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A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun
Traditionally, runaway stars are O- and B-type stars with large peculiarvelocities. We would like to extend this definition to young stars (upto ?50 Myr) of any spectral type and to identify those present in theHipparcos catalogue by applying different selection criteria, such aspeculiar space velocities or peculiar one-dimensional velocities.Runaway stars are important for studying the evolution of multiple starsystems or star clusters, as well as for identifying the origins ofneutron stars. We compile the distances, proper motions, spectral types,luminosity classes, V magnitudes and B-V colours, and we utilizeevolutionary models from different authors to obtain star ages. We studya sample of 7663 young Hipparcos stars within 3 kpc from the Sun. Theradial velocities are obtained from the literature. We investigate thedistributions of the peculiar spatial velocity and the peculiar radialvelocity as well as the peculiar tangential velocity and itsone-dimensional components and we obtain runaway star probabilities foreach star in the sample. In addition, we look for stars that aresituated outside any OB association or OB cluster and the Galactic planeas well as stars for which the velocity vector points away from themedian velocity vector of neighbouring stars or the surrounding local OBassociation/cluster (although the absolute velocity might be small). Wefind a total of 2547 runaway star candidates (with a contamination ofnormal Population I stars of 20 per cent at most). Thus, aftersubtracting these 20 per cent, the runaway frequency among young starsis about 27 per cent. We compile a catalogue of runaway stars, which isavailable via VizieR.
| XID II: Statistical Cross-Association of ROSAT Bright Source Catalog X-ray Sources with 2MASS Point Source Catalog Near-Infrared Sources
The 18,806 ROSAT All Sky Survey Bright Source Catalog (RASS/BSC) X-raysources are quantitatively cross-associated with near-infrared (NIR)sources from the Two Micron All Sky Survey Point Source Catalog(2MASS/PSC). An association catalog is presented, listing the mostlikely counterpart for each RASS/BSC source, the probability Pid that the NIR source and X-ray source are uniquelyassociated, and the probability P no-id that none of the2MASS/PSC sources are associated with the X-ray source. The catalogincludes 3853 high quality (P id>0.98) X-ray-NIR matches,2280 medium quality (0.98 >= P id>0.9) matches, and4153 low quality (0.9 >= P id>0.5) matches. Of the highquality matches, 1418 are associations that are not listed in the SIMBADdatabase, and for which no high quality match with a USNO-A2 opticalsource was presented for the RASS/BSC source in previous work. Thepresent work offers a significant number of new associations withRASS/BSC objects that will require optical/NIR spectroscopy forclassification. For example, of the 6133 P id>0.92MASS/PSC counterparts presented in the association catalog, 2411 haveno classification listed in the SIMBAD database. These 2MASS/PSC sourceswill likely include scientifically useful examples of known sourceclasses of X-ray emitters (white dwarfs, coronally active stars, activegalactic nuclei), but may also contain previously unknown sourceclasses. It is determined that all coronally active stars in theRASS/BSC should have a counterpart in the 2MASS/PSC, and that the uniqueassociation of these RASS/BSC sources with their NIR counterparts thusis confusion limited.
| Ellipsoidal Variable V1197 Orionis: Absolute Light-Velocity Analysis for Known Distance
V1197 Orionis light curves from a long-term observing program for redgiant binaries show ellipsoidal variation of small amplitude in the Vand RC bands, although not clearly in U and B. Eclipses arenot detected. All four bands show large irregular intrinsic variations,including fleeting quasi-periodicities identified by power spectra, thatdegrade analysis and may be caused by dynamical tides generated byorbital eccentricity. To deal with the absence of eclipses andconsequent lack of astrophysical and geometrical information, direct useis made of the Hipparcos parallax distance while the V and RClight curves and (older) radial velocity curves are analyzedsimultaneously in terms of absolute flux. The red giant's temperature isestimated from new spectra. This type of analysis, called InverseDistance Estimation for brevity, is new and can also be applied to otherellipsoidal variables. Advantages gained by utilization of definitedistance and temperature are discussed in regard to how radius,fractional lobe filling, and mass ratio information are expressed in theobservations. The advantages were tested in solutions of noisy syntheticdata. Also discussed and tested by simulations are ideas on the optimalnumber of light curves to be solved simultaneously under variousconditions. The dim companion has not been observed or discussed in theliterature but most solutions find its mass to be well below that of thered giant. Solutions show red giant masses that are too low forevolution to the red giant stage within the age of the Galaxy, althoughthat result is probably an artifact of the intrinsic brightnessfluctuations.
| The chromospherically active binary CFTuc revisited
This paper presents results derived from analysis of new spectroscopicand photometric observations of the chromospherically active binarysystem CFTuc. New high-resolution spectra, taken at the Mt. JohnUniversity Observatory in 2007, were analysed using two methods:cross-correlation and Fourier-based disentangling. As a result, newradial velocity curves of both components were obtained. The resultingorbital elements of CFTuc are a1 sini = 0.0254 +/- 0.0001au,a2sini = 0.0228 +/- 0.0001au, M1sini = 0.902 +/-0.005Msolar and M2sini = 1.008 +/-0.006Msolar. The cooler component of the system showsH? and CaII H&K emissions. Using simultaneous spectroscopicand photometric observations, an anticorrelation between the H?emission and the BV light curve maculation effects was found. Thisbehaviour indicates a close spatial association between photospheric andchromospheric active regions. Our spectroscopic data and recent BV lightcurves were solved simultaneously using the Wilson-Devinney code. A darkspot on the surface of the cooler component was assumed to explain largeasymmetries observed in the light curves. The following absoluteparameters of the components were determined: M1 = 1.11 +/-0.01Msolar, M2 = 1.23 +/- 0.01Msolar,R1 = 1.63 +/- 0.02Rsolar, R2 = 3.60 +/-0.02Rsolar, L1 = 3.32 +/- 0.51Lsolarand L2 = 3.91 +/- 0.84Lsolar. The primarycomponent has an age of about 5Gyr and is approaching its main-sequenceterminal age. The distance to CFTuc was calculated to be 89 +/- 6pc fromthe dynamic parallax, neglecting interstellar absorption, in agreementwith the Hipparcos value. The orbital period of the system was studiedusing the O-C analysis. The O-C diagram could be interpreted in terms ofeither two abrupt changes or a quasi-sinusoidal form superimposed on adownward parabola. These variations are discussed by reference to thecombined effect of mass transfer and mass loss, the Applegate mechanismand also a light-time effect due to the existence of a third body in thesystem.
| 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 spectroscopic study of the Algol-type binaries S Equulei and KO Aquilae: absolute parameters and mass transfer
We present and analyse high-resolution optical spectra of two Algolbinaries, namely S Equ and KO Aql, obtained with the echellespectrograph at Catania Astrophysical Observatory. New accurate radialvelocities (RVs) for the hotter primary components are obtained. Thanksto the cross-correlation procedure, we were able to measure, for thefirst time to our knowledge, RVs also for the cool secondary componentsof S Equ and KO Aql. By combining the parameters obtained from thesolution of the RV curves with those obtained from the light-curveanalysis, reliable absolute parameters of the systems have been derived.The rotational velocity of the hotter components of S Equ and KO Aql hasbeen measured and it is found that the gainers of both systems rotateabout 30 per cent faster than synchronously. This is likely due to masstransfer across the Lagrangian L1 point from the cooler tothe hotter component. The lower luminosity of the mass-gainingcomponents of these systems compared to normal main-sequence stars ofthe same mass can also be an effect of the mass transfer. The Hαprofiles were analysed with the `synthesis and subtraction' techniqueand reveal clear evidence of mass transfer and accretion structures. Inboth systems, especially before the primary eclipses and afterwards, weclearly observed extra absorption lines. From the integrated absorptionand the RV variations of these features, we found that the massaccretion is very dense around the impact region of the hottercomponents. A double-peaked emission in the spectra of S Equ was seenoutside the eclipses. One of these peaks is likely originated in aregion between the centre of mass and the cooler component, which isoccupied by the flowing matter. Furthermore, the Hα differencespectra of S Equ and KO Aql also display emission features, which shouldbe arising from the magnetic activity of the cooler components.Based on observations collected at the Catania Astrophysical Observatory(Italy).E-mail: fsoydugan@comu.edu.tr
| The outer atmosphere of the RS CVn HR 7428 .
We infer informations on the physical properties of the atmosphere ofthe RS CVn binary system HR 7428 by means of semi-empirical atmosphericmodeling. The nature of the HR 7428 H-alpha extra-absorption observedby many authors has been explored.
| 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.
| Mg II chromospheric radiative loss rates in cool active and quiet stars
The Mg II k emission line is a good indicator of the level ofchromospheric activity in late-type stars. We investigate the dependenceof this activity indicator on fundamental stellar parameters. To thispurpose we use IUE observations of the Mg II k line in 225 late-typestars of luminosity classes I-V, with different levels of chromosphericactivity. We first re-analyse the relation between Mg II k lineluminosity and stellar absolute magnitude, performing linear fits to thepoints. The ratio of Mg II surface flux to total surface flux is foundto be independent of stellar luminosity for evolved stars and toincrease with decreasing luminosity for dwarfs. We also analyse the MgII k line surface flux-metallicity connection. The Mg II k emissionlevel turns out to be not dependent on metallicity. Finally, the Mg II kline surface flux-temperature relation is investigated by treatingseparately, for the first time, a large sample of very active and normalstars. The stellar surface fluxes in the k line of normal stars arefound to be strongly dependent on the temperature and slightly dependenton the gravity, thus confirming the validity of recently proposedmodels. In contrast, data relative to RS CVn binaries and BY Dra stars,which show very strong chromospheric activity, are not justified in theframework of a description based only on acoustic waves and uniformlydistributed magnetic flux tubes so that they require more detailedmodels.
| Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters
The availability of the Hipparcos Catalogue has triggered many kinematicand dynamical studies of the solar neighbourhood. Nevertheless, thosestudies generally lacked the third component of the space velocities,i.e., the radial velocities. This work presents the kinematic analysisof 5952 K and 739 M giants in the solar neighbourhood which includes forthe first time radial velocity data from a large survey performed withthe CORAVEL spectrovelocimeter. It also uses proper motions from theTycho-2 catalogue, which are expected to be more accurate than theHipparcos ones. An important by-product of this study is the observedfraction of only 5.7% of spectroscopic binaries among M giants ascompared to 13.7% for K giants. After excluding the binaries for whichno center-of-mass velocity could be estimated, 5311 K and 719 M giantsremain in the final sample. The UV-plane constructed from these datafor the stars with precise parallaxes (σπ/π≤20%) reveals a rich small-scale structure, with several clumpscorresponding to the Hercules stream, the Sirius moving group, and theHyades and Pleiades superclusters. A maximum-likelihood method, based ona Bayesian approach, has been applied to the data, in order to make fulluse of all the available stars (not only those with precise parallaxes)and to derive the kinematic properties of these subgroups. Isochrones inthe Hertzsprung-Russell diagram reveal a very wide range of ages forstars belonging to these groups. These groups are most probably relatedto the dynamical perturbation by transient spiral waves (as recentlymodelled by De Simone et al. \cite{Simone2004}) rather than to clusterremnants. A possible explanation for the presence of younggroup/clusters in the same area of the UV-plane is that they have beenput there by the spiral wave associated with their formation, while thekinematics of the older stars of our sample has also been disturbed bythe same wave. The emerging picture is thus one of dynamical streamspervading the solar neighbourhood and travelling in the Galaxy withsimilar space velocities. The term dynamical stream is more appropriatethan the traditional term supercluster since it involves stars ofdifferent ages, not born at the same place nor at the same time. Theposition of those streams in the UV-plane is responsible for the vertexdeviation of 16.2o ± 5.6o for the wholesample. Our study suggests that the vertex deviation for youngerpopulations could have the same dynamical origin. The underlyingvelocity ellipsoid, extracted by the maximum-likelihood method afterremoval of the streams, is not centered on the value commonly acceptedfor the radial antisolar motion: it is centered on < U > =-2.78±1.07 km s-1. However, the full data set(including the various streams) does yield the usual value for theradial solar motion, when properly accounting for the biases inherent tothis kind of analysis (namely, < U > = -10.25±0.15 kms-1). This discrepancy clearly raises the essential questionof how to derive the solar motion in the presence of dynamicalperturbations altering the kinematics of the solar neighbourhood: doesthere exist in the solar neighbourhood a subset of stars having no netradial motion which can be used as a reference against which to measurethe solar motion?Based on observations performed at the Swiss 1m-telescope at OHP,France, and on data from the ESA Hipparcos astrometry satellite.Full Table \ref{taba1} is only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/430/165}
| 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.
| Composite spectra Paper 13: 93 Leonis, a chromospherically-active binary
We isolate the spectrum of the secondary component of thecomposite-binary system 93 Leonis by spectrum subtraction, classify it,and measure the mass ratio of the system. An accurate visual orbit and awell-determined parallax provide reliable measurements of orbitalinclination and distance, enabling us to determine precisely theindividual masses and other stellar parameters. The primary star is oftype ~G7 III, and the secondary is a rapidly rotating star of type A7IV. Our photographic spectra at 10 Å mm-1 areinvaluable for accurate spectral classification in such cases.By combining 23 measurements of the secondary's velocity with 102 of theprimary's and deriving a double-lined orbit, we determine the mass ratio(q=M1/M2) of 93 Leo to be 1.09 +/- 0.04. The samevalue is derived by cross-correlating high-dispersion spectra of 93 LeoB extracted from opposite nodal phases. That value of q is consonantwith previous research, but its precision is considerably improved. Weshow that random errors arising from the cross-correlation of broad,weak features constitute a natural limit to that precision.The derived masses of M1= 2.2 Msolar,M2= 2.0 Msolar for the giant and dwarf,respectively, constrain the choice of models for fitting evolutionarytracks in the (logTeff, logL) plane. The giant is almostcertainly on its first ascent of the red giant branch, and the dwarf hasevolved significantly from the main sequence. The stars fit an isochronefor log(age) = 8.95, about 0.9 Gyr. Metallicity near to solar issuggested by the close correspondence between the component spectra andthose of the respective solar-abundance standards.The primary in 93 Leo displays a marked level of chromospheric activity.By combining our high-dispersion spectra we are able to isolate emissionin the Ca II K line. The chromospheric material has a small infallvelocity, giving rise to a disc-averaged redshift of about 4 kms-1, and an unchanging velocity profile which can beattributed to a large number of small, active events like prominencesacross the surface. While we can say that there was no perceptiblechange in the emission strength over an interval of 4 months, we havenot made systematic observations to monitor its long-term stability.We contrast the components of 93 Leo with those of α Equ, whoseanalysis was the subject of Paper 11 in this series. The primarycomponents are very similar, but the two secondary components areextremely different in nature: whereas 93 Leo B is a broad-lined,apparently normal A star, the secondary of α Equ is a sharp-linedAm star of type ~kA3hA4mA9. We question why that should be, andrecommend that a greater emphasis be placed on extracting accuratestellar parameters from the components of spectroscopic binaries as ameans towards a better understanding of the vagaries of stellarevolution.93 Leo has a 9-mag visual companion which appears to be a physicalmember of the system and to be a single-lined spectroscopic binary witha period of the order of a century.
| 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.
| Classification of Spectra from the Infrared Space Observatory PHT-S Database
We have classified over 1500 infrared spectra obtained with the PHT-Sspectrometer aboard the Infrared Space Observatory according to thesystem developed for the Short Wavelength Spectrometer (SWS) spectra byKraemer et al. The majority of these spectra contribute to subclassesthat are either underrepresented in the SWS spectral database or containsources that are too faint, such as M dwarfs, to have been observed byeither the SWS or the Infrared Astronomical Satellite Low ResolutionSpectrometer. There is strong overall agreement about the chemistry ofobjects observed with both instruments. Discrepancies can usually betraced to the different wavelength ranges and sensitivities of theinstruments. Finally, a large subset of the observations (~=250 spectra)exhibit a featureless, red continuum that is consistent with emissionfrom zodiacal dust and suggest directions for further analysis of thisserendipitous measurement of the zodiacal background.Based on observations with the Infrared Space Observatory (ISO), aEuropean Space Agency (ESA) project with instruments funded by ESAMember States (especially the Principle Investigator countries: France,Germany, Netherlands, and United Kingdom) and with the participation ofthe Institute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| A study of the Mg II 2796.34 Å emission line in late-type normal and RS CVn stars
We carry out an analysis of the Mg II 2796.34 Å emission line inRS CVn stars and make a comparison with the normal stars studied in aprevious paper (Paper I). The sample of RS CVn stars consists of 34objects with known HIPPARCOS parallaxes and observed at high resolutionwith IUE. We confirm that RS CVn stars tend to possess wider Mg II linesthan normal stars having the same absolute visual magnitude. However, wecould not find any correlation between the logarithmic line width logWdeg and the absolute visual magnitude MV (theWilson-Bappu relationship) for these active stars, contrary to the caseof normal stars addressed in Paper I. On the contrary, we find that astrong correlation exists in the (MV, log LMg II)plane (LMg II is the absolute flux in the line). In thisplane, normal and RS CVn stars are distributed along two nearly parallelstraight lines with RS CVn stars being systematically brighter by ~1dex. Such a diagram provides an interesting tool to discriminate activefrom normal stars. We finally analyse the distribution of RS CVn and ofnormal stars in the (log LMg II, log Wdeg) plane,and find a strong linear correlation for normal stars, which can be usedfor distance determinations.
| Hα variations of the RS CVn type binary ER Vulpeculae
We present the results of spectroscopic observations of the activeeclipsing binary ER Vul in the 5860-6700 Å spectral range carriedout at the Catania Astrophysical Observatory. Accurate measurements ofradial velocities by using the cross-correlation technique have beenmade and a new orbital solution is given. All spectra displaychromospheric emission which fills in the Hα absorption lines ofboth components. The equivalent width (EW) of the Hα emission hasbeen measured by subtraction of a synthetic spectrum built up withspectra of inactive standard stars. The EW of total Hα emission,arisen from both components, shows a phase-dependent variation. Itreaches its maximum value just before the primary eclipse. We were ableto separate the contributions to the Hα emission from theindividual components at phases far from the eclipses. We have foundthat the secondary, cooler component is the most active and its Hαresidual emission shows the same trend as the total Hα emission,along orbital phase. This Hα equivalent width variation can bedue to plage-like structures on the chromosphere of secondary star. Inaddition, a decrease of the Hα EW around the ingress phase of theprimary eclipse is apparent.
| Reprocessing the Hipparcos Intermediate Astrometric Data of spectroscopic binaries. II. Systems with a giant component
By reanalyzing the Hipparcos Intermediate Astrometric Data of a largesample of spectroscopic binaries containing a giant, we obtain a sampleof 29 systems fulfilling a carefully derived set of constraints andhence for which we can derive an accurate orbital solution. Of these,one is a double-lined spectroscopic binary and six were not listed inthe DMSA/O section of the catalogue. Using our solutions, we derive themasses of the components in these systems and statistically analyzethem. We also briefly discuss each system individually.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997) and on data collected with theSimbad database.
| Spectral Classification of the Hot Components of a Large Sample of Stars with Composite Spectra, and Implication for the Absolute Magnitudes of the Cool Supergiant Components.
A sample of 135 stars with composite spectra has been observed in thenear-UV spectral region with the Aurélie spectrograph at theObservatoire de Haute-Provence. Using the spectral classifications ofthe cool components previously determined with near infrared spectra, weobtained reliable spectral types of the hot components of the samplesystems. The hot components were isolated by the subtraction methodusing MK standards as surrogates of the cool components. We also derivedthe visual magnitude differences between the components usingWillstrop's normalized stellar flux ratios. We propose a photometricmodel for each of these systems on the basis of our spectroscopic dataand the Hipparcos data. We bring to light a discrepancy for the Gsupergiant primaries between the visual absolute magnitudes deduced fromHipparcos parallaxes and those tabulated by Schmidt-Kaler for the GIbstars: we propose a scale of Mv-values for these stars incomposite systems. By way of statistics, about 75% of the hot componentsare dwarf or subgiant stars, and 25% should be giants. The distributionin spectral types is as follows: 41% of B-type components, 57% of typeA, and 2% of type F; 68% of the hot components have a spectral type inthe range B7 to A2. The distribution of the ΔMv-valuesshows a maximum near 0.75 mag.
| 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.
| Hα spectroscopy and BV photometry of RT Lacertae
Contemporaneous spectroscopic and photometric B V observations of the RSCVn type eclipsing binary RT Lacertae were performedin summer 2000. The photometric observations were obtained at the EgeUniversity Observatory, while the spectroscopic ones were carried out atCatania Astrophysical Observatory in the spectral range 5860-6700Å. We obtained a high quality radial velocity curve of the systemthat allowed us to give more accurate values of the orbital parameters.A steady decrease of the barycentric velocity from 1920 to 2000 has beenpointed out and has been discussed in the context of a third bodyhypothesis. Through the subtraction of a ``synthetic'' spectrum, builtup with spectra of inactive standard stars, we detected Hα excessemission which fills in the photospheric absorption profiles of bothcomponents. With the exception of a few spectra, taken close to theeclipses, in which some extra absorption or a faint double-peaked broademission appears, there is no further evidence of circumstellar matterin this system, as suggested in previous works. The hotter and moremassive star appears also as the more active at a chromospheric level,since it has a Hα flux about ten times greater than the companion,on average. Rotational modulation of the Hα emission has beendetected in both stars. The hemisphere of the more massive star facingthe observer at phase 0fp75 appears brighter (in Hα ) than thatseen at phase 0fp25 , while for the less massive G9 IV star the maximumHα emission is seen around phase 0fp0-0fp1 . From the analysis ofthe contemporaneous light curve (Lanza et al. \cite{Lanza2001}), themore massive G5 IV star results to be more active than the companion ata photospheric level, in agreement with the chromospheric behaviourobserved in Hα . In addition, the starspots of the G5 IV star aremainly located in the Hα brighter hemisphere, suggesting a closespatial association of spots and plages in this star. The G9 IV stardisplays instead the maximum Hα emission at the phase of maximumvisibility of the smaller spotted area found from the light-curveanalysis. The minimum Hα emission occurs when the more heavilyspotted region is visible. Based on observations collected at CataniaAstrophysical Observatory, Italy, and at Ege University Observatory,Turkey. Table 1 only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/388/298
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| 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.
| New physical elements of HR 7428 and its Hα behaviour.
HR 7428 is a spectroscopic binary composed of a K2II-III and a main-sequence A2 star. Thanks to a new set of radialvelocity measurements from our and IUE spectroscopy we have improved theorbital period determination and the spectroscopic elements of bothcomponents. Combining optical photometry and UV low dispersion IUEspectra we have determined new stellar parameters through photosphericsynthetic spectra using the NextGen models by Hauschildt et al.(\cite{Hau99a}, \cite{Hau99b}). The hot secondary component parametersagree with those of a typical A2 V star while the radius of the primarycool star turns out to be 40 Rsun, i.e. significantly smallerthan a previous estimate of 62 Rsun. The position of the hotand cool component on the H-R diagram is consistent with a normalevolution, without any mass exchange, of this binary system, whose ageis in the range 100-200 Myrs. The system displays a filled-in Hαprofile with significant variations both in depth and width along theorbital phase. In addition to the Hα chromospheric emissioncomponent, we have detected, at some phases, a broad extra-absorptionand emission that we relate to an inter-system cloud. Based onobservations collected at the Catania Astrophysical Observatory, Italy.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| An IUE Atlas of Pre-Main-Sequence Stars. II. Far-Ultraviolet Accretion Diagnostics in T Tauri Stars
We use our ultraviolet (UV) atlas of pre-main-sequence stars constructedfrom all useful, short-wavelength, low-resolution spectra in theInternational Ultraviolet Explorer (IUE) satellite Final Archive toanalyze the short-wavelength UV properties of 49 T Tauri stars (TTSs).We compare the line and continuum fluxes in these TTSs with each otherand with previously published parameters of these systems, includingrotation rate, infrared excess, and mass accretion rate. Theshort-wavelength continuum in the classical TTSs (CTTSs) appears tooriginate in a ~10,000 K optically thick plasma, while in the naked TTSs(NTTSs-stars without dusty disks) the continuum appears to originate inthe stellar atmosphere. We show that all of the TTSs in our sample liein the regime of ``saturated'' magnetic activity due to their smallRossby numbers. However, while some of the TTSs show emission linesurface fluxes consistent with this saturation level, many CTTSs showsignificantly stronger emission than predicted by saturation. In thesestars, the emission line luminosity in the high ionization lines presentin the spectrum between 1200 and 2000 Å correlates well with themass accretion rate. Therefore, we conclude that the bulk of theshort-wavelength emission seen in CTTSs results from accretion relatedprocesses and not from dynamo-driven magnetic activity. Using CTTSs withknown mass accretion rates, we calibrate the relationship between M andLC IV to derive the mass accretion rate for some CTTSs whichfor various reasons have never had their mass accretion rates measured.Finally, several of the CTTSs show strong emission from molecularhydrogen. While emission from H2 cannot form in gas at atemperature of ~105 K, the strength of the molecular hydrogenemission is nevertheless well correlated with all the other emissionsdisplayed in the IUE short-wavelength bandpass. This suggests that theH2 emission is in fact fluorescent emission pumped by theemission (likely Lyα) from hotter gas.
| High excitation emission lines in binary systems with roundchroms
An unexpected empirical fact, a dependence of the observed luminositiesin high excitation emission lines - 1240 NV, 1400 SiIV, 1550 CIV, 1640HeII - on the intercomponent distance a of RS CVn type close binarysystems, is revealed. It is assumed that those high excitation emissionlines are generated most probably in a cone-like region between theLagrangian point L_1 and the surface of the primary component of thesystem. The behavior of high excitation emission lines at various phasesof the eclipse in the case of two binary systems, SX Cas and 22 Vul,indicates the possibility of existence of such a `Lagrangian cone' inthe structure of common chromospheres - roundchroms - of close binarysystems as a main source of generation of high excitation emissionlines.
| 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 Wilson-Bappu relation for RS CVn stars
We investigate the extent to which the Wilson-Bappu relationship holdsfor chromospherically active binaries using the Mg ii h&k lines of41 RS CVn stars observed with IUE. The resulting fits are different fromthe relationships obtained for single, less active stars. The parallaxused were those from the hipparcos catalogue, these give a much bettercorrelation than the magnitudes taken from CABS. Within a particularluminosity class the relationship is good, however it tends to breakdown when we incorporate objects ranging in luminosity from class i tov. From model calculations there is very little dependence of the Mg iiline width on effective temperature. The line width does however dependon the column mass at the transition region boundary showing increasedline width at lower column mass. There is also a dependence on thecolumn mass adopted for the temperature minimum, however, the major anddominant parameter is the surface gravity scaling as g(-1/4) . Within aluminosity class more active objects will show larger lines widthsreflecting a higher column mass deeper in the atmosphere, e.g. at thetemperature minimum level.
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