HUBBLE-SPACE-TELESCOPE ASTROMETRIC OBSERVATIONS OF PRE-MAIN-SEQUENCE STARS FROM THE HIPPARCOS PROGRAM

We report on the first set of high angular resolution observations wit h Fine Guidance Sensor (FGS) # 3 aboard the Hubble Space Telescope of a sample of T-Tauri and Herbig Ae/Be pre-main sequence stars, which ha ve also been observed with the HIPPARCOS satellite. Among the 5 Ae/Be stars observed so far of particular interest is the new double HIC 354 88 the first close visual pair in this class of stars and possibly a c andidate orbital binary. Repeated FGS astrometry combined with the par allaxes provided by HIPPARCOS could yield the first direct determinati on of the mass of an Ae/Be type pre-main sequence system. Finally, the timely availability of these FGS measurements will help the validatio n of the algorithms applied to the HIPPARCOS data to detect and possib ly measure close pairs.