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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.
| 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
| 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.
| New absolute magnitude calibrations for detached binaries
Lutz-Kelker bias corrected absolute magnitude calibrations for thedetached binary systems with main-sequence components are presented. Theabsolute magnitudes of the calibrator stars were derived at intrinsiccolours of Johnson-Cousins and 2MASS (Two Micron All Sky Survey)photometric systems. As for the calibrator stars, 44 detached binarieswere selected from the Hipparcos catalogue, which have relative observedparallax errors smaller than 15% (σπ/π≤0.15).The calibration equations which provide the corrected absolute magnitudefor optical and near-infrared pass bands are valid for wide ranges ofcolours and absolute magnitudes: -0.18<(B-V)0<0.91,-1.6
| Long-term starspot activity of the eclipsing binaries BH Vir and WY Cnc
We present the results of multicolor photometry of the two spotted,short-period, late-type RS CVn stars BH Vir and WY Cnc. We have derivedthe parameters of the binaries’ components, and refined theirmasses, radii, and luminosities. A strong flare of WY Cnc was detectedfor the first time, and pre-flare variations of the star’sactivity studied. Our observations and published data spanning 40 yearsare analyzed using a zone starspot model. We demonstrate that the spotsare always concentrated near the equators and at intermediate latitudes,with maximum spotted areas as large as 29% for BH Vir and 21% for WYCnc. The temperature differences between spotted regions and the quietphotosphere were 2300 K (BH Vir) and 1800 K (WY Cnc). The detectedlong-term brightness variations of BH Vir suggest the existence of anactivity cycle with a probable period of 22 years. Both stars havestarspots concentrated at two active longitudes separated byapproximately half of the orbital period during all the studied seasons;these longitudes remained the same (0° and 184°) for BH Vir over40 years, whereas they migrated in the direction of the stellar rotationat a rate of 3.8°/yr for WY Cnc, suggesting a cycle of 47 years forthe migration of the active longitudes.
| Evidence of Hot Spot Activity on BH Virginis
Photoelectric light curves of BH Vir in the UBVRI bands observed byArévalo et al. in 1986 were analyzed by using the latest versionof the Wilson-Devinney program and to investigate the photometricparameters and spot activity. Satisfactory fits were obtained byassuming a hot spot only on the secondary star. The results show thatthe temperature of the spotted region relative to the photosphere,Ts / Tph, is 1.13 ± 0.027. The activeregion tends to occur at low latitude (near 81°). The results alsoshow that the mass ratio obtained from the photoelectric light curves isq = m2 / m1 = 0.971. It is close to thespectroscopic value of 0.968 obtained by Zhai et al. (1990). Thephotosphere temperature of the primary is T1 = 5969 ±11 K. After checking of the activity pattern from 1953 to 1991, theactivity cycle is estimated to be about 10 yr.
| 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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| 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.
| 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.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
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| 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.
| 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.
| Spectroscopic and Photometric Observations of the Short-Period RS CVn-Type Star UV Piscium
High-resolution spectroscopic observations around the Hα line andlong-term BVRI photometry of the eclipsing short-period RS CVn star UVPsc are presented. The simultaneous solution of our radial velocitycurves and light curves yields the following values for the globalparameters of the components: M1=1.1 Msolar,M2=0.81 Msolar, R1=1.14Rsolar, and R2=0.85 Rsolar. Themeasured rotational broadening of the spectral lines corresponds toequatorial velocities V1=68.3 and V2=53.3 kms-1. Our spectral data reveal high activity of the twostellar components and very fast variability of the Hα line in thecenter of the primary eclipse. Modeling our photometric data showstrends in the starspot behavior. The trend toward active longitude beltscan have occasional exceptions. The observed secular luminosity decreasein 1999 may signal the onset of a new magnetic activity cycle.
| Spectroscopic and photometric observations of the short-period RS CVn-type star BH Virginis
High-resolution spectroscopic observations around theHα line and BVRI photometry from 1993 to 2003 of theeclipsing short-period RS CVn star BH Vir are presented. Thesimultaneous solution of our radial velocity curves and light curvesyielded the following values for global parameters of the components:M1= 1.173 ± 0.006 Mȯ; M2=1.046 ± 0.005 Mȯ; R1= 1.22 ±0.05 Rȯ; R2= 1.11 ± 0.04Rȯ; i= 87.5° ±0.8°. The measured rotational broadening of the spectrallines corresponds to equatorial velocities V1 = 79.8 kms-1 and V2= 68.4 km s-1. Our datareveal considerable Hα emission excess of the twostellar components. We modelled the photometric data to find the sizeand location of the starspots for each year. The established decreasingtrend of the spot latitudes may indicate a latitudinal cycle of at leasta decade.Based on spectral observations collected at the National AstronomicalObservatory at Rozhen and photometric observations collected at Mt.Laguna Observatory operated by San Diego State University, research wassupported in part by the NATO Linkage grant No. PST.CLG.978810, grantNo. 8/2003 of the Shoumen University, a Cottrell College Science Awardof the Research Corporation, and grants from NASA and the GaposchkinFund administered by the AAS Small Grants Program.Photometric and spectroscopic data are only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/424/993Figures \ref{Fig2}-\ref{Fig7} and Figs. \ref{Fig9}-\ref{Fig16} are onlyavailable in electronic form at http://www.edpsciences.org
| 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.
| A Photometric Analysis and Spot Activity of BH Virginis
BH Virginis is a short-period eclipsing binary with two solar-typecomponents. The photoelectric light curves in UBVRI, observed byScaltriti et al. (1985), and in the B and 5125Å bands, observed byHoffmann (1982), were analyzed by using the 1992 version Wilson-Devinneyprogram to investigate the activity of spots. The results show thatthere was a small cool spotted active region on the secondary star in1984. The position and area of the active region in 1984 are remarkablysimilar to those in 1991. The distortion waves in the light curvesobserved by Hoffmann (1982) can be fitted satisfactorily with twohot-spot active regions: one is on the primary star, and the other is onthe secondary component. The mass ratio q = m2 /m1, obtained from photoelectric light curves, is inside therange of 0.965-0.971. It is close to the spectroscopic value of 0.968obtained by Zhai et al. (1990). To study the physical cause of thevariations and the distortions in the light curve of BH Vir, thephotoelectric observations in BV observed by Koch (1967) werere-analyzed based on a new spot model with an assumption of one coolspot active region on the primary star and two cool spot active regionson the secondary star. The fit of the new spot model to the observationsis better than that of our former result (Xiang et al. 2000). Thepresent results suggest that BH Vir may have an active cycle with aperiod of 7-10 years.
| SV Cam spot activity in December 2003
We present the analysis of new BV light curves for the active star SVCam applying the Roche model with spotted areas on the hotter primarycomponent. Two spots at medium latitudes and covering about 14% of thestellar surface were revealed. Both are 1000 K cooler than thesurrounding photosphere. The comparison with earlier seasons (2000-2003)suggests that the spots probably evolved in area longitude and latitude.Both tidal effect and activity cycle mechanisms may be in action.
| 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/.
| Kinematics of chromospherically active binaries and evidence of an orbital period decrease in binary evolution
The kinematics of 237 chromospherically active binaries (CABs) werestudied. The sample is heterogeneous with different orbits andphysically different components from F to M spectral-type main-sequencestars to G and K giants and supergiants. The computed U, V, W spacevelocities indicate that the sample is also heterogeneous in velocityspace. That is, both kinematically younger and older systems exist amongthe non-evolved main sequence and the evolved binaries containing giantsand subgiants. The kinematically young (0.95 Gyr) subsample (N= 95),which is formed according to the kinematical criteria of moving groups,was compared with the rest (N= 142) of the sample (3.86 Gyr) toinvestigate any observational clues of binary evolution. Comparing theorbital period histograms between the younger and older subsamples,evidence was found supporting the finding of Demircan that the CABs losemass (and angular momentum) and evolve towards shorter orbital periods.The evidence of mass loss is noticeable on the histograms of the totalmass (Mh+Mc), which is compared between theyounger (only N= 53 systems available) and older subsamples (only N= 66systems available). The orbital period decrease during binary evolutionis found to be clearly indicated by the kinematical ages of 6.69, 5.19and 3.02 Gyr which were found in the subsamples according to the periodranges of logP<= 0.8, 0.8 < logP<= 1.7 and 1.7 < logP<=3, respectively, among the binaries in the older subsample.
| An Assessment of Dynamical Mass Constraints on Pre-Main-Sequence Evolutionary Tracks
We have assembled a database of stars having both masses determined frommeasured orbital dynamics and sufficient spectral and photometricinformation for their placement on a theoretical H-R diagram. Our sampleconsists of 115 low-mass (M<2.0 Msolar) stars, 27pre-main-sequence and 88 main-sequence. We use a variety of availablepre-main-sequence evolutionary calculations to test the consistency ofpredicted stellar masses with dynamically determined masses. Despitesubstantial improvements in model physics over the past decade, largesystematic discrepancies still exist between empirical and theoreticallyderived masses. For main-sequence stars, all models considered predictmasses consistent with dynamical values above 1.2 Msolar andsome models predict consistent masses at solar or slightly lower masses,but no models predict consistent masses below 0.5 Msolar,with all models systematically underpredicting such low masses by5%-20%. The failure at low masses stems from the poor match of mostmodels to the empirical main sequence below temperatures of 3800 K, atwhich molecules become the dominant source of opacity and convection isthe dominant mode of energy transport. For the pre-main-sequence samplewe find similar trends. There is generally good agreement betweenpredicted and dynamical masses above 1.2 Msolar for allmodels. Below 1.2 Msolar and down to 0.3 Msolar(the lowest mass testable), most evolutionary models systematicallyunderpredict the dynamically determined masses by 10%-30%, on average,with the Lyon group models predicting marginally consistent masses inthe mean, although with large scatter. Over all mass ranges, theusefulness of dynamical mass constraints for pre-main-sequence stars isin many cases limited by the random errors caused by poorly determinedluminosities and especially temperatures of young stars. Adopting awarmer-than-dwarf temperature scale would help reconcile the systematicpre-main-sequence offset at the lowest masses, but the case for this isnot compelling, given the similar warm offset at older ages between mostsets of tracks and the empirical main sequence. Over all age ranges, thesystematic discrepancies between track-predicted and dynamicallydetermined masses appear to be dominated by inaccuracies in thetreatment of convection and in the adopted opacities.
| The spot activity of BH Virginis
In this paper, photoelectric light curves of BH Vir in 4650 and 5500Å bands observed by [PASJg, 191] were analyzed by using the 1992version Wilson-Devinney program to investigate spot activity. Theresults show that: (1) There is a large cool spotted active region onthe secondary star in 1953-1954. (2) Around phase 0.65 the distortionwaves of two color light curves can be fitted satisfactorily with twodifferent spot models, a cool spot in 5500 Å band, while a hotspot in 4650 Å band. (3) The mass ratio obtained from thephotoelectric light curves is q=m2/m1=0.967. It isclose to the spectroscopic value of 0.968 obtained by . [A&A 237,148]. (4) The photosphere temperature of the primary isT1=6052+/-8 K.
| Photoelectric Minima of Selected Eclipsing Binaries
Not Available
| A period investigation of two chromospherically active binary stars: RT Coronae Borealis and PW Herculis
Orbital period variations of two chromospherically active binarysystems, RT CrBand PW Her, arepresented. It is shown that the orbital period of RT CrB undergoes acyclic oscillation with a period of 53.9years. For PW Her, an alternatechange, with a period of 42.7years, is found to superimpose on a rapidsecular increase (dP/dt=+3.53×10-6 days/year). If theperiod oscillations of those two systems are caused by the light-timeeffect of a third body, the analysis for RT CrB indicatesthat the third body would be a low-mass main-sequence star, while, forPW Her, the massof the third body should be no less than 7.8 Msolar. Since nospectral lines of the third body were seen in PW Her from thespectroscopic study by Popper [AJ 100 (1990) 247], if there is a thirdbody in the system, it can only be a black hole. However, as bothcomponents in the two binary stars were showing strong chromosphericactivity, the alternate period variations are more plausibly explainedas the result of magnetic activity cycles. No secular period changes ofRT CrB are found,which is in agreement with the detached evolved configuration of thesystem. The long-term period increase of PW Her may indicatethat it is on an active phase of mass transfer(dm/dt=2.17×10-6 Msolar/year).
| YY Geminorum: A Very Late Type Close Binary with Possible Magnetic Stellar Wind
The O-C curve of the very late type close binary (dM1e+dM1e) YYGeminorum is formed and analyzed based on all available times of minimumlight. It is found that the orbital period shows a secular decrease withrate dP/dt=-1.08×10-8 days yr-1. There isweak evidence indicating that a small-amplitude period oscillation issuperposed on the period decrease. YY Gem is a well-detached eclipsingbinary containing two very active components. The secular perioddecrease may suggest that the system is undergoing secular mass andangular momentum loss via a magnetic stellar wind. If thesmall-amplitude oscillation is real, it can be explained either bymagnetic activity cycles or by the presence of a giant planet or browndwarf.
| CCD Times of Minima of Faint Eclipsing Binaries in 2000
196 CCD minima observations of 122 eclipsing binaries made by the authorin 2000 are presented. The observed stars were chosen from the catalogueBRKA of observing programme of BRNO-Variable Star Section of CAS.
| J and K Infrared Light Curves of the Active Binary BH Vir
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| Long-Term Study of the Starspot Activity on the Eclipsing Short-Period RS Canum Venaticorum Star UV Piscium
We present optical photometry of the short period eclipsing RS CVnsystem, UV Piscium for the years 1966-1984. After removing the spoteffects from the light curves of Vivekananda Rao and Sarma (1981), weanalyzed the cleaned data to obtain system parameters. For each lightcurve, we model the distortion waves in order to study the behaviour ofstarspots in this system.
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Observation and Astrometry data
| Constellation: | Vierge |
| Right ascension: | 13h58m24.86s |
| Declination: | -01°39'38.9" |
| Apparent magnitude: | 9.7 |
| Proper motion RA: | 4.9 |
| Proper motion Dec: | -2.7 |
| B-T magnitude: | 10.38 |
| V-T magnitude: | 9.757 |
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