Self-absorption by Vibrationally Excited H tex2html_wrap_inline11 in the HUT Spectrum of the Jovian Aurora

B. C. Wolven, P. D. Feldman (JHU)

On March 9, 1995, during the Astro-2 mission, a spectrum of the H tex2html_wrap_inline11 emission produced by the northern Jovian aurora was obtained by the Hopkins Ultraviolet Telescope (HUT). Strong Werner band transitions near 1050 and 1100 Å, in a region of the spectrum not accessible to IUE or HST, have intensities significantly weaker than those predicted by the theoretical branching ratios for optically thin emission. The observed intensities in the auroral spectrum are shown to be consistent with attenuation due to absorption by vibrationally excited H tex2html_wrap_inline11 ( tex2html_wrap_inline17 ) in the overlying atmosphere. Absorbed photons escape primarily by fluorescent scattering in transitions which connect to unpopulated vibrational levels at longer wavelengths. Hydrocarbon absorption at wavelengths less than 1400 Å is predominantly due to methane, however the methane cross section does not vary at the wavelength scales necessary to produce the observed attenuation. An Astro-2 HUT spectrum of the Jovian dayglow, produced by a combination of solar and electron-impact fluorescence, displays considerably less attenuation in the 1050-1100 Å region. We present synthetic H tex2html_wrap_inline11 fluorescence spectra which include the effects of self-absorption and demonstrate the ability to reproduce the features observed in the HUT spectra.