FUSEobservations of V592 Cas: the continuing enigma of orbitally modulated spectral signatures of accretion disc winds

Abstract

By exploiting Far Ultraviolet Spectroscopic Explorer (FUSE) satellite time-series data, we have probed the relation between accretion disc geometry and bipolar outflow in the low-inclination, nova-like cataclysmic variable (CV) V592 Cas. Our results show that the outflow is strictly modulated on the orbital period and not on the (negative or positive) superhump periods of this system. This implies that the precession of either the disc eccentricity or its tilt is not directly affecting the structure and global dynamics of the outflow. The principal variability in the ultraviolet resonance lines is characterized by Doppler shifts of the entire blueward absorption troughs, in concert for a range of low- and high-ionization cases. The repetitive behaviour is asymmetric and highly non-sinusoidal over the orbital cycle of the system. The disc wind characteristics derived here allow V592 Cas to be added to a growing number of non-magnetic CVs which exhibit orbitally modulated wind variability. The origin of the departure in axisymmetry, which has to be fixed in the binary star frame, remains to be established.