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R. Sankrit, W.P. Blair (JHU)
We present \textit{Far Ultraviolet Spectroscopic Explorer} (FUSE) observations of a region in the north-east Cygnus Loop. The emission from this region is due mainly to nonradiative shocks driven by the supernova blastwave into an ISM cloud, possibly the remnant wall of the pre-supernova cavity. Faint Balmer line filaments, visible in the optical, trace the shock front in exquisite detail. FUSE spectra were obtained, in 2000 June, at three positions with the MDRS aperture (4\arcsec\times20\arcsec) on one well-studied Balmer filament. The slit length was placed parallel to the shock front, and adjacent positions were separated by 4\arcsec\ perpendicular to the direction of the flow. With the chosen orientation, the HIRS aperture (1\farcs25\times20\arcsec) and the LWRS aperture (30\arcsec\times30\arcsec) were placed on filaments 1\farcm75 and 3\farcm5 to the northwest, respectively, from the MDRS aperture. O~VI~\lambda\lambda1032,1038 emission was detected through all the apertures in each of the three observations.
We use these spectra to study the variation of the O~VI emission line fluxes and line profiles in the post-shock flow on a 4\arcsec\ scale. (At the distance of the Cygnus Loop, 440~pc, 1\arcsec\ = 6.6\times 1015~cm.) We also study the O~VI emission at different positions along the shock front by comparing the spectra taken through different apertures. We use the distribution of the O~VI flux to constrain the extent of the post-shock flow and the properties of the shocked gas.
This work is based on data obtained for the Guaranteed Time Team by the NASA-CNES \textit{FUSE} mission operated by the Johns Hopkins University. Financial support has been provided by NASA Contract NAS5-32985.