31st Annual Meeting of the DPS, October 1999
Session 27. Comet Nuclei I
Contributed Oral Parallel Session, Tuesday, October 12, 1999, 11:20-12:00noon, Sala Pietro d'Abano

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[27.02] First Science Observations from the ESO VLT Kueyen Telescope: Comet 46P/Wirtanen, a Tiny Iceball for ROSETTA

H. Boehnhardt (ESO VLT Observatory), C. Delahodde, T. Sekiguchi (ESO Santiago de Chile), O. Hainaut (ESO La Silla Observatory), R. West (ESO Garching), J. Spyromilio, M. Tarenghi (ESO VLT Observatory), R. Schulz, G. Schwehm (ESTEC Noordwijk)

In mid May 1999 46P/Wirtanen, the target comet of ESA's ROSETTA mission, was observed during the commissioning of the 2nd Unit Telescope (UT), named Kueyen, of ESO's Very Large Telescope facility (VLT). Using the Cassegrain Focus Test Camera these observations were the first science programme performed at this UT of the VLT.

At the time of the observations the comet was 5 AU from the Sun and 4 AU from Earth. It moved outbound entering the outskirts of the Milky Way in the sky. Therefore, during planning of this programme special care was taken to select observing periods when the comet passed through a less crowded star field in the sky in order to improve the chances for its detection.

The successful Kueyen observations found the comet as a stellar object without detectable coma. The measured object brightness of 25.15 mag in R band corresponds to a nucleus radius of 550 m (assuming an albedo of 0.03). No significant brightness variations were detected and the respective measurement uncertainty is compatible with the nucleus axes ratio as given in the literature.

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