PHOTOMETRIC GEODESY OF MAIN-BELT ASTEROIDS .4. AN UPDATED ANALYSIS OF LIGHTCURVES FOR POLES, PERIODS, AND SHAPES

This is an updated analysis of main-belt asteroids extending that of Drummond et al. (1988, Icarus 76, 19-77) dor derivation of poles, periods, phase functions, and triaxial ellipsoid shapes from analysis of lightcurve maxima and minima with three independent methods. The primary dataset is from the "Photometric Geodesy" program, augmented by data in the literature. Results are presented for the first time for 250 Bettina, and significantly revised results for 10 others (15, 43, 55, 65, 88, 107, 125, 201, 354, and 694). The ensemble of 26 asteroids is also reconsidered in terms of the distributions of obliquities and triaxial shapes. Three remains a weak tendency for poles to avoid asteroid orbital planes. Two kinds of solar phase angle-amplitude relations persist and may reflect a rough/smooth surface dichotomy for our asteroids. Most asteroids studied (a sample selected to emphasize large amplitudes and rapid spins) show shapes significantly deviating from hydrostatic equilibrium figures. Seven objects (39, 45, 55, 65, 107, 130, and 216) could be Jacobi ellipsoids (or 65 a Maclaurin spheroid) if a systematic effect in our analysis slightly exaggerates axial ratios. Perhaps the hypothesized tendency for rubble pile asteroids to form quasi-equilibriu, figures is distorted by the largest cratering events (such as Stickney on Phobos) due to the mass-dominant size distribution of the asteroids. © 1991.