Evolutionary sequence of the p − T structure of the envelope. The first structure (rightmost line) is at 5 Myr, the last structure (leftmost line) is at a hypothetical age of 16 Gyr. The entire internal structure is shown, which means that the lower end of a line corresponds to the core-envelope interface, while the top end corresponds to the τ = 2/3 surface. Red indicates convective parts, black radiative layers. The actual upper part of the envelope/atmosphere will be more complex than shown here, since we only use a simple gray atmosphere in the current model.