The Structure of the Planetary Nebula NGC 2371 in the Visible and
  Mid-Infrared
  We investigate the structure of the planetary nebula (PN) NGC 2371 using
[OIII]-5007 imaging taken with the Jacobus Kapteyn 1.0 m telescope, and
[NII]-6584, [OIII]-5007 and Ha results acquired with the Hubble Space Telescope
(HST). These are supplemented with archival mid-infrared (MIR) observations
taken with the Spitzer Space Telescope (Spitzer). We note the presence of
off-axis low-ionization spokes along a PA of 65 degrees, and associated collars
of enhanced [OIII] emission. The spokes appear to consist of dense
condensations having low-excitation tails, possibly arising due to UV shadowing
and/or ram-pressure stripping of material. Line ratios imply that most of the
emission arises through photo-ionisation, and is unlikely to derive from
post-shock cooling regions. An analysis of these features in the MIR suggests
that they may also be associated with high levels of emission from polycyclic
aromatic hydrocarbons (PAHs), together with various permitted and forbidden
line transitions. Such high levels of PAH emission, where they are confirmed,
may develop as a result of preferentially enhanced FUV pumping of the
molecules, or shattering of larger grains within local shocks. Although H2
emission may also contribute to these trends, it is argued that shock-excited
transitions would lead to markedly differing results. We finally note that thin
filaments and ridges of [OIII] emission may indicate the presence of shock
activity at the limits of the interior envelope, as well as at various
positions within the shell itself. We also note that radially increasing fluxes
at 3.6, 5.8 and 8.0 microns, relative to the emission at 4.5 microns, may arise
due to enhanced PAH emission in external photo-dissociative regions (PDRs).
