SIMBAD references

We report on high angular resolution observations with Fine Guidance Sensor (FGS) No. 3 aboard the Hubble Space Telescope of five low-mass pre-main sequence stars (T Tauri stars), which have also been observed with the Hipparcos satellite. We have observed BP Tau, RU Lup, RY Lup, AK Sco, and DI Cep and have found that none of them have companions of comparable brightness with a projected separation larger than the FGS resolution limit 0".01. Nebular emission from around RY Lup, RU Lup and AK Sco has been detected. Previous observations with FGS of five intermediate-mass pre-main sequence stars (Herbig Ae/Be stars) have resulted in the discovery of the first sub-arc second binary of this class. These previous observations are also discussed here in the context of the physics of the objects.