From photoelectric $uvby\beta$ data and recent accurate synthetic and spectroscopic values of $T_{ \rm eff}$ and log~$g$ for 50 F-G supergiants, we have calculated functional relationships that lead to initial estimates of effective temperature and gravities for these types of stars. It is shown that while the $T_{ \rm eff}$ relationships are calculated using the data on young massive supergiants, they are also valid for evolved stars of similar temperatures like post-AGB and RV Tau stars. The gravity can also be predicted from the $\Delta [c_1]$ index with an uncertainty of about 0.26 dex. Although a clear and significant trend between $M_V$ and $\Delta [c_1]$ is seen, no calibration is found that predicts accurate values of $M_V$.
Categories: astro-ph.SR