Performance of the angle of arrival correction system of the I2T+ASSI stellar interferometer

The Active Stabilization in Stellar Interferometry (ASSI) recombining table, developed at Office National d'Etudes et de Recherches Aerospatiales (ONERA), France, was implemented on the two-Telescope Interferometer (I2T) of the Observatoire de la Cote d'Azur (OCA) in 1993, compensating for the atmospheric turbulence wavefront fluctuations. Initial fringe observations were made in June 1994 with a 11 m North-South baseline. In this paper, we report the performance of the ASSI table servo system for correction of the angle of arrival. Tracking accuracy of about +/-0.24 arcsec was achieved in typical seeing conditions (r(o) greater than or equal to 10 cm) and on m(v) = 2 sources. Collected data allows to compare theoretical with observed temporal power spectra of the angle of arrival fluctuations, using Kolmogorov model. Spatio-temporal seeing parameters met during observations (Fried parameter r(o) and coherence time t(o)) are estimated.