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A: Fachverband Atomphysik

A 31: Fathoming Stellar Evolution with Laboratory Precision SYSE (with MS, Q, MO, EP)

A 31.3: Hauptvortrag

Mittwoch, 19. März 2014, 15:00–15:30, Audimax

Photoabsorption and opacity in the X-ray region: The role of highly charged ions — •José R. Crespo López-Urrutia — Max-Planck-Institut für Kernphysik, Heidelberg, Germany

Within the radiative zone of stars, the contribution to opacity by highly charged ions is the dominant one. In such a dense and hot environment, X-ray opacity determines radiation transport and radiation pressure. It strongly influences the hydrostatic equilibrium, and thus the structure and dynamic evolution, e. g., oscillations and collapse, of a star. Even minor amounts of iron present there play a key role: They are essential to explain the temperature profile of the Sun and main sequence stars. Highly charged iron ions make the star core almost completely opaque to X-rays, slowing down the energy flux. On the theoretical side, opacity calculations for astrophysics require the use of approximations, and until now very few accurate experimental benchmarks have been reported for them. Recently, with the use of electron beam ion traps at X-ray sources such as free-electron lasers and synchrotron facilities, new methods have been developed for detailed studies of such X-ray photoabsorption process. The results of these experiments test the values of cross sections and resonance energies for ions in charge states which had hitherto been beyond reach, and the experimental results achieve accuracies surpassing that of current theory.