Probing MACHOs toward the Galactic Bulge

If the massive compact halo object (MACHO) fraction of the Galactic dark halois f ~ 20% as suggested by some microlensing experiments, then about 1.2% oflensing events toward the Galactic bulge are due to MACHOs. For the 40% ofthese that lie nearby (D_l < 4 kpc), measurement of their distance D_l woulddistinguish them from bulge lenses, while measurement of their transversevelocity v_l would distinguish them from disk lenses. Hence, it would bepossible to identify about 0.5%(f/20%) of all events as due to MACHOs. I showthat a planned experiment using the Space Interferometry Mission (SIMPlanetQuest) could thereby detect 1 or 2 such events. This is at the margin ofwhat is required because of a small, but non-negligible background fromspheroid stars.Comment: 11 Pages, 1 Figure, Submitted to Ap