GRAVITATIONAL MICROLENSING BY GLOBULAR-CLUSTERS

Stars in globular clusters can act either as sources for MACHOs (Massi ve Astrophysical Compact Halo Objects) located along the line of sight or as lenses for more distant background stars. Although the expected rate of microlensing events is small, such observations can lead to v ery useful results. In particular, one could get information on the sh ape of the galactic halo along different lines of sight, allowing to b atter constrain its total dark matter content. Moreover, on can also i nfer the total dark matter content of globular clusters, which is pres ently not well known. To this latter purpose, we analyse the microlens ing events towards the galactic bulge, which lie close to the three gl obular clusters NGC 6522, NGC 6528 and NGC 6540. We find evidence that some microlensing events are indeed due to MACHOs located in the glob ular clusters, suggesting, therefore, that these clusters contain a si gnificant amount of dark matter.