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Abell 14 is a poorly studied object despite being considered a born againplanetary nebula. We performed a detailed study of its 3D morphology andionization structure using the SHAPE and MOCASSIN codes. We found that Abell 14is a highly evolved, bipolar nebula with a kinematical age of $\sim$19,400 yrfor a distance of 4 kpc. The high He abundance, and N/O ratio indicate aprogenitor of 5 $M_{\odot}$ that has experienced the third dredge-up and hotbottom burning phases. The stellar parameters of the central source reveal astar at a highly evolved stage near to the white dwarf cooling track, beinginconsistent with the born again scenario. The nebula shows unexpectedly strong[N I] $\lambda 5200$ and [O I] $\lambda 6300$ emission lines indicatingpossible shock interactions. Abell 14 appears to be a member of a small groupof highly evolved, extreme Type-I PNe. The members of this group lie at thelower-left corner of the PNe regime on the [N II]/H$\alpha$ vs. [SII]/H$\alpha$ diagnostic diagram, where shock--excited regions/objects are alsoplaced. The low luminosity of their central stars, in conjunction with thelarge physical size of the nebulae, result in a very low photo-ionization rate,which can make any contribution of shock interaction easily perceptible, evenfor small velocities.

Deciphering the bipolar planetary nebula Abell 14 with 3D ionization and morphological studies