Contour plot of X computed using Eq. (12) as a function of the dimensionless intensity of the temperature increments $\text{Δ}\tilde{T}$ and of the stratification parameter $\widetilde{𝑔}$. The red solid line corresponds to the threshold value X = 0.9 separating the region of parameters in which the model predicts a Sun-like steep increase of temperature and ahot corona (X > 0.9, yellowish colours) from that where it does not (X < 0.9, bluish colours). The magenta horizontal line is the maximum value of $\widetilde{𝑔}$ as a function of M.