SETI bioastro: The nature of the close magnetic white dwarf + probable brown dwarf binary SDSS

From: LARRY KLAES (ljk4_at_msn.com)
Date: Wed Jul 19 2006 - 06:35:50 PDT

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    Paper: astro-ph/0607389
    Date: Mon, 17 Jul 2006 16:06:16 GMT (68kb)

    Title: The nature of the close magnetic white dwarf + probable brown dwarf
    binary SDSS J121209.31+013627.7

    Authors: M. R. Burleigh (1), T. R. Marsh (2), B. T. Gansicke (2), M. R. Goad
    (1), V. Dhillon (3), S. P. Littlefair (3), M. Wells (4), N. P. Bannister
    (1),
    C. P. Hurkett (1), A. Martindale (1), P. D. Dobbie (1), S. L. Casewell (1),
    D. E. A. Baker (1), J. Duke (1), J. Farihi (5), M. J. Irwin (6), P. C.
    Hewett
    (6), P. Roche (7), F. Lewis (7) ((1) Department of Physics and Astronomy,
    University of Leicester (2) Department of Physics, University of Warwick (3)
    Department of Physics and Astronomy, University of Sheffield, Sheffield, UK,
    (4) Oundle School, Northamptonshire, UK (5) Gemini Observatory, USA, (6)
    Institute of Astronomy, University of Cambridge, UK, (7) Department of
    Physics and Astronomy, University of Wales, UK)

    Comments: Submitted to MNRAS
    \\
    Optical time series photometry of the short period magnetic white dwarf +
    probable brown dwarf binary SDSS 121209.31+013627.7 reveals pulse-like
    variability in all bands from i' to u', peaking at u'. These modulations are
    most likely due to a self-eclipsing accretion hot spot on the white dwarf,
    rotating into view every 88.43 minutes. This period is commensurate with the
    radial velocity period determined by Schmidt et al. 2005 of ~90 minutes, and
    consistent with the rotation period of the accretor being equal to the
    binary
    orbital period. We combine our observations with those recently published by
    Koen and Maxted 2006 to provide an accurate ephemeris. We also detect the
    system in X-rays with Swift, and estimate the accretion rate at
    ~1x10^-13Msun
    per year. We suggest that SDSS1212 is most likely a magnetic cataclysmic
    variable in an extended state of very low accretion, similar to the
    well-studied Polar EF Eri. Alternatively, the putative brown dwarf is not
    filling its Roche Lobe and the system is a detached binary in which the
    white
    dwarf is efficiently accreting from the wind of the secondary. Six such
    post-common envelope, ``pre-Polar'' systems - termed ``low accretion rate
    Polars (LARPs)'' by Schwope et al. 2002 - have previously been identified
    through optical cyclotron emission lines. Cyclotron emission from SDSS1212
    has
    recently been detected in the near-IR Debes et al. 2006 but, if detached, it
    would be the first ``LARP'' with a probably sub-stellar secondary. It is
    unclear whether an L-dwarf wind is strong enough to provide the measured
    accretion rate. We suggest further observations to distinguish between the
    Roche Lobe over-flow and wind accretion scenarios.

    \\ ( http://arXiv.org/abs/astro-ph/0607389 , 68kb)


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