Primordial Helium Abundance: A Reanalysis of the Izotov-Thuan Spectroscopic Sample
نویسندگان
چکیده
A reanalysis is made for the helium abundance determination for the Izotov-Thuan (2004) spectroscopic sample of extragalactic H II regions. We find that the effect of underlying stellar absorption of the He I lines, which is more important for metal poor systems, affects significantly the inferred primordial helium abundance Yp obtained in the zero metallicity limit and the slope of linear extrapolation, dY/dZ. This brings Yp from 0.234±0.004 to 0.250±0.004 and dY/dZ = 4.7±1.0 to 1.1±1.4. Conservatively, this indicates the importance of the proper understanding of underlying stellar absorption for accurate determinations of the primordial helium abundance to the error of δYp ≃ 0.002− 0.004.
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