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Helium Abundance in the Most Metal-Deficient Dwarf Galaxies

Published online by Cambridge University Press:  12 April 2016

Y.I. Izotov
Y.I. Izotov*
Affiliation:
Main Astronomical Observatory, Goloseevo, Kiev-22, 252650Ukraine

Abstract

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The high-quality long-exposure spectroscopic observations of the two most-metal deficient blue compact galaxies I Zw 18 and SBS 0335–052 are discussed. We confirm previous findings that underlying stellar absorption strongly influences the observed intensities of He I emission lines in the brightest NW component of I Zw 18, and hence this component should not be used for primordial He abundance determination. The effect of underlying stellar absorption, though present, is much smaller in the SE component. The extremely high signal-to-noise ratio spectrum (≥ 100 in the continuum) of the BCG SBS 0335–052 allows us to measure the helium mass fraction with precision better than 2% in nine different regions along the slit. The weighted mean of helium mass fraction in two most metal-deficient BCGs I Zw 18 and SBS 0335–052, Y=0.2462±0.0009, after correction for the He production in massive stars results in primordial He mass fraction Yp = 0.2452±0.0009.

Type
The baryonic mass content of the Universe
Information
International Astronomical Union Colloquium , Volume 171: The Low Surface Brightness Universe , 1999 , pp. 390 - 392
Copyright
Copyright © Astronomical Society of the Pacific 1999

References

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