Detection of Ultraviolet Emission Lines in SN 1006 with the Hopkins Ultraviolet Telescope

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Abstract
The Hopkins Ultraviolet Telescope (HUT) was used during the Astro-2 space shuttle mission in 1995 March to observe emission lines of H I, He II, C IV, N V, and O VI from the faint optical Balmer line filament at the northwest edge of the SN 1006 supernova remnant. This is the first successful far-ultraviolet observation of a nonradiative shock wave with velocity in excess of 300 km s-1 and the first detection of ultraviolet emission lines from SN 1006. The observed line widths are consistent with the ~2300 km s-1 width reported for Hα, implying that the velocities of different ions are independently randomized in the shock and that ion-ion temperature equilibration is ineffective. A faint continuum in the spectrum is consistent with relatively strong dust-scattered starlight along this line of sight, visible because of the large HUT spectrograph aperture used for this observation. The relative line intensities are in reasonable agreement with existing model predictions for a 2300 km s-1 shock. However, proton excitation rates may compete with electron excitation in producing the emission lines and need to be included in the model calculations before a comprehensive analysis can be attempted.