Armagh Observatory Preprint Series No. ???

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Evolutionary Constraints Imposed by Pulsations in Extreme Helium Stars

Author: C.S.Jeffery

Reference: Proceedings of the Workshop on Binary and Variable Stars, 1999, Gunma Astronomical Observatory, Gunma Prefecture, Japan

Abstract. Extreme helium stars are highly evolved luminous stellar remnants. Their exotic surface abundances point to previous evolution through the white dwarf sequence, followed by re-ignition due to a late helium shell flash or to a binary merger. The existence of pulsations in many helium stars, due to strange-mode instabilities or the Z-bump kappa-mechanism, provide a range of diagnostics including radii from Baade's method and contraction rates from period changes. I review the basic observational and theoretical properties of extreme helium star pulsations and show how these have been used to constrain evolutionary models, with particular reference to the cases of V652 Her and BX Cir.

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