Top panel: HDO 1_0,1–0_0,0 line profile of the D/H = 1 model (in blue) versus APEX observation (in black). Middle panels: HDO 1_0,1–0_0,0 (left panel) and 1_1,1–0_0,0 (right panel) line profiles for the six different D/H ratios. Bottom panel: HDO abundance profiles as a function of the D/H ratio (see text, Sect. 5) used for these models as a function of the radial distance from the core in arcsec (top axis) and AU (bottom axis).