Hertzsprung–Russel diagram with the positions of the Aa1, Aa2, and Ab components of δ Ori and evolutionary tracks from Paxton et al. (2015). Numbers next to the main sequence indicate the theoretical masses, small numbers the theoretical gravitational acceleration log g. According to the 3-body model, the masses are 17.1, 8.5, 8.7 M_⊙. For the tertiary (Ab), it is in disagreement with the evolutionary track, but in agreement with the value of log g₃ inferred from normalised spectra (Hγ). The instability region of pulsations (β Cep type, order ℓ = 0) is indicated as grey area. Other modes (ℓ = 1, 2, 3) can be found in a very similar region (Paxton et al. 2015). Both Aa1, Ab components are located here, and they can exhibit photometric variability attributed to pulsations.