ULTRACAM photometry of the eclipsing cataclysmic variables XZ Eri and DV UMa

We present high-speed, three-colour photometry of the faint eclipsing cataclysmic variables XZ Eri and DV UMa. We determine the system parameters through two techniques: first, timings of the eclipse contact phases of the white dwarf and bright-spot using the derivative of the light curve; and secondly, a parametrized model of the eclipse fitted to the observed light curve by χ2 minimization. For both objects, we prefer the latter method, as it is less affected by photon noise and rapid flickering. For XZ Eri we obtain a mass ratio q = 0.1098 ± 0.0017 and an orbital inclination i = 80. ◦16 ± 0. ◦09. For DV UMa we derive figures of q = 0.1506 ± 0.0009 and i = 84. ◦24 ± 0. ◦07. The secondary star in XZ Eri has a very low mass Mr/M = 0.0842 ± 0.0024, placing it close to the upper limit on the mass of a brown dwarf.