A re-calibration of the luminosities of early-type stars: its effect on the Cepheid luminosity scale

We have used the most recently published data on 421 stars in 13 open clusters to recalibrate the Strömgren β index as a luminosity indicator for early type stars. Since all the clusters independently tie up with the Pleiades, previous problems involving the use of associations are avoided. Our final calibration is presented as an analytical expression in (β, c0). Analysis of evolutionary diagrams for the calibrating clusters show small trends which are best explained as due to differences in zero-point of the β index. We present a calibration for the zero-age main sequence and compare it with results by various authors. The effect of the calibration on the zero-point of the Cepheid luminosity scale is investigated in an appendix.