Optical polarimetry of P/Halley - Synthesis of the measurements in the continuum

Abstract

Ground-based observations of the linear polarization of P/Halley in the continuum by several independent groups of observers are analysed in common to produce synthetic polarization data. Curves of polarization as a function of phase angle are derived for the bright envelope around the nucleus, for the dust grains after they emerge from this envelope but are still in the vicinity of the nucleus, and for the grains at farther distances. Wavelength dependences are derived. Time variations are analysed and unusual events are noted. The in-situ polarization measurements recorded directly in the cometary environment by the instrument HOPE on board the GIOTTO space-craft are analysed within this context.