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S. M. Slivan, R. P. Binzel (MIT), M. Kaasalainen (U. Helsinki)
Rotation lightcurves of Koronis family asteroids obtained through 2001 November have been analyzed to deduce senses of rotation and spin-vector orientations for nine of the largest members of the family. Reductions using amplitude-magnitude-epoch methods based on those of Drummond {\em et al.} (1988) and reductions using the convex polyhedron inversion method of Kaasalainen and Torppa (2001) and Kaasalainen {\em at al.} (2001) were carried out independently; the quite good agreement between the two reductions increases our confidence in the results. Spin-vector determinations are now available for a total of ten members of the Koronis family, including (243) Ida, whose ground-based pole solution was confirmed by observations from the {\em Galileo} spacecraft.
The distribution of the north pole obliquities of family members is markedly bimodal, clustered near about 160\circ and 50\circ, and the anisotropy is statistically significant at greater than the 99% confidence level. Correlation between the sample objects' spin rates and obliquities forms a cluster of low-obliquity retrograde rotators with periods near 14 hours, and a second cluster of intermediate-obliquity prograde rotators with periods near 8.5 hours. Reconciling models of family formation and evolution with the unexpected alignments of spin obliquities and correlations with spin rates presents a new challenge in understanding asteroid collisional processes.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.