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

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.