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D.G. Schleicher, T.L. Farnham (Lowell Obs.), B. R. Smith (N. Ariz. U.), E. A. Blount (Beloit College), E. Nielsen (MIT), S.M. Lederer (U. Florida)
\def\deg{\ifmmode\circ\else\circ\fi} During the first five months of 1997, we obtained images of Comet Hale--Bopp (1995 O1) on a total of 39 nights using the Hall 42-inch telescope at Lowell Observatory. In order to investigate the time-variable coma morphology, the new Hale-Bopp narrowband filter set was utilized with a 20482 CCD to isolate gas emission and reflected continuum. By measuring the distance of the several dust arcs at various position angles as a function of time, we have derived an apparent rotation period of 0.4712±.0002 days (11.31 hrs) over the interval from mid-February to early May. We find no evidence of shorter-term changes in the period such as suggested by some investigators for rapid precession or complex rotation. We have also begun Monte Carlo modeling of the dust jets in an attempt to reproduce the dust morphology and to derive the pole orientation and the location of the active regions. Preliminary analysis implies that most of the morphological features can be matched with a relatively high-latitude primary source which is ``on'' throughout the rotation cycle, although it drops to a very low level on the night-side. A secondary source, causing most of the distortions in the visible arc structures, is probably located at a low ``northern'' latitude with a longitude more than 120\deg\ from the primary source. In addition, the pole orientation apparently shifted systematically with time over the interval of these observations, presumably due to a long-term precession. The effects of precession and changing viewing geometry on our derived rotation period are also being investigated. This research was supported by NASA and NSF.