Modeling the diurnal evolution of a dust feature in comet Hale-Bopp (1995 O1)

A Monte Carlo computer code for simulating dust features in comets is applied to comet Hale-Bopp in order to model the diurnal evolution of a bright jet observed, in late 1997 February, to point in the southwesterly direction from the nucleus. The jet's morphology is closely matched by a model, which is based on the assumption that the ejecta were released nearly continuously from an isolated source on the nucleus surface. The fitted characteristics include the initial direction of the ejecta's motion, the feature's overall dimensions and shape, and its temporal variations during the rotation cycle. In particular, it is found that the relatively faint appendage some 10 "-15 " directly to the south from the nucleus can be identified with the residual ejecta from the previous rotation cycle. No attempt has been made to fit the observed brightness changes, which apparently are affected by variable seeing, especially in daylight. It is suggested that if the system of concentric halos to the south from the nucleus consists of two independent branches, its southwesterly branch can be identified with the ejecta from the same jet that are several rotations old. Modeling of a jet's diurnal evolution presents a powerful tool in our quest for understanding the emission of dust from discrete active regions on cometary nuclei.