Upper panels: comparisons of 0.4 M_⊙ tracks from different authors listed in Table 2 for Z ≈ 0.02, in the HR diagram and in the (log t   (yr), log L/L_⊙) plane. Bottom left panel: 0.4 M_⊙ models computed with three values of the mixing length parameter, namely α = 1.2,1.68, and 1.9. Bottom right panel: 0.4 M_⊙ models with three different choices of the adopted boundary conditions: non-grey models as described in Sect. 2.2 (solid line), KS66 T(τ) relation plus AF94 low-temperature opacity tables (dashed line) and T(τ) relation interpolated from the Brott & Hauschildt (2005) atmosphere models plus AF94 low-temperature opacity tables (dotted line).