Asteroseismic modelling of solar-type stars: A deeper look at the treatment of initial helium abundance

TL;DR

This study investigates how different assumptions about initial helium abundance in stellar models affect the accuracy of inferred stellar properties like mass, radius, and age, using Kepler data of solar-type stars.

Contribution

It systematically compares the effects of fixed versus free initial helium abundance in stellar models on derived stellar parameters.

Findings

Masses and radii are lower when helium abundance is free.

Systematic uncertainties are about 0.9% in density, 2% in radius, 5% in mass, and 29% in age.

Uncertainties in mass and radius are within ESA's PLATO mission accuracy limits.

Abstract

Detailed understanding of stellar physics is essential towards a robust determination of stellar properties (e.g. radius, mass, and age). Among the vital input physics used in the modelling of solar-type stars which remain poorly constrained, is the initial helium abundance. To this end, when constructing stellar model grids, the initial helium abundance is estimated either (i) by using the semi-empirical helium-to-heavy element enrichment ratio, (${\Delta Y}/{\Delta Z}$), anchored to the standard Big Bang Nucleosynthesis value or (ii) by setting the initial helium abundance as a free variable. Adopting 35 low-mass, solar-type stars with multi-year Kepler photometry from the asteroseismic "LEGACY" sample, we explore the systematic uncertainties on the inferred stellar parameters (i.e., radius, mass, and age) arising from the treatment of the initial helium abundance in stellar model grids . The stellar masses and radii derived from grids with free initial helium abundance are lower compared to those from grids based on a fixed ${\Delta Y}/{\Delta Z}$ ratio. We find the systematic uncertainties on mean density, radius, mass, and age arising from grids which employ a fixed value of ${\Delta Y}/{\Delta Z}$ and those with free initial helium abundance to be $\sim$ 0.9%, $\sim$ 2%, $\sim$ 5% and $\sim$ 29%, respectively. We report that the systematic uncertainties on the inferred masses and radii arising from the treatment of initial helium abundance in stellar grids lie within the expected accuracy limits of ESA's PLATO, although this is not the case for the age.