The Optical Gravitational Lensing Experiment Monitoring of QSO 2237+0305

We present results from 2 yr of monitoring of Huchra's lens (QSO 2237+0305) with the 1.3 m Warsaw telescope on Las Campanas, Chile. Photometry in the V band was done using a newly developed method for image subtraction. Reliable subtraction without Fourier division removes all complexities associated with the presence of a bright lensing galaxy. With the positions of the lensed images adopted from Hubble Space Telescope ( HST ) measurements, it is relatively easy to fit the variable part of the flux in this system, as opposed to modeling the underlying galaxy. For the first time, we observed smooth light variation over a period of a few months, which can be naturally attributed to microlensing. We also describe automated software capable of real-time analysis of the images of QSO 2237+0305. It is expected that starting from the next observing season in 1999, an alert system will be implemented for high-amplification events in this object. The time sampling and photometric accuracy achieved should be sufficient for early detection of caustic crossings.