The β index in cool stars

If we follow recent work and in order to extend the uvby photometric calibrations to spectral types later than G0, we present an attempt to use the combined uvby and β systems for stars in the range G5-K7 and luminosity classes V to III. The behaviour in the MK-β, (b-y)-β and cl-β diagrams of the 200 stars, only good spectroscopic data being considered, suggests the usefulness of the β index as an independent parameter for late-type Main-Sequence stars, following in a natural way the general trend defined by Crawford for F- and G-type stars. © 1990 Kluwer Academic Publishers.