Analysis of the rotation period of asteroids (1865) Cerberus, (2100) Ra-Shalom, and (3103) Eger - search for the YORP effect

The spin state of small asteroids can change on a long timescale by the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect, the net torque that arises from anisotropically scattered sunlight and proper thermal radiation from an irregularly-shaped asteroid. The secular change in the rotation period caused by the YORP effect can be detected by analysis of asteroid photometric lightcurves. The authors analyzed photometric lightcurves of near-Earth asteroids Cerberus, Ra-Shalom, and Eger with the aim to detect possible deviations from the constant rotation caused by the YORP effect. They carried out new photometric observations of the three asteroids, combined the new lightcurves with archived data, and used the lightcurve inversion method to model the asteroid shape, pole direction, and rotation rate. They derived physical models for all three asteroids. They had to model Eger as a nonconvex body because the convex model failed to fit the lightcurves observed at high phase angles.