Resonance effects and the Cepheid "bump mass" anomaly.
Abstract
A secondorder iterative nonlinear pulsation theory is generalized to the nonadiabatic case, and employed to treat Cepheid models with linear normalmode periods lying in the vicinity of the resonance P2/P0 = 0.5. It is shown that resonance effects occurring in the secondorder terms influence the phases at which maxima appear on the theoretical velocity curves. Comparison of the iterative velocity curves with those given by hydrodynamic integration indicates good agreement in a sizable number of cases. Discrepancies which appear in a number of models are discussed. It is argued that the results of the present investigation strengthen the case for associating the bumps on Cepheid velocity curves with the resonance P2/P0 = 0.5. A brief discussion of the Cepheid 'bump mass' anomaly concludes the article.
 Publication:

The Astrophysical Journal
 Pub Date:
 October 1977
 DOI:
 10.1086/155565
 Bibcode:
 1977ApJ...217..160S
 Keywords:

 Cepheid Variables;
 Resonance;
 Stellar Mass;
 Variable Stars;
 Iteration;
 Nonadiabatic Conditions;
 Stellar Models;
 Stellar Motions;
 Stellar Structure;
 Velocity Distribution;
 Astronomy