High-J CO emission in the Cepheus E protostellar outflow observed with
  SOFIA/GREAT
  We present and analyze two spectrally resolved high-J CO lines towards the
molecular outflow Cep E, driven by an intermediate-mass class 0 protostar.
Using the GREAT receiver on board SOFIA, we observed the CO (12--11) and
(13--12) transitions (E_u ~ 430 and 500 K, respectively) towards one position
in the blue lobe of this outflow, that had been known to display high-velocity
molecular emission. We detect the outflow emission in both transitions, up to
extremely high velocities (~ 100 km/s with respect to the systemic velocity).
We divide the line profiles into three velocity ranges that each have
interesting spectral features: standard, intermediate, and extremely
high-velocity. One distinct bullet is detected in each of the last two. A large
velocity gradient analysis for these three velocity ranges provides constraints
on the kinetic temperature and volume density of the emitting gas, >~ 100 K and
> ~ 10^4 cm^-3, respectively. These results are in agreement with previous ISO
observations and are comparable with results obtained by Herschel for similar
objects. We conclude that high-J CO lines are a good tracer of molecular
bullets in protostellar outflows. Our analysis suggests that different physical
conditions are at work in the intermediate velocity range compared with the
standard and extremely high-velocity gas at the observed position.
