Morphologies of the Nebulae around "born-again" Central Stars of Planetary Nebulae

TL;DR

This paper investigates the diverse morphologies of nebulae around 'born-again' central stars of planetary nebulae, revealing that their ejecta are highly asymmetrical, contrasting with the more spherical shapes of typical planetary nebulae.

Contribution

It provides new insights into the morphological differences of nebulae around 'born-again' stars, highlighting their asymmetry compared to standard planetary nebulae.

Findings

Most planetary nebulae are not spherical.

'Born-again' nebulae exhibit extreme asymmetry.

Hydrogen-rich planetary nebulae tend to be more round.

Abstract

While in the past spherodicity 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 the case of those objects that underwent a very late helium flash (called VLTP objects 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, in contrast, are extremely asymmetrical.