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The Geneva-Copenhagen survey of the Solar neighbourhood II. New uvby calibrations and rediscussion of stellar ages, the G dwarf problem, age-metallicity diagram, and heating mechanisms of the disk
Context: Ages, metallicities, space velocities, and Galactic orbits ofstars in the Solar neighbourhood are fundamental observationalconstraints on models of galactic disk evolution. Understanding andminimising systematic errors and sample selection biases in the data iscrucial for their interpretation. Aims: We aim to consolidate thecalibrations of uvbyβ photometry into T_eff, [Fe/H], distance, andage for F and G stars and rediscuss the results of the Geneva-CopenhagenSurvey (Nordström et al. 2004; GCS) in terms of the evolution ofthe disk. Methods: We use recent V-K photometry, angular diameters,high-resolution spectroscopy, Hipparcos parallaxes, and extensivenumerical simulations to re-examine and verify the temperature,metallicity, distance, and reddening calibrations for the uvbyβsystem. We also highlight the selection effects inherent in theapparent-magnitude limited GCS sample. Results: We substantiallyimprove the T_eff and [Fe/H] calibrations for early F stars, wherespectroscopic temperatures have large systematic errors. A slight offsetof the GCS photometry and the non-standard helium abundance of theHyades invalidate its use for checking metallicity or age scales;however, the distances, reddenings, metallicities, and age scale for GCSfield stars require minor corrections only. Our recomputed ages are inexcellent agreement with the independent determinations by Takeda et al.(2007), indicating that isochrone ages can now be reliably determined. Conclusions: The revised G-dwarf metallicity distribution remainsincompatible with closed-box models, and the age-metallicity relationfor the thin disk remains almost flat, with large and real scatter atall ages (σ_intrinsic = 0.20 dex). Dynamical heating of the thindisk continues throughout its life; specific in-plane dynamical effectsdominate the evolution of the U and V velocities, while the W velocitiesremain random at all ages. When assigning thick and thin-disk membershipfor stars from kinematic criteria, parameters for the oldest starsshould be used to characterise the thin disk.Based in part on observations made with the Danish 0.5-m and 1.5-mtelescopes at ESO, La Silla, Chile. The full Table 1 is only availableelectronically from 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/475/519
| 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
| A large, complete, volume-limited sample of G-type dwarfs. I. Completion of Stroemgren UVBY photometry
Four-colour photometry of potential dwarf stars of types G0 to K2,selected from the Michigan Spectral Catalogues (Vol. 1-3), has beencarried out. The results are presented in a catalogue containing 4247uvby observations of 3900 stars, all south of δ = -26deg. Theoverall internal rms errors of one observation (transformed to thestandard system) of a program star in the interval 8.5 < V < 10.5are 0.0044, 0.0021, 0.0039, and 0.0059, respectively, in V, b-y, m_1_ ,and c_1_. The purpose of the catalogue, combined with earliercatalogues, is to allow selection of a large, complete, volume-limitedsample of G- and K-type dwarfs, investigate their metallicitydistribution, and compare it to predictions of various models ofgalactic chemical evolution. Future papers in this series will discussthese subjects.
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| Takýmyýldýz: | Cennet Kusu |
| Sað Açýklýk: | 14h50m32.72s |
| Yükselim: | -70°32'18.1" |
| Görünürdeki Parlaklýk: | 9.677 |
| Uzaklýk: | 119.904 parsek |
| özdevim Sað Açýklýk: | -80.4 |
| özdevim Yükselim: | -7.8 |
| B-T magnitude: | 10.357 |
| V-T magnitude: | 9.734 |
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