Member counts : a new method to constrain the tidal radii of globular clusters

We test the use of counts of globular cluster members, based on proper motions, to improve the determination of their tidal radii. The observational material consists of relative proper motions for stars in large areas enclosing the globular clusters 47 Tuc and NGC 362 (Tucholke, 1992, A&AS, 93), whose tidal radii are uncertain due to the variable background of SMC stars. For NGC 362, the member counts extend to radii larger than previous star counts. For 47 Tuc, the contamination by SMC stars is less severe, and straightforward star counts reach fainter limiting magnitudes and larger radii than the member counts