Solar heavy element abundance: constraints from frequency separation ratios of low-degree p modes

TL;DR

This study uses low-degree solar oscillation frequencies from BiSON data to precisely constrain the solar core's mean molecular weight and metallicity, supporting high metallicity models consistent with helioseismic observations.

Contribution

It provides the first high-precision seismic constraints on the solar core's composition, favoring high metallicity solar models over low metallicity ones.

Findings

Mean molecular weight in the inner 20% radius range from 0.7209 to 0.7231.

Seismic metallicity estimates range from Z=0.0187 to Z=0.0239.

Results show high metallicity models align better with helioseismic data.

Abstract

We use very precise frequencies of low-degree solar-oscillation modes measured from 4752 days of data collected by the Birmingham Solar-Oscillations Network (BiSON) to derive seismic information on the solar core. We compare these observations to results from a large Monte Carlo simulation of standard solar models, and use the results to constrain the mean molecular weight of the solar core, and the metallicity of the solar convection zone. We find that only a high value of solar metallicity is consistent with the seismic observations. We can determine the mean molecular weight of the solar core to a very high precision, and, dependent on the sequence of Monte Carlo models used, find that the average mean molecular weight in the inner 20% by radius of the Sun ranges from 0.7209 to 0.7231, with uncertainties of less than 0.5% on each value. Our lowest seismic estimate of solar metallicity is Z=0.0187 and our highest is Z=0.0239, with uncertainties in the range of 12--19%. Our results indicate that the discrepancies between solar models constructed with low metallicity and the helioseismic observations extend to the solar core and thus cannot be attributed to deficiencies in the modeling of the solar convection zone.