Shock-type inference of L1157 B2 using methanol desorption

Context . Shock types of low-velocity molecular outflows are not always well constrained. Astrochemical comparisons are often made between low-velocity and high-velocity outflows, but without considering the question of the shock type. Aims . We investigated molecular abundances of post-shock regions to determine whether strong differences between non-irradiated C-type and J-type shocks can be highlighted. One of the main application goals is to diagnose the shock type of the protostellar object L1157 B2 through the use of molecular tracers. Methods . We simulated grid sets of shock models with the Paris-Durham Shock code with velocities ranging from 5 to 19 km/s and low densities from 10 2 to 10 5 cm −3 . We computed the desorption percentage of methanol in these simulations and estimated it at higher velocities. We compared our results to observational measurements of L1157 B2 and with a benchmark of four already identified shocks. Results . L1157 B2 has been diagnosed as a non-irradiated C-type shock, and the method showed a good applicability through the benchmark. Methanol formed in the icy mantle of grains can serve to trace the differences between shock types, at least in non-irradiated conditions. A requirement for the applicability of a species as a shock-type tracer is that it does not undergo significant enhancement or destruction, but is mainly impacted by desorption processes under shocked conditions. Conclusions . The desorption percentage of methanol is a good criterion in characterizing the shock type of L1157 B2 and should be investigated as a general method to diagnose the shock type in non-irradiated regions. We identify L1157 B2 as a non-irradiated C-type shock with velocities and densities fitting with previous studies.