Comet 55P/Tempel-Tuttle Recovered at Large Heliocentric Distance

O.R. Hainaut, K.J. Meech, J. Bauer (IfA/UH), R.M. West (ESO/Garching), H. Boehnhardt (Sternwarte München)

The modern discovery of comet 55P/Tempel-Tuttle occurred in 1865; the period was found to be 33 years. Although the comet was not seen during its 1899 and 1932 approaches, it was recovered in 1966 after an intensive orbit analysis also identifying the comet with that of 1366. Tempel-Tuttle's orbital node is very close to the Earth's orbit; the match between the comet's orbit and that of the Leonid meteors, which featured very strong activity in 1833 and 1866, suggest that the comet is their parent. Very strong meteoritic activity is predicted for the 1998 and 1999 Leonid showers.

We attempted several times during the past years to observe Comet 55P/Tempel-Tuttle at large heliocentric distances. We finally recovered it on images obtained on March 4, 1997 on the Keck-II 10-m telescope on Mauna Kea, at an heliocentric distance r=4.5AU. The recovery was confirmed on March 7, using the ESO NTT at La Silla. The comet appears as a point source, showing no sign of activity. We are now regularly observing the comet in order to monitor the onset of its activity and to determine the size, colors and rotational parameters of its nucleus. Also, the newly determined orbit allows us to revisit the images which were obtained previously: since the exact position of the comet is now very well known, we can perform new image enhancements that will lead either to a detection or a very constraining brightness upper limit, giving some early points to the comet light-curve out to r=10AU. We will present these results, which are the firts direct measurements of that comet.

This work is being supported, in part, by NASA Grant NAGW-5015 and NSF grant AST 92-21318, and is based on observations collected at the European Southern Observatory, La Silla, and UH88 and Keck telescopes on Mauna Kea.