منابع مشابه
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...
متن کاملPrimordial 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...
متن کاملOn 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 ...
متن کاملBlue 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...
متن کاملOn the primordial helium content: CMB and stellar constraints
We present the results of a joint investigation aimed at constraining the primordial He content (YP ) on the basis of both the Cosmic Microwave Background (CMB) anisotropy and two stellar observables, namely the tip of the Red Giant Branch (TRGB) and the luminosity of the Zero Age Horizontal Branch (ZAHB). Current baryon density estimates based on CMB measurements cover a wide range values 0.00...
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ژورنال
عنوان ژورنال: Europhysics News
سال: 1981
ISSN: 0531-7479,1432-1092
DOI: 10.1051/epn/19811208007