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Session 19 - Solar & Planetary Systems.
Display session, Monday, January 13
Infrared imaging and spectrophotometric studies of transient activity in comets near perihelion passage can provide important information about the physical properties of comet nuclei, including the dust mass loss rate, the morphology of the dust coma, and the nature of short-term outbursts. The dependence of comet activity with heliocentric distance may be affected by many variables such as the surface state of the nucleus, the composition of the nucleus, the rotation rate of the nucleus, the location of active areas on the surface of the nucleus, and the response of the nucleus to solar heating. Variable jet activity may cause fluctuations in the size distribution of the dust that produce observable changes in the color, polarization, superheat, and silicate emission (e.g., Woodward et al. 1997; Gehrz and Ney 1992).
We present here preliminary results of our coordinated optical/infrared imaging and infrared spectroscopic monitoring of Comet Hale-Bopp during pre-perihelion passage. Near-infrared spectra obtained in 1996 June are generally featureless and can be fit with a blackbody continuum with a temperature of \approx 5000 K. Imaging observations taken in September of 1996 (heliocentric distance=2.91 AU) indicate an increase in activity of the comet nucleus with the appearance of numerous anti-sunward jets as compared to May 1996 data (heliocentric distance=4.25 AU) . These broadband JHK images (2^\prime \times 2^\prime field of view) show at least 5 jets fanning out from the nucleus. Cuts along these jets reveal that the surface brightness is falling off as r^-1 as predicted by standard models (Gehrz and Ney 1992). We will also present larger field of view (6^\prime \times 4.5^\prime) optical images (UBVRI) taken during the same period that detail the extended morphology of the comet tails.
References Gehrz,R.D. and E.P. Ney, 1992, Icarus 100,162-186. Woodward,C.E., Shure, M.A., Forrest, W.J., Jones, T.J., Gehrz, R.D., amp; Nagata, T. 1996, Icarus, 124, in press.
Acknowledgments Lyke and Saxton are NFS REU students, U. of Wyoming This research was supported in part by NSF grant AST 94-53354.
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