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The Origin of Bright X-ray Sources in Multiple Stars
Luminous X-ray stars are very often found in visual double or multiplestars. Binaries with periods of a few days possess the highest degree ofcoronal X-ray activity among regular, non-relativistic stars because oftheir fast, tidally driven rotation. But the orbital periods in visualdouble stars are too large for any direct interaction between thecompanions to take place. We suggest that most of the strongest X-raycomponents in resolved binaries are yet-undiscovered short-periodbinaries, and that a few are merged remnants of such binaries. Theomnipresence of short-period active stars, e.g., of BY-Dra-typebinaries, in multiple systems is explained via the dynamical evolutionof triple stars with large mutual inclinations. The dynamicalperturbation on the inner pair pumps up the eccentricity in a cyclicmanner, a phenomenon known as Kozai cycling. At times of closeperiapsis, tidal friction reduces the angular momentum of the binary,causing it to shrink. When the orbital period of the inner pair drops toa few days, fast surface rotation of the companions is driven by tidalforces, boosting activity by a few orders of magnitude. If the perioddrops still further, a merger may take place leaving a rapidly rotatingactive dwarf with only a distant companion.
| A catalogue of chromospherically active binary stars (third edition)
The catalogue of chromospherically active binaries (CABs) has beenrevised and updated. With 203 new identifications, the number of CABstars is increased to 409. The catalogue is available in electronicformat where each system has a number of lines (suborders) with a uniqueorder number. The columns contain data of limited numbers of selectedcross references, comments to explain peculiarities and the position ofthe binarity in case it belongs to a multiple system, classicalidentifications (RS Canum Venaticorum, BY Draconis), brightness andcolours, photometric and spectroscopic data, a description of emissionfeatures (CaII H and K, Hα, ultraviolet, infrared),X-ray luminosity, radio flux, physical quantities and orbitalinformation, where each basic entry is referenced so users can go to theoriginal sources.
| Rotational Velocities of the Components of 23 Binaries
By using high dispersion spectra obtained by the 1.8 m telescope ofBohyunsan Optical Astronomy Observatory (South Korea), multilineleast-square deconvolution of line profiles, and Fourier analysistechniques, we obtained the rotational velocities of the components of23 binary systems. The rotational velocities for nine primary, eightsecondary, and one tertiary components of these systems were determinedfor the first time. The rotational velocities for primary components ofseven systems appeared to be significantly different than thecorresponding synchronous values (more than twice as fast for fivesystems, and less than half as fast for two systems). Our velocities forAU Mon, RY Gem, and RZ Eri are significantly lower than the previouslypublished values obtained by using one or very few lines. We show thatthese discrepancies can be explained by strong blending of the lines inthe spectra of the primaries with strong lines of the secondaries, byinfluence of gaseous streams, and maybe by nonsolar chemicalcompositions.
| Comparative statistics and origin of triple and quadruple stars
The statistics of catalogued quadruple stars consisting of two binaries(hierarchy 2 + 2), is studied in comparison with triple stars, withrespective sample sizes of 81 and 724. Seven representative quadruplesystems are discussed in greater detail. The main conclusions are asfollows. (i) Quadruple systems of ? Lyr type with similar massesand inner periods are common, in 42 per cent of the sample the outermass ratio is above 0.5 and the inner periods differ by less than 10times. (ii) The distributions of the inner periods in triple andquadruple stars are similar and bimodal. The inner mass ratios do notcorrelate with the inner periods. (iii) The statistics of outer periodsand mass ratios in triples and quadruples are different. The medianouter mass ratio in triples is 0.39 independently of the outer period,which has a smooth distribution. In contrast, the outer periods of 25per cent quadruples concentrate in the narrow range from 10 to 100yr,the outer mass ratios of these tight quadruples are above 0.6 and theirtwo inner periods are similar to each other. (iv) The outer and innermass ratios in triple and quadruple stars are not mutually correlated.In 13 per cent of quadruples both inner mass ratios are above 0.85(double twins). (v) The inner and outer orbital angular momenta andperiods in triple and quadruple systems with inner periods above 30dshow some correlation, the ratio of outer-to-inner periods is mostlycomprised between 5 and 104. In the systems with small periodratios the directions of the orbital spins are correlated, while in thesystems with large ratios they are not. The properties of multiple starsdo not correspond to the products of dynamical decay of small clusters,hence the N-body dynamics is not the dominant process of theirformation. On the other hand, rotationally driven (cascade)fragmentation possibly followed by migration of inner and/or outerorbits to shorter periods is a promising scenario to explain the originof triple and quadruple stars.
| 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
| Long-Term High-Precision Monitoring of Variable Stars
Long-term and high-precision photometric and/or spectroscopic monitoringis required for the study of some variable stars: supergiants, slowlypulsating B-stars, stars with activity cycles and/or amplitudemodulation, and so on. These observations require stable and dedicatedinstrumentation.
| Mass loss and orbital period decrease in detached chromospherically active binaries
The secular evolution of the orbital angular momentum (OAM), thesystemic mass (M=M1+M2) and the orbital period of114 chromospherically active binaries (CABs) were investigated afterdetermining the kinematical ages of the subsamples which were setaccording to OAM bins. OAMs, systemic masses and orbital periods wereshown to be decreasing by the kinematical ages. The first-orderdecreasing rates of OAM, systemic mass and orbital period have beendetermined as per systemic OAM, per systemic mass and per orbitalperiod, respectively, from the kinematical ages. The ratio of d logJ/dlogM= 2.68, which were derived from the kinematics of the presentsample, implies that there must be a mechanism which amplifies theangular momentum loss (AML) times in comparison to isotropic AML ofhypothetical isotropic wind from the components. It has been shown thatsimple isotropic mass loss from the surface of a component or bothcomponents would increase the orbital period.
| A catalogue of eclipsing variables
A new catalogue of 6330 eclipsing variable stars is presented. Thecatalogue was developed from the General Catalogue of Variable Stars(GCVS) and its textual remarks by including recently publishedinformation about classification of 843 systems and making correspondingcorrections of GCVS data. The catalogue1 represents thelargest list of eclipsing binaries classified from observations.
| Physical parameters of the Algol system VW Hydrae from simultaneous analysis of GENEVA seven-colour light curves
The semi-detached eclipsing binary system VW Hydrae (P = 2.70 days) hasbeen analysed using the Wilson Devinney program, on the basis of lightcurves obtained in the GENEVA seven-colour photometric system, andradial velocity curves for both components measured with thecross-correlation technique. The physical and orbital parameters havebeen determined through a self-consistent simultaneous solution of lightcurves in seven colours and of the radial velocity curves of bothcomponents. The effective temperature of the primary component isdetermined from the photometric analysis,T=10,650±200K. It is shown that this value can be verywell determined, despite the fact the primary eclipse is partial, by theuse of colour indexes, as e.g. [B2 ‑V1]0. The absolute elements of the components arefor the primary (mass gainer), with the value of T fixed,M1 = 3.10 ± 0.07Mȯ, R1 =2.60 ± 0.01Rȯ, M=0.05±0.01, andfor the secondary (mass loser), M2 = 0.76 ±0.02Mȯ, R2 = 3.38 ±0.01Rȯ,M=2.90±0.01,T=4848±6K. Thesemi-major axis A of the relative orbit is 12.771 ±0.090Rȯ. The estimated spectral types of the componentsare about B8/9 V (primary) and F9 III. The equatorial rotationalvelocity of the primary (54 km s‑1) shows that thesystem is synchronised. The distance to VW Hya is evaluated to 1122± 42 pc, and the colour excess E[B2 ‑V1] to 0.046 ± 0.022.
| SB9: The ninth catalogue of spectroscopic binary orbits
The Ninth Catalogue of Spectroscopic Binary Orbits(http://sb9.astro.ulb.ac.be) continues the series of compilations ofspectroscopic orbits carried out over the past 35 years by Batten andcollaborators. As of 2004 May 1st, the new Catalogue holds orbits for2386 systems. Some essential differences between this catalogue and itspredecessors are outlined and three straightforward applications arepresented: (1) completeness assessment: period distribution of SB1s andSB2s; (2) shortest periods across the H-R diagram; (3)period-eccentricity relation.
| Up-to-Date Linear Elements of Eclipsing Binaries
About 1800 O-C diagrams of eclipsing binaries were analyzed and up-todate linear elements were computed. The regularly updated ephemerides(as a continuation of SAC) are available only in electronic form at theInternet address: http://www.as.ap.krakow.pl/ephem/.
| Kinematics of chromospherically active binaries and evidence of an orbital period decrease in binary evolution
The kinematics of 237 chromospherically active binaries (CABs) werestudied. The sample is heterogeneous with different orbits andphysically different components from F to M spectral-type main-sequencestars to G and K giants and supergiants. The computed U, V, W spacevelocities indicate that the sample is also heterogeneous in velocityspace. That is, both kinematically younger and older systems exist amongthe non-evolved main sequence and the evolved binaries containing giantsand subgiants. The kinematically young (0.95 Gyr) subsample (N= 95),which is formed according to the kinematical criteria of moving groups,was compared with the rest (N= 142) of the sample (3.86 Gyr) toinvestigate any observational clues of binary evolution. Comparing theorbital period histograms between the younger and older subsamples,evidence was found supporting the finding of Demircan that the CABs losemass (and angular momentum) and evolve towards shorter orbital periods.The evidence of mass loss is noticeable on the histograms of the totalmass (Mh+Mc), which is compared between theyounger (only N= 53 systems available) and older subsamples (only N= 66systems available). The orbital period decrease during binary evolutionis found to be clearly indicated by the kinematical ages of 6.69, 5.19and 3.02 Gyr which were found in the subsamples according to the periodranges of logP<= 0.8, 0.8 < logP<= 1.7 and 1.7 < logP<=3, respectively, among the binaries in the older subsample.
| Physical parameters of the Algol system CF Puppis from simultaneous analysis of Geneva 7-colour light curves
The semi-detached eclipsing binary system CF Puppis (P=7.65 days) has been analysed usingthe Wilson-Devinney program. Light curves have been obtained in theGeneva 7-colour photometric system, and radial velocity curves for bothcomponents have been measured with the cross-correlation technique. Thephysical and orbital parameters have been determined through aself-consistent simultaneous solution of light curves in seven coloursand of the radial velocity curves of both components. The absoluteelements of the components are, for the primary (mass gainer),M1=1.84+/-0.04 Msolar, R1=3.06+/-0.01Rsolar, Mbol1=1.74+/-0.02,Teff1=6671+/-27 K, and for the secondary (massloser), M2=0.38+/-0.01 Msolar, R2=5.39Rsolar, Mbol2=2.51+/-0.02,Teff2=4202+/-17 K. The semi-major axis A of therelative orbit is 21.28+/-0.15 Rsolar. The estimated spectraltypes of the components are about F3 IV (primary) and K2/3 III. CF Pup has one of the coolestcomponent A among the Algol systems. The equatorial rotationalvelocities are 24.8 (primary) and 37.0 km s-1. The secondaryis clearly synchronized, and the primary is nearly synchronized(vsyn=20.2 km s-1). The distance to CF Pup is evaluated to 506+/-16 pc, and thecolour excess E[B2-V1] to 0.033+/-0.017.
| From the Solar Corona to Clusters of Galaxies: The Radio Astronomy of Bruce Slee
Owen Bruce Slee is one of the pioneers of Australian radio astronomy.During World War II he independently discovered solar radio emission,and, after joining the CSIRO Division of Radiophysics, used a successionof increasingly more sophisticated radio telescopes to examine anamazing variety of celestial objects and phenomena. These ranged fromthe solar corona and other targets in our solar system, to differenttypes of stars and the ISM in our Galaxy, and beyond to distant galaxiesand clusters of galaxies. Although long retired, Slee continues to carryout research, with emphasis on active stars and clusters of galaxies. Aquiet and unassuming man, Slee has spent more than half a century makingan important, wide-ranging contribution to astronomy, and his workdeserves to be more widely known.
| Physical parameters of the Algol system BP Muscae from simultaneous analysis of GENEVA 7-colour light curves
The semi-detached eclipsing binary system BP Muscae has been analysedusing the Wilson-Devinney program. Light curves have been obtained inthe GENEVA 7-colour photometric system, and radial velocity curves forboth components have been measured with the spectrograph CORALIE. Thephysical and orbital parameters have been determined through aself-consistent simultaneous solution of light curves in seven coloursand of the radial velocity curves of both components. The absoluteelements of the components are, for the primary (mass gainer),M1 = 2.40 +/- 0.01 Msun, R1 = 2.64 +/-0.01 Rsun, Mbol_1 = 0.66 +/- 0.04,Teff_1 = 9180 +/- 90 K, and for the secondary (mass loser),M2 = 0.68 +/- 0.01 Msun, R2 = 3.76Rsun, Mbol_2 = 2.40 +/- 0.08, Teff_2 =5160 +/- 90 K. The semi-major axis A of the relative orbit is 13.617 +/-0.019 Rsun. The spectral type of the components are A0.5/1.5V (primary) and about G5 III. The distance to BP Mus is evaluated as 562+/- 17 pc, and the colour excess E[B2-V1] as 0.220 +/- 0.014.Based on observations collected at the Swiss 70 cm and 120 cm telescopesat the European Southern Observatory (La Silla, Chile).Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/1073
| WW Dra - ein heller BAV-Programmstern mit vielen Problemen.
Not Available
| The Evolution of Cool Algols
We apply a model of dynamo-driven mass loss, magnetic braking, and tidalfriction to the evolution of stars with cool convective envelopes; inparticular, we apply it to binary stars where the combination ofmagnetic braking and tidal friction can cause angular momentum loss fromthe orbit. For the present we consider the simplification that only onecomponent of a binary is subject to these nonconservative effects, butwe emphasize the need in some circumstances to permit such effects inboth components.The model is applied to examples of (1) the Sun, (2) BYDra binaries, (3) Am binaries, (4) RS CVn binaries, (5) Algols, and (6)post-Algols. A number of problems regarding some of these systems appearto find a natural explanation in our model. There are indications fromother systems that some coefficients in our model may vary by a factorof 2 or so from system to system; this may be a result of the chaoticnature of dynamo activity.
| 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.
| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veraenderliche Sterne e.V.
Not Available
| The comparative accuracy of photographic observations of radio stars observed at the Engelhardt Astronomical Observatory
At the Engelhardt Astronomical Observatory (EAO), we observedphotographic positions of 113 Galactic Radio Sources (GRS) in the systemPPM catalogue (Rizvanov & Dautov 1998). Analysis of their accuracyis made by comparison with the Hipparcos catalogue (Perryman et al.1997) and astrometric catalogue of radio stars in the radio window fromthe article of Walter et al. (1991). Table 2 is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/375/670
| 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
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| Two-colour photometry for 9473 components of close Hipparcos double and multiple stars
Using observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.
| The ROSAT Bright Survey: II. Catalogue of all high-galactic latitude RASS sources with PSPC countrate CR > 0.2 s-1
We present a summary of an identification program of the more than 2000X-ray sources detected during the ROSAT All-Sky Survey (Voges et al.1999) at high galactic latitude, |b| > 30degr , with countrate above0.2 s-1. This program, termed the ROSAT Bright Survey RBS, isto more than 99.5% complete. A sub-sample of 931 sources with countrateabove 0.2 s-1 in the hard spectral band between 0.5 and 2.0keV is to 100% identified. The total survey area comprises 20391deg2 at a flux limit of 2.4 x 10-12 ergcm-2 s-1 in the 0.5 - 2.0 keV band. About 1500sources of the complete sample could be identified by correlating theRBS with SIMBAD and the NED. The remaining ~ 500 sources were identifiedby low-resolution optical spectroscopy and CCD imaging utilizingtelescopes at La Silla, Calar Alto, Zelenchukskaya and Mauna Kea. Apartfrom completely untouched sources, catalogued clusters and galaxieswithout published redshift as well as catalogued galaxies with unusualhigh X-ray luminosity were included in the spectroscopic identificationprogram. Details of the observations with an on-line presentation of thefinding charts and the optical spectra will be published separately.Here we summarize our identifications in a table which contains opticaland X-ray information for each source. As a result we present the mostmassive complete sample of X-ray selected AGNs with a total of 669members and a well populated X-ray selected sample of 302 clusters ofgalaxies with redshifts up to 0.70. Three fields studied by us remainwithout optical counterpart (RBS0378, RBS1223, RBS1556). While the firstis a possible X-ray transient, the two latter are isolated neutron starcandidates (Motch et al. 1999, Schwope et al. 1999).
| 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.
| Radio star catalogue observed in San Juan (RSSJ95)
Using the data observed in San Juan with the photoelectric AstrolabeMark II of the Beijing Astronomical Observatory from February, 1992 toMarch, 1997, the radio star catalogue in San Juan(RSSJ95) has beencompiled. There are 69 radio stars in this catalogue. The positions ofthe radio stars are for the epoch of observation and the equinox J2000.0and a system close to that of the system FK5. The mean precisions are+/-2.2 ms and +/-0.035'' in right ascensions and declinations,respectively. The magnitudes of stars are from 0.9 to 10.7. Thedeclinations are from -2fdg 5 to -60(deg) . The mean epoch is 1995.1.Finally, the comparison results between the Hipparcos catalogue andRSSJ95 are given.
| Mutual irradiation and absorption and surface temperature variation in detached binary systems
In the paper, we calculate the absorbed flux of the mutual irradiationof the components in detached binary systems, and obtain the surfacetemperature distribution on the components. The maximum temperaturedifference over the surface is a measure of the deviation betweenisothermal and equipotential surfaces. For 33 late-type binary systemswith known elements, we evaluate this maximum difference. The resultshows that the isothermal-equipotential deviation is always larger inthe cooler than in the hotter components. This result supports Zhou andLeung's idea that the large difference between ``star-spots'' andsunspots is due to cyclones and anticyclones. The effect of limbdarkening (amounting to over 18% and always larger in the hottercomponent) is included in the consideration.
| Spatial corrections of ROSAT HRI observations
X-ray observations with the ROSAT High Resolution Imager (HRI) oftenhave spatial smearing on the order of 10arcsec te[(Morse 1994).]{mor94}This degradation of the intrinsic resolution of the instrument (5arcsec) can be attributed to errors in the aspect solution associated with thewobble of the space craft or with the reacquisition of the guide stars.We have developed a set of IRAF/PROS and MIDAS/EXSAS routines tominimize these effects. Our procedure attempts to isolate aspect errorsthat are repeated through each cycle of the wobble. The method assigns a``wobble phase" to each event based on the 402 second period of theROSAT wobble. The observation is grouped into a number of phase bins anda centroid is calculated for each sub-image. The corrected HRI eventlist is reconstructed by adding the sub-images which have been shiftedto a common source position. This method has shown ~ 30% reduction ofthe full width half maximum (FWHM) of an X-ray observation of the radiogalaxy 3C 120. Additional examples are presented.
| Mutual irradiation and absorption in detached binary systems and surface temperature variation.
Not Available
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