Radar and photoelectric observations of asteroid 2100 Ra-Shalom.

Ostro, S. J., A. W. Harris, D. B. Campbell, I. I. Shapiro, and J. W. Young (1984). Icarus 60, 391-403.

Results of 13-cm-wavelength radar observations and V-filter photoelectric observations of Ra-Shalom during its 1981 Aug-Sept apparition are reported. The radar data yield detections of echoes in the same sense of circular polarization as transmitted (i.e., the SC sense) as well as in the opposite (OC) sense. The estimate of the ratio of SC to OC echo power, 0.14 +/- 0.02, indicates that most, but certainly not all, of the backscattering is due to single reflections from surface elements that are fairly smooth at decimeter scales. The value obtained for the OC radar cross section on Aug 26 (1.2 0.3 km^2) is about three times larger than those obtained on Aug 23, 24, and 25. The echo bandwidth appears to be within about 1.5 Hz of 5.0 Hz on each date. The photoelectric data suggest a value, Psyn = 19.79 hr, for the synodic rotation period, and yield a composite lightcurve with two pairs of extrema. Combining this value for Psyn with a firm lower bound (4 Hz) on the maximum echo bandwidth yields a lower bound of 1.4 km on the maximum distance between Ra-Shalom's spin axis and any point on its surface.

Asteroid Radar Astronomy Publications