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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
| 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 short-period Cepheid EU Tau. I - New photometric and radial-velocity data
New Johnson UBVRI and Cousins (RI)c photometry of EU Tau from threeobservatories are used to answer the outstanding questions surroundingthe pulsation period of this short-period Cepheid. These data providealmost complete phase coverage of the pulsation cycle. It is confirmedthat EU Tau is pulsating with a single period near 2.1 days in agreementwith that found previously by Fernie. Confusion in the literature aboutthe photometric indices of the comparison star BD 18959 deg near EU Tauis shown to arise largely from misidentifications of BD 18957 deg and BD18959 deg. New radial velocities for EU Tau are reported and compared toearlier observations with CORAVEL. Contemporaneous radial velocities andphotometric data are ideally suited to a surface-brightness analysis ofthis interesting Cepheid.
| A check on EU Tauri
New uvby beta RI photometry has been obtained to check the suggestion ofGieren and Matthews (1987) that the two-day classical Cepheid EU Tau hadchanged its period slightly and also showed a secondary period half theprimary period. The present photometry does not support this suggestion.The earlier period is confirmed and improved, and there is no evidenceof a secondary period. An improved color excess is derived, and this,when compared to values from a period-color relation, supports the viewthat EU Tau is an overtone pulsator.
| Frequency analysis of the short-period Cepheid EU Tauri
New photometric and radial-velocity observations of the short-periodCepheid EU Tauri show systematic deviations from a smooth curve whenplotted in phase according to the accepted period of 2.1025 days. Thesedeviations suggest that the star may be multiperiodic, or now may have asingle period which differs from the older value. Frequency analysis ofthe existing data was undertaken to investigate these possibilities. Itis found that a better fit to the new data is obtained by using arevised primary period, P1 = 2.0895 days. Furthermore, the light andvelocity variations can be reproduced to within the observationalscatter by the sum of only two sinusoids, with periods P1 and P2 = P1/2.This apparent simple harmonic composition of the EU Tau curves is rare,if not unique, among the known short-period Cepheids. It is suggestedthat this could indicate the presence of a 2:1 resonance between thesecond and a higher overtone of pulsation in the star.
| UBV Photoelectric Photometry Catalogue (1986). III Errors and Problems on DM and HD Stars
Not Available
| Comparison Star Adjustments for the Cepheid EU Tau
Not Available
| UBV beta photometry of EU Tauri
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972PASP...84...56G&db_key=AST
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Besorolás csoportokba:
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Pozíciós és asztrometriai adatok
| Csillagkép: | Bika |
| Rektaszcenzió: | 05h46m08.44s |
| Deklináció: | +18°51'38.1" |
| Vizuális fényesség: | 7.657 |
| Távolság: | 196.85 parszek |
| RA sajátmozgás: | 12.1 |
| Dec sajátmozgás: | -12.3 |
| B-T magnitude: | 8.197 |
| V-T magnitude: | 7.702 |
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INHABITED SKY
