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Abundance and Magnetic Field Geometries of Helium-Strong and Helium-Weak Stars

Published online by Cambridge University Press:  19 July 2016

David A. Bohlender
Affiliation:
Department of Astronomy, University of Western Ontario, London, Ontario N6A 3K7
J. D. Landstreet
Affiliation:
Department of Astronomy, University of Western Ontario, London, Ontario N6A 3K7

Extract

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The helium-weak and helium-strong stars are main sequence stars with anomalously weak and strong helium lines for their spectral types respectively. Many members of the two classes have strong, globally ordered magnetic fields (Thompson and Landstreet 1985; Bohlender et al. 1987) and are currently thought to represent high temperature extensions of the Ap stars. In collaboration with C. T. Bolton (U. of Toronto), we have obtained high S/N phase resolved spectra of several stars using the coudé reticon detector at CFHT. One of the principle goals of this work is to determine abundance and surface magnetic field geometries of several helium peculiar stars with large, well-determined effective fields. We employ a line synthesis program (Landstreet 1987) that incorporates the effects of surface magnetic fields and non-uniform abundances on the observed line profiles of a star. Since these stars are rapid rotators the surface magnetic field strength must be inferred from differential magnetic intensification of lines with different magnetic sensitivities. Of the few lines with suitable strengths in these hot stars we have decided that the Si III multiplet 2 lines are best suited for this aspect of our investigation. We have also modelled the unblended He I line λ4437, ignoring magnetic effects for the time being. Individual results are discussed below.

Type
V. Magnetic Pieuds
Copyright
Copyright © Kluwer 1988 

References

Bohlender, D. A., Brown, D. N., Landstreet, J. D., and Thompson, I. B. 1987, to appear in Ap. J., 323, December 1.Google Scholar
Landstreet, J. D. 1987, paper submitted to Ap. J. Google Scholar
Thompson, I. B., and Landstreet, J. D. 1985, Ap. J. (Letters), 289, L9.Google Scholar