Friday 9 June at 3pm

Simon Jeffery - Armagh Observatory

"Evolutionary constraints imposed by the pulsations in extreme helium stars"

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 to Z-bump kappa-mechanism, provide a range of diagnostics including radii from Baade's method and contraction rates from period changes. I shall introduce 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."

http://star.arm.ac.uk/~csj/