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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 0.4-Msun eclipsing binary CU Cancri. Absolute dimensions, comparison with evolutionary models and possible evidence for a circumstellar dust disk
Photometric observations in the R and I bands of the detached M-typedouble-lined eclipsing binary CU Cnc have beenacquired and analysed. The photometric elements obtained from theanalysis of the light curves have been combined with an existingspectroscopic solution to yield high-precision (errors la 2%) absolutedimensions: MA=0.4333+/-0.0017 Msun,MB= 0.3980+/-0.0014 Msun,RA=0.4317+/-0.0052 Rsun, andRB=0.3908+/-0.0094 Rsun. The mean effectivetemperature of the system has been estimated to be Teff=3140+/-150 K by comparing multi-band photometry (optical and infrared)with synthetic colors computed from state-of-the-art model atmospheres.Additionally, we have been able to obtain an estimate for the age ( ~320 Myr) and chemical composition ([Fe/H]~ 0.0) of the binary systemthrough its membership of the Castor moving group. With all theseobservational constraints, we have carried out a critical test of recentstellar models for low-mass stars. The comparison reveals that mostevolutionary models underestimate the radius of the stars by as much as10%, thus confirming the trend observed by Torres & Ribas(\cite{TR02}) for YY Gem and V818Tau. In the mass-absolute magnitude diagram, CU Cnc isobserved to be dimmer than other stars of the same mass and this makesthe comparison with stellar models not so compelling. After ruling out anumber of different scenarios, the apparent faintness of CU Cnc can beexplained if its components are some 10% cooler than similar-mass starsor if there is some source of circumstellar dust absorption. The lattercould be a tantalizing indirect evidence for a coplanar (Vega-like)dusty disk around this relatively young M-type binary.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/239}
| 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
| Photometrie der Präsepe-Umgebung mit kurzbrennweitigen Schmidt-Spiegeln. Mit 7 Textabbildungen
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Osservazione e dati astrometrici
| Costellazione: | Cancro |
| Ascensione retta: | 08h31m41.18s |
| Declinazione: | +19°27'38.7" |
| Magnitudine apparente: | 7.793 |
| Moto proprio RA: | -54.6 |
| Moto proprio Dec: | 64 |
| B-T magnitude: | 8.574 |
| V-T magnitude: | 7.858 |
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