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 collaborationof astronomers whose primary goal is to monitor microlensing events densely andprecisely in order to detect and study anomalies that contain information aboutGalactic lenses and sources that would otherwise be unobtainable. The resultsof PLANET's highly successful first year of operation are presented here.Details of the observational setup, observing procedures, and data reductionprocedures used to track the progress in real time at the three participatingobserving sites in 1995 are discussed. The ability to follow several eventssimultaneously with a median sampling interval of 1.6 hours and a photometricprecision of better than 0.10 mag even at I=19 has been clearly demonstrated.During PLANET's 1995 pilot campaign, 10 microlensing events were monitored; thebinary nature of one of these, MACHO 95-BLG-12 was recognized by PLANET on themountain. Another event, OGLE 95-BLG-04, displayed chromaticity that may betraythe presence of blending with unresolved stars projected onto the sameresolution element. Although lasting only about a month, the campaign may allowconstraints to be placed on the number of planets with mass ratios to theparent star of 0.01 or greater.