Optical Emission Associated with the Galactic Supernova Remnant
  G179.0+2.6
  Narrow passband optical images of the large Galactic supernova remnant
G179.0+2.6 reveal a faint but nearly complete emission shell dominated by
strong [O III] 4959,5007 A line emission. The remnant's optical emission, which
consists of both diffuse and filamentary features, is brightest along its
southern and northeastern limbs. Deep H-alpha images detect little coincidence
emission indicating an unusually high [O III]/H-alpha emission ratio for such a
large and apparently old remnant. Low-dispersion optical spectra of several
regions confirm large [O III]/H-alpha line ratios with typical values around
10. The dominance of [O III] emission for the majority of the remnant's optical
filaments suggests shock velocities above 100 km/s are present throughout most
of the remnant, likely reflecting a relatively low density ambient ISM. The
remnant's unusually strong [O III] emission adds to the remnant's interesting
set of properties which include a thick radio emission shell, radial
polarization of its radio emission like that typically seen in young supernova
remnants, and an unusually slow-rotating gamma-ray pulsar with a characteristic
spin-down age ~50 kyr.
