First Detection of an Optical Dust Trail along the Orbit of 22P/Kopff

Abstract

We present the first evidence of a cometary dust trail in optical wavelengths along the orbit of 22P/Kopff, observed when the parent comet was at a heliocentric distance of 3.01 AU. We find that the surface brightness and the width of the trail become, respectively, fainter and wider as the distance from the comet nucleus increases, except for a region with delta mean anomaly ΔMA ≤ 002. This suggests that the majority of the centimeter-sized dust particles were ejected before the comet's previous perihelion passage and that they spread due to their initial velocity with respect to the comet. By comparing this trail with the IRAS data at wavelengths of 12 and 25 μm, we infer that the trail is composed of very low albedo particles (~0.01).