Origin of the Shell Structure in the Primary Outflow from IRAS 15398-3359

TL;DR

This paper investigates the shell structure in the primary outflow of IRAS 15398-3359, proposing it results from repeated expansion and compression similar to underexpanded jets in engineering, revealing insights into star formation processes.

Contribution

It introduces a novel analogy between astrophysical outflows and industrial underexpanded jets, suggesting a new explanation for the shell structure in protostellar outflows.

Findings

Shell structure observed in IRAS 15398-3359's outflow.

Similarity between astrophysical outflows and underexpanded jets.

Proposed mechanism of repeated expansion and compression.

Abstract

IRAS 15398-3359, a Class 0 protostar in Lupus I star forming region, is associated with three generations of outflows. The primary outflow, i.e., the most recent one, shows internal structure named ``shell structure'' in the near infrared emission map. The shell structure is also seen in the emission lines of CO, H$_2$CO, and others species. We find a similar structure in an underexpanded jet produced in aerodynamics and other engineering applications. A high pressure gas ejected through a nozzle expands to form a supersonic flow. When the pressure of the ejected gas becomes lower than that of the ambient gas, the jet is compressed to form a shock wave. The shock heated gas expands again to form substructures along the jet. We examine the similarity between the primary outflow of IRAS 15398-3359 and industrial underexpanded jet and the possibility that the shell structure of the former is due to repeated expansion and compression in the direction perpendicular to the jet propagation.