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

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 (CO)-C-12, (CO)-C-13 and/or (CO)-O-18 in J = 3-2, J = 4-3 and J = 7-6 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 J = 14-13 up to J = 19-18 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 similar to 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 (CO)-C-12 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.