Thermal properties of a 1.5 M_⊙ donor star at various stages in its post-MS evolution. The colours of the lines correspond to the moments the star reaches certain radii (as shown in Fig. 1), whose values are shown in the legend. Regions with grey shading are significantly superadiabatic (‘sad’; here defined as regions where ∇ − ∇_ad ≥ 0.1∇; with ). The top panel shows the run of the local thermal timescale (see Eq. (7)) with the logarithm of the fractional exterior mass, such that the stellar centre is located on the left end of the x axis, and the surface is located to the right. The bottom panel shows the run of the associated thermal mass-loss rate (see Eq. (8)) on the same horizontal axis.