8-MU-M- TO 13-MU-M SPECTROSCOPY OF COMET LEVY-1990-XX

Comet Levy 1990 XX was observed from Aug. 12 to Aug. 15, 1990, UT before perihelion with the 3-m Infrared Telescope Facility (IRTF) and the Aerospace Broadband Array Spectrograph System (BASS) using a 3.7-arcsec-diameter aperture. The spectra showed strong, structured silicate emission with peaks near 9.8 and 11.2 μm that are similar to those displayed by Comets P/Halley and Bradfield 1987 XXIX (1987s). The continuum was well fit by a graybody whose temperature is 262-277 K, significantly above the radiative equilibrium blackbody temperature of 223 K for the comet's heliocentric distance of 1.54 AU. This temperature excess requires the silicate grains to be small, less than or about 1 μm radius. © 1992.