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Astron. Astrophys. 356, 665-675 (2000)

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NLTE spectral analysis of the sdOB primary of the eclipsing binary system LB 3459 (AA Dor) *

T. Rauch

Eberhard-Karls-Universität Tübingen, Institut für Astronomie und Astrophysik, Waldhäuserstrasse 64, 72076 Tübingen, Germany

Received 2 December 1999 / Accepted 8 February 2000


We present a spectral analysis of the sdOB primary star of the binary system LB 3459 based on high-resolution high-S/N optical and UV spectra. The metal abundances are determined by means of state-of-the-art NLTE model atmospheres.

We determined [FORMULA] and [FORMULA] within very small error limits. The He (1/125 solar), C (1/265), N (1/33), O (1/12), and Si (1/5) abundances appear strongly depleted while that of Fe and Ni are roughly solar and Mg is strongly enriched by a factor of 6.

The spectroscopic distance to LB 3459 is [FORMULA]. The mass of the primary component of LB 3459 is [FORMULA] derived from comparisons with theoretical models for sdO stars in the [FORMULA] plane. The mass of the secondary is then [FORMULA] derived from the mass function. There remains some disagreement between the radius derived from [FORMULA] and the above mass, and that derived from analysis of the radial-velocity curve and the eclipse curves. LB 3459 is a close binary system which had experienced a common envelope (CE) phase during its evolution. It fits in the "low mass case B" scenario of Iben & Livio (1993) and the secondary is a brown dwarf.

The spectroscopically determined rotational velocity of the primary is [FORMULA]. Thus even bound rotation ([FORMULA]) cannot be ruled out.

Key words: book reviews – stars: binaries: eclipsing – stars: evolution – stars: fundamental parameters – stars: individual: LB 3459 – book reviews – stars: low-mass, brown dwarfs

* Based on observations collected at the European Southern Observatory, La Silla, Chile (proposals 55.D-0319, 56.C-0165) and on data retrieved from the International Ultraviolet Explorer (IUE) Final Archive

Send offprint requests to: T. Rauch

Correspondence to: rauch@astro.uni-tuebingen.de

© European Southern Observatory (ESO) 2000

Online publication: April 10, 2000