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C. A. Eberhardy (U. Washington), L. M. Woodney, D. G. Schleicher (Lowell Obs.)
Studies of periodic changes in morphological features in a cometary coma can lead to an understanding of several basic physical properties of the cometary nucleus, such as rotation rate, pole orientation, and location and composition of active regions on the surface. Mapping and modeling the position of jets as a function of time can also provide strong constraints on the outflow velocity as a function of distance, and on acceleration mechanisms. The very close approach to Earth by Comet Hyakutake (1996 B2) in March 1996 provided an excellent opportunity to study inner-coma morphology of dust and gas jets as a function of nucleus rotation.
Narrowband images obtained with the Hall 42-inch (1.1-m) telescope at Lowell Observatory on March 23-25 have recently been flux calibrated and continuum subtracted for each gas species -- CN, C2, C3, and CO+. Each species' images were then phased using our previously determined rotation period of 6.23 days (Schleicher et al. 1998) to follow a full rotation cycle. Two jets are readily visible in both the dust and the CN and C3 rotation sequences. At a projected distance of 500 km in the sunward direction, the measured projected outflow velocities of the dust and CN are approximately 0.11 and 0.15 km/s, respectively. The dust continues to accelerate out to a distance of about 3000 km, reaching 0.34 km/s, while the CN jet has a projected velocity of 0.8 km/s at 5000 km. Additional measurements and preliminary Monte Carlo modeling results will be presented. This research was supported by NASA and the NSF REU Program.