RADAR OBSERVATIONS OF ASTEROIDS 7-IRIS, 9-METIS, 12-VICTORIA, 216-KLEOPATRA, AND 654-ZELINDA

We report 13-cm wavelength radar observations of the main-belt asteroi ds 7 Iris, 9 Metis, 12 Victoria, 216 Kleopatra, and 654 Zelinda obtain ed at Arecibo between 1980 and 1989. The echoes are highly polarized y et broadly distributed in Doppler frequency, indicating that our targe ts are smooth on decimeter scales but very rough on some scale(s) larg er than about 1 m. The echo spectra are generally consistent with exis ting size, shape, and spin information based on radiometric, lightcurv e, and occultation data. All of our targets possess distinctive radar signatures that reveal large-scale topography. Reflectivity spikes wit hin narrow ranges of rotation phase suggest large flat regions on Iris , Metis, and Zelinda, while bimodal spectra imply nonconvex, possibly bifurcated shapes for Kleopatra and Victoria. Kleopatra has the highes t radar albedo yet measured for a main-belt asteroid, indicating a hig h metal concentration and making Kleopatra the best main-belt candidat e for a core remnant of a differentiated and subsequently disrupted pa rent body. Upon completion of the Arecibo telescope upgrade, there wil l be several opportunities per year to resolve main-belt asteroids wit h hundreds of delay-Doppler cells, which can be inverted to provide es timates of both three-dimensional shape and radar scattering propertie s. (C) 1995 Academic Press, Inc.