DUO (Disc Unseen Objects) is a microlensing experiment which aims to monitor around 12 million stars in the Galactic centre for signs of microlensing. The timescales and angular distribution of the microlensing events will be used to determine the Galactic disc and bulge structure and will also constrain the shape of the stellar mass function down to, and below, the hydrogen-burning limit.
DUO is unique in utilising the wide field of view of the ESO Schmidt telescope at La Scilla to obtain Schmidt plates with a 30 deg2 angular coverage. This wide coverage will allow 'mapping' of the Galactic bulge and disc. Preliminary observations have uncovered 10 microlensing candidates, demonstrating the feasibility of the project.
DUO will also generate a huge catalogue of short- and long-period variable stars, some of which will be useful as distance indicators with which to produce 3-D maps of the interstellar reddening around the Galactic centre.