Multiple Fast Molecular Outflows in the PPN CRL 618

TL;DR

This study uses high-resolution observations to reveal multiple, episodic fast molecular outflows in the pre-planetary nebula CRL 618, suggesting magneto-rotational explosions as a possible driving mechanism.

Contribution

It provides the first detailed spatial resolution of multiple outflows in CRL 618, indicating episodic bullet ejections from the central star and lobes, advancing understanding of nebula shaping processes.

Findings

Multiple outflows have similar dynamical ages and are aligned with optical lobes.

Fast molecular outflows are detected near the tips of optical lobes and inside the dense torus.

Two episodes of bullet ejections are required to explain the observed outflow structures.

Abstract

CRL 618 is a well-studied pre-planetary nebula. It has multiple highly collimated optical lobes, fast molecular outflows along the optical lobes, and an extended molecular envelope that consists of a dense torus in the equator and a tenuous round halo. Here we present our observations of this source in CO J=3-2 and HCN J=4-3 obtained with the Submillimeter Array at up to ~ 0.3" resolutions. We spatially resolve the fast molecular-outflow region previously detected in CO near the central star and find it to be composed of multiple outflows that have similar dynamical ages, and are oriented along the different optical lobes. We also detect fast molecular outflows further away from the central star near the tips of the extended optical lobes and a pair of equatorial outflows inside the dense torus. We find that two episodes of bullet ejections in different directions are needed, one producing the fast molecular outflows near the central star, and one producing the fast molecular outflows near the tips of the extended optical lobes. One possibility to launch these bullets is the magneto-rotational explosion of the stellar envelope.