  The main goal of the EXOZODI survey is to detect and characterize
circumstellar dust and to propose the first statistical study of exozodiacal
disks in the near-infrared using telescopes in both hemispheres. For this
purpose, Ertel et al. have conducted in 2012 a survey of nearby main sequence
stars with VLTI/PIONIER to search for the presence of circumstellar dust. This
survey, carried out during 12 nights, comprises about 100 stars. For each star,
we obtained typically three OBs and we searched for circumstellar emission
based on the measurement of squared visibilities at short baselines. A drop in
the measured visibilities with respect to the expected photospheric visibility
indicates the presence of resolved emission around the target star. It is
however generally not possible to conclude on the morphology of the detected
emission based solely on the squared visibilities. Here, we focus on closure
phases to search for faint companions around the whole sample. Indeed, to
derive robust statistics on the occurrence rate of bright exozodiacal disks, we
need to discriminate between companions and disks. For this reason, the main
goal of this paper is to discriminate between circumstellar disks (which show
no closure phase provided that they are point-symmetric) and faint companions
(point-like sources, creating non-zero closure phases). We also aim to reveal
new companions that do not necessarily produce a significant signature in the
squared visibilities, as the signature of the companion may show up more
prominently in the closure phases. In this process, we reveal four new stellar
companions with contrasts ranging from 2% to 95% (i.e., up to equal flux
binaries). We also tentatively detect faint companions around one other target
that will require follow-up observations to be confirmed or infirmed. We
discuss the implications of these discoveries on the results of the exozodi
survey.
