Category Archives: publication

KERNE publication: Kernel-nullers for all interferometers!

In this new study, led by PhD candidate Romain Laugier, our team has looked into what one needs to do in order to build a kernel-nuller, that is a high-contrast interferometric recombiner robust to residual piston excursions, for an array featuring an arbitrary number of telescopes.

The paper takes advantage of nice graphical representations of the inner workings of a nuller called “complex matrix plots” (but that we’ve nicknamed “Laugier-grams”) to find the properties a recombiner must exhibit in order to be robust to piston perturbations.

The same graphs were also featured a few months ago in a video recorded in French (first announced in this blog post) and later translated into English that explains why the 4-beam kernel-nuller of Martinache & Ireland (2018) works. Both videos were posted on Youtube:

Congratulations to Romain for another published paper to append to his upcoming PhD dissertation! The preprint version of the paper is available for download on the website: Romain’s PhD defense will take place in a little over a month on September 22, 2020.

Two Kernel-phase A&A papers out this month!

The April 2020 issue of Astronomy & Astrophysics will feature two papers from the Nice KERNEL team!

Paper #1: Angular Differential Kernel-phase

The first paper features the results of a study led by graduate student Romain Laugier who’s successfully adapted an angular differential observing technique commonly used in high-contrast imaging to the kernel-phase scenario. This approach, coined angular differential kernel-phase (ADK) takes advantage of the sky rotation experienced by the SCExAO instrument at the Nasmyth focus of the Subaru Telescope when the field rotator is turned off. The technique makes it possible to better calibrate the biasing effect introduced by AO-residuals in the presence of quasi-static aberrations. Whereas interferometric observations typically require to alternate between a target of interest and a calibration star, this new approach spends 100% of the observing time on the target of interest, making it a more efficient alternative.

Figure extracted from the Laugier et al (2020) publication introducing the angular differential kernel-phase observing mode.

The publication is available in open access on the Astronomy and Astrophysics website!

Paper #2: Kernel-phase… version 2.0?

The second paper features the result of a study led by KERNEL project PI Frantz Martinache. This paper goes back to the roots of kernel-phase. After several years of development of the XARA pipeline carried out in the context of the KERNEL project, it was time to revisit previous analysis results in the light of its latest developments. The paper shows that while overall successful, early uses of kernel-phase were not particularly careful. The paper shows that refined descriptions of the diffractive apertures by instruments leads to a major improvement of the kernel-phase analysis and reduces the importance of systematic errors.

Illustraction extracted from the Martinache et al (2020) publication, showing from top to bottom, how a better model of the diffractive aperture can reduce the amount of systematic error. By either increasing the density of the aperture model (middle row) or by introducing a transmission model (bottom row), the magnitude calibration signal (the red or the orange curves on the right hand side plots) can be considerably reduced in comparison with the astrophysical signal (the blue curve).

Using these new aperture modeling prescriptions, the authors then reprocess previously published observations from ground-based and space-borne observatories and shows major improvements in both cases!

In the same vein as the ADK idea at the core of the Laugier et al (2020) publication, the paper quickly explores the possibility offered by consecutive observations at multiple wavelengths. For a target whose aspect would change depending on the wavelength, spectral differential kernel-phase (SDK?) would be a powerful observing mode that would spend

The publication is of course also available in open-access on the Astronomy & Astrophysics website!