Fifty years of Solar Chemical Composition

 

Nicolas Grevesse (Liège, Belgica)

 

We shall follow the evolution of the solar chemical composition as derived from the analysis of the solar photospheric spectrum during the last fifty years and follow the progress made in the quality of the solar spectra, in the modeling of the photospheric layers, in the atomic and molecular data and in the physical processes that produce the absorption line profiles. With M. Asplund, J. Sauval and Pat Scott, we have recently re-determined the abundances of nearly all the available chemical elements in the solar photosphere, from lithium to thorium. This new analysis results from: (i) a careful selection of spectral lines of all the indicators present in the solar spectrum from the visible to the IR, discarding blended lines or taking the blends as accurately as possible into account and discussing the accuracy of the atomic and molecular data available, (ii) an analysis of these lines based on a new 3D model of the solar outer layers taking non-LTE effects into account when possible. We shall compare our values with older results and show why the new abundances of the most abundant elements (O, C) are lower than the older values. We shall also compare our new values with other recent solar abundances as well as with recent results for the solar neighbourhood and discuss some of their most important implications in solar as well as in stellar physics. Finally, future progress in the field of solar abundances from new MHD models will be suggested.