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Hubble space telescope astrometric observations of pre-main sequence stars for the HIPPARCOS program
We report on the first set of high angular resolution observations withFine Guidance Sensor (FGS) #3 aboard the Hubble Space Telescope of asample of T-Tauri and Herbig Ae/Be pre-main sequence stars, which havealso been observed with the HIPPARCOS satellite. Among the 5 Ae/Be starsobserved so far of particular interest is the new double HIPPARCOS InputCatalog (HIC) 35488 the first close visual pair in this class of starsand possibly a candidate orbital binary. Repeated FGS astrometrycombined with the parallaxes provided by HIPPARCOS could yield the firstdirect determination of the mass of an Ae/Be type pre-main sequencesystem. Finally, the timely availability of these FGS measurements willhelp the validation of the algorithms applied to the HIPPARCOS data todetect and possibly measure close pairs.
| Anomalous dust in the environment of Herbig Ae/Be stars
Photometric data in the UBVRI bands of Herbig Ae/Be stars have beenanalyzed to study the wavelength dependence of extinction to theseobjects. The color excess ratios E(U-B)/E(B-V), E(V-R)/E(B-V),E(V-I)/E(B-V) and E(V-I)/E(V-R) for these stars have been computed andcompared with those for the mean interstellar extinction. The colorexcess ratios for Herbig Ae/Be stars are found to be anomalous. For amajority of the Herbig Ae/Be stars the values of the color excess ratiosimply that the dust causing extinction to these stars is dominated bygrains that are larger in size than the average dust grain in theinterstellar medium.
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