Description

Astrochem is a code to compute the abundances of chemical species in the interstellar medium, as function of time. It is designed to study the chemistry in a variety of astronom- ical objects, including diffuse clouds, dense clouds, photodissociation regions, prestellar cores, protostars, and protostellar disks1. Astrochem reads a network of chemical reac- tions from a text file, builds a system of kinetic rates equations, and solves it using a state-of-the-art stiff ordinary differential equations (ODE) solver. The Jacobian matrix of the system is computed implicitly, so the resolution of the system is extremely fast: large networks containing several thousands of reactions are usually solved in a few seconds. In addition, Astrochem may be run in parallel on multi-cores and or multi-CPU computers. A variety of gas phase process are considered, as well as simple gas-grain interactions, such as freeze-out and desorption via several mechanisms (thermal desorption, cosmic-ray desorption and photo-desorption). The computed abundances are written in text files, and can be plotted in different ways with the tools provided with Astrochem. Chemical reactions and their rates are written in a format which is meant to be easy to read and to edit. A tool to convert chemical networks from the OSU2 and KIDA3 databases into this format is provided. Astrochem is written in C, and its source code is distributed under the terms of the GNU General Public License (GPL).