Orbital and stochastic far-ultraviolet variability in the nova-like system V3885 Sgr

Abstract

Highly time-resolved time-tagged FUSE satellite spectroscopic data are analysed to establish the far-ultraviolet (FUV) absorption line characteristics of the nova-like cataclysmic variable binary, V3885 Sgr. We determine the temporal behaviour of low (Lyβ, C III, N III) and high (S IV, P V, O VI) ion species, and highlight corresponding orbital phase modulated changes in these lines. On average, the absorption troughs are blueshifted due to a low-velocity disc wind outflow. Very rapid (∼5 min) fluctuations in the absorption lines are isolated, which are indicative of stochastic density changes. Doppler tomograms of the FUV lines are calculated which provide evidence for structures where a gas stream interacts with the accretion disc. We conclude that the line depth and velocity changes as a function of orbital phase are consistent with an asymmetry that has its origin in a line-emitting, localized disc-stream interaction region.