Spin directions of asteroids : lightcurve analysis of Koronis family members 158 Koronis and 720 Bohlinia

Abstract

Clusters of asteroids within the main-belt are referred to as dynamical families because they are believed to have originated as the result of collisional destructions of large parent bodies. Family members are the remnants of the parent body break-up and often retain some of the parent body's original rotational information. Previous studies have indicated that the Koronis dynamical family may have been relatively recently formed due to the non-random nature of the orientation of its members spin vectors. This project was undertaken to contribute to the rotational data on Koronis family members in order to better understand the unusual properties observed. The goal of this project was to determine the directions of spin of Koronis family members 158 Koronis and 720 Bohlinia. Observations were made at the MIT Wallace Astrophysical Observatory in Westford, Massachusetts during 1999. Both of the targets were determined to have a retrograde sense of rotation, which is in agreement with the previously known sense of rotation of Koronis family member 243 Ida. In addition, the synodic period of 158 Koronis was confirmed by these observations, and a new value for the sidereal period of 720 Bohlinia was found to be 8.920 ± 0.005 hours. During the course of the observations, an uncataloged asteroid was discovered and has since been assigned the designation 1999 QQ2 by the IAU Minor Planet Center.