Far Ultraviolet Spectroscopic Explorer observations of an x-ray bright region in the Vela supernova remnant

We present the results of a Far Ultraviolet Spectroscopic Explorer observat ion of an X-ray-selected knot in the Vela supernova remnant. Spectra were o btained through the 30" x 30" low-resolution aperture and the 4" x 20" medi um-resolution aperture. O VI lambda lambda 1032, 1038 and C III lambda 977 are detected strongly in both spectra, and S VI lambda lambda 933, 944 is d etected weakly only in the larger aperture spectrum. We also report the fir st detection of C II lambda 1037 emission in a supernova remnant. The spect ra show the presence of two kinematic components along the line of sight-on e 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 veloc ity of +100 km s(-1). We associate the -50 km s(-1) component with the obse rved X-ray knot and find a dynamical pressure of 3.7 x 10(-10) dyne cm(-2) driving the shock. We compare our results with data obtained using the Hopk ins Ultraviolet Telescope at nearby locations and find that differences in the spectra imply the existence of two emitting components in the X-ray kno t. 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 ha ve dramatically different ultraviolet emission. These observations demonstr ate the importance of high spectral resolution in understanding the proper physical relationships between the various emitting components in supernova remnants.