Evidence for Enhanced Helium Enrichment from Asteroseismology

The helium abundance of a star has a dramatic effect on luminosity, internal structure, and evolutionary timescales, yet direct helium measurements are unavailable for most stars. In this work, we infer stellar helium abundances by comparing observed and predicted luminosities for a sample of subgiants with asteroseismic masses from the APOKASC sample and spectroscopic parameters from recent survey compilations. Stellar luminosities are predicted using grids of theoretical stellar evolution models and offsets are attributed to helium differences from the assumed model value. From this analysis, we see clear evidence of helium enrichment correlated with metallicity, ΔY/ΔZ = 1.959 plus or minus 0.061, with the dominant error source being systematic differences in stellar fundamental parameters. Our inferred enrichment slope exceeds the value implied by a solar-calibrated helium enrichment relation, suggesting that commonly adopted assumptions regarding helium enrichment may underestimate stellar helium abundances at high metallicity. We further show that adopting the revised enrichment law can alter predicted main-sequence lifetimes by up to about 1 Gyr and, in some cases, modify stellar structure through changes in convective core development. These results demonstrate that uncertainties in helium enrichment propagate directly into stellar age determinations and highlight the importance of empirical helium constraints for stellar evolution models.