P. Brendan Byrne
Asst. Director

Dr. Patrick Brendan Byrne, Research Astronomer at Armagh Observatory, died on 16 September 1997 at the tragically early age of 49 whilst on an observing trip to the island of La Palma, in the Canary Islands, Spain. Born in Dublin on 28 September 1947, Brendan always had a love of astronomy and had a natural flair for scientific thought. He entered University College Dublin in 1966, graduating with a degree in Experimental Physics in 1970, and then worked for his Ph.D. at Dunsink Observatory. During this time he travelled to South Africa in order to use the Armagh-Dunsink-Harvard telescope in a novel experimental configuration to search for optical pulses from the black hole that was believed, even then, to exist at the centre of the Galaxy. In 1974, following this apprenticeship, he became a post-doctoral research fellow at Dunsink, and in 1977 obtained a lectureship in the Astronomy Department of the University of Cape Town. He joined the Armagh Observatory as a Research Astronomer in 1978.

His period at Armagh saw many changes, both in the quality of research facilities and in the breadth of research carried out at the Observatory. He was particularly closely involved in the introduction of new computing equipment. Brendan was Assistant Director of the Armagh Observatory from 1989 to 1996, and his advocacy and promotion of the strengths of the Observatory at all levels sowed the seeds of the continuing expansion of research at Armagh Observatory, making it currently one of the UK's leading astronomical institutes. Brendan was also a strong supporter of the Astronomical Science Group of Ireland, which has organized biannual astronomical meetings for the past 23 years and provides an important forum for the Irish astronomical community to interact, and to discuss topics of current interest and future plans.

Brendan's own area of research focused on cool star research. For many years he was involved in optical flare monitoring. Such data has allowed the determination of the bolometric flare output for several objects as a fraction of the star's total radiated output. Flares on active late-type stars are both more energetic and more frequent than is the case on the Sun. In more recent years he has been involved in stellar flares studies at other wavelength regions that are inaccessible from the ground, making him a leading expert in space astronomy. He was actively involved in projects that used space facilities such as the International Ultraviolet Explorer, ROSAT, and the Hubble Space Telescope.

He was also familiar with the use of many telescopes abroad, and made frequent observing trips to places such as South Africa, Australia, La Palma, Chile and the observatories of North America. It was during one of these observing trips that Brendan was taken ill and died.

One of his current topics was the study of star spots. Starspots, analogous to sunspots, reveal themselves on the most chromospherically active late-type stars by modulating their total visible light output with axial rotation. Spots of typical solar dimensions (<0.1% of the solar disk) would be undetectable at stellar distances. Fortunately, some of the most active stars, which are also rapid rotators, produce dark, cool spots which may cover in excess of 10% of the stellar surface area. With such huge spot concentrations, large drops in global light output occur which vary during a stellar rotation if, as is generally the case, the degree of spottedness of opposite hemispheres is different.

Another of his most recent projects was to understand the development of stellar rotation from the early rapidly rotating phase associated with star formation to the later stages of much slower rotation, similar to that observed in stars the age of the Sun. How is angular momentum gained and lost; at what stage of stellar evolution are changes most rapid; and what do the observed rotational velocities of stars, for example those formed at the same time in a single star cluster, tell us about the history of our Sun and the ages of distant stars? Recent work has cast doubt on the simple wind model. By comparing the spins of stars in young open clusters of slightly different ages, it was shown that that the initial rate of braking was a great deal faster than tau to the power of one half. Furthermore, the rate of braking depended on the stellar mass. It was proposed that two rotational brakes existed, one which took effect very early in a star's lifetime while it was rotating rapidly, and a second which was, in fact, the above wind braking relation, took over after the star had undergone initial slowing. It was further proposed that the early braking mechanism might have its origins in the rapid rotation itself and might be magnetic in nature. ``Coronal condensations" were one of the suggested mechanisms.

Brendan embarked on a large-scale programme of determining rotational velocities in a range of young open clusters with an age spread such that they span the critical years between arrival on the Main Sequence and the onset of the wind braking regime (i.e. ~30--200 Myr). The aim was to examine critically the evidence for a uniform braking law and attempt to constrain the physical mechanisms giving rise to such a law, if it exists. On the ``Coronal condensations" question he was actively involved in the study of another fast rotator, HK Aqr, and compared it to the proto-type AB Dor. His most recent work argued that cloud formation at the co-rotation radius does not apply to these objects. Based on stability arguments he and colleagues show that it is unlikely that the clouds are filament-like structures. As an alternative they consider the possibility that the clouds are instead part of large coronal loop-like structures possessing temperature inversions. The temperature inversion being caused by a decrease of the coronal heating at large distances from the star and by the increase of the cross-section towards the apex.

Further research topics included the mechanisms by which the outer layers of stars are sometimes heated to temperatures of millions of degrees; NLTE radiative transfer chromospheric modelling; the energetics of powerful eruptions of hot gas; and the processes by which hot gas, as in the solar corona, sometimes condenses and ``rains down'' on to the stellar surface. He was a world authority in all these fields, exerting influence not only through numerous national and international collaborations but also on scientific committees: work for which the astronomical community is indebted and to which he gave generously of his time.

Despite his lack of years he published 150 scientific papers and numerous popular articles, and gave many professional scientific talks. He was frequently invited to present papers at major international conferences, but still found time to promote astronomy and to give talks on all possible subjects to the general public. Brendan made a deep impression not only on the Armagh Observatory but also on the UK, Irish and world-wide astronomical community. He would sometimes remark that he was fortunate to be paid to do his ``hobby''; his colleagues are fortunate to have had the privilege to know and to work with him.

Brendan Byrne was a warm, hospitable person, with a keen sense of humour, generous with his time (particularly to his numerous students and research assistants) and provocative both in thought and expression. He was extraordinarily efficient at handling the administrative minutiae of modern astronomical science, and prolific in his scientific output. Although not an iconoclast, he was always prepared to countenance views which went against the main stream and, if the standard reasoning appeared unsound, was happy to play ``devil's advocate''. A measure of the man is that he developed personal relationships and friendships with his scientific colleagues which were life-long. He will be sadly missed by us all, in particular his wife Gay and children Anne and Conor.

BSc in Exp. Phys. Univ. Coll. Dublin 1970

PhD in Astronomy, Trinity Coll. Dublin 1974

Post-Doctoral Research Asst. Dunsink Observatory 1974-6

Senior Lecturer, Astronomy Dept., Univ. Cape Town 1977-8

Astronomer, Armagh Observatory, 1978-83

Visiting Research Fellow, Sth African Astr. Obs. 1983-4

Astronomer, Armagh Observatory, 1984-9

Asst. Director, Armagh Observatory, 1989-96

Dublin, Ireland

28 September 1947

Chairman ESA/SERC IUE Allocation Committee 1992-4

Chairman STARLINK Users' Panel 1991-3

Golfer, member Armagh Golf Club, Handicap (set of golf clubs)

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