Dame Carole Jordan, who has died aged 84, was internationally renowned for her studies of the outer atmosphere of the sun and other cool stars. In 1994 she was elected the first female president of the Royal Astronomical Society and was a fierce advocate for women in science.
When we look at the sun we see a yellow area at a temperature of 5,500C – photosphere. When light is spread across all its wavelengths, many bright and dark lines appear, corresponding to electrons being ejected and absorbed by different atoms. The strongest lines in the visible spectrum come from the thin layer above the visible surface, the chromosphere. Above this is the corona, which is millions of kilometers long and is only visible during the moon. In this region the temperature rises to 1 million degrees, so the light and optical lines are visible mainly in the extreme ultraviolet (EUV) or soft X-ray waves.
In 1962, while Carole was starting her PhD, a rocket-propelled experiment led by American astronomer Richard Tousey measured the EUV light from the sun, and found many unknown lines. Carole set out to understand these pathways and eventually became a world expert on radiation from the sun and other stars.
In his 1965 PhD thesis, Analysis of the Solar Ultraviolet Spectrum, he concluded that many of the lines were due to the transition of highly ionized metals. A neutral metal atom has 26 electrons orbiting it, but at a temperature of one million degrees most of the outer electrons are stripped, leaving the atom in an ionized state. Carole raised eyebrows by asserting that some of the EUV lines were caused by the 13-fold iron, Fe XIV. When she visited the Zeta ionized gas experiment at the UK Atomic Energy Laboratory (UKAEA) in Culham, Oxfordshire, with her supervisor, Carole could see the same lines in the lab spectrum, confirming her information.
Four years later, in his highly cited paper, The Ionization Equilibrium of Elements Between Carbon and Nickel, published in the journal of the Royal Astronomical Society in 1969, Carole established the ionization equilibrium as a function of temperature for the major ionized states of all the heavy elements ranging from carbon to nickel, a clear guide to EUV.
The launch in 1978 of the International Ultraviolet Explorer (IUE), an astronomical satellite, with EUV wavelengths from 115 to 325 nanometers, gave Carole the opportunity to expand her analyzes to other stars, and she became a well-known expert on the chromospheres of cool stars. In 1987 Carole, her PhD student, Philip Judge, and I wrote a paper on the cool unusual star Delta Andromedae, which was observed by IUE and by IRAS for infrared astronomy. This was Carole’s only trip into the infrared part of the spectrum.
From 1971 onwards he was interested in what EUV spectral lines can tell us about the structure and energy stability of the atmosphere of the sun and other stars. In the 1980s he worked on X-ray studies of solar radiation.
Born in Pinner, north-west London, Carole was the daughter of Ethel (nee Waller) and Reg Jordan – while her father was on wartime service with the RAF. While at Harrow county grammar school for girls she read books by Arthur Eddington and Fred Hoyle, and “despite this” she said (in a clever way) decided she wanted to do astronomy. He was interviewed by CW Allen, professor of astronomy at the University of London, and gave a place there.
He was fascinated by the effect of the Soviet Luna 2 spacecraft on the moon in 1959 and in 1961, while still in the first grade, he wrote his first scientific paper, called Selenological Implications Drawn from the Distortions of Craters in the Hipparchus Region of the Moon.
Allen, his PhD supervisor, suggested to Carole that he should try to solve the origin of the EUV spectral lines observed by Tousey in 1962. In the same year when he gave his opinion, 1965, he wrote a paper with Brian Fawcett and Alan Gabriel about the detailed information of all EUV lines from ionized metal.
Bob Wilson, head of the spectroscopy section at Culham, offered him a job, but he first accepted Roy Garstang’s offer at the University of Colorado, Boulder, for a nine-month post. At the meeting of the American Astronomical Society in Ithaca, New York, Carole announced that the ratio of iron to silicon in the solar corona was 10 times greater than in the photosphere.
In 1966 he became an assistant lecturer in astronomy at UCL, but was seconded to UKAEA Culham from 1966 to 1969, and never took up the position.
Between 1968 and 1973 Carole worked on helium-like (two-electron) and lithium-like (three-electron) lines in the lab and solar X-ray spectra (with Gabriel). He and Gabriel developed analytical methods that are now widely used to estimate density and temperature using these lines. He also participated in the international collaboration to launch an ultraviolet telescope by rocket into the path of the 1970 solar eclipse.
From 1969 to 1976 she continued at Culham, becoming chief scientific officer in 1971 and chief scientific officer in 1973. In 1976 Carole became a lecturer in natural sciences at Somerville College, staying at Oxford until her retirement, working as a reader in physics (1994-96) and professor 6-208 (199). He was also head of the Rudolf Peierls Institute for Theoretical Physics (2005-08).
She married UKAEA colleague Richard Peckover in 1971 and they divorced in 1983. A fellow Somerville lecturer, Roman Walczak, recalled that Carole “loved cats and was always with them.
Carole was a strong supporter of the Royal Astronomical Society, serving as secretary (1981-90) as well as president (1994-96). He also served as vice president of the Institute of Physics. He ruffled a few feathers of seniors at the RAS Dining Center by complaining about how slow it had been to accept women as members. In 2005 he was awarded the RAS gold medal.
He became a member of the Royal Society in 1990.
In 2000 Asteroid 8078 was named Carolejordan, and in 2006 Carole was made a dame. She took her work and the role of women scientists very seriously, but she was also a warm and wise friend.
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