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The Origin of Bright X-ray Sources in Multiple Stars
Luminous X-ray stars are very often found in visual double or multiplestars. Binaries with periods of a few days possess the highest degree ofcoronal X-ray activity among regular, non-relativistic stars because oftheir fast, tidally driven rotation. But the orbital periods in visualdouble stars are too large for any direct interaction between thecompanions to take place. We suggest that most of the strongest X-raycomponents in resolved binaries are yet-undiscovered short-periodbinaries, and that a few are merged remnants of such binaries. Theomnipresence of short-period active stars, e.g., of BY-Dra-typebinaries, in multiple systems is explained via the dynamical evolutionof triple stars with large mutual inclinations. The dynamicalperturbation on the inner pair pumps up the eccentricity in a cyclicmanner, a phenomenon known as Kozai cycling. At times of closeperiapsis, tidal friction reduces the angular momentum of the binary,causing it to shrink. When the orbital period of the inner pair drops toa few days, fast surface rotation of the companions is driven by tidalforces, boosting activity by a few orders of magnitude. If the perioddrops still further, a merger may take place leaving a rapidly rotatingactive dwarf with only a distant companion.
| 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.
| A Photometric Survey for Variables and Transits in the Field of Praesepe with the Kilodegree Extremely Little Telescope
The Kilodegree Extremely Little Telescope (KELT) project is a smallaperture, wide-angle search for planetary transits of solar-type stars.In this paper, we present the results of a commissioning campaign withthe KELT telescope to observe the open cluster Praesepe for 34 nights inearly 2005. Light curves were obtained for 69,337 stars, out of which weidentify 58 long-period variables and 152 periodic variables. Sixteen ofthese are previously known as variable, yielding 194 newly discoveredvariable stars for which we provide properties and light curves. We alsosearched for planetary-like transits, finding four transit candidates.Follow-up observations indicate that two of the candidates areastrophysical false positives, with two candidates remaining aspotential planetary transits.
| 35 Visual Minimum Times of 34 Eclipsing Binaries.
Not Available
| 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
| 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.
| 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.
| 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.
| 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
| The Hamburg/RASS Catalogue of optical identifications. Northern high-galactic latitude ROSAT Bright Source Catalogue X-ray sources
We present the Hamburg/RASS Catalogue (HRC) of optical identificationsof X-ray sources at high-galactic latitude. The HRC includes all X-raysources from the ROSAT Bright Source Catalogue (RASS-BSC) with galacticlatitude |b| >=30degr and declination delta >=0degr . In thispart of the sky covering ~ 10 000 deg2 the RASS-BSC contains5341 X-ray sources. For the optical identification we used blue Schmidtprism and direct plates taken for the northern hemisphere Hamburg QuasarSurvey (HQS) which are now available in digitized form. The limitingmagnitudes are 18.5 and 20, respectively. For 82% of the selectedRASS-BSC an identification could be given. For the rest either nocounterpart was visible in the error circle or a plausibleidentification was not possible. With ~ 42% AGN represent the largestgroup of X-ray emitters, ~ 31% have a stellar counterpart, whereasgalaxies and cluster of galaxies comprise only ~ 4% and ~ 5%,respectively. In ~ 3% of the RASS-BSC sources no object was visible onour blue direct plates within 40\arcsec around the X-ray sourceposition. The catalogue is used as a source for the selection of(nearly) complete samples of the various classes of X-ray emitters.
| 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.
| 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
| Einige interessante Bedeckungsveraenderliche.
Not Available
| The comparative accuracy of photographic observations of radio stars observed at the Engelhardt Astronomical Observatory
At the Engelhardt Astronomical Observatory (EAO), we observedphotographic positions of 113 Galactic Radio Sources (GRS) in the systemPPM catalogue (Rizvanov & Dautov 1998). Analysis of their accuracyis made by comparison with the Hipparcos catalogue (Perryman et al.1997) and astrometric catalogue of radio stars in the radio window fromthe article of Walter et al. (1991). Table 2 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/375/670
| 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.
| 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.
| Time Evolution of the Magnetic Activity Cycle Period. II. Results for an Expanded Stellar Sample
We further explore nondimensional relationships between the magneticdynamo cycle period P_cyc, the rotational period P_rot, the activitylevel (as observed in Ca II HK), and other stellar properties byexpanding the stellar sample studied in the first paper in this series.We do this by adding photometric and other cycles seen in active starsand the secondaries of CV systems and by selectively adding less certaincycles from the Mount Wilson HK survey; evolved stars, long-term HKtrends and secondary P_cyc are also considered. We confirm that moststars with age t>~0.1 Gyr occupy two roughly parallel branches,separated by a factor of ~6 in P_cyc, with the ratio of cycle androtational frequencies ω_cyc/Ω~Ro^-0.5, where Ro is theRossby number. Using the model of the first paper in this series, thisresult implies that the α effect increases with mean magneticfield (contrary to the traditional α-quenching concept) and thatα and ω_cyc decrease with t. Stars are not strictlysegregated onto one or the other branch by activity level, though thehigh-ω_cyc/Ω branch is primarily composed of inactive stars.The expanded data set suggests that for t>~1 Gyr, stars can havecycles on one or both branches, though among older stars, those withhigher (lower) mass tend to have their primary P_cyc on the lower(upper) ω_cyc/Ω branch. The Sun's ~80 yr Gleissberg cycleagrees with this scenario, suggesting that long-term activity ``trends''in many stars may be segments of long (P_cyc~50-100 yr) cycles not yetresolved by the data. Most very active stars (P_rot<3 days) appear tooccupy a new, third branch with ω_cyc/Ω~Ro^0.4. Many RS CVnvariables lie in a transition region between the two most activebranches. We compare our results with various models, discuss theirimplications for dynamo theory and evolution, and use them to predictP_cyc for three groups: stars with long-term HK trends, stars in youngopen clusters, and stars that may be in Maunder-like magnetic minima.
| The FIRST Unbiased Survey for Radio Stars
Comparison of the VLA FIRST survey with various catalogs of bright starsallows an examination of the prevalence of stellar radio emissionindependent of optical selection criteria. This FIRST unbiased surveyfor radio stars covers nearly 5000 deg^2 of the northern sky to a fluxdensity limit of 0.7 mJy at 20 cm. Using astrometric catalogs thatinclude proper-motion information, we have detected 26 stellar radiosources, doubling the number of such objects previously known in thisregion of high-latitude sky. We also show that, in the absence of goodproper motions, even the 1" precision of the FIRST positions isinsufficient to avoid crippling chance coincidence rates. We calculatethe fraction of radio detections as a function of stellar magnitude andshow that, when proper motions from the Guide Star Catalog II becomeavailable, the number of stellar radio source detections should increasefourfold.
| 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
| Optical positions and proper motions of radio stars
The optical positions of 31 radio stars were obtained with the 40 cmastrograph at ZoSe Section, Shanghai Observatory from 1985 to 1988. Theobservational positions and the proper motions of these radio stars inthe FK5 system are given in this paper.
| 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.
| Optical positions and proper motions of 31 radio stars.
Not Available
| RS CVn Versus Algol-Type Binaries: A Comparative Study of Their X-Ray Emission
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111.2415S&db_key=AST
| A new H-alpha survey of chromospherically active binaries.
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.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| 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.
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| קבוצת-כוכבים: | סרטן |
| התרוממות ימנית: | 08h37m30.13s |
| סירוב: | +23°33'41.6" |
| גודל גלוי: | 10.209 |
| תנועה נכונה: | -20.6 |
| תנועה נכונה: | -2.1 |
| B-T magnitude: | 10.926 |
| V-T magnitude: | 10.269 |
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