FreeEOS is a software library for calculating an equation of state for conditions in stellar interiors. The latest stable version of this library source code, FreeEOS-2.2.0, has been released on 2007-07-24.

The EOS1 free-energy model implementation has been improved for this release by scaling of intermediate results so that auxiliary variables, certain quantities associated with excitation, and their derivatives are handled in a consistent way near the underflow limit. These improvements mean there are systematic but negligible residuals between 2.2.0 and 2.1.0 results.

The robustness of the FreeEOS convergence has been substantially improved for this release by implementing the BFGS minimization technique to take over whenever the NR technique diverges. The result is that FreeEOS-2.2.0 converges for densities at least 1 dex higher than the previous calculational limit which was slightly more dense than a 0.1 solar-mass model. However, preliminary calculations for this newly accessible region for FreeEOS-2.2.0 indicate deficiencies in the EOS1 free-energy model for such conditions (see the forthcoming Paper V for the details). A substantial adjustment of the EOS1 free-energy model is in progress with the goal of reducing or overcoming these deficiencies while simultaneously maintaining or improving the existing fit of EOS1 results to the OPAL EOS_2005 results.

N.B. If you are new to FreeEOS or haven't built a recent version of FreeEOS you need to be aware that FreeEOS-2.1.0 and all subsequent versions must be built with the new CMake-based build system. (You use the "cmake" command rather than the "configure" command and follow that "cmake" command with the usual "make" and "make install". See the README file for details about how to use this new build system.)

Download the FreeEOS-2.2.0 tarball from here and have a look at the release notes and ChangeLog here.

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Copyright © 2007 Alan W. Irwin

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