Goulds bälte : en undersökning av dess utsträckning och rörelseförhållanden

Sammanfattning: To investigate the kinematics of the local system of stars and to determine the extent of the Gould belt system, bright nearby early type stars in different age groups have been examined. The mean plane of the stars younger than 20 million years was found to be inclined to the galactic plane by 19°, while the mean plane of the stars older than 60 million years is practically coincident with the galactic plane. The extinction in the galactic plane is very irregular and varies with galactic longitude; in the second and fourth quadrants of longitude the extinction is large, while it is generally lower in the other two quadrants. The solar motion and four galactic rotation parameters have been determined for the different age groups. The results show that the kinematic properties differ between the youngest and the oldest stars; while the group of the youngest stars is expanding the oldest stars follow circular differential rotation.Fainter early type stars have been observed in the galactic plane at four galactic longitudes chosen to give maximum information about a system of stars which started to expand from a small volume. In the galactic center-anticenter direction the observations have also been performed in the Gould belt. The extent of the Gould belt system, found from the study of the bright nearby stars, was confirmed by these observations, which also showed that the limits of the Gould belt represent a discontinuity not only in the spatial distribution of the young stars but also in the kinematic properties of these stars; the young stars outside Gould's belt, like the older stars in this belt, follow pure circular differential rotation.An expansion model, taking into account the irregular distribution of the obscuring matter, is probably needed for an explanation of the properties of Gould's belt.