LONG-PERIOD CEPHEIDS: MODELS AND OBSERVATIONS

We compile a list of 50 long-period Cepheids (12d \u3c P \u3c 70d) with light curves suitable for Fourier decomposition. For P \u3e 20d, the plots versus period of the Fourier quantities ϕ21, ϕ31, ϕ41, and R21 all show a slow rise, with considerable scatter. Hydrodynamic calculations are performed to model the observed stars. The theoretical light curves are converted from bolometric to visual, and the Fourier coefficients compared with the observed ones. While the theoretical values follow the observed trends in a crude, general sense, differences are noted. At the lower end of the period range the models depart systematically from the observed stars. At longer period, the differences are much less striking, perhaps being obscured by scatter in the observations. We conclude that a detailed comparison between theory and observation must await a more extensive and accurate sample of observed stars