Global Far-Ultraviolet Properties of the Cygnus Loop
  We present the C III {\lambda}977, O VI {\lambda}{\lambda}1032, 1038 and N
IV] {\lambda}1486 emission line maps of the Cygnus Loop, obtained with the
newly processed data of Spectroscopy of Plasma Evolution from Astrophysical
Radiation (SPEAR; also known as FIMS) mission. In addition, the Si IV+O IV]
line complexes around 1400 {\AA} are resolved into two separate emission lines,
whose intensity demonstrates a relatively high Si IV region predicted in the
previous study. The morphological similarity between the O VI and X-ray images,
as well as a comparison of the O VI intensity with the value expected from the
X-ray results, indicates that large portions of the observed O VI emissions
could be produced from X-ray emitting gas. Comparisons of the far-ultraviolet
(FUV) images with the optical and H I 21 cm images, reveal spatial variations
of shock-velocity populations and high FUV extinction in the direction of a
previously identified H I cloud. By calculating the FUV line ratios for several
subregions of the Cygnus Loop, we investigate the spatial variation of the
population of radiative shock velocities; and the effects of resonance
scattering, X-ray emitting gas, and non-radiative shocks. The FUV and X-ray
luminosity comparisons between the Cygnus Loop and the Vela supernova remnant
suggest that the fraction of shocks in the early evolutionary stages is much
larger in the Cygnus Loop.
