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

TL;DR

This study analyzes time-resolved FUV spectra of V3885 Sgr, revealing orbital phase-dependent absorption line variations, rapid stochastic fluctuations, and evidence of disc-stream interaction structures in the system.

Contribution

It provides the first detailed analysis of FUV line variability and disc-stream interaction in V3885 Sgr using Doppler tomography and time-resolved spectroscopy.

Findings

Absorption lines are blueshifted indicating a disc wind outflow.

Rapid (~5 min) stochastic fluctuations suggest density changes.

Doppler maps show gas stream and disc interaction regions.

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 (Ly_beta, CIII, NIII) and high (SIV, PV, OVI) 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, localised disc-stream interaction region.