Kippenhahn diagram of the 1 M_⊙ stellar model at [Fe/H] = −2.5 discussed in this paper. Time is counted backward from the last computed model. Convective regions are shaded gray. The vertical dashed red line indicates when the main proton ingestion event takes place (during the third thermal pulse). The dotted green and blue lines correspond to the maximum nuclear energy production by hydrogen and helium burning, respectively. The dashed green and blue lines delineate the hydrogen and helium-burning zones; more specifically they outline the zones in which the production of energy by hydrogen or helium burning exceeds 10 erg g⁻¹ s⁻¹.