Notes. I_r – brightness distribution function; T_b – brightness temperature estimated from I_r; V_q – visibility function; d_q – pattern size, estimated from the visibility ratio V_q/V₀; T_b,q – brightness temperature corresponding to d_q; T_b,min – minimum brightness temperature, obtained with V₀ = eV_q for the Gaussian component and V₀ = 2 V_q for the disk and the shell; T_b,lim – limiting brightness temperature, obtained with V₀ = V_q + σ_q. For the brightness temperature estimates, the respective ℐ expression give the ℐ_b term in the Planck form of the brightness temperature equation.