Radar and photoelectric observations of asteroid 2100 Ra-Shalom |
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| Authors: | Steven J Ostro Alan W Harris Donald B Campbell Irwin I Shapiro James W Young |
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| Institution: | Department of Astronomy, Cornell University, Ithaca, New York 14853, USA;Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA;National Astronomy and Ionosphere Center, Arecibo, Puerto Rico;Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, USA;Table Mountain Observatory, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA |
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| Abstract: | Results of 13-cm-wavelength radar observations and V-filter photoelectric observations of Ra- Shalom during its 1981 Aug–Sep apparition are reported. The radar data yid 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, μc = 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 km2) 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. |
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