Two-Dimensional Spectral Classification by Narrow-Band Photometry for B Stats in Clusters and Associations.

Photoelectric observations of the intensity of the lifi line have been made with the 36-inch reflector of the McDonald Observatory for B stars with available MK spectral types and for B stars in several clusters and associations. The various filter systems used are discussed, and the measures are transformed to a standard system. The color index (U-B) of the U, B, V system, when corrected for interstellar reddening, is used with the H intensities to define a two-dimensional spectral classification system Evolutionary effects on this classification system are discussed, and relative ages for the Scorpio-Centaurus cluster, the Orion association, the Persei association, the a Persei cluster, and the field stars are estimated. Mean absolute magnitudes are computed for the B8 V and B9 V stars in the ScorpioCentaurus cluster, and a comparison with the a Persei cluster yields a minimum distance modulus for it of 64 mag