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

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 multiyear 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 similar to 0.9 per cent, similar to 2 per cent, similar to 5 per cent, and similar to 29 per cent, 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.

Automated summary

The study shows that the treatment of initial helium abundance in stellar model grids significantly affects the inferred stellar parameters, especially the stellar mass and radius. The systematic uncertainties arising from different methods of handling initial helium abundance are within the expected accuracy limits of ESA's PLATO, except for the age parameter.