Context : Protostellar jets and outflows are key features of the star-formation process , and primary processes of the feedback of young stars on the interstellar medium .
Understanding the underlying shocks is necessary to explain how jet and outflow systems are launched , and to quantify their chemical and energetic impacts on the surrounding medium .

Aims : We performed a high-spectral resolution study of the [ OI ] _ { 63 \mu m } emission in the outflow of the intermediate-mass Class 0 protostar Cep E-mm .
The goal is to determine the structure of the outflow , to constrain the chemical conditions in the various components , and to understand the nature of the underlying shocks , thus probing the origin of the mass-loss phenomenon .

Methods : We present observations of the O I ^ { 3 } P _ { 1 } \rightarrow ^ { 3 } P _ { 2 } , OH between ^ { 2 } \Pi _ { 1 / 2 } J = 3 / 2 and J = 1 / 2 at 1837.8 GHz , and CO ( 16–15 ) lines with the GREAT receiver onboard SOFIA towards three positions in the Cep E protostellar outflow : Cep E-mm ( the driving protostar ) , Cep E-BI ( in the southern lobe ) , and Cep E-BII ( the terminal position in the southern lobe ) .

Results : The CO ( 16–15 ) line is detected at all three positions .
The [ OI ] _ { 63 \mu m } line is detected in Cep E-BI and BII , whereas the OH line is not detected .
In Cep E-BII , we identify three kinematical components in O I and CO .
These were already detected in CO transitions and relate to spatial components : the jet , the HH377 terminal bow-shock , and the outflow cavity .
We calculate line temperature and line integrated intensity ratios for all components .
The O I column density is higher in the outflow cavity than in the jet , which itself is higher than in the terminal shock .
The terminal shock is the region where the abundance ratio of O I to CO is the lowest ( about 0.2 ) , whereas the jet component is atomic ( N ( O I ) / N ( CO ) \sim 2.7 ) .
In the jet , we compare the [ OI ] _ { 63 \mu m } observations with shock models that successfully fit the integrated intensity of 10 CO lines .
We find that these models most likely do not fit the [ OI ] _ { 63 \mu m } data .

Conclusions : The high intensity of O I emission points towards the propagation of additional dissociative or alternative FUV-irradiated shocks , where the illumination comes from the shock itself .
A picture emerges from the sample of low-to-high mass protostellar outflows , where similar observations have been performed , with the effects of illumination increasing with the mass of the protostar .
These findings need confirmation with more observational constraints and a larger sample .