GENIE: a ground-based precursor for the IRSI-Darwin mission

During the preliminary phase A of the Ground-based European Nulling Interferometer Experiment (GENIE), a number of interferometric configurations have been studied, in the cases of exozodiacal cloud and hot Jupiter detection. Their expected performances have been computed in light of the measured or expected performances of the VLTI sub-systems. A simple Bracewell nulling interferometer, formed of two Unit Telescopes and working in the L' or N bands, has been identified as a good candidate configuration for exozodiacal cloud detection. External or internal chopping, fringe tracking and intensity matching will be critical issues for this configuration. In the case of hot Jupiter detection, a double Bracewell with internal modulation in the L' band seems well appropriate, and should allow to carry out low resolution spectroscopy on a few bright exoplanets. The basic assumptions and computations which have lead to these candidate configurations are described in this paper.