The Sensitivity of Convection Zone Depth to Stellar Abundances: An Absolute Stellar Abundance Scale from Asteroseismology

TL;DR

This paper demonstrates that the acoustic depth to the convection zone in solar-like stars can serve as an absolute, atmosphere-independent measure of stellar metallicity, with potential applications in stellar physics.

Contribution

It introduces a method to estimate stellar metallicity using asteroseismic measurements of convection zone depth, improving accuracy and independence from atmospheric models.

Findings

The normalized acoustic depth to the convection zone strongly depends on stellar mass and metallicity.

Metallicity can be estimated within 0.15-0.3 dex using asteroseismic data.

The method has implications for understanding stellar mixing and composition variations.

Abstract

The base of the convection zone is a source of acoustic glitches in the asteroseismic frequency spectra of solar-like oscillators, allowing one to precisely measure the acoustic depth to the feature. We examine the sensitivity of the depth of the convection zone to mass, stellar abundances, and input physics, and in particular, the use of a measurement of the acoustic depth to the CZ as an atmosphere-independent, absolute measure of stellar metallicities. We find that for low mass stars on the main sequence with $0.4 M_{\odot} \le M \le 1.6 M_{\odot}$, the acoustic depth to the base of the convection zone, normalized by the acoustic depth to the center of the star, $\tau_{cz,n}$, is both a strong function of mass, and varies at the 0.5-1% per 0.1 dex level in [Z/X], and is therefore also a sensitive probe of the composition. We estimate the theoretical uncertainties in the stellar models, and show that combined with reasonable observational uncertainties, we can expect measure the the metallicity to within 0.15 - 0.3 dex for solar-like stars. We discuss the applications of this work to rotational mixing, particularly in the context of the observed mid F star Li dip, and to distguishing between different mixtures of heavy elements.