Models of the Mass-Ejection Histories of pre Planetary Nebulae, IV. Magnetized Winds and the Origins of Jets, Bullets, and FLIERs

TL;DR

This paper investigates how toroidal magnetic fields in stellar winds influence the shaping of pre planetary nebulae, revealing the formation of jets, bullets, and FLIERs through magnetically driven structures.

Contribution

It introduces a model incorporating magnetic fields into stellar winds, explaining the formation of dense axial features and knots in pre planetary nebulae.

Findings

Toroidal fields create thin, dense jets and bullets at the nebula's axis.

The speed of knots depends on density contrast and wind velocity, not magnetic strength.

About 20% of observed prePNe show signatures of magnetic shaping.

Abstract

The influences and consequences of toroidal magnetic fields in shaping the visible lobes of pre planetary nebulae ("prePNe") are explored in this, the last of a series of papers of parameter studies of prePN evolution. To probe these influences we start with the steady, diverging, and field-free wind model of our previous papers and add weak to moderate toroidal fields to the winds in order to generate arrays of outcomes after 500 y, after which the structures grow almost homologously. As expected, toroidal fields in the stellar winds invariably form very thin and dense axial features whose structure is best described as a thin cold jet with an ultra-dense and neutral leading knot, or "bullet", at its tip. The speed of the leading knot depends only on the density contrast (the ratio of injected to ambient gas densities at the nozzle) and wind injection speed, but not on the field strength or opening angle. The lobes formed by the ram pressure of the winds take a variety of forms and sizes that depend primarily on the geometric structure of the injected gas and the density contrast. About 20% of the HST images of prePNe show the unique signatures of shaping by toroidal fields. Pairs of low-ionization knots seen along the major axis of fully ionized PNe, often called "FLIERs" are easily explained as the very dense, cold , and neutral remnants of magnetically formed knots.