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 X 2 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 M r /M ○. = 0.0842 ± 0.0024, placing it close to the upper limit on the mass of a brown dwarf.