Astrophysical False Positives Encountered in Wide-Field Transit Searches

Wide-field photometric transit surveys for Jupiter-sized planets are inundated by astrophysical false positives, namely systems that contain an eclipsing binary and mimic the desired photometric signature. We discuss several examples of such false alarms. These systems were initially identified as candidates by the PSST instrument at Lowell Observatory. For three of the examples, we present follow-up spectroscopy that demonstrates that these systems consist of (1) an M-dwarf in eclipse in front of a larger star, (2) two main-sequence stars presenting grazing-incidence eclipses, and (3) the blend of an eclipsing binary with the light of a third, brighter star. For an additional candidate, we present multi-color follow-up photometry during a subsequent time of eclipse, which reveals that this candidate consists of a blend of an eclipsing binary and a physically unassociated star. We discuss a couple indicators from publicly-available catalogs that can be used to identify which candidates are likely giant stars, a large source of the contaminants in such surveys.