INFRARED-SPECTROSCOPY AND PHOTOMETRY OF COMET AUSTIN 1990-V

We report IR photometry, 3-μm and 10-μm spectroscopy of Comet Austin 1990 V at the NASA IRTF in March-May 1990. The 8- to 13-μm CVF spectrum at r = 0.78 AU postperihelion exhibits a broad emission feature 15%-20% above a blackbody continuum, with a peak at 11.06 ± 0.1 μm. This feature differs from the 11.25-μm peak seen in Comets P/Halley, Bradfield 1987 XXIX, and Levy 1990 XX, suggesting differences in the mineralogy of the silicates. The 3.1- to 3.7-μm spectrum at r = 0.35 AU is featureless at the 5% level. We attribute the lack of an obvious 3.4-μm feature to masking by thermal emission from the dust rather than to an absence of the emitting organics. Austin has the characteristics of a "dust poor" comet; however, this designation refers only to the relative dust cross section, not necessarily the total mass. © 1993 by Academic Press, Inc.