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Obituary: Thomas Harry Hope (Tom) Lloyd Evans 1940-2014.

On 12 June 2014 the well-known astronomer Tom Lloyd Evans died in Scotland. For most of his career he had worked in South Africa but for the last thirteen years of his life he lived in Scotland, not far from where he grew up.

Tom was born during the Second World War on 2 December 1940 at an RAF base in Wimslow, England, where his father, Wing Commander Dudley Lloyd Evans DFC, a flying ace during the First World War, was involved in investigating aeroplane accidents. However, at the age of a few months he moved with his mother to her family's castle in the Scottish countryside. His father joined them when the war ended.

Tom attended the well-known school Fettes College in Edinburgh and it was there that one of the masters awakened his interest in astronomy. While still at school he joined the Dundee Astronomical Society and was already contributing observations to the AAVSO and the BAA. He was elected an Honorary Member of the BAA in 1956 and later on an Honorary Member of the Dundee Astronomical Society.

Career

He attended university at St Andrews, a place of which he was already very fond, graduating with first-class honours in astronomy in 1963. He stayed on at St Andrews and began a PhD there on the photometry of star clusters. This was completed in 1968, while he was at the Radcliffe Observatory.

In 1966 he joined the Radcliffe Observatory in Pretoria, then directed by David Thackeray. He remained there until it closed in 1974 except for a short period that he spent at the Royal Observatory, Edinburgh. Following this, he moved to the South African Astronomical Observatory in Cape Town where he worked, except for a sabbatical of four months at the Anglo-Australian Observatory in 1980, until his retirement in 2001. On his return to Scotland he became a Special Lecturer in the School of Chemistry at Nottingham University until 2007 and also an Honorary Lecturer at St Andrews from 2004 onwards.

Science

Unsurprisingly, in such a long career, Tom's research interests were many and varied. An early interest in the radial velocities of classical Cepheids showed that a significant number are in binary systems. This allows the possibility of determining their masses (see e.g. Lloyd Evans, 1968).

At Radcliffe, Tom took a long series of Newtonian plates of fields in the Magellanic Clouds, the Baade Clear Windows near the Galactic Centre and globular clusters. These were examined for variable stars and their light curves were extracted (e.g., Lloyd Evans, 1976). Later he used the "Unit Spectrograph" to obtain further information about the variables, finding correlations between their periods, metal content and ages. He identified the first Miras in the Magellanic Clouds, leading to the discovery that these variables obey a tight period-luminosity relation (Glass & Evans, 1981).

He continued with spectroscopy of Magellanic Cloud clusters at Sutherland and confirmed the evolutionary transition from M via S to C stars as due to material being processed by thermonuclear reactions, especially the s-process elements and carbon.

Most globular clusters show a certain degree of uniformity in the evolutionary paths followed by their late-type stars. However, the cluster Omega Cen is anomalous and Tom showed the scatter in its colour-magnitude diagram and the presence of strong s-process lines resulted from increasing quantities of processed material from different stellar generations (see e.g. Lloyd Evans, 1977).

Using results from the early infrared satellites, Tom found that certain carbon stars invisible at ordinary wavelengths and having anomalous quantities of silicon-rich dust emitting at 9.7[micro]m (expected from oxygen-rich rather than carbon-rich giants) have relatively high abundances of the heavier carbon isotope [sup.13]CO. The dust was hypothesized to have been accumulated during their earlier oxygen-rich phase in a disc associated with a binary companion (see e.g. Lloyd Evans, 1990).

Another interest of Tom's was in RV Tauri stars. These were found to have characteristic mid-infrared colours, possibly arising from dusty discs. This property was used to identify new examples of RV Tauri stars including a new class with small amplitudes in binary systems (see e.g. de Ruyter et al, 2006). A spectroscopic study of RV Tauri stars in the Large Magellanic Cloud showed that they have the same range of spectra as their galactic counterparts but that at least one is a carbon star with s-process elements as might be expected if they are post-AGB objects.

A study of V Hydrae and R Lep showed that the characteristic fading exhibited by such stars is restricted to the reddest C types, which are enveloped in dust clouds (see Lloyd Evans, 1997). During dust episodes, [C.sub.2] appears in emission instead of absorption, as may the resonance lines of Na, K and Rb. V Hya shows high-velocity gas ejection.

Since his return to Europe, Tom has collaborated with Peter Sarre (Nottingham) and Hans van Winckel (Leuven) and was particularly glad to have had the opportunity to work with students.

With Peter Sarre he carried out the first complete study of the silicon dicarbide molecule in stellar spectra, following his discovery of a carbon star (IRAS 12311-3509) with [C.sub.2] and Si[C.sub.2] emission bands, surrounded by a dusty disc (see e.g., Sarre et al, 1996).

Other professional activities

For about ten years Tom ran the Summer School for undergraduates, a precursor of the present-day NASSP programme. In addition he ran a number of South African Astronomical meetings and was the organizer of the SAAO's weekly seminars for 17 years. He was responsible for the allocation of observing time on the SAAO telescopes for several years. He occasionally served as Acting Director of SAAO for short periods and was a member for three years of the SA National Committee for the IAU. He was also Chairman for some time of the SAAO Staff Association. He was President of Commission 45 (Stellar Classification) of the IAU in 2000-03.

In 1991-92 he served as President of the Astronomical Society of Southern Africa, in which he always took a strong interest.

Tom commenced his observing career with photographic photometry and later undertook spectroscopy, infrared photometry and infrared imaging. In addition to his administrative duties, Tom was in charge of the Cassegrain "Unit" spectrograph for many years, including supervising its many transformations from Carnegie image tube to Boksenberg IPCS, to Reticon PCS, to CCD detector, with the associated optical changes. He personally took care of its optical alignment.

Personal Life

Tom, though very conservative in his political views, was very conscious of the need to keep an open outlook. He was a strong swimmer and enjoyed snorkeling and underwater photography in such places as the Comores, Mauritius, the Great Barrier Reef and Egypt. He was an enthusiastic member of the local Archaeological Society and among other things conducted a dig on the Sutherland Observatory site.

Tom was very fond of hiking and enjoyed the varied Cape flora. He belonged to the Botanical Society and became one of its walk leaders. After he returned to Scotland with his family he became a member of the Fife Mountaineering club.

He had many other interests, including aviation, and he was able to recognize most types of warplanes! He was widely read, with a large collection of books. He also liked to attend concerts and operas.

An interest in Scottish Country Dancing led Tom to meet his future wife, Marlene, who he married in December 1985. They have two children, Robert and Anne, who are now adults. Marlene, a science teacher, continues to work at a school in St Andrews.

Published Output

Tom was the author or co-author of at least 116 papers in refereed international journals, principally Monthly Notices of the Royal Astronomical Society, The Observatory and Astronomy and Astrophysics. He published 57 papers in conference proceedings, many of them of IAU Symposia. In addition he had about 38 papers in The Astronomer and the SAAO Circulars as well as many items in the International Bulletin of Variables Stars, the IAU Circular sand the Journal of the British Astronomical Association including 18 in MNASSA. He had numerous collaborators, some of the more frequent being R.M. Catchpole, M.W. Feast, I.S. Glass, D.M. Kilkenny, M.C.J. Koen, J.W. Menzies, K. Pollard, P.J. Sarre and H. van Winckel.

[Ian Glass with thanks to Marlene Lloyd Evans and Dave Kilkenny]

References

de Ruyter, S., van Winckel, H., Maas, T., Lloyd Evans, T., Waters, L. B. F. M., Dejonghe, H., 2006. Keplerian discs around post-AGB stars: a common phenomenon?

Astronomy and Astrophysics, 448, 641-653.

Glass, I.S, Evans, T.L. 1981. A period-luminosity relation for Mira variables in the Large Magellanic Cloud, Nature, 291, 303- 304.

Lloyd Evans, T., 1968. The frequency of Cepheid binaries, Monthly Notices of the Royal Astronomical Society, 141, 109-142.

Lloyd Evans, T., 1976. Red variables in the central bulge of the Galaxy. I. The period distribution of Mira variables. Monthly Notices of the Royal Astronomical Society, 174, 169-184.

Lloyd Evans, T., 1977. Near infrared photometry of globular clusters. VIII The anomalous giant branch of Omega Centauri Monthly Notices of the Royal Astronomical Society, 181, 591-598.

Lloyd Evans, T., 1990. Carbon stars with silicate dust shells. I--Carbon stars with enhanced C-13 (J stars) Monthly Notices of the Royal Astronomical Society, 243, 336-348.

Lloyd Evans, T., 1997. Spectroscopic changes and the variable mean light of carbon stars Monthly Notices of the Royal Astronomical Society, 286, 839-847.

Pollard, K. R., Lloyd Evans, T., 2000. A Spectroscopic Study of RV Tauri Stars in the LMC, in The Impact of Large-Scale Surveys on Pulsating Star Research, ASP Conference Series, Vol. 203; also IAU Colloquium No 176. Eds L. Szabados and D. Kurtz., p.116.

Sarre, P. J., Hurst, M. E., Lloyd Evans, T., 1996.Optical Absorption and Emission Bands of Si[C.sub.2] in Carbon Stars. Astrophysical Journal Letters, 471, L107-L109.
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Publication:Monthly Notes of the Astronomical Society of Southern Africa
Article Type:Obituary
Geographic Code:4EUUS
Date:Jun 1, 2014
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