Top: dimensionless damping term defined in Eq. (B.16)with l = | m | = 1, as a function of σ and χ₁. It is plotted for the subgiant model parameters given in Table A.1 at a radius r/r_t = 0.05, i.e., near the hydrogen-burning shell. The vertical orange dashed line corresponds to σ = 2B as given in Eq. (B.15). The vertical dark dashed line indicates the frequency at the separation between the retrograde and prograde parts of the damping term, , which was estimated using Eq. (B.25). The dotted line represents the retrograde transition frequency as defined in Eq. (B.21). Bottom: cut sections for different values of χ₁. The orange dashed line represents the Gaussian wave frequency spectrum defined in Eq. (B.15). The vertical dark dashed line has the same signification as in the top panel.