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

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 C 18O 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 ∼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. © ESO 2006.