A uvby beta photometric calibration of iron abundances in supergiant stars

A photometric reddening-free calibration for [Fe/H] valid far giant and supergiant stars of intermediate temperature, has been obtained using the Stromgren uvby beta system. Galactic supergiants, supergiants in the Magellanic Clouds and Galactic metal deficient red giants with spectroscopic determinations of [Fe/H] were used as calibrators. The calibration can be used to predict [Fe/H] with an accuracy of 0.33 dex, valid for stars with 0.14 < [m(1)] < 0.70 in the iron abundance range -2.5 < [Fe/H] < +0.3. This shows the potential of supergiant stars as tracers of iron abundances in other galaxies. Evidence that Galactic luminous F-G stars are intrinsically bluer than their counterparts in the Magellanic Clouds is offered.