This image of comet 55P/Tempel-Tuttle was obtained as part of a research effort at the Pic du Midi Observatory in France by a team of observers, including L. Jorda (Max Planck Institute for Aeronomie), J. Lecacheux (Meudon Observatory), F. Colas (Bureau des Longitudes, Paris), E. Frappa (Planetarium de Saint-Etienne, France) and P. Laques (Bagneres-de-Bigorre, France). The image was obtained with a 105cm telescope and a Thomson 7863 CCD camera and a broadband filter 530-900 nm. The image is the sum of 40 exposures of 240 seconds. The comet was 1.09 AU form the Sun and 0.59 AU from Earth. The left image shows the unprocessed result. By applying a median selection algorithm to the full set of images, the observers were able to efficiently remove all things that did not share the comet motion (middle image). After removing a radial 1/rho profile, a dust jet is visible (left image).
The extend of the jet structure is shown in these images. These images were obtained after a radial profile substraction and a rotational gradient. The reduction of many observation nights allowed the observers to find two possible spin periods for the comet. This informations was published in the IAU Circular 6816 on 1998, January 30th. In their posting of February 2nd, Jean Lecacheux, Eric Frappa and Francois Colas report that the rotation period of the nucleus is: 15.33 +/- 0.02 hours.