Realistic Uncertainties for Fundamental Properties of Asteroseismic Red Giants and the Interplay Between Mixing Length, Metallicity and $\nu_{\rm max}$

TL;DR

This paper investigates uncertainties in asteroseismic red giant models, focusing on parameters like mixing length and metallicity, and explores how these affect stellar property estimates and the $ u_{ m max}$ scaling relation.

Contribution

It provides a detailed characterization of model uncertainties, calibrates the $ m MLT$--[M/H] relation, and examines the interplay between $ u_{ m max}$, metallicity, and mixing length.

Findings

Model uncertainties cause ~0.4% in mass, ~0.2% in radius, and ~17% in age.

Calibrated $ m MLT$--[M/H] relation using Kepler binary data.

Incorporating the calibrated relation reduces $ u_{ m max}$ dependence on [M/H].

Abstract

Asteroseismic modelling is a powerful way to derive stellar properties. However, the derived quantities are limited by built-in assumptions used in stellar models. This work presents a detailed characterisation of stellar model uncertainties in asteroseismic red giants, focusing on the mixing-length parameter $\alpha_{\rm MLT}$, the initial helium fraction $Y_{\rm init}$, the solar abundance scale, and the overshoot parameters. First, we estimate error floors due to model uncertainties to be $\approx$0.4\% in mass, $\approx$0.2\% in radius, and $\approx$17\% in age, primarily due to the uncertain state of $\alpha_{\rm MLT}$ and $Y_{\rm init}$. The systematic uncertainties in age exceed typical statistical uncertainties, suggesting the importance of their evaluation in asteroseismic applications. Second, we demonstrate that the uncertainties from $\alpha_{\rm MLT}$ can be entirely mitigated by direct radius measurements or partially through $\nu_{\rm max}$. Utilizing radii from Kepler eclipsing binaries, we determined the $\alpha_{\rm MLT}$ values and calibrated the $\alpha_{\rm MLT}$--[M/H] relation. The correlation observed between the two variables is positive, consistent with previous studies using 1-D stellar models, but in contrast with outcomes from 3-D simulations. Third, we explore the implications of using asteroseismic modelling to test the $\nu_{\rm max}$ scaling relation. We found that a perceived dependency of $\nu_{\rm max}$ on [M/H] from individual frequency modelling can be largely removed by incorporating the calibrated $\alpha_{\rm MLT}$--[M/H] relation. Variations in $Y_{\rm init}$ can also affect $\nu_{\rm max}$ predictions. These findings suggest that $\nu_{\rm max}$ conveys information not fully captured by individual frequencies, and that it should be carefully considered as an important observable for asteroseismic modelling.