SIMBAD references

Images of the elliptical planetary nebula NGC 7009 have been obtained with narrow band filters centred in most of the main optical emission lines. The Hα and [OIII]5007A images reveal an extended, high excitation circular halo around the central elliptical body of the planetary. A [SIII]9069A image shows a localized outer condensation, previously unreported. Bidimensional plasma diagnostics have been obtained. The halo is entirely excited by photons, whereas gas dynamical effects play an important role in determining the shape and excitation of the inner regions. The existence of bow shocks may be inferred from images of forbidden to Balmer line ratios. If the shape of the inner nebula is due to rotation of the planetary nebula nucleus (PNN), the progenitor of NGC 7009 probably was a main sequence star of about 2M_☉, and the mass of the halo is approximately 1M_☉. The inner nebula contains two rings of material, probably related to episodic mass loss events. The rings are not aligned. If this misalignment is due to precession of the PNN, we find a precession period of approximately 30,000 years. If precession is being driven by a companion star, the latter is located ∼4.5R_☉ from the PNN. No common envelope would be expected at the present stage of evolution of this system.