An Analysis of the Absolute Energy Distribution in the Spectrum of δ Cephei.

Photoelectric spectrum scans and high-dispersion spectra have been analyzed to obtain the absolute energy distributions in the spectrum of a Cephei at various phases. Assuming an interstellar reddening of 0.11 in B - V, comparisons of these energy distributions with model atmospheres yield effective temperatures. Using fluxes from the model atmospheres, the observed absolute energy distributions, and the radial-velocity data, a mean radius of 40.3 + 0 8 Ro is obtained. The radius and temperature give a mean absolute visual magnitude of -3.3. A comparison of these data with those obtained previously for `? Aquilae indicates that the temperature-color relations agree if the reddening of Aquilae is increased from 0.14 to 0 20. This increases the mean absolute visual magnitude found previously from -405 to -4.25. Consideration of some recently computed model atmospheres suggests the possibility that the temperatures obtained are a little too high; if this is the case, the absolute magnitudes of a Cephei and Aquilae should be changed to -3.2 and -4.1, respectively. A suggested relation between intrinsic color, (B - V)0, and 0# is given by equation (3); a slight modification of this equation is suggested in the last section.