ON CEPHEIDS AT MAXIMUM AND MINIMUM LIGHT

It has been known for many decades that the spectral type of Cepheids at light maximum is constant with period. We use hydrodynamic pulsatio n models to explain this result in terms of the outward reach of the h ydrogen ionization front. On the other hand, we show that, at minimum light, the Cepheid photospheric temperature is mainly a function of am plitude. A number of observed Cepheids have published temperatures tha t seem too hot at both maximum and minimum. We attribute this to an ov erestimation of the reddening for these stars. A list is given.