ON THE CHARACTERISTICS AND ORIGIN OF THE EXPANSION OF THE LOCAL SYSTEM OF YOUNG OBJECTS

Some aspects of the structure and kinematics of the local system of yo ung objects, dominated by the Gould Belt, are examined using an extend ed sample of O and B stars. Its orientation, extent, age, and stellar mass are evaluated by means of a statistical separation of the compone nts of the Belt from the rest of the galactic disk in the solar neighb ourhood. We have carried out different determinations of the Oort cons tants for our stellar sample. No extreme differences from the values u sually accepted for a differentially rotating galactic disk are found, and our results suggest that the kinematics of early type stars is do minated by galactic rotation even at a local scale. The structure of t he well known local expansion is deduced from the observed trends in t he Oort constants; our results indicate that this expansion takes plac e from a line, rather than from a single point. This is found to be in agreement with our model for the origin of the Gould Belt, presented in a previous paper.