Tracing shock type with chemical diagnostics: an application to L1157
  Aims: The physical structure of a shock wave may take a form unique to its
shock type, implying that the chemistry of each shock type is unique as well.
We aim to investigate the different chemistries of J-type and C-type shocks in
order to identify unique molecular tracers of both shock types. We apply these
diagnostics to the protostellar outflow L1157 to establish whether the B2 clump
could host shocks exhibiting type-specific behaviour. Of particular interest is
the L1157-B2 clump, which has been shown to exhibit bright emission in
S-bearing species and HNCO.
  Methods: We simulate, using a parameterised approach, a planar, steady-state
J-type shock wave using UCLCHEM. We compute a grid of models using both C-type
and J-type shock models to determine the chemical abundance of shock-tracing
species as a function of distance through the shock and apply it to the L1157
outflow. We focus on known shock-tracing molecules such as H2O, HCN, and CH3
OH.
  Results: We find that a range of molecules including H2O and HCN have unique
behaviour specific to a J-type shock, but that such differences in behaviour
are only evident at low $v_{s}$ and low $n_{H}$. We find that CH3OH is enhanced
by shocks and is a reliable probe of the pre-shock gas density. However, we
find no difference between its gas-phase abundance in C-type and J-type shocks.
Finally, from our application to L1157, we find that the fractional abundances
within the B2 region are consistent with both C-type and J-type shock emission.
