In the scientific instrument, the fringes are obtained by a multiaxial beam combination in a focal plane and then are recorded using a short exposure. In the data reduction process the spatial information is averaged over the fringe peak. This does not exactly correspond to our observing conditions. However, this estimator is not easily applicable to the I2T interferometer because the telescope diameter is only slightly larger than r 0 .
Atmospheric turbulence is the factor which theoretically most affects the visibility.
We use a numerical simulation to evaluate their effect on the estimators G and R 2 . Neglecting scintillation, we generate 1024 turbulent phase wavefronts for each pupil using the simulation tool of Rousset et al. Tips and tilts are assumed to be uncorrelated between the two telescopes. Because R 2 and G are short exposure estimators, they are theoretically not affected by OPD residuals left by the fringe tracker. Visibility noises are due to intensity fluctuations on the two apertures.