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Processing of pOLychromatic interferometriC data for Astrophysics


The Jean-Marie Mariotti Center (JMMC) distributes software for preparing observations, for finding calibrators, for data reduction of the VLTI instruments, and for model fitting. Efforts are ongoing for image reconstruction and first images are obtained. But a new step forward needs to be accomplished in order to make the most of the somehow complex interferometric data. Indeed, the current interferometric data carries rich spectral information that is not fully exploited because of the difficulty to process it at the same time as the spatial information. Most usually, the data are processed for spectral channels separately, and wavelength dependency is considered afterward. Impact of stellar interferometry would be significantly enhanced with efficient means to process (x,y,{$\lambda$}) as a whole.

But the heterogeneity of the (x,y,{$\lambda$}) space needs specific progress and significant advances in signal processing. Further both the size of the parameter space for image reconstruction and the numerous possible representations of the spectrum call for innovative R&D in the fields of compressed sensing and regularization methods. As another example, the observation of complex objects shows that model fitting often captures only a part of the object features, and efficient means are needed to explore the residuals of a fit, for instance with an image reconstruction approach, with semi-parametric modeling and spatio-spectral regularizations.

Other specific difficulties come from the correlations seen between the measurements in different spectral channels, or from the different methods used by the instruments for measuring the so-called differential visibilities (differential along wavelengths). These problems call for bringing together experts from stellar interferometry and from signal processing with the aim to clarify the correct modeling of data, including noises and biases. The outcome should be to improve the current measurements or to derive more suitable tools for data processing.

In the context of the existing instruments (e.g. MIDI, AMBER, VEGA, PIONIER) and the ones currently in development ( GRAVITY, MATISSE), several scientific cases can be considered as promising but currently limited by the lack of suitable inversion tool. For instance, the study of chemical composition and fine spatial structure of dusty disk (protoplanetary or evolved ones), the study of faint companion to stars up to exoplanets, or the study of the kinematics of young or evolved circumstellar environments.


The strategy of POLCA is to first select existing data on specific objects that really need new polychromatic processing to solve some open questions, and to add new data acquired with the same intention. Around these data, we intend to formalize physical models of object, model of data, study noise statistics and correlations, and develop new algorithms suitable for a 3D approach.

This project should allow astronomers get the most of available and soon to come stellar interferometry facilities.

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Page last modified on May 09, 2013, at 03:13 PM