The mass of the sdB primary of the binary HS 2333+3927
Heber, U Drechsel, H Karl, C Ostensen, Roy Folkes, S Napiwotzki, R Altmann, M Solheim, JE Voss, B Koester, D #
Astronomical soc pacific
14th European Workshop on White Dwarfs, Proceedings vol:334 pages:357-362
ASTRONOMICAL SOCIETY OF THE PACIFIC CONFERENCE SERIES
14th European Workshop on White Dwarfs Kiel, GERMANY, JUN 19-JUL 23, 2004
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 T-eff = 36 500 K, log g = 5.70, and log(n(He)/n(H)) = -2.1.5. 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 M-circle dot for the primary. The mass of the companion is 0.29 M-circle dot. HS 2333+3927 is the only known sdB+dM system with a period above the CV period gap.