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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 appointed the first female president of the Royal Astronomical Society and she was a formidable advocate for women in science.
When we glance at the sun we see a yellow zone at a temperature of 5,500C – the photosphere. When the light is spread out into all its wavelengths, myriad bright and dark lines appear, corresponding to electrons being emitted and absorbed by different atoms. The strongest lines in the visible spectrum come from a thin layer just above the visible surface, the chromosphere. Above this lies the corona, which extends for millions of kilometres and only becomes visible during eclipses. In this zone the temperature increases to 1 million degrees, and so the light and spectral lines mainly become visible at extreme ultraviolet (EUV) or soft X-ray wavelengths.
In 1962, just as Carole was starting her PhD, a rocket-borne experiment led by the US astronomer Richard Tousey measured the EUV spectrum of the sun, and found a dozen or so unidentified emission lines. Carole set out to understand these lines and eventually became the world expert on ultraviolet spectroscopy of the sun and other stars.
In her 1965 PhD thesis, Analysis of the Solar Ultraviolet Spectrum, she concluded that several of the lines were due to transitions in highly ionized iron. A neutral iron atom has 26 electrons orbiting it, but at million-degree temperatures many of the outer electrons get stripped away, leaving the atom in an ionized state. Carole raised eyebrows by asserting that some of the EUV lines were due to 13 times ionized iron, Fe XIV. On a visit to the Zeta ionized gas experiment at the UK Atomic Energy Laboratory (UKAEA) at Culham, in Oxfordshire, with her supervisor, Carole could see the same lines in the lab spectrum, confirming her identification.
Just four years later, in her most-cited paper, The Ionization Equilibrium of Elements Between Carbon and Nickel, published in the Royal Astronomical Society journal in 1969, Carole laid out the ionization equilibrium as a function of temperature for the main ionized states of all the most common heavy elements from carbon to nickel, a definitive guide to EUV spectroscopy.
The launch in 1978 of the International Ultraviolet Explorer (IUE), an astronomical satellite, with its EUV wavelength coverage from 115 to 325 nanometres, gave Carole the opportunity to extend her analyses to other stars, and she became the acknowledged expert on the chromospheres of cool stars. In 1987 Carole, her PhD student Philip Judge and I wrote a paper on the unusual cool star Delta Andromedae, which had been observed both by IUE and by the infrared astronomy mission IRAS. This was Carole’s only excursion into the infrared part of the spectrum.
From 1971 onwards she was interested in what EUV spectral lines could tell us about the structure and energy balance of the atmosphere of the sun and other stars. In the 1980s she worked on X-ray studies of solar flares.
Born in Pinner, north-west London, Carole was the daughter of Ethel (nee Waller) and Reg Jordan - at the time 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 “in spite of this” she said (with characteristic wit) decided she wanted to do astronomy. She was interviewed by CW Allen, professor of astronomy at University College London, and offered a place there.
She was much impressed by the Soviet Luna 2 spacecraft’s impact on the moon in 1959 and in 1961, while still an undergraduate, wrote her first scientific paper, titled Selenological Implications Drawn from the Distortions of Craters in the Hipparchus Region of the Moon.
Allen, her PhD supervisor, suggested to Carole that she should try to solve the origin of the EUV spectral lines observed by Tousey in 1962. In the same year as she submitted her thesis, 1965, she wrote a paper with Brian Fawcett and Alan Gabriel on the detailed identification of all the EUV lines from ionized iron.
Bob Wilson, head of the spectroscopy division at Culham, offered her a post, but she first took up an offer by Roy Garstang at the University of Colorado, Boulder, of a nine-month postdoctoral position. At a meeting of the American Astronomical Society in Ithaca, New York, Carole announced that the abundance ratio of iron to silicon in the solar corona was 10 times greater than in the photosphere.
In 1966 she became an assistant lecturer in the department of astronomy at UCL, but was seconded to UKAEA Culham from 1966 until 1969, and never took up the position.
Between 1968 and 1973 Carole worked on helium-like (two electron) and lithium-like (three electron) spectral lines in lab and solar X-ray spectra (with Gabriel). She and Gabriel developed the now widely used diagnostic techniques for estimating densities and temperatures using these lines. She was also involved in an international collaboration to fly an ultraviolet spectrometer on a rocket into the path of the 1970 solar eclipse.
From 1969 to 1976 she continued at Culham, becoming senior scientific officer in 1971 and principal scientific officer in 1973. In 1976 Carole became tutorial fellow in natural sciences at Somerville College, remaining at Oxford until her retirement, serving as reader in physics (1994-96) and professor (1996-2008). She was also head of the Rudolf Peierls Centre for Theoretical Physics (2005-08).
She married Richard Peckover, a UKAEA colleague, in 1971 and they divorced in 1983. Her fellow tutor at Somerville, Roman Walczak, recalled that Carole “loved cats and she always had one. Her house was full of books, it had a piano, and in practice it belonged to her cat.”
Carole was a staunch supporter of the Royal Astronomical Society, serving as secretary (1981-90) as well as president (1994-96). She also served as vice-president of the Institute of Physics. She ruffled a few elderly feathers at the RAS Dining Club by complaining how slow it had been to admit women as members. In 2005 she was awarded the RAS’s gold medal.
She became a fellow 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 female scientists very seriously, but she was also a warm and witty friend.
