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HST/STIS observations of sdBV stars: testing diffusion and pulsation theory |
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| Authors: | SJ O’Toole U Heber P Chayer G Fontaine D O’Donoghue S Charpinet |
| Institution: | 1. Dr Remeis-Sternwarte, Astronomisches Institut der Universit?t, Erlangen-Nürnberg, Sternwartstr. 7, Bamberg, D-96049, Germany 2. Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD, 21218, USA 3. Département de Physique, Université de Montréal, CP 6128, Station Centreville, Montréal, QC, H3C-3J7, Canada 4. South African Astronomical Observatory, PO Box 9, Observatory, 7935, South Africa 5. Observatoire Midi-Pyrénées, 14 Avenue E. Belin, 31400, Toulouse, France |
| Abstract: | We present the initial results of an abundance analysis of echelle UV spectra of five 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 three pulsators and two 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. |
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