Nucleus and tail studies of comet P/Swift-Tuttle

CCD images of comet P/Swift-Tuttle, obtained in April 1994 with the 2.2m telescope at ESO La Silla/Chile, showed a comaless stellar nucleus. From absolute photometry we estimated the equivalent radius of the cometary nucleus to be about 11 km (assuming an albedo of 0.04 as for P/Halley) for two rotation phase angles which differ by about 75 deg. From that we conclude that the nucleus is either of rather spherical shape or that the viewing geometry was almost pole-on during our observations. An analysis of the plasma tail and inner coma of the comet by means of photographic plates and CCD images through IHW and BVR filters, obtained with the 80cm Schmidt camera and the 1.2m telescope at Calar Alto/Spain in November 1992, revealed several tail rays, head streamers and substructures in brightness excess areas in the coma. While some of the tail rays extended to several million km nuclear distance, most of them can be traced to starting points which lie in a region just 20000-35000 km projected distance tailward from the nucleus.