ON THE ABSOLUTE BRIGHTNESSES AND MASSES OF EARLY-TYPE STARS

A new empirical brightness calibration of early-type stars is presente d, entirely based on accurate binary data. This calibration agrees rem arkably well with the predictions of the most recent stellar models, b ut disagrees completely with all other currently used calibrations for early-type stars. The binaries used to derive the new calibration cov er a range of masses from about 1.3 M. to 25 M., corresponding to a te mperature range from 6700 K to 38000 K. Over the whole mass range, no systematic differences between the observed and evolutionary masses we re found. The application to the a Per cluster gives a distance modulu s which agrees perfectly with that derived by comparing its lower main -sequence to stars with known parallaxes.