Over the course of the project, the team developed powerful data analysis software called XARA that interpret images in the light of the kernel-framework: members leading personal projects put this software to the test on existing archival data and were able to demonstrate its effectiveness in a wide variety of cases - with more still in preparation. Motivated by the detection problem of very faint sources in diffraction dominated images, a special focus was put on the formulation of statistical tests where the false alarm probability rate can be controlled. This framework was then tested in a series of contexts of increasing complexity: tackling partial data saturation, the handling of field rotation, the use of apodized apertures, and contributed to increase the sensitivity of the approach. These results were published in peer reviewed journal papers primarily led by students of the project and presented in international conferences.
Designing a true high-contrast application of the kernel-framework required going back to a sparse aperture scenario, with a finite number of apertures. Our concept, called the kernel-nulller, is a very exciting prospect, that simultaneously tackles for the first time, the two major sources of noise affecting high-contrast imaging. Our baseline design of a four-beam recombiner, now informs the construction of a nuller for the VLTI, called Hi-5/VIKiNG, that is a module of the ASGARD instrument suite. VIKiNG is a novel all-in-one interferometric recombiner, whose realization using conventional optics would be difficult. We therefore turned our attention to integrated optics that offers powerful, elegant and very compact solutions to such problems. Our first kernel-nuller prototype, at the moment, probably the most complex type of photonic circuitry ever developed for astronomy, was used in the laboratory to validate the theoretical concept, and is now ready to be deployed on-sky.
The original kernel-framework however also offered possibilities for metrology applications. We were able, over the course of an engineering observing run at the telescope, to demonstrate its ability to correctly diagnose a problem plaguing high-contrast imaging instruments, called the low-wind effect, which conventional adaptive optics are unfortunately unable to tackle. After developing a polychromatic extension of the same approach, we designed and prototyped of an integrated fringe-tracking and alignment stabilization solution for the VLTI interferometer: HEIMDALLR, another module of the ASGARD instrument suite, will be installed at the focus VLTI in the second part of 2024.
