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NLTE spectral analysis of the sdOB primary of the eclipsing binary system LB 3459 (AA Dor) *
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 and 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 . The mass of the primary component of LB 3459 is derived from comparisons with theoretical models for sdO stars in the plane. The mass of the secondary is then derived from the mass function. There remains some disagreement between the radius derived from 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 . Thus even bound rotation () 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
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Online publication: April 10, 2000