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Session 62 - Comet Hyakutake Encounter.
Display session, Wednesday, June 12
The long-period Comet Hyakutake (C/1996 B2) passed 0.10 AU from Earth on 1996 March 25.3 UT, the closest approach of a comet since 1983. The doubly-fortuitous proximity (\sim 75 km/arcsec at perigee) and high intrinsic brightness provided a unique opportunity to set up a detailed observational program to study the comet's nucleus. We observed the object in the optical at the KPNO 0.9-m telescope, in the near- and thermal-infrared at NASA/IRTF, and in the microwave at VLA. Our objectives were to photometrically resolve the nucleus, obtain a cross section and albedo measurement, extract the rotation period, and obtain an estimate of the surface temperature. \par
The nucleus and near-nuclear region of the comet is a poorly studied region, owing to the typically-large geocentric distances (\sim 1 AU) which cause the flux from the coma to overwhelm any information we would get from the nucleus. In addition, gas and dust emission and small effective radii contribute to the difficulties. Thus, nuclear properties are well-known for only a handful of specimens. \par
The IRTF (19 - 22 and 24 - 25 Mar) and KPNO (19 - 23 Mar) observations were performed almost all simultaneously. The temporal coincidence of these data was a key aspect in determining properties of the nucleus; data from the two sets of wavelengths allowed us to differentiate between scattered sunlight and intrinsic emission. Observations at IRTF employed two cameras, NSFCAM (1-5 \mum) and MIRAC2 (10 \mum). Our VLA observations were performed on 27 March, observing the comet at 3.6 cm in an attempt to detect the comet's thermal microwave continuum emission. We present here results from the preliminary reduction of data from all three wavelength regimes. \par
Program listing for Wednesday