Symmetry and Asymmetry in "born again" Planetary Nebulae

TL;DR

This paper discusses the morphological diversity of planetary nebulae, especially focusing on the symmetry and asymmetry in 'born-again' PNe resulting from very late helium flashes, and explores the role of angular momentum and abundance variations.

Contribution

It highlights the distinct asymmetrical features of 'born-again' planetary nebulae and investigates the processes influencing their shape changes over short timescales.

Findings

Round PNe are a minority among nebulae.

'Born-again' PNe exhibit extreme asymmetry in ejecta.

Angular momentum and abundance variations likely influence nebula morphology.

Abstract

While in the past spheroidicity was assumed, and still is used in modeling of most nebulae, we know now that only a small number of planetary nebulae (PNe) are really spherical or at least nearly round. Round planetary nebulae are the minority of objects. In case of those objects that underwent a very late helium flash (called VLTP or "born-again" PNe) it seems to be different. The first, hydrogen rich PN, is more or less round. The ejecta from the VLTP event is extremely asymmetrically. Angular momentum is mostly assumed to be the main reason for the asymmetry in PNe. Thus we have to find processes either changing their behavior within a few hundred to a few thousands of years or change their properties dramatically due to the variation of the abundance. They most likely have a strong link or dependency with the abundance of the ejecta.