The frequency of the oscillations as a function of peak luminosity at infinity in Eddington units, when there is a delay in converting kinetic energy to luminosity δt_r = 0.1 ms (see Kluźniak et al. 1990). The stellar mass is assumed to be M = 2  M_⊙. The curves are labeled with the stellar radius (3, ...,10) in units of R_G. Filled squares indicate a value of the slope dlog T/dlog L_∞ = 30, filled circles a value of 50, and the crosses the minimum value of the slope for each curve (boxed values).