Detecting faint companions with PIONIER

One of the main goals of the PIONIER visitor instrument at VLTI is to search for faint companions around relatively bright stars. In this talk, we present a general method to search for companions in PIONIER data, with a particular emphasis on the exploitation of closure phases. Our search method is illustrated on a few exemples, including the detection of companions at the ~1% contrast level, and non-detections showing upper limits of a few 0.1% on the contrast of any companion within the interferometric field-of-view. In particular, we demonstrate that the small near-infrared excesses previously reported around several main-sequence stars with precision near-infrared interferometry is not related to the presence of low-mass companions around the target stars. The current limitations of PIONIER are shortly discussed, and we derive some general guidelines on how to best use an interferometric array for faint companion detection. Finally, we discuss how the dynamic range and angular resolution provided by of PIONIER can serve various scientific goals, ranging from low-mass companions around main sequence stars to massive binaries. We show that PIONIER could detect objects at the brown dwarf / planet boundary for young low-mass stars residing in nearby associations.