Photometric lightcurve and rotation period of Himalia (Jupiter VI)

Due to their great distance from their primaries and rapid solar perturbations of their orbits, the outer irregular satellites of the giant planets are not in tidal rotational lock. They are generally thought to be asteroid-like bodies with irregular shapes and rotation periods much shorter than the orbital ones, whose rotational properties can be found by the methods used to study asteroids. We report here the results of two sets of independent photometric CCD observations overlapping in time that were obtained using 0.35- and 1.23-m telescopes. The combined data set yields for Himalia a unique synodic rotation period of 7.7819 ± 0.0005 h, with a lightcurve amplitude of 0.20 ± 0.01 magnitudes. This determination corrects the erroneous period of ∼9.5 h published by Degewij et al. (Degewij, J., Andersson, L.E., Zellner, B. [1980a]. Icarus 44, 520–540).