Limits on the radius and a possible atmosphere of Charon from its 1980 stellar occultation

Walker's (1980) stellar occultation data for Charon are presently fit by a model which encompasses the possibility of differential refraction by an atmosphere, followed by a sudden occultation behind Charon's limb. The 601.5-km Charon radius lower limit thus obtained may serve as a constraint in models of the mutual event data; while the model fits considered support a Charonian atmosphere of indeterminate composition, time resolution is insufficient for certainty and the data may be interpretable as indications of either a slight extinction near Charon or an entirely unidentified and unassociated effect.