We present Atacama Pathfinder EXperiment ( APEX ) observations toward the massive star-forming region \objectname G240.31+0.07 in the CO J = 3–2 , 6–5 , and 7–6 lines .
We detect a parsec-sized , bipolar , and high velocity outflow in all the lines , which allow us , in combination with the existing CO J = 2–1 data , to perform a multi-line analysis of physical conditions of the outflowing gas .
The CO 7–6/6–5 , 6–5/3–2 , and 6–5/2–1 ratios are found to be nearly constant over a velocity range of \sim 5–25 km s ^ { -1 } for both blueshifted and redshifted lobes .
We carry out rotation diagram and large velocity gradient ( LVG ) calculations of the four lines , and find that the outflow is approximately isothermal with a gas temperature of \sim 50 K , and that the the CO column density clearly decreases with the outflow velocity .
If the CO abundance and the velocity gradient do not vary much , the decreasing CO column density indicates a decline in the outflow gas density with velocity .
By comparing with theoretical models of outflow driving mechanisms , our observations and calculations suggest that the massive outflow in G240.31+0.07 is being driven by a wide-angle wind and further support a disk mediated accretion at play for the formation of the central high-mass star .