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Subsystems in Nearby Solar-type Wide Binaries
We conducted a deep survey of resolved subsystems among wide binarieswith solar-type components within 67 pc of the Sun. Images of 61 starsin the K and H bands were obtained with the Near-Infrared CoronagraphicImager adaptive-optics instrument on the 8 m Gemini-South telescope. Ourmaximum detectable magnitude difference is about 5 mag and 7.8 mag at0farcs15 and 0farcs9 separations, respectively. This enables a completecensus of subsystems with stellar companions in the projected separationrange from 5 to 100 AU. Out of seven such companions found in oursample, only one was previously known. We determine that the fraction ofsubsystems with projected separations above 5 AU is 0.12 ± 0.04and that the distribution of their mass ratio is flat, with a power-lawindex of 0.2 ± 0.5. Comparing this with the properties of closerspectroscopic subsystems (separations below 1 AU), it appears that themass-ratio distribution does not depend on the separation. The frequencyof subsystems in the separation ranges below 1 AU and between 5 and 100AU is similar, about 0.15. Unbiased statistics of multiplicity higherthan 2, advanced by this work, provide constraints on star formationtheory.Based on observations obtained at the Gemini Observatory (Program IDGS-2009B-Q-49), which is operated by the Association of Universities forResearch in Astronomy, Inc., under a cooperative agreement with theNational Science Foundation on behalf of the Gemini partnership: theNational Science Foundation (United States), the Science and TechnologyFacilities Council (United Kingdom), the National Research Council(Canada), CONICYT (Chile), the Australian Research Council (Australia),Ministério da Ciência e Tecnologia (Brazil), and Ministeriode Ciencia, Tecnología e Innovación Productiva(Argentina).
| Spectroscopic characterization of a sample of southern visual binaries
Aims.We present the spectroscopic characterization of 56 pairs of visualbinaries with similar components, based on high resolution spectraacquired with FEROS at ESO La Silla. Methods: .For all stars, wemeasured radial and rotational velocities and CaII H&K emission. Results: .Five previously unknown double lined spectroscopic binarieswere found. Six other pairs show velocity differences that are notcompatible with the orbital motion of the wide pair, indicating thepresence of further companion(s) in the system. The fraction of visualbinaries that contain additional spectroscopic components is27±10%, compatible with other literature estimates. The ages ofthe components of the pairs derived from chromospheric activitytypically show apparent differences of about 0.2 dex. A few pairs show arather large difference in activity level, but in most cases this isconsistent with the variability of chromospheric emission observed forthe Sun along its magnetic cycle.
| 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
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