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 Nearinfrared 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), H 2 (2.1214 μm), and Br γ (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 H 2 emission in the core, whereas the core is prominent in the He i and Br γ recombination lines. The H 2 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 Br γ 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 0. 2 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 Br γ emerging within 0. 1 from the core at ∼±40 km s −1 .

SALT HRS Discovery of the Binary Nucleus of the Etched Hourglass Nebula MyCn 18

“…It is particularly notable for its intriguing nested hourglass structure (Sahai et al 1999; Clyne et al 2014) that closely resembles the nebular remnant of SN 1987A (e.g. Burrows et al 1995; Sugerman et al 2005), the symbiotic nebula Hen 2-104 (Corradi & Schwarz 1993; Corradi et al 2001; Santander-García et al 2008; Clyne et al 2015), and Hb 12 which may be a young PN or possibly a symbiotic nebula (Hsia, Ip, & Li 2006; Kwok & Hsia 2007; Vaytet et al 2009; Clark et al 2014). There are also strong similarities with bipolar and hourglass nebulae around several luminous blue variables (e.g.…”

Morphological study of the nested planetary nebula Hubble 12

“…The F175W image reveals one more pair of lobes (marked 'primary lobe') located outside the ionised and secondary lobes, which form a complex nested eyelike features in the equatorial region. An eye-like structure like this is also visible in the HST F215N, F212N, F160W, F110W (Hora et al 2000;Kwok & Hsia 2007;Clark et al 2014), and H 2 images (Hora & Latter 1996;Fang et al 2018), which is probably due to the intersection of the inclined outer bipolar structures (primary lobe and secondary lobe). From the F175W image, we also note that the eastern side of the outermost lobe is generally fainter than the western side.…”

“…Interactions in binary nuclei might play a major role in the shaping of PNs. The nested hourglass PNs belong to a particular group of young bipolar nebulae, which are in a short transitional stage evolving towards developed bipolar lobe (Clark et al 2014). The nested bipolar structures could be (i) produced by multiple eruptive mass ejection events in the common-envelope (CE) evolutionary stage (Corradi et al 2014), (ii) the result of practically coeval lobes, which is similar to the PN Hen 2-104 (Corradi et al 2001), or (iii) the result of an ionisation gradient excited by far-UV photons from the central source, as suggested in PN M 2-9 (Smith et al 2005).…”

Fallback in bipolar Planetary Nebulae ?

“…Two of the prominent hourglass sources, Hb 12 and MyCn 18, show a Spiderweb arc structure in the equatorial plane of the system (perpendicular to the hourglass) that has (following tradition) been explained by repeated stellar wind outflows (Clark et al 2014;Sahai et al 1999), by sequential ejections resulting from a thermal nuclear runaway (Kwok & Hsia 2007), or by episodes of activity during earlier evolutionary stages (Vaytet et al 2009). However, there is no clear explanation for a simultaneous outflow along the polar axis and the structure in the equatorial plane.…”

“…Since the bipolar PNe do not show any ionised shells that are characteristic of evolved PN, they seem to be either at a very early evolutionary stage or at the end of PN evolution. The suggestion has indeed been made for these to be low-excitation and young sources that only recently started ionising their surrounding shells and represent a short transition stage toward full development (Clark et al 2014).…”