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| Opacity Project | |
|---|---|
| Name | Opacity Project |
| Start | 1980s |
| Discipline | Atomic physics |
| Country | International |
| Institutions | University College London; Queen Mary University of London; Los Alamos National Laboratory; Lawrence Livermore National Laboratory; Max Planck Institute for Astrophysics |
| Lead | M. J. Seaton; C. J. Zeippen; P. J. Storey |
| Keywords | Atomic data; radiative opacity; photoionization; stellar interiors |
Opacity Project The Opacity Project was an international scientific collaboration that computed extensive atomic data for radiative opacities used in astrophysics, plasma physics, and stellar modelling. It produced benchmark photoionization cross sections, bound–bound transition probabilities, and monochromatic and mean opacities that informed models of Sun-like stars, Cepheid variables, and Type Ia supernova progenitors. The Project linked expertise across institutions such as University College London, Los Alamos National Laboratory, Lawrence Livermore National Laboratory, Max Planck Institute for Astrophysics, and Queen Mary University of London.
The initiative grew from needs identified in work on solar structure by groups at Cambridge University and Princeton University and discrepancies highlighted by helioseismology from teams at SOHO and Global Oscillation Network Group. Confronted with differences between observational inferences from BISON and model predictions influenced by prior opacity compilations like those from Los Alamos National Laboratory and OPAL Project researchers at Lawrence Livermore National Laboratory, proponents such as M. J. Seaton advocated a systematic, quantum-mechanical recalculation of atomic rates. Funding and policy support came from agencies including Science and Engineering Research Council (UK) and later national laboratories tied to Department of Energy (United States) programs.
The Project employed ab initio, close-coupling techniques using the R-matrix method developed within communities at Queen Mary University of London and refined with codes from Atomic Data and Analysis Structure collaborations. Calculations combined target descriptions from configuration interaction expansions influenced by approaches used at Daresbury Laboratory and utilized relativistic corrections akin to those in packages from NIST. Massive computations were performed on supercomputers at Los Alamos National Laboratory, Lawrence Livermore National Laboratory, and the European Centre for Medium-Range Weather Forecasts-era platforms, integrating photoionization, electron-impact excitation, and radiative recombination processes. The team adopted standardized data formats to interoperate with stellar evolution codes such as MESA (software), GARSTEC, and opacity-interpolators applied in CESAM and ASTEC frameworks.
Deliverables included monochromatic opacities, Rosseland and Planck mean opacities, and extensive line lists for ions across the periodic table from hydrogen through iron-peak elements like Iron and Nickel. Data were packaged in tables compatible with stellar modelling pipelines used by groups at Harvard-Smithsonian Center for Astrophysics, Max Planck Institute for Astrophysics, and observatory initiatives such as Kepler and Gaia. The Project's datasets were disseminated via collaborations with data centers like Centre de Données astronomiques de Strasbourg and cataloguing efforts at National Institute of Standards and Technology while informing opacity projects at OPAL Project counterparts and later updates by consortia in Italy and China.
Opacity Project results revised interior models of the Sun and altered inferred metal abundances used in spectroscopic analyses at institutions such as Mount Wilson Observatory and European Southern Observatory. The tables impacted interpretation of oscillation spectra from Kepler and TESS missions, constrained convective zone depths addressed by helioseismology teams, and influenced nucleosynthesis studies tied to Type II supernova modelling at Los Alamos National Laboratory. In planetary science, the data were applied in models of gas giants explored by missions like Voyager and Cassini. The Project's output underpinned opacity inputs in radiative transfer codes used by groups at Space Telescope Science Institute and informed opacity-related uncertainties considered by committees such as those convened by the International Astronomical Union.
The effort united researchers across universities and national laboratories including University College London, Queen Mary University of London, Los Alamos National Laboratory, Lawrence Livermore National Laboratory, and the Max Planck Institute for Astrophysics. Collaborative workshops and conferences were held alongside meetings of societies such as the Royal Astronomical Society and the American Astronomical Society. Computational infrastructure leveraged batch systems and parallel architectures maintained at National Energy Research Scientific Computing Center-era facilities and bespoke code repositories coordinated with groups at Daresbury Laboratory. Data stewardship practices linked outputs to archives managed by Centre de Données astronomiques de Strasbourg and usage monitored by researchers at Harvard-Smithsonian Center for Astrophysics.
The Project was praised by researchers at Cambridge University, Princeton University, and University of Chicago for its rigorous quantum treatment and comprehensive coverage, while follow-up analyses by teams at Lawrence Livermore National Laboratory and Los Alamos National Laboratory spurred debates over remaining opacity uncertainties relevant to the solar abundance problem pursued by groups at Institute of Astronomy, Cambridge and Max Planck Institute for Astrophysics. Its datasets continue to be cited in studies from asteroseismology consortia to supernova modelling groups, and its methodologies influenced successor efforts such as modern opacity re-evaluations in Italy and large-scale atomic databases curated by NIST and CDS. The legacy endures in standard opacity inputs used across stellar, planetary, and laboratory plasma research communities.