Morphological study of the nested planetary nebula Hubble 12

Abstract

We present a visible-infrared imaging study of young planetary nebula (PN) Hubble 12 (Hb 12; PN G111.8-02.8) obtained with Hubble Space Telescope (HST) archival data and our own Canada-France-Hawaii Telescope (CFHT) measurements. Deep HST and CFHT observations of this nebula reveal three pairs of bipolar structures and an arc-shaped filament near the western waist of Hb 12. The existence of nested bipolar lobes, together with the presence of H2 knots, suggest that these structures are originated from several mass-ejection events during Pre-PN phase. To understand the intrinsic structures of Hb 12, a three-dimensional model enabling the visualization of this PN at various orientations is constructed. The modelling results show that Hb 12 may resemble other nested hourglass nebulae, such as Hen 2-320 and M 2-9, suggesting that this type of PNs may be common and the morphology of PNs are not so diverse as that shown by their visual appearances. The infrared spectra show that this PN has a mixing chemistry. We discuss the possible material responsible for the unidentified infrared emissions. The analyses of the infrared spectra and the spectral energy distribution suggest the existence of a cool companion in the nucleus of this object