3 Member search

Stars can only be gravitationally bound to a star cluster if they are located inside its tidal radius. If a star cluster is seen from outside, this corresponds to a spherical region on the sky inside which stars must lie in order to be bound to the cluster. To find the members, we therefore took a rough estimate for the tidal radius (we assumed 12 pc, the tidal radius for a 1000  ${M}_{\odot}$ star cluster in the solar neighbourhood), the cluster distance from Lyngå (1987), and calculated the angular diameters of these regions. They were then searched for Hipparcos stars and 2900 stars were found altogether.