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.