~4 He abundances: Optical versus radio recombination line measurements

摘要

Accurate measurements of the ~4 He/H abundance ratio are important in constraining Big Bang nucleosynthesis, models of stellar and Galactic evolution, and H II region physics. We discuss observations of radio recombination lines using the Green Bank Telescope toward a small sample of H II regions and planetary nebulae. We report ~4He/H abundance ratio differences as high as 15 — 20% between optical and ratio data that are difficult to reconcile. Using the H regions 5206 and M17 we:determine ~4He production in the Galaxy to be dY/dZ = 1.71 ± 0.86.