Isopistonic angle for multi-aperture interferometers from isoplanatic angle

¹ Université Cady-Ayyad Faculté des sciences LPHEA, 40000 Marrakech, Morocco e-mail: telhalkouj@yahoo.fr
² Université de Nice Sophia-Antipolis UMR 6525, Parc Valrose, 06108 Nice, France
³ École Normale Supérieure, route d'Essaouira, Laboratoire d'optique et optoélectronique, 4000 Marrakech, Morocco

Received: 27 June 2007
Accepted: 27 September 2007

Abstract

Context.Extending the potential of multi-aperture telescopes toward the higher magnitudes necessary for extragalactic science needs an off-axis reference source to cophase the interferometric array.

Aims.The off-axis reference star and the science source must be within the isopistonic angle, and evaluating this parameter is crucial for estimating the potential of long-baseline interferometers for faint sources, differential astrometry, and phase-reference imaging.

Methods.We derived an analytical method of deducing the isopistonic angle from the standard atmospheric optical parameters, and used a full description of the atmospheric turbulence to validate numerical integrations.

Results.We used the analytical expression for the isopistonic angle for predictions concerning the VLT, Keck, and LBT interferometers, as well as for an array of small apertures in the Antarctica site Dome C, indicating that is might be a unique site on earth for interferometric observations of faint sources.