Wilhelm J. Altenhoff

It is with profound sadness that the Max Planck Institute for Radio Astronomy announces that Wilhelm J. Altenhoff passed away.

Wilhelm Altenhoff studied Astronomy at the University of Münster, where he earned his doctorate in 1966. He started his career by observing with the Stockert 25m radio telescope (operated by the University of Bonn). In his thesis he worked on atmospheric refraction in the radio regime, while with the Stockert telescope he conducted measurements at 11cm wavelength, which spurned his interest in radio surveys of the Galactic Plane.

After his graduation, he followed Peter Mezger to the National Radio Observatory in Green Bank. Here, with the 140ft Green Bank radio telescope, he participated in and led surveys of the Galactic plane at various wavelengths. In 1968, Altenhoff returned to Bonn where the Max Planck Institute for Radio Astronomy had recently been founded, and the construction of the 100m radio telescope in Effelsberg was in progress. In Bonn, Wilhelm Altenhoff concentrated on observations with the Effelsberg telescope that he used for a 6cm survey of the Galactic Plane, one of his most prominent achievements. With his friend and colleague Heinrich Wendker he pioneered observations of thermal radio emission from stars. A highlight was the detection of weak emission from Betelgeuse and a determination of its radio spectrum. This line of work he continued at millimeter wavelengths with the IRAM 30 meter telescope which he helped to bring into operation in the early 1980s. Taking advantage of the 30m's sensitivity, together with MPIfR-built bolometer systems, Altenhoff's focus shifted to the solar system. His pioneering measurements delivered radiometric sizes of various asteroids, trans-Neptunian objects and comets and he determined Pluto's temperature. These measurements significantly enriched our understanding of the physical processes behind cometary activity.

Wilhelm Altenhoff was always dedicated to facilitating the optimal performance of the radio telescopes he used. His many contributions to the operations of the Effelsberg telescope, which included extending its reach to 7 mm wavelength, as well as his work on commissioning and calibrating the IRAM 30m telescope on Pico Veleta, were the basis of many observations by other researchers. He was always ready to give advice to students and the technical staff, and supported efforts to make simple radio astronomical measurements accessible to the community of amateur astronomers.

Wilhelm J. Altenhoff died on August 2nd 2017 at the age of 83 years. The staff and students at the MPIfR will greatly miss their colleague and friend.