Left panel: Hertzsprung-Russell diagram of the two stars corresponding to PAIR-1, which have the same luminosity at an effective temperature of 50 kK. The dots correspond to 10, 20, 30, 40, and 50 kK. Dashed lines represent fast parts of the tracks (see main text). The model names (Table 1) are shown and are consistent in color with their corresponding curve in Figure 2. Right panel: Hydrogen mass vs. effective temperature for the same models.