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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.
| Astrometric orbits of SB^9 stars
Hipparcos Intermediate Astrometric Data (IAD) have been used to deriveastrometric orbital elements for spectroscopic binaries from the newlyreleased Ninth Catalogue of Spectroscopic Binary Orbits(SB^9). This endeavour is justified by the fact that (i) theastrometric orbital motion is often difficult to detect without theprior knowledge of the spectroscopic orbital elements, and (ii) suchknowledge was not available at the time of the construction of theHipparcos Catalogue for the spectroscopic binaries which were recentlyadded to the SB^9 catalogue. Among the 1374 binaries fromSB^9 which have an HIP entry (excluding binaries with visualcompanions, or DMSA/C in the Double and Multiple Stars Annex), 282 havedetectable orbital astrometric motion (at the 5% significance level).Among those, only 70 have astrometric orbital elements that are reliablydetermined (according to specific statistical tests), and for the firsttime for 20 systems. This represents a 8.5% increase of the number ofastrometric systems with known orbital elements (The Double and MultipleSystems Annex contains 235 of those DMSA/O systems). The detection ofthe astrometric orbital motion when the Hipparcos IAD are supplementedby the spectroscopic orbital elements is close to 100% for binaries withonly one visible component, provided that the period is in the 50-1000 drange and the parallax is >5 mas. This result is an interestingtestbed to guide the choice of algorithms and statistical tests to beused in the search for astrometric binaries during the forthcoming ESAGaia mission. Finally, orbital inclinations provided by the presentanalysis have been used to derive several astrophysical quantities. Forinstance, 29 among the 70 systems with reliable astrometric orbitalelements involve main sequence stars for which the companion mass couldbe derived. Some interesting conclusions may be drawn from this new setof stellar masses, like the enigmatic nature of the companion to theHyades F dwarf HIP 20935. This system has a mass ratio of 0.98 but thecompanion remains elusive.
| 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}
| 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.
| 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.
| 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.
| Do red giant stars pulsate in high overtones?
About 30 photometrically variable red giant stars have periods less than10d, as determined by the compilers of the Hipparcos Catalogue fromHipparcos photometric measurements. These periods, when combined withestimates of the radii and masses of these stars, and with pulsationtheory, imply that these stars are pulsating in very high overtones. Wepresent several pieces of evidence which suggest that the periods may bespurious, as a result of the particular aliasing properties of theHipparcos photometry. We conclude that the evidence for high-overtonepulsation in red giant stars is equivocal.
| The Rotation of Binary Systems with Evolved Components
In the present study we analyze the behavior of the rotational velocity,vsini, for a large sample of 134 spectroscopic binary systems with agiant star component of luminosity class III, along the spectral regionfrom middle F to middle K. The distribution of vsini as a function ofcolor index B-V seems to follow the same behavior as their singlecounterparts, with a sudden decline around G0 III. Blueward of thisspectral type, namely, for binary systems with a giant F-type component,one sees a trend for a large spread in the rotational velocities, from afew to at least 40 km s-1. Along the G and K spectral regionsthere are a considerable number of binary systems with moderate tomoderately high rotation rates. This reflects the effects ofsynchronization between rotation and orbital motions. These rotatorshave orbital periods shorter than about 250 days and circular or nearlycircular orbits. Except for these synchronized systems, the largemajority of binary systems with a giant component of spectral type laterthan G0 III are composed of slow rotators.
| CaII K Emission-Line Asymmetry among Red Giants Detected by the ROSAT Satellite
Spectra of the Ca II H and K lines are reported for a number of fieldgiants from which soft X-ray emission was detected by the ROSATsatellite. Several of these stars are RS CVn systems and exhibit verystrong Ca II emission. The majority of the noninteracting giants in thesample have MV>-2.0, as determined from Hipparcosparallaxes, and spectral types earlier than K3. The Ca II Kemission-line profile for these stars is most often double-peaked andasymmetric, with the short-wavelength peak being stronger than thelongward peak. This asymmetry is in the same sense as for the integrateddisk of the Sun. The X-ray and Ca II K-line data indicate that giants ofspectral types G and early K have coronae and chromospheres seeminglyanalogous to those of the Sun. Four M giants that were detected by ROSATwere also observed. Their Ca II emission spectra show asymmetries inwhich the violet wing is weaker than the red wing, a phenomenon that istypical of M giants in general and indicative of mass outflows in theirchromospheres. The majority of these M giants, but not all, are known tobe in binary systems, so it is possible that the X-ray emission for atleast some of them may come from a companion. Alternatively, some or allof these M giants may be examples of hybrid stars.
| Ultraviolet Emission Lines in BA and Non-BA Giants
With the Hubble Space Telescope (HST) and the Goddard High ResolutionSpectrograph we have observed four barium and three weak barium stars inthe ultraviolet spectral region, together with two nonpeculiar giantstandard stars. An additional suspected Ba star was observed with HSTand the Space Telescope Imaging Spectrograph. In the H-R diagram, threeof the observed Ba stars lie on the same evolutionary tracks as theHyades giants. Using International Ultraviolet Explorer (IUE) spectra ofpreviously studied giants together with our HST spectra, we investigatewhether the chromospheric and transition layer emission-line spectra ofthe Ba stars are different from those of nonpeculiar giants and fromthose of giants with peculiar carbon and/or nitrogen abundances. Exceptfor the Ba star HD 46407 and the suspected Ba star HD 65699, the Ba starand mild Ba star emission-line fluxes are, for a given effectivetemperature and for a given luminosity, lower than those for thenonpeculiar giants observed with IUE. In comparison with theHST-observed standard stars, the C IV λ1550-to-C II λ1335line flux ratios are smaller, but not necessarily so in comparison withall IUE-observed nonpeculiar giants. However, the C IV-to-C II line fluxratios for the Ba stars decrease with increasing carbon abundances. Thisshows that the energy balance in the lower transition layer isinfluenced by the carbon abundance. The temperature gradient appears tobe smaller in the C II line-emitting region. There does not seem to be adifference in chromospheric electron densities for the Ba and non-Bastars, though this result is rather uncertain. Based on observationswith the NASA/ESA Hubble Space Telescope obtained at the Space TelescopeScience Institute, which is operated by the Association of Universitiesfor Research in Astronomy, Inc., under NASA contract NAS 5-26555.
| 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.
| Multiwavelength optical observations of chromospherically active binary systems. III. High resolution echelle spectra from Ca ii H & K to Ca ii IRT
This is the third paper of a series aimed at studying the chromosphereof active binary systems using the information provided for severaloptical spectroscopic features. High resolution echelle spectraincluding all the optical chromospheric activity indicators from the Caii H & K to Ca ii IRT lines are analysed here for 16 systems. Thechromospheric contribution in these lines has been determined using thespectral subtraction technique. Very broad wings have been found in thesubtracted Hα profile of the very active star HU Vir. Theseprofiles are well matched using a two-component Gaussian fit (narrow andbroad) and the broad component can be interpreted as arising frommicroflaring. Red-shifted absorption features in the Hα line havebeen detected in several systems and excess emission in the blue wing ofFG UMa was also detected. These features indicate that several dynamicalprocesses, or a combination of them, may be involved. Using theE_Hα /E_Hβ ratio as a diagnostic we have detectedprominence-like extended material viewed off the limb in many stars ofthe sample, and prominences viewed against the disk at some orbitalphases in the dwarfs OU Gem and BF Lyn. The He i D3 line hasbeen detected as an absorption feature in mainly all the giants of thesample. Total filling-in of the He i D3, probably due tomicroflaring activity, is observed in HU Vir. Self-absorption with redasymmetry is detected in the Ca ii H & K lines of the giants 12 Cam,FG UMa and BM CVn. All the stars analysed show clear filled-in Ca ii IRTlines or even notable emission reversal. The small values of theE_8542/E_8498 ratio we have found indicate Ca ii IRT emission arisesfrom plage-like regions. Orbital phase modulation of the chromosphericemission has been detected in some systems, in the case of HU Virevidence of an active longitude area has been found. Based onobservations made with the Isaac Newton Telescope (INT) operated on theisland of La Palma by the Isaac Newton Group in the Spanish Observatoriodel Roque de Los Muchachos of the Instituto de Astrofísica deCanarias, and with the Nordic Optical Telescope (NOT), operated on theisland of La Palma jointly by Denmark, Finland, Iceland, Norway andSweden, in the Spanish Observatorio del Roque de los Muchachos of theInstituto de Astrofísica de Canarias. Tables 3, 5, 6, 7 also atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| A catalog of rotational and radial velocities for evolved stars
Rotational and radial velocities have been measured for about 2000evolved stars of luminosity classes IV, III, II and Ib covering thespectral region F, G and K. The survey was carried out with the CORAVELspectrometer. The precision for the radial velocities is better than0.30 km s-1, whereas for the rotational velocity measurementsthe uncertainties are typically 1.0 km s-1 for subgiants andgiants and 2.0 km s-1 for class II giants and Ib supergiants.These data will add constraints to studies of the rotational behaviourof evolved stars as well as solid informations concerning the presenceof external rotational brakes, tidal interactions in evolved binarysystems and on the link between rotation, chemical abundance and stellaractivity. In this paper we present the rotational velocity v sin i andthe mean radial velocity for the stars of luminosity classes IV, III andII. Based on observations collected at the Haute--Provence Observatory,Saint--Michel, France and at the European Southern Observatory, LaSilla, Chile. Table \ref{tab5} also available in electronic form at CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Absolute declinations with the photoelectric astrolabe at Calern Observatory (OCA)
A regular observational programme with a photoelectric astrolabe havebeen performed at ``Observatoire du Calern" (Observatoire de laCôte d'Azur, OCA, phi = +43() o44′55.011″; lambda =-0() h27() m42.44() s, Calern, Caussols, France) for the last twentyyears. It has been almost fully automatized between 1984 and 1987. Since1988 the photoelectric astrolabe was used without any modification. Inaddition to determining the daily orientation of the local vertical, theyearly analysis of the residuals permits to derive corrections to theused star catalogue \cite[(Vigouroux et al. 1992)]{vig92}. A globalreduction method was applied for the ASPHO observations. The new form ofthe equations \cite[(Martin & Leister 1997)]{mar97} give us thepossibility of using the entire set of the observing program using datataken at two zenith distances (30() o and 45() o). The program containsabout 41648 stars' transits of 269 different stars taken at``Observatoire du Calern" (OCA). The reduction was based on theHIPPARCOS system. We discuss the possibility of computing absolutedeclinations through stars belonging simultaneously to the 30() o and45() o zenith distances programmes. The absolute declination correctionswere determined for 185 stars with precision of 0.027arcsec and thevalue of the determined equator correction is -0.018arcsec +/-0.005arcsec . The instrumental effects were also determined. The meanepoch is 1995.29. Catalogue only available at CDS in electronic from viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Characterization of variable stars by robust wave variograms: an application to HIPPARCOS mission
Variogram analysis is applied to time series of variable stars. Thismethod allows to characterize time-scales of varying signals. It is wellsuited for periodic and pseudo-periodic signals. The aspects ofrobustness, bin positions and bin widths for the variogram estimator areassessed, evaluated with the help of simulations and adapted to theHipparcos photometry. For instance variogram methodology is successfullyapplied for the detection of spurious periods, the estimation ofmeasurement noise and the analysis of the pseudo-period of some typicalHipparcos variable 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.
| Optical spectroscopy of X-ray sources in the old open cluster M 67
We have obtained optical spectra of seven stars in the old galacticcluster M 67 that are unusual sources of X-rays, andinvestigate whether the X-ray emission is due to magnetic activity or tomass transfer. The two binaries below the giant branch S 1063 and S1113, the giant with the white dwarf companion S 1040 and the eccentricbinary on the subgiant branch S 1242 show magnetic activity in the formof Ca Ii H&K emission and Hα emission, suggesting that theirX-rays are coronal. The reason for the enhanced activity level in S 1040is not clear. The two wide, eccentric binaries S 1072 and S 1237 and theblue straggler S 1082 do not show evidence for Ca Ii H&K emission. Asecond spectral component is found in the spectrum of S 1082, mostclearly in the variable Hα absorption profile. We interpret thisas a signature of the proposed hot subluminous companion. Based onobservations made with the William Herschel Telescope operated on theisland of La Palma by the Isaac Newton Group in the Spanish Observatoriodel Roque de los Muchachos of the Instituto de Astrofisica de Canarias
| On the rotation-activity correlation for active binary stars
We present an investigation of rotation-activity correlations usingInternational Ultraviolet Explorer (IUE) SWP measurements of the Civemission line at 1550Angstroms for 72 active binary systems. We use astandard stellar evolution code to derive non-empirical Rossby numbers,R_0, for each star in our sample and compare the resulting Civrotation-activity correlation to that found for empirically derivedvalues of the Rossby number and that based on rotation alone. For dwarfstars our values of R_0 do not differ greatly from empirical ones and wefind a corresponding lack of improvement in correlation. Only a marginalimprovement in correlation is found for evolved components in oursample. We discuss possible additional factors, other than rotation orconvection, that may influence the activity levels in active binaries.Our observational data imply, in contrast to the theoretical predictionsof convective motions, that activity is only weakly related to mass inevolved stars. We conclude that current dynamo theory is limited in itsapplication to the study of active stars because of the uncertainty inthe angular velocity-depth profile in stellar interiors and the unknowneffects of binarity and surface gravity.
| Giantic roundchroms of binary systems SX Cas and 22 Vul.
Not Available
| The ROSAT all-sky survey catalogue of optically bright late-type giants and supergiants
We present X-ray data for all late-type (A, F, G, K, M) giants andsupergiants (luminosity classes I to III-IV) listed in the Bright StarCatalogue that have been detected in the ROSAT all-sky survey.Altogether, our catalogue contains 450 entries of X-ray emitting evolvedlate-type stars, which corresponds to an average detection rate of about11.7 percent. The selection of the sample stars, the data analysis, thecriteria for an accepted match between star and X-ray source, and thedetermination of X-ray fluxes are described. Catalogue only available atCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| UBV(RI)_C and UVBY photometry of HD 81410 and starspot distribution in RS CVn objects
We present UBVRI and uvby photometry of HD 81410 obtained on a total of40 nights during 1987-90, and an analysis of its long-term photometricbehaviour. The star is found to show two well-separated minima in itslight curve most of the time; probably there are two preferred effectivelongitudes about which spots are mainly formed. The migration of thephase of the light minimum usually seen in RS CVn stars is absent in HD81410. The rather small spread in the maximum V amplitudes observed inactive RS CVn objects seen at different inclinations of rotational axisimplies that the longitudinal asymmetry in the distribution of spots,which causes the light modulation, is largely restricted to withinaround +/-40(deg) latitudes. The total ranges of rotational periodswhich are quoted in the literature for several spotted stars based onlong-term photometry also imply a similar latitudinal extent of spotsabout the equator. We find that the light and colour curves produced byan equatorial band of spots limited by latitudes and covering the fullrange of longitudes across the hemisphere visible at light minimum canbe approximated reasonably well by two well-separated circular spots.Further, we find that the net effect in the colours produced bylimb-darkening depends on the exact distribution of spots on the stellarsurface; it could be even negligible for certain spot distributions.From the spot modeling of the light and colour curves of HD 81410 wefind that the maximum temperature difference between the photosphere andspots is around 1400 K. We also find that the light modulation is causedby several small individual spots, and during the epochs of shallowminimum spots are spread out, both latitudinally and longitudinally,over a wider region, as indicated by a higher temperature for theequivalent circular spots at those epochs. It seems that in RS CVn starsthe spots occur largely distributed about the equator as in the case ofthe Sun and the solutions which indicate polar spots result fromlimiting the number of spots in the modeling to a few. Based on theobservations collected at the European Southern Observatory, La Silla
| The age-mass relation for chromospherically active binaries. III. Lithium depletion in giant components
We present a study of the lithium abundances of a sample of evolvedcomponents of Chromospherically Active Binary Systems. We show that asignificant part of them have lithium excesses, independently of theirmass and evolutionary stage. Therefore, it can be concluded that Liabundance does not depend on age for giant components of CABS. Theseoverabundances appear to be closely related to the stellar rotation, andwe interpret them as a consequence of the transfer of angular momentumfrom the orbit to the rotation as the stars evolve in and off the MainSequence, in a similar way as it happens in the dwarf components of thesame systems and in the Tidally Locked Binaries belonging to the Hyadesand M67. Based on observations collected with the 2.2\,m telescope ofthe German-Spanish Observatorio de Calar Alto (Almeria, Spain), and withthe 2.56\,m Nordic Optical Telescope in the Spanish Observatorio delRoque de los Muchachos of the Instituto de Astrof\'\i sica de Canarias(La Palma, Spain)
| Rotational Velocities of Late-Type Stars
A calibration based on the results of Gray has been used to determineprojected rotational velocities for 133 bright stars with spectral typesof F, G, or K, most of which appear in {\it The Bright Star Catalogue}.The vast majority have {\it v} sin {\it i} $\leq$ 10 km s$^{-1}$ and,thus, are slow rotators. With the new calibration, projected rotationalvelocities have been determined for a sample of 111 late-type stars,most of which are chromospherically active. Some of the stars have hadtheir rotational velocities measured for the first time. (SECTION:Stars)
| The structure of roundchroms in close binary systems
The determination of common chromospheres - roundchroms - for 32 closebinary systems, all of RS CVn type, is described; the main parameters ofthese roundchroms - volumes, electron concentrations and masses, areestimated. Three types of roundchroms are established according to theirstructure. The empirical relationship between their electronconcentration n_e and intercomponent distance a - n_e = K a^-0.80,discovered earlier, is confirmed by data for over fifty close binarysystems. This law holds promise for the determination of component radiiof close binary systems and some parameters of their roundchroms.
| Common chromospheres - roundchroms - as a means for the study of binary systems
An independent method based on the concept of common chromospheres -roundchroms - is proposed for the determination of the radii of the maincomponents of RS CVn-type close binary systems. The essence of themethod is in the coincidence of the radius of the main component of thebinary system with the equipotential zero-velocity surface for somevalues of the Jacobi constant. As an illustration, the method is appliedto a sample of 15 RS CVn-type systems, and as a result the revised radiiof the main components in the systems are determined. The mainparameters, particularly the volumes, electron concentrations and massesof the roundchroms, are obtained as well. Empirical dependences of theelectron concentration in the roundchrom, n_e, and of the 2800 Mg iidoublet luminosity, L(Mg ii), on intercomponent distance a werediscovered, the first in the form n_e~a^-0.85 and the second in the formL(Mg ii)~a^1.66. The formation of a roundchrom in close binary systemsis inevitable, and the roundchrom is as essential a physical formationfor binary systems as are the corona and chromosphere for single stars.
| 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.
| A Search for Optical Flares in Chromospherically Active Stars
We have surveyed four years of archival UBV photometry of 69chromospherically active stars obtained with the Phoenix-10 automaticphotoelectric telescope in search of optical flares on these stars. Wedemonstrate taht, while flares can be detected in these data, the numberof events observed on evolved stars remains very small. Flares werefound only on UX Arietis, II Pegasi, and AR Piscium. (SECTION: Stars)
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Pozíciós és asztrometriai adatok
| Csillagkép: | Zsiráf |
| Rektaszcenzió: | 05h06m12.20s |
| Deklináció: | +59°01'16.0" |
| Vizuális fényesség: | 6.08 |
| Távolság: | 191.571 parszek |
| RA sajátmozgás: | -2.5 |
| Dec sajátmozgás: | -24.5 |
| B-T magnitude: | 7.522 |
| V-T magnitude: | 6.214 |
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INHABITED SKY
