Imaging observations of asteroids with Hubble Space Telescope

We present the results of two Hubble Space Telescope (HST) observing progra ms, consisting of 11 imaging observations of 10 asteroids. The primary focu s of the projects was to search for faint companions (satellites) of these asteroids, No binary systems were detected. More specifically, no companion s were found at more than 0.1 arcsec separation of brightness down to 4 mag nitudes fainter than the primary asteroid, No companions down to 6 magnitud es fainter than the primary asteroid were found at more than 0.5 arcsec sep aration. It is unlikely that companions more than 6 magnitudes fainter than a well-exposed primary would be detected. These nondetections place very s tringent limits on the existence of companion bodies for these asteroids, A secondary goal was to resolve the illuminated portion of the asteroids, Ni ne of the 10 asteroids were marginally resolved, with three of these-9 Meti s, 18 Melpomene, and 19 Fortuna-showing significant extension and brightnes s variations up to a factor of two across the illuminated portion of the re stored image. The diameters of the resolved asteroids are generally in good agreement with those in the TRIAD II file (E. F. Tedesco, 1989, In Asteroi ds II (Binzel, Gehrels, and Matthews, Eds,)), Diameters for 19 Fortuna and 624 Hektor (which are not in the TRIAD file) have been measured: 225 and 37 0 x 195 km, respectively. (C) 1999 Academic Press.