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The Hopkins Ultraviolet Telescope detected very faint emission lines of O VI, C IV, He II and perhaps N V in the spectrum of the 2000 km/s non-radiative shock wave of SN1006. The UV lines are about 2700 km/s broad. The line intensities can be used to study electron-ion temperature equilibration in shock waves, because they depend on electron temperature, while the H$\alpha$ width measures ion temperature. The intensities of the UV lines imply $T_e \ll T_i$, but the rough equality of the O VI, C IV and He II lines suggests an electron temperature above $10^6$ K. Therefore, some electron heating besides Coulomb collisions must occur. These results are in general agreement with the theory of Cargill and Papadopoulos, who predicted that plasma turbulence heats electrons to about 1/5 the ion temperature at the shock front.
This work was supported by NASA contract NAS 5-27000 to the Johns Hopkins University and NASA Grant NAG8-1074 to the Smithsonian Astrophysical Observatory.
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