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Radial-velocity study of the post-period minimum cataclysmic variable SDSSJ143317.78+101123.3 with an electron-multiplying CCD

We present high time-resolution spectroscopy of the eclipsing cataclysmic variable SDSSJ143317.78+101123.3 obtained with QUCAM2, a high-speed/low-noise electron-multiplying CCD camera. Littlefair et al. measured the mass of the secondary star in SDSSJ143317.78+101123.3 using a light-curve fitting technique and obtained a value of M2=0.060+/-0.003 Msun, making it one of the three first bona-fide detections of a brown-dwarf mass donor in a cataclysmic variable. In this paper we present a dynamical measurement supporting this important result. We measured the radial-velocity semi-amplitude of the white dwarf from the motion of the wings of the Halpha emission line and obtained a figure of K1=34+/-4 km/s, in excellent agreement with the value of K1=35+/-2 km/s predicted by Littlefair et al.'s model.