Evolutionary track (from the pre-main sequence up to the tip of the RGB) of the 1.25 M_⊙ model computed with thermohaline mixing only. The minimum and maximum luminosity of the bump are indicated (L_b,min and L_b,max respectively) as well as the luminosity L_c,th at which the thermohaline instability reaches the bottom of the convective envelope. Open symbols labelled A_1.25 to E_1.25 correspond to evolution points for which some stellar properties are discussed in the text. The panel inserted on the right of the figure shows the evolution of the stellar luminosity around the bump as a function of time. Δt_b is the time spend by the star within the luminosity bump and equals to 3.9 × 10⁷ yrs in the present case.