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D.E. Harker, C.E. Woodward (University of Wyoming, WIRO), D.H. Wooden, F.C. Witteborn (NASA Ames Research Center, Space Sciences Division), H.M. Butner (University of Arizona, SMTO)
Comets represent the frozen reservoirs of primitive proto-solar dust and ice. By studying comets, we gain not only insight into the formation of our solar system, but possibly the proto-solar environment from which the solar system originated. Remote sensing observations of comets near perihelion, when insolation increases cometary activity, allows us to examine the mineralogy of the dust grains released into the interplanetary medium. We can deduce the mineralogy of the comet dust by comparing the observed mid-infrared spectra to those derived from interplanetary dust particles (IDP's) which are collected in the atmosphere or laboratory minerals. Observations in the 10~\mum region are especially useful since most of the major silicate mineral species have sharp resonances in this region permitting an in depth analysis of the mineralogy.
We present 7.6 - 13.2~\mum infrared (IR) spectrophotometry of the inner coma of C/1996 Q1 (Tabur), obtained 1996 October 8 - 10~UT at the Wyoming Infrared Observatory with the NASA/Ames HIFOGS. At this epoch the comet was at a heliocentric distance of r=0.96~AU. The local 10~\mum continuum was fit with a 300~K blackbody, revealing a weak silicate feature. Our analysis suggests that comet Tabur most likely contains large grains of radius a\approx3\micron. Synthetic spectra derived from laboratory measurements of amorphous pyroxene and crystalline olivine can reproduce the observed 10~\mum. Comparisons of Tabur to other comets such as P/Halley 1986 III, C/1995 O1 (Hale-Bopp) and Austin 1990 V will also be discussed.