The mutliple lobes and geometric model of Hubble 12: a young planetary nebula with two pairs of H2 knots

Abstract

Hubble 12 (Hb 12) is a member of the rare group of planetary nebulae (PNs) exhibiting nested shells. Its intrinsic structures and shaping mechanism are still not fully understood. We present new near-infrared narrow band imaging observations of Hb 12 using Wide-field InfraRed Camera on the Canada-France-Hawaii Telescope (CFHT). Combining Hubble Space Telescope optical imaging and CFHT observations, we find a number of co-axial rings aligned with the bipolar lobes and two pairs of separate knots with different orientations. These rings are thought to be the manifestation of a time-variable, collimated fast wind of bipolar lobes interacting with surrounding asymptotic giant branch circumstellar medium. The existence of knots with different orientations suggests that this PN hosts a bipolar, rotating, episodic jet (BRET). We construct a three-dimensional model that allows the visualization of the nebula viewed from different orientations, and infer that this PN might have intrinsic structures similar to the young multipolar PNs, Hen 2-320 and M 2-9.