Shocked water in the Cepheus e protostellar outflow

Abstract

Context. Previous far-infrared observations at low-angular resolution have reported the presence of water associated with low-velocity outflow shocks and protostellar envelopes. Aims. We want to elucidate the origin of water emission in protostellar systems. Methods. The outflow driven by the intermediate-mass class 0 protostar Cep E is among the most luminous outflows detected so far. Using the IRAM 30 m telescope, we searched for and detected the p-H2O 313-220 line emission at 183GHz in the Cep E star-forming core. The emission arises from high-velocity gas close to the protostar, which is unresolved in the main beam of the telescope. Complementary observations at 2″ resolution with the Plateau de Bure interferometer helped establish the origin of the emission detected and the physical conditions in the emitting gas. The water line profile and its spatial distribution are very similar to those of SiO. We find that the H2O emission arises from warm (∼200 K), dense ((1-2) × 106cm-3) gas, and its abundance is enhanced by one to two orders of magnitude with respect to the protostellar envelope. Results. We detect water emission in strong shocks from the high-velocity jet at 1000 AU from the protostar. Despite the large beam size of the telescope, such emission should be detectable with Herschel. © 2011 ESO.