Hertzsprung-Russell diagram of the four evolutionary tracks with different stellar masses and metallicities described in Sect. 2. The evolution of the MS is shown as a dotted line and the evolution after the MS as a solid line. We do not show the full evolution after the MS. The locations of the stellar models that served as the background for the ray tracing analysis are indicated by the various symbols. Star symbols indicate that the central field strength B_cen, the frequency ω, and the spherical degree l were varied during the ray tracing analysis of a particular model. Full dots indicate that B_cen and ω were varied and circles indicate that only B_cen was varied.