Contents
Images
Upload your image
DSS Images Other Images
Related articles
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.
| 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.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Are the W Ursae Majoris-type systems EK Comae Berenices and UX Eridani surrounded by circumstellar matter?
The variations of the orbital periods of two nearly neglected W UMa-typeeclipsing binaries, EK Comae Berenices and UX Eridani, are presentedthrough a detailed analysis of the O C diagrams. It is found that theorbital period of EK Com is decreasing and the period of UX Eridani isincreasing, and several sudden jumps have occurred in the orbitalperiods of both binaries. We analyze the mechanism(s), which mightunderlie the changes of the orbital periods of both systems, and obtainsome new results. The long-term decrease of the orbital period of EKComae Berenices might be caused by the decrease of the orbital angularmomentum due to a magnetic stellar wind (MSW) or by mass transfer fromthe more massive to the less massive component. The secular increase inthe orbital period of UX Eridani might be caused by mass transfer fromthe less massive to the more massive star. The possible mechanisms,which underlie the sudden changes in the orbital periods of the closebinary systems are as the followings: (1) the variations of thestructure due to the variation of the magnetic field; (2) the rapid massexchange between the close binaries and their circumstellar matter.Finally, the evolutionary status of the systems EK Comae Berenices andUX Eridani is discussed.
| 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.
| 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.
| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderlichen Serne e.V.
Not Available
| Polarimetry of evolved stars. II. The carbon star R Scl
We present broadband optical polarimetry of the carbon star R Scl,primarily in the VRCIC bands. Polarimetricvariability was detected on time-scales from hours to years. Thepolarization of R Scl showed a ~ lambda -4wavelength-dependence, which we attribute to scattering by smallamorphous carbon dust grains. We deduce the properties of thecircumstellar condensations in which the scattering takes place, andfind consistency with infrared data if the condensations move ineccentric orbits. We also conclude that the condensations are tidallydispersed on a time-scale ~ 1 day. On longer time-scales, polarimetricvariations may possibly be linked with photometric variations.
| 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.
| RS CVn, V548 cyg, GK Hya: Merkwurdiges - Verfolgenswertes.
Not Available
| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veraenderliche Sterne e.V.
Not Available
| A spectroscopic study of the eclipsing binaries SV Camelopardalis and XY Ursae Majoris
High-resolution spectroscopic observations of the eclipsing RS CVn-typeactive close binaries SV Camelopardalis and XY Ursae Majoris revealexcess emission components in the Hα and Hβ lines. We haveused the spectral subtraction technique to separate the excess emissionfrom the photospheric background and find that in both stars the excessemission is associated with the secondary, cooler component. Analysis ofthe EWHα/EWHβ ratio indicates that inboth cases the emission is probably associated with surface plageregions or prominences viewed against the stellar disks. We find noevidence of excess absorption features associated with extendedprominence-like material in these systems. Based on observations made atObservatoire de Haute Provence (CNRS), France.
| 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.
| 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.
| Doppler imaging of stellar surface structure. XIII. The flaring RS CVn-binary HD 291095 = V1355 Orionis
We present the first Doppler images of the newly discovered RS CVnbinary HD 291095. The star is a synchronuously rotating subgiant in a4-day spectroscopic binary with an unseen companion and is particularlyinteresting because it is one of the few evolved stars that show largeflares. Three consecutive years of moderate-resolution KPNO spectra andcontinuous VI and by photometry with our APTs reveal a large, cool, andlong-living asymmetric polar spot. Its temperature is approximately 1100K below the average photospheric temperature. Several low latitude andeven equatorial spots were evident at the same time. We interpret thislatitudinal spot bimodality to be due to a combination of polewardmeridional circulation and more frequent magnetic reconnections near thepole than near the equator. During the 1998 Doppler-imagingobservations, a strong flare in Hα was detected which coincidedwith a meridian passage of the most asymmetric part of the polar spot.We estimate a total flare energy of 5x1034 erg typical forflares on very active RS CVn systems. No photospheric heating is evidentin our surface maps from optically thin spectral lines of varioustemperature sensitivities.
| 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.
| Mutual irradiation and absorption in detached binary systems and surface temperature variation.
Not Available
| Environments of active close binaries. II. GK Hydrae and TY Pyxidis.
High-resolution spectroscopic observations were obtained for twoeclipsing active close binary systems, GK Hydrae and TY Pyxidis. For GKHya excess emission was observed in the Balmer lines and Mg I b lineswhile TY Pyx showed excess emission in the Balmer lines and Ca iiH&K lines. The emission from GK Hya arises from a global phenomenonassociated solely with the secondary component. The lack of significantHe I D_3_ excess absorption and an analysis of the flux ratio in theBalmer lines suggest that the emission originates in prominence-likematerial seen off the limb of the star. A marginal broad excessabsorption band centered around the Balmer emission peaks may be causedby this material absorbing the stellar continuum against the disk withhigh (350km/s) line-of-sight turbulent velocities. The inference thatplage-like regions and associated star-spots are not substantial on thisstar is in agreement with the lack of spot modulation in the photometriclight curve. For TY Pyx the majority of the Hβ excess and a largerproportion of the Ca ii core emission could be attributed to a globalphenomenon on the primary. Analysis suggests that very large volumes areresponsible for the emission, however, there is no observationalevidence for the existence of discrete extended structures around TYPyx.
| EUV Emission from RS Canum Venaticorum binaries.
We performed a study of 104 RS CVn systems in the extreme ultraviolet(EUV) using the all-sky survey data obtained by the Extreme UltravioletExplorer (EUVE). The present sample includes several new RS CVndetections; 11 more than in the published EUVE catalogs, and 8 more thanin the ROSAT Wide Field Camera catalog. The ratio of detections tonon-detections remained constant throughout the sky, implying that ourdetections are not limited by the exposure time but are most likelylimited by absorption from the interstellar medium. A general trend ofincreasing Lex/B (50-180Å) flux with decreasing rotational periodis clear. The dwarf systems exhibit a leveling-off for the fasterrotators. In contrast, the evolved systems exhibit no such effect. Forthe RS CVn systems the losses in the EUV represent a smaller fraction ofthe coronal radiative losses, as compared to active late-type dwarfs.
| Environments of active close binary stars
Not Available
| The emission of the RS CVn binaries in the IRAS passbands.
In the literature, there is an ambiguity pertaining to the existence ofa far-IR excess in RS CVn systems. In the current paper we undertook astudy of the behaviour of 103 such systems in the IRAS passbands. Wefound 72 acceptable detections in the 12μm band, and 40 in the25μm band (50% more than the IRAS Point Source Catalog). Although ourfindings may be interpreted as indicating towards the existence of anexcess beyond 12μm for some systems, the evidence is not conclusivein all but two cases. These are systems GX Lib and HR 7428, with Capellabeing the only system where the IRAS fluxes in all four bands originatefrom the stellar photosphere. Given the accuracy of the data we did notfind 12μm excess for any system. We argue that the IRAS data alonecannot settle the issue, as their uncertainty is, in many cases, higherthan what the Signal-to-Noise ratio of each observation implies.Furthermore, at the higher wavelength bands the IRAS angular resolutiondrops from 0.5' at 12μm to 2' at 100μm and the background becomesvery complex, so one cannot be certain about the origin of the observedflux. The existence of IR excess in the RS CVn stars is important as faras the evolutionary scenarios for these systems are concerned. Futuremissions such as the Infrared Space Observatory will return moresensitive and accurate measurements and the ambiguity can be removed.The fluxes we quote will be helpful when planning these futureobservations, as we provide more accurate photometry and for a largerselection of sources than the IRAS Point Source Catalog.
| Cross-correlation radial velocity measurements of chromospherically active binaries.
We present observational radial velocity curves for 12 chromosphericallyactive binary systems and individual measurements for a further 5systems. These binaries are LX Per, V 471 Tau, EI Eri, OU Gem, GK Hya,TY Pyx, Z Her, MM Her, V772 Her, ER Vul, BD-004234, MY Cyg, AR Lac, KZAnd, RT And, SZ Psc and EZ Peg. Six of our target binaries do not agreewith published ephemerides or orbital parameters. We also present arigorous derivation of the resolution limit for binary starcross-correlation radial velocities. Using synthetic spectral data weinvestigate the errors induced by rotational broadening, signal-to-noiseratio, spectral-type mismatch and luminosity ratio.
| Are Rotational Axes Perpendicular to Orbital Planes in Binary Systems. III.Main Sequence and Short-Period RS CVn Stars.
Inclinations of the rotational axes, irot, are determined for46 main sequence binaries of F, G, K and M spectral type and shortperiod RS CVn systems. Seven binaries are asynchronous. The inclinationsirot are then compared with the orbital inclinations,iorb, to test the alignment between the equatorial andorbital planes. In all 39 cases of synchronous rotators irotis equal or nearly equal to iorb. In a sample of sevenasynchronous systems, at least six, and perhaps all, are non-coplanar.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| The age-mass relation for chromospherically active binaries. I. The evolutionary status
In this paper we present a study of the evolutionary status of a sampleof chromospherically active binary systems for which accuratedeterminations of their stellar parameters are available. Stellar ageshave been obtained by using evolutionary tracks. The agreement betweenthe estimates of ages for the two components of a given system is verygood, which proves the reliability of our method. It has been possibleto separate the chromospherically active binaries in three groups,according to the mass of the primary component: evolved stars withmasses in the range 2.5-5Msun_, evolved stars (subgiants)with M=~1.4Msun_ and main-sequence stars withM=~1.1Msun_. We have found a relationship between stellarmasses and ages of the formLog(Age)=9.883(+/-0.022)-2.965(+/-0.122)Log(Mass/Msun_). Thisrelationship is very close to that for stars on the TAMS. The relationcan be understood, in the framework of the evolution of the componentsand orbital elements of binary systems, as an effect of the increase ofthe stellar radius as the components evolve off the main sequence, andthe decrease of the rotation period due to tidal effects which leads toenhanced chromospheric emission levels, several times higher than thatof the Sun. The relationship has a dependence on rotation, due to thefact that for a given range of masses, younger stars rotate faster. Wehave also found that the more evolved stars are the more active, for agiven interval of rotation periods.
| Predicting the Secondary Minima Depths and Spectra of the Main Components for the Dm-Type Eclipsing Variable Stars
Not Available
| UBVRI Linear and Circular Polarization of Rs-Canum
The observed sample of 15 RS CVn binaries contains 6 systems withevidence of circumbinary dust envelopes from an IR excess, and forcomparison 6 binaries which do not show any excess, the rest of theobjects have an uncertain detection. Four of the binaries, II Peg, DKDra, GK Hya, and UX Ari were observed with phase coverages sufficientfor a second order Fourier analysis. Data for II Peg from 36 nightsspanning two observing seasons give evidence for a statisticallysignificant second harmonic in the V band with an amplitude of0.024±0.007% in the parameter Px. The modulationappears to be stronger (0.042±0.010%) during the first season(1989-90) and to have a decreased amplitude (0.013±0.010%)during the second indicating possible long-term variability. Due tothe small number of observations in the R and I bands the detectionsare less clear. The same is true for the Fourier fits of the otherobserved binaries. CQ Aur, RZ Eri, and VV Mon are polarized at the0.20% level (σ ˜ ±0.01%), but the wavelengthdependence for these binaries is consistent with interstellarpolarization. The mean polarizations for UX Ari and DK Dra are small(0.017±0.010% and 0.032±0.008%, respectively), but showa tendency to increase toward the infrared, which may indicatescattering by large dust particles in optically thin circumstellarmaterial. No correlation between the IR excess and the evidence forintrinsic polarization was found.
| A catalog of chromospherically active binary stars (second edition)
The catalog contains 206 spectroscopic binary systems with at least onelate-type component that shows Ca II H and K emission in its spectrum.These systems include the classical RS CVn binaries and BY Dra binaries.The catalog summarizes information on the photometric, spectroscopic,orbital, and physical properties of the systems as well as space motionsand positions. Up to 42 'parameters' for each stellar system are listedfollowed by the appropriate reference to direct interested colleagues tothe original papers. A comprehensive selection of further informationfor each star is given in the individual notes. In addition, the catalogcontains a candidate list of 138 stars that have similar characteristicsbut are not definitely known binaries or have not had Ca II H and Kemission observed.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Hydra |
| Right ascension: | 08h30m49.31s |
| Declination: | +02°16'26.6" |
| Apparent magnitude: | 9.379 |
| Proper motion RA: | -45.7 |
| Proper motion Dec: | 9.4 |
| B-T magnitude: | 10.27 |
| V-T magnitude: | 9.453 |
Catalogs and designations:
|
