A photometric study of four classical cepheids.

Model atmospheres are used to calculate continuum energy distributions and broad-band colors for comparison with spectral scans and broad-band photometry of the Cepheids U Sgr, Aql, S Nor, and Y Oph. The effect of line blocking on the B - V, V - R, and 1? - I colors is determined from the measured colors and scans, and the color excesses are found. The scale and variations of the temperatures of these stars are discussed in the light of available data. The variation of blanketing as a function of turbulent velocity, temperature, and gravity is discussed; and it is found that the blanketing variations are consistent with the variations of the atmospheric parameters. The radii of these Cepheids are determined from the monochromatic light curves and model atmospheres. It is found that, due to blanketing effects, the radii derived by the usual Wesselink method may be too large by up to 30 percent for some Cepheids.