Upper panel: dipole (ℓ = 1) average of the computed period spacings, , assessed in a range of periods that includes the periods observed in NGC 1501, shown as solid (dashed) curves corresponding to stages before (after) the maximum T_eff for different stellar masses. The location of NGC 1501 when we use the effective temperature derived by Werner & Herwig (2006), T_eff = 134 000  ±  10 000 K, and the dipole period spacing, Δ Π_ℓ = 1 = 20.1262 ± 0.0123 s (derived in Sect. 3.4), is highlighted with a magenta circle. The stellar mass derived from linear interpolation is M_⋆ = 0.621  ±  0.015 M_⊙ if the star is before the maximum T_eff, and it is M_⋆ = 0.624  ±  0.015 M_⊙ if the star is after the maximum T_eff. Lower panel: same as upper panel, but for the case of ℓ = 2 modes (Δ Π_ℓ = 2 = 11.9593 ± 0.0520 s). In this case, the stellar mass is M_⋆ = 0.601  ±  0.015 M_⊙ and M_⋆ = 0.606  ±  0.015 M_⊙, according to whether the star is before or after the maximum T_eff.