Image reconstruction in opticl interferometry: application to the inner regions of protoplanetary disks.

Planets are believed to form in disks of gas and dust detected around newly born stars. The study of such circumstellar disks is necessary to understand how the planets form and the origin of our solar system. At the distance of the closest star forming regions, the observation of the disk at distances ranging from 0.1 to 10 AUs corresponds to milli-arcsecond spatial scales. Infrared interferometry is a suitable tool to achieve such spatial scales and to conduct observations of the close environment of such disks. However, an interferometer does not provide a direct image of the observed object. The data obtained so far consist of a small number of measurements which can only constrain theoretical models. With the advent of recent multi-aperture interferometers, the interferometric data can be used to reconstruct images independently of any parametric model, as is routinely done in the radio frequency range. The goal of the present work is to apply the image reconstruction technique to near-infrared interferometric data of young stellar objects. Firstly, a systematic study of the image reconstruction method is done on the MiRA algorithm and practical rules for the users are derived from the tests. Moreover, the study demonstrates that the (u; v) coverage is more critical than the signal-to-noise ratio in the image reconstruction context. Secondly, the method is applied on an Herbig Ae star, MWC275, leading to the first image of a complex young stellar object. Due to the sparseness of the (u; v) coverage, an unambiguous image easy to interpret cannot be derived, even if optimal parameters are used. A methodology, using a model of the observed object, is necessary to not over-interpret the structures in the reconstructed image. Finally, the technique is applied to other young stellar objects. The new applications affirm the interest of the image reconstruction method to analyze the data, but confirm also that the images have to be interpreted carefully.