A comparison of ultraviolet, optical, and X-ray imagery of selected fieldsin the Cygnus Loop

During the Astro-1 and Astro-2 space shuttle missions in 1990 and 1995, far ultraviolet (FUV) images of five 40' diameter fields around the rim of the Cygnus Loop supernova remnant were observed with the Ultraviolet Imaging T elescope (UIT). These fields sampled a broad range of conditions, including both radiative and nonradiative shocks in various geometries and physical scales. In these shocks, the UIT B5-band samples predominantly C Iv lambda 1550 and the hydrogen two-photon recombination continuum. Smaller contribut ions are made by emission lines of [He II] lambda 1640 and O III] lambda 16 65. We present these new FUV images and compare them with optical H alpha a nd [O III] images and ROSAT HRI X-ray images. Comparing the UIT images with those from the other bands provides new insights into the spatial variatio ns and locations of these different types of emission. By comparing with sh ock-model calculations and published FUV spectroscopy at select locations, we surmise that resonance scattering in the strong FUV permitted lines is w idespread in the Cygnus Loop, especially in the bright optical filaments ty pically selected for observation in most previous studies.