Evolution of the 6  M_⊙ model star with a metallicity Z = 3 × 10⁻⁵ as a function of the time, counted from the beginning of the TP-AGB phase. The top panels reports the same quantities as in the corresponding panels of Fig. 2, but the lines corresponding to the temperature at the bottom of the convective envelope and of the mass-loss rate refer to the inter-pulse phases for readability. The bottom panels, showing the variation in surface chemistry, use the same colour-coding as in Fig. 2. The dashed cyan lines in the left panels refer to the luminosity (top) and the surface ¹⁴N of a model star calculated by doubling the OS.