DICUSSION C. The stellar yields in He-3, He-4 and Li-7: main sources, observational constraints, and problems

I am pleased to recall that the first determination of the Li–abundance in the Sun was made at the Geneva Observatory in 1975 by Edith Muller, Eric Peytremann and Ramiro de la Reza on the basis of spectra taken at Kitt Peak. The first Be determination was also made in Geneva the same year by Y. Chmielewski, J. Brault (Kitt Peak National Observatory) and E. Muller. These two outstanding works opened the door for all further investigations on these light elements. The yields of light elements are a matter where the shock of ideas frequently occurs, with new facts arising and different interpretations. This is particularly the case at present concerning the He abundance in globular clusters and the relation between the 7 Li abundances and planets. This made the discussions at IAU Symposium very lively and interesting. I will try my best to summarize the main points, restore the essence of the discussions and give a proper credit to the various contributors. Normally, stellar evolution provides the chemical yields which are used as an input for the models of the chemical evolution of galaxies. The inverse path, i.e. using the observations of galactic trends in chemistry to infer the stellar properties is like trying to derive the properties of an egg from an omelette, as stated by Jean Audouze long time ago. Nevertheless, in the case of the very early stellar generations, the only direct infos we often have on the stellar properties come from the observed trends in the chemical evolution of galaxies. In this case, we can even say that we use a “fossil omelette” to reconstruct the original stellar properties of the very early stellar generations.