Impact of a radius and composition variation on the solar subsurface layers stratification

TL;DR

This study investigates how variations in the Sun's radius and composition affect subsurface layer stratification, using theoretical models and f-mode analysis to understand their influence on solar structure and cyclic radius changes.

Contribution

It is the first to analyze the impact of radius and composition variations on solar subsurface layers through theoretical modeling and f-mode analysis.

Findings

Radius variation influences subsurface structure significantly.

Composition changes also affect the stratification.

Estimated amplitude of the 11-year radius cycle.

Abstract

Several works have reported changes of the Sun's subsurface stratification inferred from f-mode or p-mode observations. Recently a non-homologous variation of the subsurface layers with depth and time has been deduced from f-modes. Progress on this important transition zone between the solar interior and the external part supposes a good understanding of the interplay between the different processes which contribute to this variation. This paper is the first of a series where we aim to study these layers from the theoretical point of view. For this first paper, we use solar models obtained with the CESAM code, in its classical form, and analyze the properties of the computed theoretical f-modes. We examine how a pure variation in the calibrated radius influences the subsurface structure and we show also the impact of an additional change of composition on the same layers. Then we use an inversion procedure to quantify the corresponding f-mode variation and their capacity to infer the radius variation. We deduce an estimate of the amplitude of the 11-year cyclic photospheric radius variation.