L1157-B1: Water and ammonia as diagnostics of shock temperature

TL;DR

This study uses a combined chemical and shock model to analyze water and ammonia profiles in the L1157-B1 shock region, revealing that molecular emission differences are due to shock temperature variations.

Contribution

It introduces a new coupled gas-grain chemical and shock model to explain molecular emission profiles in shock regions, highlighting the role of shock temperature.

Findings

Water emission peaks at high velocities, ammonia at low velocities.

The shock temperature in B1 is close to 4000 K.

Chemical processes alone explain molecular profile differences.

Abstract

We investigate the origin and nature of the profiles of water and ammonia observ ed toward the L1157-B1 clump as part of the HIFI CHESS survey (Ceccarelli et al. 2010) using a new code coupling a gas-grain chemical model with a parametric shock model. Fir st results from the unbiased survey (Lefloch et al. 2010, Codella et al. 2010) reveal different molecular components at different excitation conditions coexisting in the B1 bow shock structure, with NH$_3$, H$_2$CO and CH$_3$OH emitting only at relatively low outflow velocities whereas H$_2$O shows bright emission at high velocities. Our model suggests that these differences are purely chemical and can be explained by the presence of a C-type shock whose maximum temperature must be close to 4000 K along the B1 clump.