* Kanazawa Institute of Technology, Nonoichi, Ishikawa 921, Japan
** Max-Planck-Institute für Kernphysik, Postfach, 103980, D-6900, Heidelberg, FRG
*** Bereich Extraterrestrische Physik, Ruhr-Universität, 4630, Bochum, FRG
Abstract:
Based on the computed equilibrium temperature of evaporating dirty water-ice grains, dirty water-ice halo is examined, taking into account of a size dependence of terminal velocity of dust at P/Halley. It is found that due to an enhanced grain's temperature caused by dirtiness, icy halo cannot extend over 100 km from the nucleus when comet approaches inside a solar distance r of 1 AU. Therefore, it is unlikely that the ice bands in the near infrared wavelengths could be detected in the cometary coma at r<1 AU.