Are the Ogle Microlenses in the Galactic Bar?

The analysis of the first two years of OGLE data revealed 9 microlensing events of the galactic bulge stars, with the characteristic time scales in the range 8.6 < t0 < 62 days, where t0 = RE/V . The optical depth to microlensing is larger than (3.3 ± 1.2) × 10, in excess of current theoretical estimates, indicating a much higher efficiency for microlensing by either bulge or disk lenses. We argue that the lenses are likely to be ordinary stars in the galactic bar, which has its long axis elongated towards us. A relation between t0 and the lens masses remains unknown until a quantitative model of bar microlensing becomes available. At this time we have no evidence that the OGLE events are related to dark matter. The geometry of lens distribution can be determined observationally when the microlensing rate is measured over a larger range of galactic longitudes, like −10 < l < +10, and the relative proper motions of the galactic bulge (bar) stars are measured with the HST. Subject headings: cosmology: dark matter – galaxy: center – galaxy: structure – gravitational lensing – stars: low mass, brown dwarfs Princeton University Observatory, Princeton, NJ 08544–1001 Warsaw University Observatory, Al. Ujazdowskie 4, 00–478 Warszawa, Poland Department of Astronomy, University of Michigan, 821 Dennison Bldg., Ann Arbor, MI 48109–1090 Carnegie Observatories, Las Campanas Observatory, Casilla 601, La Serena, Chile On leave from N. Copernicus Astronomical Center, Bartycka 18, Warszawa 00–716, Poland Visiting Astronomer, Princeton University Observatory, Princeton, NJ 08544–1001