Asteroseismic stellar modelling: systematics from the treatment of the initial helium abundance

TL;DR

This study investigates how different assumptions about initial helium abundance, estimated via the helium-to-heavy element ratio, systematically affect stellar parameter estimates in asteroseismic models of solar-type stars.

Contribution

It quantifies the systematic uncertainties in stellar radius, mass, and age arising from varying initial helium abundance assumptions in asteroseismic stellar modelling.

Findings

Higher helium-to-heavy element ratio leads to lower estimated stellar radius and mass.

Systematic uncertainties are 1.1% for radius, 2.6% for mass, and 13.1% for age.

Different initial helium assumptions significantly impact stellar parameter estimates.

Abstract

Despite the fact that the initial helium abundance is an essential ingredient in modelling solar-type stars, its abundance in these stars remains a poorly constrained observational property. This is because the effective temperature in these stars is not high enough to allow helium ionization, not allowing any conclusions on its abundance when spectroscopic techniques are employed. To this end, stellar modellers resort to estimating the initial helium abundance via a semi-empirical helium-to-heavy element ratio, anchored to the the standard Big Bang nucleosynthesis value. Depending on the choice of solar composition used in stellar model computations, the helium-to-heavy element ratio, ($\Delta Y/\Delta Z$) is found to vary between 1 and 3. In this study, we use the Kepler "LEGACY" stellar sample, for which precise seismic data is available, and explore the systematic uncertainties on the inferred stellar parameters (radius, mass, and age) arising from adopting different values of $\Delta Y/\Delta Z$, specifically, 1.4 and 2.0. The stellar grid constructed with a higher $\Delta Y / \Delta Z$ value yields lower radius and mass estimates. We found systematic uncertainties of 1.1 per cent, 2.6 per cent, and 13.1 per cent on radius, mass, and ages, respectively.