Revisiting ΔY/ΔZ from multiple main sequences in globular clusters: insight from nearby stars: ΔY/ΔZ in nearby stars and globular clusters

For nearby K dwarfs, the broadening of the observed main sequence (MS) at low metallicities is much narrower than expected from isochrones with the standard helium-to-metal enrichment ratio ΔY/ΔZ∼ 2. Though the latter value fits well the MS around solar metallicity, and agrees with independent measurements from H ii regions as well as with theoretical stellar yields and chemical evolution models, ...