Definitive Period for Asteroid (1389) Onnie

Determining the rotation period of asteroids with periods of close to 12 or 24 hours is challenging due to aliasing caused by the Earth’s rotation. No unambiguous period was available in the literature for Koronis Family member (1389) Onnie, although partial coverage suggested a period near 24 hours. We have used east and west stationary point observations of (1389) Onnie to determine a definitive period of 23.044+/-0.001 h.