Infrared monitoring of comet P/Halley

Summary

We present the results of an infrared monitoring program of comet P/Halley. Multiaperture photometry between 1 and 5 gm was obtained during 12 nights in the preperihelion phase from the Gornergrat observatory, and during 4 nights in the postperihelion phase from the ESO 1-m telescope at La Silla. In addition, 10 and 20 gm photometry was obtained on November 4 and 7, when the comet was at 1.88 AU from the Sun. An analysis of the JHK data indicates that Halley was typically somewhat redder than the Sun (<J−H> = 0.48, <H−K> = 0.18) and that its colors did not change throughout our monitoring period, implying that the properties of the dust in the coma remained constant. Also, with the exception of November 4 and March 21, when Halley was presumably undergoing an outburst, the multiaperture data are consistent with an r ⁻²density distribution of scattering dust in the coma. Furthermore, the flux from Halley in its quiescent phase increased as R ^−4.5, where R is the heliocentric distance. The 10 gm silicate feature in emission was detected at about the 2^σ level on 4 and 7 November, and from the spectral energy distribution at that time we deduced an albedo of 0.05 for the scattering dust in the coma.

Based on data collected at the TIRGO Observatory, and at the European Southern Observatory, La Silla, Chile