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G. R. Gladstone (SwRI), J.-C. Gérard, J. Gustin, D. Grodent (U. Liége), J. T. Clarke (Boston U.)
Spectral observations of Jupiter's far-ultraviolet (FUV) auroral emissions are commonly used to determine a ``color ratio, - defined as I(155-162nm) / I(123-130nm), which provides an estimate for the peak emission altitude of the aurora and thus, assuming an accurate model atmosphere, for the mean energy of precipitating electrons. This is because the nascent emission spectrum resulting from electron impact on H2 is relatively unchanging over a wide range of energy, so that differential absorption by overlying CH4 is the primary modifier of the spectral shape of the emergent FUV emissions. This method is analogous to that used at Earth, with N2 LBH auroral emissions instead of H2 Lyman and Werner bands and differential absorption by O2 rather than methane. More detailed simulations of Jupiter's FUV auroral spectra can be used to place useful constraints on higher hydrocarbons, such as acetylene and ethane. Here we present a spectral analysis of HST-STIS G140L observations taken in September 1999, which include a region with the largest color ratio yet observed (i.e., the deepest aurora). A non-linear least squares model fit to the data is used to search for the presence of several important overlying hydrocarbons with strong and distinctive FUV absorption cross sections, e.g., CH4, C2H2, C2H4, C2H6, CH3C2H, C3H8, C4H2, C2H2, and C4H10. We gratefully acknowledge support from NASA through grant NNG05GG97G.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.