Shaping the envelope of the asymptotic giant branch star W43A with a collimated fast jet

TL;DR

This study presents the first CO emission observations of the jet from the AGB star W43A, revealing its velocity, interaction with circumstellar material, and simultaneous formation with a bipolar shell, offering insights into planetary nebulae shaping.

Contribution

It provides the first detailed CO emission data tracing the jet from W43A, elucidating its launch velocity, deceleration, and role in shaping bipolar nebulae.

Findings

Jet launch velocity of 175 km/s, decelerating to 130 km/s.

Jet and bipolar shell have equal kinematical ages (~60 years).

Results inform models of bipolar planetary nebula formation.

Abstract

One of the major puzzles in the study of stellar evolution is the formation process of bipolar and multi-polar planetary nebulae. There is growing consensus that collimated jets create cavities with dense walls in the slowly-expanding (10--20 ~km~s$^{-1}$) envelope ejected in previous evolutionary phases, leading to the observed morphologies. However, the launching of the jet and the way it interacts with the circumstellar material to create such asymmetric morphologies have remained poorly known. Here we present for the first time CO emission from the asymptotic giant branch star W43A that traces the whole stream of a jet, from the vicinity of its driving stellar system out to the regions where it shapes the circumstellar envelope. We found that the jet has a launch velocity of 175~km~s$^{-1}$ and decelerates to a velocity of 130~km~s$^{-1}$ as it interacts with circumstellar material. The continuum emission reveals a bipolar shell with a compact bright dot in the centre that pinpoints the location of the driving source of the jet. The kinematical ages of the jet and the bipolar shell are equal, $\tau$$\sim$60~years, indicating that they were created simultaneously, probably by a common underlying mechanism, and in an extremely short time. These results provide key initial conditions for the theoretical models that aim to explain the formation of bipolar morphologies in the circumstellar envelopes of low and intermediate mass stars.