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The mass of the sdB primary of the binary HS 2333+3927

U. Heber·H. Drechsel·C. Karl·R. Østensen·S. Folkes·R. Napiwotzki·M. Altmann·O. Cordes·J. -E. Solheim·B. Voss·D. Koester
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Abstract

Short period sdB binaries with cool companions are crucial to understand pre-CV evolution, because they will evolve into cataclysmic variables, when the sdB will have left the extended horizontal branch. Recently we discovered the sixth such system, HS 2333+3927, consisting of an sdB star and an M dwarf (period: 0.172 d) with a very strong reflection effect, but no eclipses. The reflection is stronger than in any of the other similar systems which renders a quantitative spectral analysis very difficult because the Balmer line profiles may be disturbed by the reflected light. A spectroscopic analysis results in Teff = 36500 K, log g = 5.70, and log (n_He/n_H) = -2.15. Mass-radius relations were derived from the results of the analysis of light and radial-velocity curves. Comparison with the mass-radius relation derived from the surface gravity of the sdB star favours a rather low mass of 0.38 Msun for the primary. The mass of the companion is 0.29 M_sun. HS 2333+3927 is the only known sdB+dM system with a period above the CV period gap.

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U. Heber, H. Drechsel, C. Karl, R. Østensen, S. Folkes, R. Napiwotzki, M. Altmann, O. Cordes, J. -E. Solheim, B. Voss, D. Koester. 2004-10-08. The mass of the sdB primary of the binary HS 2333+3927. https://arxiv.org/abs/astro-ph/0410230

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