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The N2K Consortium. VII. Atmospheric Parameters of 1907 Metal-rich Stars: Finding Planet-Search Targets
We report high-precision atmospheric parameters for 1907 stars in theN2K low-resolution spectroscopic survey, designed to identify metal-richFGK dwarfs likely to harbor detectable planets. Of these stars, 284 arein the ideal temperature range for planet searches,Teff<=6000 K, and have a 10% or greater probability ofhosting planets based on their metallicities. The stars in thelow-resolution spectroscopic survey should eventually yield >60 newplanets, including 8-9 hot Jupiters. Short-period planets have alreadybeen discovered orbiting the survey targets HIP 14810 and HD 149143.
| Astrometric radial velocities. III. Hipparcos measurements of nearby star clusters and associations
Radial motions of stars in nearby moving clusters are determined fromaccurate proper motions and trigonometric parallaxes, without any use ofspectroscopy. Assuming that cluster members share the same velocityvector (apart from a random dispersion), we apply a maximum-likelihoodmethod on astrometric data from Hipparcos to compute radial and spacevelocities (and their dispersions) in the Ursa Major, Hyades, ComaBerenices, Pleiades, and Praesepe clusters, and for theScorpius-Centaurus, alpha Persei, and ``HIP 98321'' associations. Theradial motion of the Hyades cluster is determined to within 0.4 kms-1 (standard error), and that of its individual stars towithin 0.6 km s-1. For other clusters, Hipparcos data yieldastrometric radial velocities with typical accuracies of a few kms-1. A comparison of these astrometric values withspectroscopic radial velocities in the literature shows a good generalagreement and, in the case of the best-determined Hyades cluster, alsopermits searches for subtle astrophysical differences, such as evidencefor enhanced convective blueshifts of F-dwarf spectra, and decreasedgravitational redshifts in giants. Similar comparisons for the ScorpiusOB2 complex indicate some expansion of its associations, albeit slowerthan expected from their ages. As a by-product from the radial-velocitysolutions, kinematically improved parallaxes for individual stars areobtained, enabling Hertzsprung-Russell diagrams with unprecedentedaccuracy in luminosity. For the Hyades (parallax accuracy 0.3 mas), itsmain sequence resembles a thin line, possibly with wiggles in it.Although this main sequence has underpopulated regions at certaincolours (previously suggested to be ``Böhm-Vitense gaps''), suchare not visible for other clusters, and are probably spurious. Futurespace astrometry missions carry a great potential for absoluteradial-velocity determinations, insensitive to the complexities ofstellar spectra. Based on observations by the ESA Hipparcos satellite.Extended versions of Tables \ref{tab1} and \ref{tab2} are available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.125.8) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/446
| The Coma Berenices star cluster and its moving group
We report on the analysis of astrometric and photometric data fromHipparcos, Tycho and the ACT catalogue in a 1200 sq. degree field aroundthe nearby open star cluster in Coma Berenices and infer thecharacteristic features of this cluster. From a sample of 51 kinematicmembers we derive the cluster's distance, size and spatial structure aswell as its stellar content, mass and age. We find that the clusterconsists of an elliptical core-halo system with major axis parallel tothe direction of galactic motion, and of a moving group of extratidalstars. The latter have tangential distances >= 10 pc from the clustercenter, but have the same distance from the Sun, the same motion and thesame age as the stars in the core and halo. The luminosity function ofthe core-halo system steeply declines beyond absolute magnitude M_V=4.5,but that of the moving group rises towards fainter magnitudes andsuggests the existence of further low-mass members below the currentmagnitude limit. The cloud of extratidal stars witnesses the process ofdissolution of the cluster.
| Further Studies of A-Stars and F-Stars in the Region of the North Galactic Pole - Part Three - a Catalogue of Star Names and Positions
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| UVBY beta photometry of 210 B, A, and F stars in ten areas centered on extragalactic radio sources at high northern galactic latitudes
As part of a study of the reddening properties of the interstellarmedium at the South Galactic pole and particularly along the southernpart of the galactic plane, a catalog of ubvy beta photometry of 210 B,A, and F stars in 10 areas of equal size covering 160 sq deg atlatitudes higher than +30 deg is presented. Each of the observed areasis centered at radio sources that have emission or absorption in the21-cm line; and the main aim of the study is to obtain color excessesfor a comparison of neutral hydrogen column densities, tentativelyassociated with distinct clouds and with the occurrence of dust in theseclouds. V, (b-y), m1, c1, and beta are presented for the 210 stars.
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