A Fast bipolar H2 outflow from IRAS 16342-3814: an old star reliving its youth

TL;DR

This paper reports the discovery of a fast bipolar H2 outflow from the evolved star IRAS 16342-3814, resembling protostellar jets, likely powered by accretion onto a binary companion, indicating a reactivation of youthful outflow activity.

Contribution

It provides the first detailed spectroscopic evidence of a protostar-like outflow in an evolved star, highlighting accretion-driven jet mechanisms in the late stellar evolution stage.

Findings

Detected a >150 km/s bipolar H2 outflow in IRAS 16342-3814.

H2 emission is shock excited and comparable in luminosity to protostellar outflows.

Presence of hot molecular gas near the center suggests active accretion processes.

Abstract

Some evolved stars in the pre-planetary nebula phase produce highly-collimated molecular outflows that resemble the accretion-driven jets and outflows from pre-main sequence stars. We show that IRAS 16342-3814 (the Water Fountain Nebula) is such an object and present K-band integral field spectroscopy revealing a fast (> 150 km/s) bipolar H2 outflow. The H2 emission is shock excited and may arise in fast-moving clumps, accelerated by the previously observed precessing jet. The total luminosity in H2 is 0.37 L$_{\odot}$ which is comparable with that of accretion-powered outflows from Class 0 protostars. We also detect CO overtone bandhead emission in the scattered continuum, indicating hot molecular gas close to the centre, a feature also observed in a number of protostars with active jets. It seems likely that the jet and outflow in IRAS 16342-3814 are powered by accretion onto a binary companion.