ratio and spectral type of thesecondary component. We reproduced and improved the diagram in Hallaccording to the new collected data. Our plots do not support theconclusion derived by Hall that cyclic period changes are restricted tobinaries having a secondary component with spectral type later than F5.The presence of period changes among systems with a secondary componentof early type indicates that magnetic activity is one, but not the only,cause of the period variation. It is discovered that cyclic periodchanges, probably resulting from the presence of a third body, are morefrequent in EW-type binaries among close systems. Therefore, the mostplausible explanation of the cyclic period changes is the LTTE throughthe presence of a third body. Using the century-long historical recordof the times of light minimum, we analysed the cyclic period change inthe Algol binary WW Dra. It is found that the orbital period of thebinary shows a ~112.2-yr cyclic variation with an amplitude of ~0.1977d.The cyclic oscillation can be attributed to the LTTE by means of a thirdbody with a mass no less than 6.43Msolar. However, nospectral lines of the third body were discovered, indicating that it maybe a candidate black hole. The third body is orbiting the binary at adistance closer than 14.4 au and may play an important role in theevolution of this system.
| Revision of the photometric parameters of BS Cassiopeiae
Seven charge-coupled device (CCD) photometric times of light minimum ofthe overcontact binary BS Cas which were obtained from 2007 August toNovember and one CCD light curve in the R band which was observed on2007 September 24 and October 15, are presented. It is found that thelight curve of BS Cas has characteristics like a typical EW-type lightvariation. The light curve obtained by us is symmetric and shows totaleclipses, which is very useful for determining photometric parameterswith high precision. Photometric solutions were derived by using the2003 version of the Wilson-Devinney code. It shows that BS Cas is aW-subtype overcontact binary (f = 27.5% ± 0.4%) with a mass ratioof q = 2.7188 ± 0.0040. The temperature difference between thetwo components is 190 K. Analysis of the O-C curve suggests that theperiod of AE Phe shows a long-term continuous decrease at a rate ofdP/dt = -2.45 × 10-7 dyr-1. The long-time period decrease can be explained bymass transfer from the primary to the secondary.
| 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.
| Period Changes of DF Hydrae: Evidence of Mass Transfer and the Presence of a Cool Tertiary Companion
Combining our six new determined times of light minimum obtained from2001 to 2007 with others compiled from the literature, we investigatedthe period changes of DF Hydrae. The general trend of the O - C curvebased on all available data reveals that the period of the binary staris increasing continuously at a rate of dP/dt = + 1.11(±0.02)× 10-7dyr-1. After the long-term periodincrease was removed from the O - C diagram, it was discovered that theresiduals of the CCD and photoelectric observations suggest asmall-amplitude cyclic oscillation with a period of 21.5years. Thecontinuous period increase can be explained by mass transfer from thesecondary to the primary, indicating that DF Hydrae is on theTRO-controlled stage of the evolutionary scenario proposed by Qian. Thecyclic period variation suggests that DF Hydrae is a triple systemcontaining a cool tertiary component with a mass of M3sin i'= 0.21Modot in a 21.5-year orbit. By removing angularmomentum from the central binary system via Kozai oscillation or acombination of the Kozai cycle and tidal friction, the tertiarycompanion may play an important role for the formation and evolution ofthe contact system, which makes the eclipsing pair to have a shortinitial orbital period (i.e., P < 5d). In that case, thedetached progenitor of DF Hydrae evolves into the present contactconfiguration via a combination of magnetic braking and a case A masstransfer.
| An Orbital Period Investigation of the Solar-Type Overcontact Binary V700 Cygni
Not Available
| 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.
| BAV-Results of observations - Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Orbital Period Changes and Their Evolutionary Status for Weak-Contact Binaries. II. CC Comae Berenices and BV Draconis
Based on O - C curves, we present detailed period investigationsof two weak-contact binaries CC Com and BV Dra. It is found that theperiods of these two binaries have varied in a cyclic variation waysuperposed on a secular period change. The periods and amplitudes of thecyclic variations are P 3 = 23.6(±0.4) yr and A =0fd0028(±0fd0003) for CC Com and P 3 =23.8(±0.6) yr and A = 0fd0029(±0fd0003) for BV Dra. Thecyclic oscillations for these two stars may be attributed to thelight-time effect via an unseen third body, which could extract angularmomentum from the central system. If the existence of the additionalbody is true, CC Com and BV Dra may be triple system stars. For CC Com,the secular period decrease rate is dP/dt = -0.20 ×10-7 d yr-1, which suggests that themass transfers from the more massive component to the less massive one,accompanied with the angular momentum loss due to mass outflow from L2. A decrease in its orbital period will result in theshrinking of the inner and outer critical Roche lobes, and then causethe contact degree to increase. This kind of weak-contact binary with along-term period decrease may evolve into a deep contact configuration.For BV Dra, the continuous period increase rate is dP/dt = +0.29 ×10-7 d yr-1, indicating that the masstransfers from the less massive component to the more massive one. Anincrease in its orbital period may cause the separation between bothcomponents to increase, and thus the contact configuration will break,as predicted by thermal relaxation oscillation theory. Therefore, thiskind of weak-contact binary with a secular period increase will evolveinto a broken-contact configuration.
| 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.
| 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.
| High Fill-Out, Extreme Mass Ratio Overcontact Binary Systems. VIII. EM Piscium
CCD photometric observations of the newly discovered close binary, EMPiscium, obtained from 2006 December 4 to 2008 January 7, are presented.The light curves are symmetric and show complete eclipses with aneclipse duration of 54 minutes. When comparing the present light curveswith those published by González-Rojas et al., it is found thatthe depths of the two minima of the light curve have been interchanged,and the positive O'Connell effect has disappeared. The symmetric lightcurves in R and I bands were analyzed with the 2003 version of the W-Dcode. It is found that EM Piscium is a high fill-out overcontact binarysystem (f = 95.3 ± 2.7%) with an extreme mass ratio of q =0.1487, suggesting that it is on the late evolutionary stage oflate-type tidal-locked binaries. Based on the nine instances of lightminimum that we determined and those published by previousinvestigators, it is discovered that the orbital period shows a cyclicperiod variation with a period of 3.3 years, while it undergoes acontinuously rapid increase at a rate of dP/dt = +3.97 ×10-6 days year-1. The cyclic periodreveals the presence of a tertiary companion, which may play animportant role for the formation and evolution of the overcontact binaryby drawing angular momentum from the central system via Kozaioscillation or a combination of Kozai cycle and tidal friction. The highfill-out, the extreme mass ratio, and the rapid period increase maysuggest that the binary system is quickly evolving into a rapid-rotatingsingle star.
| A Photometric Study of the W UMa-Type Contact Binary RZ Com
We present results of CCD photometric observations of the short-period WUMa-type contact binary system, RZ Com. The light curve of the binaryhas changed from W-subtype to A-subtype from 1998 to 2003, then back toW-subtype in 2004. An analysis was carried out using the 2003 version ofthe Wilson-Devinney code. It is confirmed that RZ Com is a low-degree,overcontact f = 20.1% (+/-7.4%) binary system with a high inclination ofi = 81.°40 (+/-0.°40), and a mass ratio q = 2.351 (+/-0.031).Combining four newly determined times of light minimum with others inthe literature, the variations in orbital period is examined. Asmall-amplitude oscillation (A=0.0065d), with a period of 41.5 year, isdiscovered superimposed on a long-term increase at rate dP/dt =+3.97×10-8d yr-1. The period oscillation canbe explained either by the light-time effect due to the presence of anunseen third body, or by cycles of magnetic activity on the components.Combining our photometric solution with the spectroscopic elementsobtained by Mclean & Hilditch, the absolute dimensions of RZ Comare: M1 = 1.14 (+/-0.19)Modot, M2 =0.50 (+/-0.09)Modot, R1 = 1.12(+/-0.01)Rodot, R2 = 0.78(+/-0.01)Rodot and A = 2.41 (+/-0.02)Rodot.
| Multicolour CCD Photometry of Four RRab Stars
Multicolour CCD observations of three RRab stars are presented.
| 236 Minima Timings of Eclipsing Binaries Observed by Integral OMC
236 times of minima of 97 eclipsing binaries observed by ESA INTEGRALOMC 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
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Deep, Low Mass Ratio Overcontact Binary Systems. VII. QX Andromedae in the Intermediate-Age Open Cluster NGC 752
QX Andromedae is a short-period eclipsing binary in the intermediate-ageopen cluster NGC 752. Charge-coupled device photometric observations ofthe close binary system obtained from 2004 November 13 to 2006 November18 are presented. It is confirmed that the light curves show partialeclipses, and night-to-night intrinsic variations are seen. As in thecase of AH Cancri in the old open cluster M67, the light curve of QX Andseems to change between A and W types. Both the short- and long-termlight variations suggest that QX And shows strong magnetic activity,which is in agreement with its X-ray observations. The symmetric lightcurves in B and V bands obtained the night of 2004 November 13 wereanalyzed with the new version of the W-D code. It is found that QX Andis a deep overcontact binary system with a high degree of overcontact off = 55.9% and a low mass ratio of q = 0.2327, suggesting that it is inthe late stage of overcontact evolution. Based on our 23 times of lightminimum, including four recently published eclipse times, the orbitalperiod of the eclipsing binary was revised. It was discovered that theorbital period shows a continuous period increase at a rate of dP/dt =+2.48 × 10-7 days yr-1, which can beinterpreted as a mass transfer from the less massive component to themore massive one. As the period increases, the mass ratio of the systemwill decrease. It may finally evolve into a rapid-rotating single starwhen it meets the more familiar criterion that the orbital angularmomentum is less than 3 times the total spin angular momentum. Theexistence of QX And in the late evolutionary stage of an overcontactbinary in the intermediate-age open cluster NGC 752 indicates that itmay undergo strong cluster stellar interaction. This means it had a veryshort initial orbital period and could have evolved into the presentevolutionary state within the cluster age. By comparing with theevolutionary state of TX Cnc in M44, it is estimated that the lifetimeof overcontact binaries may be no less than 1 Gyr.
| New Times of Minima of Some Eclipsing Binary Stars
Not Available
| 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
| CCD Minima for Selected Eclipsing Binaries in 2007
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 Stars
Not Available
| Possibility of Ultra High-Energy Cosmic Rays from the Giant Flare in Soft Gamma Repeater 1806-20
On 2004 December 27, a giant flare from the soft gamma repeater 1806-20was observed. The radiation mechanism of the initial peak of the flarewould be controversial. In this letter we point out that veryhigh-energy cosmic rays would be produced in the case that the flare wascaused by internal shocks, as is usually considered for gamma-raybursts. The highest energy of cosmic rays can reach1019eV, if the Lorentz factor of the shocks issufficiently high. Future observations of cosmic rays will inform usabout the mechanism of the giant flare.
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