Self-absorption by vibrationally excited H2 in the Astro-2 Hopkins ultraviolet telescope spectrum of the Jovian aurora

Observed H-2 band intensities in the spectrum of the northern Jovian aurora, obtained by the Hopkins Ultraviolet Telescope (HUT) during the Astro-2 mission in March 1995, are shown to be consistent with attenuation due to absorption by vibrationally excited H-2 (v less than or equal to 2) in the overlying atmosphere. Strong Werner band transitions near 1050 and 1100 Angstrom, 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. Absorbed photons escape primarily by fluorescent scattering in transitions which connect to unpopulated vibrational levels at longer wavelengths. A spectrum of the Jovian dayglow (produced by a combination of solar and electron-impact fluorescence) obtained a few days earlier displays considerably less attenuation in the 1050-1100 Angstrom region. We present synthetic H-2 fluorescence spectra which include the effects of self-absorption and demonstrate the ability to reproduce the features observed in the HUT spectra.