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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.
| A new optical extinction law and distance estimate for the Taurus-Auriga molecular cloud
This paper presents optical spectrophotometry of field stars projectedon the Taurus-Auriga molecular cloud. We derive extinction laws forheavily reddened stars in this sample and show that the reddening lawthrough the dark cloud is nearly identical to the standard law forlambda-lambda(3600-6100) and AV approximately less than 3mag. Our spectroscopic parallaxes suggest a distance of 140 +/- 10 pcfor the northern portion of the cloud and show no compelling evidencefor a substantial variation in distance across the leading edge of thecloud.
| Near-infrared polarized images of a nebula around T Tauri
A 6-arcsec-diameter coronagraphic spot placed in front of an IR arraycamera was used to image a circumstellar nebula that lies symmetricallyaround the premain-sequence star T Tauri. The intensity of scatteredlight, measured as a function of distance from T Tauri, reveals anapproximate r exp -2.5 dependence. The distribution of polarizedintensity is modeled, and it is deduced that the radial density gradientin the T Tauri nebula is approximately proportional to r exp -1.5. The3D shape of the nebula is studied by analyzing the polarized lightdistribution in terms of the optical depth to the star along the line ofsight and the optical depth to the star in the plane of the sky. Thepresence of an infalling envelope that is actively depositing heat inthe outer disk is argued to account for the the shallow radialtemperature gradient predicted from models of flat spectrum sources likeT Tauri.
| Magnetic field structure in the Taurus dark cloud
Optical and infrared polarimetry of sources in the direction of theTaurus cloud are obtained in order to study the magnetic field in thiscloud and its possible role in the cloud's evolution. Most of the starsare background giant stars whose light shines through the cloud and ispolarized by the cloud material. The transverse component of themagnetic field, as delineated by the polarization vectors, is generallyperpendicular to the galactic plane, and the stratified structure of thecloud could be due to the effect of the magnetic field during the earlystages of collapse. Three of the 13 embedded stars are stronglypolarized with position angles nearly perpendicular to those of nearbyfield stars. The polarization of these stars is most likely intrinsic,and the direction of polarization indicates that the materialsurrounding these stars may be magnetic i.e., that the magnetic field isfrozen in this material.
| Mesures d'étoiles doubles faites au réfracteur de 38 cm de l'Observatoire de Nice
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