Fourier decomposition of RR Lyrae pulsations - Theory versus observations

Fourier decomposition is employed to compare the light curves of RR Lyrae stars with those emerging from hydrodynamic models. Very good agreement is obtained between theory and observation for the RRc stars, but in the case of the RRab stars there are significant discrepancies in the Fourier phase quantities phi(21) and phi(31). The deficiencies of the models are not remedied by replacing Carson (1976) opacities with Los Alamos opacities, nor by including dynamic zoning in the hydrogen ionization region. The theoretical velocity curves are also Fourier-analyzed to determine R(21), phi(21), and phi(31) as well as the first-order phase lag (Delta-phi)1. It is suggested that (Delta-phi)1 may be correlated with surface temperature.