Champagne Flutes and Brandy Snifters: Modelling Protostellar Outflow-Cloud Chemical Interfaces

TL;DR

This paper presents a chemo-dynamic model explaining the observed chemical compositions and shapes of protostellar outflow-cloud interfaces, highlighting the role of turbulence and ion injection in shaping molecular abundances.

Contribution

It introduces a new chemo-dynamic model that accounts for the geometry-dependent ion injection and turbulence, explaining observational biases and molecular abundances.

Findings

Wide-angled outflows have higher HCO+ abundances.

Ion-neutral chemistry is driven by turbulent mixing.

Model explains the shape bias in CO imaging.

Abstract

A rich variety of molecular species has now been observed towards hot cores in star forming regions and in the interstellar medium. An increasing body of evidence from millimetre interferometers suggests that many of these form at the interfaces between protostellar outflows and their natal molecular clouds. However, current models have remained unable to explain the origin of the observational bias towards wide-angled "brandy snifter" shaped outflows over narrower "champagne flute" shapes in carbon monoxide imaging. Furthermore, these wide-angled systems exhibit unusually high abundances of the molecular ion HCO$^+$. We present results from a chemo-dynamic model of such regions where a rich chemistry arises naturally as a result of turbulent mixing between cold, dense molecular gas and the hot, ionized outflow material. The injecta drives a rich and rapid ion-neutral chemistry in qualitative and quantitative agreement with the observations. The observational bias towards wide-angled outflows is explained naturally by the geometry-dependent ion injection rate causing rapid dissociation of CO in the younger systems.