Shaping `Ears' in planetary nebulae by early jets

TL;DR

This study uses 3D hydrodynamical simulations to demonstrate that short-lived jets preceding the main planetary nebula shell can create ear-like protrusions, explaining their rare occurrence and dependence on jet properties.

Contribution

It introduces a new model showing that early, short-lived jets can form ears in planetary nebulae, linking their formation to common envelope evolution scenarios.

Findings

Jets must be not too energetic, wide, or slow to form ears.

Ears are formed by jets that are older than the main nebula shell.

Ears are rare, observed in only a small fraction of planetary nebulae.

Abstract

We conduct three dimensional hydrodynamical numerical simulations of planetary nebula (PN) shaping and show that jets that precede the ejection of the main PN shell can form the morphological feature of ears. Ears are two opposite protrusions from the main nebula that are smaller than the main nebula and with a cross section that decreases monotonically from the base of an ear at the shell to its far end. Only a very small fraction of PNe has ears. The short-lived jets, about a year in the present simulations, interact with the regular asymptotic giant branch (AGB) wind to form the ears, while the later blown dense wind forms the main PN dense shell. Namely, the jets are older than the main PN shell. We also find that for the jets to inflate ears they cannot be too energetic, cannot be too wide, and cannot be too slow. A flow structure where short-lived jets precede the main phase of nebula ejection by a few years or less can result from a system that enters a common envelope evolution. The low mass companion accretes mass through an accretion disk and launches jets just before it enters the envelope of the giant progenitor star of the PN. Shortly after that the companion enters the envelope and spirals-in to eject the envelope that forms the main PN shell.