Equation of state and helioseismic inversions

TL;DR

This paper addresses systematic errors in helioseismic inversions caused by differences in the equation of state, proposing methods to suppress these errors and distinguish between different equations of state using solar data.

Contribution

It introduces a technique to reduce EOS-related errors in helioseismic inversions and demonstrates how to invert for differences in the adiabatic exponent Gamma_1 between equations of state.

Findings

Inversion can suppress errors from EOS discrepancies.

The method rules out the EFF EOS with current data.

Distinguishing between other EOS remains challenging.

Abstract

Inversions to determine the squared isothermal sound speed and density within the Sun often use the helium abundance Y as the second parameter. This requires the explicit use of the equation of state (EOS), thus potentially leading to systematic errors in the results if the equations of state of the reference model and the Sun are not the same. We demonstrate how this potential error can be suppressed. We also show that it is possible to invert for the intrinsic difference in the adiabatic exponent Gamma_1 between two equations of state. When applied to solar data such inversion rules out the EFF equation of state completely, while with existing data it is difficult to distinguish between other equations of state.