2003ApJ...582L..83K

Stellar evolution calculations predict the flux-weighted gravity g/T⁴_eff and absolute bolometric magnitude of blue supergiants to be strongly correlated. We use medium-resolution multiobject spectroscopy of late B and early A supergiants in two spiral galaxies, NGC 300 and NGC 3621, to demonstrate the existence of such a relationship, which proves to be surprisingly tight. An analysis of high-resolution spectra of blue supergiants in Local Group galaxies confirms this detection. We discuss the application of the relationship for extragalactic distance determinations and conservatively conclude that once properly calibrated it has the potential to allow for measurements of distance moduli out to 30.5 mag with an accuracy of 0.1 mag or better.