The 1995 pilot campaign of planet: Searching for microlensing anomalies through precise, rapid, round-the-clock monitoring

PLANET (the Probing Lensing Anomalies NETwork) is a worldwide collaboration of astronomers whose primary goal is to monitor microlensing events densel y and precisely in order to detect and study anomalies that contain informa tion about Galactic lenses and sources that would otherwise be unobtainable . The results of PLANET's highly successful first year of operation are pre sented here. Details of the observational setup, observing procedures, and data-reduction procedures used to track the progress in real time at the th ree participating observing sites in 1995 are discussed. The ability to fol low 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 bee n clearly demonstrated. During PLANET's 1995 pilot campaign, ten microlensi ng 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, w as recognized by PLANET on the mountain. Another event, OGLE 95-BLG-04, dis played chromaticity that may betray the presence of blending with unresolve d stars projected onto the same resolution element. Although lasting only a bout 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.