A Spectroscopic and Photometric Study of the be Stars.

A study is made of the Be stars brighter than magnitude 8 6 and north of declination - 20 , having spectral types on the Mount Wilson system between B0 and B5 These stars fail into two general categories: (1) a group of exceedingly high luminosity (luminosity class I on the MK system) and (2) a group of lower luminosity which seems to be cleanly separated in absolute magnitude from the first. The present paper is concerned with investigating the second group New spectral types were determined on the MK system for 175 of the 182 objects defined by the above selection for the second category A sharp maximum in the distribution according to spectral type is found at B2 It does not seem possible to account for this as a result of observational selection Photoelectric observations of the stars were made on the (U, B, V) system of Johnson and Morgan A comparison of these measures with those for standard main-sequence stars indicates that an ultraviolet excess is present for the majority of the Be stars. A comparison of the luminosities of B 1e-B2e stars located in three associations having well-determined distances indicates that these objects form a compact group in absolute magnitude, with a mean value Mv = -36 mag This result is used to determine the spectroscopic distances of the stars of classes B le-B2 Se, inclusive A plot of these stars on the galactic plane delineates the spiral arm in which the sun is located This new evidence confirms the high inclination of the arm found from the 0 associations and from the polarization observations of Hiltner The B 1e-B2e stars are not concentrated in the nearby associations but are scattered fairly uniformly along the spiral arm. This indicates that these stars are, as a class, older than the present 0 associations. Since the B2e stars lie roughly 1 mag. above the main sequence, an evolutionary age can be determined from the theoretical work of Kushwaha The latter's result indicates an age of around 30 million years for such stars. This is therefore in agreement with the observational result that these stars are not strongly concentrated in the present 0 associations.