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HST/STIS observations of sdBV stars: testing diffusion and pulsation theory

Published online by Cambridge University Press:  12 April 2016

S.J. O’Toole ,
U. Heber ,
P. Chayer ,
G. Fontaine ,
D. O’Donoghue  and
S. Charpinet
S.J. O’Toole
Affiliation:
Dr Remeis-Sternwarte, Astronomisches Institut der Universität Erlangen-Nürnberg, Sternwartstr. 7, Bamberg D-96049, Germany
U. Heber
Affiliation:
Dr Remeis-Sternwarte, Astronomisches Institut der Universität Erlangen-Nürnberg, Sternwartstr. 7, Bamberg D-96049, Germany
P. Chayer
Affiliation:
Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles St., Baltimore MD 21218, USA
G. Fontaine
Affiliation:
Département de Physique, Université de Montréal, CP 6128, Station Centreville, Montréal, QC H3C-3J7, Canada
D. O’Donoghue
Affiliation:
South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa
S. Charpinet
Affiliation:
Laboratoire d’Astrophysique, Observatoire Midi Pyrénées, 14 avenue Edouard Belin, 31400 Toulouse, France

Abstract

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We present the initial results of an abundance analysis of echelle UV spectra of 5 hot subdwarf B (sdB) stars, which form part of a study to test pulsation and diffusion calculations. SdB stars have been identified as core helium-burning objects on the extreme Horizontal Branch. Around 5% of sdB stars show short-period acoustic mode oscillations, which models predict 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 sdB stars on the basis of the surface iron abundance. Our initial analysis of HST/STIS observations of 3 pulsators and 2 non-pulsators in the near and far UV suggests this may also be the case for other iron group elements, although further work will be needed to verify this.

Type
Part 4. Early-type stars: B, A and F pulsators
Information
International Astronomical Union Colloquium , Volume 193: Variable Stars in the Local Group , 2004 , pp. 234 - 237
Copyright
Copyright © Astronomical Society of the Pacific 2004

References

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