Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
Accurate masses and radii of normal stars: modern results and applications
This article presents and discusses a critical compilation of accurate,fundamental determinations of stellar masses and radii. We haveidentified 95 detached binary systems containing 190 stars (94 eclipsingsystems, and ? Centauri) that satisfy our criterion that the massand radius of both stars be known within errors of ±3% accuracyor better. All of them are non-interacting systems, and so the starsshould have evolved as if they were single. This sample more thandoubles that of the earlier similar review by Andersen (Astron AstrophysRev 3:91-126, 1991), extends the mass range at both ends and, forthe first time, includes an extragalactic binary. In every case, we haveexamined the original data and recomputed the stellar parameters with aconsistent set of assumptions and physical constants. To these we addinterstellar reddening, effective temperature, metal abundance,rotational velocity and apsidal motion determinations when available,and we compute a number of other physical parameters, notably luminosityand distance. These accurate physical parameters reveal the effects ofstellar evolution with unprecedented clarity, and we discuss the use ofthe data in observational tests of stellar evolution models in somedetail. Earlier findings of significant structural differences betweenmoderately fast-rotating, mildly active stars and single stars, ascribedto the presence of strong magnetic and spot activity, are confirmedbeyond doubt. We also show how the best data can be used to testprescriptions for the subtle interplay between convection, diffusion,and other non-classical effects in stellar models. The amount andquality of the data also allow us to analyse the tidal evolution of thesystems in considerable depth, testing prescriptions of rotationalsynchronisation and orbital circularisation in greater detail thanpossible before. We show that the formulae for pseudo-synchronisation ofstars in eccentric orbits predict the observed rotations quite well,except for very young and/or widely separated stars. Deviations dooccur, however, especially for stars with convective envelopes. Thesuperior data set finally demonstrates that apsidal motion rates aspredicted from General Relativity plus tidal theory are in goodagreement with the best observational data. No reliable binary dataexist, which challenge General Relativity to any significant extent. Thenew data also enable us to derive empirical calibrations of M and R forsingle (post-) main-sequence stars above {0.6 M_{odot}}. Simple,polynomial functions of T eff, log g and [Fe/H] yield M and Rwithin errors of 6 and 3%, respectively. Excellent agreement is foundwith independent determinations for host stars of transiting extrasolarplanets, and good agreement with determinations of M and R from stellarmodels as constrained by trigonometric parallaxes and spectroscopicvalues of T eff and [Fe/H]. Finally, we list a set of 23interferometric binaries with masses known to be better than 3%, butwithout fundamental radius determinations (except ? Aur). Wediscuss the prospects for improving these and other stellar parametersin the near future.
| The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics
Context: Ages, chemical compositions, velocity vectors, and Galacticorbits for stars in the solar neighbourhood are fundamental test datafor models of Galactic evolution. The Geneva-Copenhagen Survey of theSolar Neighbourhood (Nordström et al. 2004; GCS), amagnitude-complete, kinematically unbiased sample of 16 682 nearby F andG dwarfs, is the largest available sample with complete data for starswith ages spanning that of the disk. Aims: We aim to improve theaccuracy of the GCS data by implementing the recent revision of theHipparcos parallaxes. Methods: The new parallaxes yield improvedastrometric distances for 12 506 stars in the GCS. We also use theparallaxes to verify the distance calibration for uvby? photometryby Holmberg et al. (2007, A&A, 475, 519; GCS II). We add newselection criteria to exclude evolved cool stars giving unreliableresults and derive distances for 3580 stars with large parallax errorsor not observed by Hipparcos. We also check the GCS II scales of T_effand [Fe/H] and find no need for change. Results: Introducing thenew distances, we recompute MV for 16 086 stars, and U, V, W,and Galactic orbital parameters for the 13 520 stars that also haveradial-velocity measurements. We also recompute stellar ages from thePadova stellar evolution models used in GCS I-II, using the new valuesof M_V, and compare them with ages from the Yale-Yonsei andVictoria-Regina models. Finally, we compare the observed age-velocityrelation in W with three simulated disk heating scenarios to show thepotential of the data. Conclusions: With these revisions, thebasic data for the GCS stars should now be as reliable as is possiblewith existing techniques. Further improvement must await consolidationof the T_eff scale from angular diameters and fluxes, and the Gaiatrigonometric parallaxes. We discuss the conditions for improvingcomputed stellar ages from new input data, and for distinguishingdifferent disk heating scenarios from data sets of the size andprecision of the GCS.Full Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/501/941
| 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.
| Absolute dimensions of eclipsing binaries. XXVI.. Setting a new standard: Masses, radii, and abundances for the F-type systems AD Bootis VZ Hydrae, and WZ Ophiuchi
Context: Accurate mass, radius, and abundance determinations frombinaries provide important information on stellar evolution, fundamentalto central fields in modern astrophysics and cosmology. Aims: Weaim to determine absolute dimensions and abundances for the three F-typemain-sequence detached eclipsing binaries AD Boo, VZ Hya, and WZ Oph andto perform a detailed comparison with results from recent stellarevolutionary models. Methods: uvby light curves and uvby?standard photometry were obtained with the Strömgren AutomaticTelescope at ESO, La Silla, radial velocity observations at CfAfacilities, and supplementary high-resolution spectra with ESO's FEROSspectrograph. State-of-the-art methods were applied for the analyses:the EBOP and Wilson-Devinney binary models, two-dimensionalcross-correlation and disentangling, and the VWA abundance analysistool. Results: Masses and radii that are precise to 0.5-0.7% and0.4-0.9%, respectively, have been established for the components, whichspan the ranges of 1.1 to 1.4 M? and 1.1 to 1.6R?. The [Fe/H] abundances are from -0.27 to +0.10, withuncertainties between 0.07 and 0.15 dex. We find indications of a slight?-element overabundance of [?/Fe] ˜ + 0.1 for WZ Oph.The secondary component of AD Boo and both components of WZ Oph appearto be slightly active. Yale-Yonsai and Victoria-Regina evolutionarymodels fit the components of AD Boo and VZ Hya almost equally well,assuming coeval formation, at ages of about 1.75/1.50 Gyr (AD Boo) and1.25/1.00 Gyr (VZ Hya). BaSTI models, however, predict somewhatdifferent ages for the primary and secondary components. For WZ Oph, themodels from all three grids are significantly hotter than observed. Alow He content, decreased envelope convection coupled with surfaceactivity, and/or higher interstellar absorption would remove thediscrepancy, but its cause has not been definitively identified. Conclusions: We have demonstrated the power of testing and comparingrecent stellar evolutionary models using eclipsing binaries, providedtheir abundances are known. The strongest limitations and challenges areset by T_eff and interstellar absorption determinations, and by theireffects on and correlation with abundance results.Based on observations carried out at the Strömgren AutomaticTelescope (SAT) and the 1.5 m and 2.2 m telescopes at ESO, La Silla,Chile (62.L-0284, 63.H-0080, 71.D-0554); the 1.5 m Wyeth reflector atthe Oak Ridge Observatory, Harvard, Massachusetts, USA; the 1.5-mTillinghast reflector and the Multiple Mirror Telescope at the F.L.?Whipple Observatory, Mt.?Hopkins, Arizona.
| New absolute magnitude calibrations for detached binaries
Lutz-Kelker bias corrected absolute magnitude calibrations for thedetached binary systems with main-sequence components are presented. Theabsolute magnitudes of the calibrator stars were derived at intrinsiccolours of Johnson-Cousins and 2MASS (Two Micron All Sky Survey)photometric systems. As for the calibrator stars, 44 detached binarieswere selected from the Hipparcos catalogue, which have relative observedparallax errors smaller than 15% (σπ/π≤0.15).The calibration equations which provide the corrected absolute magnitudefor optical and near-infrared pass bands are valid for wide ranges ofcolours and absolute magnitudes: -0.18<(B-V)0<0.91,-1.6
| Mass-luminosity relation of intermediate-mass stars
The mass-luminosity relation (MLR) for intermediate-mass stars is basedon data on detached double-lined eclipsing binaries. However, there is anotable difference between the parameters of B0V-G0V components ofeclipsing binaries and those of single stars. Single early-type starsare rapid rotators, whereas tidal forces produce synchronous rotation inclose binaries and all such pairs are synchronized, so components ofclose binaries rotate more slowly. As is well known, stellar rotationchanges stellar evolution and the global parameters of a star.In this work we collect data on fundamental parameters of stars withmasses m > 1.5msolar. They are components of binaries withP > 15 d and consequently are not synchronized with the orbitalperiods and presumably are rapid rotators. These stars are believed toevolve similarly with single stars. Modern data on masses, absolute andbolometric luminosities, radii and temperatures of detachedmain-sequence double-lined eclipsing binary components (i.e. presumablyslow rotators) are also collected.Mass-luminosity, mass-temperature and mass-radius relations of close andwide binaries are presented, as well as their Hertzsprung-Russelldiagram. For the mass range 4.5 < m/msolar < 5.5 (lateB stars) it was found that rapid rotators exhibit slightly higherluminosities and larger radii than predicted by the standard relations,and their main sequence is shifted to the right-hand side with respectto that of the close binary components. The resulting relations forrapidly and slowly rotating A-F and early B stars are not statisticallydifferent.As our estimations show, for the given mass range the effect on theinitial mass function (IMF) is marginal, but there is no way to estimatethe degree to which the effect may be important for higher masses.Available observational data for m > 12msolar are too poorto make definite conclusions. Knowledge of the MLR should come fromdynamical mass determinations of visual binaries combined with spatiallyresolved precise photometry. Then the IMF should be revised for thatmass range.
| Effect of tidal evolution in determining the ages of eclipsing-variable early main sequence close binary systems
New Claret evolutionary model-tracks, constructed for the first time forstudying close binary systems (CBS) including tidal evolution constants,are used to determine the age of 112 eclipsing-variable stars in theSvechnikov-Perevozkina catalog by the method of isochrones. There issome interest in comparing the calculated ages with previous estimatesobtained for these same close binary systems using evolutionarymodeltracks for individual stars taking their mass loss into account. Acorrelation of the ages of the principal and secondary components isnoted, which is most marked for massive close binaries with principalcomponents having masses M1 ? 3 M?. Arejuvenating effect is found to occur for the systems studied here ascalculated on the new tracks; it is most distinct for low-mass closebinaries with a total mass M1 + M2 ? 3.5M? and is predicted theoretically in terms of magneticbraking. The calculated broadband grid of isochrones, from zero-agemain-sequence (ZAMS) to the age of the galaxy, can be used forestimating the ages of close binaries from other catalogs. Ages aregiven for the 112 eclipsing-variable close binaries with detachedcomponents lying within the main sequence.
| 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.
| Astrometric orbits of SB^9 stars
Hipparcos Intermediate Astrometric Data (IAD) have been used to deriveastrometric orbital elements for spectroscopic binaries from the newlyreleased Ninth Catalogue of Spectroscopic Binary Orbits(SB^9). This endeavour is justified by the fact that (i) theastrometric orbital motion is often difficult to detect without theprior knowledge of the spectroscopic orbital elements, and (ii) suchknowledge was not available at the time of the construction of theHipparcos Catalogue for the spectroscopic binaries which were recentlyadded to the SB^9 catalogue. Among the 1374 binaries fromSB^9 which have an HIP entry (excluding binaries with visualcompanions, or DMSA/C in the Double and Multiple Stars Annex), 282 havedetectable orbital astrometric motion (at the 5% significance level).Among those, only 70 have astrometric orbital elements that are reliablydetermined (according to specific statistical tests), and for the firsttime for 20 systems. This represents a 8.5% increase of the number ofastrometric systems with known orbital elements (The Double and MultipleSystems Annex contains 235 of those DMSA/O systems). The detection ofthe astrometric orbital motion when the Hipparcos IAD are supplementedby the spectroscopic orbital elements is close to 100% for binaries withonly one visible component, provided that the period is in the 50-1000 drange and the parallax is >5 mas. This result is an interestingtestbed to guide the choice of algorithms and statistical tests to beused in the search for astrometric binaries during the forthcoming ESAGaia mission. Finally, orbital inclinations provided by the presentanalysis have been used to derive several astrophysical quantities. Forinstance, 29 among the 70 systems with reliable astrometric orbitalelements involve main sequence stars for which the companion mass couldbe derived. Some interesting conclusions may be drawn from this new setof stellar masses, like the enigmatic nature of the companion to theHyades F dwarf HIP 20935. This system has a mass ratio of 0.98 but thecompanion remains elusive.
| 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/.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
| 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.
| 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.
| 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.
| Eclipsing Binaries and the Lutz-Kelker Bias
Using examples from the literature, we demonstrate that ignoring theLutz- Kelker bias may degrade agreement between results derived fromeclipsing binaries and those based on trigonometric parallaxes. Inaddition, we show that eclipsing binaries are excellent standardcandles.
| 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
| Comparison of Parallaxes from Eclipsing Binaries Method with Hipparcos Parallaxes
The parallaxes determined by Lacy (1979) by means of eclipsing binariesmethod are compared with the Hipparcos parallaxes for 19 systems. Theresidual scatter of the distance moduli inferred from eclipsing binariesmethod - after allowing for known errors as given by Lacy and Hipparcos- is equal to 0.18 mag. It decreases to 0.08 mag when obviously notfitting semi-detached systems and systems with chromospheric activity ofcomponents are removed from the sample.
| Absolute Dimensions of Eclipsing Binaries. XXIII. The F-Type System EI Cephei
We report new radial velocity measurements made with theHarvard-Smithsonian Center for Astrophysics Digital Speedometers of theF-type double-lined eclipsing binary EI Cep (P=8.4 days), in which thesecondary is a metallic-line star. Using these and previous measurementsfrom the literature, we redetermine the masses of the components to aprecision of 0.4%, 4 to 5 times better than previously achieved. We alsoreanalyze UBV light curves for the system from the literature withmodern methods to determine the radii and the effective temperatures.The resulting stellar parameters are MA=1.7716+/-0.0066Msolar, MB=1.6801+/-0.0062 Msolar,RA=2.896+/-0.048 Rsolar,RB=2.329+/-0.044 Rsolar,TAeff=6750+/-100 K, andTBeff=6950+/-100 K. Further properties of thesystem are given in this paper. Both components are near the end oftheir main-sequence evolution, and a comparison of the observationalresults with theoretical evolutionary models gives excellent agreementwith models using two somewhat different treatments of overshooting fromthe convective cores (but not with standard models). An age of 1.4 Gyris derived for the roughly solar metallicity indicated by our lowsignal-to-noise ratio spectra. A precise spectroscopic determination ofthe metallicity of EI Cep would be very useful to place even tighterconstraints on the models. The measured projected rotational velocitiesof the stars (13 and 17 km s-1 for EI Cep A and B,respectively) are very close to, but not quite synchronized with, theorbital motion. This is in agreement with predictions from current tidaltheories, which, however, also predict that orbital circularization hasnot yet occurred, although we detect no significant eccentricity. Someof the observations reported in this paper were obtained at the MultipleMirror Telescope Observatory, a facility operated jointly by theUniversity of Arizona and the Smithsonian Institution.
| 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.
| 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.
| 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
| 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.
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
| Созвездие: | Гидра |
| Прямое восхождение: | 10h24m36.77s |
| Склонение: | -19°05'33.0" |
| Видимая звёздная величина: | 8.11 |
| Расстояние: | 90.58 парсек |
| Собственное движение RA: | -12 |
| Собственное движение Dec: | -10.5 |
| B-T magnitude: | 8.641 |
| V-T magnitude: | 8.154 |
Каталоги и обозначения:
|
