Spatial extent of three gas and dust discs that are detected by Melis et al. (2010). The dust discs are marked by grey rectangles, while the gas discs are marked by orange rectangles. To improve visibility, the discs for each system are offset vertically. For the two stellar effective temperatures used in the Melis et al. (2010) study, namely 18 500 K (red lines) and 22 000 K (blue lines), the blackbody temperature profile (light red and blue lines) is shown. A horizontal green line indicates the sublimation temperature (1500 K). The figure displays the sublimation radius for each configuration with vertical dashed lines. The dashed grey line indicates the radius of the WD, while the solid black line represents the Roche limit.