IFU spectroscopy of southern PN VI: The extraordinary chemo-dynamics of
  Hen 2-111
  In this paper we present integral field spectroscopy of the extraordinary
Type I bipolar planetary nebula Hen 2-111. In the lobes we map fast moving
knots of material with [N II]$\lambda 6584$/H$\alpha$ ratios up to 12, and with
radial velocities relative to systemic from -340 km/s up to +390 km/s. We find
evidence of a bipolar ejection event at a velocity $\sim 600$ km/s from the
central star (assumed to be a binary), which occurred about 8000yr ago. The
fast moving material is chemically quite distinct from the lower velocity gas
in the bipolar lobes., and displays very high N abundances. We show that the
fast moving N-rich knots are not photoionised by the central star, and have
constructed detailed shock models for the brightest knot. We find a pre-shock
density $\sim 6$cm$^{-3}$, and a shock velocity $\sim150$ km/s. The shock is
not fully radiative, being only $\sim 600$yr old. This shocked gas is partially
H-burnt, with a helium abundance by mass exceeding that of hydrogen, and is
interacting with partially H-burnt material ejected in an earlier episode of
mass loss. We conclude that the high-velocity material and the bipolar shell
must have originated during the late stages of evolution of a common-envelope
phase in a close binary system.
