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, (ΔY/ΔZ), 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 ΔY/ΔZ ratio. We find the systematic uncertainties on mean density, radius, mass, and age arising from grids which employ a fixed value of ΔY/ΔZ and those with free initial helium abundance to be ∼ 0.9 per cent, ∼ 2 per cent, ∼ 5 per cent, and ∼ 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. © 2020 The Author(s).
The authors acknowledge the dedicated team behind the NASA'S Kepler missions. BN thanks Verma Kuldeep, Achim Weiss, and the Stellar Evolution research group at Max-Planck-Institut fur Astrophysik (MPA) for the useful comments on this article. BN also acknowledges postdoctoral funding from the Alexander von Humboldt Foundation. AGH, JCS, and BN acknowledge funding support from Spanish public funds (including FEDER funds) for research under projects ESP2017-87676-C5-2-R and ESP2017-87676-C5-5-R. TLC acknowledges support from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no. 792848 (PULSATION). JF wishes to honor the memory of Johannes Andersen, recently passed way. JF acknowledges funding from POCH and Portuguese FCT grant SFRH/BSAB/143060/2018. CITEUC is funded by National Funds through FCT - Foundation for Science and Technology (projects UID-PB/00611/2020). MSC is supported by national funds through Fundacao para a Ciencia e a Tecnologia (FCT, Portugal) - in the form of a work contract and through the research grants UIDB/04434/2020, UIDP/04434/2020, and PTDC/FIS-AST/30389/2017, and by FEDER -Fundo Europeu de Desenvolvimento Regional through COMPETE2020 Programa Operacional Competitividade e Internacionalizacao (grant: POCI-01-0145-FEDER-030389). AGH also acknowledges support from 'FEDER/Junta de Andalucia-Consejeria de Economia y Conocimiento' under project E-FQM-041-UGR18 by Universidad de Granada. JCS also acknowledges support from project RYC-2012-09913 under the 'Ramon y Cajal' program of the Spanish Ministry of Science and Education. JC is funded by the Fundamental Research Funds for the Central Universities (grant: 19lgpy278). BA acknowledges support from the FCT PhD programme PD/BD/135226/2017. We thank the reviewer for the constructive remarks.