Asteroseismic ages of red-giant stars from grid-based modelling: the impact of systematics in effective temperature or metallicity

Abstract

An increasingly popular method to determine stellar ages of red-giant stars for the purpose of Galactic archaeology is asteroseismic grid-based modelling (GBM). In asteroseismic GBM of red-giant stars with solar-like oscillations the large frequency separation ($\Delta\nu$) and the frequency of maximum oscillation power ($\nu_{\rm max}$) are commonly used asteroseismic observables, in addition to the usual spectroscopic parameters effective temperature ($T_{\rm eff}$) and metallicity ([Fe/H]). The precision with which $\Delta\nu$ and $\nu_{\rm max}$ can be determined largely depends on the length of the timeseries data (assuming the stars are bright enough that the oscillations can be detected). The question that we aim to answer here is: with what precision should [Fe/H] and $T_{\rm eff}$ be obtained to derive stellar ages of red-giant stars through asteroseismic GBM given the precision of $\Delta\nu$ and $\nu_{\rm max}$ that we can expect from the TESS data? In most cases presented here the value of $\sigma_{\rm age}$ shows only weak, or no, dependence on the uncertainties and biases in [Fe/H] and $T_{\rm eff}$ ingested in this study. Only in case a large ($>100$~K) $T_{\rm eff}$ biases is accompanied by a small (50 K) uncertainties in $T_{\rm eff}$ on the red-giant branch, $\Delta_{\rm age}$ is of the order of or larger than $\sigma_{\rm age}$ and in these cases we expect an impact of this bias on the resulting age estimate.