Astronomy and Astrophysics – Astrophysics
Scientific paper
2003-09-02
Astrophys.Space Sci.291:427-430,2004
Astronomy and Astrophysics
Astrophysics
4 pages, 1 figure, includes Kluwer class file, to appear in "Extreme Horizontal Branch Stars and Related Objects" proceedings
Scientific paper
10.1023/B:ASTR.0000044354.35919.
We present the initial results of an abundance analysis of echelle UV spectra of 5 hot subdwarf B (sdB) stars. These stars have been identified as core helium burning objects on the extreme Horizontal Branch. Around 5% of sdBs show short-period acoustic mode oscillations. Models predict that these oscillations are due to an opacity bump caused by the ionisation of iron group elements. The necessary metal abundance has to be maintained by diffusive equilibrium between gravitational settling and radiative levitation. However, analyses of high resolution optical spectra has revealed that we cannot discriminate between pulsating and non-pulsating sdBs on the basis of the surface iron abundance. We have therefore obtained HST/STIS observations of 3 pulsators and 2 non-pulsators in the near and far UV to measure the surface abundance of elements that are unobservable from the ground. The overall aim of our study is to test diffusion and pulsation calculations by searching for significant differences between these surface abundances.
Charpinet Stephane
Chayer Pierre
Fontaine Gérard
Heber Uli
O'Donoghue Darragh
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