Morpho-kinematic and photoionization models of the multipolar structures in planetary nebula NGC 6572

Abstract

We have studied planetary nebula (PN) NGC 6572 through 3D morpho-kinematic and photoionization modelling. The 3D morphology is reconstructed from the Hubble Space Telescope images in different narrow-band filters and position–velocity spectra. The PN has a multipolar morphology consisting of highly collimated outflows. The nebular image shows signatures of multiple lobes within a spiral-ring-like structure. The multipolar structure is modelled with two bipolar shells (axes ratios ∼5.5:1 and ∼3:1), having closed and open lobes, respectively. A toroidal structure (radius:height ∼ 1:3) surrounds the shells at the waist. The toroidal axis aligns with the major axes of the bipolar shells. Our study reveals the nebula to have a history of collimated polar outflow perpendicular to a higher density equatorial wind with the outflow seemingly having episodes of changing direction of ejection. We construct a photoionization model of NGC 6572 using the optical spectra obtained at the 2 m Himalayan Chandra Telescope. For the photoionization model, we configure the input shell geometry in the form of a highly bipolar nebular shell with reference to the 3D morphology. Our photoionization model satisfactorily reproduces the observables. We estimate nebular elemental abundances, and important characteristic parameters of the central star (e.g. effective temperature, luminosity, gravity, mass, etc.) and the nebula (e.g. hydrogen density profiles, radii, etc.). We compare the resolved H β, [O III], and [N II] profiles obtained using the 4.2 m William Herschel Telescope with that from the photoionization model and find a good characteristic match.