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

TL;DR

This study uses 3D modeling to analyze Abell 14, revealing it as a highly evolved bipolar planetary nebula with shock interactions, challenging the born again scenario and providing insights into its progenitor and ionization structure.

Contribution

It presents the first detailed 3D morphological and ionization analysis of Abell 14, demonstrating its evolved state and the significance of shock interactions in its emission features.

Findings

Abell 14 is a highly evolved bipolar nebula with a kinematic age of ~19,400 years.

The central star is near the white dwarf cooling track, inconsistent with the born again scenario.

Strong [N I] and [O I] lines suggest shock interactions influence nebular emission.

Abstract

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