Effective Temperatures, Intrinsic Colours, and Surface Gravities of Yellow Supergiants and Cepheids

Effective temperatures, surface gravities, and colour excesses of supergiant stars in the spectral range F3–G3 are obtained by matching UVBGRI photometry with model atmosphere fluxes. Effective temperatures and surface brightnesses correlate very well with derived intrinsic B–V colours (UBV system) and confirm Kraft's widely-used Te – (B–V)0 relationship. Mean values of Te, (B–V)0, log g, and B.C. are given as functions of spectral class. There is very little overlap in the log g – Te plane between the pulsating and non-pulsating stars. Order-of-magnitude variations in surface gravity are found for many Cepheids which follow more closely the temperature and velocity variations than the dynamical accelerations of the atmospheres. Schwarzschild's running-wave hypothesis is revived in order to account for the behaviour of the effective surface gravity.