Spin vectors of 22 large asteroids

Rotation axes and senses of rotation have been determined for 22 asteroids with the method of P. Magnusson (1986, Icarus 68, 1-39) using lightcurve data mainly from S.J. Weidenschilling, C.R. Chapman, D.R. Davis, R. Greenberg, D.H. Levy, and S. Vail (1987, Icarus 70, 191-245). New correction formulas for the model axis ratios, taking nongeometric scattering into account, are presented. The derived spin-vector distribution for a sample of 30 large asteroids is quite isotropic with a small preference for prograde rotation. This unisotropy is significant at a 66 to 90 % confidence level, depending on the method of computation. The triaxial models do not support the idea that centrifugal forces have affected the shapes and led to near-equilibrium shapes.