The Opacity Project

Opacity is a quantity which determines the transport of radiation through matter, and which is important in many problems in physics and astronomy. To calculate opacities, one requires atomic data for a large number of processes involving the absorption and scattering of radiation. Stellar opacities are of particular interest in astrophysics because of their importance for theories of stellar structure and stellar pulsations. Taking advantage of advances in computational atomic and plasma physics and of the availability of powerful supercomputers, a collaborative effort - the International Opacity Project - has been made to compute accurate atomic data required for opacity calculations. The work includes computation of energy levels, oscillator strengths, photoionization cross-sections and parameters for pressure broadening of spectral lines. Several different methods of computation have been used to calculate the same data, thereby providing a check on the validity of the data. The Opacity Project Team is made up of 27 experts drawn from 13 leading laboratories and observatories in atomic physics and astrophysics in the USA, Europe and South America. The Project has been running since 1986.