The Mass of the sdB Primary of the Binary HS 2333+3927

Heber, U., Drechsel, H., Karl, C., Ostensen, R., Folkes, S., Napiwotzki, R., Altmann, M., Cordes, O., Solheim, J.E., Voss, B. and Koester, D. (2005) The Mass of the sdB Primary of the Binary HS 2333+3927. In: In: Procs of the 14th European Workshop on White Dwarfs - ASP Conference Papers 334 :. Astronomical Society of the Pacific, pp. 357-362. ISBN 1-58381-197-4
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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 re°ection e®ect, but no eclipses. The re°ection is stronger than in any of the other similar systems which renders a quantitative spectral analysis very di±cult because the Balmer line pro¯les may be disturbed by the re°ected light. A spectroscopic analysis results in Te® = 36 500 K, log g = 5.70, and log(nHe=nH) = ¡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 M¯ for the primary. The mass of the companion is 0.29 M¯. HS 2333+3927 is the only known sdB+dM system with a period above the CV period gap.


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