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Discovery of magnetic fields in the βCephei star ξ1 CMa and in several slowly pulsating B stars*
We present the results of a magnetic survey of a sample of eightβCephei stars and 26 slowly pulsating B (SPBs) stars with the FOcalReducer low dispersion Spectrograph at the Very Large Telescope. A weakmean longitudinal magnetic field of the order of a few hundred Gauss isdetected in the βCephei star ξ1CMa and in 13 SPBstars. The star ξ1CMa becomes the third magnetic staramong the βCephei stars. Before our study, the star ζCas wasthe only known magnetic SPB star. All magnetic SPB stars for which wegathered several magnetic field measurements show a field that varies intime. We do not find a relation between the evolution of the magneticfield with stellar age in our small sample. Our observations imply thatβCephei and SPB stars can no longer be considered as classes ofnon-magnetic pulsators, but the effect of the fields on the oscillationproperties remains to be studied.
| Computed Hβ indices from ATLAS9 model atmospheres
Aims.Grids of Hβ indices based on updated (new-ODF) ATLAS9 modelatmospheres were computed for solar and scaled solar metallicities[+0.5], [+0.2], [0.0], [ -0.5] , [ -1.0] , [ -1.5] , [ -2.0] , [ -2.5]and for α enhanced compositions [+0.5a], [0.0a], [ -0.5a] , [-1.0a] , [ -1.5a] , [ -2.0a] , [ -2.5a] , and [ -4.0a] . Methods:.Indices for T_eff > 5000 K were computed with the same methods asdescribed by Lester et al. (1986, LGK86) except for a differentnormalization of the computed natural system to the standard system.LGK86 used special ODFs to compute the fluxes. For T_eff ≤ 5000 K wecomputed the fluxes using the synthetic spectrum method. In order toassess the accuracy of the computed indices comparisons were made withthe indices computed by Smalley & Dworetsky (1995, A&A, 293,446, MD95) and with the empirical relations T_eff-Hβ given byAlonso et al. (1996, A&A, 313, 873) for several metallicities.Furthermore, for cool stars, temperatures inferred from the computedindices were compared with those of the fundamental stars listed byMD95. The same kind of comparison was made between gravities for B-typestars. Results: .The temperatures from the computed indices are ingood agreement, within the error limits, with the literature values for4750 K ≤ T_eff ≤ 8000 K, while the gravities agree for T_eff> 9000 K. The computed Hβ indices for the Sun and for Procyonare very close to the observed values. The comparison between theobserved and computed Hβ indices as function of the observedHβ has shown a very small trend which almost completely disappearswhen only stars hotter than 10 000 K are considered. The trend due tothe cool stars is probably related with the low accuracy of thefundamental T_eff which are affected by large errors for most of thestars.
| Evolution of interacting binaries with a B type primary at birth
We revisited the analytical expression for the mass ratio distributionfor non-evolved binaries with a B type primary. Selection effectsgoverning the observations were taken into account in order to comparetheory with observations. Theory was optimized so as to fit best withthe observed q-distribution of SB1s and SB2s. The accuracy of thistheoretical mass ratio distribution function is severely hindered by theuncertainties on the observations. We present a library of evolutionarycomputations for binaries with a B type primary at birth. Some liberalcomputations including loss of mass and angular momentum during binaryevolution are added to an extensive grid of conservative calculations.Our computations are compared statistically to the observeddistributions of orbital periods and mass ratios of Algols. ConservativeRoche Lobe Over Flow (RLOF) reproduces the observed distribution oforbital periods but fails to explain the observed mass ratios in therange q in [0.4-1]. In order to obtain a better fit the binaries have tolose a significant amount of matter, without losing much angularmomentum.
| Automatic classification of eclipsing binaries light curves using neural networks
In this work we present a system for the automatic classification of thelight curves of eclipsing binaries. This system is based on aclassification scheme that aims to separate eclipsing binary systemsaccording to their geometrical configuration in a modified version ofthe traditional classification scheme. The classification is performedby a Bayesian ensemble of neural networks trained with Hipparcos data ofseven different categories including eccentric binary systems and twotypes of pulsating light curve morphologies.
| Absolute dimensions of detached eclipsing binaries - I. The metallic-lined system WW Aurigae
WW Aurigae is a detached eclipsing binary composed of two metallic-linedA-type stars orbiting each other every 2.5 d. We have determined themasses and radii of both components to accuracies of 0.4 and 0.6 percent, respectively. From a cross-correlation analysis of high-resolutionspectra we find masses of 1.964 +/- 0.007 Msolar for theprimary star and 1.814 +/- 0.007 Msolar for the secondarystar. From an analysis of photoelectric uvby and UBV light curves wefind the radii of the stars to be 1.927 +/- 0.011 Rsolar and1.841 +/- 0.011 Rsolar, where the uncertainties have beencalculated using a Monte Carlo algorithm. Fundamental effectivetemperatures of the two stars have been derived, using the Hipparcosparallax of WW Aur and published ultraviolet, optical and infraredfluxes; these are 7960 +/- 420 and 7670 +/- 410 K. The masses, radii andeffective temperatures of WW Aur are only matched by theoreticalevolutionary models for a fractional initial metal abundance, Z, ofapproximately 0.06 and an age of roughly 90 Myr. This seems to be thehighest metal abundance inferred for a well-studied detached eclipsingbinary, but we find no evidence that it is related to the metallic-linednature of the stars. The circular orbit of WW Aur is in conflict withthe circularization time-scales of both the Tassoul and the Zahn tidaltheories and we suggest that this is due to pre-main-sequence evolutionor the presence of a circular orbit when the stars were formed.
| Apsidal motion in southern eccentric eclipsing binaries: V539 Ara, GG Lup, V526 Sgr and AO Vel
Several new times of minimum light have been observed photoelectricalyfor the early-type double-lined eccentric eclipsing binaries V539 Ara (P= 3.2 deg, e = 0.05), GG Lup (1.9 deg, 0.15), V526 Sgr (1.9 deg, 0.22)and AO Vel (1.6 deg, 0.07). The O{-}C diagrams are analysed using allreliable timings found in the literature and improved values for theelements of the apsidal motion are computed. We find more precise,relatively short periods of apsidal motion of about 162, 102, 155 and 54years for V539 Ara, GG Lup, V526 Sgr and AO Vel, respectively. Thecorresponding internal structure constants, log k_2, are then found tobe 2.33, 2.16, 2.36 and 2.24 under the assumption that the componentstars rotate pseudosynchronously. The relativistic effects arenegligible, being about 6 7% of the total apsidal motion rate in allsystems. Using the light-time effect solution, for V539 Ara we havefound a third component orbiting with a period of about 42 years, for AOVel we confirmed the third body with an orbital period of 33 years.
| Apsidal Motion in Binaries: Rotation of the Components
A sample of 51 separated binary systems with measured apsidal periodsand rotational velocities of the components is examined. The ranges ofthe angles of inclination of the equatorial planes of the components tothe orbital plane are estimated for these systems. The observed apsidalvelocities can be explained by assuming that the axes of rotation of thestars are nonorthogonal to the orbital plane in roughly 47% of thesystems (24 of the 51) and the rotation of the components is notsynchronized with the orbital motion in roughly 59% of the systems (30of 51). Nonorthogonality and nonsynchrony are defined as deviations from90° and a synchronized angular velocity, respectively, at levels of1 or more.
| Studies of Intermediate-Mass Stellar Models Using Eclipsing Binaries
Evolutionary computations for intermediate-mass stars are analyzed usingobserved parameters for eclipsing SB2 binaries and theoreticalparameters based on evolutionary tracks. Modern observations cannot beused to distinguish between models with and without convectiveovershooting for stars in the vicinity of the main sequence.Statistically significant discrepancies between the observed andcomputed stellar parameters are associated with systematic errors inphotometric effective temperatures. After taking into account systematiceffects, the theoretical computations fit the observational datauniformly well throughout the entire mass interval studied. Empiricaland semiempirical (i.e., reduced to the ZAMS and with solar elementalabundances) formulas for the mass-luminosity, mass-effectivetemperature, and mass-radius relations are proposed.
| 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.
| Apsidal Motion in Detached Binary Stars: Comparison of Theory and Observations
A list of 62 detached binaries having reliable data on the rotation ofthe line of apsides is considered. Theoretical estimates of the rate ofapsidal motion are obtained. These estimates are compared withobservational data. It is shown that cases in which the theoreticalestimate exceeds the observed value are several times more frequent thancases in which the theoretical value is lower than the observed one.This discrepancy increases when systems with more reliable observationaldata are considered.
| Detached double-lined eclipsing binaries as critical tests of stellar evolution. Age and metallicity determinations from the HR diagram
Detached, double-lined spectroscopic binaries that are also eclipsingprovide the most accurate determinations of stellar mass, radius,temperature and distance-independent luminosity for each of theirindividual components, and hence constitute a stringent test ofsingle-star stellar evolution theory. We compile a large sample of 60non-interacting, well-detached systems mostly with typical errorssmaller than 2% for mass and radius and smaller than 5% for effectivetemperature, and compare them with the properties predicted by stellarevolutionary tracks from a minimization method. To assess the systematicerrors introduced by a given set of tracks, we compare the resultsobtained using three widely-used independent sets of tracks, computedwith different physical ingredients (the Geneva, Padova and Granadamodels). We also test the hypothesis that the components of thesesystems are coeval and have the same metallicity, and compare thederived ages and metallicities with the ones obtained by fitting asingle isochrone to the system. Overall, there is a good agreement amongthe different determinations, and we provide a comprehensive discussionon the sub-sample of systems which either present problems or haveestimated metallicities. Although within the errors the published trackscan fit most of the systems, a large degeneracy between age andmetallicity remains. The power of the test is thus limited because themetallicities of most of the systems are unknown. The full version ofTable 6 is only available in the electronic form athttp://www.edpsciences.org
| New results on the apsidal-motion test to stellar structure and evolution including the effects of dynamic tides
We revised the current status of the apsidal-motion test to stellarstructure and evolution. The observational sample was increased by about50% in comparison to previous studies. Classical and relativisticsystems were analyzed simultaneously and only systems with accurateabsolute dimensions were considered. New interior models incorporatingrecent opacity tables, stellar rotation, mass loss, and moderate coreovershooting were used as theoretical tools to compare the predictedwith the observed shifts of the position of the periastron. The stellarmodels were computed for the precise observed masses and the adoptedchemical compositions are consistent with the corresponding tables ofopacities to avoid the inherent problems of interpolation in mass and in(X, Z). The derived chemical composition for each individual system wasused to infer the primordial helium content as well as a law ofenrichment. The values found are in good agreement with those obtainedfrom various independent sources. For the first time, the effects ofdynamic tides are taken into account systematically to determine thecontribution of the tidal distortion to the predicted apsidal-motionrate. The deviations between the apsidal-motion rates resulting from theclassical formula and those determined by taking into account theeffects of dynamic tides are presented as a function of the level ofsynchronism. For systems close to synchronisation, dynamic tides causedeviations with respect to the classical apsidal-motion formula due tothe effects of the compressibility of the stellar fluid. For systemswith higher rotational angular velocities, additional deviations due toresonances arise when the forcing frequencies of the dynamic tides comeinto the range of the free oscillation modes of the component stars. Theresulting comparison shows a good agreement between the observed andtheoretical apsidal-motion rates. No systematic effects in the sensethat models are less mass concentrated than real stars and nocorrelations with the evolutionary status of the systems were detected.
| Tidally induced radial-velocity variations in close binaries
A theoretical framework for the determination of tidally inducedradial-velocity variations in a component of a close binary ispresented. Both the free and the forced oscillations of the componentare treated as linear, isentropic perturbations of a sphericallysymmetric star. Resonances between dynamic tides and free oscillationmodes are taken into account by means of the formalism developed by{{Smeyers} et al.} (\cite{SWV1998}). The amplitude of the tidallyinduced radial-velocity variations seen by the observer depends on theorbital eccentricity and on the orbital inclination. The amplitudeincreases with increasing orbital eccentricity and is most sensitive tothe value of the orbital inclination when 20o <~ i <~70o. In the case of a 5 Msun ZAMS star with a 1.4Msun compact companion, it is shown that resonant dynamictides can lead to radial-velocity variations with amplitudes largeenough to be detected in observations. The shape of the tidally inducedradial-velocity curves varies from very irregular for orbital periodsaway from any resonances with free oscillation modes to sinusoidal fororbital periods close to a resonance with a free oscillation mode. Ourinvestigation is concluded with an application to the slowly pulsating Bstar HD 177863 showing the possibility of resonant excitation of ahigh-order second-degree g+-mode in this star.
| An empirical method to estimate the LMC distance using B-stars in eclipsing binary systems
We present a new method to determine the distance to B-stars ineclipsing binary systems. The method is completely empirical, and it isbased on the existence of a very tight linear relationship between theV-band ``zero magnitude angular diameter'' and the Strömgren colourindex c1 for B-stars; we have empirically calibrated thisrelationship using local single B-stars with accurate angular diameters,and B-stars in eclipsing binaries with precise radii and parallaxdeterminations. By studying the differential behaviour of thisrelationship as predicted by theoretical stellar evolution models, wefind that it is independent of the stellar metallicities for a range of[Fe/H] values between the solar one and that of young stars in theMagellanic Clouds. The method, which also provides the value of thereddening to the system, is discussed in detail, together with athorough estimate of the associated errors. We conclude that accurateStrömgren photometry obtainable with 1.5 m-class telescopes of theLMC eclipsing binaries HV 2274 and HV 982 will allow to obtain anempirical LMC distance with an accuracy of the order of 0.13 mag.
| 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.
| Age and Metallicity Estimates for Moderate-Mass Stars in Eclipsing Binaries
We estimate the ages and metallicities for the components of 43 binarysystems using a compilation of accurate observational data on eclipsingbinaries for which lines of both components are visible in theirspectra, together with two independent modern sets of stellar evolutionmodels computed for a wide range of masses and chemical abundances. Theuncertainties of the resulting values are computed, and their stabilityis demonstrated. The ages and metallicity are compared with thosederived in other studies using different methods, as well as withindependent estimates from photometric observations and observations ofclusters. These comparisons con firm the reliability of our ageestimates. The resulting metallicities depend significantly on thechoice of theoretical model. Comparison with independent estimatesfavors the estimates based on the evolutionary tracks of the Genevagroup.
| 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
| Estimating the ages of eclipsing variable DM-stars on the basis of the evolutionary star models by Maeder and Meynet
A set of isochrones covering a wide range of star ages from5\cdot106 to 1010 yr was built on the basis of thestellar models by A. Maeder and G. Meynet with overshooting and massloss for Population I stars with abundances (X, Y, Z) = 0.70, 0.28,0.02. The isochrones were used to compute the ages of 88 eclipsingvariable stars from the catalog by Andersen which lie on the mainsequence. The influence of initial data errors on the rezultes wasinvestigated. The ages derived are in good agreement with the results ofother authors.
| Chemical composition of eclipsing binaries: a new approach to the helium-to-metal enrichment ratio
The chemical enrichment law Y(Z) is studied by using detacheddouble-lined eclipsing binaries with accurate absolute dimensions andeffective temperatures. A sample of 50 suitable systems was collectedfrom the literature, and their effective temperatures were carefullyre-determined. The chemical composition of each of the systems wasobtained by comparison with stellar evolutionary models, under theassumption that they should fit an isochrone to the observed propertiesof the components. Evolutionary models covering a wide grid in Z and Ywere adopted for our study. An algorithm was developed for searching thebest-fitting chemical composition (and the age) for the systems, basedon the minimization of a χ2 function. The errors (andbiases) of these parameters were estimated by means of Monte Carlosimulations, with special care put on the correlations existing betweenthe errors of both components. In order to check the physicalconsistency of the results, we compared our metallicity values withempirical determinations, obtaining excellent coherence. Theindependently derived Z and Y values yielded a determination of thechemical enrichment law via weighted linear least-squares fit. Our valueof the slope, ΔY/ΔZ=2.2+/-0.8, is in good agreement withrecent results, but it has a smaller formal error and it is free ofsystematic effects. Linear extrapolation of the enrichment law to zerometals leads to an estimation of the primordial helium abundance ofYp=0.225+/-0.013, possibly affected by systematics in theeffective temperature determination.
| Intrinsically-Variable B Stars in Eclipsing Binary Systems
We have investigated the use of Hipparcos epoch photometry for studyingpossible intrinsic variability in B0-B3 stars in eclipsing binarysystems with well-determined masses.
| Apsidal Motion in Double Stars. I. Catalog
A catalog of 128 double stars with measured periods of apsidal motion iscompiled. Besides the apsidal periods, the orbital elements of binariesand physical parameters of components (masses, radii, effectivetemperatures, surface gravities) are given. The agreement of the apsidalperiods found by various authors is discussed.
| Asteroseismology of the beta Cephei stars. II. 12 (DD) Lacertae
Five pulsation modes are simultaneously excited in this well-known betaCephei star. Three of them, including the one with the largest light andradial-velocity amplitudes, form a triplet. The triplet is equidistantin frequency to within the errors of measurement, that is, 0.0003 d(-1). Explaining why the triplet should be so nearly equidistant turns outto be a real challenge to the theory. We investigate the following threeoptions: (1) rotational splitting, (2) an oblique magnetic pulsator, and(3) nonlinear phase lock. Unfortunately, apart from the frequencies, thedata are meager. Photometric indices yield the effective temperature andsurface gravity of rather low accuracy. In addition, the existingdeterminations of the spherical harmonic degree of even the strongestobserved mode are discrepant. Consequently, the model parameters are notwell constrained. We show that of the three above-mentioned options, theoblique pulsator model is unlikely because it would require excessivelystrong dipolar field or a special field geometry. The rotationalsplitting is a possibility, but only for an l = 2, p_0 mode in a modelwith specific values of the effective temperature and surface gravity.Finally, we note that the nonlinear phase lock may be the solution.However, verifying this depends on the progress of nonlinearcalculations.
| Further critical tests of stellar evolution by means of double-lined eclipsing binaries
The most accurately measured stellar masses and radii come fromdetached, double-lined eclipsing binaries, as compiled by Andersen. Wepresent a detailed quantitative comparison of these fundamental datawith evolution models for single stars computed with our evolution code,both with and without the effects of enhanced mixing or overshootingbeyond the convective cores. We use the same prescription forovershooting that Schroder, Pols & Eggleton found to reproduce theproperties of zeta Aurigae binaries. For about 80 per cent of the 49binary systems in the sample, both sets of models provide a good fit toboth stars at a single age and metallicity within the observationaluncertainties. We discuss possible causes for the discrepancies in theother systems. For only one system, AI Hya, do the enhanced-mixingmodels provide a significantly better fit to the data. For two others(WX Cep and TZ For) the fit to the enhanced-mixing models is alsobetter. None of the other systems can individually distinguish betweenthe models with and without enhanced mixing. However, the number ofsystems in a post-main-sequence phase is in much better agreement withthe enhanced-mixing models. This test provides supportive evidence forextended mixing in main-sequence stars in the range 2-3Msolar.
| Fundamental parameters, helium abundance and distance of X Persei
We present spectral observations of the Be/X-ray binary system XPersei/4U 0352+30 taken during the recent (1989-91) low-luminositydiscless phase. On the basis of new spectroscopic and photometric datathe following self-consistent values of effective temperature T_eff,surface gravity g and interstellar absorption A_v for the visiblecomponent of the system are determined: T_eff=29500+/-1500 K, logg=4.0+/-0.2 and A_v=1.05+/-0.02. The corresponding spectralclassification of the star is B0 V. The helium overabundance He/H=0.19is found, as well as the enhanced nitrogen abundance log epsilon(N)~8.4.Two possible explanations of the He excess are proposed: (a) internalenrichment of the outer layers of a massive star by CNO-cycle productsbecause of a mixing on the main-sequence evolutionary phase or (b)external accretion during the evolution of a massive close binary. Thestar has a rotational velocity vsini=215+/-10km s^-1 and is located at adistance d=700+/-300pc. The X-ray flux corresponding to this reviseddistance is of the order of 1-2x10^34erg s^-1 in the normal state, andaround 10^35erg s^-1 in the only bright state observed (1974-75).Non-LTE analysis of more recently obtained high- resolution profiles ofthe He ii lambda4686 line shows that there is no evidence for additionalheating during the high-luminosity phase.
| MSC - a catalogue of physical multiple stars
The MSC catalogue contains data on 612 physical multiple stars ofmultiplicity 3 to 7 which are hierarchical with few exceptions. Orbitalperiods, angular separations and mass ratios are estimated for eachsub-system. Orbital elements are given when available. The catalogue canbe accessed through CDS (Strasbourg). Half of the systems are within 100pc from the Sun. The comparison of the periods of close and widesub-systems reveals that there is no preferred period ratio and allpossible combinations of periods are found. The distribution of thelogarithms of short periods is bimodal, probably due to observationalselection. In 82\% of triple stars the close sub-system is related tothe primary of a wide pair. However, the analysis of mass ratiodistribution gives some support to the idea that component masses areindependently selected from the Salpeter mass function. Orbits of wideand close sub-systems are not always coplanar, although thecorresponding orbital angular momentum vectors do show a weak tendencyof alignment. Some observational programs based on the MSC aresuggested. Tables 2 and 3 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| A calibration of Geneva photometry for B to G stars in terms of Teff, log G and [M/H]
We have used recent Kurucz models and numerous standard stars to improvethe calibration of the Geneva photometric system proposed a few yearsago. A new photometric diagram for the classification of intermediatestars (8500 <= Teff <= 11000 K) is proposed and fills agap that the previous calibration had left open. Evidence is given for aclear inadequacy of the new Kurucz models in the region of the parameterspace where convection begins to take over radiation in the star'satmosphere. This problem makes the determination of the surface gravitydifficult, but leaves that of the other parameters apparentlyunaffected. The determination of metallicity is considerably improved,thanks to the homogeneous spectroscopic data published recently by\cite[Edvardsson et al. (1993)]{ref23}. Instead of showing thetraditional diagrams, we chose to publish the diagrams of the physicalparameters with the inverted grids inside, i.e. the lines of constantphotometric parameters.
| Photometric versus empirical surface gravities of eclipsing binaries.
Systematic differences in photometric stellar surface gravitydetermination are studied by means of the comparison with empiricalvalues derived from detached double-lined eclipsing binaries.Photometric gravities were computed using Moon & Dworetsky(1985MNRAS.217..305M) grids based on Kurucz (1979ApJS...40....1K)atmosphere models, and empirical gravities were taken from Andersen(1991A&ARv...3...91A). Individual Stroemgren colours and βindices of each component of the binary system have to be taken intoaccount to correctly analyze the observed differences. A compilation ofdata on a sample containing 30 detached double-lined eclipsing binarieswith accurate (=~1-2%) determination of mass and radius and availableuvbyHbeta_ photometric data is also presented. Correction ofthe differences in terms of T_eff_ and logg for the range11000K
| Absolute dimensions of eclipsing binaries. XXI. V906 Scorpii: a triple system member of M 7.
We present an analysis based on new uvby light curves and spectroscopicdata of the detached triple-lined B-type eclipsing binary V906 Sco. Theuvby light curves are analysed with an extended version of theWilson-Devinney program. The spectroscopic CCD observations are analysedwith both the Sterne and the Lehmann-Filhes methods. We conclude fromthe combined analysis that the triple system V906 Sco is a member of theopen cluster M 7 and that its B-type eclipsing components are still onthe main sequence, at an age of (2.4+/-0.3)x10^8^yrs, already close tothe TAMS (especially the more massive one). The system is older than thetime for circularization of the orbit, and the small eccentricity isprobably caused by the third component, which, however, is unlikely tobe the main responsible for the apsidal motion, probably more influencedby tidal and rotational deformation. We determine absolute dimensions ofhigh precision (errors <2%): M_A_=3.25+/-0.07, R_A_=3.52+/-0.04,M_B_=3.38+/-0.07 and R_B_=4.52+/-0.04, in solar units. The system isdetached, with both components in synchronous rotation, and thereforerepresentative for normal 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.
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Osservazione e dati astrometrici
| Costellazione: | Altare |
| Ascensione retta: | 17h50m28.20s |
| Declinazione: | -53°36'44.0" |
| Magnitudine apparente: | 5.92 |
| Distanza: | 252.525 parsec |
| Moto proprio RA: | 7.8 |
| Moto proprio Dec: | -10.2 |
| B-T magnitude: | 5.576 |
| V-T magnitude: | 5.691 |
Cataloghi e designazioni:
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