The accretion disc in BW Scl is optically thin and has a very low luminosity. The outer parts of the disc have a low density allowing the stream to flow down to the inner disc regions. The brightest part of the hotspot is located close to the circularization radius of the disc. The hotspot is optically thick and has a complex, elongated structure.
In the top panel, dynamical Doppler maps of the H-gamma emission line are shown. These maps allow examining the evolution of the appearance of the hotspot area. The individual maps were calculated using subsets of spectra (40 per cent of the whole X-shooter data set) whose midphases, shown on the map, vary from 0 to 1.
In the bottom panel standard, static maps are shown which were calculated using all the spectra.
The left maps in the full velocity range are scaled according to the average disc brightness. The right maps in which the individual tomograms are centred around the hotspot area are scaled according to their minimum and maximum values.
Reference: Neustroev V.V. & Mantynen I., 2023, accepted to MNRAS, arXiv:2212.03264
