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The Helium-to-Hydrogen Ratio of Stars in Young Clusters and Associations

Published online by Cambridge University Press:  14 August 2015

P. E. Nissen
P. E. Nissen*
Affiliation:
Institute of Astronomy, University of Aarhus, Denmark

Abstract

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A photoelectric narrow-band index, I(4026), of the He I λ 4026 line has been observed with an echelle spectrometer for B-type stars in young clusters and associations.

Model-atmosphere computations of the Strömgren [c1] index, the Hβ index, and I(4026) as functions of Teff, g and the helium-to-hydrogen ratio have been used to derive these atmospheric parameters from the observed indices for each star.

For the OriOBIb, LacOBI and Sco-Cen associations 11 out of 48 stars in the temperature range from 14 000 to 20 000 K are found to be helium poor in the sense that the derived helium-to-hydrogen ratios lie in the range from 0.05 down to very low values. In the temperature range from 20 000 to 30 000 K no helium poor stars are found, but two stars in OriOBIb are helium rich. Both of these stars show rather strong variations of the I(4026) index.

All stars in h + χ Per and CepOBIII are apparently helium deficient compared to nearby field stars.

Type
Part III/Derivation of Abundances Through Photometric and Spectroscopic Methods
Information
Symposium - International Astronomical Union , Volume 72: Abundance Effects in Classification , 1976 , pp. 81 - 83
Copyright
Copyright © Reidel 1976 

References

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