Strömgren photometry [m1₀; c1₀] diagram for our models (crosses) and for comparison, normal main-sequence stars (red dots) from the Long-Term Photometry of Variables project (Manfroid et al. 1991, to be discussed in Sect. 4.3). From the latter, only data obtained with the Danish telescope (system 7) were retained. For clarity, the models are not labelled, and only their general properties are indicated in blue. We refer to Table 3 for the values. We added observations of W Ser, B[e], and Be stars for comparison (green dots). The blue dots are the average values for the latter objects when several observations are available.