The CHESS spectral survey of star forming regions: Peering into the protostellar shock L1157-B1: I. Shock chemical complexity

Abstract

We present the first results of the unbiased survey of the L1157-B1 bow shock, obtained with HIFI in the framework of the key program Chemical HErschel Survey of Star forming regions (CHESS). The L1157 outflow is driven by a low-mass Class 0 protostar and is considered the prototype of the so-called chemically active outflows. The bright blue-shifted bow shock B1 is the ideal laboratory for studying the link between the hot (~1000–2000 K) component traced by H_2 IR-emission and the cold (~10–20 K) swept-up material. The main aim is to trace the warm gas chemically enriched by the passage of a shock and to infer the excitation conditions in L1157-B1. A total of 27 lines are identified in the 555–636 GHz region, down to an average 3σ level of 30 mK. The emission is dominated by CO(5–4) and H_(2)O(1_(10)–1_(01)) transitions, as discussed by Lefloch et al. in this volume. Here we report on the identification of lines from NH_3, H_(2)CO, CH_(3)OH, CS, HCN, and HCO^+. The comparison between the profiles produced by molecules released from dust mantles (NH_3, H_(2)CO, CH_(3)OH) and that of H_(2)O is consistent with a scenario in which water is also formed in the gas-phase in high-temperature regions where sputtering or grain-grain collisions are not efficient. The high excitation range of the observed tracers allows us to infer, for the first time for these species, the existence of a warm (≥200 K) gas component coexisting in the B1 bow structure with the cold and hot gas detected from ground.