The name Opacity Project (OP) [1] refers to an international collaboration that was formed in 1984 to calculate the extensive atomic data required to estimate stellar envelope opacities and to compute Rosseland mean opacities and other related quantities. It 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 formalism of the equation of state [2] and on the computation by ab initio methods of accurate atomic properties such as energy levels, f-values and photoionization cross sections [3]. The OP final results are discussed by Seaton et al. [4].

OP opacities have been recently revised to include inner-shell contributions [5]. The new data and a suite of easy-to-use codes to compute Rosseland means and radiative accelerations [6] can be downloaded as a tar file below.

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