Photoelectric Minima of Some Eclipsing Binary Stars
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B.R.N.O. Contributions #34
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Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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CCD Minima for Selected Eclipsing Binaries in 2007
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Photoelectric Minima of Some Eclipsing Binary Stars
We present 119 minima times of 47 eclipsing binaries.
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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.
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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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CCD Minima for Selected Eclipsing Binaries in 2005
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Pulkovo compilation of radial velocities for 35495 stars in a common system.
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Photoelectric Minima of Some Eclipsing Binary Stars
We present 70 minima times of 35 eclipsing binaries.
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Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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Physical Parameters of Components in Close Binary Systems: IV
The paper presents new geometric, photometric and absolute parameters,derived from combined spectroscopic and photometric solutions, for tencontact binary systems. The analysis shows that three systems (EF Boo,GM Dra and SW Lac) are of W-type with shallow to moderate contact. Sevensystems (V417 Aql, AH Aur, YY CrB, UX Eri, DZ Psc, GR Vir and NN Vir)are of A-type in a deep contact configuration. For six systems (V417Aql, YY CrB, GM Dra, UX Eri, SW Lac and GR Vir) a spot model isintroduced to explain the O'Connell effect in their light curves. Thephotometric and geometric elements of the systems are combined with thespectroscopic data taken at David Dunlap Observatory to yield theabsolute parameters of the components.
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CCD Times of Minima of Selected Eclipsing Binaries
682 CCD minima observations of 259 eclipsing binaries made mainly byauthor are presented. The observed stars were chosen mainly fromcatalogue BRKA of observing programme of BRNO-Variable Star Section ofCAS.
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Observational study of interacting binary stars
We present a progress report on the results obtained from photometricand spectroscopic observations of the interacting binary stars SW Cyg,RR Dra, Y Leo, and SW Lyn in our Galaxy. Analogous studies could beeventually carried out for interacting binaries in the Local Groupgalaxies. From this study we note the significant Hα line profilevariations in spectra of SW Cyg taken at two different orbital phases.
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Physical Parameters of Components in Close Binary Systems: II
We present the absolute parameters of components for five contact binarysystems: AB And, GZ And, AO Cam, DN Cam and DK Cyg. The results arebased on solutions of new multicolor light curves as well as new radialvelocity curves from the DDO radial velocity program. All five systemshave a contact configuration with low (5-13%) to intermediate (30-33%)overfilling factors.
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CCD Times of Minima of Some Eclipsing Binaries in 2003
We present CCD observations of minima of 31 eclipsing binaries observedby SAVS sky survey in 2003.
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CCD Minima for Selected Eclipsing Binaries in 2003
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Photoelectric Minima of Selected Eclipsing Binaries
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Physical parameters of components in close binary systems. I
The paper presents combined spectroscopic and photometric orbitalsolutions for four close binary systems: SW Lyn, QW Gem, AP Leo andV2150 Cyg. The photometric data are new, while the spectroscopy has beenrecently obtained within the radial velocity programme at the DavidDunlap Observatory. This paper is the first in the planned series ofinvestigations. We give an extensive description of the motivation forthe series and of the main assumptions made in our solutions. The fourtargets of this investigation span a range of typical configurations andthus present different levels of difficulty for the combinedspectroscopic and photometric orbital solutions.
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First Results of the Semi-Automatic Variability Search
A short description of the Semi-Automatic Variability Search is given.Six new red variable stars discovered recently are presented:GSC02907--00779, GSC02904--00834, GSC02908--00024, GSC02976--00401,BD+42 arc deg 1814 and HD76190.
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CCD Minima for Selected Eclipsing Binaries in 2002
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Radial Velocity Studies of Close Binary Stars. VII. Methods and Uncertainties
Methods used in the radial velocity program of short-period binarysystems at the David Dunlap Observatory are described with particularstress on the broadening-function formalism. This formalism makes itpossible to determine radial velocities from the complex spectra ofmultiple-component systems with component stars showing very differentdegrees of rotational line broadening. The statistics of random errorsof orbital parameters are discussed on the basis of the availableorbital solutions presented in the six previous papers of the series,each with 10 orbits. The difficult matter of systematic uncertainties inorbital parameters is illustrated for the typical case of GM Dra fromPaper VI. Based on data obtained at the David Dunlap Observatory,University of Toronto.
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Radial Velocity Studies of Close Binary Stars. IV.
Radial velocity measurements and sine-curve fits to the orbital velocityvariations are presented for the fourth set of 10 close binary systems:44 Boo, FI Boo, V2150 Cyg, V899 Her, EX Leo, VZ Lib, SW Lyn, V2377 Oph,Anon Psc (GSC 8-324), and HT Vir. All systems are double-linedspectroscopic binaries, with only two of them not being contact systems(SW Lyn and GSC 8-324) and five (FI Boo, V2150 Cyg, V899 Her, EX Leo,and V2377 Oph) being the recent photometric discoveries of the Hipparcosproject. Five of the binaries are triple-lined systems (44 Boo, V899Her, VZ Lib, SW Lyn, and HT Vir). Three (or possibly four) companions inthe triple-lined systems show radial velocity changes during the span ofour observations, suggesting that these are in fact quadruple systems.Several of the studied systems are prime candidates for combined lightand radial velocity synthesis solutions. Based on the data obtained atthe David Dunlap Observatory, University of Toronto.
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Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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Observational evidence and analysis of the coupling between the dynamical and the thermodynamic processes for close binaries.
Analytical methods of the orbital period, the types of its variations,the mechanisms causing the changes in the orbital period, and problemsand progresses in the orbital period study are introduced. Theproperties of the variations in te orbital period and in the lightcurve, and the connections between the changes of the orbital period andthe light curve in different types of close binaries are also reviewed.The changes of the orbital period, the variations of the light curve andtheir connections in some sample stars are studied. The statisticalrelation of the parameters in contact binaries is also investigated.
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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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The use of the NextGen model atmospheres for cool giants in a light curve synthesis code
We have written a light curve synthesis code that makes direct use ofmodel atmosphere specific intensities, in particular the NextGen modelatmosphere grid for cool giants (Teff<= 6800 K and log(g)<= 3.5, Hauschildt et al. \cite{hauschildt99}). We point out thatthese models (computed using spherical geometry) predict a limbdarkening behaviour that deviates significantly from a simple linear ortwo-parameter law (there is less intensity at the limb of the star). Thepresence of a significantly nonlinear limb darkening law has two mainconsequences. First, the ellipsoidal light curve computed for a tidallydistorted giant using the NextGen intensities is in general differentfrom the light curve computed using the same geometry but with the blackbody approximation and a one- or two-parameter limb darkening law. Inmost cases the light curves computed with the NextGen intensities havedeeper minima than their black body counterparts. Thus the light curvesolutions for binaries with a giant component obtained with models withnear linear limb darkening (either black body or plane-parallel modelatmosphere intensities) are biased. Observations over a wide wavelengthrange (i.e. both the optical and infrared) are particularly useful indiscriminating between models with nearly linear limb darkening and theNextGen models. Second, we show that rotational broadening kernels forRoche lobe filling (or nearly filling) giants can be significantlydifferent from analytic kernels due to a combination of the nonsphericalshape of the star and the radical departure from a simple limb darkeninglaw. As a result, geometrical information inferred from Vrotsin i measurements of cool giants in binary systems are likewise biased.
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Coordinates and Identifications for Sonneberg Variables on MVS 308-316
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Photoelectric Minima of Eclipsing Binaries
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Orbital period modulation and quadrupole moment changes in magnetically active close binaries
We discuss the main characteristics of the orbital period modulation inclose binaries with late-type components. We focus on the variousphysical scenarios proposed to explain this phenomenon and, inparticular, Hall's (1989) suggestion that it may be connected withmagnetic activity. Starting from the work of Applegate (1992) and Lanzaet al. (1998a), we develop an integral approach to evaluate thegravitational quadrupole moment of an active star and its variations,which we consider to be an important driver of the observed orbitalperiod changes. The method applies the tensor virial theorem afterChandrasekhar (1961) and directly relates the variation of thequadrupole moment with the changes of kinetic and magnetic energy of thestellar hydromagnetic dynamo. Particular effort has been applied inminimizing the number of free parameters entering the problem. A sampleof 46 close binaries with period changes of alternate signs has beenstudied by our method. The amplitude of the quadrupole moment changeappears to decrease with increasing angular velocity, implying that thetime-variable part of the kinetic energy of rotation varies as delta{cal T}/{cal T} ~ Omega ({-0.93+/-) 0.10}, with a correlationcoefficient of 0.83. The length of the cycle of the orbital periodmodulation seems to be correlated with the angular velocity asPmod ~ Omega ({-0.36+/-) 0.10}, but with a smallercorrelation coefficient of 0.62. These results support the suggestionthat a distributed non-linear dynamo is at work in the convectiveenvelopes of very active stars and that it strongly affects thedifferential rotation. We also discuss the energy budget of the processresponsible for the quadrupole moment variation and find that, onaverage, only ~ 10% of the energy required to maintain the differentialrotation may be lost by dissipation in the turbulent convective envelopeduring a cycle of the orbital period change. The problems of themagnetic field geometry and stability and the relationship between thelength of the activity cycle, as determined by the change of the area ofthe starspots and the orbital period modulation, respectively, are alsoaddressed.
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