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Orbital and physical parameters of eclipsing binaries from the All-Sky Automated Survey catalogue. II. Two spotted M < 1 M_? systems at different evolutionary stages
Aims: We present the results of our detailed spectroscopic andphotometric analysis of two previously unknown <1 M_? detachedeclipsing binaries: ASAS J045304-0700.4 and ASAS J082552-1622.8. Methods: With the HIgh Resolution Echelle Spectrometer (HIRES) on theKeck-I telescope, we obtained spectra of both objects covering largefractions of orbits of the systems. We also obtained V and I bandphotometry with the 1.0-m Elizabeth telescope of the South AfricanAstronomical Observatory (SAAO). The orbital and physical parameters ofthe systems were derived with the PHOEBE and JKTEBOP codes. Weinvestigated the evolutionary status of both binaries with several setsof widely-used isochrones. Results: Our modelling indicates that(1) ASAS J045304-0700.4 is an old, metal-poor, active system withcomponent masses of M1 = 0.8338 ± 0.0036M?, M2 = 0.8280 ± 0.0040M? and radii of R1 = 0.848 ± 0.005R? and R2 = 0.833 ± 0.005R?, which places it at the end of the Main Sequenceevolution - a stage rarely observed for this type of stars. (2) ASASJ082552-1622.8 is a metal-rich, active binary with component masses ofM1 = 0.7029 ± 0.0045 M?, M2= 0.6872 ± 0.0049 M? and radii of R1 =0.694+0.007-0.011 R? andR2 = 0.699+0.011-0.014R?. Both systems show significant out-of-eclipsevariations, probably owing to large, cold spots. We also investigatedthe influence of a third light in the second system.Light curves are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/526/A29
| Speckle Interferometry at the Observatorio Astronómico Nacional. II
We present speckle interferometric measurements of binary stars madeduring June of 2009 with the 1.5 m telescope of the ObservatorioAstronómico Nacional at SPM (Mexico). The data contain 189position angle and separation measures of 144 systems. The measuredangular separations range from 0arcsec.16 to 3arcsec.64. The maximummagnitude of the brighter component is 10.96. The mean error inseparation is 0arcsec.02 and in the position angles 1.5°. Some ofthe position angles were determined with the usual 180° ambiguity.
| The V-band Empirical Mass-luminosity Relation for Main Sequence Stars
Stellar mass is an indispensable parameter in the studies of stellarphysics and stellar dynamics. On the one hand, the most reliable way todetermine the stellar dynamical mass is via orbital determinations ofbinaries. On the other hand, however, most stellar masses have to beestimated by using the mass luminosity relation (MLR). Therefore, it isimportant to obtain the empirical MLR through fitting the data ofstellar dynamical mass and luminosity. The effect of metallicity canmake this relation disperse in the V-band, but studies show that this ismainly limited to the case when the stellar mass is less than0.6M? Recently, many relevant data have been accumulatedfor main sequence stars with larger masses, which make it possible tosignificantly improve the corresponding MLR. Using a fitting methodwhich can reasonably assign weights to the observational data includingtwo quantities with different dimensions, we obtain a V-band MLR basedon the dynamical masses and luminosities of 203 main sequence stars. Incomparison with the previous work, the improved MLR is statisticallysignificant, and the relative error of mass estimation reaches about 5%.Therefore, our MLR is useful not only in the studies of statisticalnature, but also in the studies of concrete stellar systems, such as thelong-term dynamical study and the short-term positioning study of aspecific multiple star system.
| Accurate masses and radii of normal stars: modern results and applications
This article presents and discusses a critical compilation of accurate,fundamental determinations of stellar masses and radii. We haveidentified 95 detached binary systems containing 190 stars (94 eclipsingsystems, and ? Centauri) that satisfy our criterion that the massand radius of both stars be known within errors of ±3% accuracyor better. All of them are non-interacting systems, and so the starsshould have evolved as if they were single. This sample more thandoubles that of the earlier similar review by Andersen (Astron AstrophysRev 3:91-126, 1991), extends the mass range at both ends and, forthe first time, includes an extragalactic binary. In every case, we haveexamined the original data and recomputed the stellar parameters with aconsistent set of assumptions and physical constants. To these we addinterstellar reddening, effective temperature, metal abundance,rotational velocity and apsidal motion determinations when available,and we compute a number of other physical parameters, notably luminosityand distance. These accurate physical parameters reveal the effects ofstellar evolution with unprecedented clarity, and we discuss the use ofthe data in observational tests of stellar evolution models in somedetail. Earlier findings of significant structural differences betweenmoderately fast-rotating, mildly active stars and single stars, ascribedto the presence of strong magnetic and spot activity, are confirmedbeyond doubt. We also show how the best data can be used to testprescriptions for the subtle interplay between convection, diffusion,and other non-classical effects in stellar models. The amount andquality of the data also allow us to analyse the tidal evolution of thesystems in considerable depth, testing prescriptions of rotationalsynchronisation and orbital circularisation in greater detail thanpossible before. We show that the formulae for pseudo-synchronisation ofstars in eccentric orbits predict the observed rotations quite well,except for very young and/or widely separated stars. Deviations dooccur, however, especially for stars with convective envelopes. Thesuperior data set finally demonstrates that apsidal motion rates aspredicted from General Relativity plus tidal theory are in goodagreement with the best observational data. No reliable binary dataexist, which challenge General Relativity to any significant extent. Thenew data also enable us to derive empirical calibrations of M and R forsingle (post-) main-sequence stars above {0.6 M_{odot}}. Simple,polynomial functions of T eff, log g and [Fe/H] yield M and Rwithin errors of 6 and 3%, respectively. Excellent agreement is foundwith independent determinations for host stars of transiting extrasolarplanets, and good agreement with determinations of M and R from stellarmodels as constrained by trigonometric parallaxes and spectroscopicvalues of T eff and [Fe/H]. Finally, we list a set of 23interferometric binaries with masses known to be better than 3%, butwithout fundamental radius determinations (except ? Aur). Wediscuss the prospects for improving these and other stellar parametersin the near future.
| XID II: Statistical Cross-Association of ROSAT Bright Source Catalog X-ray Sources with 2MASS Point Source Catalog Near-Infrared Sources
The 18,806 ROSAT All Sky Survey Bright Source Catalog (RASS/BSC) X-raysources are quantitatively cross-associated with near-infrared (NIR)sources from the Two Micron All Sky Survey Point Source Catalog(2MASS/PSC). An association catalog is presented, listing the mostlikely counterpart for each RASS/BSC source, the probability Pid that the NIR source and X-ray source are uniquelyassociated, and the probability P no-id that none of the2MASS/PSC sources are associated with the X-ray source. The catalogincludes 3853 high quality (P id>0.98) X-ray-NIR matches,2280 medium quality (0.98 >= P id>0.9) matches, and4153 low quality (0.9 >= P id>0.5) matches. Of the highquality matches, 1418 are associations that are not listed in the SIMBADdatabase, and for which no high quality match with a USNO-A2 opticalsource was presented for the RASS/BSC source in previous work. Thepresent work offers a significant number of new associations withRASS/BSC objects that will require optical/NIR spectroscopy forclassification. For example, of the 6133 P id>0.92MASS/PSC counterparts presented in the association catalog, 2411 haveno classification listed in the SIMBAD database. These 2MASS/PSC sourceswill likely include scientifically useful examples of known sourceclasses of X-ray emitters (white dwarfs, coronally active stars, activegalactic nuclei), but may also contain previously unknown sourceclasses. It is determined that all coronally active stars in theRASS/BSC should have a counterpart in the 2MASS/PSC, and that the uniqueassociation of these RASS/BSC sources with their NIR counterparts thusis confusion limited.
| Absolute dimensions of solar-type eclipsing binaries. II. V636 Centauri: A 1.05 {M}ȯ primary with an active, cool, oversize 0.85 {M}ȯ secondary
Context: The influence of stellar activity on the fundamental propertiesof stars around and below 1 Mȯ is not well understood.Accurate mass, radius, and abundance determinations from solar-typebinaries exhibiting various levels of activity are needed for a betterinsight into the structure and evolution of these stars. Aims: Weaim to determine absolute dimensions and abundances for the solar-typedetached eclipsing binary V636 Cen, and to perform a detailed comparisonwith results from recent stellar evolutionary models. Methods:uvby light curves and uvbyβ standard photometry were obtained withthe Strömgren Automatic Telescope, radial velocity observationswith the CORAVEL spectrometer, and high-resolution spectra with theFEROS spectrograph, all at ESO, La Silla. State-of-the-art methods wereapplied for the photometric and spectroscopic analyses. Results:Masses and radii that are precise to 0.5% have been established for thecomponents of V636 Cen. The 0.85 Mȯ secondary componentis moderately active with starspots and Ca ii H and K emission, and the1.05 Mȯ primary shows signs of activity as well, but ata much lower level. We derive a [Fe/H] abundance of -0.20 ± 0.08and similar abundances for Si, Ca, Ti, V, Cr, Co, and Ni. Correspondingsolar-scaled stellar models are unable to reproduce V636 Cen, especiallyits secondary component, which is ~10% larger and ~400 K cooler thanpredicted. Models adopting significantly lower mixing-length parametersl/Hp remove these discrepancies, seen also for othersolar-type binary components. For the observed [Fe/H], Claret models forl/Hp = 1.4 (primary) and 1.0 (secondary) reproduce thecomponents of V636 Cen at a common age of 1.35 Gyr. The orbit iseccentric (e = 0.135 ± 0.001), and apsidal motion with a 40%relativistic contribution has been detected. The period is U = 5 270± 335 yr, and the inferred mean central density concentrationcoefficient, log(k_2) = -1.61 ± 0.05, agrees marginally withmodel predictions. The measured rotational velocities, 13.0 ± 0.2(primary) and 11.2 ± 0.5 (secondary) km s-1, are inremarkable agreement with the theoretically predicted pseudo-synchronousvelocities, but are about 15% lower than the periastron values. Conclusions: V636 Cen and 10 other well-studied inactive and activesolar-type binaries suggest that chromospheric activity, and its effecton envelope convection, is likely to cause radius and temperaturediscrepancies, which can be removed by adjusting the model mixing lengthparameters downwards. Noting this, the sample may also lend support totheoretical 2D radiation hydrodynamics studies, which predict a slightdecrease of the mixing length parameter with increasing temperature/massfor inactive main sequence stars. More binaries are, however, needed fora description/calibration in terms of physical parameters and level ofactivity.Based on observations carried out at the Strömgren AutomaticTelescope (SAT), the Danish 1.54 m telescope, and the 1.5 m telescope(62.L-0284) at ESO, La Silla, Chile. Table A.1 is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/502/253
| Time series analysis with the VSAA method
Time series analysis is a common task in many scientific fields, and soit is in astronomy, too. Fourier Transform and Wavelet Analysis areusually applied to handle the majority of the cases. Even so, problemsarise when the time series signal presents modulation in the frequencyunder inspection. The Variable Sine Algorithmic Analysis (VSAA) is a newmethod focused exactly on this type of signals. It is based on a singlesine function with variable coefficients and it is powered by thesimplex algorithm. In cases of phenomena triggered by a single mechanism- that Fourier Transform and Wavelet Analysis fail to describepractically and efficiently - VSAA provides a straightforward solution.The method has already been applied to orbital period changes andmagnetic field variations of binary stars, as well as to the Blazhkoeffect of the pulsating RR Lyrae stars and to sunspot activity.
| 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.
| Recent Minima of 155 Eclipsing Binary Stars
The AAVSO's publication of times of minima for eclipsing binary stars has shifted from the recent publication series, Observed Minima Timings of Eclipsing Binaries, Number 1-12, back to the JAAVSO. Times of minima fromobservations made in the past eight months are presented. New lightelements for AC CMi have been calculated from recent AAVSO observations:Min(JD) = 2451978.7504 + 0.867216691 E± 0.0004 ± 0.00000024
| A catalogue of chromospherically active binary stars (third edition)
The catalogue of chromospherically active binaries (CABs) has beenrevised and updated. With 203 new identifications, the number of CABstars is increased to 409. The catalogue is available in electronicformat where each system has a number of lines (suborders) with a uniqueorder number. The columns contain data of limited numbers of selectedcross references, comments to explain peculiarities and the position ofthe binarity in case it belongs to a multiple system, classicalidentifications (RS Canum Venaticorum, BY Draconis), brightness andcolours, photometric and spectroscopic data, a description of emissionfeatures (CaII H and K, Hα, ultraviolet, infrared),X-ray luminosity, radio flux, physical quantities and orbitalinformation, where each basic entry is referenced so users can go to theoriginal sources.
| On the Period Variations of BH Virginis
In the present work, 17 new times of the light minimum for BHVir werederived from observations by Kjurkchieva etal. (2004, A&A, 424,993). Combining the new determined eclipse times with others compiledfrom the literature, the behavior of their O-C variation wasinvestigated. It has been found that the orbital period of BHVir showssome cyclic variations with three different periods: a long-periodvariation of 51.7years, and two short-period variations of 9.2years and11.8years, respectively. The mechanisms that could explain the periodchanges of the system are discussed.
| a Photometric Study of the Short-Period Close Binary V432 Persei and its Implications for the Star's Evolution
We present new multicolor charge-coupled device (CCD) photometry for theshort-period close binary V432 Per, made on six nights between 2006February and December. A period study of the system, based on allpublished and newly observed times of minimum light, reveals that theorbital period has varied as a beat effect due to the combination of asecular period increase and a sinusoidal variation, with a period of35.3 yr and semi-amplitude of 0.0104 d. The continuous period increasecan be interpreted as mass transfer from the less massive secondary starto the more massive primary component in the system with a rate of about1.16 × 10-7 M sun yr-1. Thesinusoidal component of the period variability could, in principle, beproduced by either a light-time effect due to a third body or a magneticmodulation seated in at least one component star, but light variationsdo not conform to a prediction of the second mechanism. New lightcurves, showing a total eclipse at secondary minimum and a variableO'Connell effect, are best modeled by including a third light source anda cool spot on the primary star. The model also represents Agerer'slight curves. Our results indicate V432 Per, at present, to be in abroken or a marginal contact stage, investing a hotter, more massiveprimary star with a spectral type of G4 and a cooler, less massivesecondary star with a spectral type of G8 G9. We suggest that the mostlikely explanation of the sinusoidal variation is the existence of agravitationally bound M-type tertiary companion. When all of this isverified and understood more comprehensively, the formation andevolution of this binary system should be greatly advanced.
| Mass-luminosity relation of intermediate-mass stars
The mass-luminosity relation (MLR) for intermediate-mass stars is basedon data on detached double-lined eclipsing binaries. However, there is anotable difference between the parameters of B0V-G0V components ofeclipsing binaries and those of single stars. Single early-type starsare rapid rotators, whereas tidal forces produce synchronous rotation inclose binaries and all such pairs are synchronized, so components ofclose binaries rotate more slowly. As is well known, stellar rotationchanges stellar evolution and the global parameters of a star.In this work we collect data on fundamental parameters of stars withmasses m > 1.5msolar. They are components of binaries withP > 15 d and consequently are not synchronized with the orbitalperiods and presumably are rapid rotators. These stars are believed toevolve similarly with single stars. Modern data on masses, absolute andbolometric luminosities, radii and temperatures of detachedmain-sequence double-lined eclipsing binary components (i.e. presumablyslow rotators) are also collected.Mass-luminosity, mass-temperature and mass-radius relations of close andwide binaries are presented, as well as their Hertzsprung-Russelldiagram. For the mass range 4.5 < m/msolar < 5.5 (lateB stars) it was found that rapid rotators exhibit slightly higherluminosities and larger radii than predicted by the standard relations,and their main sequence is shifted to the right-hand side with respectto that of the close binary components. The resulting relations forrapidly and slowly rotating A-F and early B stars are not statisticallydifferent.As our estimations show, for the given mass range the effect on theinitial mass function (IMF) is marginal, but there is no way to estimatethe degree to which the effect may be important for higher masses.Available observational data for m > 12msolar are too poorto make definite conclusions. Knowledge of the MLR should come fromdynamical mass determinations of visual binaries combined with spatiallyresolved precise photometry. Then the IMF should be revised for thatmass range.
| A Mechanism for Orbital Period Modulation and Irregular Orbital Period Variations in Close Binaries
Orbital period modulation is observed in many magnetically active closebinaries. It can be explained by magnetic connection between two stars.Magnetic connection produces weak force between the two stars. As themagnetic field varies periodically, the orbital period also showscyclical variations. The mechanism can also be used to explain irregularorbital period variations and orbital period jumps. The mean surfacemagnetic strength is calculated by using the Radia package, which isdedicated to 3D magnetostatics computation. On the basis of the results,a practical equation is given to calculate surface magnetic strength.
| B.R.N.O. Contributions #34
Not Available
| All-Sky Automated Survey eclipsing binaries with observed high period change rates
We present 31 bright eclipsing contact and semidetached binaries thatshowed high period change rates (HPCRs) in a 5-yr interval inobservations by the All-Sky Automated Survey. The time-scales of thesechanges range from only 50 up to 400 kyr. The orbital periods of 10binaries are increasing and of 21 are decreasing, and even a largerexcess is seen in contact binaries, where the numbers are 5 and 17,respectively. Period change has previously been noticed for only two ofthese binaries; our observations confirmed a secular period drift for SVCen and period oscillations for VY Cet. The spectroscopic quadruplesystem V1084 Sco shows both period change and brightness modulation.According to our results, the incidence of asymmetry in the brightnessat maximum light in the HPCR domain may be different from the incidencein the general population. All investigated binaries were selected froma sample of 1711 (1135 contact and 576 semidetached) that fulfilled allcriteria of data quality. We also introduce a `branch' test to check ifluminosity changes on part of the binary's photosphere have led to aspurious or poorly characterized period change detection.
| Photoelectric Minima of Some Eclipsing Binary Stars
We present 119 minima times of 47 eclipsing binaries.
| 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.
| CCD Times of Minima of Selected Eclipsing Binaries
374 CCD minima observations of 187 eclipsing binaries are presented. Theobserved stars were chosen mainly from catalogue BRKA of observingprogramme of Variable Star Section of CAS.
| 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.
| The Eclipsing Binary V1061 Cygni: Confronting Stellar Evolution Models for Active and Inactive Solar-Type Stars
We present spectroscopic and photometric observations of the eclipsingsystem V1061 Cyg (P=2.35 days). A third star is visible in the spectrum,and the system is a hierarchical triple. We combine the radialvelocities for the three stars, times of eclipse, and intermediateastrometric data from the Hipparcos mission (abscissa residuals) toestablish the elements of the outer orbit, which is eccentric and has aperiod of 15.8 yr. We determine accurate values for the masses, radii,and effective temperatures of the binary components:MAa=1.282+/-0.015 Msolar,RAa=1.615+/-0.017 Rsolar, andTAaeff=6180+/-100 K for the primary (star Aa), andMAb=0.9315+/-0.0068 Msolar,RAb=0.974+/-0.020 Rsolar, andTAbeff=5300+/-150 K for the secondary (Ab). Themass of the tertiary is determined to be MB=0.925+/-0.036Msolar and its effective temperature isTBeff=5670+/-150 K. Current stellar evolutionmodels agree well with the properties of the primary but show a verylarge discrepancy in the radius of the secondary, in the sense that thepredicted values are ~10% smaller than observed (a ~5 ? effect).In addition, the temperature is cooler than predicted, by some 200 K.These discrepancies are quite remarkable given that the star is only 7%less massive than the Sun, the calibration point of all stellar models.We identify the chromospheric activity as the likely cause of theeffect. Inactive stars agree very well with the models, while activeones such as V1061 Cyg Ab appear systematically too large and too cool.
| Starspot activity in late stars: Methods and results
Three types of methods for studying the surface inhomogeneities of coolstars and the results of their use on type BY Dra, RS CVn, FK Com, and TTau variables are discussed. The current relevance of traditionalphotometric methods and the advantages of the zonal spottedness modelare pointed out. Dependences of the maximum total areas, averagelatitudes, and temperatures of spots on the global parameters of thestars are given. Analogs of the solar cycle in the variations of theareas and latitudes of starspots are examined, as well as the effects ofdifferential rotation and active longitudes.
| Mass loss and orbital period decrease in detached chromospherically active binaries
The secular evolution of the orbital angular momentum (OAM), thesystemic mass (M=M1+M2) and the orbital period of114 chromospherically active binaries (CABs) were investigated afterdetermining the kinematical ages of the subsamples which were setaccording to OAM bins. OAMs, systemic masses and orbital periods wereshown to be decreasing by the kinematical ages. The first-orderdecreasing rates of OAM, systemic mass and orbital period have beendetermined as per systemic OAM, per systemic mass and per orbitalperiod, respectively, from the kinematical ages. The ratio of d logJ/dlogM= 2.68, which were derived from the kinematics of the presentsample, implies that there must be a mechanism which amplifies theangular momentum loss (AML) times in comparison to isotropic AML ofhypothetical isotropic wind from the components. It has been shown thatsimple isotropic mass loss from the surface of a component or bothcomponents would increase the orbital period.
| 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.
| The analysis of indexed astronomical time series - X. Significance testing of O-C data
It is assumed that O-C (`observed minus calculated') values of periodicvariable stars are determined by three processes, namely measurementerrors, random cycle-to-cycle jitter in the period, and possiblylong-term changes in the mean period. By modelling the latter as arandom walk, the covariances of all O-C values can be calculated. Thecovariances can then be used to estimate unknown model parameters, andto choose between alternative models. Pseudo-residuals which could beused in model fit assessment are also defined. The theory is illustratedby four applications to spotted stars in eclipsing binaries.
| 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.
| New Minima of Selected Eclipsing Close Binaries
We present 180 CCD and photoelectric times of minima of selected closeeclipsing binaries.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Zonal Model of Starspots. Application to RS CVn Systems
Model results on starspots in 15 chromospherically active type RS CVnbinary systems are presented. The dependences of the parameters of thespots on the principal characteristics of the stars (spectral class,luminosity class, rotation, Rossby number) are examined. Latitudinaldrift of the spots, cycles in the spot activity, and differentialrotation are found in 9 of the stars.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
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