The dust tail of Comet 1P/Halley after its perihelion in 1986 and the rotation of the nucleus

Abstract

The dust tail of Comet 1P/Halley in 1986 and the evolution of its streamers after perihelion are thoroughly investigated by means of direct modelling, determination of streamer densities, and synchrone and syndyne grids. For this purpose, 16 selected wide-field images of the comet in the red dust continuum, taken from 1986 February 22 to April 16, are used to cover the whole time interval of the observable dust tail evolution during its most active phase. In total, 10 significantly distinct streamers have been detected, which were emitted from 22 d before to 12 d after perihelion. The analysis of these streamers yields a synodic ‘basic period’ for the activity of the cometary nucleus of T0 = 2.10 ± 0.11 d. Moreover, ‘missing’ streamers indicate a complex interplay between the rotation of the nucleus and possibly its precession/nutation, and two or more distinct active regions on the nucleus. Periodicities of about 3.3 and 5.0 d or longer also seem to be present in the activity pattern. Thus the morphological analysis of the dust tail streamers independently confirms the complicated rotational pattern of Comet Halley's nucleus found from previous studies. The ‘decay’ of the dust tail and its streamers, i.e. the disappearance of the smallest particles from the tail, seems to be governed by a time-scale of ####t1/e ≈ 9 d. Typical ‘survival times’ of dust particles in the tail range from about 25 d for β = 1.0 (a ≈ 1 μm) to more than 65 d for β < 0.01 (a > 100 μm).