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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.
| A comprehensive photometric study of the Algol-type eclipsing binary: BG Pegasi
This study presents new photometric observations of classical Algol typebinary BG Peg with a ? Scuti component. The light curve modelingwas provided with the physical parameters of the component stars in theBG Peg system for the first time. After modeling light curves in B and Vfilters, the eclipse and proximity effects were removed from the lightcurve to analyze intrinsic variations caused by the hotter component ofthe system. Frequency analysis of the residuals light represents themulti-mode pulsation of the more massive component of the BG Peg systemat periods of 0.039 and 0.047 days. Two frequencies could be associatedwith non-radial (l = 2) modes. The total amplitude of the pulsationalvariability in the V light curve was found to be about 0.045 mag. Thelong-term orbital period variation of the system was also investigatedfor the first time. The O-C analysis indicates periodic variationsuperimposed on a downward parabola. The secular period variation meansthat the orbital period of the system is decreasing at a rate of-5.5 seconds per century, probably due to the magnetic activity ofthe cooler component. The tilted sinusoidal O-C variation may be causedby the gravitational effect of an unseen component around the system.
| BAV-Results of observations - Photoelectric minima of selected eclipsing binaries and maxima of pulsating stars.
Not Available
| 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.
| 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.
| Absolute parameters of the Algol binary Z Vul
Spectra in the wavelength range 4230-9150 Å and the firstlight curves of Z Vul in the infrared J, H and K bands are presented.Our infrared JHK light curves and radial velocities, together withpublished radial velocity and UBV data are analyzed in order todetermine a new set of stellar parameters. This allows us to determinenew absolute parameters of the stellar components, the interstellarreddening and the distance to the system. We discuss the rotation of theprimary star, finding that must be rotating faster than synchronous.From the visual-infrared photometry we find no evidence of IRexcess in the system.
| B.R.N.O. Contributions #36, Times of minima
Not Available
| BAV-Results of observations - Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| 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.
| B.R.N.O. Times of minima
Not Available
| 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.
| Identification, Classifications, and Absolute Properties of 773 Eclipsing Binaries Found in the Trans-Atlantic Exoplanet Survey
In recent years, we have witnessed an explosion of photometrictime-series data, collected for the purpose of finding a small number ofrare sources, such as transiting extrasolar planets and gravitationalmicrolenses. Once combed, these data are often set aside, and are notfurther searched for the many other variable sources that theyundoubtedly contain. To this end, we describe a pipeline that isdesigned to systematically analyze such data, while requiring minimaluser interaction. We ran our pipeline on a subset of the Trans-AtlanticExoplanet Survey dataset, and used it to identify and model 773eclipsing binary systems. For each system we conducted a joint analysisof its light curve, colors, and theoretical isochrones. This analysisprovided us with estimates of the binary's absolute physical properties,including the masses and ages of their stellar components, as well astheir physical separations and distances. We identified three types ofeclipsing binaries that are of particular interest and merit furtherobservations. The first category includes 11 low-mass candidates, whichmay assist current efforts to explain the discrepancies between theobservation and the models of stars at the bottom of the main sequence.The other two categories include 34 binaries with eccentric orbits, and20 binaries with abnormal light curves. Finally, this uniform catalogenabled us to identify a number of relations that provide furtherconstraints on binary population models and tidal circularizationtheory.
| B.R.N.O. Contributions #34
Not Available
| A period study and light-curve synthesis for the Algol-type semidetached binary XXCephei
We obtained CCD photometric observations of the Algol-type semidetachedbinary XXCephei (XXCep) during 15 nights from 2002 September 17 to 2003February 2, and also on 2005 January 21. Except for those data taken onthe last night of the concentrated observing season, the 3881measurements were obtained over an interval of only 106 nights. Fromthese data, four new times of minimum light were calculated. The (O- C)diagram formed from all available timings, and thus the orbital periodof the system, can be partly represented as a beat effect between twocyclical variations with different periods (yr, yr) and amplitudes(K1=0.015d, K2=0.103d), respectively. Bothphysical and non-physical interpretations of these cycles wereinvestigated. The long-term sinusoidal variation is too long formagnetic cycling in solar-type single and close binary stars. Inaddition, we have studied the effect of a possible secular periodvariation. By analysing the residuals from our Wilson-Devinney (WD)binary model, we found small light variations with a period of 5.99dwith amplitudes growing toward longer wavelengths. We think that theseoscillations may be produced by instabilities at the systemicL1 point (also occupied by the point of the cool star) andthat these instabilities are, in turn, caused by non-uniform andsporadic convection. There is also a short-period oscillation of about45min in the WD light residuals that is attributed to accretion on tothe mass-gaining primary component from a feeble gas stream originatingon the cool donor star.
| New Times of Minima of Eclipsing Binary Systems
We present 82 photoelectric minima observations of 34 eclipsingbinaries.
| 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.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| An Algol type binary with a δ Scuti component: RZ Cassiopeiae revisited
We present new BV photometry and spectroscopic observations of RZCassiopeiae. The light and radial velocity curves were formed by the newobservations which have been analyzed simultaneously by using theWilson-Dewinney code. The non-synchronous rotational velocityv1sin i = 76 ± 6 km s-1, deduced for theprimary component from the new spectroscopic observations, was alsoincorporated in the analysis. A time-series analysis of the residuallight curves revealed the multi-periodic pulsations of the primarycomponent of RZ Cas. The main peak in the frequency spectrum wasobserved at about 64.197 c d-1 in both B and V bands. Thepulsational constant was calculated to be 0.0116 days. This valuecorresponds to high overtones (n˜6) of non-radial modeoscillations. We find significant changes in the pulsational amplitudeof the primary component from year to year. The peak-to-peak pulsationalamplitude of the main frequency displays a decrease from 0.013 m in 2000to 0.002 m in 2001 and thereafter we have found an increase again in theamplitude to 0.01 m in the year 2002. We propose the mass transfer fromthe cool secondary to the pulsating primary as a possible explanationfor such remarkable changes in the pulsational behavior of the primarycomponent.
| A catalogue of close binaries located in the δ Scuti region of the Cepheid instability strip
A catalogue of close eclipsing binary systems (detached andsemidetached) with at least one of the components located in the δScuti region of the Cepheid instability strip is presented. Thepositions of the stars in the instability strip are determined by theiraccurate temperatures and luminosities. Observationally detectedbinaries (20 semidetached, four detached and one unclassified) withoscillating components were included in the catalogue as a separatetable. The primaries of the oscillating Algols tend to be located nearthe blue edge of the instability strip. Using reliable luminosities andtemperatures determined by recent photometric and spectroscopic studies,we have found that at least one or two components of 71 detached and 90semidetached systems are located in the δ Scuti region of theCepheid instability strip. In addition, 36 detached or semidetachedsystems discovered by the Hipparcos satellite were also given as aseparate list. One of their components is seen in the δ Scutiregion, according to their spectral type or B - V colours. They arepotential candidate binaries with the δ Scuti-type pulsatingcomponents which need further photometric and spectroscopic studies inbetter precision. This catalogue covers information and literaturereferences for 25 known and 197 candidate binaries with pulsatingcomponents.
| The connection between the pulsational and orbital periods for eclipsing binary systems
Considering a sample of 20 eclipsing binary systems with δ Scutitype primaries, we discovered that there is a possible relation amongthe pulsation periods of the primaries and the orbital periods of thesystems. According to this empirical relation, the longer the orbitalperiod of a binary, the longer the pulsation period of its pulsatingprimary. Among the sample, the masses of the secondaries and theseparations between the components are known for eight systems for whicha logPpuls versus logF (the gravitational pull exerted pergram of the matter on the surface of the primaries by the secondaries)diagram also verifies such an interrelation between the periods. So, asthe gravitational force applied by the secondary component onto thepulsating primary increases, its pulsation period decreases. Thedetailed physics underlying this empirical relation between the periodsneeds further confirmation, especially theoretically. However, one mustalso consider the fact that the present sample does not contain asufficiently large sample of longer period (P > 5 d) binaries.
| BVR observations and period variation of the near-contact binary ZZ Aurigae
BVR light curves of ZZ Aurigae were obtained with the 60-cm Cassegrainreflector at the Sobaek Observatory, Korea, between 2000 February and2001 February. All collected times of minimum light, including ourobservations, were used for the period study. The period variation couldbe of quasi-sinusoidal form superposed on an upward parabola. Acontinuous period increase of dP/dt=+2.3 × 10-8 dyr-1 was determined for ZZ Aur. The period ofquasi-sinusoidal variation is about ~26-31 yr. Photometric solutionswere found using the Wilson-Devinney method. The Roche configuration ofZZ Aur is that of an Algol-type semidetached system where the primarystar nearly fills its Roche lobe and the secondary star fills its lobe.The spot model was used to explain the asymmetry in the light curveknown as the O'Connell effect.
| 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.
| Precise CCD Times of Minima of Selected Eclipsing Binaries
We present 135 precise CCD minima timings for 93 eclipsing binariesobtained at Ondrejov observatory during 2003-2004.
| Gravity-darkening exponents in semi-detached binary systems from their photometric observations. II.
This second part of our study concerning gravity-darkening presents theresults for 8 semi-detached close binary systems. From the light-curveanalysis of these systems the exponent of the gravity-darkening (GDE)for the Roche lobe filling components has been empirically derived. Themethod used for the light-curve analysis is based on Roche geometry, andenables simultaneous estimation of the systems' parameters and thegravity-darkening exponents. Our analysis is restricted to theblack-body approximation which can influence in some degree theparameter estimation. The results of our analysis are: 1) For four ofthe systems, namely: TX UMa, β Per, AW Cam and TW Cas, there is avery good agreement between empirically estimated and theoreticallypredicted values for purely convective envelopes. 2) For the AI Drasystem, the estimated value of gravity-darkening exponent is greater,and for UX Her, TW And and XZ Pup lesser than corresponding theoreticalpredictions, but for all mentioned systems the obtained values of thegravity-darkening exponent are quite close to the theoretically expectedvalues. 3) Our analysis has proved generally that with the correction ofthe previously estimated mass ratios of the components within some ofthe analysed systems, the theoretical predictions of thegravity-darkening exponents for stars with convective envelopes arehighly reliable. The anomalous values of the GDE found in some earlierstudies of these systems can be considered as the consequence of theinappropriate method used to estimate the GDE. 4) The empiricalestimations of GDE given in Paper I and in the present study indicatethat in the light-curve analysis one can apply the recent theoreticalpredictions of GDE with high confidence for stars with both convectiveand radiative envelopes.
| Development of a 1-m Robotic Telescope System
Korea Astronomy & Space Science Institute (KASI) has installed a 1-mrobotic telescope at Mt. Lemmon, AZ, in collaboration with a company,Astronomical Consultants & Equipment, Inc (ACE). The telescopesystem is totally designed to make fully robotic observations, and canbe operated in both interactive and unattended robotic modes. Thetelescope is newly designed and manufactured regarding both mechanicaland optical parts. The optical system is designed to collect 80% of theincident light within 0.''5 with an f/7.5 Ritchey-Chretien design. Thetelescope mount is an equatorial fork with a friction drive system, andit allows fully programmable tracking speeds with a typical range of15'' s-1 and an accuracy of ±5''hr-1. Themount system includes an integral pointing model to correct formechanical errors and misalignments, and an auto-guide unit is alsoavailable. To gather environmental information a weather station and anall sky camera are installed at the site. In this paper we introduce thesystem design and the performance of the mechanical and optical qualityof the telescope system based on the results of test observations usingsome variable stars.
| Minima Kurt Locher 2004-2005
Minima observed 2004..2005 by Kurt Locher visually, not accepted by IBVSas part of BBSAG Bulletin.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| On a short-periodic pulsating component in the Algol-type eclipsing binary system VV UMa
We discuss on a short-periodic pulsating component in the Algol-typeeclipsing binary system VV UMa
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