Welcome on the help webpages for the calculation of radiative accelerations in stars

Evaluation of radiative accelerations is important for computing element segregation in stars. Radiative acceleration is often the leading component in atomic diffusion process, which causes inhomogeneous abundance distribution of elements. This physical process is efficient when mixing processes (turbulence, convection, large scale circulation, etc.) are weak enough. This is especially the case in stellar radiative zones, where turbulence and convection do not take place. A full discussion can be found in the book *Atomic Diffusion in Stars* by G. Michaud, G. Alecian & J. Richer, (2015, Astronomy and Astrophysics Library, Springer International Publishing, Switzerland).

Calculation of accurate radiative acceleration for a given chemical element often requires large computing resources. In particular, it needs numerical integration over the frequency of the local monochromatic radiation flux weighted by cross-sections of photoabsorption for all atomic transitions of all the ions of that element present in the considered medium. There are several methods to carry out this computation, from explicit evaluations (detailed and accurate) to semi-analytic (or parametric) approximations. On this website, some downloadable data for the numerically efficient semi-analytic method called SVP approximation are provided (Alecian & LeBlanc 2002, see also Alecian & Artru 1990, LeBlanc & Alecian 2004). The * SVP approximation* is only valid in optically thick layers (stellar interiors) and for stars with masses larger than 1 solar mass.

- Atomic diffusion
- Radiative accelerations
- Presentation of the SVP approximation
- SVP data and codes (new version, August 2020)
- Related bibliography
- Links