Owen Bruce Slee, one of radio astronomy's pioneers, died on 18 August at the age of 92, just a day after a workshop held at the University of Sydney to celebrate his life and work.
Bruce's 70-year career covered an extraordinary range of fields: solar-system phenomena (the solar corona, Jovian bursts, comet tails), Galactic astronomy (active stars, pulsars, the interstellar medium), and extragalactic objects (galaxies, clusters, quasars). He used the leading instruments of the day, from the simple Yagi antennas at Dover Heights to the Compact Array and Very Large Array. He collaborated with colleagues from 18 countries, at a time when such a range of connections was rare. Yet when Bruce had been appointed to the Division of Radiophysics in 1946 as a technical assistant, it was with the expectation of a career in electronics: "... Joe Pawsey gave me the advice that this is the path I should follow -- in other words, I could not reasonably aspire to a career on the research side of radio astronomy." (Bruce Slee, personal communication to Wayne Orchiston, 2002)
Bruce was born on 10 August 1924 in Adelaide. He was the second of three children; his father worked as a carpenter. The depression of the 1930s brought hard times: the Slees lost their home, and went to live with relatives. Bruce completed his schooling in the Adelaide Hills. Armed with good grades in the Leaving Certificate examinations, he accepted a clerical job in the Lands Department. In 1942, when he turned 18, he joined the Royal Australian Air Force.
Aircraftsman Slee was sent to Melbourne to attend a six-month radio mechanics course, and was then selected to complete a three-month radar mechanics course at Richmond Air Force Base. He was then posted to two radar stations in Western Australia, and then to one on Melville Island in Australia's north. Following this he was transferred to Radar Station 59 on the mainland, near Darwin. It was there, during the second half of 1945, that Bruce sometimes noticed distinctive 'static' when the antenna was pointing west around sunset. By driving the antenna in azimuth, he noted that the static increased when the Sun was in the beam and concluded that this 'interference' was in fact solar radio emission. Bruce did not publish this finding, but he did report it to CSIRO's Division of Radiophysics in Sydney.
This detection of 200 MHz radio emission was one of several made independently during the war. The Division of Radiophysics was already aware of the phenomenon through reports from England and New Zealand. In October 1945 Radiophysics staff began making their own successful solar observations using an antenna at the Collaroy radar station north of Sydney.
After the war, Bruce returned to his Lands Department job in Adelaide. He was subsequently contacted by Joe Pawsey, head of the radio-astronomy group at Radiophysics, about forthcoming vacancies in the Division. Pawsey visited Adelaide in August 1946, interviewed Bruce, and invited him to join the radio-astronomy group. Bruce accepted this invitation and moved to Sydney in November 1946. He was immediately posted to the Dover Heights field station as a technical assistant to John Bolton, who had arrived at Radiophysics just two months earlier.
The groundbreaking research at Dover Heights is well known. After a false start, Bolton, Slee and colleague Gordon Stanley began monitoring Cygnus A, a 'radio star' (radio source) reported by James Hey and colleagues in 1946. In November 1947 Bolton, Stanley and Slee detected a second source, Taurus A, and within the next two months five additional sources. Determining the nature of these sources required precise positions, so Bolton and Stanley made a field trip to New Zealand where they could observe the sources both rising and setting, and obtain higher-resolution interference fringes than was possible at Dover Heights. They spent three months observing Cygnus A, Taurus A, Centaurus A and Virgo A from New Zealand, while Slee continued to make parallel observations from Dover Heights. The New Zealand trip was a resounding success, and in a paper published in Nature, Bolton, Stanley and Slee (1949) associated Taurus A with the Crab Nebula, Centaurus A with NGC 5128 and Virgo A with NGC 4486. When Bruce began his first independent research project in 1950, it was studying the scintillations of the 'radio star' sources.
Soon after joining CSIRO, Bruce had begun a five-year Diploma in Radio Engineering at Sydney Technical College and followed this with a two-year Diploma in Physics. However, reasonably early in the 'radio stars' work Bruce realised that his true interest lay in astronomical research. He began a part-time BSc degree at the University of New South Wales (UNSW), graduating with first-class Honours in 1959, and became a CSIRO research officer in 1961. Ten years later UNSW awarded Bruce a DSc on the strength of his research record.
Apart from a brief interlude at the Georges Heights field station, Bruce remained at Dover Heights until transferring to Fleurs in 1954, when that field station opened. When Fleurs closed in 1963, he returned to the Radiophysics Laboratory in Sydney and continued his research programs from there, using first Parkes, then the Culgoora Radioheliograph (for non-solar observations), and then the Australia Telescope Compact Array.
Bruce wanted to contribute in a broad range of astronomical areas, focusing on observation and analysis rather than on instrumentation development or theoretical issues. Nevertheless, he was also was actively involved in designing, building, testing, operating and maintaining items hardware, from receivers, dipoles and feed horns to complete radio telescopes. He took part in building the pioneering 3.9-m parabola at Dover Heights and the famous 'hole-in-the-ground' antenna, also at Dover Heights. He also maintained and modified the Mills and Shain Cross telescopes at Fleurs and set up the various long-baseline interferometry systems that operated from this site. But despite the time and effort that he put into this side of research, Bruce's name rarely appeared on instrumentation papers. Two of those rare instances are a discussion of the principles of the sea interferometer co-authored with John Bolton (Bolton and Slee, 1953), and the basic technical account of the Mills Cross (Mills, Little, Sheridan and Slee, 1958).
The workshop to celebrate Bruce's contributions, held on 16--17 August, revisited many of fields and topics that Bruce had investigated; in some cases work he had collaborated on with workshop participants. In particular, it was an occasion for researchers engaged in the current revival of low-frequency radio astronomy to look back at what was achieved decades ago -- and in many cases, forgotten. ('Humbling' was how one described it.)
The workshop has come and gone, but courtesy of the International Astronomical Union Bruce now has the permanent tribute of an asteroid named after him, Minor Planet 9391 Slee.
Bruce is survived by his wife, Nan, and two daughters.
Further reading:
Wayne Orchiston, "From the Solar Corona to Clusters of Galaxies: The Radio Astronomy of Bruce Slee", PASA 2004, 21, 23--71
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