Departure coefficients, b, for the lowest 60 levels of Pb i and the ground state of Pb ii as a function of log τ₅₀₀₀ in the model atmospheres 5780/4.44/0 (top panel) and 4500/1.0/ − 3 (bottom panel). The first 21 levels are quoted in the right part of each panel. For all the higher excitation levels, their behaviour is very similar to that of the 188p to 217d levels, with b ≃ 1 in the solar and VMP models inside log τ₅₀₀₀ =  − 3 and  − 1, respectively. S_H = 0.1 was used throughout. The vertical lines indicate the locations of the line core formation depths for Pb i 4057 (1) and 3683 Å (2). See text for more details.