Systematic Study of L -Shell Opacity at Stellar Interior Temperatures

Abstract

The first systematic study of opacity dependence on atomic number at stellar interior temperatures is used to evaluate discrepancies between measured and modeled iron opacity [J. E. Bailey et al, Nature 517, 56 (2015)]. Hightemperature (>180 eV) chromium and nickel opacities are measured with 6-10% uncertainty, using the same methods employed in the previous iron experiments. The 10-20% experiment reproducibility demonstrates experiment reliability. The overall model-data disagreements are smaller than for iron. However, the systematic study reveals shortcomings in models for density effects, excited states, and open L-shell configurations. The 30-45% underestimate in the modeled short-wavelength quasi-continuum opacity was observed only from iron and only at temperature above 180 eV. Thus, either opacity theories are missing physics that has non-monotonic dependence on the number of bound electrons, or there is an experimental flaw unique to the iron measurement at temperatures above 180 eV.

The composition of Mars

“…The former method suggests 30 to 40% lower metal content in the Sun and the finding is at 5σ to 15σ outside the limits set by helioseismology for the Sun's surface He abundance, the sound speed in the convective zone, and the depth of the convective zone boundary. Data from experiments on the opacity of metals in high temperature plasma (Bailey et al, 2015;Nagayama et al, 2019), the composition of solar wind particles (Schmelz et al, 2012), and measurements of solar neutrino flux (Haxton et al, 2013;Agostini et al, 2018) are in mutual agreement with findings from helioseismology, regarding the Sun's metallicity. One solution to the problem is to have a significant increase in the Sun's abundance of Mg, Si, S and Fe, which leads to a hotter core temperature (Basu and Antia, 2008;Asplund et al, 2009;Bergemann and Serenelli, 2014).…”

High Resolution Photoexcitation Measurements Exacerbate the Long-Standing Fe XVII Oscillator Strength Problem

“…Similar inconsistencies were recently found in the high resolution K-shell x-ray spectra of the Perseus cluster recorded with the Hitomi microcalorimeter [71,72]. Moreover, recent opacity measurements [12,14] have highlighted serious inconsistencies in the opacity models used to describe the interiors of stars, which have to rely on calculated oscillator strengths.…”

“…conditions, velocity turbulences, and opacities [5][6][7][8][9][10][11][12][13][14][15]. However, for the past four decades, their observed intensity ratios persistently disagree with advanced plasma models, diminishing the utility of high resolution x-ray observations.…”

“…Moreover, 3C and 3D with their, among many transitions, strong absorption and emission rates can also dominate the Planck and Rosseland mean opacity of hot plasmas [64][65][66]. Therefore, an accurate determination of their oscillator strengths may help elucidating the iron opacity issue [12,14,67], if, e.g., Rosseland mean opacity models [68,69] were found to use predicted oscillator strengths also in departure from experiments. Our result exposes in simplest dipole-allowed transitions of Fe XVII a far greater issue, namely, the persistent problems in the best approximations in use, and calls for renewed efforts in further developing the theory of many-electron systems.…”

The Relevance of Nuclear Reactions for Standard Solar Models Construction

“…While the experiment has been carried out only for iron, their conclusion is that all theoretical calculations predict a too low Rosseland mean opacity, at a level of 7 ± 4%, for the temperature and density combinations realized in the experiment. Further experimental work on chromium and nickel opacities was carried out (Nagayama et al, 2019) to help evaluate discrepancies between experimental and theoretical resuls on iron opacity. Results point toward a shortcomings that affect models, particularly in the case of open electronic L-shell configurations such as is present in iron at the base of the convective envelope.…”