Postdoctoral position in Astronomical Instrumentation for the KERNEL project

Schematic representation of an early design of the KERNEL test-bench

 

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 February 1, 2019. 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. In order to develop and prototype the next generation of high-performance instruments and metrology monitoring tools for ground based telescopes and interferometers, the completion of the KERNEL project includes the construction of a general purpose test-bench, with elements that have already been successfully deployed for on-sky applications. The postdoc responsibility will be to oversee the completion of this KERNEL test-bench.

The test-bench primarily relies on a high-order segmented deformable mirror used to modulate the phase across a diffractive aperture and a high-cadence low-readout near-infrared camera, simultaneously in up to four complementary spectral bandpasses.

The multi-band aspect of the bench expands on the capability already offered by the KERNEL framework:

  • it extends the range of tolerated input instrumental phase, with applications such fringe tracking for long baseline interferometry and adaptive optics for large telescopes.
  • it provides further calibration capability, allowing for the acquisition of spectral differential kernel-phases

In addition, with its simple but agile high-contrast mode, the bench will also make it possible to experimentally validate observing strategies devised in the context of the project that bring robustness to aberrations to high-contrast direct detection.

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 development and the scientific exploitation of instrumentation in the field of high angular resolution astronomy that include active wavefront compensation either in the laboratory or at the telescope. The candidate should be willing to collaborate with and assist graduate students that will use the KERNEL bench for their research projects. The candidate will also be encouraged to take advantage of the experimental setup and the KERNEL project members expertise to pursue his/her own research interests.

The candidate must also possess a strong background in the modeling, reduction and interpretation of diffraction dominated data (interferograms and/or AO-corrected images). Experience with the Python and/or the C programming language is highly desirable.

The initial appointment will be for two years, with possible extensions up to four years. 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, and a summary of your research interests. Also arrange for three reference letters to be sent to Frantz Martinache (frantz.martinache@oca.eu). For full consideration, applications should be received before September 15, 2018, although applications will be reviewed up until the position is filled.

Habilitation à Diriger des Recherches

Dans le but de soutenir mon Habilitation à Diriger des Recherches (HDR), j’ai soumis à mes rapporteurs la première version de cette thèse, intitulée: “Repousser les limites de la diffraction pour l’astronomie à haute résolution angulaire”.

Page de garde de la HDR de Frantz

Deux versions de cette thèse sont téléchargeables ici au format PDF:

Si mes rapporteurs m’y autorisent, la soutenance de cette thèse de HDR devrait avoir lieu le jeudi 4 octobre 2018, à l’Observatoire de la Côte d’Azur, sur le site du Mont Gros.

Entrée de la Grande Coupole de l’Observatoire de la Côte d’Azur, sur la colline du Mont Gros, à Nice.

Pour les curieux, une page de Wikipedia explique ce qu’est la HDR et quel est le rôle de cette tradition qui ne semble exister qu’en Europe ainsi que dans quelques pays d’Afrique du Nord.

La thèse est évidemment écrite en LaTeX. Pour la mise en page, j’ai choisi d’utiliser la classe tufte-latex, inspirée par les publications de Edward Tufte. La lecture de son livre intitulé The Visual Display of Quantitative Information et de son essai intitulé Essay: The Cognitive Style of Powerpoint: Pitching Out Corrupts Within durant mon premier contrat de post-doctorat à l’Université de Cornell ont eu une forte influence sur ma méthode de communication scientifique: je les recommande tous les deux!

MEDITES: Parcours Gaia

Pour la troisième année, j’interviens dans le programme MEDITES dans un parcours pédagogique qui présente la recherche en astrophysique à des élèves du secondaire. Cette année, le parcours est focalisé sur les méthodes observationnelles en astronomie: astrométrie, photométrie et spectroscopie, et parlent en particulier de la mission Gaia. Les supports des présentations que j’ai préparés pour l’astrométrie et la photométrie sont disponibles ici.

La parallaxe: trouver notre place dans l’univers

Slide extrait d’une présentation sur l’astrométrie et la mesure de la parallaxe faite dans le cadre du programme MEDITES.

Photométrie et exoplanètes

Slide extrait d’une présentation sur la photométrie et les propriétés physiques des planètes extrasolaires faite dans le cadre du programme MEDITES.

Pour ce parcours, j’ai mis au point et construit une expérience constituée d’un simulateur motorisé de couple étoile-planète et d’une mesure photométrique temps réel par une photodiode connectée à une carte Arduino. J’ai également développé un petit programme d’acquisition des données collectées par la carte Arduino qui permet de faire du traitement a posteriori des données photométriques. Un tutoriel décrivant la fabrication et l’utilisation de cette expérience sera publié cette année par le site du service éducatif de l’Observatoire de la Côte d’Azur.

Kernel-nulling talk in Grenoble

These are the slides of a presentation given on March 8, 2018 at IPAG, where I present research activities related to the KERNEL project, in particular the most recent development concerning the idea of kernel-nulling interferometry.

Predicted contrast detection limits for the L-band VIKiNG instrument concept proposed by Martinache & Ireland.

You can access the presentation file directly here.

December Stromlo KERNEL seminar

Presentation slides of a seminar given at Mt. Stromlo Observatory, in Canberra, Australia.

KERNEL: crack open the walnut
Slide extracted from a presentation introducing the the principles behind kernel-phase and KERNEL project. Click on image to download or access the presentation file!

Parallactic effect while driving

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Wherever I go, the Moon is following me!!

It is an experience surprisingly shared by many: Have you ever felt like the Moon was following you as you drive along a straight road at night? Are we really all that special or is there a simple explanation to this very common perception?

If you carefully look at the following animation, you will notice that, as our character drives along the road, things in the picture do not apparently move at the same speed. Right by the car, the roadside seems to fly by, while the trees, a little further away do seem to move a little slower. The far away mountains also drift, albeit very slowly.

Consider this, the distance that separates the road from the mountains is only of a few dozens of kilometers and they already barely seem to move as one drives by. With this in mind, are you really that surprised that the Moon (400,000 km away) and the stars (light years away) do seem immobile?


Of course, if you wait long enough, because of the Earth’s spin, the postion of the Moon and the stars will begin to drift. But let’s assume that for a few minutes, they don’t. As our character drives along the road, and covers some distance, by looking at how much the mountains have drifted in relation with the “fixed” sky (measuring an angle), he should be able to tell how far the mountain range is from the road.

In astronomy, this principle is used to figure out the distance to the most nearby stars.

The theory of optical stellar interferometry

These videos are part of Section 2 of the on-line course “Eagle Eye Astronomy”, initially released on France Université Numérique. These have recently been re-uploaded on youtube and close-captioned, to help better understand the audio track despite the French accent.

Turn the constraint of diffraction into an advantage: the interferometric trick

Understanding interference fringes: an electromagnetic theory of light

Stars are not lasers: a better model for ordinary light sources

Self-coherence and spatial incoherence of astronomical sources

Transit photométrique

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Simulation du transit d’une exoplanète

Cette page propose une simulation numérique du phénomène de transit photométrique d’une planète extrasolaire. Les contrôles de l’expérience, permettent tour à tour de changer:

  • Le diamètre apparent de la planète (en fraction de diamètre de l’étoile). Ex: une valeur de 0.5 veut dire que la planète a un diamètre apparent qui est la moitié de celui de l’étoile.
  • L’inclinaison de l’orbite (en degrés), variant de 0 (système observé par la tranche) à 90 degrés (système vu par les pôles).
  • Le niveau de bruit de la mesure photométrique, exprimé en pourcentage sur la valeur de référence (100%). Une valeur de 0 signifie que les mesures sont parfaites. Le bruit est simulé suivant une distribution gaussienne.

Le cadran de droite permet de visualiser le système: l’étoile, la planète et l’orbite de la planète (circulaire, en blanc) autour de l’étoile. La partie basse affiche la courbe de lumière du système pour les paramètres sélectionnés. Dans le cadran de droite, l’utilisateur peut, en cliquant sur la planète et en la promenant le long de son orbite, relier les différentes parties de la courbe de lumière à la position instantanée de la planète, grâce à la marque jaune superposée à la courbe. Il peut aussi utiliser le slider “position de la planète”.

 

Contrôles


Mode haute sensibilité


Position de la planète
(degrés)

Diamètre de la planète
(x diamètre étoile)
Inclinaison de l’orbite
(degrés)
Niveau de bruit
(%)


Coherence length

Coherence length and bandwitdh

A finite spectral bandwidth results in some spectral decorrelation of the electric field emanating from a source: even with a true point source, you will only observe the interference phenomenon (mutual coherence of the field) over a finite range of optical path difference (OPD) that is constrained by the coherence length.

Coherence length: Λ0 = λ²/Δλ

An purely monochromatic and phase-calibrated signal like the one coming out of a very good laser would exhibit an infinite coherence length, represented by the green curve plotted below.

Change the bandpass of the filter (here expressed as 1/R=Δλ/λ) to see its effect on the coherence length (the blue curve).

For a given bandpass (say 0.05 and 0.1), how many fringes can you make out in the fringe packet? How do the two quantities (bandpass, number of fringes) relate to each other?



Bandpass

This tool was developed as a part of the on-line course Eagle Eye Astronomy, hosted on the France Université Numérique website.

KERNEL pipeline on GitHub!

One of the pillars on which the KERNEL project rests is a data processing pipeline that aims at being as versatile and portable as possible, for general astrophysics purposes as well as for metrology. The maintenance of this tool is one of the tasks listed among the work packages that make up the bulk of the KERNEL project. Since the idea is to make the pipeline available to the community at large, it was decided to host the source code on an open access repository on GitHub. The new package is called XARA, an acronym that stands for eXtreme Angular Resolution Astronomy, and can be downloaded right here. This package is an evolution of a previous incarnation called PYSCO (Python Self-Calibrating Observables), that was hosted on the now defunct Google Code platform. The most notable difference is that it is properly packaged and can be installed, so that its classes and functions can be called from anywhere in your python scripts.

It is accompanied by a convenient simulation package of eXtreme Adaptive Optics (XAO) astutely called XAOSIM and also made available on GitHub. Keep in mind that both are work in progress, that will be regularly updated over the course of the KERNEL project, as features are added and bugs are accounted for, so always check for the latest update of these tools before using them!