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Space Telescope Science Institute
Spectroscopy of 51 Peg B: Search for Atmospheric Signatures

A. Coustenis, J. Schneider, D. Bockelee-Morvan, H. Rauer, R. Wittemberg
Paris-Meudon Observatory, France

E. Chassefiere
LMD/CNRS, France

T. Greene
Institute for Astronomy, Univ. of Hawaii, Honolulu HI

A. Penny
Rutherford Lab., Oxon, UK

T. Guillot
Univ. of Arizona, Tucson AZ

The planet in orbit around 51 Peg has, according to theoretical models, moved into its current position from farther away and its atmosphere may therefore be strongly evaporating. The molecules released by the upper parts of the atmosphere must be rapidly ionized and could form an envelope around the planet. If the planet passes in front of the star, this envelope is in favorable geometric conditions (the inclination angle of the orbit is close to 90º) which allow it to occult the star. Absorption lines due to the signatures of atmospheric ions could then be observed.

We have observed 51 Peg alone and during the transit of the planet in front of the star on Aug. 18, 19, 27, 29, Sept. 3 and 4 1996 with CSHELL at IRTF and CGS4 at UKIRT. Our aim is to look for absorption lines from the material evaporated around the planet while occulting the star that would enable us to infer information on the nature of the atmosphere around the planet. The data reduction is currently under way and we will present preliminary results.