On the opacity change required to compensate for the revised solar composition

TL;DR

This study quantifies the necessary intrinsic opacity increase to reconcile revised solar composition models with helioseismic data, finding a variable increase of about 30% near the convection zone base.

Contribution

It introduces a method to determine the opacity change needed to offset composition revisions in solar models, aligning them with helioseismic observations.

Findings

Opacity increase of ~30% near the convection zone base

A simple cubic fit models the opacity change as a function of temperature

Revised composition models can match original sound-speed profiles with adjusted opacity

Abstract

Recent revisions of the determination of the solar composition have resulted in solar models in marked disagreement with helioseismic inferences. The effect of the composition change on the model is largely caused by the change in the opacity. Thus we wish to determine an intrinsic opacity change that would compensate for the revision of the composition. By comparing models computed with the old and revised composition we determine the required opacity change. Models are computed with the opacity thus modified and used as reference in helioseismic inversions to determine the difference between the solar and model sound speed. An opacity increase varying from around 30 per cent near the base of the convection zone to a few percent in the solar core results in a sound-speed profile, with the revised composition, which is essentially indistinguishable from the original solar model. As a function of the logarithm of temperature this is well represented by a simple cubic fit. The physical realism of such a change remains debatable, however.