Abundance of Helium in Stellar Atmospheres

Helium abundance in stellar atmospheres has been the subject of several recent investigations, essentially induced by progresses in the computation of non-grey model atmospheres (including line blanketing in the far U.V.), by considerable advances in the theory of Stark broadening of helium lines, by non local thermodynamic equilibrium (LTE) work for the helium spectrum and more fundamentally by the intrinsic importance of the helium over hydrogen ratio in cosmological theories.