TEMPERATURES OF DELTA-CEP AND NONVARIABLE SUPERGIANTS

This study is a comparison of the energy distributions of nonvariable supergiants and delta Cep with model atmospheres. The data include IUE spectra from 1700 to 3200 Angstrom, and broadband B, V, R(C), I-C, J, H, and K. The model atmosphere comparisons cover a range of temperatu res, gravities, and microturbulence. Both the nonvariables and delta C ep are a good fit to the Kraft (B-V)(0)-temperature relation. The delt a Cep observations match energy distributions using reasonable values of gravity and microturbulence. For the hotter phases, a larger gravit y is required than for the cooler phases, but this value results in a good fit to energy distribution, including the excess ultraviolet flux found previously. Similarly, the energy distribution for the piston p hase can also be reproduced, but a large value of microturbulence (lar ger than similar or equal to 6 km s(-1)) would be very difficult to ac commodate. The most interesting result concerns the nonradiative flux found by Morossi et al. [A&A, 277, 173 (1993)] at the shortest wavelen gths. It is found in nonvariable supergiants, however it is nonexisten t or much reduced in the delta Cep observations. This suggests an alte ration to the atmospheric structure caused by pulsation. This is in ag reement with and explains the recent ROSAT observation of the Cepheid zeta Gem by Sasselov & Sabbey [RMxA&A, 29, 215 (1994)]. It was not det ected, meaning that it's x-ray flux is at least 20 times less than com parable nonvariable supergiants. Pulsation apparently inhibits upper a tmosphere heating, so that a hot corona is not formed. (C) 1996 Americ an Astronomical Society.