ULTRACAM photometry of the eclipsing cataclysmic variable OU Vir

We present high-speed, three-colour photometry of the faint eclipsing cataclysmic variable OU Vir. For the first time in OU Vir, separate eclipses of the white dwarf and the bright spot have been observed. We use timings of these eclipses to derive a purely photometric model of the system, obtaining a mass ratio of q= 0.175 +/- 0.025, an inclination of and a disc radius of R_d/a= 0.2315 +/- 0.0150. We separate the white dwarf eclipse from the light curve and, by fitting a blackbody spectrum to its flux in each passband, obtain a white dwarf temperature of T= 13900 +/- 600 K and a distance of D= 51 +/- 17 pc. Assuming that the primary obeys the Nauenberg mass-radius relation for white dwarfs and allowing for temperature effects, we also find a primary mass M_w/M_solar= 0.89 +/- 0.20, a primary radius R_w/R_solar= 0.0097 +/- 0.0031 and an orbital separation a/R_solar= 0.74 +/- 0.05.