Eugene H. Avrett
Harvard-Smithsonian Center for Astrophysics
60 Garden Street, Cambridge, MA 02138


Pandora is a general-purpose non-LTE computer program for calculating stellar atmosphere models and detailed line and continuum spectra. The program was written by Eugene Avrett and Rudolf Loeser during more than 40 years, into early 2007. Gene Avrett devised and specified Pandora's astrophysics and numerical methods, while Rudy Loeser designed and built the program and superintended its actual ongoing use until he retired. Most of the code development was done using VAX/VMS, although the code itself is OS independent. The code was ported to Ultrix, SunOS and finally to Linux. Sylvain Korzennik helped the port to Linux and helps maintain the Linux version, providing some limited support.

Pandora supports ongoing research by Gene Avrett and his collaborators on various specific problems of radiative transfer. Recent applications include extensive modeling of the outer atmosphere of the Sun and other late-type stars, including effects of mass flows; the atmospheric response to external ionizing radiation; and the effects of ion diffusion. Pandora can also be used for simple illustrative studies of optically thick non-LTE spectral line formation for different multilevel atoms and atmospheric models, using plane-parallel and spherical geometries. The program output files include extensive documentation and explanations of the computational procedures so that the results are reasonably self-explanatory.

For an overall description of the program, see the document "Modeling with Pandora", available as a PostScript, or a PDF file.

An excellent set of lecture notes on "Radiative Transfer in Stellar Atmospheres" by Robert J. Rutten can be found on his web site . The "Astronomy course material on radiative transfer and spectral line formation in stellar atmospheres" is a graduate-level introduction to the subject and may serve as a foundation for understanding the Pandora calculation. You may also want to read Gene Avrett's lecture notes "Introduction to non-LTE Radiative Transfer and Atmospheric Modeling".

Computer-proficient researchers who understand basic stellar atmosphere theory and modeling, and who are willing to make the effort to become successful users, are welcome to obtain from CfA a version of Pandora (see below).

How to Become a User of Pandora

Learning to use Pandora successfully generally requires some time and effort. You will need a Fortran compiler, some good understanding of radiative transfer, and the patience to read through the documentation. We do not have resources to provide user support.

Pandora is a non-interactive program written in Fortran77 over more than 40 years of development. It compiles and runs successfully using either the Intel or the Portland Group Fortran compilers (tested under Linux).

Procedures to build and run the program (using Linux), using either compilers, are provided. The code should compile using any standard f77 compiler (under any OS), although run-time errors may occur (esp. for I/Os) and the supplied scripts to drive the program may need to be adapted or rewritten.

NOTE: It does not compile with GNU's Fortran copmpiler (gfortran), although a skilled (and patient) programer could modify the code to teh idiosycraties of the GNU compiler (the GNU consortium decided no to follow decades of practice and have not implementeed things that all other commetial compoiler do - you get what you pay for).

You can sample the flavor of the program by reading the following file.

To get Pandora running and to learn to use it, you can download one of the available versions: