2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/5657We show that in evolved stars, even at relatively low surface amplitudes, nonradial modes become strongly nonlinear in the hydrogen shell source, where the Brunt-Vaisala frequency has its absolute maximum. The measure of nonlinearity is the product of horizontal displacement times the radial wavenumber. It becomes large already in evolved delta-Scuti stars. This nonlinearity presents a major problem for interpretations of amplitude modulation in RR Lyrae stars in terms of nonradial mode excitation.4 pages, 2 figures, to appear in "Asteroseismology Across the HR Diagram", Eds. Thompson M.J., Cunha M.S., Monteiro M.J.P.F.G., Kluwer, 2003Astrophysicstext