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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.
| Surface density of extremely red objects with R - J ≥ 5
We present the results of a wide-field survey for extremely red objects(EROs), based on J and R band imaging. The survey covers 2.89deg2, consisting of 50 single fields, each approximately 210arcmin2 in size. This survey provides a sample of 60 extendedobjects with a colour of R-J ≥ 5 and J band magnitudes more than10σ above background (18^mag≤ J ≤ 20^mag). Thirty five ofthese objects have been detected in both J and R-band. We derive asurface density for such EROs of 5.7±0.1×10-3arcmin-2, which is about seven times lower than for galaxieswith R-K≥6. Stellar population models suggest that these EROs aremassive galaxies with an old stellar population in a redshift range of1.4≤ z ≤ 3.0. For this scenario, we estimate the co-movingvolume density to be (9.57 ± 1.24) ×10-6Mpc-3.
| 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.
| 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.
| Discovery of four close binary stars in Sagittarius
Not Available
| The tidal effects on the lithium abundance of binary systems with giant component
We analyse the behavior of lithium abundance as a function of effectivetemperature, projected rotational velocity, orbital period andeccentricity for a sample of 68 binary systems with giant component andorbital period ranging from about 10 to 6400 days. For these binarysystems the Li abundances show a gradual decrease with temperature,paralleling the well established result for single giants. We have alsoobserved a dependence of lithium content on rotation. Binary systemswith moderate to high rotation present also moderate to high Li content.This study shows also that synchronized binary systems with giantcomponent seem to retain more of their original lithium than theunsynchronized systems. For orbital periods lower than 100 to 250 days,typically the period of synchronization for this kind of binary systems,lithium depleted stars seems to be unusual. The suggestion is made thatthere is an ``inhibited zone" in which synchronized binary systems withgiant component having lithium abundance lower than a threshold levelshould be unusual. Based on observations collected at ESO, La Silla.
| Speckle Observations of Composite Star Candidates
Speckle observations are reported for 53 stars with composite spectraselected from the Michigan Spectral Catalogue in an effort to improvethe orbits of known binaries and to discover new binaries among thisclass of objects. The data were obtained using the 1.3 and 2.4 mtelescopes at the Michigan-Dartmouth-MIT Observatory and the GeorgiaTech Research Institute speckle imaging system. For 50 stars in thesample for which no indication of duplicity was found in our data, wemay place an upper limit of <=0.2" on the separations at the epochsof observation. Three stars were resolved, including HD 26796, alsodiscovered to be double by Hipparcos. A discussion of the accuracy ofthe measurements based on comparisons with speckle standard stars ispresented.
| 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
| 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.
| 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.
| Eclipsing Binaries in the OGLE Variable Star Catalog. III. Long-Period Contact Systems
A sample of contact binaries discovered by the OGLE project in Baade'swindow, with orbital periods longer than 1 day and with available colorand light-curve data, has been analyzed. It consists of only 32 systems,in contrast to 388 W Ursae Majoris type systems with shorter periodsthat were analyzed before. Most systems are very distant and areprobably located close to or in the Galactic bulge. Two groups ofcontact binaries are seen in the sample: (1) a continuation of the W UMatype sequence, extending up to the orbital periods of 1.3-1.5 days, butrather sharply ending in this period range; and (2) an inhomogeneousgroup of rare systems with long periods up to 26 days, all with redcolors and relatively shallow eclipses. While the systems of the firstgroup share most of the characteristics of the typical W UMa typesystems (except that they are on the average brighter and more distant,and hence more reddened), the long-period systems do not seem to form anearly-type extension of contact binaries, but may consist of a mixtureof late-type objects, including tidally distorted red giants withinvisible companions.
| 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)
| The ROSAT All-Sky Survey of Active Binary Coronae. III. Quiescent Coronal Properties for the BY Draconis--Type Binaries
We present X-ray observations of 35 active late-type BY Draconis dwarfbinary systems and 28 evolved binary systems, similar in nature to theRS Canum Venaticorum systems, obtained with the Position SensitiveProportional Counter (PSPC) during the ROSAT All-Sky Survey phase of themission. Of this sample, 52 targets were detected in exposures ofroughly 600 s or less. When these new data are combined with the earlierresults from Dempsey et al. (1993b), this survey represents the largestsample of active binary systems observed to date at any wavelength,including X-rays. We expand our investigation of how coronal properties(e.g., surface flux, luminosity, etc.) correlate with stellar parameters(e.g., rotation period, color, etc.) and confirm the conclusions ofDempsey et al. (1993b). Rotation period provides the best correlationwith X-ray surface flux with F_{{X}}~P^{-0.59+/-0.10}_{{rot}} for theentire sample. We find no evidence for a "basal" or nonmagnetic X-rayflux component. We model the low-resolution pulse-height spectra for 12systems with two-temperature thermal plasmas. The derived temperaturesfor the BY Dra systems are identical to those previously derived foractive evolved giants and subgiants in close binaries (Dempsey et al.1993c). We also show that the dependence of temperature and emissionmeasures on rotation period is the same for the dwarf, subgiant, andgiant binaries.
| A new H-alpha survey of chromospherically active binaries.
Not Available
| 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)
| A Catalogue of Correlations Between Eclipsing Binaries and Other Categories of Double Stars
Among the 9110 stars in The Bright Star Catalogue, there are 225eclipsing or ellipsoidal variables. A search has been made for these incatalogues of spectroscopic binaries, visual double or multiple stars,speckle interferometry, occulation binaries, and galatic clusters. Themajority of the photometric binaries are also members of groups ofhigher multiplicity. The variables are in systems ranging from one to 91stars, five on the average. 199 are either spectroscopic binaries (SB)or stars with variable radial velocity, with orbital periods known for160. Photometric periods are lacking for 48 while SB periods areavailable for 23 of these. Observers with photoelectric equipment areencouraged to plan observations to test if the SB periods are consistentwith photometric data. Observers are likewise encouraged to examinethose stars for which the photometric and SB periods appear to beinconsistent. Parallaxes are available for 86 of the stars, 41 of themindicating distances nearer than 50 parsecs.
| Classification of Population II Stars in the Vilnius Photometric System. I. Methods
The methods used for classification of Population II stars in theVilnius photometric system are described. An extensive set of standardswith known astrophysical parameters compiled from the literature sourcesis given. These standard stars are classified in the Vilnius photometricsystem using the methods described. The accuracy of classification isevaluated by a comparison of the astrophysical parameters derived fromthe Vilnius photometric system with those estimated from spectroscopicstudies as well as from photometric data in other systems. For dwarfsand subdwarfs, we find a satisfactory agreement between our reddeningsand those estimated in the uvbyscriptstyle beta system. The standarddeviation of [Fe/H] deter mined in the Vilnius system is about 0.2 dex.The absolute magnitude for dwarfs and subdwarfs is estimated with anaccuracy of scriptstyle <=0.5 mag.
| The behaviour of the excess CA II H and K and Hɛ emissions in chromospherically active binaries.
In this work we analyze the behaviour of the excess Ca II H and K andHɛ emissions in a sample of 73 chromospherically active binarysystems (RS CVn and BY Dra classes), of different activity levels andluminosity classes. This sample includes the 53 stars analyzed byFernandez-Figueroa et al. (1994) and the observations of 28 systemsdescribed by Montes et al. (1995c). By using the spectral subtractiontechnique (subtraction of a synthesized stellar spectrum constructedfrom reference stars of spectral type and luminosity class similar tothose of the binary star components) we obtain the active-chromospherecontribution to the Ca II H and K lines in these 73 systems. We havedetermined the excess Ca II H and K emission equivalent widths andconverted them into surface fluxes. The emissions arising from eachcomponent were obtained when it was possible to deblend bothcontributions. We have found that the components of active binaries aregenerally stronger emitters than single active stars for a giveneffective temperature and rotation rate. A slight decline of the excessCa II H and K emissions towards longer rotation periods, P_rot_, andlarger Rossby numbers, R_0_, is found. When we use R_0_ instead ofP_rot_ the scatter is reduced and a saturation at R_0_=~0.3 is observed.A good correlation between the excess Ca II K and Hɛchromospheric emission fluxes has been found. The correlations obtainedbetween the excess Ca II K emission and other activity indicators, (C IVin the transition region, and X-rays in the corona) indicate that theexponents of the power-law relations increase with the formationtemperature of the spectral features.
| On the link between coronal activity and orbital period in evolved binary stars.
The analysis of the relationship between X-emission flux and orbitalperiod indicates a drop in the X-ray emission of binaries with evolvedcomponents at orbital periods of about 100 days: Intense X-ray emittershave an orbital period lower than 100 days, whereas with an orbitalperiod greater than about 100 days are weak X-ray emitters. Thiscritical period corresponds to the orbital period separating binarysystems with circular orbits from those of eccentric orbits.
| H-alpha measurements for cool giants
The H-alpha line in a cool star is usually an indication of theconditions in its chromosphere. I have collected H-alpha spectra of manynorthern G-M stars, which show how the strength and shape of the H-alphaline change with spectral type. These observations detect surprisinglittle variation in absoption-line depth (Rc approximately0.23 +/- 0.08), linewidth (FWHD approximately 1.44 +/- 0.22 A), orequivalent width (EW approximately 1.12 +/- 0.17 A) among G5-M5 IIIgiants. Lines in the more luminous stars tend to be broader and strongerby 30%-40% than in the Class III giants, while the H-alpha absorptiontends to weaken among the cooler M giants. Velocities of H-alpha andnearby photospheric lines are the same to within 1.4 +/- 4.4 km/s forthe whole group. To interpret these observations, I have calculatedH-alpha profiles, Ly-alpha strengths, and (C II) strengths for a seriesof model chromospheres representing a cool giant star like alpha Tau.Results are sensitive to the mass of the chromosphere, to chromospherictemperature, to clumping of the gas, and to the assumed physics of lineformation. The ubiquitous nature of H-alpha in cool giants and the greatdepth of observed lines argue that chromospheres of giants cover theirstellar disks uniformly and are homogeneous on a large scale. This isquite different from conditions on a small scale: To obtain a highenough electron density with the theoretical models, both to explain theexitation of hydrogen and possibly also to give the observed C IImultiplet ratios, the gas is probably clumped. The 6540-6580 A spectraof 240 stars are plotted in an Appendix, which identifies the date ofobservation and marks positions of strong telluric lines on eachspectrum. I assess the effects of telluric lines and estimates that thestrength of scattered light is approximately 5% of the continuum inthese spectra. I give the measurements of H-alpha as well as equivalentwidths of two prominent photospheric lines, Fe I lambda 6546 and Ca Ilambda 6572, which strengthen with advancing spectral type.
| Application of the spectral subtraction technique to the CA II H & K and Hɛ lines in a sample of chromospherically active binaries.
We present new spectroscopic observations in the Ca II H & K lineregion for a sample of 28 chromospherically active binary systems (RSCVn and BY Dra classes), with different activity levels. By using thespectral subtraction technique (subtraction of a synthesized stellarspectrum constructed from reference stars of similar spectral type andluminosity class) we obtain the active-chromosphere contribution to theCa II H & K lines and to the Hɛ line when it is present. Wehave compared the emission equivalent widths obtained with thistechnique with those obtained by reconstruction of the absorption lineprofile below the emission peak(s). The emissions arising from eachindividual star were obtained when it was possible to deblend thecontribution of both components. The Ca II line profiles correspondingto different seasons and orbital phases are analysed in order todetermine the contribution of each component and to study thechromospheric activity variations.
| 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.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| On the link between rotation and coronal activity in evolved stars.
We analyse the behaviour of coronal activity as a function of rotationfor a large sample of single and binary evolved stars for which we haveobtained CORAVEL high precision rotational velocities. This study showsthat tidal effects play a direct role in determining the X-ray activitylevel in binary evolved stars. The circularisation of the orbit is anecessary property for enhanced coronal activity in evolved binarystars.
| The active dynamo stars: RS CVn, BY Dra, FK Com, Algol, W UMa, and T Tau
Not Available
| A deep atmospheric eclipse of AL Velorum
I have obtained new International Ultraviolet Explorer (IUE)observations in 1992 to search for an accretion column in and to analyzean atmospheric eclipse of AL Vel, a low luminosity zeta Aurigae binary.Rich shell spectra recorded at three phases of atmospheric eclipse givecolumn densities and excitation temperatures for the chromospheric gas.The chromospheric density falls off exponentially with a scale height of3 solar radius, an order of magnitude greater than expected for supportby thermal motions. Excitation temperatures at 2 - 5 scale heights intothe chromosphere are approximately 7000 K, with Doppler widths near 17km/s. Absorption features that could be formed in an accretion columnwere detected at phases 0.70 and 0.75 in a series of spectra spanningthe range 0.63-0.80 in orbital phase. They imply a very slowacceleration of the wind, consistent with results for other zeta Aurbinaries, but the wind speed implied is inconsistent with profiles ofwind lines. The terminal velocity of this wind, greater than orapproximately = 360 km/s, is higher than that in any of the other zetaAur binaries. Wind and chromospheric features in 1992 were much moreprominent than in 1988, which implies that both the wind andchromosphere were much more massive: we seem to have witnessed in 1992 aburst of activity with a mass-loss rate greater than 10-8solar mass/yr.
| Are the Rotational Axes Perpendicular to the Orbital Planes in the Binary Systems? II. Synchronous Long-Period RS CVn Stars
Inclinations of the rotational axes, irot, are determined for37 synchronous long-period RS CVn binaries by combining v sin imeasurements with rotational period information. These inclinations arethen compared with the orbital inclinations of the systems,iorb, to test the alignment between the equatorial andorbital planes. Contrary to the asynchronous RS CVn systems (see PaperI), in all 37 cases irot is equal or nearly equal toiorb, and the assumption about coplanarity of theirequatorial and orbital planes is justified.
| Speckle observations of visual and spectroscopic binaries. V.
Not Available
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