The Opacity Project: R-Matrix Calculcations for Astrophysical Plasma Opacities

Surprisingly, solar abundances of common light elements C, N, O, Ne, etc. are uncertain by large amounts of up to ~50\%. Radiation flow in stars is governed by interior opacities of heavier elements, especially Fe. However, there are serious disagreements between current theoretical models based on the Distorted Wave approximation and experiment. We are continuing more accurate but complex Breit-Pauli R-matrix calculations for Fe ions important at the radiative and convection zones boundary, Fe~XVI-Fe~XIX. Large-scale calculations for photoionization cross sections and transition probabilities have been carried out including the heretofore neglected autoionization resonance features and plasma broadening thereof. Fe~XVII BPRM calculations include 218 coupled fine structure levels in the Fe~XVIII target wavefunction expansion, and Fe~XVIII calculations include 276 levels of Fe~XIX. It is found that huge photoexcitation-of-core (PEC) or Seaton resonances make the dominant contribution to bound-free opacity. Convergence and completeness of coupled channel wavefunction expansions and calculated opacities is also addressed.