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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.
| Relativistic apsidal motion in eccentric eclipsing binaries
Context. The study of apsidal motion in detached eclipsing binarysystems is known to be an important source of information about stellarinternal structure as well as the possibility of verifying of GeneralRelativity outside the Solar System. Aims: As part of thelong-term Ond?ejov and Ostrava observational projects, we aim tomeasure precise times of minima for eccentric eclipsing binaries, neededfor the accurate determination of apsidal motion, providing a suitabletest of the effects of General Relativity. Methods: About seventynew times of minimum light recorded with photoelectric or CCDphotometers were obtained for ten eccentric-orbit eclipsing binarieswith significant relativistic apsidal motion. Their O-C diagrams wereanalysed using all reliable timings found in the literature, and new orimproved elements of apsidal motion were obtained. Results: Weconfirm very long periods of apsidal motion for all systems. For BF Draand V1094 Tau, we present the first apsidal-motion solution. Therelativistic effects are dominant, representing up to 100% of the totalobservable apsidal-motion rate in several systems. The theoretical andobserved values of the internal structure constant k 2 werecompared for systems with lower relativistic contribution. Using thelight-time effect solution, we predict a faint third component for V1094Tau orbiting with a short period of about 8 years.Partly based on photoelectric observations secured at the HvarObservatory, Faculty of Geodesy, Zagreb, Croatia, in October 2008.
| Absolute Dimensions of the F-Type Eclipsing Binary Star VZ Cephei
We present new V-band differential photometry and radial velocitymeasurements of the unevolved, 1.18 day period, F+G-type, double-linedeclipsing binary VZ Cep. We determine accurate values for the absolutemasses, radii, and effective temperatures as follows: M A =1.402 ± 0.015 M sun, R A = 1.534 ±0.012 R sun, and T eff = 6690 ± 160 K forthe primary, and M B = 1.1077 ± 0.0083 Msun, R B = 1.042 ± 0.039 R sun,and T eff = 5720 ± 120 K for the secondary. Acomparison with current stellar evolution models suggests an age of 1.4Gyr for a metallicity that is near solar. The temperature differencebetween the stars, which is much better determined than the absolutevalues, is found to be ~ 250 K larger than predicted by theory. If allof this discrepancy is attributed to the secondary (which would then betoo cool compared to models), the effect would be consistent withsimilar differences found for other low-mass stars, generally believedto be associated with chromospheric activity. However, the radius of VZCep B (which unlike the primary, still has a thin convective envelope)appears normal, whereas in other stars affected by activity the radiusis systematically larger than predicted. Thus, VZ Cep poses a challengenot only to standard theory but also to our understanding of thediscrepancies in other low-mass systems.
| Combined effects of tidal and rotational distortions on the equilibrium configuration of low-mass, pre-main sequence stars
Context: In close binary systems, the axial rotation and the mutualtidal forces of the component stars deform each other and destroy theirspherical symmetry by means of the respective disturbing potentials. Aims: We present new models for low-mass, pre-main sequence stars thatinclude the combined distortion effects of tidal and rotational forceson the equilibrium configuration of stars. Using our theoreticalresults, we aim at investigating the effects of interaction betweentides and rotation on the stellar structure and evolution. Methods: The Kippenhahn & Thomas (1970, in Stellar Rotation, ed.A. Slettebak) approximation, along with the Clairaut-Legendre expansionfor the gravitational potential of a self-gravitating body, is used totake the effects of tidal and rotational distortions on the stellarconfiguration into account. Results: We obtained values ofinternal structure constants for low-mass, pre-main sequence stars fromstellar evolutionary models that consider the combined effects ofrotation and tidal forces due to a companion star. We also derived a newexpression for the rotational inertia of a tidally and rotationallydistorted star. Our values corresponding to standard models (with nodistortions) are compatible with those available in literature. Ourdistorted models were successfully used to analyze the eclipsing binarysystem EK Cep, reproducing the stellar radii, effective temperatureratio, lithium depletion, rotational velocities, and the apsidal motionrate in the age interval of 15.5-16.7 Myr. Conclusions: In thelow-mass range, the assumption that harmonics greater than j=2 can beneglected seems not to be fully justified, although it is widely usedwhen analyzing the apsidal motion of binary systems. The non-standardevolutionary tracks are cooler than the standard ones, mainly forlow-mass stars. Distorted models predict more mass-concentrated stars atthe zero-age main-sequence than standard models.The full version of Table [see full text] is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/494/209
| The mass of young stellar objects.
Not Available
| Artificial Intelligence Approach to the Determination of Physical Properties of Eclipsing Binaries. I. The EBAI Project
Achieving maximum scientific results from the overwhelming volume ofastronomical data to be acquired over the next few decades demandsnovel, fully automatic methods of data analysis. Here we concentrate oneclipsing binary (EB) stars, a prime source of astrophysicalinformation, of which only some hundreds have been rigorously analyzed,but whose numbers will reach millions in a decade. We describe theartificial neural network (ANN) approach which is able to surmount thehuman bottleneck and permit EB-based scientific yield to keep pace withfuture data rates. The ANN, following training on a sample of 33,235model light curves, outputs a set of approximate model parameters[T2/T1, (R1+R2)/a,esinω, ecosω, and sini] for each input light curve data set.The obtained parameters can then be readily passed to sophisticatedmodeling engines. We also describe a novel method polyfit forpreprocessing observational light curves before inputting their data tothe ANN and present the results and analysis of testing the approach onsynthetic data and on real data including 50 binaries from the Catalogand Atlas of Eclipsing Binaries (CALEB) database and 2580 light curvesfrom OGLE survey data. The success rate, defined by less than a 10%error in the network output parameter values, is approximately 90% forthe OGLE sample and close to 100% for the CALEB sample-sufficient for areliable statistical analysis. The code is made available to the public.Our approach is applicable to EB light curves of all classes; this firstpaper in the eclipsing binaries via artificial intelligence (EBAI)series focuses on detached EBs, which is the class most challenging forthis approach.
| The role of the stellar rotation on the internal constitution of PV Cassiopeiae
Aims: It has been suggested that the observed apsidal-motion of PV Casagrees with theoretical predictions. However, this view is not supportedby other investigations of the same system. By using standard androtating models, we re-analyse the evolutionary status of PV Cas, whichis poorly established, especially its apsidal-motion. Methods: Wecomputed standard (without rotation) stellar models for the preciseobserved masses of PV Cas by considering a moderate amount of coreovershooting (?_ov = 0.2). Rotating models - assuming solid-bodyrotation and local conservation of angular momentum - were also computedto verify the influence of rotation on the astrophysical properties ofthe system. Results: Considering the limitations of thetheoretical models, rotation does not appear to have a significantinfluence on the modelling of PV Cas. Rotating, in addition to standardmodels, are able to reproduce the the masses, radii, and TR (effectivetemperature ratio) of PV Cas without a rapidly rotating core, surroundedby a slowly rotating envelope. Although our rotating models provide moremass-concentrated configurations, the improvement is insufficient toreproduce the observed apsidal-motion rate. Given the error bars, thediscrepancy between theory and observation, in terms of apsidal-motion,appears to be real.
| The pre-main-sequence eclipsing binary ASAS J052821+0338.5
Aims: In this paper we present the first results of a detailedspectroscopic and photometric analysis of the V = 11.7meclipsing binary ASAS J052821+0338.5. Methods: With the FIES spectrograph at the Nordic Optical Telescope,we obtained a series of high-resolution spectra (R ? 47 000) coveringthe entire orbit of the system. In addition we obtained simultaneousbroadband photometry from three small aperture telescopes. From thesespectroscopic and photometric data we have derived the system's orbitalparameters and determined the fundamental stellar parameters of the twocomponents. Results: Our results indicate that ASASJ052821+0338.5 is a K1/K3 pre-main-sequence eclipsing binary, withcomponent masses of 1.38 {M}? and 1.33{M}? and a period of 3.87 days, located at a distance of280 ± 30 pc. The kinematics, physical location, and theevolutionary status of the two stars suggest that ASAS J052821+0338.5 isa member of the 11 Myr old Orion OB1a subassociation. The systems alsoexhibits smooth 0.15m out-of-eclipse variations that aresimilar to those found in RS CVn binaries. Furthermore, the parameterswe derived are consistent with the 10-13 Myr isochrones of the popularBaraffe stellar evolutionary models.Based on observations made with the NordicOptical Telescope.
| Seismic evolution of low/intermediate mass PMS stars
This article presents a study of the evolution of the internal structureand seismic properties expected for low/intermediate mass Pre-MainSequence (PMS) stars. Seismic and non-seismic properties of PMS starswere analysed. This was done using 0.8 to 4.4 M_? stellar models atstages ranging from the end of the Hayashi track up to the Zero-AgeMain-Sequence (ZAMS). This research concludes that, forintermediate-mass stars (M > 1.3 M_?), diagrams comparing theeffective temperature (T_eff) against the small separation can providean alternative to Christensen-Dalsgaard (C-D) diagrams. The impact ofthe metal abundance of intermediate mass stars (2.5-4.4 M_?) hasover their seismic properties is also evaluated.
| 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
| Applicability of colour index calibrations to T Tauri stars
We examine the applicability of effective temperature scales of several broad band colours to T Tauri stars (TTS). We take into account different colour systems as well as stellar parameters like metallicity and surface gravity which influence the conversion from colour indices or spectral type to effective temperature. For a large sample of TTS, we derive temperatures from broad band colour indices and check if they are consistent in a statistical sense with temperatures inferred from spectral types. There are some scales (for V-H, V-K, I-J, J-H, and J-K) which indeed predict the same temperatures as the spectral types and therefore can be at least used to confirm effective temperatures. Furthermore, we examine whether TTS with dynamically derived masses can be used for a test of evolutionary models and effective temperature calibrations. We compare the observed parameters of the eclipsing T Tauri binary V1642 Ori A to the predictions of evolutionary models in both the H-R and the Kiel diagram using temperatures derived with several colour index scales. We check whether the evolutionary models and the colour index scales are consistent with coevality and the dynamical masses of the binary components. It turns out that the Kiel diagram offers a stricter test than the H-R diagram. Only the evolutionary models of \cite {BCAH98} with mixing length parameter ?=1.9 and of \cite{DM94,DM97} show consistent results in the Kiel diagram in combination with some conversion scales of \cite{HBS00} and of \cite{KH95}.
| 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.
| Determination of the axial rotation rate using apsidal motion for early-type eclipsing binaries
Because the modern theory of stellar structure and evolution has a soundobservational basis, we can consider that the apsidal parametersk2 computed in terms of this theory correctly reflect theradial density distribution in stars of different masses and spectraltypes. This allows us to address the problem of apsidal motion in closebinary systems in a new way. Unlike the traditional approach, in thispaper we use the observed apsidal periods Uobs to estimatethe angular axial velocities of components, ωr, atfixed model values of k2. We use this approach to analyse theobservational data for 28 eclipsing systems with known Uobsand early-type primaries (M >= 1.6 Msolar or Te>= 6000 K). We measure the age of the system in units of thesynchronization time, t/tsyn.Our analysis yielded the following results. (i) There is a clearcorrelation between ωr/ωsyn andt/tsyn: the younger a star, the higher the angular velocityof its axial rotation in units of ωsyn, the angularvelocity at pseudo-synchronization. This correlation is more significantand obvious if the synchronization time, tsyn, is computed interms of the Zahn theory. (ii) This observational fact implies that thesynchronization of early-type components in close binary systemscontinues on the main sequence. The synchronization times for the innerlayers of the components (i.e. those that are responsible for apsidalmotion) are about 1.6 and 3.1 dex longer than those predicted by thetheories of Zahn and Tassoul, respectively. The average initial angularvelocities (for the zero-age main sequence) are equal toω0/ωsyn ~ 2.0. The dependence of theparameter E2 on stellar mass probably needs to be refined inthe Zahn theory. (iii) Some components of the eclipsing systems of thesample studied show radially differential axial rotation. This isconsistent with the Zahn theory, which predicts that the synchronizationstarts at the surface, where radiative damping of dynamical tidesoccurs, and develops toward the interior. Therefore, one would expectthe inner parts of young double early-type stars to rotate faster thanthe outer parts.
| B.R.N.O. Contributions #34
Not Available
| A new catalogue of eclipsing binary stars with eccentric orbits
A new catalogue of eclipsing binary stars with eccentric orbits ispresented. The catalogue lists the physical parameters (includingapsidal motion parameters) of 124 eclipsing binaries with eccentricorbits. In addition, the catalogue also contains a list of 150 candidatesystems, about which not much is known at present.Full version of the catalogue is available online (see the SupplementaryMaterial section at the end of this paper) and in electronic form at theCDS via http://cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/MNRAS/(vol)/ (page)E-mail: ibulut@comu.edu.tr
| 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.
| Calibration of the pre-main sequence RS Chamaleontis binary system
Context: The calibration of binary systems with accurately known massesand/or radii provides powerful tools to test stellar structure andevolution theory and to determine the age and helium content of stars.We study the eclipsing double-lined spectroscopic binary system RS Cha,for which we have accurate observations of the parameters of both stars(masses, radii, luminosities, effective temperatures and metallicity).Aims: We have calculated several sets of stellar models for thecomponents of the RS Cha system, with the aim of reproducingsimultaneously the available observational constraints and to estimatethe age and initial helium abundance of the system. Methods:Using the CESAM stellar evolution code, we model both componentsstarting from the initial mass and metallicity and adjusting the inputparameters and physics in order to satisfy the observationalconstraints. Results: We find that the observations cannot bereproduced if we assume that the abundance ratios are solar but they aresatisfied if carbon and nitrogen are depleted in the RS Cha system withrespect to the Sun. This is in accordance with the abundances observedin other young stars. The RS Cha system is in an evolutionary stage atthe end of the PMS phase where models are not strongly sensitive tovarious physical uncertainties. However we show that the oscillations ofthese two stars, which have been detected, would be able to discriminatebetween different options in the physical description of thisevolutionary phase.
| Visual Minima Timings of Eclipsing Binaries Observed in the Years 1992 - 1996
The paper contains a list of 283 new times of minima and 77 revisedtimes of minima for 63 eclipsing binaries derived by the author fromhis visual observations.
| New Times of Minima of Eclipsing Binary Systems
We present 82 photoelectric minima observations of 34 eclipsingbinaries.
| CCD Times of Minima of Selected Eclipsing Binaries
374 CCD minima observations of 187 eclipsing binaries are presented. Theobserved stars were chosen mainly from catalogue BRKA of observingprogramme of Variable Star Section of CAS.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| A catalogue of close binaries located in the δ Scuti region of the Cepheid instability strip
A catalogue of close eclipsing binary systems (detached andsemidetached) with at least one of the components located in the δScuti region of the Cepheid instability strip is presented. Thepositions of the stars in the instability strip are determined by theiraccurate temperatures and luminosities. Observationally detectedbinaries (20 semidetached, four detached and one unclassified) withoscillating components were included in the catalogue as a separatetable. The primaries of the oscillating Algols tend to be located nearthe blue edge of the instability strip. Using reliable luminosities andtemperatures determined by recent photometric and spectroscopic studies,we have found that at least one or two components of 71 detached and 90semidetached systems are located in the δ Scuti region of theCepheid instability strip. In addition, 36 detached or semidetachedsystems discovered by the Hipparcos satellite were also given as aseparate list. One of their components is seen in the δ Scutiregion, according to their spectral type or B - V colours. They arepotential candidate binaries with the δ Scuti-type pulsatingcomponents which need further photometric and spectroscopic studies inbetter precision. This catalogue covers information and literaturereferences for 25 known and 197 candidate binaries with pulsatingcomponents.
| New grids of stellar models including tidal-evolution constants up to carbon burning. III. From 0.8 to 125 Mȯ: the Large Magellanic Cloud (Z = 0.007-0.01)
In this paper, we present new specific stellar models for the LargeMagellanic Cloud. In order to take the observational uncertainties inthe chemical composition into account, we have computed two grids: (X,Z) = (0.730, 0.010) and (0.739, 0.007). The covered mass range was 0.80up to 125 Mȯ. The effects of rotation can beinvestigated by using the gravity-darkening exponents that are availablefor each track. The tidal constant E_2, depth of the convective outerzone, and the radius of gyration are computed and presented in asuitable format for studying the tidal evolution of a given closebinary. The isochrones (and also those corresponding to the previousgrids) will be presented in a future paper.
| New Times of Minima of Eclipsing Binary Systems and of Maximum of SXPHE Type Stars
We present 64 photoelectric minima observations of 31 eclipsingbinaries. We also report three new times of maxima of three SXPHE typepulsating stars.
| 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.
| The evolutionary status of EK Cephei: rotating and standard models
The evolutionary status of the double-lined eclipsing binary EK Cep isreanalysed. Due to problems with the empirical determination of itseffective temperatures, we have used a different approach to compare theobservations with theoretical models: we have adopted the effectivetemperature ratio, which is a better determined parameter from lightcurve analysis, instead of their absolute values. Such an approach issupported observationally by the inconsistency found in the photometricdistances for both components of EK Cep. By using the effectivetemperature ratio, masses, radii, apsidal-motion rate and lithiumdepletion, we have found that standard models are able to fit thephysical properties of EK Cep simultaneously at the same isochrone. Inthe case of rotating models, we have also found acceptable solutionswithout the need for a very fast rotating core.On the other hand, the apsidal-motion rate of EK Cep is criticallyrevised.
| The eclipsing binary PV Cas: a case of strong differential rotation in depth
In this study, we show that only models with differential rotation, asopposed to non-rotation or solid-body rotation for the components of PVCas, are in satisfactory agreement with the observations (includingconstraints on the apsidal advance rate and the synchronous rotation ofthe components in addition to their luminosities and radii). Internalrotation profiles found for solar and metal-rich chemical compositionsare similar to each other in that only a small part of the outermostregions is rotating very slowly (veq~ 65kms -1)and the rest is rotating very rapidly. Confirmation of Ap-likevariations in the light curve of the system leads us to search for aconnection between this type (and similar types) of internal rotationand chemically peculiar stars. The temperature difference between theblue sides of the main sequence for the normal and for the magnetic Apstars may arise from such a connection, since we find a similardifference between the models with this kind of rotation and thenon-rotating models of somewhat lower mass.
| What are the temperatures of T Tauri stars?. Constraints from coeval formation of young eclipsing binaries
We show how the assumption of coeval formation can be used to constrainthe effective temperatures of the components of young eclipsingdouble-lined spectroscopic binaries. Our method extends the approach ofWhite et al. (1999) to a two-step analysis. The first step comparesevolutionary models to the observed masses and radii and selects thosemodels that predict ages that are consistent with coeval formation. Thesecond step then uses these models to constrain the effectivetemperatures. We applied the method to literature values of the stellarparameters of the eclipsing binaries RX J0529.4+0041A and V1174 Ori and confirm thatV1174 Ori A has dwarf-like temperatures at an age of9 Myrs, while we cannot draw any conclusions for RXJ0529.4+0041 A and V1174 Ori B. Consideringthese binaries, we find that none of the evolutionary models givescoeval solutions simultaneously in mass, radius and effectivetemperature.
| 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.
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| Yükselim: | +69°41'34.1" |
| Görünürdeki Parlaklýk: | 7.887 |
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