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] λ6584/Hα ratios up to 12, and with radial velocities relative to systemic from -340 up to +390 km s^-1. We find evidence of a bipolar ejection event at a velocity ~600 km s^-1 from the central star (assumed to be a binary), which occurred about 8000 yr ago. The fastmoving 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 photoionized by the central star, and have constructed detailed shock models for the brightest knot. We find a pre-shock density ~6 cm^-3, and a shock velocity ~150 km s^-1. The shock is not fully radiative, being only ~600 yr old. This shocked gas is partially H-burnt, with 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.