Bulletin of the American Physical Society
55th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Monday–Friday, June 3–7, 2024; Fort Worth, Texas
Session C11: V: Molecules, Collisions, and Spectroscopy
2:00 PM–4:00 PM,
Tuesday, June 4, 2024
Room: Virtual Room 1
Chair: Tijs Karman, Harvard - Smithsonian Center for Astrophysics
Abstract: C11.00002 : The Iron Project: R-Matrix calculations for opacities~II.: Photoionization and oscillator strengths of iron ions Fe~XVII, Fe~XVIII, and Fe~XIX*
2:12 PM–2:24 PM
Presenter:
Sultana N Nahar
(Ohio State Univ - Columbus)
Authors:
Sultana N Nahar
(Ohio State Univ - Columbus)
Lianshui Zhao
(The Ohio State University)
Werner Eissner
(Stuttgart University)
Anil K Pradhan
(The Ohio State University)
Together, Fe XVII, Fe XVIII and Fe XIX contribute 85\% of iron ion fractions 20\%, 39\% and 26\% respectively, at the BCZ physical conditions of temperature T $\sim$ $2.11 \times 10^6$K and electron density N$_e$ = $3.1 \times 10^{22}$cc. We report heretofore the most extensive R-matrix atomic calculations
for these ions for bound-bound and bound-free transitions, the two main processes of radiation absorption. We consider wavefunction expansions with
218 target or core ion fine structure levels of Fe XVIII for Fe XVII, 276 levels of Fe XIX for Fe XVIII, in the Breit-Pauli R-matrix (BPRM) approximation, and
180 LS terms (equivalent to 415 fine structure levels) of Fe XX for Fe XIX calculations. These large target expansions which includes core ion excitations to
n=2,3,4 complexes enable accuracy and convergence of photoionization cross sections, as well as inclusion of high lying resonances. The resulting R-matrix datasets include 454 bound levels for Fe XVII, 1174 levels for Fe XVIII, and 1626 for Fe XIX~up to $n\leq$ 10 and $l$=0 - 9. Corresponding datasets of
oscillator strengths for photoabsorption are: 20,951 transitions for Fe XVII, 141,869 for Fe XVIII, and 289,291 for Fe XIX. Photoionization cross
sections have obtained for all bound fine structure levels of Fe XVII and Fe XVIII, and for 900 bound LS states of Fe XIX. Selected results demonstrating prominent characteristic features of photoionization are presented, particularly the wide Seaton resonances due to PEC (photoexcitation-of-core) formed via high-lying core excitations with $\Delta n=1$ that significantly impact bound-free opacity.
*Computational facility: Ohio Supercomputer Center
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