Computer Programs

Plane-Parallel Codes

I compute the structure of stellar atmospheres using computer programs based on the Atlas codes developed by Robert Kurucz. Kurucz has two versions of his program. The older version is named Atlas9, and it assumes traditional plane-parallel geometry, hydrostatic pressure equilibrium and LTE populations. Its important contribution is the inclusion of the opacity from millions of atomic, ionic and molecular spectral lines using opacity distribution functions (ODFs) that have been pre-computed for a wide range of temperatures, pressures, compositions and microscopic velocity fields. The newer Atlas12 version differs from the Atlas9 code by employing an opacity sampling (OS) of the spectral lines, which eliminates the discrete values of temperature and pressure imposed by the ODFs, as well as providing complete flexibility in choosing the composition and the microscopic velocity fields, both of which might vary with depth.

My versions of the Atlas codes try to remain true to the intent of the originals available from Kurucz, but they have been completely rewritten to modify the programs in a number of ways, including:

To avoid confusion, the modified version of Atlas9 is called Atlas_ODF and the modified version of Atlas12 is called Atlas_OS. Compressed tar files of the source files can be accessed at Atlas_ODF and Atlas_OS.

ODFs are available from either Kurucz or from Fiorella Castelli, which are recommended by Kurucz. The Castelli and Kurucz ODF files have different dimensions for the pressures and temperatures. Instructions have been added to Atlas_ODF to identify which dimensions to use, but the defaults are the Castelli dimensions.

The binary ODFs files provided by either Castelli or Kurucz are read and rewritten as binary files using the program bdf2bin. The purpose of this is to:

Using the original ODF files downloaded from Castelli or Kurcuz will lead to an error because the Atlas_ODF code assumes this conversion has been done. The validity of the conversion can be checked by using the program test_newbdf to convert the reformated ODF file from binary to ASCII, and then using the program bdf2asc to write out the original ODF as ASCII. The two outputs should be identical. These programs are included in the Atlas_ODF distribution.

Atlas_OS uses the line lists given on the Kurucz web site.

In addition to the programs to compute model atmospheres, the Kurucz programs to compute synthetic spectra have also been modified in the same way as the Atlas_ODF and Atlas_OS programs. These are included in the Atlas_ODF distribution.

Spherical Codes

Spherical versions of both Atlas_ODF and Atlas_OS have been developed, called SAtlas_ODF and SAtlas_OS and described in Lester & Neilson, 2008, Astronomy & Astrophysics, vol. 491, p. 633. Because these programs use spherical geometry for the atmospheres, only the Rybicki radiative transfer routine is appropriate. The source code files are available at SAtlas_ODF and SAtlas_OS, and the SAtlas_ODF distribution has spherical versions of the spectrum synthesis programs.