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.
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Spin angular momentum evolution of the long-period Algols
We consider the spin angular momentum evolution of the accretingcomponents of Algol-type binary stars. In wider Algols the accretion isthrough a disc so that the accreted material can transfer enough angularmomentum to the gainer that material at its equator should be spinningat breakup. We demonstrate that even a small amount of mass transfer,much less than required to produce today's mass ratios, transfers enoughangular momentum to spin the gainer up to this critical rotationvelocity. However the accretors in these systems have spins typicallybetween 10 and 40per cent of the critical rate. So some mechanism forangular momentum loss from the gainers is required. Unlike solar-typechromospherically active stars, with enhanced magnetic activity whichleads to angular momentum and mass loss, the gainers in classical Algolshave radiative envelopes. We further find that normal radiative tidesare far too weak to account for the necessary angular momentum loss.Thus enhanced mass loss in a stellar wind seems to be required tospin-down the gainers in classical Algol systems. We consider generationof magnetic fields in the radiative atmospheres in a differentiallyrotating star and the possibility of angular momentum loss driven bystrong stellar winds in the intermediate-mass stars, such as theprimaries of the Algols. Differential rotation, induced by the accretionitself, may produce such winds which carry away enough angular momentumto reduce their rotational velocities to the today's observed values. Weapply this model to two systems with initial periods of 5d, one withinitial masses 5 and and the other with 3.2 and . Our calculations showthat, if the mass outflow rate in the stellar wind is about 10per centof the accretion rate and the dipole magnetic field is stronger thanabout 1kG, the spin rate of the gainer is reduced to below breakupvelocity even in the fast phase of mass transfer. Larger mass loss isneeded for smaller magnetic fields. The slow rotation of the gainers inthe classical Algol systems is explained by a balance between thespin-up by mass accretion and spin-down by a stellar wind linked to amagnetic field.
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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.
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A list of minima and maxima timings
The list contains minima of eclipsing and maxima of pulsating stars, itcontinues the list published in OEJV 0073.
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Minima of long period eclipsing stars
This is the first of a planned seria of minima lists. It contains onlyfive stars, UU Cas, EK Cas, RS Cep, EX Cep, KL Cep.
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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.
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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.
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Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderliche Sterne e.V.
Not Available
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SB9: The ninth catalogue of spectroscopic binary orbits
The Ninth Catalogue of Spectroscopic Binary Orbits(http://sb9.astro.ulb.ac.be) continues the series of compilations ofspectroscopic orbits carried out over the past 35 years by Batten andcollaborators. As of 2004 May 1st, the new Catalogue holds orbits for2386 systems. Some essential differences between this catalogue and itspredecessors are outlined and three straightforward applications arepresented: (1) completeness assessment: period distribution of SB1s andSB2s; (2) shortest periods across the H-R diagram; (3)period-eccentricity relation.
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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/.
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Catalogue of Algol type binary stars
A catalogue of (411) Algol-type (semi-detached) binary stars ispresented in the form of five separate tables of information. Thecatalogue has developed from an earlier version by including more recentinformation and an improved layout. A sixth table lists (1872) candidateAlgols, about which fewer details are known at present. Some issuesrelating to the classification and interpretation of Algol-like binariesare also discussed.Catalogue is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/417/263
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Search for A-F Spectral type pulsating components in Algol-type eclipsing binary systems
We present the results of a systematic search for pulsating componentsin Algol-type eclipsing binary systems. A total number of 14 eclipsingbinaries with A-F spectral type primary components were observed for 22nights. We confirmed small-amplitude oscillating features of a recentlydetected pulsator TW Dra, which has a pulsating period of 0.053 day anda semi-amplitude of about 5 mmag in B-passband. We discovered newpulsating components in two eclipsing binaries of RX Hya and AB Per. Theprimary component of RX Hya is pulsating with a dominant period of 0.052day and a semi-amplitude of about 7 mmag. AB Per has also a pulsatingcomponent with a period of 0.196 day and a semi-amplitude of about 10mmag in B-passband. We suggest that these two new pulsators are membersof the newly introduced group of mass-accreting pulsating stars insemi-detached Algol-type eclipsing binary systems.Table 4 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/231
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Beobachtungsegebnisse Bundesdeutsche Arbeitsgemainschaft fur Veranderliche Sterne e.V.
Not Available
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The Origin of Cyclic Period Changes in Close Binaries: The Case of the Algol Binary WW Cygni
Year- to decade-long cyclic orbital period changes have been observed inseveral classes of close binary systems, including Algol, W UrsaeMajoris, and RS Canum Venaticorum systems and the cataclysmic variables.The origin of these changes is unknown, but mass loss, apsidal motion,magnetic activity, and the presence of a third body have all beenproposed. In this paper, we use new CCD observations and thecentury-long historical record of the times of primary eclipse for WWCygni to explore the cause of these period changes. WW Cyg is an Algolbinary whose orbital period undergoes a 56 yr cyclic variation with anamplitude of ~0.02 days. We consider and reject the hypotheses of masstransfer, mass loss, apsidal motion, and the gravitational influence ofan unseen companion as the cause for these changes. A model proposed byApplegate, which invokes changes in the gravitational quadrupole momentof the convective and rotating secondary star, is the most likelyexplanation of this star's orbital period changes. This finding is basedon an examination of WW Cyg's residual O-C curve and an analysis of theperiod changes seen in 66 other Algols. Variations in the gravitationalquadrupole moment are also considered to be the most likely explanationfor the cyclic period changes observed in several different types ofbinary systems.
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Aktion Langperiodische Bedeckungsveranderliche.
Not Available
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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.
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Is asynchronism in semidetached binary systems real?
We analyze statistical relationships between the parameters ofAlgol-type binaries with asynchronous rotation of the primary componentsand provide observational evidence for denser, more extended gaseousenvelopes in the eclipsing systems of this group. We conclude thatasynchronism of the primary components in such systems is not real. Thelines that are used to determine the rotational velocities of thesecomponents originate mostly in the part of the atmosphere which acquiresan additional angular momentum during the interaction with the gasstream and produces a transient accretion disk near the equatorialplane.
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Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
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KU Cygni: New Spectroscopic and Photometric Solutions of a Long-Period Accretion-Disk Binary
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.2378O&db_key=AST
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DN Orionis: A Long-Period Mass-Transferring "Slightly Detached" Algol Binary
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.1809E&db_key=AST
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Rapid H-alpha emission variations in accretion disks in long-period ALGOLS
We demonstrate the continuous presence of large variations indouble-peaked H-alpha long period Algol-type binaries, using recentlyobtained CCD spectra. Most fluctuations occur on a time scale less thanor = an orbital period and a steady state in H-alpha emission ia neverreached. In AD Her (P = 10 d), H-alpha emission dropped in strength morethan a factor of five in one seven-day interval. Contemporay O I lambdaobservations showed no significant changes in oxygen absorption strengthor radial velocity during this time. We tentatively suggest that H-alphavariations arise from an inner-disk instability, possibly triggered bysmall modulations in the mass-transfer rate. This behavior isreminiscent of some cataclysmic variables.
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O I lamba 7774 absorption as a tracer of streams and disks in nondegenerate binary stars
We propose a new spectroscopic approach for observing circumstellarmatter in binary stars, based on the neutral oxygen lambda 7774absorption lines. We present oxygen equivalent widths and radialvelocities in 20 nondegenerate eclipsing binaries. We note limitationsand advantages of using this line to trace circumstellar matter inbinary systems, and confirm the presence of streams and rotatingaccretion disks in a number of short- long-period Algol systems. Wediscuss evidence for geometrically thick disks, and describe a smallradial infall superimposed on disk rotation in most long-period systems.We speculate that infall may be related to viscous dissipation in disks.We emphasize the great sensitivity of lambda 7774 in studying thekinematics of circumstellar matter in many nondegenerate binary stars.
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RS Cephei: New photometric solutions including rapid rotation, and new spectroscopic observations
Using the Wilson program, new system parameters for the long-periodmass-transferring binary RS Cephei are derived from new spectroscopicobservations and a new solution of Olson's photometric data.Color-dependent uncertaintities in the photometric mass ratio arediscussed. I through v observations made from 1980 to 1985 areessentially free of circumsteller contamination, but a simultaneousIybvu solution reveals about 0.6 mag of excess ultraviolet radiation inprimary eclipse totality, probably from uneclipsed continuous emissionfrom an accretion disk around the hotter star. The ultraviolet diskluminosity will help to constrain estimates of the physical propertiesof the disk, to be found later.
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Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
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New rotational velocities for eclipsing binaries, and a comparison of spectroscopic and photometric rotations
Rotational velocities are determined spectroscopically for 38 eclipsingbinaries, including many long-period, nominally semidetached, systems.We note that spectroscopic rotations may differ from rotations derivedfrom light-curve modeling using the Wilson-Devinney program. In'direct-impact' mass-transferring systems, or in most systems withperiods smaller than about 7 days, observations suggest that the tworotations are usually about the same. In cases where the stream missesthe gainer and an accretion disk forms, however, photometric rotationestimates often exceed spectroscopic determinations. The possiblephysical significance of this situation is briefly discussed. Doubt iscast on the likelihood that the rotation of the hot component of U Sgehas changed detectably in the last 30 years.
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Radio observations of peculiar emission-line Algol binary stars
Twelve peculiar emission-line Algol (PELA) binaries were observed at cmwavelengths. Six of these objects, WW And (tentative), KX And, AM Aur,V644 Mon, DN Ori, and AY Per were detected at the 100 to 400 micro-Jylevel, corresponding to luminosity densities of order 10 exp 17erg/s/Hz. These luminosity densities, combined with nearly flat cmspectra and high brightness temperatures, are consistent with thenonthermal gyrosynchrotron radiation model proposed as the result ofobservations from the previous PELA survey. Also, the star V367 Cyg wasreobserved at thirteen different orbital phases; no variability wasfound within the errors. V367 Cyg's lack of variability andwell-determined average spectral index, however, imply the possibilityof a different emission mechanism, thermal bremsstrahlung, although thenonthermal model cannot be entirely ruled out. The characteristicbrightness temperature of thermal bremsstrahlung is only about 10,000 K,which means that the radius of the emission region would have to be muchlarger than previously assumed, about 10 AU. Suggestions for furtherobservations of all previously observed PELAS are presented in order todetermine the correct emission mechanism.
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Light-curve solutions for S CANCRI and TT Hydrae with rapid rotation
Physical model light- and velocity-curve solutions for S Cancri and TTHydrae are obtained, and analyses with incorporation of asynchronousrotation are carried out. A photometric rotation rate for the primarystar of TT Hya is determined, and excellent agreement with results fromspectral line profiles is found. Both separate light- and velocity-curvesolutions and simultaneous light-velocity solutions are listed. Thephotometric rotation for S Cnc from existing light curves isindeterminate, but is compatible with line profile measures. Evidencefor third light from the light curves of S Cnc is found. An explanationfor the apparent conflict between the rotational states andmass-transfer activities of the two binaries is suggested.
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Diagnostics of circumstellar gas in Algol-type close binary systems
The physical properties of circumstellar gas in Algol-type semidetachedsystems are analyzed, and observational data are reviewed. It is foundthat the basic kinematic and morphological properties of thecircumstellar and circumbinary gaseous media can be interpreted in termsof a strong anisotropic stellar wind, in accordance with the conceptionof Tout and Hall (1991).
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Radio Emission From Peculiar Emission-Line Algol Binaries
Not Available
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A summary of the investigations of semi-detached close binaries (1986 - 1988).
The author presents a concise review of the investigations ofsemi-detached close binaries which is based upon the papers included inthe book "Algols" edited by A. H. Batten (1989).
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INHABITED SKY
