Michael John Seaton. 16 January 1923 — 29 May 2007

Mike Seaton was an outstanding atomic physicist and astrophysicist with a wide range of research interests. His work at University College London (UCL), where he spent all his professional career, laid the foundations of the modern theory of electron–atom and electron–ion collisions and the crucial role of this theory and associated calculations in the analysis of astronomical spectra. His work in astrophysics ranged from seminal papers on the central stars of planetary nebulae and density diagnostics, using forbidden lines, to the Seaton extinction curve, the theory of diffusion in stars and many other topics. Indeed, in the 1950s and 1960s Mike was publishing papers on a whole range of topics that each became major research areas in the years that followed. For example, Mike’s collaboration over some 30 years with Donald Osterbrock laid the foundation of our understanding of physical processes in planetary nebulae. In addition, while on sabbatical at the Institut d’astrophysique de Paris in 1954–55 Mike began a highly influential series of papers on quantum defect theory (QDT); applications of this theory were to resonance phenomena in electron–ion collisions and to photoionization. In addition, Mike led major research programmes on radiative recombination in gaseous nebulae and on dielectronic recombination. Mike and his group at UCL were leaders in the development of general computer codes for atomic structure and collision processes. This made possible the first accurate electron–Fe ii calculation. Major initiatives that grew out of the availability of these computer codes were the international Opacity Project, proposed and led by Mike, and the international Iron Project proposed by and initially led by David Hummer. These projects, which involved collaboration with research workers from many countries, have been of crucial importance, solving many problems in atomic physics and astronomy. Mike Seaton was President of the Royal Astronomical Society for the period 1978–81, and his tenure at UCL coincided with the golden age of atomic astrophysics, for which he was largely responsible.