The effect of wavefront corrugations on fringe motion in an astronomical interferometer with spatial filters

Numerical simulations of atmospheric turbulence and AO wavefront correction are performed to investigate the timescale for fringe motion in optical interferometers with spatial filters. These simulations focus especially on partial AO correction, where only a finite number of Zernike modes are compensated. The fringe motion is found to depend strongly on both the aperture diameter and the level of AO correction used. In all of the simulations the coherence timescale for interference fringes is found to decrease dramatically when the Strehl ratio provided by the AO correction is <~30%. For AO systems which give perfect compensation of a limited number of Zernike modes, the aperture size which gives the optimum signal for fringe phase tracking is calculated. For AO systems which provide noisy compensation of Zernike modes (but are perfectly piston-neutral), the noise properties of the AO system determine the coherence timescale of the fringes when the Strehl ratio is <~30%