SOLAR ELEMENT ABUNDANCES, NON-LTE LINE FORMATION IN COOL STARS AND ATOMIC DATA

The composition of solar and meteoritic matter serves as a primary ref erence for cosmochemical studies. Element abundances in the Sun - and in cool stars in general - are usually determined by spectroscopy of a stellar atmosphere whose properties differ from most laboratory sourc es: (i) there are strong gradients of temperature and pressure, (ii) t he main constituents are neutral hydrogen and helium, while the fracti onal abundance of electrons is only approximate to 10(-4), (iii) the p lasma is immersed in an intense, anisotropic radiation field, and is h ighly turbulent. The present contribution discusses meteoritic and sol ar abundances and their suitability as cosmic reference data. Also add ressed are mayor diagnostic problems encountered in the analysis of th e photospheric line spectrum of cool stars - in particular line broade ning and deviations from LTE in neutral iron. This paper is an update of a review [1] given at the 1987 Meudon symposium on high-S/N stellar spectroscopy.