1999MNRAS.306..753M

We detect the likely optical counterpart to previously reported X-ray QPOs in spectrophotometry of the intermediate polar GK Per during the 1996 dwarf nova outburst. The characteristic time-scales range between 4000 and 6000 s. Although the QPOs are an order of magnitude longer than those detected in the other dwarf novae we show that a new QPO model is not required to explain the long time-scale observed. We demonstrate that the observations are consistent with oscillations being the result of normal time-scale QPOs beating with the spin period of the white dwarf. We determine the spectral class of the companion to be consistent with its quiescent classification and find no significant evidence for irradiation over its inner face. We detect the white dwarf spin period in line fluxes, V/R ratios and Doppler-broadened emission profiles.