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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.
| Modelling the colour-brightness relation of chromospherically active stars
The photometric flux of chromospherically active, spotted starsgenerally becomes redder and fainter when large starspots rotate intoview on the stellar disc. However, some of the most active RS CVnsystems show a bluer flux as they get fainter. Modelling of one suchsystem (UX Ari) has shown that hot, bright, photospheric facular regionsaccompanying the cool, dark spots on the cooler, more active componentare a possible explanation. The bluer flux of the hotter, less activecomponent does not appear to be sufficient to explain the observedbehaviour. We have begun a search for additional chromosphericallyactive stars with a similar relation between colour and brightness, toinvestigate whether these relations can be explained in the same way.Our results for V711 Tau and RS CVn are presented here, and we concludethat the photospheric faculae remain the most probable explanation forthe observed behaviour.
| The Chromospherically Active Contact Binary CE Leonis
We present complete VRI light curves of the contact binary CE Leo andprovide detailed photometric solutions, as well as an analysis of itsperiod variation. A total of 73 times of minima over 50 years, includingour observations, were used for the period study. The complex periodvariation can be sorted into a linear period improvement, a period ofP=0.30342771 days, a secular period increase at the rate ofP/P=+3.05×10-7 days yr-1, and a 22.6+/-0.5yr periodic component. The ~22.6 yr periodic variation in the O-Cresiduals most likely arises from the light-travel time effect from alow-mass (m3~0.3Msolarsini) dM tertiary companionmoving in an eccentric (e'=0.61+/-0.04) orbit. However, it isalso possible that this periodic variation arises from the effects of amagnetic activity cycle, known as the Applegate mechanism. The lightcurves show asymmetries in the two different maxima. The 1998 lightcurves show that primary maximunm was 0.042, 0.038, and 0.038 magbrighter than secondary maximum in V, R, and I, respectively. Thedurations of totality for three epochs were 18.3 minutes in 1989, 19.7minutes in 1998, and 18.8 minutes in 2001. The relative depth of primaryminimum was found to vary between 1.20 and 1.32 mag. We have analyzedthe light curves from the three epochs using the 1993 version of theWilson-Devinney differential corrections computer code to find a uniquesolution for CE Leo. The corresponding spectral type of the secondarystar from the colors and effective temperature is ~dK2. The asymmetriclight curves can be explained by the effects of starspots. We find thatthe light curves are best fitted by employing a cool spot on the cooler,larger component of the system. The spot-effect parameter SE=0.05 foundfor CE Leo is relatively large for W UMa binaries.
| Times of Minima for Some Eclipsing Binaries
Times of minima for a number of some eclipsing binaries are presented.
| 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.
| 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
| Chromospheric activity and unique solution of SZ Psc
We have confirmed that the MgII h and k emission lines of SZ Psc aremainly enhanced by the K subgiant component of the system, using theradial velocities reduced from the emission lines. The intensityvariation of the emission line is correlated with the orbital phase ofSZ Psc. The shape of light curves of SZ Psc were changing every season.The three representative light curves of three different epochs, 1978,1979 and 1981, were selected to find a unique solution of SZ Psc whichcan explain the variation of light curves. The binary parameters,including inclination, mass ratio, temperatures and potentials of bothcomponents for the three epochs coincide, although the shapes of lightcurves for three epochs are different from each other. Changing onlyspot parameters, the model light curves fit to the observed light curvesfor three epochs. This means that the variation of spot location andsize is the main reason for changing the shape of light curves.
| Long-term photometric behaviour of the RS CVn binary RT Lacertae
A sequence of the seasonal light curves of RT Lac, covering the period1978-2000, is analysed in the framework of the starspot hypothesis todefine the spot distribution, based on the interpretation of the B-bandobservations. The analysis of the corresponding light curves is madeusing Djurašević's inverse-problem method. To explain thelight-curve variations we modelled the binary system using a Roche modelthat involved regions containing spots on both components. Satisfactoryfits were obtained assuming spots on both components. The more-massiveG5 primary appears to be the most active star in the system and itsspotted areas are mainly responsible for the light-curve distortions.Spots are concentrated around longitudes 45degr -170degr and at highlatitudes (above 45degr ). Our analysis indicates two spots withdiameters of ~ 10degr -50degr on both hemispheres of the primary.However, the less-massive cool component seems to have only one spotwhich covers a relatively small area. Total spotted area of themore-massive primary component indicates clear evidence for a short-termactivity cycle with a period of 8.4 yr, and a possible long-term cyclewith a period of 33.5 yr. The G9IV secondary does not show any evidencefor an activity cycle, its spot coverage appearing rather constant atabout 10% of its surface. The variation of the orbital period seems tobe correlated with the total activity level of the system. Inparticular, the decrement of the orbital period appears to be associatedwith minimum spottedness and sizeable changes of the surface spotpattern distribution on the surface of each star. This result, ifconfirmed by the future observations, can provide further support forrecently proposed models for connection between the magnetic activityand orbital period variations.
| Effect of chromospheric activity on the mean colours of late-type stars. II. Is (B-V)0 also affected?
We confirm the existence of an ``excess'' in the mean dereddened(U-B)0 colour of active single-lined spectroscopic giantsover quiescent stars of the same spectral type and find evidence forthis ``excess'' in (B-V)0, although at a lower scale, whenplotted against (R-I)0. This result suggests that the use of(B-V)0 calibrations to determine fundamental parameters orspectral types for late-type active stars should be taken with caution.Since magnetic activity is definitely involved, these and similarcalibrations using (U-B)0 and/or (B-V)0 should notbe used for the study of late-type young clusters' members or late-typepre-main sequence stars without some consideration. Instead,near-infrared colours like (R-I)0 should be bettertemperature indicators for these stars.
| WW Dra - ein heller BAV-Programmstern mit vielen Problemen.
Not Available
| Determination of the Ages of Close Binary Stars on the Main Sequence from Evolutionary Model Stars of Claret and Gimenez
A grid of isochrones, covering a wide range of stellar ages from thezero-age main sequence to 10 billion years, is calculated in the presentwork on the basis of the model stars of Claret and Gimenez withallowance for convective overshoot and mass loss by the components. Theages of 88 eclipsing variables on the main sequence from Andersen'scatalog and 100 chromospherically active stars from Strassmeier'scatalog are calculated with a description of the method of optimuminterpolation. Comparisons with age determinations by other authors aregiven and good agreement is established.
| Solar spots as prototypes for stellar spots
What is the nature of what we commonly refer to as starspots? The answerto that question determines what we can learn from the study ofstarspots about stars, their internal dynamics, and their magneticactivity. Observations of the Sun, the only cool star that we canobserve in detail, naturally led to the hypothesis that starspots inother cool stars are magneto-convective phenomena in which a magneticfield substantially affects the structure of a stellar atmosphere.Spectral line features, eclipse light curves, and intensity modulationsare consistent with that hypothesis. Yet for almost all stars for whichstarspots are reported, the surface coverage is very much higher thanfor the Sun, while many stars manifest spots at high latitudes where theSun has never been seen to do so. In this review, I address how wellstarspots compare to sunspots, discuss some differences expected whenmoving away from the Sun in the HR diagram or in level of activity, andidentify resources to further deepen our understanding.
| Vitesses radiales photoélectriques de binaires àéclipses. VI. Orbites spectroscopiques et éléments physiques de 12 étoiles doubles Photoelectric radial velocities of eclipsing binaries VI. Orbital and physical elements of 12 double stars
Spectroscopic orbits of the 12 eclipsing binary systems, TW And, CD And,RS Ari, RU Cnc, TW Cnc, UU Cnc, V788 Cyg, AW Her, MM Her, RV Lib, EW Oriand ZZ UMa are obtained from Coravel and Elodie radial velocitymeasurements. We obtain a first orbit for CD And, RS Ari, TW Cnc, andV788 Cyg. For the systems TW And, RU Cnc, UU Cnc, AW Her, MM Her, RVLib, EW Ori and ZZ UMa, the new spectroscopic orbits are either betteror of quality comparable to that previously published. The physicalproperties of these systems were estimated with the photometricparameters from available data except CD And, TW Cnc, UU Cnc, V788 Cygand RV Lib for which we found a model compatible with the observations.The systems RU Cnc, AW Her, MM Her and RV Lib belong to RS CVn group. Ingeneral these systems were difficult to observe with Coravel, on the onehand because the stars are relatively weak and on the other hand becauseof nature of the components giving peaks of correlation with weakcontrast. La plupart des observations ont étéeffectuées àl'Observatoire de Haute-Provence (CNRS).Based, in part, on observations collected at the European SouthernObservatory, la Silla, Chile. La Table 1 est disponible seulement sousforme électronique au CDS via ftp à cdsarc.u-strasbg.fr(130.79.128.5) ou viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/387/850
| 149 Bedeckungssterne der BAV-Programme. Eine Analyse der Beobachtungstatigkeit seit den Angangen.
Not Available
| Das Brunner Punktesystem.
Not Available
| The Catania Automatic Photoelectric Telescope on Mt. Etna: a systematic study of magnetically active stars
A photometric monitoring of about 50 magnetically active stars, that arespread almost all over the H-R diagram, was initiated at the mountainstation of Catania Observatory on Mt. Etna (1750-m a.s.l.) in 1992 withan 80-cm robotic telescope (APT-80) built by AutoScope Co. (USA). Thissystematic survey is now approaching its 10th year anniversary. For mostof the stars, quite well defined solar-like spot maps have been derivedfrom UBV data obtained in different epochs. These data have allowed usto investigate some relevant characteristics of spot activity andvariability on stars, and to obtain clear evidence of long-term activitycycles, in the range from a few to about 10 years, on some of theobserved targets. Starspot maps are constructed by using advanced tools,such as massive parallel computing and are based on Maximum Entropy andTikhonov regularization criteria. Selected results are here presented.Our systematic observation program is still underway and a secondAPT80/2, equipped with a CCD camera, will pair the APT80/1 on the samesite. Its operation is foreseen for mid 2002.
| BVR photometry and Hα spectroscopy of RS CVn type binary MM Herculis
The RS CVn type eclipsing binary MM Herculis wasobserved photo-electrically using B, V and R filters in 1998 and 1999and the light and colour curves were obtained. Spectroscopicobservations were carried out in 1999. The new light and colour curvesare anti-correlated with the observations of 1997, i.e. the system isbluer when it is faintest. The variations of the brightnesses at eachspecial phase (0.0, 0.25, 0.5, and 0.75) show an almost cyclic changewith a period of about 6 years. This value is in good agreement with themigration periods of the spots suggested by us previously. Theoutside-of-eclipse wave in the light curve shows a minimum at phase~0.50, and the mean colour of the system is the bluest at the samephase. When the spots located on the cooler component are seen aroundphase 0.50, the amplitude of the light variation outside eclipse islarger than the others. Such variation may be caused by the effect ofthe hotter component. Spectroscopic observations of the system werecarried out in the spectral range 5860-6700 Å. The subtraction ofa ``synthetic'' spectrum, built up with spectra of inactive standardstars, allows us to detect an Hα emission excess only from thecool component. New radial velocity measurements of the system wereobtained and analyzed for the orbital parameters. Based on observationscollected at the Ege University Observatory, Turkey, and at the CataniaAstrophysical Observatory, Italy.
| The Northern ROSAT All-Sky (NORAS) Galaxy Cluster Survey. I. X-Ray Properties of Clusters Detected as Extended X-Ray Sources
In the construction of an X-ray-selected sample of galaxy clusters forcosmological studies, we have assembled a sample of 495 X-ray sourcesfound to show extended X-ray emission in the first processing of theROSAT All-Sky Survey. The sample covers the celestial region withdeclination δ>=0deg and Galactic latitude|bII|>=20deg and comprises sources with a countrate >=0.06 counts s-1 and a source extent likelihood ofL>=7. In an optical follow-up identification program we find 378(76%) of these sources to be clusters of galaxies. It was necessary toreanalyze the sources in this sample with a new X-ray sourcecharacterization technique to provide more precise values for the X-rayflux and source extent than obtained from the standard processing. Thisnew method, termed growth curve analysis (GCA), has the advantage overprevious methods in its ability to be robust, to be easy to model and tointegrate into simulations, to provide diagnostic plots for visualinspection, and to make extensive use of the X-ray data. The sourceparameters obtained assist the source identification and provide moreprecise X-ray fluxes. This reanalysis is based on data from the morerecent second processing of the ROSAT Survey. We present a catalog ofthe cluster sources with the X-ray properties obtained as well as a listof the previously flagged extended sources that are found to have anoncluster counterpart. We discuss the process of source identificationfrom the combination of optical and X-ray data. To investigate theoverall completeness of the cluster sample as a function of the X-rayflux limit, we extend the search for X-ray cluster sources to the dataof the second processing of the ROSAT Survey for the northern sky regionbetween 9h and 14h in right ascension. We includethe search for X-ray emission of known clusters as well as a newinvestigation of extended X-ray sources. In the course of this search wefind X-ray emission from 85 additional Abell clusters and 56 veryprobable cluster candidates among the newly found extended sources. Acomparison of the X-ray cluster number counts of the NORAS sample withthe ROSAT-ESO Flux-limited X-Ray (REFLEX) Cluster Survey results leadsto an estimate of the completeness of the NORAS sample of ROSAT All-SkySurvey (RASS) I extended clusters of about 50% at an X-ray flux ofFX(0.1-2.4 keV)=3×10-12 ergs s-1cm-2. The estimated completeness achieved by adding thesupplementary sample in the study area amounts to about 82% incomparison to REFLEX. The low completeness introduces an uncertainty inthe use of the sample for cosmological statistical studies that will becured with the completion of the continuing Northern ROSAT All-Sky(NORAS) Cluster Survey project. Results reported here are based onobservations made with the Multiple Mirror Telescope, a joint facilityof the Smithsonian Institution and the University of Arizona.
| On the origin of binaries with twin components
The existence of a statistically significant excess of dwarf binarieswith mass ratios from 0.95 to 1, as first noted by Lucy & Ricco (?),is confirmed by modern data. Excess of such binaries, called twins, isfound only for periods shorter than 40 days, and in the 2-30 days periodrange they constitute 10-20% of the total binary population. Twins musthave been formed by a special mechanism. It cannot be a mass transfer incontact pre-main-sequence binaries, fission is also unlikely. As shownby Bate (2000), accretion onto a close binary shifts mass ratio towards1, so twins may originate from binaries that became close while stillsurrounded by massive envelopes. Many twins are members ofhigher-multiplicity systems and/or clusters, which probably explains anearly formation of a close binary by stellar dynamics.
| Spin and orbital angular momentum exchange in binary star systems. II. Ascending the giant branch: a new path to FK Comae stars
Using the model by Keppens (1997), we investigate the angular momentum(AM) evolution in asymmetric binary star systems from Zero-Age MainSequence times until at least one component has ascended the giantbranch. We concentrate on stars ranging in mass from 0.9 Msun- 1.7 Msun, in almost synchronous, short period systems(P_orb<9 days). We address synchronization and circularization bytidal interaction, allowing for structural evolution and stellar winds.A Weber-Davis prescription is used to quantify the wind influence,thereby accounting for changes in its acceleration mechanism from theinterplay of the evolving thermal-magneto-centrifugal effects. Weidentify a scenario for fast in-spiraling components with d ln P_orb/dt=~ -{cal O}(10-8) which is primarily driven by faststructural evolution as the heaviest component ascends the giant branch.This leads to the formation of contact systems, which ultimatelycoalesce and form FK Comae-like objects on relatively short timescalesdue to the continuing expansion of the primary. The obtained mass lossrates and orbital period variations d ln P_orb/dt are confronted withtheir observed ranges. The predicted mass loss rates agree with thesolar value on the main sequence and with the Reimers relation in thegiant phase. Observations of period evolution in close, active binariessuggest, however, that other influences than those considered here mustplay an important role. Finally, we point out how the mass asymmetry ofthe binary system can be a crucial ingredient in the angular momentumevolution: while the primary dictates the spin-orbital AM exchange inthe system, the slowly evolving lighter component can develop anefficient magneto-centrifugally driven wind and thereby drain the AMfrom the system.
| New Photoelectric Minima and Light Elements of MM Herculis
In this study, the times of minima obtained from 1998-1999 photometricobservations of MM Herculis are presented and the new light elements aregiven. The variation of residuals can either be the result of alight-time effect or magnetic activity.
| Three-Colour Photometry of MM Herculis During 1998-1999
Not Available
| On X-Ray Variability in Active Binary Stars
We have compared the X-ray emissions of active binary stars observed atvarious epochs by the Einstein and ROSAT satellites in order toinvestigate the nature of their X-ray variability. The primary aim ofthis work is to determine whether or not active binaries exhibitlong-term variations in X-ray emission, perhaps analogous to theobserved cyclic behavior of solar magnetic activity. We find that, whilethe mean level of emission of the sample remains steady, comparison ofdifferent ROSAT observations of the same stars shows significantvariation on timescales <~2 yr, with an ``effective variability''ΔI/I=0.32+/-0.04, where I and ΔI represent the mean emissionand variation from the mean emission, respectively. A comparison of theROSAT All-Sky Survey and later pointed observations with earlierobservations of the same stars carried out with Einstein yields onlymarginal evidence for a larger variation (ΔI/I=0.38+/-0.04 forEinstein vs. ROSAT All-Sky Survey and 0.46+/-0.05 for Einstein vs. ROSATpointed) at these longer timescales (~10 yr), thus indicating thepossible presence of a long-term component to the variability. Whetheror not this long-term component is due to the presence of cyclicvariability cannot be decided on the basis of existing data. However,assuming that this component is analogous to the observed cyclicvariability of the Sun, we find that the relative magnitude of thecyclic component in the ROSAT passband can, at most, be a factor of 4,i.e., I_cyc/I_min<4. This is to be compared with the correspondingbut significantly higher solar value of ~10-10^2 derived from GOES,Yohkoh, and Solrad data. These results are consistent with thesuggestions of earlier studies that a turbulent or distributive dynamomight be responsible for the observed magnetic activity on the mostactive, rapidly rotating stars.
| The activity pattern on MM Herculis: spots and faculae
The RS CVn type eclipsing binary MM Herculis was observed using B, V,and R filters in 1997 and the light and colour curves were obtained. Thelong-term (1976-1997) variations in the brightness and colour of thesystem were revealed by examining 12 light and colour curves. The reasonfor the variations in the B-V colour curves may be the photosphericbright facular structures that surround starspots. The system is bluestwhen at its faintest. Migration periods of 5.8 and 5.9 years have beenfound for the two spots or spot groups, which are located on the coolercomponent. The spots that are located within the longitude difference of180° seem to approach each other with a period of six years. In thiscase the amplitudes of the light curves increase, the system's meanbrightness decreases and its mean colour becomes bluer.
| New Photoelectric Photometry of MM Herculis
Not Available
| Mutual irradiation and absorption and surface temperature variation in detached binary systems
In the paper, we calculate the absorbed flux of the mutual irradiationof the components in detached binary systems, and obtain the surfacetemperature distribution on the components. The maximum temperaturedifference over the surface is a measure of the deviation betweenisothermal and equipotential surfaces. For 33 late-type binary systemswith known elements, we evaluate this maximum difference. The resultshows that the isothermal-equipotential deviation is always larger inthe cooler than in the hotter components. This result supports Zhou andLeung's idea that the large difference between ``star-spots'' andsunspots is due to cyclones and anticyclones. The effect of limbdarkening (amounting to over 18% and always larger in the hottercomponent) is included in the consideration.
| Photoelectric and CCD times of minima of several eclipsing binary systems
We present several photoelectric and CCD minima observations of severaleclipsing binaries. Most of them are apsidal motion stars (or at leastcandidate ones).
| Mutual irradiation and absorption in detached binary systems and surface temperature variation.
Not Available
| Accurate Positions for Radio Stars as Determined from CCD Observations in the Extragalactic Reference Frame.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1679S&db_key=AST
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