We have recently shown that a posteriori co-phasing of multi-spectral interferograms was possible.<sup>1</sup> In this contribution, we extend our approach so that it can be applied to actual data as provided by Amber <sup>2</sup> or Matisse instruments. The main advantage of the proposed post-processing technique is that it requires no modifications of the instruments and yields interferometric observables with higher SNR and much fewer unknowns (in particular for the Fourier phase) than conventional measurements. In order to perform the co-phasing of a complete sequence of interferograms, we jointly estimate a global phase template and the frame dependent optical path errors due to the turbulence. We show that this strategy is effective for very low SNR data. We assess the effectiveness of our method on simulated and actual AMBER data. We also compare the lowest SNR that can be achieved to the theoretical bounds and estimate the gain in sensitivity compared to usual interferometric data.
We present a method to recontruct temperature map directly from spectro-interferometric data. It uses a sparse coding method to describe each pixel as a blackbody. Results are shown on the Herbig Be HD98922. Aside from recovering the mean environment temperature of 1654K in agreement with the photometry, this technique allows us to study the temperature distribution in the first astronomical units around the star.
This paper presents an extension of the spatio-spectral (“3D”) image reconstruction algorithm called PAINTER (Polychromatic opticAl INTErferometric Reconstruction software). The algorithm is able to solve large scale problems and relies on an iterative process, which alternates estimation of polychromatic images and of complex visibilities. The complex visibilities are not only estimated from squared moduli and closure phases, but also from differential phases, which helps to constrain the polychromatic reconstruction. Alternative methods to construct the specific differential phases used in PAINTER are proposed. Simulations on synthetic data illustrate the specificities of the proposed methods.
Image reconstruction in optical interferometry has gained considerable importance for astrophysical studies during the last decade. This has been mainly due to improvements in the imaging capabilities of existing interferometers and the expectation of new facilities in the coming years. However, despite the advances made so far, image synthesis in optical interferometry is still an open field of research. Since 2004, the community has organized a biennial contest to formally test the different methods and algorithms for image reconstruction. In 2016, we celebrated the 7th edition of the "Interferometric Imaging Beauty Contest". This initiative represented an open call to participate in the reconstruction of a selected set of simulated targets with a wavelength-dependent morphology as they could be observed by the 2nd generation of VLTI instruments. This contest represents a unique opportunity to benchmark, in a systematic way, the current advances and limitations in the field, as well as to discuss possible future approaches. In this contribution, we summarize: (a) the rules of the 2016 contest; (b) the different data sets used and the selection procedure; (c) the methods and results obtained by each one of the participants; and (d) the metric used to select the best reconstructed images. Finally, we named Karl-Heinz Hofmann and the group of the Max-Planck-Institut fur Radioastronomie as winners of this edition of the contest.
This paper describes a method of beam-combination in the so-called hypertelescope imaging technique recently introduced by Labeyrie in optical interferometry. The method we propose is an alternative to the Michelson pupil reconfiguration that suffers from the loss of the classical object-image convolution relation. From elementary theory of Fourier optics we demonstrate that this problem can be solved by observing in a combined pupil plane instead of an image plane. The point-source intensity distribution (PSID) of this interferometric "image" tends towards a psuedo Airy disc (similar to that of a giant monolithic telescope) for a sufficiently large number of telescopes. Our method is applicable to snap-shot imaging of extended sources with a field comparable to the Airy pattern of single telescopes operated in a co-phased multi-aperture interferometric array. It thus allows to apply conveniently pupil plane coronagraphy. Our technique called Interferometric Remapped Array Nulling (IRAN) is particularly suitable for high dynamic imaging of extra-solar planetary companions, circumstellar nebulosities or extra-galactic objects where long baseline interferometry would closely probe the central regions of AGNs for instance.