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Fine Structure in the Main Sequence: Primordial Helium and ΔY/ΔZ

Published online by Cambridge University Press:  07 August 2017

B.E.J. Pagel
B.E.J. Pagel*
Affiliation:
NORDITA, Blegdamsvej 17, Dk-2100 Copenhagen ø, Denmark

Abstract

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The primordial helium abundance YP is important for cosmology and the ratio δY/δZ constrains models of stellar evolution. While the most accurate estimates of both quantities now come from emission lines in HII regions, significant information comes from effects of helium content on stellar structure including in particular the location of the main sequence as a function of metallicity and age. HIPPARCOS parallaxes with 1 or 2 mas accuracy will naturally lead to great advances in this type of study for stars with metallicities down to about 0.1 solar, but sub-mas accuracy will be needed in order to extend it to stars of still lower metallicity.

Type
2. Current and Future Needs for Very Accurate Astrometry
Information
Symposium - International Astronomical Union , Volume 166: Astronomical and Astrophysical Objectives of Sub-Milliarcsecond Optical Astrometry , 1995 , pp. 181 - 186
Copyright
Copyright © Kluwer 1995 

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