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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
| UBVRIJH photometry of two new luminous δ Scuti stars and the discovery of δ Scuti pulsation in the most evolved Ap star known
Time-series photometry of the Hipparcos variable stars HD 199434 and21190 is reported. Both stars are pulsators of the δ Scuti type.Reclassifications of the MK types of the stars, based on newspectrograms, are given. HD 21190 is found to be F2III SrEuSi:, makingit the most evolved Ap star known. Its Strömgren photometricindices support the peculiar spectral type. It is also one of the mostevolved δ Scuti stars known. Its combined Ap-δ Scuti naturemakes it an important test of models of pulsation in peculiar starsrecently developed by Turcotte et al., although it is more extreme thanany model they examined. Physical parameters of both stars are estimatedfrom Strömgren and Hβ photometry, and Hipparcos absolutemagnitudes. We attempt mode identifications based on amplitude ratiosand phase differences from our photometry. The dominant pulsation of HD21190 may be an overtone radial mode. The model fits for HD 199434 areeven less satisfactory, but favour an l=2 mode. Given the good qualityand wavelength coverage of our data, the poor results from theapplication of the photometric theory of mode identification may callinto question the use of that technique.
| 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
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| Takýmyýldýz: | Tavus |
| Sað Açýklýk: | 20h42m54.07s |
| Yükselim: | -71°55'38.5" |
| Görünürdeki Parlaklýk: | 7.62 |
| Uzaklýk: | 92.937 parsek |
| özdevim Sað Açýklýk: | -42.6 |
| özdevim Yükselim: | 20.1 |
| B-T magnitude: | 8.006 |
| V-T magnitude: | 7.652 |
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