The semi-period T of the oscillation in geometrical units as a function of peak luminosity at infinity in Eddington units, when kinetic energy is instantaneously converted to luminosity (δt_r = 0). The corresponding frequency f = 1/(2T) can be read off in kHz from the right vertical axis. 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_∞ = 50, filled circles a value of 100, and the crosses the minimum value of the logarithmic derivative for each curve.