  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 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 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.
