LONG-PERIOD CEPHEIDS - MODELS AND OBSERVATIONS

We compile a list of 50 long-period Cepheids (12(d) < P < 70(d)) with light curves suitable for Fourier decomposition. For P > 20(d), the pl ots versus period of the Fourier quantities phi(21), phi(31), phi(41), and R(21) all show a slow rise, with considerable scatter. Hydrodynam ic calculations are performed to model the observed stars. The theoret ical light curves are converted from bolometric to visual, and the Fou rier coefficients compared with the observed ones. While the theoretic al values follow the observed trends in a crude, general sense, differ ences are noted. At the lower end of the period range the models depar t systematically from the observed stars. At longer period, the differ ences are much less striking, perhaps being obscured by scatter in the observations. We conclude that a detailed comparison between theory a nd observation must await a more extensive and accurate sample of obse rved stars.