The study of the rotational properties of the Cybele asteroids is one of the major tools to investigate their physical nature and to provide a reference against which the collisional evolution of the main belt can be compared. Until recently, outer belt asteroids have been poorly studied because of their large heliocentric distance and the corresponding faintness. Up to now the Cybele asteroid population gathers about 100 objects, among which about 25% have a known rotational period. We present photometric lightcurve and rotational periods of 5 Cybele asteroids never observed before, and, in order to investigate possible differences between the rotational properties (spin rate and lightcurve amplitudes) of the Cybele objects and the main belt asteroids in a comparable size range (i.e., diameter D in the range 50 km < D < 250 km), a statistical analysis has been performed. A Kolmogorov--Smirnov test was applied to compare the lightcurve amplitudes of Cybele asteroids with those of main belt asteroids. Even though the obtained consistence level value is not so high to allow conclusive results, it seems that the two samples of asteroids have similar shape distributions. Moreover, on the basis of our statistical analysis, Cybele objects seem to have ``primordial'' rotational properties: their spin rate distribution is quite similar to that of the ``original'' asteroid population, found by Fulchignoni et al. (1995, A&A, 299, 929). Furthermore, we found a shortage of slow rotators among the Cybele asteroids, suggesting that this population experienced a collisional evolution less intense then the main belt one: this scenario is in agreement with the smaller flux density of ``projectiles'' in the Cybele group region.
AAS/Division for Planetary Sciences Meeting Abstracts #28
- Pub Date:
- September 1996