We propose an experimental program to generate high accuracy atomic data for the FE XXV and FE XXVI emission diagnostics. Theoretical calculations of specific rate coefficients have estimated…

This is a $623,361 grant awarded by the National Aeronautics and Space Administration (NASA) Shared Services Center to the Smithsonian Astrophysical Observatory, a division of the Smithsonian Institution. The grant funds an experimental program to generate highly accurate atomic data for the iron emission lines of Fe XXV and Fe XXVI, which are important for diagnostic measurements in astrophysics. The program will use Electron Beam Ion Traps (EBITs) at the National Institute of Standards and Technology (NIST) and Clemson University to test existing theoretical calculations and measure the spectra of hydrogen-like and helium-like argon as benchmarks. The goal is to improve the accuracy of atomic data used in X-ray spectroscopy, which is critical for determining electron temperatures in galaxy clusters and enabling more precise cosmological measurements. This grant does not have a set-aside designation and is intended to be completed by December 31, 2021.

We propose an experimental program to generate high accuracy atomic data for the FE XXV and FE XXVI emission diagnostics. Theoretical calculations of specific rate coefficients have estimated accuracies ranging from 5 to 30%. The individual uncertainties may translate into uncertainties on the measurement of interest, e.g. electron temperature, of 30%. Ebit measurements will test the existing theoretical calculations, both the line emission and the individual atomic rates for various processes, including excitation, recombination and ionization. We also measure the spectra of H- and he-like AR for comparison to theory. For AR the resonance line series will provide another benchmark for the atomic physics data. We will conduct the experiments at electron beam ION traps (EBITS) at NIST and clemson university. We will explore in detail broad ranges in parameter space for which the accuracy of the atomic data might be low, e.g. near the threshold where resonances contribute to the collision strength. The ebit measurements will help set priorities for future theoretical calculations. Our program will use the NIST ebit combined with a pair of crystal spectrometers to (a) measure diagnostic line ratios over a range in parameter space (B) conduct detailed experiments to assess the accuracy of rates for individual atomic processes and, (C) evaluate the existing theory and determine its accuracy for input to atomdb. We will use the ebit at clemson to extract and recombining ions to test recombination rates. We expect to make relatively rapid progress by regularly communicating the results from our experiments and assessments to the atomic physics and astrophysics communities. Cosmology using clusters of galaxies relies on a highly accurate measurement of the electron temperature. With current CCD spectra, the shape of the high energy continuum, dominanted by bremsstrahlung, provides the best temperature determination. The microcalorimeter on the X-RAY astrophysics recovery mission, as demonstrated by hitomi, will easily determine the ratio of the fluxes of the strong allowed transitions of FE XXV and FE XXVI, as well as for the temperature-sensitive line ratio of the he-like FE XXV for high signal-to-noise cluster data. Improvements to the accuracy of these diagnostics will significantly reduce the systematics from cluster cosmology. These data will also be of broad use for other sources as well. Our team will make improved atomic data available to the astronomy community in a timely manner through atomdb.