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Thomas H. Legg (1929–2011)

Legg was a pioneer of the Canadian radio astronomy, helping build the Algonquin Radio Observatory. He was a major contributor to Canadian VLBI efforts and was the first to show that the separation of double radio sources varies inversely with redshift.

Published onDec 28, 2020
Thomas H. Legg (1929–2011)

Thomas H. Legg on the ARO Site 3 dish. Photo courtesy of the Legg family.

Thomas H. Legg died on the 14th of June, 2011.

Thomas Harry Legg was born in Kamloops BC had an early passion for physics and astronomy. After graduating with honors in Engineering Physics from UBC in 1953, he spent a year installing radars on the Pinetree air defense line, worked on microwave diffraction at the Defense Research Board, and earned an M.Sc, in Physics from McGill University in 1956. Following further work at DRB, he returned to McGill to receive a PhD in Physics in 1960.

Tom joined the National Research Council in May 1960 to work with Canadian radio astronomy pioneer Arthur Covington. Other radio astronomers then at NRC were Norman Broten, Gladys Harvey, and Wilfred Medd. The main instruments were a 150 foot wave-guide array, phase-switched (for signal correlation) with a 150 ft interferometer, and a four foot diameter dish used for solar radio-flux measurements. These were at Goth Hill, part of farmer Goth's acreage just south of Ottawa.

The development of what was to become the Algonquin Radio Observatory had just then gotten underway and the first projects there were originated by Covington: the building of a 6 foot diameter solar flux monitor and the design of an interferometer for solar observations. When finished, the interferometer consisted of 32 evenly spaced and 8 widely spaced 10 foot dishes which, at a 10 cm wavelength, provided a 15 arc-second fan beam. Tom spent several years with Covington, planning and building this instrument and then observing the sun and the more intense radio sources with it.

In the meantime, plans for a major large telescope for ARO were developing quickly, championed early on by Norm Broten and Wilf Medd, and strongly supported and encouraged by then Assistant Director of NRC Radio and Electrical Engineering Division, Donald McKinley. McKinley played a crucial role in obtaining some 5 million dollars for the project. The result, designed by Freeman Fox and Partners, London, and built by principle contractor Dominion Bridge was an operating 150 ft diameter telescope in April, 1966.

Prospects for the new telescope, then the largest in North America, soon attracted other astronomers to the radio astronomy group: Lorne Doherty in the early 60's, Lloyd Higgs, John MacLeod, Bryan Andrew and Chris Purton in the mid 60's, and Andy Woodsworth, Jack Locke, Dave Fort, Lorne Avery, Paul Feldman, Jacques Vallee, Henry Matthews and Russell Redman over the following 15 years or so.

Beginning in 1960, well before the 150 ft existed, a group of Canadian radio astronomers, Tom included, began exploring ways of joining very widely spaced telescopes into interferometers. The possibility had been suggested by cosmic-ray scientist D. C. Rose at the 1960 dedication of the 85 ft DRAO telescope at Penticton, BC. Meetings considering such a scheme gradually became more focused but real progress began when University of Toronto Professor Alan Yen discovered that moderately priced video tape recorders were available. These were first-generation former CBC machines, each the size of a small room. Don McKinley again played a key role in getting money not only for recorders but also for the other necessity, a pair of exquisitely stable and accurate Hydrogen maser clocks, one each for U of T and Queen's University. NRC also bought and paid for the two 1420 MHz receiver and synthesizer units required to turn them into useful oscillators for VLBI experiments.

From then on development was rapid, resulting in successful tests in 1966 and, in 1967. Tom was a member of the Canadian team that in 1967 that combined signals from the ARO 150 foot with the DRAO, Penticton 85 foot radio telescopes, 3000 km apart, to successfully measure very distant radio sources in extremely fine detail. In 1971 the team was awarded the Rumford Prize by the American Academy of Arts and Sciences, an honour shared with two other groups from the U.S., the Harvard-MIT Group and the NRAO-Cornell Group.

The first Canadian transatlantic VLBI observations were made in June of 1968 with ARO technologist Joseph (‘Hydrogen-maser’) Fletcher, fellow astronomer Rupert Clark and Tom manning the outstation at Jodrell Bank while shivering in England's mid-summer cold.

There followed years of exploiting the unprecedented resolution of VLBI, with joint papers published on a long list of quasars and active galaxies, as well as a pulsar and galactic H2O and NH3 maser sources. Meanwhile, Wayne Cannon, of Toronto’s York University, used the astronomical results, and later his own observations, for an energetic program in geodesy.

Of particular interests to Tom were ‘superluminal’ sources involving speeds apparently greater than that of light and getting true quantitative images of source structure. The latter aim was much aided by following sources across the sky for long times, a technique resulting in the first image of an active galactic nucleus. In related work, Tom was the first to show that the separation of double radio sources varies inversely with redshift thereby bolstering the then still controversial notion that redshifts measure quasar distances.

From 1978 to 1980, Tom wrote three increasingly detailed proposals that Canada’s size and VLBI expertise be exploited by augmenting ARO with an array of from 5 to 8 simpler telescopes built across the country. The proposals gained strong support from universities and both optical and radio astronomers and resulted in a planning committee chaired by U of T Professor Ernie Seaquist and a formal request for funding. Iterative, image-processing software devised by Dave Fort and Howard Yee was key in showing that the array would give very high-resolution images of excellent fidelity. The array fell just short of being funded in Canada but an independently developed project in the US later became the present highly successful Very Long Baseline Array. Tom participated in a small but enjoyable way on the VLBA configuration and antenna committees.

In the 1980’s, after resurfacing of the 150 ft for mm wavelengths was not funded, the ARO telescope was superseded by a Canadian share in the James Clerk Maxwell Telescope (JCMT) in Hawaii. Astronomers at NRC-Ottawa were encouraged to facilitate the use of the JCMT facility by non-government astronomers. To this end, Tom and Morley Bell worked on focal plane arrays for the new telescope, resulting, eventually, in a patent for small new planar ‘quasi-optical’ antennas. Later Tom proposed an antenna at the other extreme, a new type of very large antenna adopted as the Canadian design submission for the international “Square Kilometer Array” project.

Over the years, an interest in instrumentation and measurement, shared by many radio astronomers, led to papers on antenna pattern smoothing, phase meters, a new Fourier transform relationship, aperture-plane surface-error measurement, holography, mm-wave wide-band matching and, with Morley and U of A colleagues, a planar focal-plane array.

In 1992 Tom, with an international team, used the JCMT in an unsuccessful first attempt at 3mm wavelength transpacific VLBI. Others have recently been successful and have resolved the black hole at the centre of our galaxy with a 50 micro arc-second beam.

Tom retired in 1995 and after retirement as a Senior Research Scientist, he continued as a National Research Council “Guest Worker” in radio astronomy until shortly before his death, on 14 June 2011, rounding out 51 years of doing what he loved.

Reproduced from the IAU-URSI Historical Radio Astronomy Working Group Biographical Memoirs.


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