Category Archives: astrophysics

Kernel-phase in space

This week, the results of the proposal selection for the Cycle 1 General Observers (GO) program with JWST were announced. In total, some 6000 hours of observing time were awarded to a large number of programs. The details of the GO program can be found on the dedicated STScI webpage.

All of that is great news on its own: the community has been waiting for JWST for a while now and now everybody is really getting ready to do the first observations with this amazing observing facility… but the reason I bring this up here is because, of all of these programs, it turns out that three are directly relevant to what we do in the context of the KERNEL project… and have the word “kernel-phase” in their title!

Two of these programs have been awarded their own time.

The first one is called “Multiplicity Survey of 20 Y Dwarfs with NIRCam Kernel Phase Interferometry“. It is a program led by Loïc Albert (Université de Montreal) that greatly benefited from the paper we published in 2019. As a result, no less than 38.8 hours of observing time were awarded to this program, that will use the kernel-phase technique, combined with the detection algorithm outlined in the paper to look for companions around a sample of 20 very cool sub-stellar objects known as Y-dwarfs. Our team will naturally contribute to the analysis of the data, using the kernel-phase pipeline developed over the course of the KERNEL project.

The second project is called “High resolution, high contrast kernel phase imaging with NIRCam“. It is a smaller program of 4.3 hours of observing time, led by Jens Kammerer, a recent PhD graduate (co-supervised by me) who recently joined STScI. Here, the plan is to target one specific object (HIP 75056 A), known to host a 20-30 Jupiter mass brown dwarf companion to fine tune the kernel-phase analysis procedures.

And an archival proposal… already?!

I was also surprised to discover that, although no data obviously already exists, there is already an archival research proposal called “Kernel-Phase Detection Limits for Planet Discovery with JWST” that was awarded to Samuel Factor, from the University of Texas.

Kernel-phase: a new standard?

To see three different projects directly bear the name “kernel-phase” in their title for the first observing programs by one of the most important observing facilities of the decade to come is a very nice thing to witness! To think that out of the 6000 hours of GO time, more than 40 (not even accounting for the commissioning) aim to take full advantage of kernel-phase is humbling.

I guess after having been a very unusual and marginal observing technique for over a decade, the idea is finally making its way through the brains of observers… who see it as a valid alternative to sparse aperture masking interferometry, particularly onboard a space borne telescope. This means that we have approximately one year to make sure that our pipeline and our detection procedures are razor sharp and ready to be used the moment the data becomes available!

Postdoctoral position in High Angular Resolution Astronomy

The KERNEL project, hosted by Observatoire de la Cote d’Azur (OCA) invites applications for a postdoctoral research position in the field of high-angular resolution astronomy starting no later than July 1, 2020. This position is funded by the European Research Council (ERC – CoG – grand agreement #683029) under the European Union’s Horizon 2020 research and innovation program.

The KERNEL project

KERNEL aims at enabling every optical and infrared astronomical facility to reach its ultimate angular resolution potential, often pushing beyond the formal diffraction limit, while preserving the full sensitivity. By looking at astronomical data as the result of an interferometric process, the KERNEL framework brings much needed robustness to high-performance observing techniques, required for instance for the direct detection of extrasolar planets.

The mission

The KERNEL framework offers a wide range applications that go from the post-processing of available archival data to high-performance focal plane metrology, partly coupled with high-contrast imaging. KERNEL now benefits from advanced data reduction tools developed over the course of the project whose effectiveness has been demonstrated by results featured in multiple peer reviewed publications.

In addition to coronagraphic imaging, observing campaigns carried out over the last five years by exoplanet hunting high-contrast imaging instruments have also made extensive use of non-coronagraphic observing modes. The KERNEL project is therefore looking for a postdoc candidate with experience in the processing of data produced by such high-contrast imaging instruments, for further processing exploit the KERNEL software tools. Anticipated applications include the KERNEL processing of sparse aperture masking (SAM) or non-redundant masking (NRM) interferometry data as well as non-saturated well-sampled full-aperture imaging data. In both cases, careful processing using the KERNEL tools will make it possible to probe for the presence of companions and asymmetric structures at very small angular separations.

How to apply

A Ph.D. in astronomy, physics, or a closely related field is mandatory. We are interested in individuals with several years of post-PhD research experience in the exploitation of high angular resolution astronomy instrumentation. The candidate would be joining an international team and be willing to collaborate with graduate students and other postdocs. The candidate will also be encouraged to find ways to apply the tools of the KERNEL project to pursue his/her personal research interests.

The candidate must possess a strong background in the modeling, reduction and interpretation of diffraction dominated data. Experience with the Python and/or the C programming language is highly desirable.

The initial appointment will be for one year. The successful candidate will be hosted by the Lagrange Laboratory, with a lab located on the campus of Valrose, downtown the beautiful city of Nice, France.

To apply, please send a copy of your curriculum vitae, list of publications and a summary of your research interests. Also arrange for two to three reference letters to be sent to Frantz Martinache ( For full consideration, applications should be received before May 4, 2020, although applications will be reviewed up until the position is filled.

This job offer has been posted on the Euraxess website.

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!

KERNEL-Nuller: vidéo explicative

Il y maintenant bientôt deux ans, j’annonçais sur ce site l’acceptation d’un article publié avec mon collègue Mike Ireland présentant un mode d’observation interférométrique haut contraste robuste aux petites erreurs de correction par un suiveur de franges: le kernel-nuller.

Notre équipe à Nice est, en collaborant avec l’entreprise Bright Photonics en train de faire fabriquer un premier prototype de kernel-nuller, sous forme de composant d’optique intégrée. La situation sanitaire du COVID-19 complique un peu le calendrier de cette activité et de la thèse de doctorat qui y est liée, mais nous devrions pouvoir annoncer cette année, des résultats partiels d’une première intégration d’un tel composant sur un banc optique.

En attendant de voir ce composant en action, voici une vidéo mise en ligne il y a quelques jours, expliquant ce qui distingue le kernel-nuller du nuller interférométrique initialement imaginé par Ronald Bracewell à la fin des années 1970… et illustre comment le concept fonctionne!

Kernel-phase imaging VLT/NACO paper!

In this new publication using the tools developed in the context of the KERNEL project, ANU-based PhD student Jens Kammerer announces the detection of eight low-mass companions to stars observed using VLT/NACO in the L-band, five of which were previously unknown,

Among these new companions, two appear at angular separations ranging between 0.8 and 1.2 λ/D (i.e. 80 and 110mas⁠), demonstrating that from the ground, kernel-phase makes it possible to achieve a resolution better than the traditionally accepted diffraction limit of a telescope.

Corner-plot of the best-fitting parameters for the two close companion candidates HIP50156 (top) and HIP39718 (bottom) recovered by the kernel-analysis of archival VLT/NACO L-band images.

Congratulations to Jens whose paper was accepted for publication by the Monthly Notices of the Royal Astronomical Society (MNRAS) and should appear in the June 2019 edition of the journal! The preprint version of the paper is already available for download on the website:

Kernel-phase science paper accepted by A&A!

Romain Laugier, PhD student contributing to the KERNEL project, saw his first paper accepted by the journal Astronomy & Astrophysics. The paper shows how images affected by some amount of saturation can be salvaged to make them kernel-compatible again.

Using an archival HST/NICMOS dataset from 1997, Romain was able to show on a known low-mass binary that the recovery algorithm is effective. The signature of the 4.36 magnitude contrast companion, invisible in the original image, is present in the kernel-phase extracted from that image. This kernel-signature was used to constrain the position and contrast of the companion.

Saturated HST/NICMOS image of Gl 494.

This new resolved observation of the low mass companion to Gl 494 along with other recently published images, combined with a long series of archival radial velocity observations by two instruments, lead to very strong constraints on the orbital elements, and ultimately, the dynamical masses of this binary object.

Visual orbit of Gl 494 b.
Radial velocity of Gl 494 induced by the presence of the low mass companion.

Congratulations to Romain for successfully bringing this paper to the finish line: may this be the first of many others to come! The preprint version of the paper is available for download on the website: