Gothenburg, Sweden, 21 Jan. 1908 - Copenhagen, Denmark, 4 July 1987
Title Professor Emeritus of Astronomy and Director, NORDITA, Copenhagen, Denmark
Nomination 2 Dec. 1975
Summary of scientific research
Prior to 1931 my research was in classical astronomy, namely, meridian astronomy and celestial mechanics. After that yar most of my work was devoted to astrophysics. I investigated problems of stellar structure, particularly questions related to the chemical composition of stellar interiors. Further, I worked on problems of stellar atmospheres including the question of the chemical composition of the solar atmosphere. Research work on physical and chemical properties of interstellar matter led to results regarding ionisation and density of interstellar hydrogen.
From 1951 I have worked on problems of determination of stellar ages and stellar composition indices through combination of theory and observation, developing photometric meethods applicable in large-scale surveys of field stars. The application of these methods has led to results concerning the older stars of our Galaxy which have a bearing on problems of the chemical and dynamical evolution of the Galaxy.