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We present the first high quality far--ultraviolet spectrum of a filament in the Puppis A supernova remnant (SNR), obtained with the Hopkins Ultraviolet Telescope during the Astro--2 Space Shuttle mission in 1995 March. This observation was made possible by the much higher sensitivity of HUT to diffuse emission in comparison to other ultraviolet telescopes. The 1920 s spectrum covers the 825 -- 1850 \AA\ spectral range with $\sim$3 \AA\ resolution and shows numerous lines of C, N, O, Si, Ne, and He, including O VI $\lambda\lambda$1032,1038, and C III $\lambda$977 in the spectral region below Ly$\alpha$.
The filament observed is in the eastern region of Puppis A, near the brightest X--ray region, and corresponds to a shocked interstellar cloud. Optically the filament shows strong [O III] emission, characteristic of a relatively young, ``incomplete" shock. However, the HUT spectrum is basically consistent with a steady flow shock model of V = 160 -- 180 km/s and solar abundances, within uncertainties of the interstellar extinction to the filament. Thus, this filament may have a fairly complete cooling zone with little of the coolest ``recombination" zone yet established. Puppis A is only the fourth galactic SNR to be observed successfully in the far--ultraviolet, after the Cygnus Loop, Vela, and Crab Nebula SNRs.
This research is supported by NASA contract NAS 5-27000 to the Johns Hopkins University.
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