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S. B. Peschke (ISO Data Centre, Vilspa, Spain), E. Gruen (MPI fuer Kernphysik, Heidelberg, Germany), M. Stickel (MPI fuer Astronomie, Heidelberg, Germany), C.M. Lisse (STScI, Baltimore, USA), I. Heinrichsen (IPAC, Pasadena, USA), ISOPHOT Comet Team
We observed comets Hale-Bopp, Kopff, Wild, Chiron and Schwassmann-Wachmann 1 with the ISO satellite multiple times, covering a wavelength range from 3-175microns. From these photometric observations, spectral energy distributions were derived. Multi-aperture photometry was carried out for each comet and radial intensity profiles were derived which were also compared to optical profiles and the ISOCAM data, where available. The ISOCAM data provide radial intensity profiles without the positioning uncertainty of the aperture photometry by ISOPHOT. The comets were at different heliocentric distances ranging from 1.7 to 8.3AU, thus various states of activity were sampled and an evolution of coma activity and brightness is seen. The datasets were reduced homogeneously with various methods, with and without the official data reduction software, and consistent results could be achieved for most observations while for extreme fluxes, very low and very high, large uncertainties were found depending on the data reduction scheme applied. The derived spectral energy distributions were compared to various synthetic spectral energy distributions. Silicate, carbon and icy grain spectra at the appropriate heliocentric distance were computed, mixed and compared to the observed spectral energy distribution to learn more about the material composition and the grain size distribution within the various comae.