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R.J. Whiteley (University of Arizona/LPL), D.J. Tholen (University of Hawaii/IfA), C.W. Hergenrother (University of Arizona/LPL)
The discovery of 1998 KY26, and the identification of its 10.7 minute spin period (Ostro et al. 1999), and the earlier observations of 1995 HM and its 97.2 minute period (Steel et al. 1997), showed that very fast rotation rates were possible for small asteroids. Asteroids 1998 WB2, 1999 SF10, and 1999 TY2 have recently been demonstrated to be very rapidly rotating (Pravec et al. 2000) as well. The common characteristic of these five fast-rotating objects is their small size; all of them are less than about 200 meters in diameter. Theoretical work (Harris 1996, and Pravec and Harris 2000) suggests that a limiting rotation period of about 2.2 hours separates objects of this size and smaller from larger bodies. The physical interpretation for this strong segregation of spin rates is that objects smaller than a few hundred meters in diameter are all monolithic bodies that retain the tensile strength to rotate at such extreme rates. Objects much larger than a few hundred meters in size simply do not rotate with periods shorter than 2.2 hours, as has been shown by Pravec et al. (2000). In this work we present the lightcurve analysis of four more fast rotators, 2000 AG6, 2000 DO8, and 2000 EB14, and 2000 HB24. Their periods of 4.56, 10.44, 107.4, and 13.05 minutes, respectively, and their small sizes (all are less than about 200 meters in diameter), make them similar to the already known monolithic asteroids. We discuss the possibility of correlations between the sizes and spin rates of all the known monolithic asteroids. We will derive the approximate values for the sizes, axial ratios, and specific rotational energies of the known fast rotators. Finally, we will suggest, on the basis of our kinematic analysis, an origin for the small monolithic asteroids and ask whether or not asteroids smaller than 200 meters can rotate more slowly than the critical rotation limit.