1998ApJ...509..687A

PLANET (the Probing Lensing Anomalies NETwork) is a worldwide collaboration of astronomers whose primary goal is to monitor microlensing events densely and precisely in order to detect and study anomalies that contain information about Galactic lenses and sources that would otherwise be unobtainable. The results of PLANET's highly successful first year of operation are presented here. Details of the observational setup, observing procedures, and data-reduction procedures used to track the progress in real time at the three participating observing sites in 1995 are discussed. The ability to follow several events simultaneously with a median sampling interval of 1.6 hr and a photometric precision of better than 0.10 mag even at I = 19 has been clearly demonstrated. During PLANET's 1995 pilot campaign, ten microlensing events were monitored, resulting in the most precise and densely-sampled light curves to date; the binary nature of one of these, MACHO 95-BLG-12, was recognized by PLANET on the mountain. Another event, OGLE 95-BLG-04, displayed chromaticity that may betray the presence of blending with unresolved stars projected onto the same resolution element. Although lasting only about a month, the campaign may allow constraints to be placed on the number of planets with mass ratios to the parent star of 0.01 or greater.