2012MNRAS.421..149C

Purely photometric models can be used to determine the binary parameters of eclipsing cataclysmic variables (CVs) with a high degree of precision. However, the photometric method relies on a number of assumptions, and to date there have been very few independent checks of this method in the literature. We present time-resolved spectroscopy of the P= 90.9 min eclipsing CV OY Carinae obtained with X-shooter on the Very Large Telescope (VLT), in which we detect the donor star from K I lines in the J band. We measure the radial velocity amplitude of the donor star K₂= 470.0 ±2.7 km/s, consistent with predictions based upon the photometric method (470±7 km/s). Additionally, the spectra obtained in the UVB arm of X-shooter show a series of Fe I and Fe II lines with a phase and velocity consistent with an origin in the accretion disc. This is the first unambiguous detection at optical wavelengths of the `iron curtain' of disc material which has been previously reported to veil the white dwarf in this system. The velocities of these lines do not track the white dwarf, reflecting a distortion of the outer disc that we see also in Doppler images. This is evidence for considerable radial motion in the outer disc, at up to 90 km/s towards and away from the white dwarf.