The cosmic production of helium

We estimate the cosmic production rate of helium relative to metals (DeltaY/DeltaZ) using K dwarf stars in the Hipparcos catalog with accurate spectroscopic metallicities. The best fitting value is DeltaY/DeltaZ = 2.1 +/- 0.4 at the 68% confidence level. Our derived value agrees with determinations from H II regions and with theoretical predictions from stellar yields with standard assumptions for the initial mass function. The amount of helium in stars determines how long they live and therefore how fast they will enrich the interstellar medium with fresh material.