Fig. 3: Double-peak shape of optical emission lines.
From: A helium-burning white dwarf binary as a supersoft X-ray source
Flux-normalized optical spectra of different He lines (as labelled on the top right of each panel) taken with the SALT/HRS spectrograph at three different epochs: 15 September 2020 (dashed lines), 5 October 2020 (dotted lines) and 6 October 2020 (solid lines). The peak separation of all the main lines is similar, including that of He II. The vertical dotted lines indicate a peak separation of ±60 km s−1. The relative variation of blue/red peaks is usually explained as the orbiting hotspot created by the impact of the accretion stream on the outer edge of the accretion disk.
