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Primordial Helium and DeltaY/DeltaZ from H II Regions and from Fine Structure in the Main Sequence Based on HIPPARCOS Parallaxes

Girardi, L.; Høg, E.; Pagel, B. E. J. +3 more

The primordial helium abundance YP is important for cosmology and the ratio DeltaY/DeltaZ of the changes relative to primordial abundances constrains models of stellar evolution. While the most accurate estimates of YP come from emission lines in extragalactic H II regions, they involve an extrapolation to zero metallicity which itself is closely …

Lithium Abundance in Pop.II Stars A post-HIPPARCOS discussion

Spite, M.; Hill, V.; Spite, F.

The relation between the lithium abundance observed in Population II stars and the primordial abundance, is still an open question (see Cayrel and Duncan, this meeting). A few recent results are discussed. HIPPARCOS data show that the standard model of stellar evolution can explain the 6Li detection in HD 84937, suggesting a negligible depletion o…