A DETAILED STUDY OF THE STRUCTURE OF THE NESTED PLANETARY NEBULA, Hb 12, THE MATRYOSHKA NEBULA

Abstract

We present near-IR, integral field spectroscopic observations of the planetary nebula (PN) Hb 12 using Near-infrared Integral Field Spectrograph (NIFS) on Gemini-North. Combining NIFS with the adaptive optics system Altair, we provide a detailed study of the core and inner structure of this PN. We focus the analysis in the prominent emission lines [Fe II] (1.6436 μm), He I (2.0585 μm), H2 (2.1214 μm), and Brγ (2.16553 μm). We find that the [Fe II] emission traces a tilted system of bipolar lobes, with the northern lobe being redshifted and the southern lobe blueshifted. The [Fe II] emission is very faint at the core and only present close to the systemic velocity. There is no H2 emission in the core, whereas the core is prominent in the He I and Brγ recombination lines. The H2 emission is concentrated in equatorial arcs of emission surrounding the core and expanding at ~30 km s–1. These arcs are compared with Hubble Space Telescope images and shown to represent nested loops belonging to the inner sections of a much larger bipolar structure that replicates the inner one. The He I and Brγ emission from the core clearly show a cylindrical central cavity that seems to represent the inner walls of an equatorial density enhancement or torus. The torus is 02 wide (≡200 AU radius at a distance of 2000 pc) and expanding at ≤30 km s–1. The eastern wall of the inner torus is consistently more intense than the western wall, which could indicate the presence of an off-center star, such as is observed in the similar hourglass PN, MyCn 18. A bipolar outflow is also detected in Brγ emerging within 01 from the core at ~ ± 40 km s–1.