Impacts of pure shocks in the BHR71 bipolar outflow
  During the formation of a star, material is ejected along powerful jets that
impact the ambient material. This outflow regulates star formation by e.g.
inducing turbulence and heating the surrounding gas. Understanding the
associated shocks is therefore essential to the study of star formation. We
present comparisons of shock models with CO, H2, and SiO observations in a
'pure' shock position in the BHR71 bipolar outflow. These comparisons provide
an insight into the shock and pre-shock characteristics, and allow us to
understand the energetic and chemical feedback of star formation on Galactic
scales. New CO (Jup = 16, 11, 7, 6, 4, 3) observations from the shocked regions
with the SOFIA and APEX telescopes are presented and combined with earlier H2
and SiO data (from the Spitzer and APEX telescopes). The integrated intensities
are compared to a grid of models that were obtained from a
magneto-hydrodynamical shock code which calculates the dynamical and chemical
structure of these regions combined with a radiative transfer module based on
the 'large velocity gradient' approximation. The CO emission leads us to update
the conclusions of our previous shock analysis: pre-shock densities of 1e4 cm-3
and shock velocities around 20-25 km s-1 are still constrained, but older ages
are inferred ( 4000 years). We evaluate the contribution of shocks to the
excitation of CO around forming stars. The SiO observations are compatible with
a scenario where less than 4% of the pre-shock SiO belongs to the grain
mantles. We infer outflow parameters: a mass of 1.8x1e-2 Msun was measured in
our beam, in which a momentum of 0.4 Msun km s-1 is dissipated, for an energy
of 4.2x1e43erg. We analyse the energetics of the outflow species by species.
Comparing our results with previous studies highlights their dependence on the
method: H2 observations only are not sufficient to evaluate the mass of
outflows.
