EDP Sciences
Free access
Volume 406, Number 3, August II 2003
Page(s) 1167 - 1174
Section Physical and chemical processes
DOI http://dx.doi.org/10.1051/0004-6361:20030662

A&A 406, 1167-1174 (2003)
DOI: 10.1051/0004-6361:20030662

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

G. Daigne1 and J.-F. Lestrade2

1  Observatoire Aquitain des Sciences de l'Univers, BP 89, 33270 Floirac, France
2  Observatoire de Paris-CNRS, 77 Av. Denfert-Rochereau, 75014 Paris, France
    e-mail: lestrade@obspm.fr

(Received 9 October 2002 / Accepted 18 April 2003)

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. the 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.

Key words: atmospheric effects -- techniques: interferometric -- methods: observational -- astrometry -- infrared: general

Offprint request: G. Daigne, daigne@obs.u-bordeaux1.fr

© ESO 2003

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