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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.
| Tertiary companions to close spectroscopic binaries
We have surveyed a sample of 165 solar-type spectroscopic binaries (SB)with periods from 1 to 30 days for higher-order multiplicity. Asubsample of 62 targets were observed with the NACO adaptive opticssystem and 13 new physical tertiary companions were detected. Anadditional 12 new wide companions (5 still tentative) were found usingthe 2MASS all-sky survey. The binaries belong to 161 stellar systems; ofthese 64 are triple, 11 quadruple and 7 quintuple. After correction forincompleteness, the fraction of SBs with additional companions is foundto be 63% ± 5%. We find that this fraction is a strong functionof the SB period P, reaching 96% for P<3d and dropping to34% for P>12^d. Period distributions of SBs with and withouttertiaries are significantly different, but their mass ratiodistributions are identical. The statistical data on the multiplicity ofclose SBs presented in this paper indicates that the periods and massratios of SBs were established very early, but the periods of SB systemswith triples were further shortened by angular momentum exchange withcompanions.
| 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.
| 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.
| Observational Tests and Predictive Stellar Evolution. II. Nonstandard Models
We examine contributions of second-order physical processes to theresults of stellar evolution calculations that are amenable to directobservational testing. In the first paper in the series, we establishedbaseline results using only physics that were common to modern stellarevolution codes. In this paper we establish how much of the discrepancybetween observations and baseline models is due to particular elementsof new physics in the areas of mixing, diffusion, equations of state,and opacities. We then consider the impact of the observationaluncertainties on the maximum predictive accuracy achievable by a stellarevolution code. The Sun is an optimal case because of the precise andabundant observations and the relative simplicity of the underlyingstellar physics. The standard model is capable of matching the structureof the Sun as determined by helioseismology and gross surfaceobservables to better than a percent. Given an initial mass and surfacecomposition within the observational errors, and no current observablesas additional constraints for which the models can be optimized, it isnot possible to predict the Sun's current state to better than ~7%.Convectively induced mixing in radiative regions, terrestriallycalibrated by multidimensional numerical hydrodynamic simulations,dramatically improves the predictions for radii, luminosity, and apsidalmotions of eclipsing binaries while simultaneously maintainingconsistency with observed light element depletion and turnoff ages inyoung clusters. Systematic errors in core size for models of massivebinaries disappear with more complete mixing physics, and acceptablefits are achieved for all of the binaries without calibration of freeparameters. The lack of accurate abundance determinations for binariesis now the main obstacle to improving stellar models using this type oftest.
| An Assessment of Dynamical Mass Constraints on Pre-Main-Sequence Evolutionary Tracks
We have assembled a database of stars having both masses determined frommeasured orbital dynamics and sufficient spectral and photometricinformation for their placement on a theoretical H-R diagram. Our sampleconsists of 115 low-mass (M<2.0 Msolar) stars, 27pre-main-sequence and 88 main-sequence. We use a variety of availablepre-main-sequence evolutionary calculations to test the consistency ofpredicted stellar masses with dynamically determined masses. Despitesubstantial improvements in model physics over the past decade, largesystematic discrepancies still exist between empirical and theoreticallyderived masses. For main-sequence stars, all models considered predictmasses consistent with dynamical values above 1.2 Msolar andsome models predict consistent masses at solar or slightly lower masses,but no models predict consistent masses below 0.5 Msolar,with all models systematically underpredicting such low masses by5%-20%. The failure at low masses stems from the poor match of mostmodels to the empirical main sequence below temperatures of 3800 K, atwhich molecules become the dominant source of opacity and convection isthe dominant mode of energy transport. For the pre-main-sequence samplewe find similar trends. There is generally good agreement betweenpredicted and dynamical masses above 1.2 Msolar for allmodels. Below 1.2 Msolar and down to 0.3 Msolar(the lowest mass testable), most evolutionary models systematicallyunderpredict the dynamically determined masses by 10%-30%, on average,with the Lyon group models predicting marginally consistent masses inthe mean, although with large scatter. Over all mass ranges, theusefulness of dynamical mass constraints for pre-main-sequence stars isin many cases limited by the random errors caused by poorly determinedluminosities and especially temperatures of young stars. Adopting awarmer-than-dwarf temperature scale would help reconcile the systematicpre-main-sequence offset at the lowest masses, but the case for this isnot compelling, given the similar warm offset at older ages between mostsets of tracks and the empirical main sequence. Over all age ranges, thesystematic discrepancies between track-predicted and dynamicallydetermined masses appear to be dominated by inaccuracies in thetreatment of convection and in the adopted opacities.
| 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
| On the anomaly of Balmer line profiles of A-type stars. Fundamental binary systems
In previous work, Gardiner et al. (\cite{GKS99}) found evidence for adiscrepancy between the Teff obtained from Balmer lines withthat from photometry and fundamental values for A-type stars. Aninvestigation into this anomaly is presented using Balmer line profilesof stars in binary system with fundamental values of bothTeff and log g. A revision of the fundamental parameters forbinary systems given by Smalley & Dworetsky (\cite{SD95}) is alsopresented. The Teff obtained by fitting Hα and Hβline profiles is compared to the fundamental values and those obtainedfrom uvby photometry. We find that the discrepancy found by Gardiner etal. (\cite{GKS99}) for stars in the range 7000 K <~ Teff<~ 9000 K is no longer evident. Partly based on DENIS data obtainedat the European Southern Observatory.
| 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.
| 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.
| 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.
| Observational Tests and Predictive Stellar Evolution
We compare 18 binary systems with precisely determined radii and massesfrom 23 to 1.1 Msolar and stellar evolution models producedwith our newly revised code TYCHO. ``Overshooting'' and rotationalmixing were suppressed in order to establish a baseline for isolatingthese and other hydrodynamic effects. Acceptable coeval fits are foundfor 16 pairs without optimizing for heavy-element or helium abundance.The precision of these tests is limited by the accuracies of theobserved effective temperatures. High-dispersion spectra and detailedatmospheric modeling should give more accurate effective temperaturesand heavy-element abundances. PV Cas, a peculiar early A system, EK CepB, a known post-T Tauri star, and RS Cha, a member of a young OBassociation, are matched by pre-main-sequence models. Predicted massloss agrees with upper limits from IUE for CW Cep A and B. Relativelypoor fits are obtained for binaries having at least one component in themass range 1.7
| Surface Brightness--Color Relation for Eclipsing Binaries with ubvy Photometry
The relation between visual surface brightness and (b-y)_0 color indexis constructed for eclipsing binaries with Hipparcos parallaxes andphotometry in the Stromgren four-color ubvy system. The relation isconsistent with the Popper relation derived for stars with angulardiameters obtained mainly from interferometry or from the lunaroccultation method. It is shown that the Lutz-Kelker correction tomagnitudes is in this case negligible.
| 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
| The mass dependence of the overshooting parameter determined from eclipsing binary data
High-precision data on absolute dimensions of evolved eclipsing binarieshave been used for a quantitative evaluation of the significance ofconvective overshoot in the stellar core. Eight detached double-linedeclipsing binaries with components close to or beyond the terminal agemain sequence (TAMS) and masses between 2 and 12Msolar havebeen compared with evolutionary models using different overshootingparameters. The results are robust and indicate a systematic increase ofthe amount of convective overshoot with the stellar mass. Suchdetermination constitutes a fundamental point for stellar structure andevolution theory.
| 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.
| 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.
| Times of Minima of Some Southern Eclipsing Binaries
Not Available
| HIPPARCOS Parallaxes of Eclipsing Binaries and the Radiative Flux Scale
Eclipsing binaries with Hipparcos parallaxes are found to define aradiative flux relation for main-sequence stars in the B6-F0 range aboutas well as stars with angular diameters and to extend the range to F8.The fluxes of components of binaries showing large intrinsic variationsfall well below the curve for other stars and its extension to lowertemperatures. Angular diameters of main-sequence stars obtained with thenew generation of stellar interferometers should improve and extend theflux calibration. Based on data from the ESA Hipparcos satellite.
| Effective temperature of detached eclipsing binaries from HIPPARCOS parallax
Effective temperatures of detached eclipsing binaries computed throughHipparcos trigonometric parallaxes are compared with the photometricdeterminations. The former are based on the values of the radius, theapparent visual magnitude and the bolometric correction of the star,whereas the latter are obtained from standard calibrations usingStromgren or Johnson colour indices. The working sample contains allwell-studied detached double-lined eclipsing binaries belonging to theHipparcos catalogue and with relative errors in the parallaxes smallerthan 20%. They cover a temperature range from 5000 K to 25000 K. A smallsystematic trend of 0.010 dex (s.d. 0.010) for T_eff <= 10000 K andof 0.015 dex (s.d. 0.060) for T_eff > 10000 K is observed between thetwo temperature determinations, that could be due to inaccuracies onphotometric effective temperatures. Based on data from the ESA Hipparcosastrometry satellite
| The Absolute Dimensions of Eclipsing Binaries. XXII. The Unevolved F-Type System HS Hydrae
Abstract image available at:http://adsabs.harvard.edu/abs/1997AJ....114.2764T
| The role of convection on the UVBY colours of A, F, and G stars
We discuss the effects of convection on the theoretical uvby colours ofA, F, and G stars. The standard mixing-length theory atlas9 models ofKurucz (1993), with and without approximate overshooting, are comparedto models using the turbulent convection theory proposed by Canuto &Mazzitelli (1991, 1992) and implemented by Kupka (1996a). Comparisonwith fundamental T_eff and log g stars reveals that the Canuto &Mazzitelli models give results that are generally superior to standardmixing-length theory (MLT) without convective overshooting. MLT modelswith overshooting are found to be clearly discrepant. This is supportedby comparisons of non-fundamental stars, with T_eff obtained from theInfrared Flux Method and log g from stellar evolutionary models for opencluster stars. The Canuto & Mazzitelli theory gives values of(b-y)_0 and c_0 that are in best overall agreement with observations.Investigations of the m_0 index reveal that all of the treatments ofconvection presented here give values that are significantly discrepantfor models with T_eff < 6000 K. It is unclear as to whether this isdue to problems with the treatment of convection, missing opacity, orsome other reason. None of the models give totally satisfactory m_0indices for hotter stars, but the Canuto & Mazzitelli models are inclosest overall agreement above 7000 K. Grids of uvby colours, based onthe CM treatment of convection, are presented. These grids represent animprovement over the colours obtained from models using themixing-length theory. The agreement with fundamental stars enables thecolours to be used directly without the need for semi-empiricaladjustments that were necessary with the earlier colour grids. Table~5is only available at the CDS via anonymous ftp 130.79.128.5 or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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
| 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.
| 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.
| The calibration of uvbyβ photometry for B, A and F stars. I. Fundamental atmospheric parameters.
We present an investigation into the determination of fundamental valuesof T_eff_ and logg. A re-evaluation of the fundamental values of T_eff_determined by Code et al. using modern flux measurements is presented,but there are no significant changes. A determination of fundamentalvalues of T_eff_ for four binary systems with fundamental logg valueshas been performed. Medium-resolution Hβ profiles of thefundamental stars have been obtained and compared to theoreticalprofiles in order to provide estimates of the parameters that have notbeen obtained in a fundamental manner. We have calculated a table ofsynthetic β indices which explicitly include the effects ofmetal-line blocking. We find that these β indices are in goodagreement with the photometric values. A comparison of theoretical uvbycolours is also presented, and found to be in very good agreement withthe photometric colours.
| Effective Temperature Bolometric Correction and Mass Calibration of O-F
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.268..119B&db_key=AST
| The photometric method of extrasolar planet detection revisited
We investigate the geometry concerning the photometric method ofextrasolar planet detection, i.e., the detection of dimunition of aparent star's brightness during a planetary transit. Under theassumption that planetary orbital inclinations can be defined by aGaussian with a sigma of 10 deg centered on the parent star's equatorialplane, Monte Carlo simulations suggest that for a given star observed atan inclination of exactly 90 deg, the probability of at least oneEarth-sized or larger planet being suitably placed for transits isapproximately 4%. This probability drops to 3% for a star observed at aninclination of 80 deg, and is still approximately 0.5% for a starobserved at an inclination of 60 deg. If one can select 100 stars with apre-determined inclination equal or greater than 80 deg, the probabilityof at least one planet being suitably configured for transits is 95%.The majority of transit events are due to planets in small-a orbitssimilar to the Earth and Venus; thus, the photometric method inprinciple is the method best suited for the detection of Earthlikeplanets. The photometric method also allows for testing whether or notplanets can exist within binary systems. This can ge done by selectingbinary systems observed at high orbital inclinations, both eclipsingbinaries and wider visual binaries. For a 'real-world' example, we lookat the alpha Centauri system (i = 79.2 deg). If we assume that theequatorial planes of both components coincide with the system's orbitalplane, Monte Carlo simulations suggest that the probability of at leastone planet (of either component) being suitably configured for transitsis approximately 8%. In conclusion, we present a non-exhaustive list ofsolar-type stars, both single and within binary systems, which exhibit ahigh equatorial inclination. These objects may be considered aspreliminary candidates for planetary searches via the photometricmethod.
| The active dynamo stars: RS CVn, BY Dra, FK Com, Algol, W UMa, and T Tau
Not Available
| Catalogue of astrophysical parameters of binary systems
Not Available
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