Flows along cometary tails in the Helix planetary nebula NGC 7293
  Previous velocity images which reveal flows of ionized gas along the most
prominent cometary tail (from Knot 38) in the Helix planetary nebula are
compared with that taken at optical wavelengths with the Hubble Space Telescope
and with an image in the emission from molecular hydrogen. The flows from the
second most prominent tail from Knot 14 are also considered. The kinematics of
the tail from the more complex Knot 32, shown here for the first time, also
reveals an acceleration away from the central star. All of the tails are
explained as accelerating ionized flows of ablated material driven by the
previous, mildly supersonic, AGB wind from the central star. The longest tail
of ionized gas, even though formed by this mechanism in a very clumpy medium,
as revealed by the emission from molecular hydrogen, appears to be a coherent
outflowing feature.
