The Observational Study On Rotation And Shape Of The Asteroids

According to the evolution theory of the solar system, the planets were formed from collapse of the planetesimal clouds. The asteroids, occupying the transition region between the rocky terrestrial planets and the outer gas giants with special configuration, underwent the collision evolution process. Thus, the physical parameters of the asteroids provide us with a blueprint about the conditions of the early solar system and the boundary conditions for the its evolution. Especially, the study of representative objects, can finish this task efficiently.The photometric observation of the asteroids is an important way to study their physical parameters. The rotation and shape parameters of the asteroids derived from the lightcurves are necessary data for the evolution studies of the solar system and theirselves. In order to select the proper objects to observe and analyze, we made a statistic study on the rotational period, and selected the asteroids with diameter of about 125km as the objects. We had observed more than ten selected asteroids using 1-meter telescope in Yunnan Observatory during 2000 to 2002. The observational data of seven asteroids had been reduced and analyzed. Wehave derived their synodic periods and estimated the shape and orientation of rotational axis for one asteroid.In this thesis, several aspects were involved: (1) Why do we study the asteroids? (2) Based on two classical photometric models of the asteroids, the luminosity variation of the asteroids were introduced. There is significant difference between the luminosity variation due to the rotation surrounding a unique axis and the one due to rotation accompanying with the precession and the eclipse of binary asteroids. (3) We introduced the methods to estimate the shape and rotation of the asteroids with the lightcurves. With the improved NEWTON iteration method, we propose a method to solve the problem on the convergence of the iteration when the initial value is far from the real solution. (4) Before the presentation of results of our observations and analysis, the corrections for the CCD images and the methods to analyze the observational data were introduced. (5) In order to analyze the lightcurves of (469) with multi-periods, the theories about the precession of the asteroids and the eclipse of the binary asteroids were involved. By these basic theories, we give an explanation for the light variation of (469).As long as the number of the samples is increased and the methods of estimation for the rotation and shape of the asteroids are improved continuously, this kind of research will help us to understand the evolution of the asteroids, and even the evolution of the solar system.