2001ApJ...549..416S

We present the results of a Far Ultraviolet Spectroscopic Explorer observation of an X-ray-selected knot in the Vela supernova remnant. Spectra were obtained through the 30''x30'' low-resolution aperture and the 4''x20'' medium-resolution aperture. O VI λλ1032, 1038 and C III λ977 are detected strongly in both spectra, and S VI λλ933, 944 is detected weakly only in the larger aperture spectrum. We also report the first detection of C II λ1037 emission in a supernova remnant. The spectra show the presence of two kinematic components along the line of sight–one with both low- and high-excitation emission centered at a velocity of -50 km.s^–1 and another with only low-excitation emission centered at a velocity of +100 km.s^–1. We associate the -50 km.s^–1 component with the observed X-ray knot and find a dynamical pressure of 3.7x10^–10 dyne.cm^–2 driving the shock. We compare our results with data obtained using the Hopkins Ultraviolet Telescope at nearby locations and find that differences in the spectra imply the existence of two emitting components in the X-ray knot. Based on the X-ray morphology seen in a ROSAT HRI image, we identify two distinct regions that can be associated with these two components which have dramatically different ultraviolet emission. These observations demonstrate the importance of high spectral resolution in understanding the proper physical relationships between the various emitting components in supernova remnants.