IR Photometry and Spectra of Io Occultations in 1997

J.D. Goguen, D.L. Blaney, G.J. Veeder, D.L. Matson, T.V. Johnson (JPL), P.D. Nicholson, T.H. Hayward, J.E. Van Cleve (Cornell U.), D. Toomey, L. Bergknut, C. Kaminski, W. Golisch, D. Griep (NASA IRTF, U. Hawaii)

We report results of IR measurements of occultations of Io by Europa made at the NASA IRTF and Palomar, observations that we use to map the thermal emission from Io's volcanos at high spatial resolution. The figure illustrates one result from tex2html_wrap_inline14 =8.7 tex2html_wrap_inline16 m photometry of the 4/18/97 UT occultation. The graph plots the combined flux from both satellites, normalized to the unocculted flux, versus UT with 4 times labelled. A bright hot spot containing tex2html_wrap_inline18 50% of the total flux disappears behind Europa's limb between times 1 & 2 and reappears between times 3 & 4. The image shows a map of Io and the outline of Europa's limb at these 4 times based on the Galileo navigation ephemeris (courtesy W. Owen). The eruption lies within the region of overlap of the 4 limb projections, squarely centered on Loki Patera. The lightcurve shows that no other comparably bright hot spots were occulted. The data set we are analyzing includes 8.2-11.2 tex2html_wrap_inline16 m spectra of the 3/28/97 UT occultation acquired with SpectroCAM-10 on the Palomar 5-m.