Opacity is a quantity which determines the transport of radiation through matter, and 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, photoionisation 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 30 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.
The Opacity Project Volume 1 is the first of a two-volume reference work produced by the international Opacity Project. It is divided into two parts:
*Reprints of 31 key research papers elaborating the theoretical physical basis and computational methods used to produce the data. These papers provide essential background for researchers to understand how the data are produced.
*Tables of energy levels and oscillator strengths for atoms and ions of the elements He to Si.
The Opacity Project Volume 2 is the second of a two-volume reference work produced by the international Opacity Project. It contains tables of energy levels and oscillator strengths for the elements S, Ar, Ca and Fe.