SOFIA observations of CO(12-11) emission along the L1157 bipolar outflow

TL;DR

This study uses SOFIA observations of CO(12-11) emission along the L1157 bipolar outflow to analyze gas physical conditions, revealing consistent line ratios and identifying a low-velocity, intermediate-temperature gas component.

Contribution

First detailed CO(12-11) emission measurements along the L1157 outflow, providing new constraints on gas density and temperature in the outflow region.

Findings

Constant line ratios along the outflow

Gas density estimated between 10^5 and 10^6 cm^-3

Gas temperature estimated between 60 and 100 K

Abstract

Carbon monoxide is an excellent tracer of the physical conditions of gas in molecular outflows from young stars. To understand the outflow mechanism we need to investigate the origin of the molecular emission and the structure and interaction of the outflowing molecular gas. Deriving the physical parameters of the gas will help us to trace and understand the various gas components in the flow. We observed CO(12-11) line emission at various positions along the L1157 bipolar outflow with GREAT aboard SOFIA. Comparing these new data with CO(2-1), we find basically constant line ratios along the outflow and even at the position of the source. These line ratios lead us to estimates of 10^5 to 10^6 cm^-3 for the gas density and 60 to 100 K for the gas temperature of the outflowing gas. The constrained density and temperature values indicate that we are mostly tracing a low-velocity gas component everywhere along the outflow, which is intermediate between the already known cold gas component, which gets entrained into the flow, and the hot gas, which gets shocked in the outflow.