MCDONALD OBSERVATORY DATA ON THE COMET SHOEMAKER-LEVY-9 IMPACTS ON JUPITER AND THE RESULTING HAZE PARTICLES

Simultaneous light curves of the Comet Shoemaker-Levy 9 fragment R and V impacts were measured with the McDonald Observatory 2.7 m and 0.8 m telescopes, at wavelengths of 2.12 mu m and 0.893 mu m, respectively. The R impact was clearly detected at 2.12 mu m, but not at 0.893 mu m , leading to an upper limit on the ''main event'' temperature of 1300K . The V impact was not detected. A possible detection of the U impact at 2.12 mu m was recorded. CCD spectrophotometry of Jupiter was obtain ed with the McDonald 2.1 m telescope during the Shoemaker-Levy 9 impac t period (17 July-23 July 1994 UT; Barker et al. (1994) Bull. Aln. Ast ron. Sec. 26, 1569). Spectra of Jupiter from 0.55 to 1.08 mu m (10 Ang strom resolution) were obtained using a long-slit CCD spectrograph (ES 2), with a seeing-limited spatial resolution of about 1-2 ''. Impact r egions were darker than neighboring non-impact regions by some 5-10% a t all wavelengths except in the strong methane absorption bands (0.727 , 0.864, and 0.890 mu m) where the impact sites are brighter. Aerosol models of this spectral change are examined. The grey absorption obser ved is not typical of a population of particles much smaller than the wavelength. Neither is the similar haze brightening seen in two methan e bands of similar strength at 0.727 and 0.864 mu m. Our radiative tra nsfer models of the H and E impact sites favor broad particle size dis tributions, with a mean particle radius [r] = 0.25 mu m and a log-norm al size distribution of width b approximate to 0.6. A constant imagina ry refractive index of 0.006 in this wavelength range provides an adeq uate spectral fit to the H data, while an index of 0.012 better fits t he E data. Additional ES2 Jupiter spectra from June 1995 with both ''b lue'' (0.31-0.58 mu m) and ''red'' (0.55-1.08 mu m) gratings were obta ined. Blue spectra and images still show some evidence for residual im pact haze opacity near the impact latitudes; red spectra and images do not. Apparently sedimentation of the larger particles in a broad init ial size distribution has removed the red opacity. (C) 1997 Elsevier S cience Ltd. All rights reserved.