SIMBAD references

We investigate the origin of the small, chemically rich molecular clumps observed along the main axis of chemically rich outflows such as CB3 and L1157. We develop a chemical model where we explore the chemical evolution of these clumps, assuming that they either partially pre-exist before the outflow, or are newly formed by the impact of the outflow on the surrounding medium. The effects of the impact of the outflow are reproduced by density and temperature changes in the clump. We find that the observed abundances of CH₃OH, SO and SO₂are best reproduced by assuming a scenario where the dense molecular gas observed probably pre-exists in the interstellar medium before the formation of their exciting (proto)stars. We also find that the clumpiness and the rich chemistry of the clumps are a consequence of a pre-existing density enhancement and of its interaction with the outflow.