Chemical profile of model sequence Lm20510-5 (M_init = 0.54 M_⊙) (A) and Lm21010-5 (M_init = 1.0 M_⊙) (B). The remaining initial parameters are the same for both model sequences: f_acc = 1.0, Ṁ = 5 × 10^-8M_⊙/ yr and log (L_init/L_⊙) = −2. Included are the three most abundant isotopes He⁴, C¹² and O¹⁶ in units of relative mass per shell over the shell’s mass coordinate. Solid lines represent the profile at the time of the start of mass accretion at t = 0 yr, dashed lines at the midpoint of the accretion phase at t ~ 1.55 Myr(A) and t ~ 0.3 Myr(B), dotted lines just after the point of He-ignition at t = 3.11 Myr(A) and t = 0.64 Myr(B). The inset is a zoom of the area of the initial envelope-core interface (the interface is shown as a dashed gray line), where the initial profile has been omitted for the sake of clarity.