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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
| Broad-band Multicolor Photometry and Polarimetry of Spotted Stars
We have confirmed the BY Dra-type variability of the active spottedstars MS Ser, LQ Hya, VY Ari, and EK Dra using simultaneous UBVRIphotometric and polarimetric observations. We have also reliablydetected the intrinsic linear polarization of their radiation and itsrotational modulation in U due to the inhomogeneous distribution ofactive magnetized regions over the surfaces of the stars. Modeling ofthe linear polarization based on the Zeeman effect indicates that allthe stars display strong local magnetic fields (about 2 kG, similar tothose in sunspots), with filling factors of up to 40% of the totalstellar surface. The magnetized regions coincide with cool photosphericspots detected in photoelectric observations.
| Spots and Active Regions on the Emission-Line Star VY Ari
Quasi-simultaneous photoelectric and spectroscopic observations havebeen made of the active spotted star VY Ari, showing an increase in theequivalent width of pure emission in the H line with a decrease in thestar's brightness. Such an increase indicates a relationship betweenactive regions in the chromosphere and the cool photospheric spots. Thephotometric variability of VY Ari can be described entirely in terms ofa zonal model. The spotted regions occupy up to 41% of the star's totalsurface, with the temperature difference between the quiet photosphereand a spot of 1300 K. The spots lie at middle and low latitudes.
| Speckle Interferometry at the US Naval Observatory. VI.
The results of 1068 speckle interferometric observations of doublestars, made with the 26 inch (0.66 m) refractor of the US NavalObservatory, are presented. These observations are averaged into 841means of 815 binary stars. The systems range in separation from 0.22" to6.01" with a mean separation of 2.21" and have a limiting secondarymagnitude of V=12.5. This is the sixth in a series of papers presentingmeasures obtained with this system, and it covers the period 1999January 1 through 2000 January 9.
| Two-colour photometry for 9473 components of close Hipparcos double and multiple stars
Using observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.
| Spottedness of the emission-line dwarfs V775 Her, VY Ari, OU Gem, and V1005 Ori in 1974-1993
Not Available
| The active chromosphere binary HD 17433 (VY Arietis)
The sixth-magnitude K star HD 17433 (VY Ari) is shown to be anactive-chromosphere binary with an orbital period of 13.198 days. Aphotometric (rotational) period of 17.4 days is indicated by theexisting photometry, implying that HD 17433 is not in synchronousrotation. In the optical, H-alpha is seen in emission, with variableprofile and intensity; He I lambda-5876 is present in absorption. IUEobservations show chromospheric and transition-region emission lineswith surface fluxes up to 200 times greater than those observed in thequiet sun. The luminosity and radius are appropriate for a subgiant, andthe kinematics suggest Pleiades group membership. The presence of alithium absorption feature indicates it may either be a young object,possibly a pre-main sequence star or an evolved spotted RS CVn system.Interpretations from the optical measurement of the magnetic fieldstrength of HD 17433 are given.
| The Variability of HD 17433
Not Available
| Mesures d'étoiles doubles faites au réfracteur de 38 cm de l'Observatoire de Nice
Not Available
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