PPN as Explosions: Bullets vs Jets and Nebular Shaping

TL;DR

This paper compares jet and bullet models for proto-planetary nebulae outflows, finding bullets better explain observed collimation, ring structures, and multipolar flows, suggesting explosive MHD mechanisms as the driving process.

Contribution

It demonstrates that bullet models more accurately reproduce PPN features than jet models, proposing explosive MHD processes as the outflow mechanism.

Findings

Bullets lead to greater collimation of outflows.

Bullets better explain ring-like structures in PPN CRL 618.

Bullets reproduce the Hubble-flow kinematics in some PPN.

Abstract

Many proto-planetary nebulae (PPN) appear as narrow collimated structures sometimes showing multiple, roughly aligned lobes. In addition, many PPN flows have been shown to have short acceleration times. In this paper we explore whether jet or ``bullet'' (a massive clump) models fit the observations of individual collimated lobes adequately by comparing simulations of both radiatively cooled (stable) jets and bullets. We find that the clump model is somewhat favored over jets because (1) it leads to greater collimation of outflows (2) it accounts better and more naturally for ring-like structures observed in the PPN CRL 618, and (3) it is more successful in reproducing the Hubble-flow character of observed kinematics in some PPN. In addition, bullets naturally account for observed multipolar flows, since the likely MHD launch mechanisms required to drive outflows make multiple non-aligned jets unlikely. Thus we argue that PPN outflows may be driven by explosive MHD launch mechanisms such as those discussed in the context of supernovae (SNe) and gamma-ray bursts(GRB).