The bow-shock and high-speed jet in the faint, 40 arcmin diameter, outer
  halo of the evolved Helix planetary nebula (NGC 7293)
  In previous, very deep, optical images of NGC 7293 both a feature that has
the morphology of a bow-shock and one with that of a jet were discovered in the
faint 40 arcmin diameter halo of the nebula. Spatially resolved longslit
profiles of the Halpha and [N II] 6548, 6584 A nebular emission lines from both
features have now been obtained.
  The bow-shaped feature has been found to have Halpha radial velocities close
to the systemic heliocentric radial velocity, -27 km/s, of NGC 7293 and is
faint in the [N II] 6548, 6584 A emission lines. Furthermore, the full width of
these profiles matches the relative motion of NGC 7293 with its ambient
interstellar medium consequently it is deduced that the feature is a real
bow-shock caused by the motion of NGC 7293 as it ploughs through this medium.
The proper motion of the central star also points towards this halo feature
which substantiates this interpretation of its origin.
  Similarly [N II] 6584 A line profiles reveal that the jet-like filament is
indeed a collimated outflow, as suggested by its morphology, at around 300 km/s
with turbulent widths of around 50 km/s. It's low Halpha/[N II] 6548, 6584 A
brightness ratio suggests collisional ionization as expected in a high-speed
jet.
