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Shock chemistry in the young bipolar outflow L 1157

R. Bachiller tex2html_wrap_inline729 and M. Pérez Gutiérrez tex2html_wrap_inline729
tex2html_wrap_inline729 Observatorio Astronómico Nacional, Apartado 1143, E-28800 Alcalá de Henares, Spain
Abstract: We present the first results from a recent survey of molecular lines in L1157, a highly-collimated bipolar molecular outflow driven by a Class 0 protostar. These observations are used to study the chemical alterations produced by a violent highly-collimated outflow. Different molecular lines are observed to trace different components of the gas. Some molecules (C tex2html_wrap_inline721 H tex2html_wrap_inline663 , N tex2html_wrap_inline663 H tex2html_wrap_inline699 , H tex2html_wrap_inline715 CO tex2html_wrap_inline699 , DCO tex2html_wrap_inline699 ) are abundant in the quiescent medium but are not observed at high velocities. Lines from these molecules are the best tracers of the concentration of dense gas around the protostar. In addition, we find that some otherwise rare molecules (e.g. SiO, CH tex2html_wrap_inline721 OH, H tex2html_wrap_inline663 CO, HCN, CN, SO, SO tex2html_wrap_inline663 ) are enhanced by at least an order of magnitude at the shocked region. Our observations provide estimates of the enhancement factors for such species. Strong gradients in the chemical composition are observed along the outflow blue lobe which could be due to the evolution in time of the chemical processes. We briefly discuss the chemistry of the most important molecules, devoting special attention to the species which are thought to be abundant in interstellar ice mantles.
Accepted by Astrophysical Journal Letters.