2003/01/24 by Rafal M. Nowakowski, Wojciech A. Dziembowski
Physics and Astronomy · #astro-ph
published as Astrophys.Space Sci. 284 (2003) 273-276 · 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
arxiv created 2003/01/24 · arxiv updated 2009/12/01
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.