Opacity Calculations for Stellar Astrophysics

I review the role of radiative opacity in asterosismology, as well as recent progress and remaining challenges in its calculation, highlighting the modeling difficulties, such as the accounting for myriads of lines or plasma density effects. A particular attention is paid to iron, due to its role in the understanding of Beta-Cephei- and SPB-type stars, as well as of the Sun. The importance of laboratory experiments to check the quality of the computed data is underlined and some X-ray and XUV laser and Z-pinch photo-absorption measured spectra are compared with predictions of the fine-structure opacity code SCO-RCG. An analysis of the recent and unexplained iron opacity measurements performed on the Z machine in conditions close to the ones of the base of the convective zone of the Sun is presented and several theoretical aspects are discussed, such as collisional excitation, auto-ionization, multi-photon processes or line broadening.