RADAR APERTURE SYNTHESIS OBSERVATIONS OF ASTEROIDS

We report results of Goldstone-VLA, radar aperture-synthesis observati ons of the mainbelt asteroids 324 Bamberga and 7 Iris and the near-Ear th asteroids 1991 EE and 4179 Toutatis. Simultaneous resolution of ech oes in both angle and Doppler frequency provide new constraints on the mainbelt asteroids' pole directions: Bamberga's spin vector is within 40 degrees of the south ecliptic pole, and the twofold ambiguity in I ris' pole direction (P. Magnusson, 1989, in Asteroids II, pp. 1180-119 0) is resolved in favor of the ecliptic coordinates lambda = 15 degree s, beta = +25 degrees. For Bamberga, monostatic and bistatic radar ech oes and VLA thermal-emission measurements, also reported here, are con sistent with radiometric estimates of Bamberga's size and with the hyp othesis that the asteroid is overlain by a regolith having a porosity of similar to 50%. Our near-Earth asteroid measurements required the d evelopment of new on-line VLA software that allows imaging of objects that are in the telescope's ''near field.'' This software has been suc cessfully tested on Toutatis at a distance of 0.06 AU and will be esse ntial for VLA observations of Earth-approaching comets. (C) 1994 Acade mic Press, Inc.