Integration of the atmospheric fluctuations in a dual-field optical interferometer: the short exposure regime

Spatial phase-referencing in dual-field optical interferometry is reconsidered. Our analysis is based on the 2-sample variance of the differential phase between target and reference star. We show that averaging over time of the atmospheric effects depends on this 2-sample phase variance (Allan variance) rather than on the true variance. The proper expression for fringe smearing beyond the isoplanatic angle is derived. With simulations of atmospheric effects, based on a Paranal turbulence model, we show how the performances of a dual-field optical interferometer can be evaluated in a diagram 'separation angle' versus 'magnitude of faint object'. In this diagram, a domain with short exposure is found to be most useful for interferometry, with about the same magnitude limits in the H and K bands. With star counts from a Galaxy model, we evaluate the sky coverage for differential astrometry and detection of exoplanets, i.e. likelihood of faint reference stars in the vicinity of a bright target. With the 2mass survey, we evaluate sky coverage for phase-referencing, i.e. avaibility of a bright enough star for main delay tracking in the vicinity of any target direction.Comment: 9 pages, 8 figures, accepted for publication in A&

Wavefront outer scale deduced from interferometric dispersed fringes

Astronomy and Astrophysics, v. 448, p. 1225-1234, 2006. http://dx.doi.org/10.1051/0004-6361:20052806International audienc

Modelling the optical effects of atmospheric turbulence in High Angular Resolution astronomical observations: wavefront coherences and related parameters

The structure function (or the power spectrum)of phase fluctuations induced by atmospheric turbulence is the main quantity which must be known to optimize the High Angular Resolution techniques used for astronomical observations. It allows to evaluate the state of coherence of the perturbed wavefronts. In this paper are firstly recalled classical results concerning the propagation of the luminous waves through the terrestrial atmosphere and consequently the image formation. Then, different models generally used to describe the optical effects of atmospheric turbulence, due to numerous thin layers, are presented and their influence discussed. A second order statistical analysis is performed and the coherence parameters deduced. The necessity of measuring these parameters appears evident and dedicated monitors must be built

How to Monte-Carlo Simulate the Optical Turbulence Boilingbeyond the Frozen Flow Hypothesis

Proceedings of the Symposium on Seeing, n/a, pp. 208-209 (2007)International audienc

MOSP : Monitor of Outer Scale Profile

Proceedings of the Symposium on Seeing, n/a, pp. 31-36 (2007)International audienc

On the isoplanatic patch size in High Angular Resolution Techniques

International audienceTo reach a high performance with an adaptive optics system, we need a calibration using a reference source. This latter should be located in the same isoplanatic domain as the science source. Different techniques and methods have been developed leading to estimations of the isoplanatic patch but all are model-dependent. We developed a new technique for the estimation of the isoplanatic angle based on an extended object. This technique is now part of our new turbulence profile monitor PML (Profiler of Moon Limb) based on the observation of the Moon limb or Sun edge. The first statistics of the isoplanatic angle with this new technique are presented and compared to the exiting techniques based on scintillation measurements or other turbulence parameters such as Fried parameter and/or C2n profile

An optical turbulence profiler for the terrestrial atmosphere boundary-layer

Proceedings of the Symposium on Seeing, n/a, pp. 26-28 (2007)International audienc

MOSP : a new instrument to measure wavefront outer scale profiles

Conference OSA - Adaptive Optics : Analysis and Methods Meeting, n/a, (2007)International audienc

Measurements of profiles of the wavefront outer scale using observations of the limb of the Moon

MNRAS, 377, pp. 1236-1244 (2007)International audienc