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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.
| Mining the Metal-rich Stars for Planets
We examine the correlation between stellar metallicity and the presenceof short-period planets. It appears that approximately 1% of dwarf starsin the solar neighborhood harbor short-period planets characterized bynear-circular orbits and orbital periods P<20 days. However, amongthe most metal-rich stars (defined as having [Fe/H]>0.2 dex), itappears that the fraction increases to 10%. Using the Hipparcos databaseand the Hauck & Mermilliod compilation of Strömgren uvbyphotometry, we identify a sample of 206 metal-rich stars of spectraltype K, G and F which have an enhanced probability of harboringshort-period planets. Many of these stars would be excellent candidatesfor addition to radial velocity surveys. We have searched the Hipparcosepoch photometry for transiting planets within our 206 star catalog. Wefind that the quality of the Hipparcos data is not high enough to permitunambiguous transit detections. It is, however, possible to identifycandidate transit periods. We then discuss various ramifications of thestellar metallicity-planet connection. First, we show that there ispreliminary evidence for increasing metallicity with increasing stellarmass among known planet-bearing stars. This trend can be explained by ascenario in which planet-bearing stars accrete an average of 30M⊕ of rocky material after the gaseous protoplanetarydisk phase has ended. We present dynamical calculations which suggestthat a survey of metallicities of spectroscopic binary stars can be usedto understand the root cause of the stellar metallicity-planetconnection.
| CCD photometry and astrometry of visual double and multiple stars of the HIPPARCOS Catalogue. II. CCD photometry and differential astrometry of 288 southern ``Intermediate'' systems
We present photometric and astrometric data of about 280 visual doublestars of the ``intermediate'' class, i.e. with angular separationsmainly in the range 2arcsec < rho < 12arcsec . The observationshave been obtained in 1991-92 with a CCD camera attached to the 91 cmDutch telescope at ESO La Silla, Chile. Differential magnitudes of thedouble star components as well as magnitudes and colour indices of theindividual components have been determined in the Cousins V and Ipassbands with an internal error of about 0.005 mag and an externalaccuracy of less than 0.03 mag. In addition, angular separations havebeen secured to an internal accuracy of 0.004arcsec and position anglesto about 0.05degr. Tables 1 to 4 are only available in electronic format the CDS via ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html. Based on observationscollected at the European Southern Observatory, La Silla, Chile.
| A photometric study of wide visual double stars. III - Wide visual double stars with F-type primaries
Fifty-one wide visual double stars with F-type primaries have beenobserved in the uvby, H-beta system. MK class, color excess, absolutemagnitude, effective temperature and distance have been derived fromcalibrations of the above systems. From the distances derived here andthe astrometric data, taken from the literature, it appears that atleast 75 percent of them can be 'physical pairs'. Nevertheless, about 33percent of the double stars in this sample seem to have a realseparation of their components larger than 0.01 parsecs. That means thatthese stars are not gravitationally bound, but they have a commonorigin. For this season, the values of their astrophysical parametersare usually very close together.
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