The available atomic data used for interpreting and modeling x-ray observations are reviewed The applications for these data can be divided into several levels of detail, ranging from compilations which can be used with direct inspection of raw data, such as line finding lists, to synthetic spectra which attempt to fit to an entire observed dataset simultaneously This review covers cosmic sources driven by both electron ionization and photoionization and touches briefly on planetary surfaces and atmospheres The applications to x-ray astronomy, the available data, and recommendations for astronomical users are all reviewed, and an attempt to point out the applications where the shortcomings are greatest is also given

http://ned.ipac.caltech.edu/level5/Sept06/Kallman/paper.pdf

Atomic data for x-ray astrophysics

The n=2-1 spectral emission pattern of heliumlike argon, together with the associated satellite emission originating from lithiumlike argon have been measured with high-resolution x-ray spectroscopy at the Berlin electron-beam ion trap. The observed line intensity across a wide range of excitation energies was weighted by an electron-energy distribution to analyze as a function of plasma temperature the line ratios between KLL dielectronic recombination satellites, in particular the j+z, j, and k satellites, and the w-resonance line. A good agreement between various theoretical models is found, supporting the method of line-ratio measurement as a temperature diagnostic for plasmas. A value for the so-called R-line ratio is determined and calculations with the HULLAC suite of codes predict it to be electron density independent over a wide range.

Spectroscopy of heliumlike argon resonance and satellite lines for plasma temperature diagnostics.

The wavelengths of the 1s2s2p-1s22s and 1s2p2-1s22p transitions in Ar15+ have been measured using a crystal spectrometer and an electron beam ion trap. These spectral lines are satellites to the n = 2 resonance lines of He-like Ar16+ and play an important diagnostic role in high-temperature plasmas directed toward fusion research. The results of these measurements are compared with a number of different theoretical results, demonstrating the relative accuracy of these theoretical approaches.

http://iopscience.iop.org/article/10.1088/0953-4075/34/20/309/pdf

Wavelength measurements of the satellite transitions to the n = 2 resonance lines of helium-like argon

Cosmic plasma conditions created in an electron beam ion trap (EBIT) make it possible to simulate the dependencies of key diagnostic X-ray lines on density, temperature, and excitation conditions that exist in astrophysical sources. We used a microcalorimeter for such laboratory astrophysics studies because it has a resolving power ≈1000, quantum efficiency approaching 100%, and a bandwidth that spans the X-ray energies from 0.2 keV to 10 keV. Our microcalorimeter, coupled with an X-ray optic to increase the effective solid angle, provides a significant new capability for laboratory astrophysics measurements. Broadband spectra obtained from the National Institute of Standards and Technology EBIT with an energy resolution approaching that of a Bragg crystal spectrometer are presented for nitrogen, oxygen, neon, argon, and krypton in various stages of ionization. We have compared the measured line intensities to theoretical predictions for an EBIT plasma.

Laboratory Astrophysics Survey Of Key X-Ray Diagnostic Lines Using A Microcalorimeter On An Electron Beam Ion Trap

The abundance of potassium is derived from X-ray lines observed during flares by the RESIK instrument on the solar mission CORONAS-F between 3.53 A and 3.57 A. The lines include those emitted by He-like K and Li-like K dielectronic satellites, which have been synthesized using the CHIANTI atomic code and newly calculated atomic data. There is good agreement between observed and synthesized spectra, and the theoretical behavior of the spectra with varying temperature estimated from the ratio of the two GOES channels is correctly predicted. The observed fluxes of the He-like K resonance line per unit emission measure give log A(K) = 5.86 (on a scale log A(H) = 12), with a total range of a factor 2.9. This is higher than photospheric abundance estimates by a factor 5.5, a slightly greater enhancement than for other elements with first ionization potential (FIP) less than ~10 eV. There is, then, the possibility that enrichment of low-FIP elements in coronal plasmas depends weakly on the value of the FIP which for K is extremely low (4.34 eV). Our work also suggests that fractionation of elements to form the FIP effect occurs in the low chromosphere rather than higher up, as in some models.

/pdf/highly-ionized-potassium-lines-in-solar-x-ray-spectra-and-57l9264tgf.pdf

Highly ionized potassium lines in solar x-ray spectra and the abundance of potassium

Theoretical X-ray spectra of Ar XVII lines and Ar XVI satellites at approximately 4 angstrom, derived from R-matrix code and other calculations, are compared with solar-flare observations obtained with the SMM Flat Crystal Spectrometer. There is good agreement between the observed line features and those in the theoretical spectra, and the comparison leads to best-fit values of electron temperature for the observed solar flares. We present wavelengths for the Ar XVII and some Ar XVI lines, measured from the observed spectra, which have better precision than previous values. In addition, the coronal Ar/S abundance is determined from the relative intensities of Ar XVII lines to those of nearby S XV transitions, and the value of this ratio is discussed in the light of previous work.

Helium-like Argon Line Emission in Solar Flares

Calculations of excitation rates in Ar+16 and of nearby dielectronic satellite lines have been used to synthesize X‐ray spectra in the range 3.9–4.1 A where lines due to the chief n=1–2 transitions occur. These show excellent agreement with high‐resolution spectra obtained with the Alcator C tokamak.

Calculated ar-xvii line-intensities and comparison with spectra from the alcator-c tokamak

Satellite intensity factors F2*(s to f) of hydrogen-like silicon, calcium, titanium, and iron ions have been calculated for 1s epsilon l -> 2l'nl" -> 1snl" dielectronic-recombination processes. The relevant atomic parameters have been calculated explicitly for all intermediate resonance states up to n=8. Calculations have been performed in the intermediate coupling scheme using ab initio configuration interaction structures and wavefunctions computed using the Hartree-Fock atomic model. The 1/n3 scaling, which has often been used in extrapolating the F2*(s to f) functions for n>or=4, is tested against these explicitly calculated values. The authors find that the 1/n3 scaling can yield erroneous results for individual satellite lines. The satellite intensity factors summed over all states of each n, however, are in good agreement with the 1/n3 scaling as n approaches 8.

Variation of dielectronic satellite intensity factors with n for 1s epsilon l -> 2l'nl" -> 1snl" dielectronic-recombination processes in selected hydrogen-like ions

Helium like sulphur X-ray emission in solar flares and laboratory plasmas.

Total radiative rates, total Auger rates and lifetimes of levels of the Be-like configuration 1s2s2p2 are presented for argon and titanium ions. Similar results are also reported for levels of the configuration 1s2s2p3p for argon. Wavelengths and line intensity factors in the transitions of initial levels of 1s2s2p2 to final levels of 1s22s2p are presented for argon. These calculations were performed in the intermediate coupling scheme using the Hartree-Fock atomic model.

Lifetimes of Be-like levels of argon and titanium

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