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K-Shell Photoabsorption along the Silicon Isonuclear sequence

Presentation #302.03 in the session “Laboratory Astrophysics Division (LAD): Fundamental Nuclear and Atomic Data for Compact Objects”.

Published onJun 18, 2021
K-Shell Photoabsorption along the Silicon Isonuclear sequence

Photoabsorption cross sections for the entire isonuclear sequence neutral Si I through Si XII ions have been computed using an R-matrix method with the inclusion of important spectator Auger broadening effects of K-shell-excited autoionizing resonances. Further, relativistic contributions in Si XII are also calculated within the framework of a Breit-Pauli R-matrix (BPRM) method. Background cross sections are in good overall agreement with earlier resonanceless photoionization cross sections, indicating that the outer L-shell and M-shell photoabsorption features are taken into account properly. Comparison with the earlier BPRM cross sections for S II – Si XII [M. C. Witthoeft, et al., ApJ 182, 127 (2009); ApJ 192, 7 (2011)] shows good agreement in general for the resonance strengths and widths. However, those earlier calculations did not take into account the strong outer-shell electron relaxation following inner-shell photoexcitation or photoionization, and there are also noticeable discontinuities found in those earlier cross sections resulting from switching on and off the spectator Auger broadening of resonances, which is now resolved. The computed cross sections have been used for the detailed analysis of the gaseous component of the atomic Si K edge by using high-resolution Chandra spectra of low-mass X-ray binaries [E. Gatuzz, et al., MNRAS 498, l20 (2020)].

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