P − T profiles near the atmosphere of acceptable and unacceptable models. Colors and line styles are the same as in Figs. 2 and 3. For lines with same color and style, models with Z = 0 and Z = Z_max are shown. Thick lines indicate acceptable models; compare these also to Fig. 3. The green shaded area marks the P − T regime for acceptable models. However, models in this regime are only acceptable when they also have a large enough amount of metals in their envelopes.