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Preprint B/99

Spectral analysis of the multi mode pulsating subluminous B star PG 1605+072

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

(1) Dr. Remeis-Sternwarte, Astronomisches Institut der Universität Erlangen-Nürnberg, Sternwartstr. 7, D-96049 Bamberg, Germany
(2) Palomar Observatory 105-24, California Institute of Technology, Pasadena, CA 91125, USA
(3) Institut für Astronomie und Astrophysik, Astronomie, Universität Tübingen, Waldhäuser Str. 64, D-72076 Tübingen, Germany

To appear in: Astronomy and Astrophysics

Abstract. PG 1605+072 has unique pulsational properties amongst the members of the new class of pulsating sdB EC 14026 stars. It has the longest periods and the richest, most puzzling frequency spectrum (55 periods). We present a quantitative analysis of a Keck HIRES spectrum using NLTE and LTE model atmospheres. Atmospheric parameters (T_eff, log g, log(nHe/nH)), metal abundances, and the rotational velocity are determined. He, C, N and O are subsolar as well as the intermediate mass elements Mg and Si, whereas Ne and Fe are solar. This abundance pattern is caused by diffusion. PG 1605+072 displays considerable line broadening probably caused by rotation (v sini = 39 km/s, P<8.7h) and, therefore, is predicted to evolve into an unusually fast rotating white dwarf. Unequal rotational splitting may explain its puzzling pulsation pattern. The solar Fe abundance and the rapid rotation nicely confirms recent predictions of diffusion/pulsation models.

Key words: stars: abundances - stars: atmospheres - stars: oscillations - stars: horizontal branch - stars: rotation - stars: individual: PG 1605+072

Paper (157k gzip'ed Postscript including figures)

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