Fast molecular jet from L1157-mm.

Context. L1157-mm powers a molecular outflow that is well-known for its shock-induced chemical activity in several hot-spots. Aims. We have studied the molecular emission toward L1157-mm searching for a jet component responsible for these spots. Methods. We used the IRAM 30 m telescope to observe the vicinity of L1157-mm in several lines of SiO. Results. The SiO(5-4) and SiO(6-5) spectra toward L1157-mm present blue and red detached components about 45 km s-1 away from the ambient cloud. These extremely high-velocity (EHV) components are similar to those found in the L1448 and IRAS 04166+2706 outflows and probably arise from a molecular jet driven by L1157-mm. Observations of off-center positions indicate that the jet is unresolved in SiO(5-4) (<11"). Conclusions. The EHV jet seen in SiO probably excites L1157-B1 and the other chemically active spots of the L1157 outflow. [ABSTRACT FROM AUTHOR]