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F. Marchis, I. de Pater (UC-Berkeley), D. Le Mignant (Keck Observatory), H. Roe (UC-Berkeley), T. Fusco (ONERA), J.R. Graham (UC-Berkeley), R. Prange (Obs. de Paris), B. Macintosh (LLNL), Keck Science Team
Volcanically active Io remains a mysterious and intriguing moon, despite numerous spacecraft flybys. Groundbased monitoring programs help characterize the time evolution of Io's volcanic activity, such as the frequency, spatial distribution and temperature of hot spots and outbursts. The satellite was observed intensively in December 2001 with the Keck II Adaptive Optics (AO) system and its recently installed near-infrared camera NIRC2. The spatial resolution after applying the MISTRAL myopic deconvolution method (130 km in K band and 200 km in L band) is better than that of the global images from the Galileo/NIMS instrument. A movie produced from 12 pictures taken every 30\circ in Ionian longitude provides a complete survey of Io's surface during one full rotation. A total of 26 active hot spots were detected in L band (3.8\mum), and approximatively three times more in M band (4.7\mum). One active hot spot is seen in K band (2.2\mum) in the Pele area. While Io is in Jupiter's shadow, it is invisible to the wavefront sensor, but its hot spots are easily visible in the near-infrared. We imaged Io during the 18 Dec. 2001 eclipse using Ganymede (30" from Io, moving relative to Io at ~0.5"/min) as a reference source. Although isoplanatic effects limited AO performance, numerous spots are detected at both K' and L'. We will show the results of detailed studies (temperature, emission area, nature) for several of the hot spots.
Keck Science team is composed of S. Kwok, P. Amico, R. Campbell, F. Chaffee, A. Conrad, A. Contos, B. Goodrich, G. Hill, D. Sprayberry, P. Stomski, P. Wizinowich (W.M. Keck Observatory).
This work has been supported in part by the National Science Foundation Science and Technology Center for Adaptive Optics, managed by the University of California at Santa Cruz under cooperative agreement No. AST-9876783.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.