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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
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| On the starspot temperature of HD 12545
We have applied two different versions of the photometric spot-modelingtechnique to the spotted RS CVn-type binary HD 12545. NewUBV(RI)c photometry from early 1991 showed the star with anexceptionally large amplitude of 0.50 mag in V and 0.12 mag in V - I anda rotation period of 24.30 +/- 0.02 d which suggests a spot coverage ofapproximately 20 percent of the entire stellar surface. Such large lightand color amplitudes allowed us to separate effects ofwavelength-dependent limb darkening from spot temperature with highconfidence. This in turn makes it possible to obtain the, so far, mostprecise relative starspot temperature of 1100 +/- 35 K for a spotted,late-type star other than the sun. The U - B and B - V values and theminimum radius for HD 12545 suggest a K0III classification rather thanthe G5IV reported earlier. From a single, high-resolution spectrum of HD12545 we found a strong LiI 6707 A line with an equivalent width of 100+/- 15 mA (log n(Li) is approximately equal to 1.75), suggestive of arelatively young giant. In contrast, with our new spectral typeclassification, minimum stellar radius, and the observed mass function,we determine a space-velocity vector of 105 km/s, suggestive of an olddisk star.
| UBV photometry of stars whose positions are accurately known. IV
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987A&AS...68..211O&db_key=AST
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Osservazione e dati astrometrici
| Costellazione: | Triangolo |
| Ascensione retta: | 02h07m52.77s |
| Declinazione: | +35°33'13.7" |
| Magnitudine apparente: | 7.535 |
| Distanza: | 76.511 parsec |
| Moto proprio RA: | -43.1 |
| Moto proprio Dec: | -24.6 |
| B-T magnitude: | 7.905 |
| V-T magnitude: | 7.566 |
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