Eric Silver

Harvard-Smithsonian Center for Astrophysics

X-Ray Spectroscopy of Highly Charged Ions in Laboratory and Astrophysical Plasmas

The x-ray telescopes and spectrometers flown on Chandra and XMM-Newton have provided astronomers with a wealth of X-ray lines from a range of sources such as Active Galactic Nuclei, stellar coronae, X-ray binary star systems, and supernova remnants. Complex plasma modeling codes are used to interpret the spectral line observations to obtain an understanding of the highly charged ions and their influence on the physical conditions in these objects. The temperature distribution, electron and ion densities, elemental composition, and ionization states of individual constituents are just several plasma properties that can be determined from spectroscopic measurements. The accuracy of the plasma models depends critically on the availability of complete sets of detailed atomic data over a wide range of plasma conditions. Currently, much of this data is either lacking or is not reliable.

On Earth, the behavior of highly charged ions can be studied spectroscopically in an Electron Beam Ion Trap (EBIT). The EBIT produces customized, well-characterized, homogeneous plasmas for a wide variety of precision measurements. It is uniquely capable of simulating specific astrophysical plasma conditions to systematically examine how the atomic structure and dynamics of plasma ions influence the energy release in cosmic x-ray sources. As a byproduct, a comprehensive data base is becoming available for comparison with theoretical atomic physics calculations.

In this talk, I will review how an EBIT is used to perform experiments in atomic and plasma physics relevant to astrophysical plasmas. Spectral measurements with a broad bandwidth, high resolution X-ray microcalorimeter will be presented from experiments that simulate the conditions of stellar coronae via electron collisions with ions. Experiments that mimic the exotic photoionized plasma conditions in the gas near black holes are planned and will also be discussed.

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