Atomic Data from the Opacity Project

Abstract

The name Opacity Project (OP) refers to an international collaboration that was formed in 1984 to calculate the extensive atomic data required to estimate stellar envelope opacities. The project has involved research groups from France, Germany, the United Kingdom, the United States and Venezuela. The approach adopted by the OP to calculate opacities is based on a new equation-of-state formalism (see the series of papers “The equation of state for stellar envelopes”, ref. [1] and contributions thereafter) and on the calculation of accurate atomic properties such as energy levels, fvalues and photoionisation cross sections (see the series of papers “Atomic Data for Opacity Calculations”, ref. [2] and contributions thereafter). The theoretical framework used to compute ionic states (bound and free) and their radiative properties is based on the close-coupling formalism of scattering theory [3] and on the R-matrix numerical approach developed by Burke and collaborators [4]. Considerable improvements and extensions were introduced in the R-matrix package to adapt it for this task, thus producing a powerful computational tool to study both collisional and radiative properties of electronion systems. In particular, an innovative treatment of the asymptotic region has led to high efficiency and speed in computation, and allows unobserved bound states to be calculated since initial energy estimates are no longer required [5].