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Workshop on Binary and Variable Stars Gunma Astronomical Observatory, 1999

Summary: Workshop on Binary and Variable Stars
Gunma Astronomical Observatory, 1999
Evolutionary Constraints Imposed by Pulsations in
Extreme Helium Stars
Simon Je ery
Armagh Observatory, College Hill, Armagh BT61 9DG, Northern
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 ash or to a binary merger. The existence of pulsations in
many helium stars, due to strange-mode instabilities or the Z-bump -
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.
1. Extreme Helium Stars
The late stages of stellar evolution are characterized by extremes. Stellar struc-
ture and surface properties change much more rapidly than during earlier phases


Source: Armagh Observatory
Jeffery, Simon - Armagh Observatory


Collections: Physics