13 research outputs found
Thermal radiation processes
We discuss the different physical processes that are important to understand
the thermal X-ray emission and absorption spectra of the diffuse gas in
clusters of galaxies and the warm-hot intergalactic medium. The ionisation
balance, line and continuum emission and absorption properties are reviewed and
several practical examples are given that illustrate the most important
diagnostic features in the X-ray spectra.Comment: 37 pages, 16 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 9; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
Anthropogenic Space Weather
Anthropogenic effects on the space environment started in the late 19th
century and reached their peak in the 1960s when high-altitude nuclear
explosions were carried out by the USA and the Soviet Union. These explosions
created artificial radiation belts near Earth that resulted in major damages to
several satellites. Another, unexpected impact of the high-altitude nuclear
tests was the electromagnetic pulse (EMP) that can have devastating effects
over a large geographic area (as large as the continental United States). Other
anthropogenic impacts on the space environment include chemical release ex-
periments, high-frequency wave heating of the ionosphere and the interaction of
VLF waves with the radiation belts. This paper reviews the fundamental physical
process behind these phenomena and discusses the observations of their impacts.Comment: 71 pages, 35 figure
FREE-FREE GAUNT FACTORS
The hydrogenic (unscreened coulomb) free-free gaunt factors are computed for a wide range of initial energies and photon frequencies. In addition, an average over initial energies with the Maxwell-Boltzmann distribution is performed to give the temperatureaveraged gaunt factors for use in opacity calculations. These are presented as functions of Z/sup 2//kT and h nu /kT. The relation between these gaunt factors and the rate of bremsstrahlung energy production is given, as is the total energy emitted as a function of Z/sup 2//kT. (auth