| Description |
During the earliest embedded stages of star formation the young star interacts with its surroundings through high velocity shocks and UV radiation, providing feedback on the medium from which the star is forming. At the same time, in-falling gas is heated to several 100 K by the accretion luminosity. How much energy is lost from the system through each of these processes? Is there an evolutionary trend in terms of the relative contributions from shocks and UV radiation? To address these questions and to observationally differentiate the different heating mechanisms, velocity-resolved observations are required.Herschel-PACS has revealed that highly excited CO emission (up to J=44-43; Eup virgul 5400 K) is present towards most low-mass protostars, revealing a warm/hot component not detected previously with ISO. The PACS observations reveal directly that CO is one of the best tracers of energetic processes in protostars. To quantify emission, a model was constructed incorporating the shock- and UV-heating mechanisms. While the model is successful in reproducing observations from three sources, it also makes very specific predictions regarding the line-shape of velocity-resolved high-J CO emission. The model furthermore predicts an evolutionary sequence where CO emission in younger sources is dominated by shock heating, as opposed to UV-heating being dominant at later evolutionary stages.To test the model and its validity for more than three sources, we propose to observe the highest excited CO line possible with HIFI, the CO 16-15 line. Velocity-resolved data will immediately allow us to quantify how much emission is caused by the different heating mechanisms. Furthermore, such data will allow us to measure the different heating contributions for this line directly, thus benchmarking our model and its underlying assumptions. |
