CESAM: a free code for stellar evolution calculations

TL;DR

CESAM is a comprehensive, robust, and accurate code for 1D stellar evolution calculations, incorporating microscopic diffusion, angular momentum transport, and advanced numerical methods for stability and precision.

Contribution

It introduces a new numerical framework with collocation and B-spline methods for stable, precise stellar evolution modeling, including diffusion and convection processes.

Findings

Stable and robust calculations with exact solution restitution.

Automatic mesh refinement improves local accuracy.

Accurate modeling of chemical evolution and atmosphere restoration.

Abstract

The Cesam code is a consistent set of programs and routines which perform calculations of 1D quasi-hydrostatic stellar evolution including microscopic diffusion of chemical species and diffusion of angular momentum. The solution of the quasi-static equilibrium is performed by a collocation method based on piecewise polynomials approximations projected on a B-spline basis; that allows stable and robust calculations, and the exact restitution of the solution, not only at grid points, even for the discontinuous variables. Other advantages are the monitoring by only one parameter of the accuracy and its improvement by super-convergence. An automatic mesh refinement has been designed for adjusting the localisations of grid points according to the changes of unknowns. For standard models, the evolution of the chemical composition is solved by stiffly stable schemes of orders up to four; in the convection zones mixing and evolution of chemical are simultaneous. The solution of the diffusion equation employs the Galerkin finite elements scheme; the mixing of chemicals is then performed by a strong turbulent diffusion. A precise restoration of the atmosphere is allowed for.