The pulsation of Delta-Scuti stars

Evolution, linear pulsation, and nonlinear pulsation codes were combined to produce nonlinear models of Delta-Scuti stars in an instability region extending over 3.8T_e<3.95 and 0.6L/L<2.0. The linear analysis upheld the consensus that they are normal Population I stars of about 2M, in stages of evolution corresponding to central hydrogen burning and shell hydrogen burning. The growth rates were very slow; driving was due to an opacity mechanism in the second helium ionization region; periods and period ratios of the lowest modes of the models were in the same range as those observed. A wide range of nonlinear models was investigated. When eigenfunctions from the linear analysis were used as initial velocity profiles, it was found that the dominant peak in the periodogram of the light curve corresponded to the mode initiated. For a small subset of models, limiting amplitudes were identified, and were found to be in close agreement with observed light amplitudes.