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Høg E. Pagel B.E.J. Portinari L. Thejll P.A. Macdonald J. Girardi L. 《Space Science Reviews》1998,84(1-2):115-126
The primordial helium abundance YP is important for cosmology and the ratio Y/Z 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 Y/Z. Recently certain systematic effects have come to light in this exercise which make it useful to have an independent estimate of Y/Z 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. 相似文献
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