Letter to the Editor

Warm molecular gas in the envelope and outflow of IRAS 12496-7650 (DK Chamaeleontis)

¹ Leiden Observatory, Leiden University Niels Bohrweg 2, 2333 CA, Leiden, The Netherlands e-mail: kempen@strw.leidenuniv.nl
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³ European Southern Observatory, Casille 19001, Santiago, Chile

Received: 31 March 2006
Accepted: 9 May 2006

Abstract

Aims.To obtain insight into the physical structure of the warm gas in the inner envelope of protostars and the interaction with the outflow.

Methods.Sub-millimeter observations of ¹²CO, ¹³CO and/or C¹⁸O in –2, –3 and –6 were obtained with the APEX Telescope towards IRAS 12496-7650, an intermediate mass young stellar object. The data are compared to ISO-LWS observations of CO –13 up to –18 lines to test the different proposed origins of the CO lines.

Results.The outflow is prominently detected in the 3–2 and 4–3 lines, but not seen at similar velocities in the 7–6 line, constraining the temperature in the high-velocity (>5 km s^-1 from line center) gas to less than 50 K, much lower than inferred from the analysis of the ISO-LWS data. In addition, no isothermal gas model can reproduce the emission in both the 7–6 and the higher-J ISO-LWS lines. The 7–6 line probably originates in the inner (<250 AU) region of the envelope at ~150 K. Detailed radiative transfer calculations suggest that the ISO-LWS lines are excited by a different mechanism, possibly related to the larger-scale outflow. All possible mechanisms on scales smaller than 8'' are excluded. High-resolution continuum as well as high-J ¹²CO and isotopic line mapping are needed to better constrain the structure of the warm gas in the inner envelope and the interaction with the outflow.