Kilo-Second Quasi-Periodic Oscillations in the Cataclysmic Variable DW Cancri

Our photometric monitoring revealed that DW Cnc, which was originally classified as a dwarf nova (V = 15–17.5), remained at a bright state of Rc =1 4.68 ± 0.07 for 61days. In conjunction with optical spectra lacking a strong He II emission line, we propose that the object is not a dwarf nova, but a non-magnetic nova-like variable. Throughout our monitoring, the object showed strong quasi-periodic oscillations (QPOs) with amplitudes reaching about 0.3mag. Our period analysis yielded a power spectrum with two peaks of QPOs, whose center periods are 37.5 ±0.1 and 73.4 ±0.4min and, furthermore, with a significant power in frequencies lower than the QPOs. DW Cnc is a unique cataclysmic variable in which kilo-second QPOs were continuously detected for 61days. We propose two possible interpretations of DW Cnc: (i) A permanent superhumper below the period minimum of hydrogen-rich cataclysmic variables. (ii) A nova-like variable having an orbital period over 3hours. In this case, the QPOs may be caused by trapped disk oscillations.