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Preprint 10k/00

Spectral analysis of four multi mode pulsating sdB stars

U. Heber (1), I.N. Reid (2), K. Werner (3)

(1) Dr. Remeis­Sternwarte, Astronomisches Institut der Universität Erlangen­Nürnberg, D­96049, Bamberg, Germany
(2) Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, USA
(3) Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany

To appear in: The 12th European Workshop on White Dwarfs, ASP Conference Series, Vol. xxx, 2001, H.L. Shipman and J.L. Provencal, eds.

Abstract. Four members of the new class of pulsating sdB stars (EC 14026 stars) are analysed from Keck HIRES spectra using line blanketed NLTE and LTE model atmospheres. Atmospheric parameters (Teff, log g, He/H), metal abundances and rotational velocities are determined. All programme stars are found to be helium deficient, with He/H ranging from 1/80 solar for Feige 48 to 1/3 solar for PG 1219+534. Most metals are also depleted. The abundances of C, O, Ne, Mg, Al and Si in the high gravity programme stars KPD 2109+4401 and PG 1219+534 are considerably lower than in the lower gravity stars Feige 48 and PG 1605+072. This results strongly point towards the action of diffusion processes. The abundances could be explained by an equilibrium between gravitational settling and radiative levitation. Surprisingly iron is found to be solar to within error limits in all programme stars irrespective of their gravity. In PG 1605+072 the spectral lines are broadened, probably due to rotation and vrot sin i = 39 km/s is derived. For the three other programme stars the metal lines are very sharp and vrot sin i has to be very low (vrot sin i < 5-10 km/s).

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Paper (190k gzip'ed Postscript including figures)

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