Six-color photometry of stars. VIII. The pulsating star Beta Cephei

The light-curves of p Cephei in six colors show the same retardation of phase in the longer wave lengths as do the curves of the regular Cepheid variables. When the variation in area, due to the pulsating radius, is taken out of the final light-curves, the resulting radiation-curves for the different colors agree in phase. Because of the small amplitudes, 0.05 and 0.01 mag. in the ultraviolet and infrared, respectively, the solution for the radius of the star from a combination of the light- and velocity-curves would be indeterminate, except for the condition that the ratio of the amplitudes in short and long wave lengths should agree with the calculated ratio for small variations in the temperature of a B1 star at 23,O00 . When the photometric and spectroscopic data for p Cephei are analyzed on this basis, the radius of the star comes out as R = 9.0 RO, and the absolute magnitude Mpv= -4.2. Although these values could be improved by simultaneous photometric and spectroscopic measures over the same cycles, the variations of this star are satisfactorily explained on the pulsation theory.