The revision of the standard Los Alamos opacities in the 1980-1990s by a
group from the Lawrence Livermore National Laboratory (OPAL) and the Opacity
Project (OP) consortium was an early example of collaborative big-data science,
leading to reliable data deliverables (atomic databases, monochromatic
opacities, mean opacities, and radiative accelerations) widely used since then
to solve a variety of important astrophysical problems. Nowadays the precision
of the OPAL and OP opacities, and even of new tables (OPLIB) by Los Alamos, is
a recurrent topic in a hot debate involving stringent comparisons between
theory, laboratory experiments, and solar and stellar observations in
sophisticated research fields: the standard solar model (SSM), helio and
asteroseismology, non-LTE 3D hydrodynamic photospheric modeling, nuclear
reaction rates, solar neutrino observations, computational atomic physics, and
plasma experiments. In this context, an unexpected downward revision of the
solar photospheric metal abundances in 2005 spoiled a very precise agreement
between the helioseismic indicators (the radius of the convection zone
boundary, the sound-speed profile, and helium surface abundance) and SSM
benchmarks, which could be somehow reestablished with a substantial opacity
increase. Recent laboratory measurements of the iron opacity in physical
conditions similar to the boundary of the solar convection zone have indeed
predicted significant increases (30-400%), although new systematic improvements
and comparisons of the computed tables have not yet been able to reproduce
them. We give an overview of this controversy, and within the OP approach,
discuss some of the theoretical shortcomings that could be impairing a more
complete and accurate opacity accountingComment: 31 pages, 10 figures. This review is originally based on a talk given
at the 12th International Colloquium on Atomic Spectra and Oscillator
Strengths for Astrophysical and Laboratory Plasmas, Sao Paulo, Brazil, July
2016. It has been published in the Atoms online journa
