Primordial Helium-3 Redux: The Helium Isotope Ratio of the Orion Nebula*

The Primordial Helium Abundance

The primordial abundance of He, YP , is one of the hottest themes in present-day astronomy, mostly due to its cosmological relevance. The disagreement between different determinations has been currently reduced to the 1-2% level, but these differences are still large enough to have deep implications for Big-Bang nucleosynthesis. It is therefore crucial to estimate precisely the uncertainties in...

On the Abundance of Primordial Helium

We have used recent observations of helium-4, nitrogen and oxygen from some four dozen, low metallicity, extra-galactic HII regions to define mean N versus O, He versus N and He versus O relations which are extrapolated to zero metallicity to determine the primordial He mass fraction YP . The data and various subsets of the data, selected on the basis of nitrogen and oxygen, are all consistent ...

Primordial helium recombination. II. Two-photon processes

Interpretation of precision measurements of the cosmic microwave background (CMB) will require a detailed understanding of the recombination era, which determines such quantities as the acoustic oscillation scale and the Silk damping scale. This paper is the second in a series devoted to the subject of helium recombination, with a focus on two-photon processes in He I. The standard treatment of...

Changes in the atmospheric helium isotope ratio over the past 40 years

Blue compact galaxies and the primordial 4 Helium abundance

Blue compact galaxies (BCG) are ideal objects in which to derive the primordial He abundance because they are chemically young and have not had a significant stellar He contribution. We discuss a self-consistent method which makes use of all the brightest He I emission lines in the optical range and solves consistently for the electron density of the He II zone. We pay particular attention to e...