Prof. Dr. Klaas Sjoerds de Boer (1941 – 2022)

The German Astronomical Society (Astronomische Gesellschaft) mourns the death of its long-time member Prof. Dr. Klaas S. de Boer, who passed away on March 15, 2022 in his native city Groningen.

Especially during his time as chair and professor of astronomy at the observatory of the University of Bonn between 1986 and 2007, he influenced several generations of young astronomers, many of whom still do research and teach in leading positions today.

Klaas de Boer grew up in Groningen, where he studied astronomy and physics and completed his PhD in 1974 under Stuart Pottasch on the topic of interstellar absorption lines in the UV - a topic that was to accompany him throughout his scientific career. He also completed his first postdoctoral position in Groningen before moving to the University of Wisconsin in 1978 to join the research group of Blair Savage. In this scientifically very fruitful environment, he produced groundbreaking work, e.g. on the measurement of the hot coronal gas of the Milky Way and the Magellanic Clouds, but also on his second scientific mainstay, the astrophysics of stellar populations and the structure of the Milky Way. His path then led him initially to the University of Tübingen from 1981 to 1985. After a secondment to the Royal Greenwich Observatory in Herstmonceux in 1985 by the University of Groningen,
he was appointed Professor of Astronomy at the Observatory of the University of Bonn in 1986, succeeding Hans Schmidt.

Klaas de Boer was an impressive research personality, an ever-motivating supervisor and mentor, and an inspiring University teacher. His commitment to the promotion of young scientists was expressed, among other things, via his participation in the joint Bonn-Bochum Research Training Groups, in which the Magellanic Clouds and other dwarf galaxies were made the central topic. Thus, for many years, as an eloquent scientist and gentleman, he was the defining "face" of the Bonn Observatory. In addition to his more than 250 scientific publications, which he published with his collaborators and in various international collaborations, the communication of astronomical findings to the public was particularly close to his heart, which was reflected in numerous public lectures and essays on the Internet.

Klaas de Boer was also committed to the further development of the technical foundations of observational astronomy, be it for space-based observational projects (e.g. IUE, DIVA and Gaia) or in the expert committee of the collaborative research of the BMBF and the DLR. Accordingly, the institute he lead was also able to contribute to instrumentation projects (BUSCA at Calar Alto, "Bonn Shutter"). In addition, he was a member of the Board of Directors of Astronomy and Astrophysics for many years, representing Germany. The careful and accurate preparation of scientific (and non-scientific) texts was always an important concern for him, which he always focused on in his work with his numerous PhD and diploma students.

With Klaas de Boer we have lost an outstanding research personality, an insightful mentor and supervisor, and a good friend whose impact will live on in the many scientists he trained.