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

¹ Thüringer Landessternwarte, Sternwarte 5, 07778 Tautenburg, Germany
e-mail: jochen@tls-tautenburg.de
² INAF-Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monteporzio Catone, Italy
³ Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁴ LERMA, UMR 8112 du CNRS, Observatoire de Paris, École Normale Supérieure, 24 rue Lhomond, 75231 Paris Cedex 05, France

Received: 27 January 2012
Accepted: 5 March 2012

Abstract

Context. Carbon monoxide is an excellent tracer of the physical conditions of gas in molecular outflows from young stars.

Aims. 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.

Methods. We observed CO (12–11) line emission at various positions along the L1157 bipolar outflow with GREAT aboard SOFIA.

Results. 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 10⁵ to 10⁶ cm^-3 for the gas density and 60 to 100 K for the gas temperature of the outflowing gas.

Conclusions. 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.