Context : OH is a key molecule in H _ { 2 } O chemistry , a valuable tool for probing physical conditions , and an important contributor to the cooling of shock regions around high-mass protostars .
OH participates in the re-distribution of energy from the protostar towards the surrounding Interstellar Medium .

Aims : Our aim is to assess the origin of the OH emission from the Cepheus A massive star-forming region and to constrain the physical conditions prevailing in the emitting gas .
We thus want to probe the processes at work during the formation of massive stars .

Methods : We present spectrally resolved observations of OH towards the protostellar outflows region of Cepheus A with the GREAT spectrometer onboard the Stratospheric Observatory for Infrared Astronomy ( SOFIA ) telescope .
Three triplets were observed at 1834.7 GHz , 1837.8 GHz , and 2514.3 GHz ( 163.4 \mu m , 163.1 \mu m between the ^ { 2 } \Pi _ { 1 / 2 } J = 3 / 2 and J = 1 / 2 states , and 119.2 \mu m , a ground transition between the ^ { 2 } \Pi _ { 3 / 2 } J = 5 / 2 and J = 3 / 2 states ) , at angular resolutions of 16 \aas@@fstack { \prime \prime } 3 , 16 \aas@@fstack { \prime \prime } 3 , and 11 \aas@@fstack { \prime \prime } 9 , respectively .
We also present the CO ( 16–15 ) spectrum at the same position .
We compared the integrated intensities in the redshifted wings to the results of shock models .

Results : The two OH triplets near 163 \mu m are detected in emission , but with blending hyperfine structure unresolved .
Their profiles and that of CO ( 16–15 ) can be fitted by a combination of two or three Gaussians .
The observed 119.2 \mu m triplet is seen in absorption , since its blending hyperfine structure is unresolved , but with three line-of-sight components and a blueshifted emission wing consistent with that of the other lines .
The OH line wings are similar to those of CO , suggesting that they emanate from the same shocked structure .

Conclusions : Under this common origin assumption , the observations fall within the model predictions and within the range of use of our model only if we consider that four shock structures are caught in our beam .
Overall , our comparisons suggest that all the observations might be consistently fitted by a J-type shock model with a high pre-shock density ( n _ { H } > 10 ^ { 5 } cm ^ { -3 } ) , a high shock velocity ( \varv _ { s } \gtrsim 25 km s ^ { -1 } ) , and with a filling factor of the order of unity .
Such a high pre-shock density is generally found in shocks associated to high-mass protostars , contrary to low-mass ones .