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Description
Walraven photometry is presented of established and probable members of the Scorpio-Centaurus OB association. For each star, effective temperature and surface gravity are derived using Kurucz atmosphere models (1979ApJS...40....1K). From the Straizys and Kuriliene (1981Ap&SS..80..353S) tables, absolute magnitudes are calculated. Distance moduli and visual extinctions are determined for all stars. From a comparison of the HR-diagrams of the stars in each subgroup with theoretical isochrones, the ages of the three subgroups are derived. The distances to the three subgroups are shown to be different; there is a general trend (also within each subgroup) for the distances to be larger at higher galactic longitudes. The visual extinction in the youngest subgroup Upper-Scorpius, is well correlated with the IRAS 100-micron map. The distance toward the Ophiuchus dark clouds is found to be 125 pc, based on the photometric distances to the stars. Most of the early-type stars in Upper-Scorpius are located at the far side of the dark clouds.
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