MULTIFREQUENCY COMPARISON OF CEPHEIDS AND NONVARIABLE SUPERGIANTS

New IUE data and infrared J, H, K, L, and M observations have been obt ained for nonvariable yellow supergiants and the prototype classical C epheid delta Cephei. These data have been combined with data in the li terature to make a comparison between nonvariable yellow supergiants a nd delta Cephei from the ultraviolet through the near infrared. The su pergiant sequence shows a smooth progression of energy distributions w ith spectral type over this extended wavelength range. The delta Cephe i energy distributions on the descending branch of the light curve (fr ee-fall portion of the pulsation curve) are well matched by supergiant energy distributions with the same (B- V)0 for most phases. At the ho ttest phases, however, there is some extra flux at 3000 angstrom as co mpared with the nonvariables. The delta Cephei observation on the asce nding branch of the light curve (''piston'' phase of the pulsation cyc le) has slightly more ultraviolet light than would be predicted from e ither the supergiant observations or the free-fall delta Cephei phases .