Real-time difference imaging analysis of MOA Galactic bulge observations during 2000

We describe observations carried out by the MOA group of the Galactic bulge during 2000 that were designed to detect efficiently gravitational microle nsing of faint stars in which the magnification is high and/or of short dur ation. These events are particularly useful for studies of extrasolar plane ts and faint stars. Approximately 17 deg(2) were monitored at a sampling ra te of up to six times per night. The images were analysed in real time usin g a difference imaging technique. 20 microlensing candidates were detected, of which eight were alerted to the microlensing community whilst in progre ss. Approximately half of the candidates had high magnifications (greater t han or similar to 10), at least one had very high magnification (greater th an or similar to 50), and one exhibited a clear parallax effect. The detail s of these events are reported here, together with details of the on-line d ifference imaging technique. Some nova-like events were also observed and t hese are described, together with one asteroid.