Airborne and groundbased spectrophotometry of comet P/Halley from 5–13 micrometers

Summary

Spectrophotometry from 5–10μm (Δλ/λ ≈ 0.02) of comet Halley was obtained from the Kuiper Airborne Observatory on 1985 December 12.1 and 1986 April 8.6 and 10.5, UT. 8–13 μm data were obtained on 17.2 December 1985 from the Nickel Telescope at Lick Observatory. The spectra show a strong broad emission band at 10 μm and a weak feature at 6.8 μm. We do not confirm the strong 7.5 μm emission feature observed by the Vega 1 spacecraft.

The 10 μm band, identified with silicate materials, has substructure indicative of crystalline material. The band can be fitted by combining spectral data from a sample of interplanetary dust particles. The primary component of the silicate emission is due to olivine. The 6.8 μm emission feature can be due either to carbonates or the C—H deformation mode in organic molecules. The lack of other emission bands is used to place limits on the types of organic molecules responsible for the emission observed by others at 3.4 μm.

Color temperatures significantly higher than the equilibrium blackbody temperature indicate that small particles are abundant in the coma. Significant spatial and temporal variations in the spectrum have been observed and show trends similar to those observed by the spacecraft and from the ground. Temporal variability of the silicate emission relative to the 5–8 μm continuum suggests that there are at least two physically separate components of the dust.