Radius evolution of a 1.2 M_⊙ stellar evolution model mass track (in red) from Baraffe et al. (2015) for Y = 0.28 (solid lines) and Y = 0.29 (dashed lines). Y is the initial helium mass fraction. This is shown with the evolution of the stellar central temperature (T_C; black), the stellar central density (ρ_C; cyan), and the mass of the convective core (M_CC; purple) as a fraction of the maximum value attained between 4 and 45 Myr (see Sect. 4). In the case of Y = 0.28 (solid lines), these maximum values are T_C = 1.530 × 10⁷ K, ρ_C = 78.596 g cm⁻³, and M_CC = 0.1023 M_⊙; in the case of Y = 0.29 (dashed lines), these are T_C = 1.555 × 10⁷ K, ρ_C = 80.575 g cm⁻³, and M_CC = 0.1097 M_⊙.