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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.
| Radial velocities. Measurements of 2800 B2-F5 stars for HIPPARCOS
Radial velocities have been determined for a sample of 2930 B2-F5 stars,95% observed by the Hipparcos satellite in the north hemisphere and 80%without reliable radial velocity up to now. Observations were obtainedat the Observatoire de Haute Provence with a dispersion of 80Ä,mm(-1) with the aim of studying stellar and galactic dynamics.Radial velocities have been measured by correlation with templates ofthe same spectral class. The mean obtained precision is 3.0 km s(-1)with three observations. A new MK spectral classification is estimatedfor all stars. Based on observations made at the Haute ProvenceObservatory, France and on data from The Hipparcos Catalogue, ESA.Tables 4, 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.htm
| The diffusion of gallium in main-sequence peculiar stars
New observations of the gallium abundance in main-sequence peculiarstars are now available in the literature. The present paper analysesthese new data in the framework of the diffusion processes. Theradiative accelerations of gallium are computed, with up-to-date galliumline data, in various physical conditions of stable main-sequence staratmospheres. Zero mass loss is assumed. The role of the 1400 Aabsorption feature, attributed to Si II autoionization, is investigatedand appears of minor importance. The main observed trends (theanti-correlation between the gallium and silicon overabundances in Apstars and the smaller gallium enhancement for lower effectivetemperature) may be explained by the calculations on the galliumdiffusion presented here. It is proposed here that the presence of amagnetic field modifies strongly the gallium accumulation.
| Mesures d'étoiles doubles faites au rĝfraceur de 38 cm de l'Observatoire de Nice
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