Distributions of the tachocline version of the absolute values of phase velocity V_t of waves, modulating the stellar activity pattern, estimated with Eq. (5) for the drift rates D₁ and D₂ from Table A.1, versus the log of the stellar effective temperature T. (a) the negative drifts (rhombi); (b) the positive drifts (squares). The tachocline radius R_t, as well as other stellar parameters, are taken from the models of the main sequence fast rotators in Amard et al. (2019) with maximal surface gravity. The labeled curves depict the theoretic predictions for the different waves in tachoclines of the main sequence stars, according to the dispersion relations from Zaqarashvili (2018) and Gachechiladze et al. (2019), taking the most observable lowest-number spherical harmonics (n = m = 1). The numbers near the theoretical curves for the equatorial magneto-Kelvin waves in panel (a) indicate the assumed thicknesses of the tachocline in units of R_*. Blue lines of the Alfvén velocity V_A in panels (a) and (b) are calculated for B = 50 kG (solid), B = 100 kG (dashed, upper), and B = 25 kG (dashed, lower). Panel (c) shows the range of the actual values (grey) of the small parameter β = V_A/(ΩR_t)≪1 used for the solving of the dispersion equations for the considered wave modes in the shallow-fluid approximation.