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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.
| Coronal Activity from the ASAS Eclipsing Binaries
We combine the catalog of eclipsing binaries from the All Sky AutomatedSurvey (ASAS) with the ROSAT All Sky Survey (RASS). The combinationresults in 836 eclipsing binaries that display coronal activity and isthe largest sample of active binary stars assembled to date. By usingthe (V-I) colors of the ASAS eclipsing binary catalog, we are able todetermine the distances and thus bolometric luminosities for themajority of eclipsing binaries that display significant stellaractivity. A typical value for the ratio of soft X-ray to bolometricluminosity is LX/Lbol? a few×10-4, similar to the ratio of soft X-ray to bolometricflux FX/Fbol in the most active regions of theSun. Unlike rapidly rotating isolated late-type dwarfs - stars withsignificant outer convection zones - a tight correlation between Rossbynumber and activity of eclipsing binaries is absent. We find evidencefor the saturation effect and marginal evidence for the so-called``super-saturation'' phenomena. Our work shows that wide-field stellarvariability searches can produce a high yield of binary stars withstrong coronal activity.The combined ASAS and RASS catalog, as well as the results of this workare available for download.
| 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.
| 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.
| V781 Tauri: a W Ursae Majoris binary with decreasing period
We analyze light curves of the W UMa type eclipsing binary V781 Taurifrom three epochs and radial velocity curves from two epochssimultaneously, including previously unpublished B and V data. Theoverall time span is from 1983 to 2000 and the solution is donecoherently in time (not phase) with five light curves and two sets ofprimary and secondary velocity curves. Minor systematic differencesamong the individual light curves are not large enough to undermine thevalue of a coherent solution that represents 18 years of observations.Times of minima confirm a period of 0.34491d and the general solutionfinds a small period change, dP/P, of(5.08±{04})×10-11 that represents recentbehavior. The eclipse timings cover the last half-century and find dP/Pabout four times smaller, corresponding to a period change time scale,P/(dP/dt) of about 6 million years. The system is over-contact with afilling factor of 0.205. The solution produces a temperature differenceof about 260 K between the components, an inclination of 65.9dg, and amass ratio M_2/M_1=2.47. Separate solutions of the several light curvesthat incorporate dark spots find parameters that differ little fromcurve to curve. Absolute masses, luminosities, radii and the distanceare derived, with luminosities and distance based on star 1 being oftype G0V. The orbital angular momentum is compared with those of other WUMa type binaries and is normal. The star to star mass flow that one caninfer from dP/dt is opposite to that expected from TRO (ThermalRelaxation Oscillator) theory, but pertains to a time span that is veryshort compared to the time scale of TRO oscillations.
| 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.
| Catalogue of the orbital elements, masses, and luminosities for short-periodic RS CVn-type eclipsing systems
New data on the orbital elements, masses, and luminosities werecollected for 31 pre-contact binary systems of short-periodic {RS}{CVn}-type. We treat the catalogued data statistically in order toaccurately define the properties and evolutionary status of each classsystem. The ages of pre-contact systems were estimated by the isochronemethod. Numerous comments and bibliographic references to the catalogueare also included.
| Times of Minima for Neglected Eclipsing Binaries in 2004
Times of minima obtained during 2004 for a number of neglected eclipsingbinaries are presented.
| 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
| Up-to-Date Linear Elements of Eclipsing Binaries
About 1800 O-C diagrams of eclipsing binaries were analyzed and up-todate linear elements were computed. The regularly updated ephemerides(as a continuation of SAC) are available only in electronic form at theInternet address: http://www.as.ap.krakow.pl/ephem/.
| 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.
| 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.
| 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.
| 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.
| 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.
| 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.
| The Variable Period of V366 Cassiopeiae
Not Available
| Absolute Magnitude Calibration for the W UMa-Type Systems Based on HIPPARCOS Data
Hipparcos parallax data for 40 contact binary stars of the W UMa-type(with epsilon M_V < 0.5) are used to derive a new, (B-V)-basedabsolute-magnitude calibration of the form M_V = M_V(log P,B-V). Thecalibration covers the ranges 0.26 < (B-V)_0 < 1.14, 0.24 < P< 1.15 day, and 1.4 < M_V < 6.1; it is based on a solutionweighted by relative errors in the parallaxes (2.7% to 24%). Previouscalibrations have not been based on such a wide period and color space,and while they have been able to predict M_V with sufficient accuracyfor systems closely following the well-known period-color relation, thenew calibration should be able to give also good predictions for moreexotic ``outlying'' contact binary systems. The main limitations of thiscalibration are the inadequate quality of the ground-based photometricdata, and the restriction to the (B-V) index, which is more sensitive tometallicity effects than the (V-I) index; metallicities are, however,basically unknown for the local W UMa-type systems. (SECTION: Stars)
| The properties of W Ursae Majoris contact binaries: new results and old problems.
The physical properties of W UMa binary systems are revisited on thebasis of the observational data published in the last decade and of therecent theoretical studies on angular-momentum-loss-driven secularevolution. The absolute elements (masses, radii, luminosities) arederived by an inference method and a calibration based on the availablehigh quality spectroscopic orbits. The derived age (8Gy) agrees with theestimate of Guinan and Bradstreet from space motions. The analysis ofthe resulting physical parameters shows little correlation between thestandard classification in A and W subtype (first proposed by Binnendijk(1970) and only related to the light curve morphology) and theevolutionary status and origin of the systems. Most A-subtype systemsseem to have no evolutionary link with W-subtype ones. The relationbetween total mass and mass ratio for the "bona fide" sample alsosuggests that mass loss from the system may play an important role.
| The structure of late-type contact binaries
A unified treatment of late-type and early-type contact binaries basedon the assumption of hydrostatic equilibrium is extended here andapplied to late-type systems assuming systems in a steady state withminimized mass motions. A survey of configurations with M/M(solar) = 2or greater is presented, and the observational facts are shown to agreewith the theory.
| Contact and near-contact binary systems. VII - EZ Hydrae, AD Phoenicis and RS Columbae
BVRIc photometry is presented for three late-type contactbinaries: EZ Hydrae, AD Phoenicis and RS Columbae. EZ Hydrae isidentified as a W-type system of orbital period 0.45 day, while ADPhoenicis and RS Columbae are probably A-type systems, with orbitalperiods of 0.38 and 0.67 day, respectively. Although a value for themass ratio of EZ Hydrae had been obtained from spectroscopicobservations, no photometric solution could be obtained because ofsevere 'disturbances' in its light curve. On the other hand, photometricsolutions were obtained for AD Phoenicis and RS Columbae, but these werevery insensitive to mass ratio, which tended toward the unlikely valueof unity.
| Statistics of categorized eclipsing binary systems Lightcurve shapes, periods, and spectral types
The statistics of the light curve morphologies, eclipse depths, orbitalperiods, and spectral types of about 1000 eclipsing binary systems areexamined, after attempting to subdivide these binaries into variousbasic evolutionary categories. The applicability of statisticalcriteria, based on light curve morphologies and eclipse depths, for thecategorization of eclipsing binaries has been found more limited thanpreviously believed. In particular, EW-type light curves turn out to begood indicators of contact systems (though not conversely), while EA-and EB-type light curves have little physical significance. Moreover,the study reveals a strong deficit of short-period noncontact systems inthe whole spectral range, together with an underabundance of early-typecontact binaries (compared with the number of late-type contact pairs).Interestingly, the distribution of evolved Algol-type systems isshifted, on average, to periods longer than those of unevolved detachedsystems in the OB and early A spectral range (and to shorter periods inthe F spectral range).
| Violet and ultraviolet continua of W UMa systems on the basis of UVBY photometry observations
New observations of 17 southern WUMa systems are discussed together withprevious uvby data for 44 systems to determine properties of violet andultraviolet spectral distributions and to relate them to theperiod-color relation. The interstellar-reddening-corrected delta(m1)values extend from -0.02 to +0.10, which could be interpreted by aplausible range of metallicities; the most positive values of delta(m1)and largest ultraviolet excesses are observed for systems having theshortest periods at a given spectral type. The reddening-correcteddelta(c1) values are close to zero and are only slightly positive forearlier spectral types - mean delta (cl) = +0.04 for (b-y)O less than0.31 - indicating only very slight evolutionary advancement. Traces of adelta(cl) = -delta(ml) correlation for least evolved systems - smallestdelta(cl) - leave the possibility of intrinsic excesses still open.
| A uvby, beta photometric survey of southern hemisphere
A uvby, beta photometric study of southern hemisphere eclipsing binarystars has been undertaken at Cerro Tololo Inter-American Observatory.The standardized colors and V magnitudes for 288 binaries at quadratureand/or at minimum are presented, along with an indication of theaccuracy of the standardization and photometry. Discussions of theresolving time of the pulse-counting photometers and of the atmosphericextinction at CTIO are included.
| A catalogue of parameters for eclipsing binaries
Not Available
| RS Columbae, A New W Ursae Majoris System
Not Available
| Louisiana State University Observatory Baton Rouge.
Not Available
| Metal-to-H ratios in the Galaxy as indicated by narrow-band photometry of Cepheids.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1966AJ.....71..615W&db_key=AST
| Southern Cepheid Photometry.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1961ApJS....6..253I&db_key=AST
| La répartition galactique des céphéides
Not Available
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| Görünürdeki Parlaklýk: | 9.683 |
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