Computation of Atomic Astrophysical Opacities

Abstract

Abstract: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 accounting.

New Solar Metallicity Measurements

“…The sound speed u(r) is inferred to be ∼1% lower than predicted at the bottom of the convective zone boundary (CZB, a discrepancy of about 10σ), whereas the surface helium abundance Y s and the CZB R b are approximately 7% lower and 1.5% higher than those deduced from helioseismology, which amount to discrepancies of approximately 6σ and 15σ, respectively. Various solutions to the problem have been proposed, including exotic energy transport due to captured dark matter (see, e.g., [6][7][8][9][10][11]), missing opacity [12][13][14], and enhanced convection [15]. It is worth pointing out that a revised prediction for the iron opacity at solar interior temperatures hints at a 30-400% higher opacity than predicted, which goes in the direction of solving the problem, although it only provides half the missing opacity [16].…”

Quantifying uncertainties in the solar axion flux and their impact on determining axion model parameters

“…[33], who generate a sample of about 10,000 solar models from a Monte Carlo (MC) simulation. 11 As mentioned earlier, the solar abundance problem [34,52,[60][61][62][63] currently still persists, with models from the high-Z as well as the low-Z category being favoured by helioseimology and photospheric observations, respectively. To cover both extremes, we pick representative models from both categories.…”

“…Another observation is that all of the available solar models fail to consistently explain both seismological observations and photospheric measurements. This is known as the solar metallicity or abundance problem [34,52,[60][61][62][63] in the literature, which has not yet been resolved. Table 3 shows an overview of all opacity codes that we have considered.…”

“…At these energies, the different opacity codes produce noticeably diverging results. This issue was already discussed in the context of the solar abundance problem [63] but it also has consequences for solar axion searches: for example, even if the peaks can be experimentally resolved, the uncertainty in the opacity calculation causes problems for abundance measurements of solar metals [28]. Since this is an unresolved issue, we can still only estimate the uncertainty in the solar axion flux around the peaks by comparing different opacity codes.…”

Number of populated electronic configurations in a hot dense plasma

“…The calculation of radiative transport properties and equations state from first principles are of key importance in the modeling of a wide variety of high energy density plasmas, which exist both in stellar interiors [1][2][3][4][5][6][7][8][9][10][11] and in terrestrial laboratories, such as Z-pinch and highpower laser facilities [12][13][14][15][16][17][18][19][20]. These macroscopic quantities entail a very sophisticated interplay between plasma physics and atomic physics.…”