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

Abstract

Abstract Our photometric monitoring revealed that DW Cnc, which was originally classified as a dwarf nova ($ V=15 \hbox{--} 17.5$), remained at a bright state of $ R_\mathrm{c}=14.68\pm 0.07$ for 61 days. 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 0.3 mag. Our period analysis yielded a power spectrum with two peaks of QPOs, whose center periods are $ 37.5\pm 0.1$ and $ 73.4\pm 0.4 \,\mathrm{min}$ 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 61 days. 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 3 hours. In this case, the QPOs may be caused by trapped disk oscillations.