Ansolute Magnitudes of Stars in the Scorpo-Centaurus Association.

Absolute magnitudes for well-established members of the Scorpio-Centaurus association have been determined from newly derived proper motions and recently published photoelectric and photographic photometry Radial velocities and spectral classifications based on new observations collected by the author at the McDonald Observatory have also been incorporated The analysis of the proper motions and the radial velocities and the determination of the absolute magnitudes are based mainly on the expansion hypothesis The conventional type of treatment, involving the assumption that the various parts of the association participate in differential galactic rotation, has also been carried out However, its results are rejected on the basis of various arguments, one of which is the large and unexplained K term in the radial velocities The individual absolute magnitudes are given in Table 1 The mean values per spectral class, in Table 7, are only slightly different from provisional values communicated earlier by Blanuw Apart from the relative motions of the members of the association due to the general expansion, the internal motions are found to be of the order of 1 0 km/sec or less The age of the association, or rather of its oldest parts, is estimated to be about 20 million years From the proper motions and the spectral classifications of the faint B-type stars in the densest part of the association, that is in Scorpius, it is concluded that the association contains a large number of late B-type stars These spectral classifications are based on observations with the Yerkes 404nch refractor The details of the computation of the proper motions are described in the appendix at the end of the article