37th DPS Meeting, 4-9 September 2005
Session 49 Pluto and Charon
Oral, Thursday, September 8, 2005, 9:00-10:00am, Law LG19

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[49.05] The 11 July 2005 Charon stellar occultation

B. Sicardy, F. Colas, T. Widemann, A. Bellucci, E. Frappa, E. Gendron, S. Lacour, J. Lecacheux, S. Pau, J. Quintanilla, S. Renner, F. Roques, F. Vachier (Obs. Paris, France), N. Ageorges, O. Hainaut (ESO/Paranal, Chile), W. Beisker (IOTA - ES), A. Maury (Space Obs, S. Pedro, Chile), D. Lazzaro, R. Martins, C. Veiga (Obs. Nacional, Brazil), O. Mousis, P. Rousselot (Obs. Besancon, France), J.-F. Lecampion (Obs. Bordeaux, France), H. Levato (Obs. El Leoncito, Argentina), R. Zalles (Obs. Tarija, Bolivia)

On 11 july 2005, Pluto's satellite Charon will occult a I~14.5 magnitude star. The zone of visibility of this event includes Brazil, Uruguay, Paraguay, Argentina, Bolivia, Chile and Peru. A campaign has been organized to record the occultation from several large telescopes (Paranal/ESO/Chile, La Silla/ESO/Chile, El Leoncito/Argentina, Pico dos Dias/Brazil, etc...), and smaller fixed and portable telescopes in the other countries.The aims of this observations are: [1-] Measure Charon's size to within an accuracy of ~5 km. The present Charon radius, presently estimated between 600 and 650 km, yields an uncertain density of 1.4-1.8g/cm3. A better size estimation will contrain better the density, and thus, the composition of the satellite. [2-] A re-analysis of the mutual events observed in the 1980's can then better constrain Pluto's size once Charon radius has been determined. Again, a better density for Pluto - presently estimated at 1.8-2.1 g/cm3 - can be derived. [3-] Finally, we will search for a faint Charon's atmosphere. The limit of detection for such an atmosphere is estimated to about 10 nanobar at Charon surface, i.e. one thousand times smaller than Pluto's present atmosphere. If such an atmosphere is discovered, this will be an important step for better understanding the appearance and maintenance of atmospheres around TNO's in general.

We thank the Paris Observatory Scientific Board and the French Programme National de Planétologie for support.

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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.