Morphological study of the nested planetary nebula Hubble 12
  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
suggests that these structures originated from several mass-ejection events
during the pre-PN phase. To understand the intrinsic structures of Hb 12, a
three-dimensional model enabling the visualisation of this PN at various
orientations was 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 PN may be common and the morphologies of PNs are
not so diverse as is shown by their visual appearances. The infrared spectra
show that this PN has a mixed chemistry. We discuss the possible material that
may cause 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.
