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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.
| On the distance to the Chamaeleon I and II associations
Constraints on the distances to the dark clouds Chamaeleon I and II areinvestigated in detail. A compilation of photometric data, spectraltypes and absolute magnitudes for field stars towards each cloud ispresented, and results are used to examine the distribution of reddeningwith distance along each line of sight. The distances to starsassociated with reflection nebulae in each cloud are examined in detail.On the basis of these results, we deduce the most probable distance ofCha I to be 160+/-15pc, and that of Cha II to be 178+/-18pc. Anexamination of the mean fluxes of T Tauri stars in each cloud providesindependent evidence to suggest that Cha II is significantly moredistant than Cha I. Both clouds appear to be embedded in a macroscopicsheet-like structure extending over much of the Chamaeleon-Musca-Cruxregion. The Chamaeleon III and DC\ts 300.2--16.9 clouds are probablypart of the same structure, with probable distances ~ 140--160pc.
| Chamaeleon II - Distance determination and HR diagram
Photometric and spectroscopic observations of the classical T Tauristars in the Chamaeleon II dark cloud are presented. The distance to ChaII is 200 +/- 20 pc, based on a plot of extinction versus distance forfield stars seen against the cloud. The ages of the premain-sequencestars in Cha II range between 10 exp 5 and 10 exp 7 yr. The stellarpopulation of the Cha II cloud consists mostly of low mass stars - atleast 17 of the 19 known T Tauri stars in Cha II have masses less than 1solar mass. The only intermediate mass star in the cloud is IRAS12496-7650, a highly embedded Herbig Ae star. The mass function of ChaII resembles that of the Lupus complex, and there are a larger fractionof low mass stars in Cha II than there are in the Taurus-Auriga region.
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