Pre-planetary nebulae: a context for principles, progress, and questions on how binaries and magnetic fields produce jets

TL;DR

This paper reviews how binary interactions and magnetic fields influence the formation of asymmetric jets in pre-planetary nebulae, highlighting two main accretion-driven jet classes and discussing open questions.

Contribution

It categorizes two classes of PPN jets based on binary separation and explores the role of magnetic fields in jet formation and shaping.

Findings

Two broad classes of PPN jets identified: PPN-W and PPN-C.

Progress in observations and theory links magnetic fields to jet engines.

Open questions remain about magnetic field origins and jet mechanisms.

Abstract

Astrophysical outflows treated initially as spherically symmetric often show evidence for asymmetry once seen at higher resolution. The preponderance of aspherical and multipolar planetary nebulae (PN) and pre-planetary nebulae (PPN) was evident after many observations from the Hubble Space Telescope. Binary interactions have long been thought to be essential for shaping asymmetric PN/PPN, but how? PPN are the more kinematically demanding of the two, and warrant particular focus. I address how progress from observation and theory suggests two broad classes of accretion driven PPN jets: one for wider binaries (PPN-W) where the companion is outside the outer radius of the giant and accretes via Roche lobe overflow, and the other which occurs in the later stages of common envelope evolution (CEE) for close binaries (PPN-C). The physics within these scenarios connects to progress and open questions about the role and origin of magnetic fields in the engines and in astrophysical jets more generally.