Study of X-ray emission from solar active regions.

A study of the X-ray emission from solar coronal active regions is presented. The observations were made with two instruments: (1) a collimated Bragg crystal spectrometer with high spectral resolution (400 < ?/? ? < 1000) and moderate spatial resolution (about 3 arc min), and (2) a grazing incidence telescope which obtained broad wavelength-band images with high spatial resolution (about 2 arc sec). Chapter 1 gives a brief review of the relevant physics, with particular emphasis on the Sun's soft X-ray emission (i.e. 1 < wavelength,? < 25 A). The plasma and atomic physics required to interpret the X-ray observations are summarised in Chapter 2. The instruments used in this work were the (sounding) rocket-borne Leicester Mk. 3 Bragg spectrometer, and the American Science and Engineering (ASE) X-ray telescope S-054, aboard the Skylab Apollo Telescope mount. The instruments and data analysis techniques are described in Chapter 3. The data are interpreted in terms of thermal emission from an optically thin plasma. In Chapter 4, coronal active region models, are derived, of electron density and emission measure (ne2?v) as a function of electron temperature and spatial location. Abundances are derived for the elements oxygen, neon, sodium, magnesium, aluminium, silicon, iron and nickel in the solar corona. Chapters 5, 6 and 7 describe observations and interpretation of spectra of ions belonging to particular isoelectronic sequences, namely: Chapter 5, the Helium-like ions 0 VII, Ne IX and Mg XI; Chapter 6, the Neon-like ions Fe XVII and Ni XIX, Chapter 7, Fluorine-like Fe XVIII and Oxygen-like Fe XIX.