First stellar occultation by Cybele was observed on October 17, 1979 in the Soviet Union. A diameter of 230 km was derived, closely matching the diameter of 237 km determined by the IRAS satellite.
During the same occultation, a hint of a possible 11 km wide satellite was detected. [1] (http://cfa-www.harvard.edu/iauc/03400/03439.html)