Prof. Dr. Dieter Reimers (1943 - 2021)

On June 9, 2021, Prof. Dieter Reimers died unexpectedly at the age of 77 years in Postfeld (Schleswig-Holstein, Germany). From 1980 to 2009, Dieter Reimers was a professor at Universität Hamburg and Hamburger Sternwarte. He was born November 25, 1943 in Rüde (Schleswig-Holstein). After finishing school in 1963, he studied Physics at the universities in Kiel and Bonn. He obtained his PhD in May, 1969 with Prof. Unsöld in Kiel and habilitated in 1972 in the disciplines Astronomy and Theoretical Physics, also at the Universität Kiel.

 In 1973 and 1976 Dieter Reimers conducted research in the U.S. at the Mt. Wilson and Palomar observatories and at Caltech (Pasadena). In 1976, he became a lecturer (H2) at Universität Kiel. In 1980, he was appointed professor (C4) for Astronomy at Universität Hamburg where he worked at the Hamburger Sternwarte until his retirement in 2009. Already in 1977, he took over as the managing director at Hamburger Sternwarte, an office he held for many years. From 1988 to 1992, Dieter Reimers presided the „Observing Programmes Committee“ of ESO, from 1995 to 2002, he was the scientific delegate of the Federal Republic of Germany in the council of ESO, and from 2007 to 2009, chairman of the „Rat Deutscher Sternwarten“.

Dieter Reimers was an extremely successful scientist and remained scientifically active until the end. In his early years he worked on the atmospheres and spectra of stars and the Sun. In addition to conducting research on the final stages of stellar evolution and White Dwarfs, he studied the causes of mass loss in red giant stars. In 1975 he discovered a relation between their mass loss rate and their fundamental stellar parameters ("Reimer's Law"), which is still used today in modified form in modern model calculations of stellar evolution. In his Hamburg years he continued this work with his "stellar working group”. In order to determine the amount and composition of the gas and dust in the circumstellar shells formed by the mass loss, he preferentially observed binary stars, in which the companion probes the shell step by step as it orbits the giant.

 Following his appointment at the Sternwarte, Dieter Reimers increasingly turned to observational cosmology, a field which was rapidly developing at the time. With his “extragalactic working group” he used the Hamburg Schmidt telescope at the Calar Alto Observatory in Spain for a long-term observing program to survey the northern sky spectroscopically. For the first time, the spectra recorded photographically on glass plates were digitized with a newly acquired measuring machine. This enabled computer-aided classification of the millions of observed objects, which was much more efficient than the previous searches for extraordinary objects with a magnifying glass and eye. The survey was later extended to the southern sky using the ESO Schmidt telescope at the La Silla Observatory in Chile.

 The surveys produced a multitude of spectacular discoveries. Particularly noteworthy was the discovery of a large number of very bright quasars, which became Reimers’ main focus. His investigations of the ultraviolet spectra of quasars, together with those of a large number of his doctoral students, had a significant and long-lasting impact on our understanding of bright quasars. This work included his unique studies of the intergalactic medium, which causes numerous absorption lines in the spectra of quasars. For these observations, Reimers was awarded substantial amounts of observing time on the Hubble Space Telescope. Indeed, for a long period in the 1990s he won more time on this unique and highly demanded telescope than anyone else in the German astronomical community.

 The surveys led to numerous collaborations in Germany and abroad, with new Hamburg discoveries of hot stars, variable cataclysmic stars, gravitational lenses and emission-line galaxies being further investigated at other institutes. The surveys were veritable treasure chests in which jewels were unexpectedly found, such as the discovery of the then most metal-poor star in the Milky Way in 2001.

 Reimers played an important role in transforming the Hamburger Sternwarte, which for a long time saw itself as a classic optical observatory, into a modern astrophysical institute. He supported the emerging field of space-based astronomy by allowing the spectroscopic surveys to be used for the identification X-ray sources that were newly discovered by the German ROSAT satellite (1990-1999). As a result, X-ray astronomy developed into a key research area at the institute. Early on, he also recognized the importance of the LOFAR radio interferometer for expanding the observatory's research portfolio into the field of radio astronomy. Indeed, the establishment of the now very active radio astronomy group at the institute is largely owed to his initiative during the last few years before his retirement. Ultimately, this led to the participation of the Hamburger Sternwarte / Universität Hamburg in the LOFAR consortium, and to the construction of a LOFAR station in Norderstedt in 2015.

 As an educator, Dieter Reimers was deeply committed to supporting and fostering young talents. Over the course of his career, he trained a large number of young scientists and primed them for a successful career inside and outside of academia.

 In Dieter Reimers the Hamburger Sternwarte has not only lost an internationally outstanding scientist, but also an energetic, ever helpful and extremely popular colleague. He will be deeply missed by all.

 Dieter Engels and Jochen Liske on behalf of the Hamburger Sternwarte

Hamburger Sternwarte

Universität Hamburg

Gojenbergsweg 112

21029 Hamburg

Germany