  We present a spatially-resolved ultraviolet spectrum of a non-radiative shock
front in the Cygnus Loop, obtained with the Space Telescope Imaging
Spectrograph (STIS) on board the Hubble Space Telescope (HST). The spectrum
covers the wavelength range 1118 - 1716 angstroms, with an effective spectral
resolution of ~12 angstroms. The 0.1" spatial resolution of these data provides
a huge improvement over earlier ultraviolet spectra, allowing us to study the
spatial distribution of high ionization line emission directly behind the shock
front. We are able to isolate individual shock features in our spectrum by
comparing the STIS spectrum with a WFPC2 H-alpha image of the region. Isolating
the brightest shock tangency, we identify lines of NV, CIV, HeII, OV, OIV] and
SiIV, and NIV] as well as the hydrogen 2-photon continuum. The NV line peaks
about 0.3" behind the CIV and HeII emission and is spatially broader. Also, the
observed line ratios of CIV and HeII to NV are higher in our bright shock
spectrum than in previous observations of the same filament obtained through
much larger apertures, indicating that there must be a more widely distributed
component of the NV emission. We calculate shock models and show that the
observed separation between the CIV and NV emission zones and observed line
intensities constrain the combinations of shock velocity and pre-shock density
that are allowed.
