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Issue A&A Volume 400, Number 2, March III 2003 Page(s) 795 - 803 Section Physical and chemical processes DOI 10.1051/0004-6361:20030072

A&A 400, 795-803 (2003)
DOI: 10.1051/0004-6361:20030072

On marginally resolved objects in optical interferometry

R. Lachaume

Observatoire de Grenoble, Laboratoire d'Astrophysique de Grenoble, Université Joseph Fourier, BP 53, 38041 Grenoble Cedex, France
(Received 13 November 2002 / Accepted 19 December 2002)

Abstract
With the present and soon-to-be breakthrough of optical interferometry, countless objects shall be within reach of interferometers; yet, most of them are expected to remain only marginally resolved with hectometric baselines.

In this paper, we tackle the problem of deriving the properties of a marginally resolved object from its optical visibilities. We show that they depend on the moments of flux distribution of the object: centre, mean angular size, asymmetry, and curtosis. We also point out that the visibility amplitude is a second-order phenomenon, whereas the phase is a combination of a first-order term, giving the location of the photocentre, and a third-order term, more difficult to detect than the visibility amplitude, giving an asymmetry coefficient of the object. We then demonstrate that optical visibilities are not a good model constraint while the object stays marginally resolved, unless observations are carried out at different wavelengths. Finally, we show an application of this formalism to circumstellar discs.

Key words: methods: data analysis -- techniques: interferometric

© ESO 2003

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