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Space Science Reviews

, Volume 84, Issue 1–2, pp 115–126 | Cite as

Primordial Helium and ΔY/ΔZ from H II Regions and from Fine Structure in the Main Sequence Based on Hipparcos Parallaxes

  • E. Høg
  • B.E.J. Pagel
  • L. Portinari
  • P.A. Thejll
  • J. Macdonald
  • L. Girardi
Article

Abstract

The primordial helium abundance YP is important for cosmology and the ratio ΔY/ΔZ 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 tied up with the slope ΔY/ΔZ. Recently certain systematic effects have come to light in this exercise which make it useful to have an independent estimate of ΔY/ΔZ from fine structure in the main sequence of nearby stars. We derive such an estimate from Hipparcos data for stars with Z ≤ Z⊙ and find values between 2 and 3, which are consistent with stellar models, but still have a large uncertainty.

galaxies: abundances ISM: abundances stars: abundances stars: evolution 

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Copyright information

© Kluwer Academic Publishers 1998

Authors and Affiliations

  • E. Høg
    • 1
  • B.E.J. Pagel
    • 2
  • L. Portinari
    • 2
  • P.A. Thejll
    • 2
  • J. Macdonald
    • 3
  • L. Girardi
    • 4
  1. 1.University ObservatoryNBIfAFGCopenhagen ØDenmark
  2. 2.NORDITACopenhagen ØDenmark
  3. 3.Department of Physics and AstronomyUniversity of DelawareNewarkUSA
  4. 4.Dipartimento di AstronomiaVicolo dell'Osservatorio 5PadovaItaly

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