Nonlinearity of nonradial modes in evolved stars
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We 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, 2003
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, 2003