High Angular Resolution Thermal Infrared Imaging and Spectroscopy of Comet Hale-Bopp

T.L. Hayward (Cornell University), M.S. Hanner (JPL/Caltech)

We present 5 to 18  tex2html_wrap_inline11 m images and spectra of comet Hale-Bopp taken with SpectroCam-10 on the 5m Hale telescope. We observed the comet during three runs between June and September 1996, and three additional runs between February and April 1997. Our data track the gradual warming of dust grains in the inner coma between June when the comet was 4.2 AU from the sun and late March when it was near perihelion, and the evolution of the prominent 10  tex2html_wrap_inline11 m silicate emission feature during this interval. The feature steadily increased in strength as Hale-Bopp approached the sun, but spectral structure attributed to a crystalline olivine grain component remained relatively constant. Our observations indicate that there was little change in grain emission properties over a wide temperature range, although an increasing ratio of small particles to large may explain the increased contrast of the silicate feature near perihelion. We will also report the results of high spatial resolution spectral mapping of the inner coma conducted near perihelion.