Catching a grown-up starfish planetary nebula – I. Morpho-kinematical study of PC 22

Abstract We present the first part of an investigation on the planetary nebula (PN) PC 22 that focuses on the use of deep imaging and high-resolution echelle spectroscopy to perform a detailed morpho-kinematical analysis. PC 22 is revealed to be a multipolar PN emitting predominantly in [O iii] and displaying multiple non-symmetric outflows. Its central region is found to be also particularly inhomogeneous with a series of low-ionization structures (knots) located on the path of the outflows. The morpho-kinematical model obtained with shape indicates that (i) the de-projected velocities of the outflows are rather large, ≥100 km s−1, while the central region has expansion velocities in the range ∼25 to ∼45 km s−1 following the ‘Wilson effect’; (ii) the majority of the measured structures share similar inclination, ≃100°, i.e. they are coplanar; (iii) and all outflows and lobes are coeval (within the uncertainties). All these results make us to suggest that PC 22 is an evolved starfish PN. We propose that the mechanism responsible for the morphology of PC 22 consists of a wind-shell interaction, where the fast post-asymptotic giant branch (AGB) wind flows through a filamentary AGB shell with some large voids.