Polarimetry of comet P/Halley: continuum versus molecular bands

Abstract

Measurements of the linear polarization of molecular bands in comets P/Halley and Hartley-Good are presented. The measured bands are the C2 Swan (5140 Å), the CN (3880 Å), the C3 (4060 Å) and the OH (3090 Å). The phase angle dependence of the polarization of C2, C3 and CN is in good agreement with theory. However the polarization of OH is found 5 times smaller than expected. The direction of polarization of C2, C3 and OH is usually perpendicular to the scattering plane, though some measurements are parallel to it. For CN half the measures show significant deviations from the perpendicular to the scattering plane.