Athena is a grid-based code for astrophysical gas dynamics being developed with support of the NSF Information Technology Research (ITR) program. This User's Guide describes version 1.0 (hereafter referred to as athena1.0); the first publically released version of the code.
The primary goal of the Athena project is to develop a robust and flexible code with multiple-physics options in a variety of geometries, using flexible gridding methods, and optimized for modern shared or distributed memory parallel machines. This code is necessary to enable increasingly sophisticated investigations of a wide variety of problems in astrophysical gas dynamics. As part of the project, Athena will be made freely available to the astrophysics community, along with complete documentation and web-based training material. Although the capabilities of athena1.0 are quite restricted compared to the ultimate goals of the project, it is being freely distributed consistent with this open source philosophy.
The athena1.0 code contains algorithms for the following:
There are four basic sources of documentation for Athena
Users of athena1.0 should have a basic, working knowledge of the Unix operating system, access to a C compiler, and a graphics package for plotting one-dimensional tabular data. Some familiarity with code management using Makefiles is helpful but not necessary.
The equations solved by athena1.0 can be written in conservative form as
For isothermal MHD, the fifth components of and are dropped, and equation (3) is replaced with , where is a constant (the isothermal speed of sound). For adiabatic hydrodynamics, the last two components of and are dropped, as well as all terms involving the magnetic field in equations (2) and (3). For isothermal hydrodynamics, the last three components of and are dropped, as well as all terms involving the magnetic field in equations (2) and (3).