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A.A. Homich, R.D. Gehrz (UofM), M.S. Hanner (JPL/Caltech), A.T. Tokunaga (UofHI)
We present an analysis of the combined infrared data obtained on Comet P/Halley 1986 III acquired by Gehrz and Ney (1992), Hanner et al. (1987), Tokunaga et al. (1986, 1988), Green et al. (1986), Ryan and Campins (1991), Campins and Ryan (1989), and Bregman et al. (1987). This data base, the largest single body of infrared photometric data for any comet, spans a wavelength range from 0.7 to 23 \mum and describes the activity of P/Halley at heliocentric distances from 0.6 to 3.0 AU. The quantitative corrections and calibration procedures required to intercompare the individual data sets are described. Long-term trends in the heliocentric dependance of P/Halley's grain color temperature Tobs, silicate emission optical strength M10, grain albedo A, grain superheat S, apparent luminosity L, and infrared monochromatic fluxes are discussed. The infrared data sets are compared with data sets at other wavelengths for evidence of short-duration bursts associated with the activity of the comet's nucleus. We conclude that short duration outbursts at small heliocentric distances produce small grains whose thermal emission during the outburst dominates the normal background thermal emission from larger grains. These outbursts are not observed at heliocentric distances larger than 2.0 AU pre-perihelion, but cannot be ruled out for the post-perihelion data. We discuss the nuclear activity implied by both the long-term trends and the short period outburst behavior.
This research was supported by NASA, the National Science Foundation, the U.S. Air Force, the University of Minnesota Institute of Technology Dean's Office and Graduate School, and the University of Wyoming.