The Formation of a Multiple Planetary Nebula:Hubble Space Telescope/WFPC2 Observations of KJPN 8

Abstract

KjPn 8 is an extreme polypolar planetary nebula with a large-scale structure characterized by a giant biconical envelope. Spasmodic bipolar ejections in changing directions have occurred over thousands of years to create this peculiar nebula. Narrowband images of the core of KjPn 8 have now been obtained with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope (HST) and are reported here. The central star is finally revealed in these observations, and its compact nebular core is resolved into a remarkably young elliptical ring, currently expanding at only 16 km s^-1. This ring is the ionized inner region of larger molecular CO and H₂ counterparts, all sharing the same orientation. The highest speed and youngest outflows are perpendicular to this central ring, which is identified as the latest event in the creation of this nebula. It is shown that the formation history of KjPn 8 has involved two distinct and consecutive planetary nebulae-like events, probably originating from a binary core evolution with components of very similar mass. These characteristics indicate that KjPn 8 may be a rare object in our Galaxy and the first ever detected of this class.