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Absolute dimensions of solar-type eclipsing binaries. II. V636 Centauri: A 1.05 {M}ȯ primary with an active, cool, oversize 0.85 {M}ȯ secondary
Context: The influence of stellar activity on the fundamental propertiesof stars around and below 1 Mȯ is not well understood.Accurate mass, radius, and abundance determinations from solar-typebinaries exhibiting various levels of activity are needed for a betterinsight into the structure and evolution of these stars. Aims: Weaim to determine absolute dimensions and abundances for the solar-typedetached eclipsing binary V636 Cen, and to perform a detailed comparisonwith results from recent stellar evolutionary models. Methods:uvby light curves and uvbyβ standard photometry were obtained withthe Strömgren Automatic Telescope, radial velocity observationswith the CORAVEL spectrometer, and high-resolution spectra with theFEROS spectrograph, all at ESO, La Silla. State-of-the-art methods wereapplied for the photometric and spectroscopic analyses. Results:Masses and radii that are precise to 0.5% have been established for thecomponents of V636 Cen. The 0.85 Mȯ secondary componentis moderately active with starspots and Ca ii H and K emission, and the1.05 Mȯ primary shows signs of activity as well, but ata much lower level. We derive a [Fe/H] abundance of -0.20 ± 0.08and similar abundances for Si, Ca, Ti, V, Cr, Co, and Ni. Correspondingsolar-scaled stellar models are unable to reproduce V636 Cen, especiallyits secondary component, which is ~10% larger and ~400 K cooler thanpredicted. Models adopting significantly lower mixing-length parametersl/Hp remove these discrepancies, seen also for othersolar-type binary components. For the observed [Fe/H], Claret models forl/Hp = 1.4 (primary) and 1.0 (secondary) reproduce thecomponents of V636 Cen at a common age of 1.35 Gyr. The orbit iseccentric (e = 0.135 ± 0.001), and apsidal motion with a 40%relativistic contribution has been detected. The period is U = 5 270± 335 yr, and the inferred mean central density concentrationcoefficient, log(k_2) = -1.61 ± 0.05, agrees marginally withmodel predictions. The measured rotational velocities, 13.0 ± 0.2(primary) and 11.2 ± 0.5 (secondary) km s-1, are inremarkable agreement with the theoretically predicted pseudo-synchronousvelocities, but are about 15% lower than the periastron values. Conclusions: V636 Cen and 10 other well-studied inactive and activesolar-type binaries suggest that chromospheric activity, and its effecton envelope convection, is likely to cause radius and temperaturediscrepancies, which can be removed by adjusting the model mixing lengthparameters downwards. Noting this, the sample may also lend support totheoretical 2D radiation hydrodynamics studies, which predict a slightdecrease of the mixing length parameter with increasing temperature/massfor inactive main sequence stars. More binaries are, however, needed fora description/calibration in terms of physical parameters and level ofactivity.Based on observations carried out at the Strömgren AutomaticTelescope (SAT), the Danish 1.54 m telescope, and the 1.5 m telescope(62.L-0284) at ESO, La Silla, Chile. Table A.1 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/502/253
| 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
| 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
| 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.
| New Elements for 80 Eclipsing Binaries VII.
This research presents new elements for 80 eclipsing binaries found withthe help of the ASAS-3, Hipparcos and NSVS databases.
| 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
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| Stroemgren photometry of F- and G-type stars brighter than V = 9.6. I. UVBY photometry
Within the framework of a large photometric observing program, designedto investigate the Galaxy's structure and evolution, Hβ photometryis being made for about 9000 stars. As a by-product, supplementary uvbyphotometry has been made. The results are presented in a cataloguecontaining 6924 uvby observations of 6190 stars, all south ofδ=+38deg. The overall internal rms errors of one observation(transformed to the standard system) of a program star in the interval6.5
| The chemical evolution of the solar neighborhood. I - A bias-free reduction technique and data sample
The possible ways of measuring the age-metallicity relation for thegalactic disk in the neighborhood of the sun are discussed. It is shownthat the use of a field star sample chosen on the basis of effectivetemperature introduces a bias which results in a monotonic increase inthe metal abundance of the disk with time. However, if theage-metallicity relation for the disk can be shown to satisfy certaincriteria, the bias introduced in such a sample can be neglected: thegalactic disk apparently satisfies the criteria. It is concluded that asample analyzed through the use of uvby and H(beta) photometry inconjunction with a self-consistent set of theoretical isochronesprovides the least biased, most accurate estimate of the age-metallicityrelation for the disk.
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Osservazione e dati astrometrici
| Costellazione: | Dorado |
| Ascensione retta: | 04h46m52.26s |
| Declinazione: | -60°36'12.7" |
| Magnitudine apparente: | 7.739 |
| Distanza: | 65.189 parsec |
| Moto proprio RA: | 50 |
| Moto proprio Dec: | 132 |
| B-T magnitude: | 8.419 |
| V-T magnitude: | 7.796 |
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