Physical Hertzsprung-Russell diagram. Stars in the SMC are plotted in red. Stars with an IR excess are indicated by a green plus sign. Stars that show eclipsing or ellipsoidal variations according to OGLE are indicated by a blue cross. The tracks plotted with × are the lowest initial mass tracks of Vassiliadis & Wood (1993) for the LMC (0.945 M_⊙), and SMC (0.89 M_⊙, in red). The final masses are 0.555 and 0.558 M_⊙, respectively. The tracks plotted with a ∗ are the lowest initial mass tracks of Miller Bertolami (2016) for a metallicity of Z = 0.01 (1.0 M_⊙, current mass 0.534 M_⊙), and Z = 0.001 (0.9 M_⊙, current mass 0.536 M_⊙, in red). In both tracks every tick marked represents 500 yr of evolution. The blue and red edge of the fundamental mode IS of BLH (between log L ~ 1.81–2.1, for a mass of 0.65 M_⊙) and FU ACs (between log L ~ 1.77–2.4) are indicated by the solid line (see text). The vertical dotted lines indicate the location of most of the variables at higher luminosity (see text). Some stars are labelled by their identifier.