Line Broadening and the Solar Opacity Problem

Abstract

The calculation of line widths constitutes theoretical and computational challenges in the calculation of opacities of hot dense plasmas. Opacity models use line broadening approximations that are untested at stellar interior conditions. Moreover, calculations of atomic spectra of the sun, indicate a large discrepancy in the K-shell line widths between several atomic codes and the OP. In this work, the atomic code STAR is used to study the sensitivity of solar opacities to line-broadening. Variations in the solar opacity profile, due to an increase of the Stark widths resulting from discrepancies with OP, are compared, in light of the solar opacity problem, with the required opacity variations of the present day sun, as imposed by helioseismic and neutrino observations. The resulting variation profile, is much larger than the discrepancy between different atomic codes, agrees qualitatively with the missing opacity profile, recovers about half of the missing opacity nearby the convection boundary and has a little effect in the internal regions. Since it is hard to estimate quantitatively the uncertainty in the Stark widths, we show that an increase of all line widths by a factor of about ∼ 100 recovers quantitatively the missing opacity. These results emphasize the possibility that photoexcitation processes are not modeled properly, and more specifically, highlight the need for a better theoretical characterization of the line broadening phenomena at stellar interior conditions and of the uncertainty due to the way it is implemented by atomic codes. Subject headings: dense matter -plasmas -atomic processes -atomic data -opacity -Sun:interior

The Effect of Ionic Correlations on Radiative Properties in the Solar Interior and Terrestrial Experiments

“…SOLAR RADIATIVE ZONE The complicated interactions between an ion and its environment give rise to important phenomena such as collisional line broadening (Dimitrijevic & Konjevic (1987); Krief et al (2016a)) and ionization potential depression (Ciricosta et al (2016)). In addition, the plasma environment affects the local atomic potential and the boundary conditions of atomic wavefunctions.…”

Computation of Atomic Astrophysical Opacities

“…As mentioned in Section 4, a study of line profiles in opacity calculations has shown that OP K-line widths are largely discrepant with those in other plasma models in conditions akin to the solar CZB [27]. Such a finding in fact reflects essential differences in the treatment of ionic models in opacity calculations; i.e., between the OP multichannel representations (see Figure 1) and the simpler uncoupled, or in some cases statistical, versions adopted by other projects that become particularly conspicuous in spectator-electron processes.…”

“…In particular we discuss spectator-electron processes responsible for the broad and asymmetric resonances arising from core photoexcitation, K-shell resonance widths, and ionization edges since it has been recently shown that the solar opacity profile is sensitive to the Stark broadening of K lines [27].…”

Progress in Global Helioseismology: A New Light on the Solar Modeling Problem and Its Implications for Solar-Like Stars

“…The equation of state used by different groups to compute the tables may explain some of the differences 4 . However, the large differences observed in the Bailey et al (2015) experiment results may also be linked to other issues in current opacity computations (Nahar and Pradhan, 2016;Krief et al, 2016;Pain and Gilleron, 2019). Figure 8.…”