SIMBAD references

Luminous FG supergiants can be used as extragalactic distance indicators. In order to fully exploit the properties of these bright stars, we must first learn how to measure their luminosities. Based primarily on classical Cepheids and supergiants in clusters and OB associations, we have derived 80 empirical relations connecting the line depth ratios of Feii/Fei lines with the absolute magnitudes M_v and the effective temperatures T_eff. These relations have been applied to estimate the absolute magnitudes of 98 FG supergiants with an error of ±0.26mag. The application range of our calibrations is spectral types F2-G8 and luminosity classes I and II (absolute magnitudes M_v, -0.5 to -8 mag). A comparison of our M_vdeterminations with values from the literature shows good agreement.