The idea of this colloquium was first put forward by Prof. P. Keenan when he visited the Centre de Donnees Stellaires, in September 1982. Dr. A. Florsch, Director of the Strasbourg Observatory, kindly accepted to field it at Strasbourg. The scientific organization of the colloquium was in charge of a Committee chaired by Prof. P.C. Keenan and composed by M. Feast, A. Florsch, B. Gustafsson, D. Harmer, M. Jaschek (secretary), R. McClure, A. Maeder,...